0

Cardiovascular

2017;():V001T01A001. doi:10.1115/DMD2017-3302.
FREE TO VIEW

Atrial fibrillation (AF) is the most common sustained cardiac arrhythmia affecting approximately 3 million Americans, and is a prognostic marker for stroke, heart failure and even death [1]. 12-lead electrocardiogram (ECG) is used to monitor normal sinus rhythm (NSR) and also detect AF. Although the persistent form of AF can be detected relatively easy, detecting paroxysmal AF is often a challenge since requiring continuous monitoring, which becomes expensive and cumbersome to collect lot of ECG data [1]. Several researchers have attempted to develop new methods to discriminate NSR and AF which are based on R-R interval analysis, linear methods, filtering, spectral analysis, statistical approaches such as entropy etc. which faces limitation of successfully detecting AF of all types with high sensitivity and specificity using short time ECG data [1–3]. The major issues with these approaches is that they often distort the ECG by several pre-processing steps with filters, do not provide reliable discrimination using short ECG time series data and many of them lack real-time capability that makes it difficult to trust the data for diagnosis and treatment. Both clinical and scientific communities recognize these difficulties and the necessity to develop novel methods that can enable accurate monitoring and detection of AF [2]. In addition, robust detection and classification algorithms are essential for delivering appropriate therapy for implantable cardioverter defibrillators (ICD) to provide lifesaving timely action.

In this work, the authors propose and demonstrate the application of a multiscale frequency (MSF) approach [4] for accurate detection and discrimination between AF and NSR ECG traces taken from publically available Physionet database. The MSF approach takes into account the contribution from various frequencies in ECG and thus yield valuable information regarding the chaotic nature of AF. Therefore, we demonstrate that MSF can capture the complexity of AF which is associated with higher MSF value compared with NSR thus enabling robust discrimination e AF manifests itself with numerous chaotic frequencies within the body surface ECG,. We validate the feasibility of this technique to discriminate NSR from AF.

Commentary by Dr. Valentin Fuster
2017;():V001T01A002. doi:10.1115/DMD2017-3325.
FREE TO VIEW

While great strides continue to be made in the treatment of congestive heart failure using mechanical ventricular assist devices (VADs), several longstanding difficulties associated with pumping blood continue to limit their long-term use. Among the most troublesome has been the persistent risk of clot formation at the blood-device interface, which generally requires VAD recipients to undergo costly — and potentially dangerous — anticoagulation therapy for the duration of the implant. Another serious and persistent problem with long-term use of these pumps is the increased risk of infection associated with the use of percutaneous drivelines.

To address these issues we are currently exploring a new approach to blood pump design that aims to solve both these problems by avoiding them altogether. Toward that end, we propose to harness the body’s own endogenous energy stores in order to eliminate the need to transmit energy across the skin. Further, we intend to transfer the energy from this internal power source to the circulation without contacting the blood to obviate the thrombogenic risks imposed by devices placed directly into the bloodstream.

To power the implant we will employ a device developed previously by our group called a muscle energy converter (MEC), shown in Figure 1. The MEC is, in essence, an implantable hydraulic actuator powered by the latissimus dorsi (LD) muscle with the capacity to transmit up to 1.37 joules of contractile work per stroke [1]. By training the muscle to express fatigue-resistant oxidative fibers and stimulating the LD to contract in coordination with the cardiac cycle, the MEC captures and transmits this contractile energy as a high-pressure low-volume (5 cc) hydraulic pulse that can be used, in principle, to actuate an implanted pulsatile blood pump.

The goal of this research is to use the low-volume output of the MEC to drive a polymer-based aortic compression device for long-term circulatory support. In this context it is important to note that the idea of applying a counterpulsation device around the ascending aorta is not new. Indeed, this approach has been validated by clinical trials recently completed by Sunshine Heart Inc. showing that displacing 20 cc of blood at the aortic root has significant therapeutic benefits [2]. Unfortunately, while the pneumatic ‘C-Pulse’ device solves the blood-contacting problem, it suffers from the same limitations as traditional VADs — i.e., driveline infections. The device described here achieves the same volumetric displacement as the SSH device via geometric amplification of MEC outputs. Thus, through this mechanism we believe the low-volume power output of the MEC can be used to support heart failure patients while addressing the major limitations associated with long-term VAD use.

Topics: Design , Muscle
Commentary by Dr. Valentin Fuster
2017;():V001T01A003. doi:10.1115/DMD2017-3345.
FREE TO VIEW

The purpose of this test method is to assist in the determination of the thrombogenic potential of medical materials exposed to human whole blood. By evaluating surface-induced activation, platelet adherence to a material, and platelet and leukocyte depletion from blood, a material’s potential for thrombus formation can be assessed. If a significant decrease in platelets and/or leukocytes is observed in whole blood when compared to a blank control, the tested material has the potential to induce an in-vivo thrombogenic response.

The present standard for the testing of platelet and leukocyte response to cardiovascular materials, ASTM F2888-13, Standard Test Method for Platelet Leukocyte Count - An In-Vitro Measure for Hemocompatibility Assessment of Cardiovascular Materials [1], mandates the use of several reference materials in the presence of blood anticoagulated with sodium citrate. This study was designed to address the relevance of the assay method when using a potent anticoagulant, 3.2% sodium citrate, to evaluate the thrombogenic potential of medical devices. Current studies on this question are under investigation at the FDA also with the intent of improving the standard methods for this assay by evaluating blood anticoagulated with 2–3 IU/mL of heparin [2]. For this study, the effects of several biomaterials were evaluated when exposed to blood anticoagulated with sodium citrate and, concurrently, an even lower dose of heparin at 1 IU/mL also used by our laboratory in a new circulating in vitro assay for thrombogenicity [3]. We believe this test method allows for a sensitive assay that can more accurately predict potential thrombogenic outcomes of cardiovascular materials, while maintaining appropriate responses in both positive and negative control materials.

Commentary by Dr. Valentin Fuster
2017;():V001T01A004. doi:10.1115/DMD2017-3385.
FREE TO VIEW

Thrombogenicity testing is often a requirement for regulatory approval of many types of blood-contacting medical devices [1, 2]. This study describes the continuing improvement in design and characterization of a minimally-heparinized in vitro blood-loop assay which utilizes freshly drawn ovine blood. These modifications were made after studies using this in vitro model were submitted to the FDA in lieu of the in vivo nonanticoagulated venous implant (NAVI) thrombogenicity test. After extensive discussions with FDA reviewers, several modifications which further characterize and improve the assay have been included: 1). Improved temperature control of the blood before and during the incubation period, 2). Improved uniformity and reproducibility of loop geometry, specifically the length of working space for device deployment and a fixed curvature for the radius of the return segment of the loop, 3). Additional measurement of blood parameters prior to and during the incubation period, complete blood counts and activated clotting time (ACT), 4). More rigorous management of ACT, 5). Measurement of non-adherent thrombus formation in the blood, 6).Incorporation of a legally marketed predicate comparator device in all the assays, and 7).Physical characterization of the positive controls. This validated method with enhanced characterization and more reproducible methods allows for a more robust and reliable assay. These results continue to support the premise that this in vitro blood loop assay may eventually supplant the NAVI model for routine hemocompatibility testing for catheter-like blood contacting medical devices.

Commentary by Dr. Valentin Fuster
2017;():V001T01A005. doi:10.1115/DMD2017-3389.
FREE TO VIEW

Coronary arteries are located on the surface of the heart and supply oxygenated blood to the myocardium and other components of the heart. The two coronary arteries located above the aortic arch are the Left Coronary Artery (LCA) and Right Coronary Artery (RCA). The LCA branches into the Left Anterior Descending (LAD) and the Left Circumflex (LCx) while the RCA branches into the Right Marginal Artery (RMA) and Post Descending Artery (PDA). The coronary arteries are likened to a complex tube-like structure, and the motion of the heart cause changes in pressure, which allows proper blood circulation during the systolic and diastolic phases [1].

Since it is essential to understand the physiological and hemodynamical behavior of the heart and coronary arteries, numerous studies have been conducted at different artery locations in the heart. Most of the research has focused on the branches between the LAD and LCx, with little or no attention directed towards the take-off angle the LCA makes with the aortic root. Although it has been reported that certain take-off angles of left main (LM) can be considered anomalous, findings have documented that such take off angles can make the artery prone to atherosclerosis and sudanophilia diseases [2]. Computational Fluid Dynamics (CFD) has in recent years been used to solve a wide variety of fluid flow challenges, and can be used for this study.

The goal of this study is to use CFD techniques to study the hemodynamics of the different take-off angles of the left coronary artery from the aortic root. This will help identify areas in the left coronary artery that could be prone to atherosclerosis buildup.

Commentary by Dr. Valentin Fuster
2017;():V001T01A006. doi:10.1115/DMD2017-3413.
FREE TO VIEW

Recently, the radiofrequency ablation catheter is widely used in the treatment of atrial fibrillation. Radiofrequency catheter tip is inserted through femoral vein puncture and pushed to the heart cavity. The radio frequency energy is applied to the ablation lesion on the inner wall of the heart, and then the heart cells die to achieve the aim of treatment[1]. During the treatment, however, the patients need repeated ablation because of the ineffective ablation, and the complications may occur. Continuous pulmonary vein lesion and isolation of wall is very important to increase the success of surgery [2]. Research [3] shows that the contact force between catheter tip and the tissue of inner heart is a key factor influencing the lesion size.

In order to monitor the contact force, many force sensors have been studied. Fukuda [4] used semiconductor strain gage outside of the catheter to monitor the contact force. Peirs [5] monitored the contact force by optical technology.

The disadvantages of the current sensors are using special expensive signal detecting and analyzing instrument, such as Endosense (SMART touch), which will increase the cost tremendously. For clinical application, it is necessary to develop a low cost sensor with enough accuracy which can also be used in the catheter for contact force measurement.

This paper focuses on designing a novel force-voltage transferring sensor. The sensor consists of a Ni-Ti alloy tube and several strain gages. With the compact design of a spiral structure, it can reduce the overall cost while keeping a good performance at the same time. The price of SMART touch catheter is 4, 348 dollars. The proposed design will be as much as 20–30 percent below SMART’s price.

Commentary by Dr. Valentin Fuster
2017;():V001T01A007. doi:10.1115/DMD2017-3422.
FREE TO VIEW

Ventricular assist devices (VADs) have become an accepted method of treating end-stage heart failure over the last few decades. In recent years, the use of rotary blood pumps (RBPs) as continuous flow VADs has surged ahead, and virtually eliminated the use of pulsatile-flow or volume-displacement pumps for implantable, chronic mechanical circulatory support (MCS). As the use of RBPs has become commonplace for the treatment of end-stage heart failure, the need for an implantable right-side MCS device for adults [1] and implantable MCS for the pediatric population has increased. Development of an implantable device specific to these populations includes unique challenges of anatomic placement and fixation.

Computational Fluid Dynamics (CFD) is the use of numerical methods and algorithms to solve and analyze problems involving fluid flow. CFD has become a standard tool when designing RBPs, as it can calculate pressure-flow characteristics for a given rotary impeller speed. Additionally, through calculation of shear forces, CFD can also predict hemocompatibility by means of constitutive equations derived from empirical data. Particle image velocimetry (PIV), also known as flow visualization, is an optical measurement technique used to obtain velocity in fluids, which can be employed experimentally to verify CFD-based predictions of flow field. PIV also permits more rapid investigation of the RBP operativing range and transient conditions than can be achieved with CFD due to computational requirements.

We have developed a RBP platform for chronic use with CFD to optimize hemodynamic performance. The miniaturized device includes unique inlet geometry with a rotating impeller and a vaned-diffuser in a 7mm axial hydraulic diameter. The design scheme separates the bearing and motor region from the primary flow path to further improve hemocompatibility and reduce the pump size without compromising the hydraulic capacity.

Here we report CFD and PIV results of our device geometry optimized for right-sided MCS.

Commentary by Dr. Valentin Fuster
2017;():V001T01A008. doi:10.1115/DMD2017-3429.
FREE TO VIEW

A valveless shear-driven micro-fluidic pump design (SDMFP) for hemodynamic applications is presented in this work. One of the possible medical and biomedical applications is in-vivo hemodynamic (human blood circulation) support/assist. One or more SDMFPs can be inserted/implanted into vascular lumens in a form of a stent/duct in series and/or in parallel (bypass duct) to support blood circulation in-vivo. A comprehensive review of various micro-pump designs up to about mid 2000’s is given in [1,2]. Many of micropump designs considered are not suitable for in-vivo or even in-vitro medical/biomedical applications.

Operating principles, design, and SDMFP features are given in [3]. A particular design used in cardiovascular applications has no moving valves. SDMFP with Gourney-flap type valves to support high-pressure applications are developed for other applications. SDMFP could be fully bi-directional and can control its operation on the run using embedded microcontrollers and sensors. Estimated efficiency is high with low leakage resulting in low power consumption. Proprietary “fish-scale” surface coating ShearQ™ designs are implemented to improve unidirectional flow pumping efficiency. Bi-directional feature may be especially critical when clogging of blood vessels is detected. By automatically and temporarily switching into the reverse-mode operation and retrogressive flow, while inducing suction-head for a short time periods it is hoped that possibly blood conduits can be cleared/unclogged and the normal forward-flow operation resumed. Such may be an important feature if SDMFP is used in-vivo, such as, in coronary arteries which are prone to clogging leading to cardiac-arrest.

Commentary by Dr. Valentin Fuster
2017;():V001T01A009. doi:10.1115/DMD2017-3431.
FREE TO VIEW

Monophasic action potentials (MAPs) have long been used as a means to study the focal electrical activity of the myocardium. [1, 2] Upon the application of adequate contact force, the signals provide important insights into focal depolarization and repolarization, activation timing, and focal arrhythmic behaviors. [3–6]

Within our laboratory we have developed an isolated physiologic, four-chamber working, large mammalian heart model (the Visible Heart® methodology) to study cardiac devices and their interactions with the myocardium. [7] Through the use of a modified Krebs-Henseleit buffer, we can uniquely visualize the device-tissue interface: in this study, the placement of catheters.

The purpose of this study was two-fold. First, we demonstrated the long term stability of MAP recordings in an in situ swine model. Second, we showed the relationship between MAPs recorded from in vitro and in situ preparations of each specimen.

Commentary by Dr. Valentin Fuster
2017;():V001T01A010. doi:10.1115/DMD2017-3444.
FREE TO VIEW

Blood pressure is an indicator of a cardiovascular functioning and could provide early symptoms of cardiovascular system impairment. Blood pressure measurement using catheterization technique is considered the gold standard for blood pressure measurement [1]. However, due its invasive nature and complexity, non-invasive techniques of blood pressure estimation such as auscultation, oscillometry, and volume clamping have gained wide popularity [1]. While these non-invasive cuff based methodologies provide a good estimate of blood pressure, they are limited by their inability to provide a continuous estimate of blood pressure [1–2]. Continuous blood pressure estimate is critical for monitoring cardiovascular diseases such as hypertension and heart failure.

Pulse transit time (PTT) is a time taken by a pulse wave to travel between a proximal and distal arterial site [3]. The speed at which pulse wave travels in the artery has been found to be proportional to blood pressure [1, 3]. A rise in blood pressure would cause blood vessels to increase in diameter resulting in a stiffer arterial wall and shorter PTT [1–3]. To avail such relationship with blood pressure, PTT has been extensively used as a marker of arterial elasticity and a non-invasive surrogate for arterial blood pressure estimation.

Typically, a combination of electrocardiogram (ECG) and photoplethysmogram (PPG) or arterial blood pressure (ABP) signal is used for the purpose of blood pressure estimation [3], where the proximal and distal timing of PTT (also referred as pulse arrival time, PAT) is marked by R peak of ECG and a foot/peak of a PPG, respectively. In the literature, it has been shown that PAT derived using ECG-PPG combination infers an inaccurate estimate of blood pressure due to the inclusion of isovolumetric contraction period [1–3, 4].

Seismocardiogram (SCG) is a recording of chest acceleration due to heart movement, from which the opening and closing of the aortic valve can be obtained [5]. There is a distinct point on the dorso-ventral SCG signal that marks the opening of the aortic valve (annotated as AO). In the literature, AO has been proposed for timing the onset of the proximal pulse of the wave [6–8]. A combination of AO as a proximal pulse and PPG as a distal pulse has been used to derive pulse transit time and is shown to be correlated with blood pressure [7]. Ballistocardiogram (BCG) which is a measure of recoil forces of a human body in response to pumping of blood in blood vessels has also been explored as an alternative to ECG for timing proximal pulse [5, 9].

Use of SCG or BCG for timing the proximal point of a pulse can overcome the limitation of ECG-based PTT computation [6–7, 9]. However, a limitation of current blood pressure estimation systems is the requirement of two morphologically different signals, one for annotating the proximal (ECG, SCG, BCG) and other for annotating the distal (PPG, ABP) timing of a pulse wave. In the current research, we introduce a methodology to derive PTT from seismocardiograms alone. Two accelerometers were used for such purpose, one was placed on the xiphoid process of the sternum (marks proximal timing) and the other one was placed on the external carotid artery (marks distal timing). PTT was derived as a time taken by a pulse wave to travel between AO of both the xiphoidal and carotid SCG.

Commentary by Dr. Valentin Fuster
2017;():V001T01A011. doi:10.1115/DMD2017-3468.
FREE TO VIEW

Mitral Regurgitation (MR) is a malfunction of the mitral valve where the blood flows backward because of improper closure of the valve. The blood flows back through the mitral valve to the left atrium during the contraction of the left ventricle. This condition usually causes shortness of breath, fatigue, lightheadedness, and a rapid heartbeat. It is estimated that 2% of the global population have significant mitral valve disease. In US, more than 200,000 patients are diagnosed with this condition each year [1]. Current treatments include anticoagulation medication, and surgeries to replace or repair the dysfunctional mitral valve.

Open heart surgery has been the conventional approach to repair or replace the mitral valve. However, for a large percentage of patients (almost 30%), open heart surgery carries increased risk of mortality and morbidity due to their advanced age and dysfunction of the left ventricle [2]. Recently, less invasive, transcatheter approaches to mitral valve disease have been developed to decrease the surgical risk for these patients. [3]. One of the approaches that has recently shown promising outcomes is the placement of a MitraClip system (Abbott Vascular, Inc., Santa Clara, California) to stop or decrease the undesired leakage. MitraClip is a metal clip coated with fabric that is implanted on the mitral valve leaflets to allow the valve to close more completely. After clip placement, blood flows in an assisted fashion as the mitral valve opens and closes on the either sides of the clip.

