ASME Conference Presenter Attendance Policy and Archival Proceedings

2013;():V03AT00A001. doi:10.1115/IMECE2013-NS3A.

This online compilation of papers from the ASME 2013 International Mechanical Engineering Congress and Exposition (IMECE2013) represents the archival version of the Conference Proceedings. According to ASME’s conference presenter attendance policy, if a paper is not presented at the Conference, the paper will not be published in the official archival Proceedings, which are registered with the Library of Congress and are submitted for abstracting and indexing. The paper also will not be published in The ASME Digital Collection and may not be cited as a published paper.

Commentary by Dr. Valentin Fuster

Biomedical and Biotechnology Engineering: Bioinspired Materials and Structures

2013;():V03AT03A001. doi:10.1115/IMECE2013-65041.

The field of tissue engineering and regenerative medicine is an interdisciplinary field that applies the principles of engineering and life sciences toward the development of biological substitutes that restore, maintain, or improve tissue function or a whole organ. The process involves seeding cells onto biocompatible scaffolds that temporarily act as a supporting structure for cells to attach and grow. Scaffolds for tissue regeneration must present a viable microenvironment for the living cells to adhere, proliferate, and exhibit the necessary tissue function. Electrospinning is an emerging area where polymeric fibers can be fabricated in the micro-nano scale. The flexibility of this process allows for including a wide array of synthetic and natural biocompatible polymers in the scaffold composition, inclusion of bioactive molecules (e.g. DNA, proteins) for enhancing therapeutic applications, and ability to control material and mechanical properties via the electrospinning process — all advantageous parameters that contribute to the promise of utilizing electrospun scaffolds in tissue repair. Biocompatible materials, such as polycaprolactone (PCL), have been used extensively to fabricate scaffolds using electrospinning technique, to study cell compatibility and to evaluate cell functionality for nerve tissue engineering applications. The objective of this study is to quantify the effects of the addition of valproic acid to PCL nanofiber scaffolds created through the electrospinning process with regards to cell proliferation. Valproic acid is a commonly used therapeutic drug for the treatment of epilepsy and bipolar disorder. To determine the effects of the presence of valproic acid (VA), Wharton’s jelly mesenchymal stem cells (MSC) are seeded to the two scaffolds. Wharton’s jelly MSC are multipotent adult stem cells present in the umbilical cord and drawn from their matrix [1,2,3]. These stem cells have renowned ability for use in cell therapy and organ regeneration. This study tests the hypothesis that the presence of valproic acid in PCL nanofiber scaffolds will enhance cell proliferation. Structural and morphological characterization of the scaffolds is also carried out. Fiber diameter and tensile properties of the scaffolds with and without valproic acid are also observed. Such studies will enable us to understand the effects of drugs such as valproic acid on stem cells and will aid in designing scaffolds for applications in nerve regeneration.

Commentary by Dr. Valentin Fuster
2013;():V03AT03A002. doi:10.1115/IMECE2013-66118.

Cartilage defects, which are caused by a variety of reasons such as traumatic injuries, osteoarthritis, or osteoporosis, represent common and severe clinical problems. Each year, over 6 million people visit hospitals in the U.S. for various knee, wrist, and ankle problems. As modern medicine advances, new and novel methodologies have been explored and developed in order to solve and improve current medical problems. One of the areas of investigation that has thus far proven to be very promising is tissue engineering. Since cartilage matrix is nanocomposite, the goal of the current work is to use nanomaterials and nano/microfabrication methods to create novel biologically inspired tissue engineered osteochondral scaffolds for facilitating human bone marrow mesenchymal stem cell (MSC) differentiation. 3D printed polymer constructs were designed to mimic the osteochondral region of articulate joint, and to have enhanced mechanical characteristics when compared to traditional designs. Fabricated scaffolds were also subject to surface modification, both with a chemically functionalized acetylated collagen coating and through absorption via poly-L-lysine coated carbon nanotubes. In vitro proliferation results demonstrated not only that incorporation of the biomimetic carbon nanotubes and poly L-lysine coating and acetylated collagen can induce more proliferation of MSCs than controls, but that more controlled and biomimetically designed features also enhance proliferation of MSCs.

Topics: Bone , Stem cells
Commentary by Dr. Valentin Fuster

Biomedical and Biotechnology Engineering: Biomechanics of Trauma due to Accidents, Surgery or Weapons

2013;():V03AT03A003. doi:10.1115/IMECE2013-62643.

Spiral humerus fractures associated with extreme muscular torsion loading have been well documented in literature. Throwing motions and arm wrestling are the two causes most often researched, while spiral fractures associated with gymnastics have received less attention. The purpose of this study is to explore the factors that may contribute to torsional failure of the humerus while performing a gymnastics move known as a muscle-up. Primary motivation for this study was the result of the author sustaining a spiral fracture to the distal aspect of her left humerus while attempting a muscle-up. To the author’s knowledge, no previous studies analyzing the forces imposed on the upper extremities during a muscle-up have been conducted.

Utilizing the author’s estimated anthropometric measurements and the kinematic and kinetic constraints of the muscle-up activity, the torque acting about the long axis of the humerus was determined in two ways. First, an analytical approach was used to calculate the forces and moments within a simplified linkage representation of the upper extremity for several representative muscle-up postures. The second method was a computer simulation that modeled the entire body with muscles in several different kinematic positions and outputted internal body elbow joint net moments.

The analytical approach resulted in torques between 12.0 N·m and 29.3 N·m. The kinetics derived with the computer simulation revealed joint reaction torques between 13 N·m and 38 N·m and net axial torques between 29.1 N·m and 69.1 N·m acting on the left humerus. The internal moments predicted using the computer simulation were above the author’s minimum predicted torque, 53 N·m, associated with humerus fracture initiation.

Although there may be many factors that contribute to spiral humerus fracture, in this study, it was determined that the kinematic positions of the muscle-up movement are sufficiently extreme so as to produce torques capable of resulting in spiral humerus fracture.

Commentary by Dr. Valentin Fuster
2013;():V03AT03A004. doi:10.1115/IMECE2013-63015.

Recent wars have heightened the need to better protect dismounted soldiers against emerging blast and ballistic threats. Traumatic Brain Injury (TBI) due to blast and ballistic loading has been a subject of many recent studies. In this paper, we report a numerical study to understand the effects of load transmitted through a combat helmet and pad system to the head and eventually to the brain during a blast event. The ALE module in LS-DYNA was used to model the interactions between fluid (air) and the structure (helmet/head assembly). The geometry model for the head was generated from the MRI scan of a human head. For computational simplicity, four major components of the head are modeled: skin, bone, cerebrospinal fluid (CSF) and brain. A spherical shape blast wave was generated by using a spherical shell air zone surrounding the helmet/head structure. A numerical evaluation of boundary conditions and numerical algorithm to capture the wave transmission was carried out first in a simpler geometry. The ConWep function was used to apply blast pressure to the 3D model. The blast pressure amplitude was found to reduce as it propagated through the foam pads, indicating the latter’s utility in mitigating blast effects. It is also shown that the blast loads are only partially transmitted to the head. In the calculation where foam pads were not used, the pressure in the skin was found to be higher due to the underwash effect in the gap between the helmet and skin, which amplified the blast pressure.

Commentary by Dr. Valentin Fuster
2013;():V03AT03A005. doi:10.1115/IMECE2013-63023.

Today there are several armor technologies for reducing penetration injuries. Some of the best technologies are light weight, but alone the trauma to the wearer remains significant. The areal density of a new Hybrid Composite Armor (HCA) maintaining compliance with level III NIJ 0101.06 standards was evaluated using ballistic testing and FEM. This new HCA has a multilayered composite design tailored for Behind Armor Blunt Trauma (BABT) reduction. Three areal densities of HCA were ballistic tested using 7.62 FMJ Lead Core projectiles and measurements of Back Face Signature (BFS) and V50 velocities were collected. For comparison, baseline monolith inserts of similar areal densities were also tested. A critical areal density was found to qualify for the standard while demonstrating a 29.4% reduction in BFS (and hence BABT) in comparison to its baseline. This armor design showed the greatest known propensity to reduce injury both due to the light weight and improved trauma performance compared to existing commercial designs. Numerical simulations in finite element code were carried out to validate with the experimental results. A method for evaluating change-in-velocity and volumetric stress distribution plots was presented using a mock HCA-P2 model. In the future, a similar FEA scheme can be used for predicting the ballistic limit and estimating improvements possible in BABT reduction for HCA concepts with relative design changes.

Topics: Density , Armor
Commentary by Dr. Valentin Fuster
2013;():V03AT03A006. doi:10.1115/IMECE2013-63053.

Traumatic brain injury (TBI) has long been known as one of the most anonymous reasons for death around the world. A presentation of a model of what happens in the process has been under study for many years; and yet it remains a question due to physiological, geometrical and computational complications. Although the facilities for soft tissue modeling have improved and the precise CT-imaging of human head has revealed novel details of brain, skull and the interface (the meninges), a comprehensive FEM model of TBI is still being studied. This study aims to present an optimized model of human head including the brain, skull, and the meninges after a comprehensive study of the previous models. The model is then used to investigate the effects of various sudden velocity-acceleration impulses on the strain field of the brain by using FE method. Next, the results are summed up and compared with an existing criterion on damage threshold in the brain during trauma. To reach this aim, a full geometrical model of a 30-year-old patient’s head has been generated from CT-scan and MR data. The model has been exposed to 20 angular velocity-acceleration pulses. Subsequently, the changes in the strain field have been compared with the results obtained in the previous studies yielding acceptable accordance with a major previous criterion. The results also show that certain criteria can be generated on the threshold of damage in the brain.

Commentary by Dr. Valentin Fuster
2013;():V03AT03A007. doi:10.1115/IMECE2013-63257.

Warfighters who survive encounters with improvised explosive devices (IEDs) may incur mild traumatic brain injury (mTBI) due to blast overpressure effects. Since existing head injury criteria are mostly based on head kinematics, head acceleration is one key metric to be measured. A blast wave travels at supersonic speed with a very sharp peak overpressure rise followed by a rapid decay within a short duration. For the surface area that is covered by the helmet, the cushion/suspension subsystem is responsible for mitigating the blast effects on the head, while the exposed area of the head or face would receive a direct blast loading. Computational fluid dynamic (CFD) simulations of a blast on an upright warfighter show a significant reduction in peak force to the head when a helmet is worn. For a helmet with an attached eye-shield, the load to the head from a front blast can be reduced further. A field study was conducted to verify that the increased load partitioned away from face and to the helmet and cushioning system would result in decreased head acceleration. Blast field tests were conducted using 4 lbs. of cylindrical C4 charges at 92″ standoff. Head acceleration was measured using combinations of a free hanging mid-size standard ISO headform fitted with Team Wendy (TW) pads, an advanced combat helmet (ACH), and an eye-shield. Tests were performed with the blast hitting the front, side and back of the helmeted headform system. Headform accelerations ranging from 120–465g were recorded based on blast direction and the amount of head protection. To validate the three-dimensional Navier-Stokes’ based CFD simulations, a custom-designed blast overpressure bust (BOB) containing 22 surface pressure sensors was mounted on top of the BTD to measure the pressure distribution over the head and face when exposed to a blast. The incident overpressure of the blast was 0.25MPa, with reflected pressures reaching 1.0MPa.

Topics: Stress
Commentary by Dr. Valentin Fuster
2013;():V03AT03A008. doi:10.1115/IMECE2013-63260.

There is significant concern that blast overpressure can cause mild traumatic brain injury (mTBI). An accurate understanding of the blast flow and overpressure event as well as it’s interaction with the head and helmet system is a necessary first step in establishing loading conditions to the head. It also provides a means for model validation and other predictive capabilities. A custom-designed Blast Overpressure Bust (BOB) containing 22 surface pressure sensors was rigidly mounted in a live-fire blast event. The blast field tests were conducted in an open field using 4 lbs. of cylindrical C4 charges suspended 48″ above the pad. The BOB was mounted to a torso surrogate and positioned 92″ from the hanging charge. The BOB was oriented at blast impact angles of 0 (front-facing), 45, 90, and 180 degrees. The BOB was tested in both bare and helmeted configurations. Data recorded across a bare headform at each angle established a baseline for the pressure trace at each sensor location. Two helmeted cases were investigated: Advanced Combat Helmet (ACH) with the sling suspension system and ACH with Team Wendy pads. Results showed peak pressures on exposed surfaces normal to the blast were ∼1200kPa with side-on pressures of ∼400kPa. The addition of a helmet did not alter the peak normal pressures, but showed slight to moderate increases in pressure beneath the helmet based on the amount of cushioning present. The sling suspension, which leaves an open gap between the head and helmet, resulted in several recorded amplification points beneath the helmet with the peaks reaching ∼800kPa. The Team Wendy pads trials, which effectively fill the gap between the head and helmet, showed amplifications with peaks of ∼500kPa. An additional set of tests was conducted using an ingress barrier positioned between the head and helmet at the brim. Results showed pressures under the helmet that were lower than the bare headform trials. While it was shown that adding a helmet did in fact increase pressures relative to the bare headform case, these amplifications were still far less than the peak pressure exerted on the exposed surfaces of the headform. The data presented herein is the most robust data set to date for pressures exerted on a helmeted headform and is considered applicable to the first 3–5ms of an unconstrained system, during which time motion is minimal.

