ASME Conference Presenter Attendance Policy and Archival Proceedings

2017;():V003T00A001. doi:10.1115/IMECE2017-NS3.

This online compilation of papers from the ASME 2017 International Mechanical Engineering Congress and Exposition (IMECE2017) 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presenter attendance policy, if a paper is not presented at the Conference by an author of the paper, the paper will not be published in the official archival Proceedings, which are registered with the Library of Congress and are submitted for abstracting and indexing. The paper also will not be published in The ASME Digital Collection and may not be cited as a published paper.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: Biomedical Imaging and Tissue Characterization

2017;():V003T04A001. doi:10.1115/IMECE2017-70062.

This paper presents the feasibility of using holographic microwave imaging (HMI) method for diagnosing lung tumour. A numerical imaging system is developed to evaluate the working principle, which includes a realistic CT-based thorax model. Results show that various small lung tumours with arbitrary shapes, sizes and locations can be identified in the reconstructed images. The HMI approach has a potential for lung cancer detection.

Topics: Microwaves , Cancer , Lung , Imaging
Commentary by Dr. Valentin Fuster
2017;():V003T04A002. doi:10.1115/IMECE2017-70063.

Microwave imaging (MI) has been considered as an alternative way to X-ray mammography for breast cancer detection. This paper presents a compressive sensing based holographic microwave imaging (CS-HMI) approach for diagnosing of breast cancer. A numerical imaging system is developed to validate the proposed CS-HMI approach, which includes a realistic human breast phantom and measurement model. Small breast tumour can be detected in the reconstructed CS-HMI image via Split Bregman (SB) with using 10% measurement data. Simulation and experimental results show that CS-HMI has the ability to produce high quality image by using significantly less measurement data and operation time.

Topics: Microwaves , Cancer , Imaging
Commentary by Dr. Valentin Fuster
2017;():V003T04A003. doi:10.1115/IMECE2017-70356.

Traumatic brain injury (TBI) often happens when the brain tissue undergoes a high rate mechanical load. Although numerous research works have been carried out to study the mechanical characterization of brain matter under quasi-static (strain rate ≤ 100 S−1) loading but a limited amount of experimental studies are available for brain tissue behavior under dynamic strain rates (strain rate ≥ 100 S−1). In this paper, the results of a study on mechanical properties of ovine brain tissue under unconfined compression tests are to be presented. The samples were compressed under uniaxial strain rates of 0.0667, 3.33, 6.667, 33.33, 66.667 and 200 S−1. The brain tissue presents a stiffer response with increasing strain rate, showing a time-dependent behavior. So the hyperelastic-only models are not adequate to exhibit the brain viscoelasticity. Therefore, two hyper-viscoelastic constitutive equations based on power function model and Mooney-Rivlin energy function are applied to the results with quasi-static strain rate (≤ 100 S−1). Good agreement of experimental and theoretical has been achieved for results of the low strain rates. It is concluded that the obtained material parameters from quasi-static tests are not appropriate enough to fit the result with the high strain rate of 200 S−1. The study will further provide new insight into a better understanding of the rate-dependency behavior of the brain tissue under dynamic conditions. This is essential in the development of constitutive material characteristics for an efficient human brain finite element models to predict TBI under impact condition or high motion.

Commentary by Dr. Valentin Fuster
2017;():V003T04A004. doi:10.1115/IMECE2017-72426.

Intravascular ultrasound approach has shown its advantages for thrombectomy. Catheter-directed ultrasound techniques have realized safe therapies by suppressing mechanical contact and penetration of excessive ultrasound energy through the tissue. One limitation of this approach is the lack of the sufficient ultrasound energy for fast thrombectomy because typical catheter-mounted transducers have high-frequency and low acoustic power. In this work, we aim to resolve this problem by designing miniaturized focused ultrasound transducers for improved therapeutic efficacy, which can generate low-frequency, sufficient pressure output within the confined insonation beam. This study builds upon our previous initial design of sub-megahertz, forward-looking, focused ultrasound transducers for preliminary in vitro study on microbubble-mediated thrombolysis. 650 kHz, forward-looking, concave-aperture ultrasound transducers were designed and mounted on 5–6 F catheters. The effect of design factors including aperture diameter, radius-of-curvature, and concave lens acoustic impedance on focusing performance were analyzed by using finite element analysis. Although the theoretical prerequisites for ideal beam focusing were not fulfilled due to the spatial limitation, the simulation results showed that practical design of the concave lens with the small geometrical aperture still enables to generate confined beam with a reasonable focal gain. Experimental validation results confirmed that the focal gain of 9 dB can be achievable. The measured transmitting sensitivity of the concave aperture transducer is 22.5 kPa/Vpp.