The whole procedure for placement of the MitraClip in Transcatheter Mitral Valve Repair (TMVR) takes 2 to 3 hours under general anesthesia. A transesophageal echocardiogram is used to observe the blood flow and to trace the placement of the clip. A catheter is guided inside the femoral artery after percutaneous access is established. Then a guide wire is inserted to reach the mitral valve. At this time the MitraClip is threaded into the target position between the leaflets, and then, the guide is removed. Precise placement and orientation must be achieved at this point to best secure the clip with the minimum leakage possible. Since the implantation is being done inside a beating heart, this precise placement is the most challenging part of the surgery. Currently trial and error along with precise measurements are being utilized to find the best position.

This work introduces an innovative MitraClip locator device based on the most advanced materials and actuators to assist in the positioning of the MitraClip during implantation; this would potentially facilitate the most challenging and improtant step of the procedure. Currently, doctors are spending most of their surgical time (roughly 90 min) finding the correct orientation for the clip. The proposed self-actuated MitraClip locator device uses active Shape Memory Alloys (SMAs), Nitinol wires, in order to expedite surgical procedures with a higher precision. SMA wires have been used in medical devices safely and effectively [4,5]. Fig. 1 shows the schematic picture of our novel design that includes evenly distributed SMA wires inside a shaft to enable orientations in multiple directions. This design is proposed as a scaled model for preliminary testing. After thorough testing and evaluation on this model a real size prototype will be made for the real application.

This work presents a detailed design of our innovative device. This device has been fabricated and tested to show the proof of concept. The main purpose of this work is to show the feasibility of achieving movements in multiple directions using three shape memory alloy wires. As a long term plan, the authors aim to have this mechanism (while its accuracy and safety is assured) attached behind the MitraClip to facilitate controlled, accurate positioning.

Commentary by Dr. Valentin Fuster
2017;():V001T01A012. doi:10.1115/DMD2017-3475.
FREE TO VIEW

An estimated 6 million people in the United States have an unruptured cerebral aneurysm [1]. If left untreated, these aneurysms can rupture and to lead to severe brain function impairment or even death. Shape memory polymer (SMP) foams have been proposed for use to optimize endovascular embolization in place of current embolization devices [2,3].

SMPs are capable of actuating from a programmed secondary geometry to their expanded primary geometry in response to a stimulus, such as body temperature [4]. The expanded foam geometry provides an interface for embolization of the aneurysm to occur, however, treatment with these devices has limited visibility under fluoroscopy.

Previous work by Hasan et al. increased radiopacity through the incorporation of tungsten (W) nanoparticles. These composite foams showed successful x-ray visibility, but aggregate disruption of the SMP matrix led to decreased mechanical properties [5].

This work addresses limitations of composite SMP foams, namely toughness, by chemically incorporating x-ray visible monomers, such as the triodobenzene containing monomer, 5-Amino-2,4,6-triiodoisophthalic acid (AT), into the material composition. These materials enable contrast agent loading without disrupting the polymer matrix. This polymer foam system was characterized to determine the clinical relevance of the improved radiopaque SMP foam for occlusion devices.

Commentary by Dr. Valentin Fuster
2017;():V001T01A013. doi:10.1115/DMD2017-3480.
FREE TO VIEW

Current compression garments are often made from a spandex-type elastic material with static levels of compression and can become uncomfortable and difficult to don/doff [1]. This limits their usability, especially for unhealthy or aging populations. The only current alternative to elastic compression stockings are inflatable compression sleeves that are controllable, but highly immobile and must be tethered to an inflation source [2]. Neither design offers a solution that is simultaneously low profile, mobile, and controllable. Here we present the design and development of compression garments with embedded shape-changing materials that can produce controllable compression without the need for a bulky inflation system. This active materials approach enables dynamic control over the degree, timing and location of compression, and allows for graded, synchronized, pulsed, and peristaltic compression patterns, which provide the medical benefit of moving fluid in the body [2]. Such a design combines the best features of both elastic and inflatable compression garments: a slim, low-profile form factor that is easy to don/doff and provides dynamic control.

Shape memory alloy (SMA) coil actuators, as described by Holschuh et al., [3] have the ability to apply compressive forces to the body when paired with passive textiles and wrapped circumferentially around the body. These actuators are engineered to contract when heated, creating controllable forces and displacements that are modulated through an applied current. SMA compression garments (SMA-CG) have important applications, from consumer uses to clinical interventions, including: augmenting venous return for conditions of orthostatic intolerance (e.g., postural orthostatic tachycardia syndrome (POTS)); cardiac rehabilitation in heart failure patients; lymphedema venous insufficiency; reducing deep vein thrombosis (DVT) risk; sports performance; and countermeasures for flight or space flight.

While the potential uses for this technology are broad, the basic design is similar across many conditions. Key research areas include: 1) identifying and addressing design considerations relevant to prototype development of SMA-CG; 2) determining the compression thresholds needed to dynamically oppose orthostatic changes; and 3) evaluating the effectiveness of the prototypes for augmented venous return by synchronizing compression during cardiac diastole. Here, we focus on the first question: design of SMA-CG prototypes.

Topics: Design , Compression
Commentary by Dr. Valentin Fuster
2017;():V001T01A014. doi:10.1115/DMD2017-3491.
FREE TO VIEW

Developing a successful cardiac device requires detailed knowledge of cardiac mechanical properties. For example, tissue failure characteristics and compliance feed into design criteria for many pacemaker leads (Zhao et al., 2011).

In the right atrium, tensile forces are exerted on the right atrial appendage in multiple clinical procedures. In a traditional lead implant, mechanical manipulations with a stylet aid a clinician in assessing lead fixation, with a seldom used “tug” test providing additional input. Atrial lead dislodgement remains one of the top complications for bradycardia pacing leads (Chahuan et al., 1994), in part because there is no standard mechanical assessment at implant to verify fixation. Thus, a deeper understanding of forces exerted on the atrium during implant, is fundamental to understanding the problem. Further characterization of the biomechanics relevant to atrial device implants will provide valuable design input for fixation tests and help drive research toward new atrial fixation mechanisms.

This study aims to better define the relationships between right atrial stiffness and the chamber pressures within the right atrium, so to characterize the link between tensile displacement within the right atrium, and the force exerted on an implanted device in a functional heart. These experiments quantitatively define the fixation force of a fixed cardiac device with a given pulled displacement; i.e. displacing the device a given distance will effectively ensure the experimentally derived fixation force.

Commentary by Dr. Valentin Fuster
2017;():V001T01A015. doi:10.1115/DMD2017-3498.
FREE TO VIEW

The American black bear (Ursus americanus) has been called a metabolic marvel6. In northern Minnesota, where we have conducted long-term physiological and ecological studies of this species, bears may remain in their winter dens for 6 months or more without eating, drinking, urinating or defecating and yet lose very little muscle mass2. We also found that hibernating black bears elicit asystolic events of over 30 seconds and experience an exaggerated respiratory sinus arrhythmia2. In this previous work we employed Medtronic Reveal® XT devices that required us to visit the den and temporarily extract the bear (under anesthesia) to download the stored data.4 Here we describe Medtronic’s latest generation of Insertable Cardiac Monitor (ICM), the Reveal LINQ™, which enables continuous transmission of data via a relay station from the den site3. Black bear hibernation physiology remains of high interest because of the multiple potential applications to human medicine.

ICMs have been used for nearly two decades by clinicians as a critical diagnostic tool to assess the nature of cardiac arrhythmias in humans. Such devices are primarily implanted subcutaneously to record electrocardiograms. The device size, battery life and transmission capabilities have evolved in recent years. The first devices were relatively large and a programmer was needed to retrieve information during each clinical (or in our case, den visit). These devices were programmed to capture cardiac incidents such as asystolic events, arrhythmias and tachycardias and apply algorithms that ensure proper data collection: e.g. ectopy rejection and p-wave presence algorithms.

The new generation Reveal LINQ was made to telemetrically transmit heart data from human patients, but we needed to develop a system to enable transmission from bear dens, which are remote (cannot easily be checked and adjusted) and are subject to extreme winter weather conditions. Besides the advantage of these devices transmitting data automatically, they are considerably smaller and thus less prone to rejection by the extraordinary immune system of the hibernating bear1.

Topics: Physiology
Commentary by Dr. Valentin Fuster
2017;():V001T01A016. doi:10.1115/DMD2017-3516.
FREE TO VIEW

Vascular guidewires are commonly used during interventional surgery to help introduce and position intravascular catheters at the treatment site. Nitinol (NiTi) and stainless steel are the most commonly used alloys in guidewires and a thin layer of polymer coating is usually applied on the guidewire surface to reduce friction within the lumen of blood vessels. Hydrophobic (e.g. PTFE) or hydrophilic (e.g., hyaluronic acid (HA), polyvinylpyrrolidone (PVP), etc.) coatings may be used for this purpose, but coating separation/flaking has been reported from intravascular medical devices [1]. Coating fragments may cause serious adverse events in patients, including pulmonary embolism and infarction, myocardial embolism, necrosis, and death. Hydrophilic polymer emboli in patients has also been reported [2][3][4]. By 2015, the Environmental Protection Agency (EPA) required device manufacturers to phase out the use of the surfactant, perfluorooctanoic acid (PFOA), a potential carcinogen during polytetrafluoroethylene (PTFE) coating manufacturing [5]. Such changes in manufacturing processes need to be evaluated for their effects on coating performance. Of special concern is flaking of coatings, a multifactorial phenomenon that may be related to changes in device design, manufacturing, pre-conditioning, storage, and/or clinical use. There is no comprehensive standard for assessment of coating performance on guidewires. The objective of this study was to evaluate hydrophilic coating integrity and durability during in vitro soaking and bending stress tests.

Topics: Coatings
Commentary by Dr. Valentin Fuster
2017;():V001T01A017. doi:10.1115/DMD2017-3520.
FREE TO VIEW

While the use of pulsatile- and continuous-flow ventricular assist devices (VADs) has become widely accepted as an acceptable treatment for end-stage heart failure in adults over the last three decades, the technology development for pediatric-specific patients is lagging behind that of adult devices. Only one pulsatile-flow VAD has been approved for use in pediatric patients in the U.S., just five years ago [1]. One continuous-flow device was approved specific to this population under Humanitarian Device Exemption (HDE), but is not in clinical use today [2]. As continuous-flow rotary blood pumps (RBPs) have become commonplace for mechanical circulatory support (MCS) in adults due to smaller size and greater reliability, significant resources have gone into the development of RBPs for pediatric use [3]. Further, RBPs designed for adult MCS have been used off-label in pediatric patients [4]. Development of an implantable device specific to a pediatric population includes challenges of anatomic placement and fixation.

We have developed a RBP for adult MCS specific to right heart failure using computational fluid dynamics (CFD) and flow visualization [5]. The miniaturized device includes a rotating impeller and a vaned-diffuser in a 7 mm axial hydraulic diameter. As seen in Figure 1, the hydrodynamic characteristics suitable for a right-VAD (RVAD) may also be suitable for pediatric patients. Currently, the only approved device is placed extracorporeal due to size constraints in the intended population [1]. This report shows results of computational simulations for anatomic fit and fluid flow studies of our device geometry in pediatric patients.

Topics: Blood , Design , Pumps , Pediatrics
Commentary by Dr. Valentin Fuster
2017;():V001T01A018. doi:10.1115/DMD2017-3542.
FREE TO VIEW

Ablations have become the gold clinical standard of drug resistant atrial fibrillation (AF). AF is projected to affect 50 million people by the year 20501. Today, two primary methods of ablation are used clinically: radio frequency and cryoablation. These ablation technologies are equally effective1 but still cause complications. A majority of these complications arise from the fact that both technologies require a thermal change in the tissue to cause cell death.

Thermal change of the tissue while effective, can be subject to many different variables that may result in collateral damage. These include levels of focal blood flow, location of vessels near the ablation site, and/or adjacent tissue damage causing clinical issues such as esophageal fistulas or phrenic nerve injury. Irreversible Electroporation serves as a possible non-thermal alternative. This therapy is a train of high voltage (>500V/cm) short DC pulses that cause pores to form in the cell membrane. If a large enough electric field is applied, then the pores in the cell membrane can cause permanent damage resulting in cell death.

To date, the majority of irreversible electroporation research that has been done has examined the use of this approach for treating cancerous tumors in the skin, prostate, and liver. Very little study of this potential treatment relating to the heart has been done other than synchronizing delivery of the therapy with the heartbeat to not induce ventricular fibrillation. The appeal of a potentially more predictable lesion would be highly desired in this clinical realm. Here we present initial investigations as to the functional response of cardiac tissue to electroporative energy via the NanoKnife.

Commentary by Dr. Valentin Fuster

Neuroengineering

2017;():V001T02A001. doi:10.1115/DMD2017-3407.
FREE TO VIEW

Deep Brain Stimulation (DBS) has demonstrated outstanding results for the treatment of medically intractable Parkinson’s disease (PD), essential tremor and other neurological and psychiatric disorders, such as Obsessive Compulsive Disorder (OCD) and major depression [1,2]. Despite widespread proliferation, efficacy of DBS treatment is limited primarily because of two key limitations as shown in Fig. 1: (a) non-specific activation of regions implicated in DBS side effects, and (b) inefficient neurostimulation due to complex anatomical structure and axonal orientations of target regions. Thus, there is a need to develop approaches to DBS that achieve more precise target selection and efficient activation of axonal pathways within the brain.

Recent efforts in target selection has focused on shaping the stimulation field by using multichannel electrodes for current steering [3]. These multichannel electrodes are limited to cylindrical lead configuration and can only correct for small spatial localization errors, and they do not utilize the direction of the electrical field’s gradients to stimulate neurons depending on their orientation (mainly orientation of axons). Thus, there is a critical need for new electrode architectures that enable both spatial steering and stimulation field orientation tuning capabilities. Here we present the Flex-DBS, a novel DBS electrode lead architecture that harnesses recent advances in flexible probe fabrication and precision guidance strategy to mechanically reconfigure electrodes in three dimensional orientations within anatomically complex brain tissue. Further, it incorporates dense arrays of electrodes with each lead that allow stimulation field orientation tuning.

Commentary by Dr. Valentin Fuster
2017;():V001T02A002. doi:10.1115/DMD2017-3408.
FREE TO VIEW

Epilepsy is a prevalent neurological disorder affecting 65 million people globally [1]. Anti-epileptic medications fail to provide effective seizure control for 30% of patients, placing them at a 7–17% risk of Sudden Unexplained Death in Epilepsy and recurrent seizures. Surgical resection of the seizure focus is a potentially curative treatment for patients with seizures that electrophysiologically correlate to a focal lesion. For these patients, focal surgical resection can result in 60–70% seizure-freedom rates [2]. However, open resection carries the risk of cognitive impairment or focal neurologic deficit [3].

Recent innovations in MRI enable high resolution soft tissue visualization, and real-time temperature monitoring, making MR-guided ablation therapy a promising minimally invasive technique to restrict the tissue destruction to just the seizure focus. Commercial products (e.g., Visualase, Medtronic Inc.; ClearPoint, MRI Interventions Inc.; NeuroBlate, Monteris Inc.) have recently been introduced for MR-guided laser-based thermal ablation. These products require the physician drill a hole into the skull for ablation probe placement, and may not always be able to ablate the entire seizure focus when the structure has a curved shape (such as the hippocampus) [4]. Incomplete ablation of the seizure focus would lead to seizure recurrence.

We have recently proposed concentric-tube steerable needles as a means to address these challenges [4–7]. They enable nonlinear trajectories and offer the potential to enter the brain through the patient’s cheek via a natural opening in the skull base (i.e. the foramen ovale). We have designed and fabricated an MR-compatible robotic system to provide high resolution actuation for helical needle deployment [5]. We have shown in simulation that the curved medial axis of hippocampus can be accessed via a helical needle that delivers the ablation probe into the brain [4]. These preliminary results suggest that MR-guided robotic transforamenal thermal therapy could potentially provide a less invasive approach for potentially curative epilepsy treatment. In this paper we present our first results delivering heat along curved paths in brain phantoms and imaging the resulting treatment zones using MRI.

Commentary by Dr. Valentin Fuster
2017;():V001T02A003. doi:10.1115/DMD2017-3454.
FREE TO VIEW

Electrotherapeutic devices require an electrode for coupling with the body. The most common electrodes are made of conducting corrosion resistance materials (e.g., TiN, Ir-IrO2, Pt) plus a coupling layer (e.g., electrolyte). The electrode is the location where redox reaction take place between the device and the tissue. As such, it must conduct both electrons and ions. The reactions can be capacitive, involving the charging and discharging of the electrode-electrolyte double layer, or faradaic. Capacitive charge-injection is more desirable than faradic charge-injection because no chemical species are created or consumed during a stimulation pulse. Most noble metal based electrodes are faradic or pseudo-capacitive, which can lead to performance changes over time. In addition, under the high rate of charge injection and high current density conditions of a neuromuscular stimulation pulse, access to all the accessible charges is limited by the interfacial resistance and low surface area at the electrode [1]. A particularly critical point is the passage of current between the surface of the skin and the electrical contact connected by wire to the device, which requires a low stable resistance that does not vary with time, humidity [2].

We have developed new hybrid mixed-ionic-electronic conductors (MIECs) that have the potential to overcome these deficiencies. The MIECs are an interconnected network of electrical and ionic conductors in an elastomeric matrix that provide: (1) high surface area for efficient capacitive charge-discharge; (2) high ionic conductivity for low interfacial resistance; (3) low ohmic resistance; and (4) excellent flexibility and toughness. Carbon nanotubes (CNTs) are the electrical conductors in the MIEC and hyaluronic acid (HA), along with moisture and ions, is the ionic conductor. Unlike the current state-of-the-art, conducting noble metals, this system exhibits good mechanical properties, high conductivity (up to 3000 mS/cm), high moisture retention (up to 100wt%) and high ion mobility, leading to facile electrode kinetics. This simple yet efficient system is promising for the fabrication of a variety of high performance flexible electrodes.