Commentary by Dr. Valentin Fuster
2013;():V03AT03A009. doi:10.1115/IMECE2013-63732.

Detonation of a high explosive (HE) produces shock-blast wave, noise, shrapnel, and gaseous product; while direct exposure to blast is a concern near the epicenter; shock-blast can affect subjects even at farther distances. The latter is characterized as the primary blast with blast overpressure, time duration, and impulse as shock-blast wave parameters (SWPs). These parameters in turn are a function of the strength of the HE and the distance from the epicenter. It is extremely important to carefully design and operate the shock tube to produce a field relevant SWPs. In this work, we examine the relationship between shock tube adjustable parameters (SAPs) and SWPs to deduce relationship that can be used to control the blast profile and emulate the field conditions.

In order to determine these relationships, 30 experiments by varying the membrane thickness, breech length (66.68 to 1209.68 mm) and measurement location was performed. Finally, ConWep was utilized for the comparison of TNT shock-blast profiles with the profiles obtained from shock tube.

From these experiments, we observed the following: (a) burst pressure increases with increase in the number of membrane used (membrane thickness) and does not vary significantly with increase in the breech length; (b) within the test section, overpressure and Mach number increases linearly with increase in the burst pressure; however, positive time duration increases with increase in the breech length; (c) near the exit of the shock tube, there is a significant reduction in the positive time duration (PTD) regardless of the breech length.

Commentary by Dr. Valentin Fuster
2013;():V03AT03A010. doi:10.1115/IMECE2013-63910.

Blast induced neurotrauma (BINT), and posttraumatic stress disorder (PTSD) are identified as the “signature injuries” of recent conflicts in Iraq and Afghanistan. The occurrence of mild to moderate traumatic brain injury (TBI) in blasts is controversial in the medical and scientific communities because the manifesting symptoms occur without visible injuries. Whether the primary blast waves alone can cause TBI is still an open question, and this work is aimed to address this issue. We hypothesize that if a significant level of intracranial pressure (ICP) pulse occurs within the brain parenchyma when the head is subjected to pure primary blast, then blast induced TBI is likely to occur.

In order to test this hypothesis, three post mortem human heads are subjected to simulated primary blast loading conditions of varying intensities (70 kPa, 140 kPa and 200 kPa) at the Trauma Mechanics Research Facility (TMRF), University of Nebraska-Lincoln. The specimens are placed inside the 711 mm × 711 mm square shock tube at a section where known profiles of incident primary blast (Friedlander waveform in this case) are obtained. These profiles correspond to specific field conditions (explosive strength and stand-off distance). The specimen is filled with a brain simulant prior to experiments. ICPs, surface pressures, and surface strains are measured at 11 different locations on each post mortem human head. A total of 27 experiments are included in the analysis.

Experimental results show that significant levels of ICP occur throughout the brain simulant. The maximum peak ICP is measured at the coup site (nearest to the blast) and gradually decreases towards the countercoup site. When the incident blast intensity is increased, there is a statistically significant increase in the peak ICP and total impulse (p<0.05). Even after five decades of research, the brain injury threshold values for blunt impact cases are based on limited experiments and extensive numerical simulations; these are still evolving for sports-related concussion injuries. Ward in 1980 suggested that no brain injury will occur when the ICP<173 kPa, moderate to severe injury will occur when 173 kPa<ICP<235 kPa and severe injury will occur when ICP>235 kPa for blunt impacts. Based on these criteria, no injury will occur at incident blast overpressure level of 70 kPa, moderate to severe injuries will occur at 140 kPa and severe head injury will occur at the incident blast overpressure intensity of 200 kPa. However, more work is needed to confirm this finding since peak ICP alone may not be sufficient to predict the injury outcome.

Commentary by Dr. Valentin Fuster
2013;():V03AT03A011. doi:10.1115/IMECE2013-64587.

Complementary to animal testing and analysis of clinical data, a validated anatomy and physiology based mathematical models can provide capabilities for a better understanding of blast wave brain injury mechanisms, animal-human injury scaling, assessing and improving protective armor. We developed the 3D “virtual” animal models for multi-scale computational simulations of blast induced injury. A multi-scale modeling tool, CoBi, has been adopted for the analysis of blast wave primary TBI mechanisms and coupled biomechanics events. The shock wave over a rat in a shock tube was modeled by the CFD method. The primary biomechanics FEM study uses anatomic based animal geometry with a high resolution brain model. The virtual rat model has been validated against recently collected data from shock tube tests on rodents, including pressure time history in the free-stream and inside the rat brain. The model has been used to conduct parametric simulations to study the effect of animal placement location in the shock tube, and different loading orientations on the rat response. We also compared the rat brain biomechanical response between simulations of a free-to-move and a protected or constrained rat under the same shock tube loading to identify the role of body protection and head movement and on the rat TBI. The implications of these results suggest that virtual animal model could be used to predict the biomechanical response in the blast TBI event, and help design the protection against the blast TBI.

Commentary by Dr. Valentin Fuster
2013;():V03AT03A012. doi:10.1115/IMECE2013-64803.

Experiments were conducted to determine bacteria distribution trends in wound cavities of simplified surrogate extremities shot using small caliber projectiles. Two different shapes of targets, cylindrical and square, were used in this study. Cylindrical targets are more representative of an extremity but create difficulties while conducting tests due to inconsistent cavity lengths and optical distortions. Square targets, which are not as susceptible to the problems mentioned above, could be used in place of cylindrical ones if their shape does not significantly affect the distribution of bacteria within the wound cavity. Surface contamination of the targets in the experiments was represented using a circular piece of filter paper moistened with a solution with a known amount of Escherichia coli strain K-12. The projectiles used were 11.43-mm (0.45-in) caliber round nose projectiles shot from a commercially available air rifle. The permanent cavities were extracted from the targets and sliced into small, evenly spaced segments and the area surrounding the permanent cavities was removed with a biopsy punch. The radial tears that were made by the formation of the temporary cavity and surround the permanent cavity were removed using a scalpel. The permanent cavity and radial tears for each section were processed and plated on agar plates. Commercial software was used to count the number of colony forming units on each plate and the percentage of the total bacterial colony count per segment was determined. High speed video and motion analysis software was used to qualitatively and quantitatively compare the temporary cavities in the cylindrical and square targets. The data from the experiments showed that the bacteria distribution trends for the cylindrical and square targets were similar even though the maximum openings of the temporary cavity at the entrance and exit locations were higher for the cylindrical ones. For both target shapes, the bacterium was evenly distributed between the permanent cavity and the radial tears in the middle sections of the “wound tracks.” In addition, significantly higher amounts of bacterium were found in the entrance and exit segments compared with the rest of the segments in the “wound tracks”.

Topics: Projectiles , Bacteria
Commentary by Dr. Valentin Fuster
2013;():V03AT03A013. doi:10.1115/IMECE2013-64821.

Strains and pressures in the brain are known to be influenced by rotation of the head in response to loading. This brain rotation is governed by the motion of the head, as permitted by the neck, due to loading conditions. In order to better understand the effect neck characteristics have on pressures and strains in the brain, a human head finite element model (HHFEM) was attached to two neck FEMs: a standard, well characterized Hybrid III Anthropometric Test Device neck FEM; and a high fidelity parametric probabilistic human FEM neck that has been hierarchically validated. The Hybrid III neck is well-established in automotive injury prevention studies, but is known to be much stiffer than in vivo human necks. The parametric FEM is based on CT scans and anatomic data, and the components of the model are validated against biomechanical tests at the component and system level. Both integrated head-neck models were loaded using pressure histories based on shock tube exposures. The shock tube loading applied to these head models were obtained using a computational fluid dynamics (CFD) model of the HHFEM surface in front of a 6 inch diameter shock tube. The calculated pressure-time histories were then applied to the head-neck models. The global head rotations, pressures, brain displacements, and brain strains of both head-neck models were compared for shock tube driver pressures from 517 to 862 kPa. The intracranial pressure response occurred in the first 1 to 5 msec, after blast impact, prior to a significant kinematic response, and was very similar between the two models. The global head rotations and the strains in the brain occurred at 20 to 100 msec after blast impact, and both were approximately two times higher in the model using the head parametric probabilistic neck FEM (H2PN), as compared to the model using the head Hybrid III neck FEM (H3N). It was also discovered that the H2PN exhibited an initial backward and small downward motion in the first 10 ms not seen in the H3N. The increased displacements and strains were the primary difference between the two combined models, indicating that neck constraints are a significant factor in the strains induced by blast loading to the head. Therefore neck constraints should be carefully controlled in studies of brain strain due to blast, but neck constraints are less important if pressure response is the only response parameter of primary interest.

Topics: Kinematics , Brain
Commentary by Dr. Valentin Fuster
2013;():V03AT03A014. doi:10.1115/IMECE2013-64959.

In combat zones, warfighters may be exposed to multiple threat types that can result in impacts to the head. These head impacts can lead to traumatic brain injury (TBI) or other functional or cognitive impairments, depending on the impact location, duration, and severity. Personal protective equipment mitigates the damage to the head, and current equipment design efforts focus on high-level protective metrics such as local helmet deformations and penetrations, as well as global accelerations or rotations of the head. Advances in brain imaging and mapping have made it possible to couple brain regions with specific functions, which could lead to higher resolution injury models and a more integrated helmet design process.

The Naval Research Laboratory has developed a design tool to relate cognitive and functional brain regions from the literature to representative threat models for a head-helmet system. In this study, the philosophy and methods behind this augmented design tool and some of its applications are discussed. Through surveying detailed brain mappings and Brodmann functional areas, spatial coordinates for a coarse and a fine brain model were identified, scaled, and positioned within a three-dimensional model of the head. Projectile threats to the brain from all directions were simulated to evaluate the vulnerability of specific brain regions for a given protective helmet geometry. Using this platform, a variety of design tools were developed to investigate the functional effects of making geometric changes to the helmet.

Topics: Design , Brain
Commentary by Dr. Valentin Fuster
2013;():V03AT03A015. doi:10.1115/IMECE2013-64971.

A single point acceleration measurement at the center of gravity (C.G) of the rigid headform has been typically used to assess the head injuries under the blunt loading conditions. The head protective equipment (e.g. Helmets) used in sports, vehicles and defense fields are developed and tested based on this single point acceleration. This raises two critical questions; 1) can a homogeneous rigid headform represent the heterogeneous skull-brain complex; 2) If not, which is the critical point of measurement in the compliant headform. To answer these questions, compliant (acrylic gel complex) and rigid (aluminum body) head surrogates with an identical mass are subjected to similar blunt loading conditions. Target surfaces of different stiffness and an impact velocity of 1 m/s are employed to evaluate the critical difference in the head surrogates. Acceleration (C.G) and shell strain (impact location) in the compliant surrogate and acceleration (C.G) and the impact force in the rigid surrogate are experimentally measured. Experimental and computational studies illustrate that the acceleration field in the gel-filled case varies from coup to counter-coup region; however, the acceleration field in the rigid headform is uniform. The variation in the acceleration field is influenced by the shell deformation that in turn depends on the stiffness of the target surface. In deformable target surfaces, the acceleration and head injury criterion (HIC) values are higher in the compliant surrogate than the rigid surrogate; the effect is reversed for rigid target surfaces.

Commentary by Dr. Valentin Fuster
2013;():V03AT03A016. doi:10.1115/IMECE2013-64992.

Blast-induced traumatic brain injury (bTBI) has been called the signature wound of war in the past decade. The mechanisms of such injuries are not yet completely understood. One of the proposed hypotheses is the transfer of pressure wave from large torso blood vessels to the cerebrovasculature as a major contributing factor to bTBI. The aim of this study was to investigate this hypothesis by measuring cerebral blood pressure rise during blast exposure and comparing two scenarios of head-only or chest-only exposures to the blast wave. The results showed that the cerebral blood pressure rise was significantly higher in chest-only exposure, and caused infiltration of blood-borne macrophages into the brain. It is concluded that a significantly high pressure wave transfers from torso to cerebrovasculature during exposure of the chest to a blast wave. This wave may lead to blood-brain barrier disruption and consequently trigger secondary neuronal damage.

Commentary by Dr. Valentin Fuster
2013;():V03AT03A017. doi:10.1115/IMECE2013-65138.