Commentary by Dr. Valentin Fuster

Biomedical and Biotechnology Engineering: Biotransport (Fluid, Heat and Mass)

2017;():V003T04A005. doi:10.1115/IMECE2017-71137.

Objective: In clinical treatment, ash cleaning is an effective way to enhance the thermal efficiency of moxibustion. Understanding the thermal characteristics of moxibustion therapy with ash cleaning is necessary to improve its clinical efficiency. Method: Temperature distributions of burning moxa sticks were measured with an infrared camera. The moxa burning duration was set at 20min with different ash cleaning cycles (3min, 4min, 5min and no ash cleaning). A moxa stick burning model with ash cleaning was built to analyze the detailed burning discipline and compared with experimental results. In addition, temperature distributions of in-vitro tissue during moxibustion with different ash cleaning cycles were obtained using thermocouples and infrared camera. Results: Ash cleaning has effectively extended the high-temperature areas of moxa sticks and accelerated the burning velocity. Shorter ash cleaning cycle led to higher average temperature of moxa sticks. The simulated results agreed well with experimental data, which indicates that the moxa stick burning model with ash cleaning is reliable to reveal the burning discipline of moxa sticks. For in-vitro tissue, ash cleaning induced obvious temperature rise at tissue surface and slight rise in deep tissue. Compared with 3 min and 5 min, the ash cleaning cycle of 4 min is the recommended value.

Commentary by Dr. Valentin Fuster
2017;():V003T04A006. doi:10.1115/IMECE2017-71346.

Cancellous bone contains bone marrow where hematopoietic stem cells (HSCs) are produced. Those cells represent an interest in the treatment of leukemia during which transplantation of bone marrow is performed to replace patient degraded cells. HSCs are usually harvested by a puncture in the cancellous bone of the donor’s ilium using a needle. However, this procedure can cause severe burden to the donor because of its high invasiveness. The flow of bone marrow is strongly related to the harvesting of HSCs and permeability is one of the major parameters to characterize cancellous bone. Previous researches have already shown an anisotropy of permeability in femur, whereas punctures are usually performed in the iliac cancellous bone.

The objective of this paper is to characterize the anisotropic permeability of iliac cancellous bone.

Digital images of a porcine iliac cancellous bone sample were obtained by micro-computed tomography (micro-CT), and three locations were selected to fabricate bone models, reproduced by 3D printing at three times magnification. To compare the structure of manufactured models, porosity and its variations along X, Y and Z direction were evaluated from micro-CT images.

To measure permeability, a specific perfusion system was developed. The pressure drop between the upstream and the downstream of bone models were measured at different flow rates, reaching a Reynolds number of 27–158, appropriate for the aspiration condition. Darcy-Forchheimer’s law was then applied to calculate the permeability and Forchheimer coefficient of bone models.

Results revealed different porosities and resultant permeabilities for each bone nodels. A positive correlation links those two parameters. Different fluctuations of porosity were evaluated along each direction although no significant difference of average porosity was observed. On the other hand, different permeabilities and Forchheimer coefficients were measured in each direction with various degrees of anisotropy. Permeabilities in three orthogonal directions of the model ranged from 1.96 × 10−10 to 4.29 × 10−10 m2. Results indicate that transport properties in cancellous bone depend on the flow directions. The anisotropy of permeability can be used for evaluation of flow in cancellous bone.

Commentary by Dr. Valentin Fuster
2017;():V003T04A007. doi:10.1115/IMECE2017-71426.

In this work an in-vitro flow experiment is conducted to elucidate the flow behavior in simplified aortic dissection (AD) disease geometries. In AD, the innermost layer of the aortic wall is locally and partially torn allowing blood to flow between the wall layers forming a parallel blood stream in what is known as the false lumen. The aim of this work is to elucidate the disease flow physics, and to provide guidance in diagnostic radiology, particularly contrast injected computed tomography (CT), where understanding flow patterns and mixing behavior is important for accurate diagnosis. In contrast-CT, dye is injected in the peripheral blood stream to illuminate the blood vessels and identify vascular abnormalities. The flow patterns and the dye transport dynamics impact the nature of the CT images and their interpretation. Particle image velocimetry (PIV) is used to quantify the AD flow fields, and laser-induced fluorescence (LIF) is implemented to visualize and assess the mixing behavior of dye in the false and true lumens. Interesting flow patterns are revealed and discussed in the context of their possible contribution to tear expansion and flapping, and to the elevated mean pressure in the false lumen that is reported in the literature.

Commentary by Dr. Valentin Fuster

Biomedical and Biotechnology Engineering: Clinical Applications of Bioengineering

2017;():V003T04A008. doi:10.1115/IMECE2017-70835.