Commentary by Dr. Valentin Fuster

Orthopedics

2017;():V001T03A001. doi:10.1115/DMD2017-3361.
FREE TO VIEW

Upper-limb motor impairment is caused by a wide variety of diseases, including Duchenne muscular dystrophy (DMD), stroke, and arthrogryposis multiplex congenita [1,2]. The resultant arm dysfunction can cause the patient to be incapable of many daily tasks, and therefore increasingly reliant on others for their care. Since many of the underlying diseases are either chronic or incurable, some current therapeutics take the form of orthotic devices that assist upper limb function, thereby improving patient quality of life [1]. One such example is the Wilmington Robotic Exoskeleton (WREX), consisting of a set of gravity-counterbalancing exoskeleton arms attached to either a full upper-body brace, or in previous models, a wheelchair [1]. This device and its successors have proven to be significant aids in allowing patients to perform everyday tasks such as eating and writing [1]. However, according to both patients and physicians, this device and others, while effective, are often underutilized due to factors including brace size and weight, low device comfort, unappealing brace aesthetics, low range of motion, and lack of brace adjustability. In order to increase patient utilization of exoskeleton arm systems, we thus propose the replacement of the current brace system with a novel vest device, designed specifically for increased patient comfort, device adjustability, aesthetics, and range of motion, while preserving the existing strength and durability of current solutions.

Commentary by Dr. Valentin Fuster
2017;():V001T03A002. doi:10.1115/DMD2017-3364.
FREE TO VIEW

In clinical settings, doctors classify pulmonary disorders into two main categories, obstructive lung disease and restrictive lung disease. The former is characterized by the airway obstruction which is associated with several disorders like chronic bronchitis, asthma, bronchiectasis, and emphysema [1]. The latter is caused by different conditions where one of the triggers is tied to the spine deformity. In general, a pulmonary function test (PFT) [2] is used to evaluate and diagnose lung function, and physicians depend on the test results to identify the disease patterns of the patients (obstructive or restrictive lung disease). In the PFT, some parameters including total lung capacity (TLC), vital capacity (VC), and residual volume (RV) can infer the lung volume and lung capacity. Other parameters, such as forced vital capacity (FVC) and forced expiratory volume in the first second (FEV1), are often employed to assess the pulmonary mechanics.

Scoliosis is an abnormal lateral curvature of the spine which involves not only the curvature from side to side but also an axial rotation of the vertebrae. Restrictive lung disease often happens in scoliosis patients, especially with severe spine deformity. Spine deformity if left untreated may lead to progression of the spinal curve, respiratory complications, and the reduction of life expectancy due to the decrease in thoracic volume for lung expansion. However, the relationship between thoracic volume and pulmonary function is not broadly discussed, and anatomic abnormalities in spine deformity (ex: scoliosis, kyphosis, and osteoporosis) can affect thoracic volume. Adequate thoracic volume is needed to promote pulmonary function. Previous literature has shown that the deformity of the thoracic rib cage will have detrimental effects on the respiratory function in adolescent idiopathic scoliosis patients [3–4]. In this paper, we aim to correlate thoracic volume and the parameters in PFTs in adult scoliosis patients 25–35 years after receiving treatments during their adolescence, either with physical bracing or spinal fusion surgery.

Topics: Scoliosis
Commentary by Dr. Valentin Fuster
2017;():V001T03A003. doi:10.1115/DMD2017-3374.
FREE TO VIEW

Carpal Tunnel Syndrome (CTS) affects roughly 3%–6% of the working population ages 18–64 [1]. This affliction is caused by applying stress on the median nerve that is routed through the carpal tunnel while it is at a positive or negative angle, greater than 15 degrees in either direction, to the human wrist [2]. The median nerve can become inflamed and swollen due to pressure from the palmar carpal ligament causing numbness, stiffness and in some cases severe pain. Tasks like typing can become nearly impossible when the median nerve is inflamed. A number of products on the market and research prototypes have been suggested that try to alleviate CTS strains, however, these designs are generally passive e.g. braces, splints, etc. Instead of actively trying to adjust the wrist angle, the general trend is to prop the wrist up with some sort of rigid ramp, similar to the bottom of a keyboard [3]. The goal of this work is to design a wearable, soft-actuated, robotic sleeve that will dynamically adjust the position of the wrist in real-time to a neutral angle to prevent or release CTS strains.

Topics: Tunnels
Commentary by Dr. Valentin Fuster
2017;():V001T03A004. doi:10.1115/DMD2017-3437.
FREE TO VIEW

Wheelchair-bound patients suffer from a number of constraining ailments that affect the digestive, respiratory, circulatory, and integumentary system. The increased risk of pressure ulcers in wheelchair users can be attributed to the combination of consistent single-point pressure and lack of regional movement for an extended period of time, leading to reduced blood circulation to the lower extremities. Pressure ulcers are especially prevalent in elderly wheelchair-bound patients due to the increased fragility of the skin with age. A study by Stockton and Parker estimated the rate of pressure ulcers in all wheelchair users to be nearly 60% [1] and the 2010 US Census reported that 30.6 million Americans have a major mobility disability that require the assistance of a wheelchair, cane or walker [2].

Products currently on the market claim to either distribute pressure more evenly across the surface or stimulate the region of pressure. The former include gel cushions which ease stress by distributing the pressure load but do not initiate movement, while the latter regularly alternate mechanical cushions that initiate movement but do not target region of highest load. Because many patients are unable to independently identify, communicate, or adjust their bodies when there is excess pressure being placed on a specific area, a method of reducing a patient’s single-point pressure on a seat without requiring direct user input could greatly improve the quality of life of wheelchair users.

Topics: Pressure , Wheelchairs
Commentary by Dr. Valentin Fuster
2017;():V001T03A005. doi:10.1115/DMD2017-3438.
FREE TO VIEW

The physical impairment caused by OA of a single lower extremity joint is comparable to that reported for major life-altering disorders such as end-stage kidney disease and heart failure. (Buckwalter, et al) [1]

Ankle distraction arthroplasty has been shown to greatly decrease pain due to end-stage ankle arthritis. Unlike arthrodesis (fusion of the joint), distraction arthroplasty maintains the joint’s natural movement, and it is far less complicated than total joint replacement surgery. There is a considerable body of research supporting the idea that distraction of an end-stage arthritic joint (most of the work thus far has been done on ankles, although there has also been some investigation of the efficacy of the treatment for knee arthritis) for a period of weeks allows the growth of new tissue in the joint. Although this tissue is not true articular cartilage, distraction arthroplasty has been shown to significantly decrease pain and, in the majority of cases, to be a long lasting remedy for a condition that would otherwise commonly be treated with arthrodesis. [2]

Devices currently available for this procedure are generally quite complicated because they are designed for a wide range of functions related to bone fixation. This versatility also tends to make those systems larger and more expensive, and their aggressively mechanical appearance makes potential joint distraction patients hesitant to select the procedure. While fracture patients may not have a choice about being treated with such devices, elective patients are instinctively resistant to their use, even when assured that the end result will most likely significantly improve in the quality of their lives.

Commentary by Dr. Valentin Fuster
2017;():V001T03A005e. doi:10.1115/DMD2017-3438e.
FREE TO VIEW

This erratum corrects errors that appeared in the paper “Development of a Simplified Ankle Distractor” which was published in Proceedings of the 2017 Design of Medical Devices Conference, 2017 Design of Medical Devices Conference, V001T03A005, April 2017, DMD2017-3438, doi: 10.1115/DMD2017-3438.

Commentary by Dr. Valentin Fuster
2017;():V001T03A006. doi:10.1115/DMD2017-3456.
FREE TO VIEW

Lower limb length discrepancy (LLD), defined by unequal length of paired lower limbs, contributes to lower back pain, osteoarthritis of the hip, and stress fractures [1–3]. The Center for Disease Control and Prevention estimated that there were approximately 700 children born with LLD each year in US [4]. Patients may receive distraction osteogenesis treatment, in which an osteotomy is performed on the shorter limb, and mechanical force is applied to gradually distract the two halves of the bone during the healing process. This stretches the bone callus during healing to achieve desired limb length upon callus consolidation [5].

The current correction devices are external fixators that leave unsightly scars and are prone to infection [6]. While recently developed intramedullary devices address many of the persistent issues with external lengthening devices, size limitations and potential damage to the bone growth plates make them impractical for use in children [7, 8]. The proposed research addresses an unmet need by developing a novel implantable extramedullary device for LLD correction that is targeted for pediatric use. The device will be implantable, submuscular, and fixed to the outside surface of the bone (extramedullary), thus allowing for use in children without concern for injury to the growth plates. The device’s function will be similar to an external fixator; however, it will not require exposed hardware, which increases risk of infection, or muscle penetration from the pins, which causes pain. Additionally, the device incorporates real-time control of the distraction rate, reducing the risk of complications arising from fixed rate distraction such as premature consolidation and non-union of the callus. [9–11].

The investigators of this study have previously designed and constructed a distraction mechanism prototype and test frame [10]. The current study aims to validate the real-time controller of the prototype.

Commentary by Dr. Valentin Fuster
2017;():V001T03A007. doi:10.1115/DMD2017-3530.
FREE TO VIEW

Seligson [1] describes how Hoffmann and Jaquet, a medical doctor and an engineer, respectively, developed the original Hoffmann fixator as a tool to stabilize human fractures with minimal invasiveness.

Whether being utilized in mass trauma injury situations such as the 2010 Haitian earthquake, within our emerging geriatric population, or in veterinary applications, external fixation is widely used [1–4]. In this investigation, a rod-to-wire coupling, shown in Figure 1, and hereafter referred to as the R2W clamp, has been designed and validation tested for Stryker Orthopaedic’s Hoffmann II (HII) External Fixation System. As the name implies, this clamp has the purpose of connecting 8mm rods to 1.5mm or 2mm Kirschner (k-) wires or olive wires to stabilize bony fragments in the lower extremity, thus expediting healing in a trauma case. This paper summarizes the results of the validation tests conducted on prototype clamps.

This clamp effectively allows placement of a wire to further stabilize a frame [3] by allowing wire placement without the addition of an intermediate ring, as shown in Figure 2. The wire could be added to any configuration with two parallel rods extending in plane with the bone.

As shown in Figure 3, the R2W clamp can be positioned “outboard” with the rod between it and the bone, or “inboard” between the rod and the bone, allowing the surgeon geometric flexibility. The use of two k-wires is recommended to stabilize each bone fragment [5].

One of the goals of the validation testing was to determine the effectiveness and functional safety of the clamp as related to surgically applied k-wire tensions of either 50 kg or 100 kg.

Since it is feasible that surgeons may tighten, loosen, then retighten the clamp while positioning it during surgery, the effects of clamp retightenings on the performance of the R2W clamp were also evaluated [4].

Topics: Testing , Orthopedics , Damage
Commentary by Dr. Valentin Fuster

Urologic

2017;():V001T04A001. doi:10.1115/DMD2017-3433.
FREE TO VIEW

Overactive bladder (OAB) syndrome is characterized by symptoms of urgency, with or without incontinence, usually with increased voiding frequency and nocturia [1], and is prevalent throughout the world [2]. Chronic OAB symptoms are studied with validated surveys, while acute symptoms can be assessed using bladder diaries. These methods may be subject to recall bias, since diaries are typically completed after voiding. The accepted standard for clinical assessment of bladder function and sensation is a urodynamics (UD) study which involves filling the bladder with a catheter. During a UD study, three verbal sensory thresholds (VSTs) are recorded [3]. These thresholds, First Sensation, First Desire to void, and Strong Desire to void, only provide limited, episodic information about acute sensation during filling. Thus, there is a clear need for a tool to evaluate the development of real-time bladder sensation during bladder filling. The objective of this study was to develop a novel Sensation Meter, a patient interface implemented on a touchscreen device that continuously records the patient’s real-time, unprompted sensation of bladder fullness.

Topics: Catheters
Commentary by Dr. Valentin Fuster
2017;():V001T04A002. doi:10.1115/DMD2017-3450.
FREE TO VIEW

Vesicoureteral reflux (VUR) is the backward flow of urine from the bladder into the kidneys. There are many reasons for this reflux. In 1959, Paquin recommended a tunnel length 5 times the diameter of the ureter to prevent VUR based on anatomical comparisons of postmortem specimens of patients with and without VUR [1]. This has become the standard for current ureteral reimplantation surgery. In 1969, Lyon proposed that the shape of the ureteral orifice was more important than the intravesical tunnel for ureterovesical junction (UVJ) competence [2]. However, this was only considered as a supplement to Paquin’s theory. Lyon’s theory might come into play when using bulking agents to affect the shape and configuration of the ureteral orifice but is not directly taken into consideration during surgical ureteral reimplants. Since Paquin and Lyon, little research has looked at parameters regulating the prevention of VUR or leaking from Mitrofanoff type conduits. A case-control study of megaureter reimplants with and without ureteral tailoring demonstrated equivalent outcomes [3], raising concerns about the validity of the 5:1 rule. Most recently, Villanueva et al. reported that the tunnel length of ureter, which can be modified depending on different surgery cases, is not strictly required to have a 5:1 ratio of the diameter to the length [4]. Accurate quantification of the parameters that affect the ureter mechanics is helpful to improve surgical technique.

The aim of this work was to quantitatively inspect Lyon’s theory, i.e., the relationship of intravesical tunnel length and orifice shape with respect to VUR by measuring the pressure required to collapse the ureter for preventing backflow. An enhanced three-dimensional (3D) numerical model was developed considering the interaction between the ureteral orifice and the bladder wall. Parametric studies were then conducted to determine the sensitivity of UVJ competence to the spatial configuration of the intravesical tunnel as well as the ureteral orifice (UO). Two common ureteral orifice shapes, “golf” and “volcano,” as well as different intravesical ureteral tunnel length/diameter ratios, were examined. The required closure pressure was then compared.

Topics: Junctions , Tunnels
Commentary by Dr. Valentin Fuster

Rehabilitation

2017;():V001T05A001. doi:10.1115/DMD2017-3328.
FREE TO VIEW

The human ankle plays a major role in locomotion as it the first major joint to transfer the ground reaction torques to the rest of the body while providing power for locomotion and stability. One of the main causes of the ankle impedance modulation is muscle activation [1, 2], which can tune the ankle’s stiffness and damping during the stance phase of gait. The ankle’s time-varying impedance is also task dependent, meaning that different activities such as walking at different speeds, turning, and climbing/descending stairs would impose different profiles of time-varying impedance modulation.

The impedance control is commonly used in the control of powered ankle-foot prostheses; however, the information on time-varying impedance of the ankle during the stance phase is limited in the literature. The only previous study during the stance phase, to the best of the authors knowledge, reported the human ankle impedance at four points of the stance phase in dorsiflexion-plantarflexion (DP) [1] during walking. To expand previous work and estimate the impedance in inversion-eversion (IE), a vibrating platform was fabricated (Fig. 1) [3]. The platform allows the ankle impedance to be estimated at 250 Hz in both DP and IE, including combined rotations in both degrees of freedom (DOF) simultaneously. The results can be used in a 2-DOF powered ankle-foot prosthesis developed by the authors, which is capable of mimicking the ankle kinetics and kinematics in the frontal and sagittal planes [4]. The vibrating platform can also be used to tune the prosthesis to assure it properly mimics the human ankle dynamics. This paper describes the results of the preliminary experiments using the vibrating platform on 4 male subjects. For the first time, the time-varying impedance of the human ankle in both DP and IE during walking in a straight line are reported.

Commentary by Dr. Valentin Fuster
2017;():V001T05A002. doi:10.1115/DMD2017-3330.
FREE TO VIEW

Veterans with spinal cord injury (SCI) are at high risk for developing debilitating pressure injuries, particularly to their seated areas (e.g. coccyx, sacral and gluteal) [1]. To prevent development of a pressure injury the Veteran with SCI is encouraged to invoke multiple prevention strategies [2]. One recommended prevention strategy is to conduct twice daily skin self-screenings. Skin self-screening is usually conducted in the bed, prior to arising in the morning and prior to sleep in the evening. The current method to conduct skin self-screening utilizes a mirror at the end of a long handle. The Veteran with SCI examines at-risk areas for changes in their skin integrity such as discoloration, swelling, or changes in skin texture. This method can take up to 20 minutes to complete. In the event there is a change to skin integrity, the pressure injury prevention protocol advises the Veteran with SCI to off-load that particular area for at least 24 hours [3]. Further, he/she is advised to consult with their skin specialist if the area does not resolve to normal color or texture within that next 24 hour period. The consequences of ignoring an early stage pressure injury can be serious e.g. weeks to months of hospitalization attempting to heal the injury, tens to hundreds of thousands of dollars in healthcare costs, possible surgery to close the wound and possibly death [4].

Informal interviews with Veterans with SCI clarified and validated that conducting skin screening with the mirror could be very challenging due to barriers such as: not having a baseline image to compare to; the mirror image not being viewable to the user due to lack of user flexibility or body habitus; the mirror does not easily allow a complete view of all the at-risk areas; the user not being able to discern what he/she is actually viewing possibly due to mirror image distortion and limited visual acuity.

The need for a better skin self-screening device was evidenced by the advanced pressure injuries Veterans presented to their healthcare providers. Finding a pressure injury in the early stages of development and intervening immediately, such as repositioning, can improve the trajectory of the injury [5]. Therefore the project goal was to offer a better tool for and improve the efficacy of skin self-screening for the Veterans with SCI. To overcome the identified barriers, our team of VA clinicians and engineers of the Minneapolis Adaptive Design & Engineering (MADE) program invented such a device at the Minneapolis VA. This paper presents the patient centered iterative process that was used to develop a skin self-screening device and the future directions for this technology.

Topics: Skin , Wounds , Spinal cord
Commentary by Dr. Valentin Fuster
2017;():V001T05A003. doi:10.1115/DMD2017-3398.
FREE TO VIEW

Lower-limb amputation affects the ambulation ability and quality of life of about 600,000 individuals in the United States alone1. Individuals with transfemoral amputation typically walk slower, expend more energy, and have a higher risk of falls than able-bodied individuals2. Ambulation activities such as climbing ramps or stairs or standing up from a seated position are much more difficult than for able-bodied persons. Advances in prosthetic technologies are needed to improve the ambulation ability of above-knee amputees.

Passive knee prostheses are lightweight, robust, and quiet, but can only perform activities with dissipative dynamics. Powered prostheses3 overcome this limitation by motorizing the prosthetic joints throughout the entire day, thus enabling the achievement of more activities. However, the prosthesis actuator must then accommodate a wide range of speed and torque to support the various activities, plus provide power over the course of the entire day. Consequently, powered prostheses provide the ability to perform more tasks at the expense of substantial weight, noise, and battery life, which in turn affect their acceptability and clinical viability.