Tactical officers and military personnel who train in explosive entry techniques regularly put themselves at risk of blast exposure. The overpressure conditions in complex military and law enforcement environments, such as interior doors, hallways, and stairwells, cannot be accurately predicted by standard blast models which were developed from outdoor, free-field blasts. In both training and operations, small, low-cost blast overpressure sensors would provide the benefit of tracking exposure levels of at-risk individuals. The sensors would allow, for the first time, direct determination of safe stand-off distances and positioning for personnel during explosive breaching. Overpressure, impulse, and acceleration data has been captured for a series of interior and exterior blasts, demonstrating the utility of the Blast Gauge system as a training and research tool to quantify blast overpressure in complex environments.

Commentary by Dr. Valentin Fuster
2013;():V03AT03A018. doi:10.1115/IMECE2013-65154.

Injury prediction and mitigation are common overarching goals of modern biomechanical research. This research is fundamental to preventing and mitigating injuries sustained by those exposed to dangerous conditions including but not limited to occupational hazards, warfighter risks, automotive accidents, etc. Unlike traditional mechanical system research, biological systems are difficult and costly to test resulting in a need for robust and accurate numerical simulations. Models of the cervical spine are complex, nonlinear systems that must accurately model dynamic loading, large deflections, elastic, and viscoelastic behavior. In addition to individual complexities, population variance in both material properties and shape must be taken into account for accurate injury prediction.

As part of a hierarchical validation and verification (V&V) methodology, lateral impact cadaveric cervical spine experiments were compared to a high fidelity statistical shape finite element model (SSFEM) of the cervical spine and head. Specimens were mounted to a sled and accelerated using a pendulum impact with 1, 2, and 3 m/s impact velocities. The kinematics of the head and all individual cervical vertebrae were recorded with a Vicon motion capture system along with sled acceleration data. Sled accelerations were used as input boundary conditions for the probabilistic study using the SSFEM. Head and vertebrae rotations between the experimental and model responses were then compared.

A latin hypercube probabilistic analysis was performed for each impact velocity to determine the probabilistic response of each rotation metric. When comparing these responses, both the average and variation must be taken into consideration. This is accomplished using a quantitative validation metric based on the area between the cumulative distribution functions (CDF) of experimental response and the computed probabilistic response. Our results showed a very good match between the model and experiment at the higher impact velocities and a slightly stiffer response at lower rates. These results are consistent with previous validation studies performed with this SSFEM.

By expanding the validation data set with lateral impact loading, greater confidence in the model is obtained under different loading modes. This confidence allows the model to be used for probability of injury predictions as well as to identify important system variables in preventing injuries. High fidelity numeric modeling allows for rapid and cost effective assessment of hazardous loading conditions and safety equipment compared to experimental modeling. The knowledge gained from these modeling studies is fundamental and necessary for safe and effective design and injury mitigation.

Commentary by Dr. Valentin Fuster
2013;():V03AT03A019. doi:10.1115/IMECE2013-66546.

Traumatic Brain Injury (TBI) contributes to a major number of deaths and cases of permanent disability each year. Falls are the leading cause of TBI with the highest rates for children 0–4 years old and for adults age 75 and older. Accordingly, there is a significant interest in fall-related injury mechanism and head impact. Since the dynamics of human fall and head injury mechanisms are highly variable due to the inherent and complex nature of human falling, the aim of the present study is to describe the dynamics of backward falls and risk of injury due to head impact. In order to have a better understanding of head impact, A HYBRID III 5th Percentile Female test (Denton ATD, Inc.) instrumented with a tri-axial accelerometer with measuring range of ±500g at the center of gravity of the head was dropped from standing posture by using a controlled release mechanism. The dynamic model of fall was captured using a T-series Vicon motion capture system synchronized with a force plate to measure the impact force and a tri-axial accelerometer to measure the impact acceleration of the head. The acceleration impact data measured at 20 KHz and the motion capture system was capable to retrieve 500 samples per second. The primary objective of this study was to determine the equivalent mass involved during head impact due to a backward fall. This effective mass is a key quantity to design the head impact experimental setups, protection devices and computer simulations of head impact. Based on the force and acceleration measurements in several tests, the head impact effective mass is approximately found to be the mass of head itself plus 48% the neck mass. Two scenarios of backward fall were studied and discussed. First, falling while the hip joints are involved and the trunk moves forward and second, falling while the hip joints act like a fixed joint. For the first scenario the impact forces and accelerations peak measured using the HYBRID III were found to be 10±1.8KN and 255±42g, respectively, and for the second scenario the larger impact forces, 14.5±0.9KN, and acceleration peaks, 364±27g, were measured in all tests.

Commentary by Dr. Valentin Fuster
2013;():V03AT03A020. doi:10.1115/IMECE2013-66794.

In order to expand on potential injury mechanisms to the brain, a micromechanical structural representation of the gray matter must be developed. The gray matter contains a high volume of capillary vasculature that supplies the necessary oxygen required for maintaining healthy cell and brain function. Even short disruptions in this blood supply and the accompanying dissolved oxygen can lead to neuronal cell damage and death. It has been shown that increased shearing forces within the blood, such as those found near stents and artificial heart valves, can lead to platelet activation and aggregation, causing clots to form and potential disruptions in blood flow and oxygen distribution. Current macro-scale computational brain modeling can incorporate the larger main vasculature of the brain, but it becomes too computationally expensive to incorporate the smaller vessels. These larger scale models can be used to reveal how forces to the head are transmitted down to a scale slightly larger than the smallest capillaries within the gray matter. In order to investigate the response and potential damage to capillaries and platelets within the brain, a micromechanical computational model is developed incorporating the gray matter, capillaries, and blood, which is composed of plasma, red blood cells, and platelets. The red blood cells are a necessary component for the model for damage as it comprises almost half of the volume of blood and is the major contributor to the non-Newtonian behavior. The model combines both fluids and viscoelastic solid materials (the gray matter and the vascular wall). The deviatoric stress, strain and strain rate of the platelets in response to an externally applied load is measured and will determine the potential for platelet aggregation and clot formation. The micromechanical model is also used to provide verification and refinement for existing constitutive models for the gray matter used in meso- and macro-scale computational models.

Commentary by Dr. Valentin Fuster

Biomedical and Biotechnology Engineering: Clinical Applications of Bioengineering

2013;():V03AT03A021. doi:10.1115/IMECE2013-62553.

Currently, there are approximately 33,000 total knee arthroplasty revision surgeries each year. This number is expected to increase with the aging population. During revision surgeries, metal implants are often secured to the tibial plateau by creating a mantel of polymethylmethacrylate (bone cement) that must be removed during revision, often times by sagittal sawing. Presently, there are no published studies on the mechanics of bone cement removal by a sawing process. The aim of this research was to quantify the effect of blade speed and applied thrust force on the volumetric cutting rate of bone cement. A custom reciprocating saw with variable stroke length was used to conduct a three factor Design of Experiments. Two levels, without center-points, were sufficient to model the effect of stroke length, thrust force, and reciprocating speed on cutting rate. The results demonstrate a linear relationship between both force and cutting rate, and blade speed and cutting rate. A cutting rate model was developed by regression analysis of the experimental data. The model has applications in haptic feedback for surgical simulators. This study provides a basis for understanding the operational parameters of the bone saw, which is the first step in designing saw blades for cutting bone cement as these designs may differ significantly from those optimized to cut cortical bone.

Commentary by Dr. Valentin Fuster
2013;():V03AT03A022. doi:10.1115/IMECE2013-62554.

Surgical bone screws can be subjected to cyclic bending loads when plating constructs are used in the fixation of weight bearing members. While extensive research has been conducted on axial loading that leads to screw pull-out, there is a gap in our understanding of how asymmetric bending loads contribute to screw fracture. The focus of this research was to examine the effect of screw length (20 mm and 40 mm) and cancellous bone density (0.48 g/cm3 and 0.24 g/cm3) on the relative stiffness of 6.5 mm cancellous bone screws subjected to a cantilever bending load. It was hypothesized that longer screws in higher density cancellous bone would result in less screw deflection, supporting clinical practice. For testing, synthetic composite bone was used to simulate the characteristics of natural bone while subjecting screws to quasi-static loading with a universal testing machine. Contrary to the hypothesis, neither screw length nor cancellous bone density resulted in a statistically significant difference (p > 0.05) in deflection for loading up 450 N. The cortical shelf appeared to support the majority of the bending load through compression, rather than acting as a fulcrum. When the 3.0 mm cortex was removed, there was a significant difference in deflection due to both screw length and cancellous bone density.

Commentary by Dr. Valentin Fuster
2013;():V03AT03A023. doi:10.1115/IMECE2013-62556.

Thermal necrosis of bone occurs at sustained temperatures above approximately 47°C. During joint replacement surgery, resection of bone by sawing can heat the bone above this necrotic threshold, thereby inducing cellular damage and negatively affecting surgical outcomes. The aim of this research was to investigate the effect of saw blade speed and applied thrust force on the heating of bone. A sagittal sawing fixture was used to make cuts in cortical bovine bone, while thermocouples were used to characterize the temperature profile from the cut surface. A full factorial Design of Experiments was performed to determine the relative effects of blade speed and applied thrust force on temperature. When comparing the effect of speed to force in the regression analysis, the effect of force on temperature (p < 0.001) was 2.5 times more significant than speed (p = 0.005). The interaction of speed and force was not statistically significant (p > 0.05). The results of this research can be used in the development of training simulators, where virtual surgeries with haptic feedback can be accompanied by the related temperatures in proximity to the cut. From a clinical perspective, the results indicate that aggressive cutting at higher blade speed and greater thrust force results in lower temperatures in the surrounding bone.

Commentary by Dr. Valentin Fuster
2013;():V03AT03A024. doi:10.1115/IMECE2013-62557.

A sagittal saw is used for resection of bone during joint replacement surgery. During sawing, tissue at the cut surface can be damaged by high temperatures, which may lead to aseptic loosening of implants. To date, there have been no studies relating sagittal sawing parameters to the level of tissue necrosis. The aim of this study was to determine the feasibility of using histopathological analysis in assessing the severity of thermal necrosis due to sawing. All sawing experiments were performed on cortical bone taken from fresh bovine femur. A two factor, two level design of experiments was performed looking at applied thrust force from 15 N to 30 N and blade oscillation speed from 12,000 cpm to 18,000 cpm. Each cut was subjected to standard histological preparation and the depth of empty lacunae was measured. Both experimental factors, force and speed, showed a statistically significant effect on the depth of thermal necrosis (p< 0.05). However, the interaction of speed and force did not prove to be statistically significant (p = 0.22). From a clinical perspective, the results indicate that choosing higher blade speeds and applying greater force can reduce the amount of thermal damage during sagittal sawing.

Topics: Sawing , Bone
Commentary by Dr. Valentin Fuster
2013;():V03AT03A025. doi:10.1115/IMECE2013-62791.

Radiofrequency (RF) catheter ablation is a highly effective treatment for many cardiac arrhythmias, especially for tachyarrhythmia. RF energy is introduced through the catheter onto the endocardial surface to destroy the abnormal heart tissue causing the heart rhythm disorder. Many parameters relate to myocardial temperature, such as RF power, tissue contact, and blood flow. Blood flow is an important factor that has a cooling effect on myocardium and affects the final lesion size. Many previous studies have shown that under temperature control, lesion sizes are larger and tissue temperatures rise faster with a high flow rate. If the flow causes a decrease in the temperature of the catheter tip, the generator will increase the power output to maintain the tip at a constant temperature. However, few studies of RF catheter ablation have investigated how ablation affects blood flow. Observation of the flow pattern around the catheter can help to determine the mechanism of the flow effects on the temperature of the catheter tip. The purpose of this study is to observe the flow pattern during ablation using an in-vitro circulation system developed for Particle Image Velocimetry (PIV). We developed an open-channel circulation system to simulate blood flow. The mold for the open-channel was built with acrylic boards for transparency. The working fluid was 0.9% saline, which was used at room temperature (20°C). Instead of animal myocardium, we used a poly (vinyl alcohol) hydrogel (PVA-H), which has mechanical characteristics that approximate those of biological soft tissue, and contact with the PVA-H surface by the catheter is similar to that with myocardium. A 7 Fr catheter with a 4-mm ablation electrode tip was set perpendicular to the PVA-H surface, and the contact weight between the electrode of the catheter and the PVA-H surface was 2.2 gf. To measure the temperature profile in the PVA-H, a K-type thermocouple with the diameter of 0.5 mm was placed at the depth of 2 mm from the surface. The thermocouple tip was always placed on the catheter axis. The flow pattern at the location where the catheter was held was observed by a high speed camera, and the resulting images were analyzed by particle image velocimetry (PIV). The results showed that in the absence of applied flow, convection flow from the electrode is observed in the areas around the catheter. However, under a 1.6 L/min flow rate, convection flow disappears. In conclusion, blood flow could decrease the catheter tip temperature, and the influence of ablation in the flow around the catheter disappeared.

Commentary by Dr. Valentin Fuster
2013;():V03AT03A026. doi:10.1115/IMECE2013-62844.