To address these shortcomings, we propose a hybrid actuation design for prosthetic knees. The proposed hybrid actuation system uses a motor, transmission, and control only for those activities requiring net-positive mechanical energy, such as climbing on stairs and ramps or performing sit-to-stand transfers. For non-positive mechanical energy tasks, such as standing and walking, the motor and transmission are mechanically disconnected, and passive knee components are used alone, thus achieving improved joint dynamics, and avoiding any electrical energy consumption.

Topics: Prostheses
Commentary by Dr. Valentin Fuster
2017;():V001T05A004. doi:10.1115/DMD2017-3409.
FREE TO VIEW

Though there are a variety of prosthetic limbs that address the motor deficits associated with amputation, there has been relatively little progress in restoring sensation. Prosthetic limbs provide little direct sensory feedback of the forces they encounter in the environment, but “closing the loop” between sensation and action can make a great difference in performance [1].

For users of lower limb prostheses, stair descent is a difficult and dangerous task. The difficulty in stair descent can be attributed to three different factors: 1) Absence of tactile and haptic sensations at the bottom of the foot. Although force on the prosthetic socket provides some haptic feedback of the terrain being stepped on, this feedback does not provide information on the location of the staircase edge. 2) Insufficient ankle flexion of lower limb prostheses. Dorsiflexion of the physiological ankle during stair descent is about 27°. Even prostheses that provide active dorsiflexion provide less than this number, and regular prostheses provide almost no ankle dorsiflexion. The first two factors are analogous to the sensation of stair descent for someone without amputation wearing ski boots. 3) Prosthetic feet are optimized for flat-ground walking, offering undesirable energy storage at ankle flexion and energy return at toe-off. This can result in unwanted extra energy at the end of stance phase, propelling the user forward down the stairs.

Most lower limb prosthesis designs focus on flat ground walking, but there has been less progress in addressing the challenges of stair descent. One technique that users of prosthetic lower limbs can use for addressing these challenges is to employ an “overhanging toe” foot placement strategy. Under this strategy, the edge of the staircase is used as a pivot point for the foot to roll over the stair. This reduces the need for ankle flexion by allowing the knee and hip to compensate, and avoids storing energy in the prosthetic spring. This strategy is dynamic, and requires the user to know the amount of toe overhang to adjust the movement of the rest of the body. Most haptic devices built to assist individuals wearing prostheses focus on upper extremity tasks [2–4] or standing and walking [5,6]. Whereas previous lower limb sensory replacement systems have targeted standing measures, here we focus on stair descent. The system provides cues of the stair edge location via vibrotactile stimulations on the thigh.

Commentary by Dr. Valentin Fuster
2017;():V001T05A005. doi:10.1115/DMD2017-3424.
FREE TO VIEW

In clinical gait therapy, the quality of gait analysis is critical for developing a training plan and monitoring patient progress. Ground contact forces (GCFs) are often recorded to estimate joint torques which can quantify a patient’s needs and strength development. They are also useful in designing and controlling rehabilitative and assistive devices. In clinical gait analysis, force plates are used to measure GCFs objectively and precisely [1, 2]. Currently, forces sensitive resistors (FSR) are often used as a mobile platform to measure GCFs. FSR based platforms exhibit considerable hysteresis and have low durability, some requiring replacement after only 5-hour long uses. As an alternative to FSR, a pair of sensor-embedded shoes (smart shoes) relying on air pressure sensors has been presented in previous research [3]. Some details regarding the precise characteristics of the sensing abilities were unknown, though, generating unanticipated errors during use.

In this paper, the sensing units of wireless smart shoes are characterized and tested to verify their capability to provide real-time and accurate GCF measurements. For the prototype, silicon tubes were sealed on one end, wound into coils, secured to the underside of the shoe’s insole at four points of interest (heel, toe, the first and fourth metatarsophalangeal joint) routed outside the shoe, and their open ends are connected to air pressure sensors as shown in Fig. 1(a). The pressure sensors were placed on a circuit board along with a battery and microcontroller responsible for reading sensor outputs and wirelessly communicating data to a nearby device, as shown in Fig. 1(c). The sensing unit on the lateral side of the shoe is 1.2″ × 1.3″ × 3.95″. A series of calibration tests were first performed on the tube-insole subsystem in isolation to test linearity, repeatability, and hysteresis. Then practical experiments were performed on a healthy subject to determine the accuracy of GCF measurement. A previously presented hysteresis filter was implemented in practical testing [4].

Commentary by Dr. Valentin Fuster
2017;():V001T05A006. doi:10.1115/DMD2017-3425.
FREE TO VIEW

Sit-to-stand and stand-to-sit transitions (STS), as one of the most demanding functional task in daily life, are affected by aging or stroke and other neurological injuries. Lower-limb exoskeletons can provide extra assistance for affected limbs to recover functional activities [1]. Several studies presented locomotion mode recognition of sitting, standing and STS, or only STS, or static modes [2–6]. They are based on fusing information of the mechanical sensors worn on the human body, e.g. inertial measurement unit (IMU) [2–4], plantar pressure force [5], barometric pressure[2], EMG [6]. However, most of them put sensors on the human body and did not show experiments integrated with exoskeletons. Since the physical interaction between the exoskeleton and human body, the recognition method might be different when wearing a real exoskeleton.

To deal with these problems, in this study we proposed a recognition method about STS based on the multi-sensor fusion information of interior sensors of a light-weight bionic knee exoskeleton (BioKEX). A simple classifier based on Support Vector Machine (SVM) was used considering the computational cost of the processing unit in exoskeleton.

Commentary by Dr. Valentin Fuster
2017;():V001T05A007. doi:10.1115/DMD2017-3428.
FREE TO VIEW

Spondylitis is a very common back and neck ailment that is reported to account for one-third of social problems causing difficulty at work. It is caused due to the inflammation in vertebral joints. Its condition goes undetected until the symptoms, such as that of severe pain, develops. It causes stinging pain which is focused around cervical region of vertebra, the shoulders and the lumbar region of the spine. Accordingly, it is classified into three types: cervical, thoracic and lumbosacral spondylosis. This is different from spondylitis which causes pain due to inflammation.

Many existing devices use electric current to bring relief from pain. Transcutaneous electrical nerve stimulation (TENS) is one of the most commonly used devices in this aspect. However, though this has been able to bring effective results to its patients, there is a whole lot of controversy in conditions it should be used to treat.

Studies have shown these devices to bring relief by suppressing the signals from the brain. They are not advised for patients with pacemakers or any kind of electronically powered implantable devices. They are less effective where the skin is numb or in places where there is decreased sensation. It depends entirely on the working of the nerve beneath the surface and may cause irritation on the skin if the current is too high. Moreover, these devices need to be avoided in area where infection is present. High precaution needs to be taken when working with epilepsy patients and pregnant women; the electrical stimulation can interfere with the fetus development.

With such a wide range of drawbacks, there is a need for a mechanical solution which can redress these problems and provide an effective and ergonomic solution. Along with overcoming the present barriers, research has been done to demonstrate the positive effects of vibration in increase of bone density, increase of muscle mass, increase of blood circulation, reduced back pain, reduced joint pain and boost in metabolism. The given paper discusses a device wherein vibrational motors have been incorporated, under the control of a microcontroller, to generate the requisite g-force needed for the purpose of pain alleviation and increase of bone density.

Commentary by Dr. Valentin Fuster
2017;():V001T05A008. doi:10.1115/DMD2017-3442.
FREE TO VIEW

According to National Institute of Neurological Disorders and Stroke (NINDS), a division of National Institutes of Health (NIH), about 80% adults suffer from low back pain at some point in time and about 2 out of 10 people who are affected by acute low back pain develop chronic low back pain with persistent symptoms at one year [1]. Though in some cases, treatment does relieve chronic low back pain, but in other cases, pain persists despite treatment. Mostly, the lower back pain is of mechanical nature, i.e., disruption in the way the components of the back (the spine, muscle, intervertebral discs, and nerves) fit together and move. The causes of lower back pain can be imputed to various conditions such as sprains and strains, osteoarthritis, herniated discs, whiplash, compression fracture, scoliosis, stenosis, inflammation of joints, osteoporosis. It not only causes pain, but also severs the economy of a nation. It is a major contributor to missed workdays [1]. Research indicates that the total indirect costs due to back pain accrue to more than $100 billion annually [2]. Not many people can afford traveling by car or taxi to office, especially in developing countries and in cities with high traffic, where people prefer to travel by two-wheelers for their access to work and other amenities. However, people with lumbar problems are recommended not to use two-wheelers as the movement of the body on uneven roads or while braking/accelerating may increase the pain and discomfort. This reduces the productivity of not only the individual and the firm but also the productivity of the country as a whole.

Commentary by Dr. Valentin Fuster
2017;():V001T05A009. doi:10.1115/DMD2017-3447.
FREE TO VIEW

Autism is a developmental disorder characterized by atypical social interactions and repetitive behaviors/restricted interests[1]. It is found that children with autism also experience delayed or impaired motor skills development [2]. It would be advantageous to develop methods that precisely evaluate these motor skills impairments. The use of robots for evaluating upper limb motor competency have been looked at in the stroke literature [3]. We would like to leverage robotic tools for motor skills assessment but with focus for children with autism spectrum disorder.

Robotic methodologies provide a unique way of testing upper limb motor skills. For instance, if a person holds on to the end of a robot arm and moves the robot arm in space, the robot can apply forces and prevent or assist the person with these motions. In this fashion, the robot can apply perturbations in a repeatable and precise manner with high fidelity.

Since individuals with autism have anxieties interacting with other individuals[4], using an impersonal robot would alleviate the anxiety of social interactions. These individuals learn motor skills best with consistent repetition and strong reinforcement, qualities that robots provide.

Therefore, a robot based evaluation strategy and therapy paradigm for children with Autism would be beneficial for the community.

Topics: Engines , Motors , Robotics
Commentary by Dr. Valentin Fuster
2017;():V001T05A010. doi:10.1115/DMD2017-3464.
FREE TO VIEW

Most commercially available lower-limb prostheses are designed for walking, not for standing. The Minneapolis VA Health Care System has developed a bimodal prosthetic ankle-foot system with distinct modes for walking and standing [1]. With this device, a prosthesis user can select standing or walking mode in order to maximize standing stability or walking functionality, depending on the activity and context. Additionally, the prosthesis was designed to allow for an “automatic mode” to switch between standing and walking modes based on readings from an onboard Inertial Measurement Unit (IMU) without requiring user interaction to manually switch modes. A smartphone app was also developed to facilitate changing between walking, standing and automatic modes.

The prosthesis described in [1] was used in a pilot study with 18 Veterans with lower-limb amputations to test static, dynamic, and functional postural stability. As part of the study, 17 Veterans were asked for qualitative feedback on the bimodal ankle-foot system (Table 1).

The majority of participants (82%) expressed an interest in having an automatic mode. The participants also indicated that the automatic mode would need to reach walking mode on their first step and to lock the ankle quickly once the standing position was achieved. When asked about how they wanted to control the modes of the prosthesis, 82% wanted to use a physical switch and only 12% wanted to use a smartphone app. The results indicated that the following major design changes would be needed:

1) A fast and accurate automatic mode

2) A physical switch for mode changes

This paper describes the use of machine learning algorithms to create an improved automatic mode and the use of stakeholder feedback to design a physical switch for the bimodal ankle-foot system.

Commentary by Dr. Valentin Fuster
2017;():V001T05A011. doi:10.1115/DMD2017-3466.
FREE TO VIEW

Peripheral neuropathy (PN), commonly caused by diabetes mellitus, is a debilitating condition that currently affects approximately 20 million Americans. Chronic symptoms of PN often involve pain and weakness of the lower limbs, with eventual sensation loss on the plantar surfaces of the feet. According to epidemiological studies, reduced foot sole sensation has been linked to decreased standing stability [1] and an increased risk of falling [2]. Consequently, cost-effective interventions are needed to improve balance and mobility in this population.

A growing body of research suggests that vibrotactile cues delivered to sensate areas of the lower limb may be an effective way to provide information about foot sole pressure to PN patients who experience poor balance control. Indeed, sensory substitution devices that provide vibrotactile feedback have been shown to aid in balance and improve postural control in various patient populations [3–7]. However, none of these technologies have been based on measurements of foot pressure nor have they been used as a balance prosthesis.

The goal of this study was to investigate the effect of a new external lower-limb sensory prosthesis, the Walkasins™, on the balance and gait of individuals with PN who experience balance problems [8]. Walkasins™ consist of two parts: a leg unit and a foot pad (Figure 1). The leg unit wraps around the lower leg of the user and contains electronics for reading foot pad pressure signals, a microprocessor, and four vibrating motors that provide gentle tactile sensory cues to the front, back, medial, and lateral surfaces of the user’s leg. These cues reflect real-time foot pressure information at a location above the ankle where skin sensation is still present. The leg unit has a power button, two status LEDs, and a reset button (not shown in Figure 1). Power is supplied by a rechargeable internal battery. The foot pad is a thin consumable sole insert that can be cut to size and fit into a regular shoe. The foot pad connects to the leg unit through a physical cable. In this study, subjects performed gait and balance assessments with and without the Walkasins™ turned on in order to determine its short-term effects.

Topics: Prostheses
Commentary by Dr. Valentin Fuster
2017;():V001T05A012. doi:10.1115/DMD2017-3499.
FREE TO VIEW

An estimated 3.26 million manual wheelchair users (MWUs) exist in the United States [1]. MWUs report a high incidence of upper extremity joint pain largely attributed to wheelchair propulsion, which exposes the upper limbs to high forces and torques repetitively over time [2]. There exists a clear need for assistive wheelchair technologies capable of reducing the loads experienced by the upper extremity joints during propulsion.

IntelliWheels, Inc. has developed multi-geared wheel systems, including both low and high gear systems, where a planetary gear train connects the wheel hub to the wheel hand rim. Decreasing gear ratio, we hypothesize, may reduce the forces and torques required by the user during propulsion. To evaluate this claim, we constructed and validated an instrumented wheelchair hand rim system capable of use on either geared or standard wheelchair wheels. Commercially available devices exist to perform wheelchair kinetics, such as the SmartWheel (SW) (Three River Holdings LLC; Mesa, AZ, USA), however, these devices require the use of a manufacturer specified wheel. As a result, a custom solution was required to interface with the geared wheels used in this study.

Topics: Wheelchairs
Commentary by Dr. Valentin Fuster
2017;():V001T05A013. doi:10.1115/DMD2017-3501.
FREE TO VIEW

Impaired mobility is ranked as one of the most important factors that have both physical and mental impacts on patients’ life [1]. The impacts are especially serious for the rapidly expanding elderly population in the United States, which is expected to reach 71 million, approximately 20% of the total population, by 2030 [2]. Existing assistive tools, such as cane and walker/rollator, are helpful for such mobility-challenged individuals by providing additional support in walking. However, such tools also disrupt the users’ walking rhythm and increase their metabolic energy consumption. Wheelchairs, especially powered wheelchairs, are also used extensively among this population. Although wheelchairs are effective in transporting patients, they largely preclude the users’ lower limb muscle activities and bone load-carrying, and accelerate the musculoskeletal degeneration of the user’s lower limb [3].

To address the issues with existing assistive tools, the authors developed a new motorized robotic walker for mobility-challenged users. With the objective of assisting the users’ ambulation in a safe and convenient way, the robotic walker features two independently controlled wheels for the maneuverability of the robot, and two parallel bars for the user support in walking. Unlike similar robotic walkers in prior works (e.g. [4]), no wearable sensors are required for the user. Instead, a 3D computer vision system is used to measure the relative position of the user versus the robot, and the control commands are generated accordingly. The details of the robot design and control are presented in subsequent section.

Topics: Robotics
Commentary by Dr. Valentin Fuster
2017;():V001T05A014. doi:10.1115/DMD2017-3504.
FREE TO VIEW

In human walking, the ankle plays an important role of supplying power needed for the forward motion [1]. However, traditional transtibial (TT, a.k.a. below-knee, BK) prostheses are passive, lacking the ability of generating power output in the prosthetic ankle. Consequently, amputees fitted with such prostheses suffer from multiple issues (asymmetric gait, greater metabolic energy expenditure, etc.).

To address such issues, researchers have explored various technical approaches to develop powered TT prostheses. Hydraulics and pneumatics have been attempted, leveraging the high power density with these actuators (e.g. [2]). Electromagnetic actuators were used more extensively with its technological maturity and convenience in packaging. Typical examples include the multiple prototypes developed by the MIT Biomechatronics Group (e.g., [3]), the SPARKy project, and the Vanderbilt Transtibial Prosthesis.

The TT prostheses mentioned above all include powered ankle joints to provide power for the users’ locomotion. However, cost and complexity are often given lower priority than performance in the development of such devices. Powered TT prosthesis is a typical low-volume product from a commercial perspective, and the resulting high cost is a major hurdle for the large-scale adoption among amputee users. General robotic components (motors, gearsets, etc.), in contrary, are produced in large quantities with relatively low prices. Such contrast is the major inspiration for this work: the goal is to develop a modular powered TT prosthesis based on low-cost commercial robotic components while minimizing the complexity in manufacturing and assembly.

Commentary by Dr. Valentin Fuster
2017;():V001T05A015. doi:10.1115/DMD2017-3507.
FREE TO VIEW

Standing from a seated position is a common, yet dynamically challenging task. Due to the vertical ascent of the body center of gravity, sit-to-stand (STS) transition requires high torque output from the knee. As a result, STS transition poses a major barrier to the mobility of individuals with lower-limb issues, including the transfemoral (TF, also known as above-knee) amputees. A study showed that unilateral TF amputees suffer from high asymmetry in ground reaction forces (53∼69%) and knee moments (110∼124%), while the asymmetry for healthy controls is less than 7% [1]. Note that, although a powered TF prosthesis (Power Knee™) was used in this study, it generated resistance in the STS and thus produced similar results as the passive devices. The inability of existing prostheses in generating knee torque and regulating the torque delivery in the STS seriously affects the mobility of TF amputees in their daily life.

Motivated by this issue, researchers have developed numerous powered TF prostheses (e.g., Vanderbilt powered TF prostheses [2]). These devices are able to generate torque and power for challenging tasks such as STS transition. Making full use of such capability, however, requires an effective controller. Currently, walking control for powered prostheses has been well established, but STS control is much less investigated. Varol et al. developed a multi-mode TF prosthesis controller, in which STS is treated as a transitional motion between sitting and standing states [2]. However, no details were provided on the rationale of the STS controller structure or the determination of the control parameters.

In this paper, a new prosthesis control approach is presented, which regulates the power and torque delivery in the STS process. Inspired by the biomechanical behavior of the knee in the STS motion, the new controller provides two desired functions (gradual loading of the knee at the beginning, and automatic adjustment of the knee torque according to motion progress) with a single equation. Combined with a simple yet reliable triggering condition, the proposed control approach is able to provide natural STS motion for the powered knee prosthesis users.

Commentary by Dr. Valentin Fuster
2017;():V001T05A016. doi:10.1115/DMD2017-3518.
FREE TO VIEW

Hydraulic actuators are commonly used in mechanical systems, and actuator efficiency is one of the most important factors in these systems [1]. The energy loss to overcome friction force makes the actuator less efficient. Wearable rehabilitation robotics is one of the applications of hydraulic actuators. Hydraulic cylinders deliver the power extracted from the external resources and/or less stroke-affected limbs to the more stroke-affected limbs (Fig. 1).

O-ring seal, rolling diaphragm, and gap seal cylinders are three common technologies that have been used in different hydraulic systems for years. O-ring seal actuators use an O-ring seal between the piston and cylinder. Rolling diaphragm actuators have a diaphragm between the cylinder and piston which rolls back and forth. In gap seal cylinders, there is a gap between the piston and cylinder. Since it is a tradeoff between leakage and friction, leakage between the two chambers in these cylinders is tolerated to reduce friction (Fig. 2). One study examined low friction cylinders in a low pressure hydraulic transmission [2]. In this study, rolling diaphragm cylinders were used in the transmission, but the restriction on stroke length of these cylinders is a problem that needs to be solved. Commercial rolling diaphragms are manufactured using compression molding of a sheet rubber and woven fabric [2], a manufacturing method that limits the stroke length to no more than the bore of the cylinder. Rolling diaphragm cylinders with the higher stroke-to-bore ratios could multiply the work per cycle of the system [2]. Furthermore, there are limitations of using short stroke length rolling diaphragm cylinders [3] [4].

A more thorough friction evaluation of various cylinder technologies is needed to determine which technology has the lowest friction and is most appropriate for low pressure hydraulic systems like rehabilitation robots. Developing a low friction, leakage-free cylinder without stroke limitations is needed for small hydraulics.

Using an experimental test, we measured the resistance forces in three types of cylinders: O-ring, gap seal, and rolling diaphragm. The cylinders were tested at low-pressure and with mineral oil to determine the lowest friction cylinder technology. The same friction test was performed in a novel, long-stroke, rolling diaphragm cylinder (LSRD) to compare it in two different thicknesses with commercial actuators.

Commentary by Dr. Valentin Fuster
2017;():V001T05A017. doi:10.1115/DMD2017-3526.
FREE TO VIEW

Performing exercises, especially cutting and pivoting activities, with poor lower extremity mechanics can lead to severe damage of the knee, such as anterior cruciate ligament (ACL) tears [1]. A common movement pattern observed in at-risk athletes is knee valgus. This term refers to the medial collapse of the knee (when the knees falls inward towards the center of the body). Intervention to prevent knee valgus could reduce the chance of injury for at-risk athletes, or re-injury for those recovering from a knee injury.

Currently, in patients with knee injuries, knee valgus is monitored by physical therapists, who observe a patient’s movements visually during exercise. The therapists instruct patients on how to identify valgus and how they might correct it. Visual diagnosis of valgus can be difficult and subjective, thereby allowing the unavoidable presence of human error. In addition, monitoring in real time is only possible when the patient is with a therapist. Several studies have focused on the issue of accurate detection of knee valgus by using a variety of systems such as 2D and 3D motion capture systems to track knee and hip movements, dynamometers, and electromyography [2][3][4]. Although these systems are able to determine knee valgus, they are difficult to use, require expensive equipment, and do not provide real-time feedback outside of the clinic setting. The purpose of this study was to inform the design of a valgus-sensing legging by exploring sensor placement options to maximize the magnitude of the sensor response difference between valgus and non-valgus knee bends.

Topics: Design
Commentary by Dr. Valentin Fuster
2017;():V001T05A018. doi:10.1115/DMD2017-3537.
FREE TO VIEW

In the U.S. alone, 7.5 million individuals have survived stroke, traumatic brain injury, and spinal cord injury, and over a million new patients are diagnosed every year [1]. Most of these patients will need gait rehabilitation. Body weight supported gait training is a widely used rehabilitation therapy to improve gait function [2]. Commonly, a physical therapist provides assistance using a gait belt to support the patient. Sometimes two or three therapists may be needed for severely impaired patients. Bodyweight supported treadmill training uses a harness attached to an overhead lift to support body weight [2], however harness systems often cause discomfort and may take significant time to set up and take down.

Lite Run Corporation has developed a system for the treatment of patients with gait and balance difficulties that uses differential air pressure inside a specially designed suit to reduce up to 50 percent of a patient’s body weight. The suit facilitates patient ambulation using technology like that in astronaut spacesuits to achieve comfort and flexibility. Potential benefits include longer therapy sessions due to greater comfort and greater unweighting, as well as the therapeutic benefits of being upright and walking for subjects unable to stand independently.

The suit is used in conjunction with the Gait Trainer device shown in Figure 1 which provides air pressure to the suit and support for the patient. Gait Trainer features include: 1) electro-mechanical and pneumatic controls to support the suit and patient when rising from sitting to standing and ambulating during therapy — so that a single therapist can safely transfer a patient from a wheelchair and practice gait therapy; 2) an open design that permits access to patient’s body and legs by the therapist; 3) a compact profile that provides easy maneuverability; 4) a “base spread” function that permits positioning close to a patient when seated in wheel chair, bed or therapy table. Together these features provide safety and stability for the patient and reduced physical burden on the therapist.

The objectives for the current study were to establish the safety and feasibility of the Gait Trainer, validate user design requirements, and to test the hypothesis that the rate of perceived exertion when using the device is significantly less than during unaided walking therapy.

Topics: Weight (Mass) , Safety
Commentary by Dr. Valentin Fuster
2017;():V001T05A019. doi:10.1115/DMD2017-3541.
FREE TO VIEW

Maintaining upright stance is a complex process, it requires appropriate functioning of a postural control system which consists of inputs from somatosensory, vestibular, musculoskeletal, and proprioceptive systems as well as from several brain regions [1–4]. A concussion is defined as a brain injury caused due to unexpected acceleration/deceleration of the head causing temporary alteration of brain function and it is a prevalent source of injury to football athletes [1]. With the altered function of the brain, the ability to maintain postural equilibrium becomes challenging due to the inability of individuals to respond promptly to stressors, thus, making maintenance of postural equilibrium rather difficult for individuals with a concussion. Effects of concussion on postural ability are shown to last up to three days post injury [5]. Postural stability test, therefore, can be performed to make a valid return to play (RTP) decision, pre-mature RTP is shown to have been catastrophic due to its potential to permanently impair previously affected region/functioning [1,5]. Postural sway data (center of pressure, COP) is traditionally analyzed to study the postural control. Therefore, COP can provide critical information regarding individual’s ability to maintain upright stance post injury.

A more sensitive concussion assessment tool based on electroencephalogram (EEG) is used to accurately track effects of concussion [6]. However, sophisticated electrode placement requirement inhibits its immediate applicability. In current preliminary research, we attempt to differentiate athletes with a history of concussion (experimental) from healthy (control) using postural data. In order to do so, a concept of empirical mode decomposition (EMD) was adopted. EMD has shown evidence in the literature to infer vital information pertaining to the complex underlying physiological phenomenon [4, 7–8]. In the current research, the resultant COP (COPr) was decomposed into its finite set of band-limited signals termed as intrinsic mode functions (IMFs) [8], a set of linear and nonlinear features were extracted from COPr and its IMfs. Lastly, a test of significance was conducted to infer the potential of postural data for differentiating concussed from healthy athletes.

Topics: Stability
Commentary by Dr. Valentin Fuster
2017;():V001T05A020. doi:10.1115/DMD2017-3543.
FREE TO VIEW

Parkinson’s disease (PD) is a neurodegenerative disorder known to affect movement. Approximately seven million people around the world suffer from PD [1]. Tremor in one hand characterizes the onset of PD. Population suffering with PD shows symptoms of slowed movement. Consequently, PD patients struggle to complete a simple task like picking up a book. This slowness of movement is called bradykinesia. Bradykinesia measurement is vital for monitoring the progression of PD.

The current method of assessing bradykinesia requires patients to perform certain motor tasks in clinical settings. A Unified Parkinson Disease Rating Scale (UPDRS) score is assigned to each task based on the observation by a physician. However, PD patients do not always show natural symptoms during a clinical visit. Also, subjective bias occurs during such assessment of bradykinesia [2]. To overcome these limitations, several attempts have been made to quantify bradykinesia using wearable sensors [3]. Accelerometer, gyroscope or a combination of both have been employed for acquisition of movement data to evaluate bradykinesia [3].

Time domain parameters derived from sensor signals for characterizing bradykinesia which includes speed, amplitude, hesitations, and halt have been evaluated in previous studies. However, the effect of frequency domain parameters and non-linear features extracted from sensor signals for evaluating the severity of bradykinesia is unknown. Whether or not it leads to an improvement in the assessment of bradykinesia needs to be investigated. It is known that the patients suffering from severe bradykinesia have their movement signal distorted due to unpredictable movement or hesitation. Nonlinear features can characterize the degree of complexity and provide further relevant insights regarding the severity of bradykinesia.

In this study, we investigated the efficacy of various frequency-domain and nonlinear parameters to quantify bradykinesia. The objective was to develop a predictive model based on a combination of sophisticated linear (frequency) and non-linear features derived from the sensor signal which has not been previously explored in the literature.

Commentary by Dr. Valentin Fuster

MEMS and Nano

2017;():V001T07A001. doi:10.1115/DMD2017-3375.
FREE TO VIEW

Due to the anatomical and physiological similarities to humans that include similar heart size, flow rate, skin, liver enzymes and bone healing, porcine models as a powerful investigational platform have been widely used in research areas such as diabetes, obesity and islet transplantation [1]. The advantages of relative low cost, ease in handling and comparatively short period of breeding time may make swine provide a promising solution to the shortage of human donors and difficulty in isolating purified islets from adult human in future. Porcine cytokines play a significant role in innate immunity, apoptosis, angiogenesis, cell growth and differentiation. They are involved in cellular responses, maintenance of homeostasis, and disease states such as inflammatory disease, cardiovascular disease, and cancer. Thus, the technologies to analyze the expression of cytokines are developed rapidly and are still hot topics. The traditional approach for cytokine detection and quantification is the use of an enzyme-linked immunosorbent assay (ELISA). However, its inability to do multiplex test calls for more robust detection system. Biochip-based assay for the detection of biological agents using giant magnetoresistive (GMR) sensors and magnetic nanoparticles have emerged recently [2, 3]. It is proved that the nanomagnetic biosensor technology has advantages of low cost, high sensitivity, multiplexity, and real-time signal readout. The integration of GMR biosensor and use of weak magnetic fields allow to eventually realize point-of-care and portability. In addition, interferon gamma (IFNγ) is one of the most important porcine cytokines, and is associated with a number of autoinflammatory and autoimmune diseases. In this work, IFNγ is selected as a model target for the detection of porcine cytokine using nanomagnetic GMR biosensor.

Topics: Biosensors
Commentary by Dr. Valentin Fuster
2017;():V001T07A002. doi:10.1115/DMD2017-3458.
FREE TO VIEW

Heart failure (HF) is a serious condition in which the heart cannot pump sufficient blood to sustain the metabolic needs of the body. A common indication of failure is a low ejection fraction, or the volumetric proportion of blood ejected when the ventricle contracts. In end-stage HF, support from a ventricular assist device (VAD) can assume some or all of the heart’s pumping work, improving the ejection fraction and restoring normal circulation. VAD therapy options for end-stage right heart failure (RHF) are limited, with only a few FDA-approved devices available for mechanical circulatory support [1]. These devices are based on continuous flow impellers; and despite anticoagulation therapy, use of currently available VADs is associated with thrombogenic risk since the blood must contact artificial non-biologic surfaces.

An implantable VAD for RHF based on soft robotic pulsatile assistance has previously been proposed [2]. This device is comprised of a contractile element that is anchored to the ventricular septum and the right ventricle (RV) free wall. The device is programmed to contract in synchrony with the native heart beat and assist in approximating the septum and free wall together in order to augment blood ejection (Fig. 1). Potential advantages of this approach include reduced risk of thrombosis, since there is no blood flow through the lumen of the device, and the possibility for minimally invasive deployment of the device under ultrasound guidance.

A key component in this VAD concept is the anchoring mechanism that couples the contractile actuator to the ventricular septum. In this work, we report design, fabrication and testing of a new septal anchor design. We exploit the emerging technology of pop-up MEMS [3] in order to fabricate a collapsible anchoring mechanism. Origami-inspired engineering and pop-up MEMS manufacturing techniques have previously been used for developing disposable and low-cost medical tools and devices [4]. The pop-up anchor can be deployed into the left ventricle (LV) via a standard delivery sheath. We validate the load bearing ability of the anchor and demonstrate deployment in an ex vivo simulation.

Commentary by Dr. Valentin Fuster

Surgical Tools

2017;():V001T08A001. doi:10.1115/DMD2017-3305.
FREE TO VIEW

Endoscopic closure after endoscopic mucosal resection (EMR), endoscopic submucosal dissection (EMR) or endoscopic full-thickness resection (EFTR) is necessary to eliminate serious complications. Through-the-Scope clips are usually used in treating GI bleeding and perforation for their convenience and reliable outcome, but they are not ideal when the perforation size is larger than 2 cm since their opening width is limited. Several approaches are introduced to reinforce the performance of clips in regarding gathering edges of large defect by using endoloop and clips with double-channel endoscope [1]. Recently, an innovative endoscopic suturing technique using slipknot string and clips with single-channel endoscope has been reported, which resulted in shorter procedure time [2]. However, slipknot cannot maintain for a long time when exposing to distractions due to its poor holding strength.

We have designed and fabricated an endoscopic clipping device and reported its initial ex-vivo results [3]. In this paper, a new suturing method is presented by using this device incorporated with a 4S-Modified Roeder (4SMR) knot, which enables such device to close large defect in a short time. Furthermore, the mechanical strength of 4SMR knot is also studied.

Commentary by Dr. Valentin Fuster
2017;():V001T08A002. doi:10.1115/DMD2017-3327.
FREE TO VIEW

Minimally invasive surgery (MIS), including laparoscopy, endoscopy and colonoscopy, refers to performance of diagnostic or surgical intervention in the internal body cavity through small incisions (or no incisions) to reduce the recovery time and minimize scarring [1]. It has gained worldwide popularity since the first report of laparoscopic cholecystectomy in the mid-1980s due to lower complications, cosmetic benefits and quick recovery [2] and has grown to include robotic approaches. One of the main challenges for this type of surgery is to provide sufficient real-time visual feedback using cameras. To address issues of narrow visual field and limited workspace in surgical visual feedback, existing devices may use onboard motors to provide pan and tilt orientation for the camera [3, 4], which makes the system bulky and expensive. (Here we draw a distinction from wire-driven steerable laparoscopes and constrain the discussion to robotic devices.)

In this paper, we present a novel camera system with a parallel structure and elastic platform which has three active degrees of freedom (DOFs) to increase the visual field and implement a mechanical zoom function. This camera head can be mounted on various surgical robots (e.g. [5]) or can be inserted as a standalone device. The novelty of this device lies in its elastic platform, and the authors are unaware of this type of design or its kinematic analysis being presented previously.

Topics: Surgery
Commentary by Dr. Valentin Fuster
2017;():V001T08A003. doi:10.1115/DMD2017-3329.
FREE TO VIEW

Natural orifice transluminal endoscopic surgery (NOTES) is a method in which tools are passed through a natural orifice to the surgical site. This removes the need for external incisions, which can allow patients to recover more quickly without any visible abdominal scarring. This surgical method also has several limitations including limited space, complex lumen geography, and difficult visualization [1]. To address these problems, researchers have developed various tools, including endoscope-based robots [2], and insertable bimanual robots [3]. However, some of the aforementioned constraints/limitations remain, and consideration of accessories for use with these tools remains relevant.

Our lab designed a multifunctional NOTES robot, which consists of a snakelike linkage driven by cables that are attached to motors in an external housing to navigate through the lumen geometry; it also includes a bimanual end effector with interchangeable tool tips [4]. This paper introduces the design of an adjustable table mount to address the limitations related to transluminal insertion. It provides four passive degrees of freedom (DOFs) to grossly place the robot, and enables the robot to be fixed on surgical tables with different sizes. Benchtop testing on a surgical table with a patient mannequin demonstrates its functionality.

Topics: Robots , Design
Commentary by Dr. Valentin Fuster
2017;():V001T08A004. doi:10.1115/DMD2017-3342.
FREE TO VIEW

Commercial donut pillows are used during lengthy surgical operations. With the patient anesthetized, the multiple pressure points on the head and wrinkling of the skin cut off blood circulation in the face, which leads to facial decubitus ulcers [1].

Cellular type materials such as foam, which are used in these pillows, are very effective in reducing pressure points by transferring pressure into shear forces [2]. In a similar way to surgical pillows, these materials are used to reduce foot pain due to plantar pressure in foot orthotics [3].

However, these same shear forces lead to wrinkling of the skin which generates sores. These shear forces are related to shear stress in the pillow. Pressure normal to the pillow surface is related to normal stress in the pillow, which also leads to soring. Thus, the optimal pillow design, which reduces sores due to pressure points and wrinkling, would be characterized by the design where optimal values of the normal and shear stress are obtained [2].

In a previous study [2], a surgical pillow design was developed which implemented foam wedges. The angle these foam wedges made with the transverse plane was determined to be the angle that gave minimal values of the normal and shear stresses. Thus this new pillow design reduced pressure sores as well as sores due to wrinkling of the skin.

The use of foam wedges has some fundamental disadvantages. Chief among these disadvantages is that the wedges have planar surfaces which do not match the curvature of the human body well. This tends to make the wedges uncomfortable and ineffective. In addition, the manufacturing of small wedges which then have to be connected to the main pillow structure is cumbersome and inefficient.