Standard medical practice is known to have a history of varying definition of “standard”. As with any industry with multiple entities, each entity defines their standards and expectations according to what they believe is their customers’ (i.e. patients) needs and preferences. Recently, our research on developing a predictive wound care assessment methodology and system has extended our study into analyzing evidence-based best practices in wound care clinics. Our research on wound healing predictive model systems, revealed key differences in operational practice between the clinics that were visited in different institutional settings. The scope of this study evaluates our observed wound care practice and wound care treatment to determine if there is a common set of effective practice that can be developed to better standardize care. The purpose of this paper is to compare and contrast the operational practice and procedures at various community and teaching hospitals to determine if there is an ideal combination of tools and standard techniques that would be most beneficial to patient wound care. This paper will focus on methods of patient wound care. We will then present a model of “Evidence-Based Best Practices of Wound Care Assessment” that is based on the observation and interactions with various hospitals.

Topics: Teaching , Biomedicine
Commentary by Dr. Valentin Fuster
2013;():V03AT03A027. doi:10.1115/IMECE2013-62899.

Knowledge of the movements of the whole spine and lumbosacral joint is important for evaluating clinical pathologic conditions that may potentially produce unstable situations in human body movements. At present there are few studies that report systematic three-dimensional (3D) movement and force analysis of the whole spine. In this paper, a fully discretized bio-fidelity 3D musculoskeletal simulation model for biomechanical (kinematic) analysis of scoliosis for a patient with right thoracolumbar scoliosis is presented. It is important to note that this method can be used for modeling various types of scoliosis. It should be noted that this is the first time that such a detailed model of this kind has been constructed according to known literature.

The combined loading conditions acting on the intervertebral joints and corresponding angles between vertebrae were analyzed during lateral bending through the motion capturing and musculoskeletal modeling of two female subjects, one with normal spine and the other with scoliosis. The scoliosis subject who participated in this study has thoracolumbar scoliosis with convexity to the right. Since lateral bending is one of the typical tasks used by clinicians to determine the severity of scoliosis condition, the motion data of the subjects in lateral bending while standing was captured. These motion data were assigned to train the musculoskeletal multi-body models for the inverse and forward dynamics simulations.

The mobility of the ribcage, joint angle, as well as joint force were analyzed using the developed simulation model. According to the results obtained the combined loadings at the lumbar joints in the scoliosis model are considerably higher than the loads of the normal model in this exercise. This research has investigated the effect of thoracolumbar scoliosis on spinal angles and joint forces in lateral bending by the application of motion data capturing and virtual musculoskeletal modeling. The results of this study contribute to a better understanding of human spine biomechanics and help future investigations on scoliosis to understand its development as well as improved treatment processes.

Topics: Scoliosis
Commentary by Dr. Valentin Fuster
2013;():V03AT03A028. doi:10.1115/IMECE2013-63132.

This paper extends our previously presented two-dimensional (2-D) Holographic Microwave Imaging Array (HMIA) system for early breast tumour detection to three-dimensional (3-D) imaging, and demonstrates its efficacy using experimental data obtained with a breast phantom. This work describes an experimental setup to collect data to form a 3-D breast image. The obtained experimental result proves that the 3-D HMIA system has potential to become a screening and diagnostic tool that could supplement clinical breast examination through its sensitivity, quantitative record storage, ease-of-use, and inherent low cost.

Commentary by Dr. Valentin Fuster
2013;():V03AT03A029. doi:10.1115/IMECE2013-63179.

A review of the state of the art in prosthetic hands is presented; this review covers the most common commercial prosthesis and prototypes under development.

In this analysis, prosthetic devices were divided in six systems: actuation, reduction, blocking, transmission, flexion and support. The information obtained is presented according to those systems.

The most important features of each system are presented together with their relationship with the performance of the entire prosthesis. An analysis that indicates the way in which prosthesis take advantage of the capabilities of current technologies is presented. Recommendations for improving the performance of upper limb prosthesis are proposed.

Commentary by Dr. Valentin Fuster
2013;():V03AT03A030. doi:10.1115/IMECE2013-63355.

Microscopic Magnetic Resonance Elastography (μMRE) could be useful in estimating the shear stiffness of biological or other samples of small dimension. In this study, a silicon rubber phantom shell with liquid inside of it was measured using μMRE. A parametric simulation study of a simplified axisymmetric shell model was performed in order to interpret the wave propagation and how it is affected by the material parameter values.

Commentary by Dr. Valentin Fuster
2013;():V03AT03A031. doi:10.1115/IMECE2013-63739.

Minimally invasive surgery (MIS) is known to be a difficult procedure to master due to its complexity, compared to traditional open surgery. Therefore, an objective and quantitative assessment tool is highly required in MIS, which can be used for determining surgeon’s skills, evaluating educational programs and providing subjects with unbiased feedback. The goal of this paper is to review various assessment methods, summarize capabilities of the methods, and suggest future possible improvements. Specifically, this paper categorize existing methods into two groups: the first and the most well known group focuses on the analysis of surgical motions, and the other group uses force and torque as a key metric. Specifically, motion analysis includes tracking the body, tool, or hand motions of a surgeon, either from teleoperated robotic systems or surgical simulators using different sensors like wireless or electromagnetic motion tracking sensors, video-glove-based input devices, optical tracking system, or magnetic tracking technologies. Sometimes data explored form this method is synchronized with eye-gaze data (what a surgeon looks at while operating), or videographic data. Using motion analysis actually the number of movements, rate of movements, total path length, movement variability, time taken to complete the operation, average or peak velocity are considered for assessing surgical skills. On the other hand, the methods in the second group assess the skills based on force and toque data that surgeons apply through surgical instruments. More specifically, these methods use different kind of sensors placed on the grasper. Different force and torque measurement systems, hidden-Markov-model-based analysis, simulated models with criteria, and Virtual reality have been developed, allowing for the quantification of the performance of surgeons.

Although, each method has its own advantageous, and according to the kind of surgical task and evaluation, these methods can be used successfully to assess surgical skills, to provide predictive validity for each of these methods more study is needed. Also, future works should improve the efficiency of each method and move toward automated, low-cost and real time assessment methods.

Topics: Surgery
Commentary by Dr. Valentin Fuster
2013;():V03AT03A032. doi:10.1115/IMECE2013-63859.

This paper proposes a new Patient-Specific Aneurysm CFD Model (PSAM) which is based on the energy strain function combined with dilated vessel wall stress-strain relationship to predict aneurysm rupture. The PSAM relies on the available mechanical properties and parameters obtained from a personalized model. A personalized model is developed based on instantaneous arterial deformations obtained from Doppler Ultrasound (US) images at 6–9 MHz. It is shown that PSAM has the ability to correlate the deformation wall energy based on continuous patient-specifics in predicting rupture.

Commentary by Dr. Valentin Fuster
2013;():V03AT03A033. doi:10.1115/IMECE2013-63922.

Background and purpose: Recently, the number of endovascular treatments has increased worldwide because of advances in minimally invasive surgery. We considered the effect of reduced flow due to stent implantation and proposed the design of stent strut pattern from the viewpoint of fluid dynamics. We developed an optimized stent strut pattern using a computational fluid dynamics (CFD) system. A classification of cerebral aneurysms was proposed using the aspect ratio (AR) and the stent strut pattern was optimized. The results of optimal stent strut pattern for reduced blood flow speed and wall shear stress were different, and the influence of the AR values was small because there was no dependence on relationship between blood flow and the AR values due to the use of a straight pipe in the parent artery. The classification of blood flow pattern in a cerebral aneurysm must consider the parent artery curves. In this study, we investigated the relationship between the blood flow pattern in cerebral aneurysms and parent artery curves using CFD.

Methods: To investigate the influence of blood flow based on the parent artery curve, the parent artery shape was constructed as follows. Patient-specific parent artery shape with a cerebral aneurysm was reconstructed using OsiriX. Center line was extracted using a vascular modeling tool kit. The parent artery shape was reconstructed based on this center line using CAD. The diameter of the parent artery was 4 mm. The cerebral aneurysm shape was a combination of a straight pipe and a half sphere, and the AR value was fixed at 1.0. The cerebral aneurysm position varied from the original position to a 180° rotated position.

Tetrahedral numerical mesh was generated with a commercial mesh generator (ICEM CFD 14.0; Ansys Inc.) for the CFD analysis. The numerical blood flow simulation was performed on a supercomputer using the commercial ANSYS FLUENT 6.3 software package and the finite volume method, and a steady flow simulation was performed. Boundary conditions were set for velocity at the inlet, pressure at the outlet, no-slip parent artery, and stent surface. Reynolds numbers at the inlet determined from the mean blood flow speed were 240 and 600.

Results and discussion: In this study, we revealed the blood flow pattern in some cerebral aneurysms using CFD. The pattern in a cerebral aneurysm was influenced by the aneurysm direction and parent artery curves. The blood flow pattern in a neck cerebral aneurysm was classified into two types.

Topics: Aneurysms , Blood flow
Commentary by Dr. Valentin Fuster
2013;():V03AT03A034. doi:10.1115/IMECE2013-63933.

The purpose of this study is to apply the computational fluid dynamics (CFD) technique to evaluate the tracheal airway pressure change before and after the vascular ring surgery (VRS) based on patient computed tomography (CT) images. Computer simulation results also show that after a surgical treatment the pressure drop in the tracheal airway was significantly decreased, especially for low inspiratory and expiratory velocities. In other words, the flow resistance in the tracheal airway becomes decreased after the VRS when the airway is expanded. The airway flow resistance of tracheal stenosis caused by CVR can be augmented by increased air flow velocity. Numerical results show that the pressure drop in the tracheal airway was 0.1099 Pa for the inlet inspiratory velocity of 10 cm/s before the VRS. After the VRS, the pressure drop was reduced and became 0.0598 Pa. In the meantime, the improvement gain was 45.58%. In word words, the pressure drop was reduced after the vascular ring surgery. Therefore, the CFD approach can be a useful method for quantifying the change of airway resistance and evaluating the effectiveness of relief of tracheal stenosis by the VRS.

Commentary by Dr. Valentin Fuster
2013;():V03AT03A035. doi:10.1115/IMECE2013-64435.

Hemodynamics is considered to be one of the indices to evaluate the effects of the treatment by coil embolization for cerebral aneurysms. For the sake of detailed analysis of hemodynamics in coil-embolized aneurysms, we develop a virtual coil model based on the mechanical theory that the coil deforms toward minimizing the elastic energy, and represent a realistic configuration of the embolized coils in the aneurysm by the insertion simulation. Then, the blood flow analysis is done by solving the N.S. and continuity equations numerically with the finite volume method using polyhedral mesh. The coil insertion simulation demonstrated that almost uniform distribution of the coil in the aneurysm was achieved at over 10% packing density of the coil. The blood flow analysis using the virtual coil model showed that the flow momentum inside the aneurysm was reduced to less than 10% by coil embolization with a packing density over 20%. In comparison to the simulation results using a porous media model for the embolized coil, there was no significant difference in the reduction ratio of the flow momentum in the aneurysm by coil embolization. However, local flow dynamics evaluated by the flow vorticity was different in the virtual coil model and the porous media model, in particular at the neck region of the aneurysm.

Commentary by Dr. Valentin Fuster
2013;():V03AT03A036. doi:10.1115/IMECE2013-64509.

Objective: Neck pain is a prevalent musculoskeletal (MSK) complaint and costly societal burden. Doctors of chiropractic (DCs) provide manual therapies for neck pain patients to relieve discomfort and improve physical function. Manual cervical distraction (MCD) is a chiropractic procedure for neck pain. During MCD, the patient lies face down on a specially designed chiropractic table. The DC gently moves the head and neck in a cephalic direction while holding a gentle broad manual contact over the posterior neck, to create traction effects. MCD traction force profiles vary between clinicians making standardization of treatment delivery challenging. This paper reports on a bioengineering technology developed to provide clinicians with auditory and graphical feedback on the magnitude of cervical traction forces applied during MCD to simulated patients during training for a randomized controlled trial (RCT).

Methods: The Cox flexion-distraction chiropractic table is designed with a moveable headpiece. The table allows for long axis horizontal movement of the head and neck, while the patient’s trunk and legs rest on fixed table sections. We instrument-modified this table with three-dimensional force transducers to measure the traction forces applied by the doctor. Motion Monitor software collects data from force transducers. The software displays the magnitude of traction forces graphically as a function of time. Real-time audible feedback produces a steady tone when measured traction forces are <20N, no tone when forces range between 20–50N, and an audible tone when forces exceed 50N. Peer debriefing from simulated patients reinforces traction force data from the bioengineering technology.

Results: We used audible and graphical feedback to train and certify DCs to apply traction forces to the cervical spine of simulated patients within three specific ranges. This technology supports a RCT designed to assess the ability of clinicians to deliver MCD within specified force ranges to patients randomized to different force dosages as an intervention. Future applications may include training chiropractic students and clinicians to deliver the MCD treatment.

Commentary by Dr. Valentin Fuster
2013;():V03AT03A037. doi:10.1115/IMECE2013-64784.