In this study, a new pillow design was developed which is based on the contour of the patient’s body to generate supportive surfaces that not only match the patient’s shape exactly but which minimizes normal and shear stresses.

Topics: Surgery
Commentary by Dr. Valentin Fuster
2017;():V001T08A005. doi:10.1115/DMD2017-3347.
FREE TO VIEW

Cardiovascular diseases including atherosclerosis, thrombosis, aneurysm and arrhythmia remain the major cause of mortality in developed countries, accounting for 34% of deaths each year [1]. Commonly used minimally invasive vascular intervention with using catheters leads to higher success rate than open surgery [2].

Integrating robotic technologies into active control of catheters in teleoperation manner has promised to reduce radiation exposure to surgeons and improve accuracy during electro-physiological (EP) procedures [1]. Common used commercial robotic EP catheter platforms such as Sensei (Hansen Medical Inc., USA) and Niobe (Stereotaxis Inc., USA) are usually composed of a catheter driver (slave side) which can be remotely controlled by a console operator (master side). However, the Sensei catheters are more rigid and bigger than standard catheters because of their two-layer-sheath structure; and Magnetic Niobe systems are huge and expensive.

In this paper, we propose a mechanism of remote-driving catheterization platforms in which a commercial tip-steerable ablation catheter (St. Jude Medical Inc., USA) (Fig. 1) is manipulated by a catheter driver in three degree of freedoms (DOF) (insertion/withdrawal, rotation and tip deflection). In addition, we also present the design of the control software based on Object-Oriented Programming (OOP) method which is expected to give the other researchers a guide line during robotic catheter design.

Commentary by Dr. Valentin Fuster
2017;():V001T08A006. doi:10.1115/DMD2017-3352.
FREE TO VIEW

The implementation of origami techniques into disposable surgical robotic tools is a promising research area with numerous clinical applications. Origami allows for flat foldable structures that can fit through small incisions, reducing patient scarring and recovery time as well as surgical costs. Devices that can provide tight navigation through curved anatomical pathways are crucial during these types of surgery, and can cost anywhere from hundreds to several thousands of dollars. It was hypothesized that an origami design based on a chain of deployable compliant rolling-contact elements (D-COREs) could be applied to design and fabricate a medical endoscope from a single sheet of 2D material (Fig. 1) to simplify fabrication and reduce the cost to under $100 [1–3]. We used software to model the physical actuation range of the endoscope and tested actuation of the D-COREs with shape-memory alloy (SMA).

Commentary by Dr. Valentin Fuster
2017;():V001T08A007. doi:10.1115/DMD2017-3356.
FREE TO VIEW

Prostate cancer is the most common male cancer in the United States with an estimated 181,000 new cases and 26,000 deaths in 2016 [1]. Transrectal ultrasound (TRUS) guided biopsy is the gold standard for definitive diagnosis in which the imaging and needle insertion are both done transrectally. Since ultrasound guidance results in insufficient sensitivity of prostate cancer diagnosis (40–60%), fusion of preoperative MRI with real-time US has been proposed to increase the sensitivity (∼ 90%). Transperineal biopsies have recently gained attention using a brachytherapy grid to biopsy through the perineum rather than the rectum, practically eliminating the possibility of infection.

To enable MR-US fusion, electromagnetic tracking system is commonly used to make a 3D volume out of a stack of 2D US images acquired during an initial sweep of prostate. The EM tracking however is somewhat undesirable as it adds to the cost of the procedure and is prone to inaccuracies. Therefore, in this study, we propose a method that eliminates the need for such external tracking devices and inserts the needle transperineally thus reducing infection risks. Also, the procedure is more comfortable to the patient since the TRUS probe is eliminated. A patient specific grid template is designed based on the MR image of the patient.

Commentary by Dr. Valentin Fuster
2017;():V001T08A008. doi:10.1115/DMD2017-3370.
FREE TO VIEW

There has been an emerging interest in high intensity focused ultrasound (HIFU) for therapeutic applications. By means of its thermal or mechanical effects, HIFU is able to serve as a direct tool for tissue ablation, or an indirect moderating medium to manipulate microbubbles or perform heating (hyperthermia) for the purpose of targeted drug delivery. The development and testing of HIFU based phased arrays is favorable as their elements allow for individual phasing to steer and focus the beam. While FDA has already approved tissue ablation by HIFU for the treatment of uterine fibroids (2004) and pain from bone metastases (2012), development continues on other possible applications that are less forgiving of incomplete treatment, such as thermal necrosis of malignant masses.

Ideally, each element, of such an array must have its own fully programmable electrical driving channel, which allows the control of delay, phase, and amplitude of the output from each element. To enable full control, each channel needs a waveform generator, an amplification device, and an impedance matching circuit between driver and acoustic element.

Similar projects utilizing this approach to drive therapeutic arrays include a 512-channel therapy system which was built at the University of Michigan using low cost Field-Programmable Gate Arrays (FPGA) microcontroller and highly efficient MOSFET switching amplifiers [1]. However, this system lacks the ability to drive both, continuous wave (CW) and transient short duty-cycle high power pulses.

This paper presents a hybrid system, which is able to perform CW and transient short duty-cycle high power excitation. In the following we will describe the design, programming, fabrication, and evaluation of this radiofrequency (RF) driver system as used in our laboratory for a 1.5 MHz center frequency, 298-element array (Imasonic SA, Besancon, France) [2], FPGA-controlled amplifier boards and matching circuitry. Advantages of our design include: 1. Inexpensive components (<$15/channel); 2. Ability to program/drive individual output channels independently; 3. Sufficient time and amplitude resolution for various acoustic pattern design; 4. Capability of hybrid switching between low power CW and short duty cycle, high instantaneous power.

Commentary by Dr. Valentin Fuster
2017;():V001T08A009. doi:10.1115/DMD2017-3372.
FREE TO VIEW

There is a trend towards miniaturization in surgical robotics with the objective of making surgeries less invasive [1]. There has also been increasing recent interest in hand-held robots because of their ability to maintain the current surgical workflow [2, 3]. We have previously presented a system that integrates small-diameter concentric tube robots [4, 5] into a hand-held robotic device [3], as shown in Figure 1. This robot was designed for transurethral laser surgery in the prostate. It provides the surgeon with two dexterous manipulators through a 5mm port in a traditional transurethral endoscope. This system enables the surgeon to retract tissue and aim a fiber optic laser simultaneously to resect prostate tissue.

This robot provides the surgeon with a total of ten degrees of freedom (DOF) that must be simultaneously coordinated, including endoscope orientation (3 DOF), endoscope insertion (1 DOF), as well as the tip position of each concentric tube manipulator (3 DOF per manipulator). In [3], a simple user interface was employed that involved thumb joysticks (which also had pushbutton capability) and a unidirectional index finger trigger, as shown in Figure 2 (Left). The thumb joysticks were mapped to manipulator tip motion in the plane of the endoscope image, and the trigger was used for motion perpendicular to the plane. Whether the finger trigger extended or retracted the tip of the concentric tube manipulator was toggled via the pushbutton capability of the thumb joystick. While surgeons could learn this mapping with some effort, and were able to use it to accomplish a cadaver study, the experiments made clear that further work was needed in creating an intuitive user interface — particularly with respect to how motion perpendicular to the image plane is controlled. This paper describes a first step toward improving the user interface; we integrate a bidirectional dial input in place of the unidirectional index finger trigger, so that extension and retraction perpendicular to the image plane can be controlled without the need for a pushbutton toggle. In this paper we describe the design of this dial input and present the results of a user study comparing it to the interface in [3].

Commentary by Dr. Valentin Fuster
2017;():V001T08A010. doi:10.1115/DMD2017-3377.
FREE TO VIEW

Bicoronal approach is commonly used to repair intracranial trauma [1,2]. However, this approach requires long operation time and may lead to a long-lasting visible scar. In addition, patients stay in the hospital for several days. Therefore the demand for minimally invasive operation technique is increasing for reduction of facial bone fracture.

Yoo et al. reported closed reduction technique using a thread-tapper device [3]. This method uses the tapper as a tool to make a thread of screw tightening a bolt. The method needs small incision. By pulling out the tapper, the depressed bone segment can be easily recovered.

Another method is to use a hook. This device can be inserted into a small hole in the skin [4]. The screw is used for reducing multi-fragmented segments of anterior wall of frontal sinus. Two or more small screws are inserted into fragmented segments, and then pulled out simultaneously [5]. These closed reduction surgical devices have advantages of reducing operation time and scars, and quickening recovery. However, they can be only applied if the tapper or screw can be inserted into the depressed bone segments.

In this technical brief, we propose a spiral tool and pulling mechanism for closed reduction facial bone fracture. Using prototypes, we present that the suggested surgical tool and mechanism are good alternatives for reduction of facial bone.

Topics: Bone fractures
Commentary by Dr. Valentin Fuster
2017;():V001T08A011. doi:10.1115/DMD2017-3391.
FREE TO VIEW

Flexible endoscopy, a procedure during which an operator pushes a semi-rigid endoscope through a patient’s gastrointestinal tract, has been the gold-standard screening method for colon cancer screening (colonoscopy) for over 50 years. Owing to the large amounts of tissue stress that result from the need for transmitting a force to the tip of the endoscope while the device wraps through the bowel, implementing a front-actuated endoscopy system has been a popular area of research [1]. The pursuit of such a concept was accelerated by the advent of ingestible capsule endoscopes, which, since then, have been augmented by researchers to include therapeutic capabilities, modalities for maneuverability, amongst other diagnostic functions [2]. One of the more common approaches investigated has been the use of magnetic fields to apply forces and torques to steer the tip of an endoscope [3]. Recent efforts in magnetic actuation have resulted in the use of robot manipulators with permanent magnets at their end effectors that are used to manipulate endoscopes with embedded permanent magnets.

Recently, we implemented closed loop control of a tethered magnetic capsule by using real-time magnetic localization and the linearization of a magnetic wrench applied to the capsule by the actuating magnet [4]. This control was implemented in 2 degrees-of-freedom (DoF) in position (in the horizontal plane) and 2 DoF in orientation (panning and tilting). One DoF in position is lost owing to the tethered capsule being actuated in air and thus lacking a restoring force to counter the high field gradient. The 3rd orientation DoF is lost owing to the axial symmetry of the permanent magnet in the capsule; this prevents the application of torque in the axial direction and thus controlled roll and introduces a singularity in the capsule’s actuation. Although another dipole could be used to eliminate this singularity, this would complicate both the actuation and localization methods. In this manuscript, we consider the consequences of the embedded magnet (EM) being radially offset from the center of the capsule while being manipulated by an external actuating magnet (AM).

We have developed a tethered capsule endoscope that contains a cylindrical EM (11.11 mm in length and diameter) with a residual flux density of 1.48 T that is offset by 1.85 mm from the center of the capsule; a distance that is less than 10% of the capsule diameter. Our investigation into the topic results from repeated observation of the capsule’s preference to align such that the internal magnet is closest to the actuating magnet (AM).

The AM is a cylindrical magnet (101.6 mm in length and diameter) with a residual flux density of 1.48 T that is mounted at the end effector of a 6 DoF manipulator, as seen in Figure 1. In this manuscript, we evaluate the torqueing effects of the presence of this magnet offset with the goal of determining whether the torque effect is negligible, or impacts capsule motion and thus can potentially be used for the benefit of endoscope manipulation. A concept schematic of this effect is shown in Figure 2. A discussion of how to use this torque is beyond the scope of this manuscript. To the authors’ knowledge, the use of such concept in permanent-magnet based control has not been investigated.

Commentary by Dr. Valentin Fuster
2017;():V001T08A012. doi:10.1115/DMD2017-3399.
FREE TO VIEW

Laparoscopic and robotic surgeries of the abdomen require a trocar to facilitate entry and removal of instrumentation. Some of these trocars are 5mm or less, but some trocars for these surgeries are larger, with 8mm to 15mm trocars commonly used. One of the well-known problems seen in minimally invasive surgery to the abdomen is the resulting defect left in the abdominal wall following removal of the trocars. Occasionally, especially after removal of larger trocars, a defect is left that is large enough to allow omentum or segments of small intestine to become entrapped within the resulting space in the abdominal wall. These trocar site hernias can cause pain, but they also may lead to small bowel obstruction and bowel ischemia or even infarction, perforation and death. The likelihood of a trocar site hernia is increased when the minimally invasive procedure requires removal of an organ or a mass. This often requires dilatation of the trocar site opening.1,2,3

Re-operation to reduce and repair trocar site hernias adds significant cost to the healthcare system. Two separate studies report that incidence of trocar site hernias are in the ranges of 0.65%–2.8%4 and 1.5%–1.8%5,6. Based on a 2016 report published by the American Society for Metabolic and Bariatric Surgery (ASMBS), 196,0007 bariatric procedures were performed in 2015. Assuming an average incidence rate of 1.7%, and based on the cost analysis provided by a 2008 case study8, in bariatric surgery alone, it is estimated that the treatment and hospitalization of such hernias adds an additional $86.2M to healthcare costs.

Several methods and devices exist to prevent the occurrence of trocar site hernias. However, closing superficial fascia externally is difficult, especially in obese patients, and often requires extending the skin incision significantly. Most instruments to close the potential hernia site involve introducing a hollow needle with a built-in, grasping device through tissue on one side of the defect and into the abdominal cavity. This puts internal structures at risk for potential injury. One end of suture is introduced with this needle and then using a separate instrument through a different trocar this suture is held while the needle is removed. The needle device is then re-introduced through tissue on the opposite side of the defect, and the suture is handed back to the needle device and pulled out completing a U-stitch to close the potential hernia site. If a surgeon inserts a finger into the abdomen along the trocar site to guide the needle, there is the potential for injury to the surgeon’s finger.

Therefore, we set about to design a device to close trocar site defects that would work efficiently, while being safe from injury to the patient or the surgeon, and preferably without the need for a separate instrument through a different trocar to assist.

Topics: Surgery
Commentary by Dr. Valentin Fuster
2017;():V001T08A013. doi:10.1115/DMD2017-3400.
FREE TO VIEW

In Amyotrophic Lateral Sclerosis (ALS), neurons controlling voluntary muscles die, resulting in muscle weakness. Small animal studies have shown that neurons experience some regeneration when stem cells are injected into the ventral horn of the spinal cord [1]. These results led to large animal and human trials investigating the effects of injecting stem cells into the spinal cord. Direct injection is used for delivering cells as cells do not have to migrate to the therapy site and visual confirmation is possible [2]. This requires a multi-level laminectomy as well as dissection of the dura mater to expose the cell delivery site. In order to adopt this ALS treatment in regular clinical workflow, a minimally invasive alternative for spinal cord cell therapy is desirable.

Image-guided needle targeting and positioning systems have been developed by numerous groups which use computed tomography or ultrasound for image guidance. However, MRI must be used for this ALS study because it is the only imaging system capable of visualizing the necessary anatomical locations for delivering cellular therapeutics to the spinal cord; the cell therapy target is the gray matter within the ventral horn of the spinal cord, and only MRI can detect the contrast between gray and white matter. Innomotion and NeuroArm have been used for MRI-guided interventions [3, 4] but they are complex, take a long time to set up, and take up a great deal of space in the MRI bore. An initial solution by our research group provided targeting solutions using an adjustable template on the spine, but was manually adjusted, targeted solely on a grid, and lacked a second rotation axis[5].

The presented device, SpinoBot, percutaneously directs therapeutics under MRI guidance into the spinal cord, allowing accurate and minimally invasive spinal therapies. This study examines the accuracy and workflow of MRI-guided cellular therapeutics injections using SpinoBot, a targeting and injection needle guidance system.

Commentary by Dr. Valentin Fuster
2017;():V001T08A014. doi:10.1115/DMD2017-3410.
FREE TO VIEW

Over the past decade, natural orifice transluminal endoscopic surgery (NOTES) has developed out of a merger of endoscopy and surgery [1]. NOTES offers the advantages of avoiding external incisions and scars, reducing pain, and shortening recovery time by using natural body orifices as the primary portal of entry for surgeries [2]. The NOTES platform consists of a flexible, hollow body — enabling travel in the interior of the human body — and the distal end (head), the mechanical structure of which is based off of the snake bone. After the distal end passes through a natural orifice, through a transluminal opening of the stomach, vagina, bladder, or colon, and reaches the target working place in the peritoneal cavity, several therapeutic and imaging tools can be passed through the hollow conduit of the NOTES’ body for surgeries [3].

The traditional snake bone design presents two major problems. First, the movement is constrained to two bending degrees-of-freedom (DOF). A need to reorient the tool then often requires the entire body to be rotated by the physician, an unwieldly manipulation that both hinders convenience and results in imprecise control. Second, the traditional fabrication process is tedious and therefore lends to higher manufacturing costs; the bending joints must be first individually machined then assembled together piece-by-piece using rotation pins.

We propose a novel design for the snake bone that introduces an additional DOF via rotation and is simple and cost-effective to machine. The revised snake bone design features rotation segments controlled by wires that a physician can readily manipulate for increased control and convenience. Further, because surgical tools that pass through the NOTES body conduit are also installed on snake bone structures, the introduction of rotation to the snake bone design increases each tool’s mobility and manipulation. This advance therefore presents the potential to decrease both the number of required tools and the overall diameter of the NOTES body. Finally, the body is machined as a single element and therefore minimizes the work of assembly.

Topics: Bone , Design
Commentary by Dr. Valentin Fuster
2017;():V001T08A015. doi:10.1115/DMD2017-3421.
FREE TO VIEW

Endoscopic nasal surgery is with minimal invasiveness for the surgical treatment of nasal disease. During traditional functional endoscopic sinus surgery (FESS), the surgeon uses one hand to hold the surgical instrument leaving the other hand to hold the endoscope. When the surgeon needs to use two hands to perform some complex procedure, an assistant surgeon is required to help holding the endoscope, and this requires good teamwork and long-time training. To solve this problem, researchers proposed to use robots to hold the endoscope, freeing the surgeon’s hands for bimanual operation. Sun developed a passive arm with pneumatic locking mechanism to hold the endoscope in FESS, but the surgeon needs to adjust the pose of the endoscope manually, which interrupts the surgery flow and lengthens the surgery time [1]. Many motor-driven endoscope holders have been proposed in literature [2], the surgeon interact with the robot with joystick, voice command, pedals or head movement [3–5]. However, there exists some drawbacks with these interacting methods, for example, joystick requires one of the surgeon’s hands, voice command is usually subject to interference and has long time-delay, foot pedals and head movement distract surgeon’s attention. Lin used a foot-attached IMU sensor to control an active robotic endoscopic holder, the inversion/eversion and abduction/adduction motions of foot are used to select and control different joints, but the motor can be only selected in order, which is unhandy for the four-joint scenario [6].