Osteoporosis is a systemic skeleton disease, characterized by a low bone mass and micro-architectural deterioration of bone tissue with consecutive increasing of fragile bones and susceptibility of fractures. Risk facture, advanced ages, family history, rheumatoid arthritis, low calcium intake, physical inactivity, and low body weight can lead to this condition. The aim of treatment in osteoporosis is to grow-up the bone mineral density of the skeleton and to increase resorption of formed bone, used diverse methods as medications, conservative measures, weight reduction, physical and occupational therapy, mechanical support devices and surgery. This paper presents a balneal-conservative treatment applied to 82 patients diagnosed with osteoporosis from Rehabilitation Clinical Hospital of Felix Spa in 2011–2012, which has combined with a kinetotherapy and medication treatment. The complex rehabilitation treatment involves balneal-physical-kinetic recovery treatment that must be periodical repeated every six months, while the subjects themselves at home followed the kinetotherapy with drugs between balneal-treatments at hospital. The significance of rehabilitation treatment for the osteoporosis patients is to rise both functional and independence level, and improving their quality life. DEXA, Qualeffo-41 Test, fragility fractures, difference of height patients, using the statistical analysis have performed the evaluation of trial. These results emphasized the efficiency of balneal-rehabilitation treatment with main accent on respect the kinetotherapy applied the osteoporosis patients. The future research will be focused upon the implementation of vibration therapy with balneal-conservative treatment on patients with osteoporosis to reduce the therapy time and improving the quality patients life.

Commentary by Dr. Valentin Fuster
2013;():V03AT03A038. doi:10.1115/IMECE2013-65112.

Measurement of the electromagnetic (EM) properties of tissue such as electrical conductivity, permittivity, and eddy current characteristics can be used in clinical medicine for characterizing and distinguishing soft tissue morphology. Such measurements can yield complementary information to what can be obtained using analysis with an optical microscope. An example is the assessment of margins during the surgical resection of occult tumors. In current practice, the surgeon relies on pre-operative imaging modalities, sight and palpation to locate and attempt to fully resect the tumor(s). Frozen section pathological assessment offers the only other resource available to the surgeon for margin analysis, but it is incomplete because only a small fraction of the resected tissue is examined and it is often not feasible to wait for the results of the frozen section analysis before completing the surgery. This paper describes a characterization and imaging method based on variations in electromagnetic tissue properties to assess the surgical margins of resected tissues. This is noteworthy because accurate margin assessment has been shown to significantly improve long term patient outcomes[1].

Commentary by Dr. Valentin Fuster
2013;():V03AT03A039. doi:10.1115/IMECE2013-65149.

Traumatic brain injury (TBI) is one of the most important problems in biomechanical engineering, and there have been many experiments conducted in order to characterize the mechanical properties of brain tissue. However, obtaining fresh human brain tissue is difficult, if not impossible. Also, the sample preparation and testing protocols must be carried out with great delicacy because brain tissue is very soft and vulnerable to being deformed under a very small amount of load. Most importantly, according to several researchers, each sample must be tested only one time as the tissue may be damaged and its characteristics subsequently changed. This paper is intended to examine the amount of decay that can happen in material characteristics due to retesting. A stress relaxation test is conducted on the same samples of the swine brain tissue multiple times in small and large deformations. The mechanical properties of the substance are calculated before and after retesting, and the constants of the tissue, as mechanical characteristics, are determined and compared. Short- and long-term moduli, relaxation times and relaxation functions are calculated and compared to understand how much they decay after repeating the experiments. The results show that retesting does not significantly change the elastic part of the tissue characteristics, but the viscous behavior shows a relatively sizeable change. The ability to account for the material decay of the samples due to repetition of the experiments results in the need for fewer samples and less preparation time and effort.

Commentary by Dr. Valentin Fuster
2013;():V03AT03A040. doi:10.1115/IMECE2013-65499.

This paper presents the literature review on the design criteria for intervertebral disc prosthesis. The design criteria relate to the design features that intervertebral prosthesis must accomplish (i.e. fixation to bones, spine mobility, energy absorption and etcetera). The need to improve the performance has led to changes in the features which reflect in the current design criteria.

Currently, the disc prosthesis technology is experiencing a generational change. The first generation was thoroughly studied while the second generation is in the clinical tests stage. During the time the first generation prostheses were applied in patients there was not a clear trend in the clinical results which produced a lack of trust and reliability in the performance of the disc prosthesis. The changes in the design features of one generation compared to the next generation are based in the deepening in the knowledge of the problem and the results obtained with the first generation prostheses.

Some design criteria were identified for the first generation. These criteria were not completely characterized since there was not enough information to be used by the designer. This lack of characterization of most design criteria produced many different versions without a clear focus which help to define the basic design features of disc prostheses. This document presents the necessary information to thoroughly characterize the design criteria outlining the missing information for the design criteria found. An analysis is done of the design criteria in the second generation of prosthesis.

Finally if the information contained in the design criteria is enough, the clinical results would be better focused to achieve a more repeatable, reproducible and reliable process for a total disc intervertebral prosthesis replacement as now is considered the vertebral fusion, this is a gold standard.

Commentary by Dr. Valentin Fuster
2013;():V03AT03A041. doi:10.1115/IMECE2013-65737.

Physiological hand tremors are unwanted involuntary motions which affect the precision of surgeons during microsurgery. For precision surgical procedures, the magnitude of tremors is high as compared to the thickness of vessel or tissue being operated at surgical site. Hence the chances of causing irreversible damages in the nearby locations is very high, particularly in case of neural and vitreoretinal surgeries. Furthermore, human hand stability is a skill to be acquired with extensive training, it decreases with age and limits the number of surgeons qualified to perform microsurgery. Control of tremors is therefore, a major challenge for the surgeons at global level. In this paper, we have shown an effective implementation of a compliant manipulator system to successfully measure and suppress tremors. The compliant manipulators offer inherent advantageous over rigid systems, for example, more accuracy, no friction, no wear and tear, flexibility which would help preserving surgical feel and easy controllability from microsurgical point of view. Three different control schemes include feedback from lowpass filtering and an adaptive filtering are implemented and compared. The effective adaptive control scheme shows promising results in reducing tremors at the surgeon’s tool tip by ∼96%, when holding at a point and by ∼68% while carrying out a voluntary motion.

Topics: Robotics , Physiology
Commentary by Dr. Valentin Fuster
2013;():V03AT03A042. doi:10.1115/IMECE2013-65830.

Non-rigid image registration is an important and challenge work in image processing. The demons algorithm is one of the most effective non-rigid image registration methods. However, it is only suitable for images with small deformation. In recent years, many improving techniques are proposed. The free form deformation method based on B-spline function is widely employed in non-rigid image registration and is good at dealing with large deformation image registration. However, the performance of the demons algorithm is better than that of the B-spline method in dealing with small deformation registration. Therefore, in this paper, we propose to combine the demons algorithm and the B-spline method. The new method consists of two steps: First, it applies the B-spline method to deal with the large deformation. Then, it uses the demons algorithm to treat the small deformation. The testing results show that the new method is effective in dealing images with both small and large deformations. Comparing to the demons algorithm as well as the B-spline method, the new method has the smallest registration error and hence, is the best.

Commentary by Dr. Valentin Fuster
2013;():V03AT03A043. doi:10.1115/IMECE2013-66430.

Tissue engineering is a promising aspect of regenerative medicine that is aimed at constructing functional tissues and organs. While progresses in tissue engineering have led successful clinic applications, challenges remain for more complex tissues/organs that require concerted efforts from multiple types of cells. One of the key issues in building replacements for complex tissues/organs is to mimic the organ’s complex natural organization using a mixture of engineered materials and living cells [1]. Electrospinning has shown promise as a technique to create the microenvironment necessary for cell growth and proliferation for tissue engineering applications[2–4], while multiple fabrication methods have been developed to manipulate live cells(e.g. cell printing) [5–7]. To this end, a system integrating polymer electrospinning technique and pressure-driven cell deposition method is currently under development for forming hybrid tissue constructs with living cells and polymers. This study focuses on examining morphology of electrospun fibers as function of processing parameters including working distance and solution flow rate.

Commentary by Dr. Valentin Fuster

Biomedical and Biotechnology Engineering: Computational Modeling and Device Design

2013;():V03AT03A044. doi:10.1115/IMECE2013-62305.

Previous biological experiments show that the fish use their muscles to stiffen their bodies for improving the swimming performance. Inspired by that, we propose a planar model of oscillatory propulsor with variable stiffness using hyper redundant serial-parallel mechanisms to mimic a fish. Our goal in the paper is to identify the swimming characteristics with respect to the body stiffness. Moreover, a simulation model is presented and its results show that the swimming performance is largely dependent on the body stiffness and the driven frequency. Our primary conclusions include: 1) when the driven frequency is closed to the design frequency, the robotic fish with the calculated body stiffness has a super swimming performance. 2) Driven at the design frequency, the forward speed of robotic fish is linearly proportional to the driving frequency and the Strouhal number is consistent with the experiment results 0.25<St<0.35.

Topics: Stiffness
Commentary by Dr. Valentin Fuster
2013;():V03AT03A045. doi:10.1115/IMECE2013-62327.

Wheelchair ergometers facilitate wheelchair related studies as they allow controlled experiments to be performed inside the laboratory. However, the results obtained from these experiments are of limited value unless we use wheelchair ergometers that biomechanically represent real-world wheelchair propulsion. We could not find any wheelchair ergometers in the literature to date, that have been validated considering all of these important biomechanical criteria: Velocity and acceleration, force and moment, trunk swing, inertial effect, energy consumption and the resistive force against propulsion.

In this paper we have considered wheelchair propulsion on an ergometer and have compared it to straight-line floor wheelchair propulsion. From equating these two situations, we have found the necessary conditions to meet the above criteria. Finally, we propose three models for a wheelchair ergometer that satisfies these conditions and will be able to biomechanically represent straight-line floor wheelchair propulsion.

Commentary by Dr. Valentin Fuster
2013;():V03AT03A046. doi:10.1115/IMECE2013-62384.

Molecular dynamics simulations are performed to provide valuable information about the translocation of four single-stranded DNAs with ten identical bases through graphene nanopore with diameter of 2 nm. The monolayer graphene nanopore is highly sensitive to ssDNA translocation events and the 10-base resolution detection can be realized by electrophoreticly threading ssDNA through graphene nanopore. Due to the similar sizes of the four nucleotides, the blockage current is unlikely to provide a distinguishable signal. However, by simply monitoring and analyzing the translocation time of poly(dA)10, poly(dC)10, poly(dG)10 and poly(dT)10 though graphene pore, each ssDNA can be identified and characterized.

Commentary by Dr. Valentin Fuster
2013;():V03AT03A047. doi:10.1115/IMECE2013-62407.

Atherosclerosis is a vascular disease that reduces arterial lumen size through plaque deposition and arterial wall thickening. The pathological complications of atherosclerosis, namely heart disease and stroke, remain the leading cause of mortality in the world. The most common interventional procedure against atherosclerosis involves the placement of an intravascular stent. Intravascular stents are small tube like structures placed into Stenotic arteries to restore the blood flow. In this study CFD analysis is performed on the femoral artery by considering blood flow as a pulsating, incompressible and Newtonian flow over a realistic velocity waveform of the femoral artery. The artery is considered as a rigid and straight with a branch. The governing transient Navier-Stokes equations are solved using commercial software code Star-CCM+. Simulations are performed on healthy, atherosclerosis affected and Stented femoral arteries. Velocity and wall shear stress fields over the cardiac cycle are analyzed to predict the outcome of the interventions in terms of recirculation and stagnation regions and identify improved stent designs. The flow patterns in the arteries are highly modulating along with the cardiac cycle and a strong function of the waveform created by the heartbeat. The complex blood flow pattern with slow moving regions, flow separation and recirculatory form near the wall during cardiac cycle is the major contributing factor to the formation of the atherosclerotic plaque at that location. It was demonstrated that adverse flow field created upstream and downstream of the blockage may cause enhanced growth in size of the blockage. The stent design also plays significant role in the possibility of restenosis.

Commentary by Dr. Valentin Fuster
2013;():V03AT03A048. doi:10.1115/IMECE2013-62505.

Anterior cruciate ligament (ACL) injury is a common and painful injury that occurs approximately 250,000 times annually in the U.S. [1]. Articular cartilage and meniscal injuries are also associated with ACL injuries [2]. ACL injuries can often lead to degenerative osteoarthritis of the articular cartilage [2]. An epidemiology study of athletic injuries by Majewski et al. [3] determined that out of 19,530 sports injuries, 20% were ACL injuries and 8% were medial collateral ligament (MCL) injuries.

Commentary by Dr. Valentin Fuster
2013;():V03AT03A049. doi:10.1115/IMECE2013-62589.