In this paper, a similar foot-attached IMU sensor is used, and the joints are selected in an easier manner, based on the angle of plantarflexion. Rather than the angle, the angular velocity of abduction/adduction is utilized to control the moving direction of the active joint. This paper describes the test result of the proposed control interface.

Commentary by Dr. Valentin Fuster
2017;():V001T08A016. doi:10.1115/DMD2017-3435.
FREE TO VIEW

Orthopaedic resident training has been, and continues to be, in a state of flux. Initially, there were limits placed on the number of hours a resident could work in a week [1]. Later, residency programs were required to provide laboratory-based training in basic surgical skill for first year residents [2]. Now there is a push towards a competency-based training program that graduates residents who demonstrate their acquisition of adequate surgical skills [3]. With each of these shifts in the training model, programs and institutions have looked increasingly to simulation-based training to ease the way. Simulation offers opportunities to train surgeons quickly, provide essential feedback to foster improvement, and assess skill acquisition. With the broad swath of requirements to satisfy in orthopaedic surgical skills training, a simulation platform must support an array of training capabilities for resident practice and performance assessment.

Wire navigation is a central skill in orthopaedics that has a broad variety of applications. In this task, surgeons must use 2D intra-operative fluoroscopic images to visualize the 3D anatomy of a patient and place a wire along a specified path through bone. In some situations, placing the wire is the final task; in others the wire serves as a guide for subsequently placed cannulated implants. Regardless of the situation, the placement of the wire in the bone directly influences the surgical result for the patient.

We previously presented the design of a wire navigation surgical simulator dedicated specifically to hip wire navigation [4]. Our experience with the dozens of surgeons and residents who have used the simulator suggest that they find the general skill of guiding a wire to be relatively abstract. They are more drawn to practicing specific surgeries rather than the general skill. To address this need, we have modified the simulator to present new surgical procedures, while still exercising the underlying skill of wire navigation. We also learned that the task of directing the fluoroscope in order to acquire appropriate view angles for making surgical decisions is integral to surgical wire navigation, so we extended the simulator to include this important aspect of surgical skill.

Commentary by Dr. Valentin Fuster
2017;():V001T08A017. doi:10.1115/DMD2017-3436.
FREE TO VIEW

Medical simulation plays a critical role in the training of surgical and medical residents. Training simulators give residents an environment to practice a wide variety of procedures where they can learn and make mistakes without harming a living patient [1]. In recent years, much research has been conducted on applying haptic or force feedback technology to surgical simulators in order to create more effective training devices [2]. Simulators such as the LapSim (laparoscopic simulator) and the PalpSim (palpitation needle insertion simulator) have both utilized haptic feedback arms to provide the physical sensation of performing surgical procedures to the user [3, 4]. The haptic simulator shown in Fig. 1 is currently in development. This virtual reality haptic robotic simulator for central venous catheterization (CVC) utilizes a haptic feedback arm to provide the feeling of a syringe being inserted into neck tissue [5].

Currently, there is little experimental data relating needle force to depth. To determine the forces necessary to program into the haptic robotic device, a force sensing syringe was developed and cadaver experiments were performed. This paper presents the development of a syringe which can accurately measure needle insertion force and the proceeding experiments conducted using this device on a fresh frozen cadaver. The results of these cadaver needle insertions are characterized into force profiles for needle insertion force that are implemented into the haptic based CVC simulator.

Topics: Haptics , Robotics , needles
Commentary by Dr. Valentin Fuster
2017;():V001T08A018. doi:10.1115/DMD2017-3441.
FREE TO VIEW

Laparoscopic surgery is a practice of minimally invasive surgery (MIS) performed in the abdominal area. Prior to surgery, instead of exposing the target region to air as in a typical conventional open surgery, “key holes” are opened for positioning ports, through which surgical tools (e.g. laparoscope, needle drivers, etc.) are inserted. MIS therefore minimizes trauma and reduces the risk of hemorrhaging and infection. MIS also generates economic benefits such as shorter hospitalization time for patients and better utilization of operating rooms and wards for hospitals. MIS procedures, however, require extra dexterity from surgeons: they must use instruments with little to none haptic feedback to remotely manipulate tissue within a limited range of motion, assisted by an indirect view from laparoscope. Such unintuitive operations not only require additional training, but also increase the risk of medical errors. Thus, the development of novel surgical devices that can provide a better operating experience will allow surgeons to deliver safer and more effective surgeries.

At the advent of MIS only rigid straight laparoscopic instruments were available. Therefore, surgeons used multiple incisions to position the tools and achieve triangulation. In single port laparoscopic surgeries (SPLS), only one incision is made for positioning a port. Two rigid straight instruments inserted through one incision cannot provide sufficient triangulation for operations. Rigid bent, or articulated, instruments can achieve triangulation, but the tools must intersect at a point. The mapping to control the end-effector, therefore, must be inverted such that the right hand controls the left end-effector, and vice versa [1]. Given this inverted mapping, surgeons need to undergo extra training to intuitively control the end-effector, and greater attention is required toward operating the device, which can potentially detract from the ability of surgeons to focus on procedures. The disadvantage of an inverted mapping can be overcome by providing additional mobility with flexible tools and actuating structures [2]. For example, Transenterix has developed a flexible laparoscopic device which utilizes a cable-driven system for articulation of the end-effectors. However, using flexible elements as the driving mechanism can result in new problems such as diminished force feedback [3].

In 2015, a novel design of an articulated single port laparoscopic device was presented with 6 degrees of freedom (DOF). The system provides intuitive control, accurate force feedback, and sufficient manipulation for laparoscopic procedures.

The design proposed in this paper keeps much of the functional features in the previous model, including 1:1 mapping and force feedback, while incorporating flexible hydraulic graspers. The articulated mechanism was redesigned to have a symmetrical structure, which is more intuitive to control and provides better operating angles for surgeons. Joint structures are redesigned for enhanced robustness and misalignment prevention. Kinematic analysis is presented for the proposed mechanisms, which is used to determine the manipulator workspace.

Topics: Design , Surgery
Commentary by Dr. Valentin Fuster
2017;():V001T08A019. doi:10.1115/DMD2017-3451.
FREE TO VIEW

Intracerebral Hemorrhage (ICH) is the deadliest form of stroke and occurs when blood, leaked from a ruptured vessel pools in the brain forming a pool of semi-coagulated blood called a hematoma. 1 in 50 people will have an ICH in their lifetime [1] and the 30-day mortality rate is 43% with half of the deaths occurring in the acute phase, which motivates the need for safe and rapid treatment. However, literature reviews show no significant benefit of surgical removal vs. “watchful waiting”, despite the potential value of decompressing the brain. It has been hypothesized that this is due to the significant disruption of healthy brain tissue required to reach the hemorrhagic site in open brain surgery.

Recent studies conducted on phantom models have shown that a robotic needle made from curved, concentric, elastic tubes can reach a hemorrhagic site through a needle-sized path to successfully aspirate the hematoma. This approach has the potential to decompress the brain with far less disruption to surrounding brain tissue [4]. Those initial experiments were conducted under guidance from periodic (low rate) CT [2]. The need for intraoperative imaging was motivated by the fact that the brain shifts during aspiration, collapsing to fill the cavity left by voided blood. This approach has the potential advantage of “one stop shopping”, since ICH is typically diagnosed in the CT scanner. It is appealing to treat ICH immediately after diagnosis, while the patient is still in the scanner. However, CT also has the drawback of requiring ionizing radiation, as well as providing only intermittent images rather than real-time information.

In this paper, we consider a Magnetic Resonance Imaging (MRI) guided approach, which provides the converse in terms of both benefits and drawbacks. MRI is not typically used to diagnose ICH, but it can provide detailed soft-tissue and hematoma contrast [3], and fast image updates, enabling real-time monitoring of brain deformation during the aspiration process. Toward performing ICH aspiration with a concentric tube robot in an MRI environment, this paper presents accuracy and MR-compatibility tests for a new MR-compatible robot designed for ICH removal.

Commentary by Dr. Valentin Fuster
2017;():V001T08A020. doi:10.1115/DMD2017-3457.
FREE TO VIEW

Surgical needles are commonly used by medical professionals to reach target locations inside of the body for disease diagnosis or other medical interventions — such as biopsy, brachytheraphy, thermal ablation, and drug delivery [1, 2]. The effectiveness of these procedures depends on the accuracy with which the needle tips reach the targets, such as tumors or certain organs/tissues. In procedures, such as deep brain stimulation and prostate brachytheraphy, it is impossible to reach the surgical sites via simple needle trajectory because of anatomical constraints. Although needles are considered minimally invasive devices, needle insertion still causes tissue damage of varying degrees so it is desirable to reach multiple targets, or multiple sites on a single target, to obtain multiple high-quality biopsy samples with each insertion [1, 2].

Recently there has been a substantial and growing interest in the medical community to develop innovative surgical needles for percutaneous interventional procedures. The answer to the challenge of developing advanced surgical needles could be found in nature. Insects such as honeybees (Fig. 1), mosquitos, and horse flies have sophisticated sting mechanics and stinger structures, which they use to steer their stingers to a specific target, such as a human, and to release their venom in a certain path in skin [3]. We are studying these mechanisms, evolved in nature over millions of years, as a basis to develop bioinspired needles.

Surgical needles are typically consisted of a hollow cylindrical component (cannula) and an inner solid cylindrical component (stylet). Our hypothesis is that a surgical needle (stylet) that mimics insect stinger mechanics and structures can be easily controlled for sophisticated needle steering during surgery and can result in more effective and less invasive percutaneous procedures. The focus of this work is to mimic honeybee stinger such as shown in Fig. 1 to design innovative surgery needles.

One of the critical issues in designing surgery needles is the insertion force required to penetrate and to navigate the needle inside the tissue [2]. Larger insertion forces increase tissue damages thus may result in a more painful procedure [2]. Another consideration is the needle trajectory path (needle tip deflection) and the difficulty to control the needle path. The needle deviates from the target and thus it is very difficult to navigate the needle in the tissue. There is a need to design advanced surgery needles that provide smaller insertion force. This can lead to a less invasive procedure, in other words, less tissue damage and pain [3]. The needle trajectory path of these new needle designs must be understood for the needle design optimization.

As stated previously, it is hypothesized that a honeybee-inspired needle can be utilized to reduce the insertion force. In this work, the experimental work to understand the mechanics of bioinspired needles is presented. 3D printing of the needles and their insertion tests are performed to investigate the effect of the needle designs on the insertion force and the needle deflection (trajectory path) curves. Understanding these factors should shed some lights on some design parameters to develop innovative surgery needles.

Commentary by Dr. Valentin Fuster
2017;():V001T08A021. doi:10.1115/DMD2017-3470.
FREE TO VIEW

Shape memory alloy (SMA) based active needles [1] have shown the potential to introduce remarkable improvements to many percutaneous needle-based procedures such as thermal ablation, brachytherapy and breast biopsy. Brachytherapy for instance is a common procedure to treat early stage prostate cancer because its superior clinical outcome. Prostate cancer is sex specific and only affects males; it is more prevalent in elderly males, ages 65–74 years old [2]. There is projected to be a 24% increase in cancer cases for men by 2020, this would mean approximately 1 million new cases each year [3]. There was a study in 2015 [4] that examined the needle placement accuracy for brachytherapy procedure while implementing the use of a 3D navigation system, Surgical Planning and Orientation Computer System. The study examined the Target Registration Error (TRE) for single and multiple needle placements. Analysis of the 250 different targets showed a mean Target Registration Error for single needle applications of (1.1 ± 0.4 mm), (0.9 ± 0.3 mm), and (0.7 ± 0.3 mm) in the x, y, and z directions, respectively. The maximum deviation was found 2.3 mm. In another study by Podder et al. [5], the effects of dose distribution has been discussed which has a high influence on the clinical outcome. The study shows that the curvilinear approach by the active needle would introduce the potential for improving dose distribution, reducing number of needles and resulting is better clinical outcome.

Actuating the surgical needles for higher accuracy, SMAs are considered as suitable actuators [6] because of their lightweight, high force and energy density. However, SMA actuated needle will be more complex and may incur additional inaccuracy; thereby after development of a robust active needle, control studies sound very necessary. The focus of this work is to introduce an innovative design of an active needle, and to fabricate the device to demonstrate its capability of creating a high maneuverability at the needle tip. This design of the active needle privileges from actuation of a comparatively long SMA wire to create a considerable amount of deflection, while minimizing the tissue rupture.

Most of the needles today are made of stainless steel, titanium or Nitinol; they are ensured to be sturdy enough to puncture the tissue and overcome its resistance during insertion. This would limit the flexibility of the needles. In our previous designs [7,8], a joint element was included in design to provide more dexterity to the needle’s structure. Despite of the fact that this soft element increased the needle’s flexibility; the design introduced a high tissue rupture during actuation because of the gap between the body of the needle and the SMA actuator. The amount of rupture was increasing with larger deflection of the needle. This work decreases the rupture to a reasonable amount while even a higher deflection compared to our previous design is achieved.

Table 1 lists general specifications and approximations of dimensions and requirements that have been tried to be addressed in the current design as much as possible. There will be still future work to meet some other factors discussed at the end of this study.

Commentary by Dr. Valentin Fuster
2017;():V001T08A022. doi:10.1115/DMD2017-3505.
FREE TO VIEW

Breast lesion tissue can be extremely stiff, e.g. calcification or soft, e.g. adipose. When performing needle biopsy, too small or scanty samples can be retrieved due to the tissue is mainly compressed instead of being cut. In order to studying the tissue cutting performance in various cutting conditions, tissue-mimicking phantoms are frequently used as a surrogate of human tissue. The advantage of using tissue phantoms is that their mechanical properties can be controlled. The stiffness of a tissue phantom can be measured by an indentation test. Previous studies have demonstrated mathematic models to estimate Young’s moduli of tissue phantoms from force-displacement data with an adjustable coefficient according to the geometry of the indenter.

Tissue force reactions occurred needle insertion has been largely researched [1], but few studies investigated the tissue cutting with a rotational needle, which is a cutting method largely used in the breast needle biopsy. Research has demonstrated that the influence of rotation can significantly reduce the insertion force [2], but the experiment was conducted on a specific formula of silicone-based tissue phantoms.

This paper served as a pilot study of a large-scale experiment to study the effect of rotational cutting on various cutting conditions and target materials, including artificial and biological soft tissues. Two most common types of soft tissue phantoms, biopolymers (gelatin gels and agar) and chemically synthesized polymers (polydimethylsiloxane, PDMS) were investigated. Indentation tests were performed to estimate the mechanical properties of tissue phantoms which were then verified by finite element simulations. Tissue cutting tests with and without rotation were conducted to evaluate the effect of needle rotation on the tissue force reactions.

Commentary by Dr. Valentin Fuster
2017;():V001T08A023. doi:10.1115/DMD2017-3508.
FREE TO VIEW

Hepatocellular carcinoma (HCC), commonly known as the liver cancer, is a severe health concern worldwide. For patients with liver tumors that are difficult to remove through traditional treatments such as radiation, chemotherapy and partial hepatectomy, there is the option of radiofrequency ablation (RFA) treatment. RFA is a minimally invasive procedure that is currently treating liver tumors that are relatively small in size. Radiofrequency ablation uses currents to heat up the tissue of the tumor. Once the temperature of the tissue reaches approximately 60° C tissue necrosis begins to occur [1]. With current RFA probes, ablation lesions are typically 3–5.5 cm in diameter [2]. It is important that all of the tumor tissue is ablated, so it is necessary to also kill a small amount of the surrounding healthy tissue. At least 1 cm of healthy tissue should be ablated to ensure the tumor will not recur [2]. Hence, many studies [3, 4] have attempted to increase the RFA ablation zone through various methods including adding saline to the tissue, predicting the optimal power level, etc.

To focus on safely increasing the size of the ablation zone and to improve upon the spherical geometry of the tumors, the “Christmas tree” and “umbrella” style probes [5], which utilize multi-pronged electrodes (tines), are currently available in the market. The electrodes, or wires of the probe, are responsible for producing heat and making contact with the liver tissue at all time in order to execute the tissue ablation. For the umbrella and Christmas tree style probes, the drawbacks include: 1. the gauge of the tines limit the ablation scope of the probes; 2. their ability to achieve higher volumes of cell death are limited due to their static geometry, which has fixed diameters; 3. towards the outer edge of the tumor, due to their static geometry and the loss of contact with live tissues, the rate of killing cancerous cells decreases drastically due to the decrease in heat transfer rate, which is a result of the lack of heat sink from perfusion in the live tissues [6].

It was noticed that an improvement could be made to the efficiency of these multi-pronged electrodes if they were free to expand as the area of tissue was ablated. Therefore, a novel dynamic RFA probe was proposed by Lau and Han and numerical simulations using COMSOL Multiphysics Joule heating module have concluded that this dynamic RFA probe can achieve a higher ablation volume with a shorter procedure time [7]. The main goal of this study is to realize the design of this dynamic RFA probe with expandable electrodes to create the largest and most replicable ablation zone. In this study, the deployment mechanism and the proposed design of the dynamic probe are discussed and the analytical solutions of the electrode expansion profiles are presented. The ablation zones are estimated analytically based on the dynamic expansion of the electrodes.

Commentary by Dr. Valentin Fuster
2017;():V001T08A024. doi:10.1115/DMD2017-3511.
FREE TO VIEW

Prostate cancer is the most common cancer among males, leading to approximately 27,000 deaths in the United States [1]. Focal laser ablation (FLA) has been shown to be a promising approach for prostate cancer treatment with the advantage of efficiently ablating the cancer cells while inflicting less damage on the surrounding tissues. In current FLA procedures, a rigid template — with holes spacing of 5mm — guides the FLA catheter to the target position. Drawbacks of the conventional approach for catheter targeting are 1) limited degrees of freedom (DoF) and 2) a low insertion resolution. In addition, the targeting capability of the rigid template is compromised when the pubic arch or nerve bundles intersect the catheter trajectory. We hypothesized that a compact design of an MRI-conditional robot with two active planar DoFs, one passive rotation DoF, and remote catheter insertion capacities could enhance the clinical workflow required for MRI-guided FLA prostate procedures.