The finite element method at the micro scale (mFEM) has been gaining in popularity to simulate biomechanical effects. In this paper, a 3D mFEM model is developed to simulate sawing of cortical bone under 2D orthogonal cutting conditions. The aim of the research was to develop a predictive model of the sawing forces and to report them as a function of depth of cut. To obtain the micro geometric input, a heterogeneous anisotropic model was created from several images taken via an optical microscope of the cortex of adult mid-diaphysal bovine femur. In order to identify the various regions representing the micro-architecture of cortical bone, such as osteons, Haversian canals, lamellae and lacunae, MATLAB was utilized for intelligent image processing based on pulsed coupled neural networks. After each micro-phase in the image was assigned the proper mechanical properties, these material-tagged micro-features were imported into the finite element method (FEM) solver. Results from the simulation were correlated to cutting force data that was determined experimentally. Experiments were conducted with individual stainless steel saw blade teeth that were removed from a typical surgical saw blade. The teeth were 0.64 mm thick, with a rake and clearance angle of −10 and 60 degrees, respectively. Representative of clinical conditions for power bone sawing, depths of cut per tooth between 2.5 micrometer and 10 micrometer were investigated. The simulated cutting forces from the mFEM model compared favorably to the experimental data.

Commentary by Dr. Valentin Fuster
2013;():V03AT03A050. doi:10.1115/IMECE2013-62832.

Both medicine and engineering disciplines use problem-solving techniques to address different needs. The solutions often require an understanding of complex system behavior, identification of important system factors, and prediction of the outcome prior to application. This paper presents an introduction to integrated computer-aided approach to support developments in the field of biomedical devices, particularly for those used with orthopaedic surgery applications. The modern design process is first introduced as a road map to establish design that is robust, cost and time effective in order to satisfy the needs of the medical community. The coverage includes methods such as: function abstraction and decomposition, quality function deployment (QFD), case-based design (CBD) methodology, and risk management in design of orthopedic implants.

Commentary by Dr. Valentin Fuster
2013;():V03AT03A051. doi:10.1115/IMECE2013-62904.

In this study we used computational fluid dynamics (CFD) to analyze the therapeutic effect of an oral device (mandibular advancement splint – MAS, that protrudes the lower jaw during sleep) as a treatment for Obstructive Sleep Apnea (OSA). Anatomically-accurate upper airway (UA) computational models were reconstructed from magnetic resonance images (MRI) of 7 patients with and without a MAS device fitted. CFD simulations of UA airflow were performed at the maximum flow rate during inspiration. The CFD results indicated the lowest pressure often occurs close to the soft palate and the base of the tongue. The airway pressure gradient was estimated as the best indicator for treatment response since the change in the pressure drop forms a linear correlation with the change in patients’ Apnea-Hypopnea Index (AHI). This correlation has the potential to be developed into a model for predicting the outcome of the MAS treatment. However the rigid wall assumption of CFD models is the major uncertainty. To overcome this uncertainty we set up a full fluid-structure interaction model for a typical responder case with a compliant UA wall. The results demonstrated the different UA flow field associated with using MAS alleviated the airway collapse, which was successfully predicted for the untreated patient. We thus show for the first time that FSI is more accurate than CFD with rigid walls for the study of OSA, and can predict treatment response. Comparison of the FSI and CFD results for the UA flow and pressure profiles showed variation between the models. The structural deflection in oropharynx effectively reformed the flow pattern, however, the maximum pressure drops of both results were close. This supports the competence of the CFD method in clinical applications, where maximum pressure drop data can be used to develop a treatment-predicting model.

Commentary by Dr. Valentin Fuster
2013;():V03AT03A052. doi:10.1115/IMECE2013-63027.

A computational fluid dynamics (CFD) study was carried out with data comparison to provide guidance for the control of open shock tube wave expansion to simulate field blast loadings for the conduct of biomechanical blast overpressure tests against surrogate test models. The technique involves the addition of a diffuser to the shock tube to prevent overexpansion before the shock wave impacts the test model. Mild traumatic brain injury (mTBI) has been identified as the signature injury for the conflicts in Iraq and Afghanistan, and blast overpressure from improvised explosive devices (IEDs) has been hypothesized as a significant mTBI risk factor. Research in the understanding of the mechanism of blast induced mTBI has been very active, which requires blast testing using animal and physical models. Full scale field blast testing is expensive. The use of shock tubes is clearly a viable cost effective laboratory method with many advantages. CFD simulations with data comparison show that without a diffuser, the shock wave exiting the tube tends to over expand producing an incident waveform with a short positive duration followed by a significant negative phase that is different from a Friedlander wave. However, the overexpansion effects can be mitigated by a diffuser. Shock tube tests also support the simulation results in which a diffuser improves the waveform from the shock tube. CFD simulations were validated by shock tube tests.

Topics: Testing , Shock tubes
Commentary by Dr. Valentin Fuster
2013;():V03AT03A053. doi:10.1115/IMECE2013-63046.

Human body functions as a network of mechanically coupled parts (components) that work together to form a complete system; these body components can experience failure when in service. Specifically, failure such as arthritis may be caused by articulations at the hip and knee joints. One of such solutions to this failure is the total hip replacement. Materials used in this prosthesis, therefore play an important role in the success of the implant. One of the most commonly used implant material in modern day arthroplasty is the Ti6Al4V alloy, because of its excellent resistance to wear and corrosion in the human body environment. In reality, such implant in service may be subjected to impact loading (at a velocity of about 250–1000m/s), leading to deformation. Typical, examples include an implanted patient involved in an automobile crash and a golf ball hitting an implanted patient at the point of implantation. In this study, the wear and tear resistance property of Ti6Al4V alloy is determined by performing simulation on the high strain rate deformation behavior of IN718 super alloy material and Ti6Al4V plated Inconel material. The maximum stress localized within the plated Inconel material is lesser than that in the unplated material. This shows that Ti6Al4V alloy prevents the localization of stress in the parent Inconel material and is therefore a good wear prevention material, under impact conditions. Also, the impact characterization behavior of Ti6Al4V material is performed in this research in order to determine the maximum stress allowable in the titanium alloy before ultimate failure. Simulation of the high strain rate behavior of the Ti6Al4V alloy is performed at velocities in the range 9–20m/s. It is observed that the localized stress within the Ti6Al4V alloy increases with increased impact velocity. A maximum localized stress is observed in the material beyond which the Ti6Al4V alloy experiences failure. The result of the simulation process helps in determining the maximum impact which an implanted patient can therefore be exposed to and the preventive measures that can be taken in order to guarantee safety of the implanted patient.

Commentary by Dr. Valentin Fuster
2013;():V03AT03A054. doi:10.1115/IMECE2013-63380.

This article describes a novel method of indirect estimation of intra-ocular pressure using tactile sensors. Two sensor calibration methods have been demonstrated: an artificial neural network (ANN) model and a phenomenological reduced-parameter model based on finite element analysis. The ANN method showed superior performance with an accuracy of +/− 0.7 mmHg, while the reduced order method showed an accuracy of +/− 3.11 mmHg. The latter method however allows calibration of the tactile tonometer from a single pressure measurement if the geometry of the probes is known and satisfying certain solvability conditions. The ANN method was demonstrated using experiment data, while the reduced-order model was tested numerically. Due to its indirect and non-invasive nature, the proposed tactile measurement method can be used in the development of a self-administered home tonometer for management of glaucoma, however the presence of an eye lid might require modification of the calibration procedure outlined here.

Topics: Calibration
Commentary by Dr. Valentin Fuster
2013;():V03AT03A055. doi:10.1115/IMECE2013-63507.

3′-Deoxy-3′-18F-fluorothymidine (18F-FLT) is a radiotracer which accumulates in proliferating cells and is used for positron emission tomography (PET) imaging. This study investigates the heterogeneous transport and uptake of FLT in tumors, aiming to understand the links between FLT dynamics described by a mechanistic spatial-temporal model and by a simplified 3-compartment model, and to study the validity of the compartment model.

In the proposed multi-scale spatial-temporal model, the tumor consists of vasculature, interstitium and tumor cells. The heterogeneous spatial-temporal distribution of FLT is determined by a convection-diffusion-reaction equation, numerically solved using the finite difference method (FDM). Physiological parameters were collated from the literature and used as model coefficients, and vascular maps were created based on histological micro-vascular density (MVD). Results show that the multi-scale model can generate FLT time activity curves (TACs) similar to TACs derived from clinical PET images. And so long as the region of interest (ROI) is a near-closed system, a 3-compartment model can recover reasonable estimates of averaged FLT dynamics.

Commentary by Dr. Valentin Fuster
2013;():V03AT03A056. doi:10.1115/IMECE2013-63647.

According to INEGI (National Institute for Statistics and Geography), in 2004 there were around 730,000 people in Mexico with the need of some kind of mechanical aid to regain ability to walk. Support equipment for regaining the ability to walk normally is manufactured outside of Mexico. This equipment is complex and very expensive. In this work, the design of a walking ability rehabilitation aid is presented. This work is carried out applying the modular design concept. This ensures that all client needs are fulfilled by the resultant product, and that these needs are measurable and controllable. Basic idea behind this design is supporting part of patient’s weight and that of an exoskeleton on a mechanical device. Basic kinematics and dynamic calculation are presented, as well as simulations results. This information shows the feasibility of building and operating this rehabilitation walking aid.

Topics: Design
Commentary by Dr. Valentin Fuster
2013;():V03AT03A057. doi:10.1115/IMECE2013-63689.

Modular designs give orthopaedic surgeons a greater flexibility to custom fit the implant to the patients bone while performing total hip arthroplasty. Titanium alloy (Ti6Al4V (ASTM F-136)) is typically used for modular hip implant stems. This highly corrosion resistant alloy forms passive surface oxide films spontaneously. However, with modular designs, micro-motion may occur at the taper junctions during mechanical loading. Crevices between the taper junctions may allow the body fluids to enter and remain stagnant. These conditions make the modular tapers susceptible to fatigue and mechanically assisted crevice corrosion. The in vivo degradation of metal alloy implants compromises the structural integrity. The influence of stress induced corrosion and pitting leading to the in vivo catastrophic failure of a titanium-alloy modular implant in cementless total hip arthroplasty was numerically investigated. The effect of pit geometric parameters are discussed in terms of taper performance.

Commentary by Dr. Valentin Fuster
2013;():V03AT03A058. doi:10.1115/IMECE2013-63776.

The Fontan surgery is performed on patients with a single ventricle heart defect to prevent the combination of highly-oxygenated and poorly-oxygenated blood. Blood flow in total cavopulmonary connection (TCPC) which culminates an ordinary Fontan operation is practically steady-state but this flow is not appropriate for respiratory systems. This article investigates an approach in Fontan surgery that has been recently proposed in order to make the pulmonary blood flow pulsating. Moreover, for investigating the compliance of vessels and its effects on blood flow in TCPC, we have used the FSI (Fluid Structure Interaction) method as well as rigid wall assumption for comparison purposes. Our TCPC model structure has obtained from CT Angiography (CTA) scan of a single ventricle patient who has undergone a normal Fontan surgery. In this new procedure, pulmonary stenosis (PS), containing high pressure and pulsating flow, has been added to the original geometry for pulsating the main flow and then its effect on the general flow in left and right pulmonary arteries has been studied by increasing the inlet velocity to PS. In overall, our results show that this new approach increases the pulsations of pulmonary flow.

Commentary by Dr. Valentin Fuster
2013;():V03AT03A059. doi:10.1115/IMECE2013-63789.

In this paper, a multibody dynamics model of the shoulder-upper arm complex is presented. Three major bones clavicle, scapula, and humerus in the shoulder-upper arm complex are represented by rigid bodies. The soft tissues such as tendons, ligaments, and muscles are modeled as springs and dampers respectively attached to the rigid bodies. The joints between the bones are expressed as ideal kinematic joints. Kane’s equations are then used to derive equations of motion of this multibody system.

Based on the model, a person’s stand-up motion, aided by shoulder-upper arm complex force for lifting his/her upper body weight is analyzed. Commercial computer software is used to create the multibody shoulder-upper arm complex computational model and then carry out simulation. The model may be utilized in motion analysis of elderly people and sports medicine to study fatigue mechanism and prevent injuries of the shoulder-upper arm complex.

Commentary by Dr. Valentin Fuster
2013;():V03AT03A060. doi:10.1115/IMECE2013-63795.

The human knee joint has a three dimensional geometry with multiple body articulations that produce complex mechanical responses under loads that occur in everyday life and sports activities. Knowledge of the complex mechanical interactions of these load bearing structures is of help when the treatment of relevant diseases is evaluated and assisting devices are designed.

The anterior cruciate ligament in the knee connects the femur to the tibia and is often torn during a sudden twisting motion, resulting in knee instability. The objective of this work is to study the mechanical behavior of the human knee joint in typical everyday activities and evaluate the differences in its response for three different states, intact, injured and reconstructed knee. Three equivalent finite element models were developed. For the reconstructed model a novel repair device developed and patented by the authors was employed.

For the verification of the developed models, static load cases presented in a previous modeling work were used. Mechanical stresses calculated for the load cases studied, were very close to results presented in previous experimentally verified work, in both load distribution and maximum calculated load values.

Commentary by Dr. Valentin Fuster
2013;():V03AT03A061. doi:10.1115/IMECE2013-63822.

Dental implants are a valuable, safe and predictable solution for patients suffering from tooth loss. The implant shape plays a great role in the success of dental implant, due to its effect on stress distribution in the surrounding bones. Therefore, optimizing some of implant shape parameters may improve stress distribution and consequently may lead to an increase in implant success rate. In this study, the 3D finite element analysis is used to investigate the influence of the number of threads in the neck of the implant on the implant-cortical bone interface stresses. The stress distribution along the implant-bone interface and their displacements were determined using ABAQUS/CAE 6.10 software. Overall, the stress was highest in the cortical bone at the neck of implant and lowest in the cancellous bone regardless of the number of threads in contact with cortical bone. On the other hand, reducing the number of threads in the neck resulted in a decrease in the developed stresses in both types of bones. The developed stresses around the bones decreased gradually in cortical bones and dramatically in cancellous bones when the number of threads decreased in the neck of implant. The stress reduction between the smooth neck to the fully threaded neck decreased the developed stresses by 24% in the cortical bone. However, due to improve the implant osseointegration, it is recommended to keep one or two threads in the cortical bone.

Commentary by Dr. Valentin Fuster
2013;():V03AT03A062. doi:10.1115/IMECE2013-63879.

Abdominal aortic aneurysm (AAA), local dilations of the infrarenal aorta, is the 13th leading cause of mortality in US. Various tools have been used to investigate the effect of blood flow on the mechanics of AAA, which might predict its fracture potential, a life-threaten event. The modeling techniques are gaining popularity, including the partially or fully coupled fluid-structure interaction method (p-FSI and f-FSI, respectively) and the static computational solid stress (CSS) analyses. In the present study, comparison among the above mentioned three computational methods were performed to identify the effective means to characterize the effects of pulsatile turbulent blood flow on predicting the stress distribution on AAA. Results have shown that ignorance of blood flow in simulation will underestimate the wall stress calculation and the flexibility of aneurysm wall has a large impact in simulating the blood through the AAA.

Commentary by Dr. Valentin Fuster
2013;():V03AT03A063. doi:10.1115/IMECE2013-63973.

In orthodontic treatment, anchorage is the most important element that affects the treatment’s success. To improve the load bearing capacity of the anchorage there are several devices developed in recent decades such as midpalatal implants and onplants but they also have limitation on directions of applied load and their support position adjustability.

The purpose of this study was to investigate the efficiency of a new anchorage device by analyzing the load-bearing and stress distribution among the cortical and cancellous bones of the mandible as well as the anchorage system components using nonlinear 3D Finite Element (FE) method. The new device is composed of an adjustable stainless steel plate equipped with bracket and mounted with two titanium mini-screws into the mandible. The response of this new system was compared to an isolated mini-screw system under different loading scenarios.

A maximum of 500gr force was applied in different directions on the bracket and the isolated mini-screw head to simulate the orthodontic loading. Using the new anchorage device reduced von-Mises stress in the whole structure approximately by 50% comparing to the isolated mini-screw. In the cortical bone and depending on the direction of the applied force, von-Mises stress decreased from 6 to 3MPa under vertical shear force and from 6 to 1.5MPa under horizontal and inclined shear forces. In the cancellous bone the stress decreased similarly as in the cortical bone from 0.6 to ≈0.3MPa under horizontal and inclined shear. Under vertical shear force the decrease was less significant from 0.57MPa to 0.5MPa.

This new device while offering wide fields of orthodontic forces applications thanks to its bracket provides the same resistive force (500gr) as the isolated mini-screw with much lower stresses in the bone and anchorage implant as well. The next step is to investigate the efficiency of this new device in the teeth movement.

Commentary by Dr. Valentin Fuster
2013;():V03AT03A064. doi:10.1115/IMECE2013-64200.

Infrared thermography is one of the promising and non-invasive imaging approaches which can be performed either in passive or in active mode. Due to its inherent capabilities, viz., fast, safe and subsurface feature extraction, this technique has been widely used in bio-medical imaging. In conventional passive approach, imaging may not provide enough contrast for detection of subsurface skin lesion. However, this limitation can be surmounted by using active thermography technique in which controlled energy is being supplied to the skin. This controlled stimulus not only helps in the detection of deeper subsurface details but also helps in getting the quantitative information of hidden features. Apart from the various widely used active approaches such as modulated lock-in thermography (LT) and high peak power pulsed based thermography (Pulsed Thermography - PT and Pulse Phase Thermography - PPT) techniques, the present article highlights an alternative approach which can be performed in less time as compared to LT and with much less peak powers as compared to pulsed based thermography (PT and PPT) techniques.

The present work utilizes a non-stationary thermal wave imaging approach to map the subsurface skin lesion. The multilayered skin has been modeled and simulated for a given frequency modulated heat stimulus using 3-dimensional bio-heat equation.

Topics: Waves , Skin , Imaging
Commentary by Dr. Valentin Fuster
2013;():V03AT03A065. doi:10.1115/IMECE2013-64276.

The main goal of this work is to present the design of a new locking system for a Stance Control Knee Ankle Foot Orthosis (SCKAFO). The purpose of this solution is to support patients with gait disorders, namely patients with muscular weakness and dystrophy in quadriceps femoris muscle group.

The proposed system is able to perform two distinct functions. The first one deals with the locking situation of the orthosis during the stance phase of human gait, in which contact between the foot and the ground occurs. The second function is associated with unlocking situation of the orthosis during the swing phase, in order to allow for the flexion motion of the knee. Thus, in the context of the present work sensors, are used to detect the key phases that characterize the human gait, allowing for the correct system performance. These sensors are placed into anatomical relevant locations and allow the evaluation of the joint angles and accelerations during human gait. Subsequently, the information collected by these sensors is interpreted by a microcontroller that controls the actuation system in order to lock or unlock the knee orthosis locking mechanism.

Finally, a physical prototype was built and tested in a traditional knee orthosis, which will allow for its validation. From the preliminary results, it can be stated that the model proposed here differs from the available commercial solutions in the measure that it is dynamic and does not require foot sensors to determine the human gait phases to define the lock/unlock.

Topics: Design , Orthotics , Knee
Commentary by Dr. Valentin Fuster
2013;():V03AT03A066. doi:10.1115/IMECE2013-64295.

Recently, the investigation of cell-activation and tissue regeneration process has shown the great progress in the biomedical and biomechanical research fields. In this study fabricated Biomedical-Micro Electric Mechanical System (Bio-MEMS) to examine accurately the cell activation by introducing the cell patterning assignment technique, which consists of the photolithograph method to generate the MEMS device and the cell patterning technique by using the dielectrophoresis (DEP) method.

In the development of Bio-MEMS devices for cell culture and micro-bioreactor system, unresolved subjects, 1) the fundamental mechanism of cell activation, 2) the flow control of culture medium 3) the accurate cell pattern technique and 4) the implementation of positive DEP methods, are remained. In this study, we fabricate 2-D patterns of point by using the DEP method introducing the positive effects and the trap method by employing the gravity effect and the adhesion technique, to reveal the fundamental mechanism of cell activations, such as the nerve cell axon extension.

We succeed to establish the cell patterning technique by using a novel electrode design technique, such as 2-D patterns of point. The results is shown that our novel approach using comprehensive designed electrodes is superior to cell patterning. Therefore, our device able to produce neural network consists of a large number of cells.

Commentary by Dr. Valentin Fuster
2013;():V03AT03A067. doi:10.1115/IMECE2013-64356.

This paper investigates swing-phase cavitation formation and collapse in a novel artificial hip joint using a well-established transient mass-conserving finite element cavitation algorithm. Elastic elements and ellipsoidal cup surface geometry are incorporated into the new design to promote and enhance ‘squeeze-film’ action over ‘wedge-film’ action employed in conventional artificial hip joints. During the swing phase of the gait cycle, the lubricant film undergoes cavitation from normal separation of ball and cup surfaces. Reformation of a complete lubricant film is predicted over a wide range of sub-ambient cavitation threshold pressures, ball velocities, ellipticity specifications, and ball initial positions that are likely to be encountered in practice.

Commentary by Dr. Valentin Fuster
2013;():V03AT03A068. doi:10.1115/IMECE2013-64677.

The number of sensors placed on warfighters’ personal protective equipment (PPE) continues to increase each year. It is important to be able to accurately measure the dynamic response of PPE in order to characterize new sensors that are meant to track warfighter movement. In an effort to help predict head motion, a method has been developed to accurately measure the angular and linear acceleration of a semi-rigid helmet using four triaxial linear accelerometers. This four-accelerometer array configuration is based on the 3-2-2-2 nine accelerometer package (NAP) method and was tailored to accurately measure the helmet response during impact and blast overpressure events. Method development and testing were performed using U.S. Army Advanced Combat Helmets. Since angular motion calculation using the NAP method requires orthogonal sensor placement, it was necessary to revise the standard NAP sensor configuration to account for the geometric constraints of a helmet. Modal analysis was performed to determine the locations of least vibration, and shock tube and drop tests were conducted to investigate helmet flex during impacts. Knowledge concerning the dominant vibration modes of the helmet guided accelerometer placement and helped mitigate the effects of sensor data oscillation on the calculated angular motion. Local helmet deformation strongly depends on the impact site; several accelerometer array configurations were developed to account for various impact directions. Linear accelerations were measured and angular accelerations were calculated for guided free drop and shock tube tests in the laboratory. In guided free drop tests, the helmet and headform were dropped onto an anvil at various velocities and were allowed to freely bounce after impact. In shock tube tests, the helmet and headform were allowed to swing freely when subjected to a high shock wave simulating an IED blast. The modified NAP method was able to accurately measure the linear and angular acceleration of the helmet for both types of tests. The angular motion calculation was validated using a high-speed video camera recording the helmet response at 10,000 frames per second. Results were also compared to angular rate sensors available on the market. It was determined that with a detailed understanding of a semi-rigid body’s vibration and proper placement of linear accelerometers, angular acceleration during high-shock impacts can be accurately calculated for semi-rigid, irregular shaped objects. This accelerometer placement method has been applied to several other military grade helmets and been used in models predicting head motion from helmet motion data.

Commentary by Dr. Valentin Fuster
2013;():V03AT03A069. doi:10.1115/IMECE2013-64808.

Lipoproteins are biochemical compounds containing both proteins and lipids. These particles carry chemicals like cholesterol and triglycerides that are not soluble in aqueous solutions. This paper presents modeling of lipoprotein system using coarse grain molecular dynamics technique and stability analysis of this system in a water solution like blood. A high density lipoprotein (HDL) that consists of two annular monomers is modeled. Also there are lipid bilayers located in center of the rings, so the whole HDL and lipid bilayers are called lipoprotein system. First, all atom model is provided and then coarse-grain model is obtained using MARTINI technique. Modeling of the system in all atom and coarse-grain is performed by VMD and simulation is executed by NAMD. System is simulated for 400ns with time step of 20fs in NPT ensemble. System temperature assumed similar to normal human body temperature. Finally the structure shape and stability of system were considered and results were analyzed.

Topics: Density , Stability , Modeling
Commentary by Dr. Valentin Fuster
2013;():V03AT03A070. doi:10.1115/IMECE2013-64926.

Fractures of the distal femur are severe traumatic injuries that are treated with the utilization of internal fixation devices. Current preclinical device designs have primarily been investigated without observance of femoral muscle group effects — in addition to joint hip reaction forces — and irregular geometry of the human femora. This has led to a need to optimize the performance and fit of internal fixation devices to produce maximal reliability and structural integrity. The present study utilizes a systematic design approach that employs computer-aided modeling, robust design methodology, finite element methods, and optimization processes for a femoral locking plate system. In doing so, a computer-aided model was constructed to illustrate a distal femoral fracture fixation system. Femoral muscle force directions and magnitudes associated with a normal walking gait cycle were inputted into the system to simulate realistic loading conditions. In conjunction with finite element methods, the model was used to assess stress and strain distributions along the femur, femoral plate, and screws. Subsequently, optimization processes were then employed to assess the effects of varying device geometric parameters and bone topology on the bone-implant stress distributions and overall device design. The proposed simulation-based optimization process was able to yield a more accurate representation of the biomechanics within the bone-implant interaction by taking into consideration the substantial effects of femoral muscle groups. In doing so, a robust device design is developed which improves overall performance via minimizing weight and maximizing overall factor of safety.

Topics: Simulation , Muscle
Commentary by Dr. Valentin Fuster
2013;():V03AT03A071. doi:10.1115/IMECE2013-65013.