Commentary by Dr. Valentin Fuster
2017;():V001T08A025. doi:10.1115/DMD2017-3525.
FREE TO VIEW

Current surgical skill assessment methods are often based on the kinematics of manual surgical instruments during tool-tissue interactions. Though kinematic data are generally regarded as a sufficient basis for skill assessment, the inclusion of kinetic information would allow the assessment of measures such as “respect for tissue” and force control, which are also important aspects of surgical proficiency. Kinetic data would also provide a richer data set upon which automated surgical motion segmentation and classification algorithms can be developed. However, the kinetics of tool-tissue interactions are seldom included in assessments, due largely to the difficulty of mounting small sensors — typically silicon strain gauges — onto surgical instruments to capture force data. Electromagnetic (EM) or optical trackers used for kinematic measurement are often tethered, and thus having tethered force sensors also mounted on the same surgical instruments would complicate the experimental process and could affect/distort the acquired data by impeding the natural manual motions of surgeons.

We present a surgical skill assessment platform which places the kinetic sensors in the environment, not on the instruments, to reduce the physical encumbrance of the system to the surgeon. This system can capture kinetic data using a standalone force/torque sensor embedded in a custom designed workspace platform, and kinematic data using EM trackers placed on the instruments. This portable platform enables the empirical characterization of open surgery motion trajectories and corresponding kinetic data without need for a centralized acquisition site, and will eventually be integrated into a completely untethered skill assessment system.

Topics: Surgery
Commentary by Dr. Valentin Fuster
2017;():V001T08A026. doi:10.1115/DMD2017-3527.
FREE TO VIEW

Limited treatment options are available for treating Amyotrophic Lateral Sclerosis (ALS) (1). Small animal models have shown promise in halting neurodegeneration associated with ALS where cellular therapeutics are delivered to the ventral horn of the spinal cord (2), although this procedure is invasive and requires multi-level laminectomy and dissection of the dura mater (Fig. 1). We hypothesized that SpinoBof, a robotic needle guidance platform (Fig. 2) could deliver cellular therapeutics to the ventral horn percutaneously under MRI guidance, enhancing upon existing invasive and time-consuming techniques for targeting injection sites.

Commentary by Dr. Valentin Fuster
2017;():V001T08A027. doi:10.1115/DMD2017-3532.
FREE TO VIEW

An eye speculum is a device that holds the eyelids and lashes out of the way during ophthalmologic procedures. As described by Lam, et. al, ophthalmological surgical pain is usually controlled using eye drops [1]. However, in many cases the major source of pain or discomfort for the patients is not due to the surgery itself, but rather due to the eye speculum forcing the eye lids open [1]. Eyeball and eyelid physiological variation from patient to patient can cause variations in patient pain, and make it difficult for one speculum design to universally work for most patients [1]. Some eye specula include tubes for aspiration that is used to remove excess tear production on the eyeball surface. As aspirating speculum may aggravate dry eyes after surgery, the aspirating capabilities are ideally optional and at the discretion of the surgeon [2].

Fayers, et. al., found that vibration-assisted anesthesia during upper eyelid surgery had a beneficial pain reduction effect [3]. Additionally, vibrational anesthesia has been used in cosmetic and dental facial procedures [4, 5], but the inclusion of a vibrational anesthetic component to an eye speculum is novel.

A new eye speculum was design to minimize eye speculum patient pain, and be more universal with respect to patient eye shapes. It allows single-handed use by the surgeon, and optional eyeball aspiration. Most uniquely, it also incorporates an optional vibrational anesthesia component. The educational pedagogical aspects of this project were previously described by one of the authors. [6]

Topics: Design
Commentary by Dr. Valentin Fuster
2017;():V001T08A028. doi:10.1115/DMD2017-3536.
FREE TO VIEW

Brachytherapy is one the most effective treatment modalities for both gynecological (GYN) cancer and prostate cancer. The clinical outcome of brachytherapy, both high-dose-rate (HDR) and low-dose-rate (LDR), depends on the precision of the desired or planned dose distribution and delivery. In HDR procedure, the accuracy of reconstruction of catheters or needles (e.g. Syed catheter or Simon-Heyman capsule for GYN or needles for prostate) from CT images can significantly affect the accuracy of dose distribution in the treatment (dosimetric) plan, which can result in unwanted clinical outcome. In current practice, an authorized medical physicist manually reconstructs the catheters or needles for dosimetric plan, which determines the position and dwell time for the radiation source for delivering the prescription dose to the target volume sparing organs at risk (OARs) as much as possible. It is not only challenging but also time consuming for reconstructing all the catheters or needles (ranging 15–20) manually, slice-by-slice in CT images. As shown in Fig. 1, the needles on the right (HDR catheters) have created so much artifacts in CT images that it is almost impossible to reconstruct those applicators (catheters/ needles) manually. Additionally, the reconstruction can be operator dependent and can be inaccurate and inconsistent.

In this study, we have investigated the applicability of electromagnetic (EM) sensor-based navigation for fast and accurate reconstruction of HDR catheters and needles.

Commentary by Dr. Valentin Fuster
2017;():V001T08A029. doi:10.1115/DMD2017-3547.
FREE TO VIEW

Laparoscopic surgery has widely replaced open surgery due to the advantages it has for patients both during surgery and post-surgery recovery. Due to inversion and remote access to the surgical site, haptics feedback is altered with laparoscopic surgical instruments [1]. This leads to excessive exertion of force [2]. Many intra operative errors like tissue injury in laparoscopic surgery are due to texertion of large forces [2]. Over the years, virtual reality (VR) based laparoscopic surgical simulators with haptics feedback have been instrumental in teaching basic and advanced laparoscopic skills to residents and surgeons [3]. However, a major limitation in modern day VR based simulator training systems is that they do not effectively teach the bimanual impedance-based laparoscopic skills. Past studies on VR based laparoscopic training have captured the skills sets of residents and surgeons using force and psychomotor metrics [3, 4]. However, till date none have explored the effects of experience on impedance based training. In this study, we analyze the impedance skills of residents and surgeons using custom developed novel bimanual laparoscopic skills trainer.

Topics: Design , Haptics , Feedback
Commentary by Dr. Valentin Fuster

Computer Modeling and Simulation

2017;():V001T09A001. doi:10.1115/DMD2017-3331.
FREE TO VIEW

A Stellite 25 17mm tube valve based upon the Björk-Shiley Monostrut (BSM) valve design was developed for use in the Penn State Pediatric Ventricular Assist Device (PVAD) pump [1]. The hook of the valve was designed to hold a Delrin occluding disc in place while allowing the disc to tilt open 70 degrees from the closed position. Unlike common design constraints which remain in the elastic region, the hook experiences plastic deformation twice during the assembly process, making the material choice of Stellite 25 imperative.

Stellite 25 is a cobalt-chromium-tungsten-nickel alloy (Co-20Cr-15W-10Ni) belonging to the material family of superalloys which are commonly used for wear-resistant applications exposed to heat, abrasion, and galling [2, 3]. Along with its excellent in vivo corrosion resistance [4], Stellite 25 exhibits high strength and ductility which permit the hook to be plastically deformed during disc installation while remaining below the strain to failure [3, 4]. Together these qualities make Stellite 25 an ideal material choice for the 17mm tube valve application.

Predicting the resultant stresses and strains is critical for determining the safety and structural reliability of the Stellite 25 17mm tube valve for the PVAD after assembly. After performing finite element analysis (FEA), the simulation results were validated by deflection experiments and metallurgical investigations.

Commentary by Dr. Valentin Fuster
2017;():V001T09A002. doi:10.1115/DMD2017-3393.
FREE TO VIEW

In clinical ophthalmic surgery, patient’s eye is not fixed and non-steady state. Surgical operation will be extremely complex and dangerous, which need doctors have a good hand-eye coordination and operating accuracy. Recently, the development of surgical training system promotes the learning speed of clinical experience. Some of them are based on animal specimens. The operating habits and perceptions are similar to the real situation. However, the live animal experiments are more and more challenged by animal ethics. the live animal experiments will be unable to meet the growing demand for training. Others are based on Virtual Reality (VR), which use software to produce realistic images, haptic and other sensations [1]. However, the operating habits and perceptions are quite different from the real situation, and the operating object is stationary. Therefore, it is necessary to develop a device that can simulate the physiological movement of eye to make the result of training can be as close as possible to the actual surgical procedure.

In this paper, an eye movement simulator based on 3-DOF parallel mechanism is presented. The simulator is also equipped with flexure joint, which simulates the biomechanical properties of extraocular muscles. The design and analysis of mechanical will be described.

Commentary by Dr. Valentin Fuster
2017;():V001T09A003. doi:10.1115/DMD2017-3406.
FREE TO VIEW

Recent works have suggested that aneurysm size and shape might not be the only indicators to predict aneurysm rupture. Rather, the long-term interaction between hemodynamics and aneurysmal wall via the loading condition (i.e shear stress and pressure) may also be important. In this work, we investigate the impact of flow pulsatility on the hemodynamic patterns on aneurysmal dome during its growth using numerical simulation.

Commentary by Dr. Valentin Fuster
2017;():V001T09A004. doi:10.1115/DMD2017-3412.
FREE TO VIEW

Endovascular aneurysm repair (EVAR) techniques have been widely used for the treatment of abdominal aortic aneurysm (AAA). EVAR is associated with lower postoperative morbidity and mortality than traditional surgical procedure to treat AAA [1]. However, during the patient’s follow-up, postoperative complications may occur and secondary interventions are required [2].

Stent-grafts fixation in the vessel affects the success of endovascular aneurysm repair. Researches indicate that insufficient stent-graft radial force is attributed to post-surgery complications, such as prosthesis migration and endoleak type I [3, 4]. Endoleak type I happens when there is not a complete contact between stent graft rings and vessel wall. A great radial force can prevent full obturation in the landing zone. The distal endograft fixation also has a great influence on proximal endograft migration after EVAR [5]. Therefore the radial force of the stent plays a significant role.

Single stent-graft ring comprise a series of expandable Z-shaped structural elements (known as “struts”). Currently, there are series of Z-shaped stent-grafts on the market and the struts number ranges from 5 to 12. This work intends to analyze the influence of stent-graft struts number on the radial force. Finite-element analysis (FEA) and experimental method are used.

Topics: stents
Commentary by Dr. Valentin Fuster
2017;():V001T09A005. doi:10.1115/DMD2017-3439.
FREE TO VIEW

In recent years, outbreaks of highly contagious diseases, like the Ebola virus, have motivated vigorous efforts to screen travelers entering the United States, especially at airports. Screening involves monitoring the body temperature of entering travelers, and blocking entry of those showing a fever, indicating a potential infection. Typically, screening is performed using commercially available non-contact infrared thermometers (NCITs). These thermometers require specific use protocols (e.g., working distances) to provide accurate results, which may not be followed by inspectors reluctant to approach potentially contagious travelers. Furthermore, the NCITs’ accuracy is based on an assumption that the NCIT readings from a forehead will predict the body core temperatures using a simple common one-size-fits-all correction offset. Unfortunately, the temperature detected on the forehead surface by an NCIT may not represent the true body core temperature, due to the changing conditions of the external environment and/or surface conditions of the forehead skin. It is not clear whether the correction factor is able to adjust to the thermal environment, or whether the surface condition of the forehead, including sweat and skin tone, affects the NCIT readings.

Before a clinical study is conducted to understand the differences between the forehead temperatures and the body core temperatures, a computational model to simulate temperature distribution inside and on the surface of the body is a cost-effective way to identify factors that influence the temperatures and to study the reasons for their deviations. The objectives of this study were to 1) develop a numerical whole-body model and perform computational heat transfer simulations of different body geometries and 2) perform parametric studies to evaluate the effect of environmental factors, such as air temperature and heat transfer coefficient, on the differences between the forehead temperature and body core temperature. This data can be used to evaluate correction factors or needed to use the measured forehead temperature to predict the body core temperature.

Commentary by Dr. Valentin Fuster
2017;():V001T09A006. doi:10.1115/DMD2017-3443.
FREE TO VIEW

Vacuum-assisted biopsy (VAB) is a widely used technology to sample lesion tissue for breast cancer diagnosis. The technology is designed to retrieve tougher and larger breast tissue samples.

The majority of VAB tools utilize a so-called rotational cutting method, in which the cutting needle simultaneously rotates and translates to produce both tangential and normal forces at the cutting surface of the tissue. The introduction of the tangential force can significantly reduce the cutting force measured in the axial direction. As a result, higher quality of tissue samples can be obtained as the samples are less deformed while being removed. The slice-push ratio, i.e. the ratio of the speed component parallel to the cutting edge to the speed component perpendicular to the cutting edge, was previously found to be the most important factor to influence the cutting force [1]. However, these studies only investigated the cases in low translational cutting speeds in a small-scale experiment.

In this paper, we present a finite element (FE) model based on surface-based cohesive behavior, which simulates the rotational cutting method used in VAB to predict the progressive damage and the cutting force of soft tissue phantoms. The model is validated using the experimental data provided in the previous study [1]. The validated model will allow us to explore more cutting conditions, such as higher translational speeds, larger range of slice-push ratio, and tissue properties. The model can also be used to optimize design parameters of current VAB needles and to evaluate new VAB needle designs.

Commentary by Dr. Valentin Fuster
2017;():V001T09A007. doi:10.1115/DMD2017-3446.
FREE TO VIEW

Personal protective equipment (PPE) such as respirators will form the first line of defense in the event of a public health emergency including an airborne pandemic or a bio-terror attack. The two major pathways by which virus-carrying aerosols can reach the human lungs through these PPEs are: a) the intrinsic penetration through porous layers of the PPE and b) the leakage through gaps between the PPE and a person’s face [1, 2]. The contribution from the second pathway can be significantly reduced using fit-testing i.e. by choosing the appropriately sized respirator for a specific face. Unfortunately, in case of an emergency, it would not be possible to fit-test the entire US population. In this scenario, excessive leakage can occur through the gaps. [1]. Hence, it is critical to identify the potential anatomical leak sites (gaps) and quantify the amount of aerosol leakage through surgical respirators for the average US population.

At the behest of Office of Counterterrorism and Emerging Threats, the Center for Devices and Radiological Health, US Food and Drug Administration (FDA), has been developing a comprehensive risk assessment model for determining the risk to different populations in case of an “off-label” use of such PPEs, i.e. for public emergency scenarios for which these FDA cleared respirators were not intended to be used. In order to develop the risk assessment model, establishing a correlation between the respirator gaps and aerosol leakage between the face and the respirator is critical. A previous study [3] identified the gaps of N95 surgical respirators for a large population and quantified the aerosol leak using computational fluid dynamics. However, the gap surface area, which is a key parameter required for establishing the gap-aerosol leak correlation, has not been quantified before.

In this study, gaps were identified and the gap surface areas were quantified for multiple head-respirator combinations under realistic conditions using imaging coupled with computer-aided design and modeling.

Commentary by Dr. Valentin Fuster
2017;():V001T09A008. doi:10.1115/DMD2017-3455.
FREE TO VIEW

Percutaneous coronary intervention (PCI) is the most common revascularization procedure, in which, fibrocalcific plaques are found in 17–35% of patients undergoing PCI [1]. Numbers will rise with population aging and prolonged statin treatment. Calcifications often lead to stent under expansion and strut malapposition, with increased risk of thrombosis and in-stent restenosis [2]. Presence of calcium strongly inhibits stent performance, a well-documented metric for outcome [3]. The goal of this work is to develop the finite element models for inspecting the influence of the calcium arc extent on the stenting outcomes, such as the stress and strain distribution within the plaque, and the lumen gain following stenting. Finite element method is an effective tool to reveal the mechanism of the stent expansion and its interaction with target lesion, provide guidance for optimal clinical outcomes.

Commentary by Dr. Valentin Fuster
2017;():V001T09A009. doi:10.1115/DMD2017-3472.
FREE TO VIEW

The recent and rapid developments of immersive, interactive 3D environments have been critical in advancing interfaces for entertainment, design, and education. For cardiovascular research, our laboratory and others have been able to use such software tools for the construction of heart models from DICOM files. These models can then be printed in hard or soft plastic from a 3D printer. In general, such models are considered useful for surgical planning and education; these modalities are being applied as critical tools in the field of cardiovascular research.

Recently, the development of virtual reality (VR) has introduced a new modality for exploring 3D virtual structures with high resolution, high flexibility, and fast turn-around times. Until recently, the adoption of these technologies has been hindered by the high costs of VR goggles and the complexities in their setup. New developments in phone software and hardware, however, have alleviated some of these difficulties by allowing smartphone screens, graphics units, and gyroscopes to provide the necessary technologies for VR. In this way, phones can be placed inside a headset holder and used freely, without being connected to the computer.

Here we explore the utility of using this VR setup in the context of internal heart anatomy visualization.

Commentary by Dr. Valentin Fuster
2017;():V001T09A010. doi:10.1115/DMD2017-3473.
FREE TO VIEW

An implantable cardiac pacemaker is used to modify and treat irregular heartbeats [1] and invented in 1958 [2]. Devices have no fixation or fixed to the heart wall. No fixation leads lay in the bottom of heart cavities, while fixed leads have tines (passive) or a helix screw (active) to attach to the heart. Lead geometries and material properties vary between companies, with geometric sizing based primarily on the internal mechanics of the lead.

Finite element analysis (FEA), computational fluid dynamics (CFD) and bench-top simulations are used to evaluate cardiac leads. These simulations analyze only one lead and struggle to compare and test variations in lead designs. Advanced computational resources can run many computer simulations of anatomical environments, however model complexity increases the time to run each simulation.

To address this issue, we present a simplified parameterized design space for cardiac pacemaker leads in the right atrium. This information will be used to run multiple simulations of leads in blood flow, for visualization in a single virtual reality (VR) environment and allow the designer to iterate through many design variations (See Figure 1).

Topics: Pacemakers
Commentary by Dr. Valentin Fuster
2017;():V001T09A011. doi:10.1115/DMD2017-3496.
FREE TO VIEW

This research presents a virtual reality simulator for total hip replacement surgery. The simulator supports a library of 3D hip stem models for different sizes and manufacturers. The 3D hip stems can be adjusted in size and shape by parametric software and sent for 3D printing. Biocompatible materials such as titanium enable the 3D printed stems to be directly implanted on patients.

Currently surgical simulation for orthopaedic procedures is not as advanced as other surgical disciplines. As a result there are only limited training simulators available for o