Trocar insertion is the first step in laparoscopic surgery procedures. It is a difficult procedure to learn and practice because it is carried out almost entirely without any visual feedback of the organs underlying the tissues being punctured. A majority of injuries are attributed to excessive use of force by surgeons. So there is a need for a haptic based computer simulator to train and improve the trocar insertion skills. In this paper, a new methodology for the modeling of trocar insertion is proposed. First, trocar insertion data (force/torque, displacement, etc.) are collected from animal models. Based on this data, a material model is computed using a hyper-elastic finite element computation (FEM). Using the FEM model, tissue deformation of the abdominal wall is calculated off-line for various conditions of tissue puncture. Deformation data are used to train a neural network which is, in turn, used to compute a real time virtual trocar insertion simulation. Force feedback is also modeled based on clinical data and is integrated into the simulator. This novel method allows for precise trocar insertion simulation based on prior FEM offline computation. The proposed system was implemented in a laboratory environment.

Topics: Haptics , Modeling
Commentary by Dr. Valentin Fuster
2013;():V03AT03A072. doi:10.1115/IMECE2013-65073.

In this study, detonation of TNT was simulated using an FE code and the resulting mechanical behavior of air, in which the explosion took place, was studied as a function of distance. Incident and reflected pressure and impulse profiles were compared with published data. In addition, an FE model of a shock tube setup at Temple University was developed using equations of state for Helium and air as the driver and driven fluids. The characteristics of the shock wave developed from explosive blast and shock tube were compared. It was shown that merely the two variables commonly used in the literature to compare the results from a shock tube to that of blast, i.e., peak incident pressure and positive duration, could not thoroughly include all the characteristics of the shock wave. Other parameters such as reflected pressure and impulse, which includes the velocity of the particles in addition to the pressure, are also needed to describe the shock wave.

Commentary by Dr. Valentin Fuster
2013;():V03AT03A073. doi:10.1115/IMECE2013-65083.

The human brain trabeculae contain strands of collagen tissues connecting the arachnoid to the pia mater. In this paper the mechanotransductions of the external loads to the head passing through different trabecular architectures of the subarachnoid space were investigated. This has been accomplished by creating several local 2-D models consist of skull, dura mater, arachnoid, trabecular architecture and the brain. Different orientations of several architectures of the trabeculae were also analyzed. All models were subjected to the same loading and constraints. The strains in the brain for each model of the architecture and morphology were determined and compared to other corresponding models. It is concluded that the strain in the brain is less where the tree-shape trabeculae are upright, where the branches are attached to the arachnoid mater and the stems are attached to the pia mater. In addition, in the case of other morphologies the strain in the brain is less when the ratio of the trabecular area to the CSF space is less.

Topics: Stress , Brain
Commentary by Dr. Valentin Fuster
2013;():V03AT03A074. doi:10.1115/IMECE2013-65111.

Typically for young children and elders, the asthma treatment procedure using pMDI devices bring some usage coordination difficulties. Therefore, and accordingly to several asthma treatment guidelines, the prescription of a VHC, as an add-on device for the pMDI, is advisable. These devices consist of an expansion chamber where the air slows down, as well as, the pMDI spray plume. Allowing the patient to breathe whenever he wants, independently from the moment of the pMDI actuation, also reduces the “cold-freon” effect and allows a more effective evaporation of the propellant. The effectiveness evaluation of VHC and pMDI devices is made through the quantification of drug delivered to the patient lungs. A simple collection filter is not enough for an accurate assessment of the device. Since the size of the particles delivered matter the most, the use of an impaction apparatus is essential. Accordingly to the Canadian normative for VHC assessment (CAN/CSA/Z264.1-02:2008), the experimental testing shall be done by using a breath simulator instead of a constant flow pump. The evolution of these tests shall move towards more realistic testing conditions. This work reports the project and construction an experimental setup for a correct assessment of the VHC devices effectiveness. The experimental setup is based in the work of Foss & Keppel (1999) and the contribution of Finlay (1998) and Miller (2002). The project and optimization of the major components, such as, breath cycle simulator by means of a cam-follower mechanism, a mixing cone and the vacuum pump used, are herein described and discussed.

Commentary by Dr. Valentin Fuster
2013;():V03AT03A075. doi:10.1115/IMECE2013-65120.

Spherical shells have been employed to model impacts to human heads; however, an ellipsoidal shell is that is more realistic model of the head has not fully investigated. In this paper, impact of an elastic ellipsoidal shell with an elastic flat half space is analytically analyzed and a closed-form solution is derived which led to a complex differential equation. Due to the complexity of the impact equation it could not be solved by standard solutions. Therefore, the Newtonian method and a linearization scheme are employed to simplify this equation in order to obtain the response of the impact problem and the closed-form solution. The analytical solutions are validated by finite element method. Good agreement between the closed form solution and the FE results is observed. To show the difference, the ellipsoidal solutions are also compared to the spherical solutions. To the best of our knowledge, this method and its closed-form solution have not been addressed in the literature. It is concluded that the closed-form solution is trustworthy and can be used to investigate the impact of the skull (as an elastic ellipsoidal shell) with a rigid or elastic plate, including the skull deformation and parametric studies. This solution could be expanded to include the brain materials inside the ellipsoidal shell.

Topics: Deformation
Commentary by Dr. Valentin Fuster
2013;():V03AT03A076. doi:10.1115/IMECE2013-65125.

The Head Injury Criterion (HIC) has been employed as a measure of traumatic brain injury arising from an impact involving linear acceleration. Some investigators have been reported the shortcomings of the HIC regarding the angular accelerations, head mass and the precise threshold of injury level [1, 2]. In this study the effect of acceleration curves, as a frontal impact, and the HIC values on the strain in the brain was critically analyzed. Specifically in this paper, the strains in the brain for three sets of acceleration pulses, where the peak of the curve takes place early or later (advanced or delayed) during the pulse time, were investigated. The results of this study indicate that for two different acceleration pulses, with the same peak value, duration and the same HIC values the strains in the brain are different. Therefore there is a need for further research leading to better criteria or modification of the HIC as it relates to the Traumatic Brain Injury (TBI).

Topics: Wounds
Commentary by Dr. Valentin Fuster
2013;():V03AT03A077. doi:10.1115/IMECE2013-65140.

The results of a computational study on the effect of the body on biomechanical responses of a helmeted human head under various blast load orientations are presented in this work. The focus of the work is to study the effects of the human head model boundary conditions on mechanical responses of the head such as variations of intracranial pressure (ICP). In this work, finite element models of the helmet, padding system, and head components are used for a dynamic nonlinear analysis. Appropriate contacts and conditions are applied between different components of the head, pads and helmet. Blast is modeled in a free space. Two different blast wave orientations with respect to head position are set, so that, blast waves tackle the front and back of the head. Standard trinitrotoluene is selected as the high explosive (HE) material. The standoff distance in all cases is one meter from the explosion site and the mass of HE is 200 grams. To study the effect of the body, three different boundary conditions are considered; the head-neck model is free; the base of the neck is completely fixed; and the head-neck model is attached to the body. Comparing the results shows that the level of ICP and shear stress on the brain are similar during the first five milliseconds after the head is hit by the blast waves. It explains the fact that the rest of the body does not have any contribution to the response of the head during the first 5 milliseconds. However, the conclusion is just reasonable for the presented blast situations and different blast wave incidents as well as more directions must be considered.

Topics: Biomechanics
Commentary by Dr. Valentin Fuster
2013;():V03AT03A078. doi:10.1115/IMECE2013-65227.

Emotions are what make us human and emotions are what make us different. A person can make a list of such expressions about the role of human emotions, as they play a central role in our lives, in our interactions with others and the surrounding environment. Emotions are in a broad sense the regulators of our interaction with the world as they play a central role in our perception of the world and in our knowledge construction.

In another angle, sensations are our immediate detector of the surrounding environment as, since ever, we see, touch and smell what is around us, we ear friendly voices or run from predator’s sounds and taste food that keep us alive. Both emotions and sensations can be used to describe our living and our main interactions with the world.

However, despite that important role of senses and emotions, there is a poor representation of sensorial information and lack of understanding of emotions from the side of computational systems. Subsequently it is noticeable the absence of support to acquire and fully represent human sensorial experience and lack of ability to represent, and appropriately react, from those systems to emotional activity. The proposed work consists in developing a framework that acquires knowledge about human emotions from self-reporting or the interaction with Internet objects and media. In particular, it intends to facilitate their emotions description at the Internet from proposed samples of sensorial information allowing a later management of that knowledge for the most diverse objectives, as an example, for searching objects or media through similarities of emotional and sensorial patterns.

Topics: Internet
Commentary by Dr. Valentin Fuster
2013;():V03AT03A079. doi:10.1115/IMECE2013-65335.

The current computational effort will focus on the numerical analysis of current tiling disk MHVs. In this work an implicit fluid-structure-interaction (FSI) simulation of the Bjork-Shiley design was carried out using in-house codes implemented in the commercial code software FLUENT™. In-house codes in the form of journal files, schemes, and user-defined functions (UDFs) were integrated to automate the inner iterations and enable communication between the fluid and the moving disk at the interfaces. Based on the investigations of the current simulations, a new design aiming at improving the hemodynamic performance is suggested. Hemodynamics of the flow in current tilting-disk valves is compared with the suggested design and it is concluded that the suggested design has a better hemodynamic performance in terms of shear stress values and residence times.

Commentary by Dr. Valentin Fuster
2013;():V03AT03A080. doi:10.1115/IMECE2013-65358.

The objective of this paper is to document design lessons learned in the development of low-cost lower-limb prosthetic devices. Four design principles are introduced based on the authors′ experience redesigning a low-cost prosthetic knee mechanism. These design principles are valuable sources to complete the conceptual design of the knee mechanism in the absence of a unique or exact methodology that comprises all the aspects concerning engineering design.

The paper defines the motivation to improve life quality by restoring knee functionality in terms of mobility and stability. Subsequent sections explore the state of the art, design constraints, gait analysis, and 3-D modeling using CAD. The model is validated using kinematic and structural simulation in NX 7.5™ covering basic geometric parameters and motion assumptions. The four conceptual design principles are: Hybrid Design Model, Simultaneous Modeling, Multidisciplinary Pulses, and Built-in and Post-design Optimization. Each principle is presented to exemplify its contribution in the knee mechanism redesign. Finally, the design principles are intended to assist the designer with empirical guidelines in the development of prosthetic devices.

Commentary by Dr. Valentin Fuster
2013;():V03AT03A081. doi:10.1115/IMECE2013-65592.

This article evaluates an M-order Adaptive Kalman filter analysis on Steady-State Visual Evoked Potentials (SSVEPs). This model is based on finding the original brain source signals from their combined observed EEG signals. At each time step, observed brain signals are filtered according to their ideal reference signals measured from 10, 11, 12 and 13 Hz LED stimuli. SSVEP response detection is based on maximum Signal to Noise Ratio (SNR) of the brain source signals. In each test, the average system accuracy is calculated with and without overlapped time-windows along with system Information Transfer Rate (ITR). The overall system accuracy and ITR are showing promising level of SSVEP detection for future online BCI systems.

Commentary by Dr. Valentin Fuster
2013;():V03AT03A082. doi:10.1115/IMECE2013-65640.

In this work, the decellularized porcine small intestinal submucosa extracellular matrix (SIS-ECM), obtained from the commercial product under the trade name of CorMatrix, were tested in uniaxial tension. Preconditioning under cyclic loading of 2 N was conducted to stabilize the mechanical response of the tissue. The influence of rehydration time on the mechanical properties of the tissue was evaluated. Results suggested that the stiffness of SIS-ECM decreased with longer rehydration time. Considering the application of CorMatrix in pericardial closure, the native pericardium samples were also tested. The comparison indicated that the native pericardium is softer than rehydrated CorMatrix. This work can facilitate the surgeons to better choose the appropriate rehydration time when conducting the extracardiac implantations, such as pericardial reconstruction, pericardial closure, etc.

Commentary by Dr. Valentin Fuster
2013;():V03AT03A083. doi:10.1115/IMECE2013-65736.

We report on the modeling and experimental validation of a photopolymerizable hydrogel for the replacement of the interior of the intervertebral disc (so called Nucleus Pulposus).

The hydrogel is initially injected in its liquid form and then photopolymerized inside via a small catheter. The light necessary for the photopolymerization is constrained to a small light guide to keep the surgical procedure as minimally invasive as possible.

During polymerization, the material’s absorption and scattering coefficients change and directly influence local polymerization rates and hence the mechanical properties. Quantitative scattering and absorption values as well as monomer conversion rates of the hydrogel sample were validated using a Monte Carlo model for photopolymerization. By controlling the input light pattern, local material properties can be engineered, such as elastic modulus and swelling ratio to match the set of requirements for the implant.

Experiments were conducted by polymerizing a hydrogel in a column-like volume using an optical fiber for light delivery. Quantitative scattering and absorption values as well as monomer conversion rates of the hydrogel sample were validated using a newly established Monte Carlo model for photopolymerization. The results were used to study and predict 3D polymerization patterns for different illumination configurations. Swelling ratio and elastic modulus were measured as a function of monomer conversion. Preliminary results on hydrogel fatigue tests in an in-vitro bovine disc will be shown.

Commentary by Dr. Valentin Fuster

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