We examined glioma tissues immediately after en-bloc removal during surgery and measured elastic modulus, viscosity, and viscoelasticity of the gray and white matter to confirm the feasibility of measurement using an indentation device. Measurements were obtained from excised parenchymal brain tumor tissue of four adult patients. The white matter exhibited higher elastic modulus than the gray matter in all patients. Viscoelasticity analysis was performed in two patients, with viscoelastic behavior observed in the white but not in the gray matter in both patients. The loss of viscoelasticity in the white matter observed in one patient may be related to the calcification visible in the preoperative computed tomography image.

Topics: Viscoelasticity
Commentary by Dr. Valentin Fuster
2017;():V003T04A009. doi:10.1115/IMECE2017-71042.

A proximal femur fracture due to osteoporosis is one of serious health care problems in aging societies. Osteosynthesis with pin or screw type of implants, such as Hansson pin (HP), Dual SC Screw (DSCS), is widely used for femoral neck fracture treatment in Japan. Unfortunately, some complications such as secondary fractures, especially peri-prosthetic fractures, may occur during postoperative rehabilitation period. In order to reveal the potential cause of the postoperative fracture from the viewpoint of the biomechanics, authors had already performed the dynamic stress analysis of the treated proximal femur based on finite element (FE) analysis. The final goal of our project is to establish the reliable postoperative bone fracture risk assessment method in response to the daily activity including mainly walking. The aim of this study is to propose a novel elastic multi body analysis method based on FE analysis for proximal femur biomechanics. Patient-specific 3D left hip joint FE model was constructed from an elderly female volunteer’s CT images. The model consists of the pelvis, proximal femur, cartilage and DSCS, as multi bodies. The dynamic loading and boundary conditions were applied to the model for simulating a gait motion. Direction and magnitude of the loads varies in response to the gait motion. The time dependent loading forces; hip contact, gluteus medius, gluteus maximus, tensor fasciae latae and adductor, acting around the hip joint was obtained by inverse dynamic analysis of a human gait using in-house lower-limb musculoskeletal model. These loading and boundary conditions for simulating the gait motion are the major technical advantages of the proposed multi body analysis comparing with the conventional static FE analysis. Time varying stress distribution during the gait was evaluated by using dynamic explicit method via ABAQUS. In order to visually demonstrate dynamic stress distribution, we examined the time varying von Mises stresses at the representative points located on the cortical surface of the proximal femur; femoral head, fracture surface and around the lateral insertion holes. The results indicate significant increase of the stresses around the proximal lateral insertion holes for DSCS treatment. Maximum stress values are good agreement with the previous static FE analysis, on the other hand, these biomechanical discussions based on the stress time histories are only obtained from the proposed method. It is indicated that the proposed method is feasible to support the better pre- and postoperative clinical decisions, which is the main contribution of this study.

Commentary by Dr. Valentin Fuster
2017;():V003T04A010. doi:10.1115/IMECE2017-71522.

Presented in this work is a detailed methodology of how to properly print 3-dimensional (3D) heart models starting from computed tomography (CT) scan and using the Mimics Innovation Suite (Mimics and 3-matic) software package (from Materialize, Leuven, Belgium). The methodology starts by segmenting the clinical DICOM files to retain masks of gray value range of interest. Specifically, retained is the blood volume contained in the heart. Using Mimics, this is accomplished by creating mask and then editing and refining the relevant mask in order to isolate the blood within a certain range of Hounsfield Units (HU). A second mask is created using different gray value ranges to isolate the tissues of the heart. Both 3D models are transferred to 3-matic where integrated Boolean operations are executed to subtract the geometric entities thus retaining the 3D geometry of the heart (including myocardium, cavities, and arteries) of interest. The retained model geometry consists of the muscle surface of the heart and enclosing the hollowed cavities inside that represent the blood volume. Following further processing in 3-matic, the 3D model is now ready for 3D printing. At the American University of Beirut (AUB), a ProJet 3510 SD (3D Systems) is employed to print the heart models (both sectioned and whole). Printed 3D models are employed within the Program for Congenital Heart Disease at AUB that represents a model for clinical applications, education, and research as the first such initiative in Lebanon and the Middle East region.

Commentary by Dr. Valentin Fuster
2017;():V003T04A011. doi:10.1115/IMECE2017-72240.

Sleep apnea and other sleeping disorders impair health and quality of life. Polysomnography is the primary method for diagnosis, but involves cost and utilization of medical resources, which limit access for potential patients. The clinical environment and sensors of polysomnography hinder typical sleep patterns in many individuals, thus degrading the analysis. Sensors suitable for at-home monitoring of sleep have recently become available. At-home monitoring of sleep may improve diagnosis due to increased familiarity for sleeping and ability for multiple sleep sessions, as well as lowering the cost. However, more robust algorithms would be needed to partially compensate for the less controlled conditions and sensor systems. A mat with a grid of force sensors has become available. This study was developing a state machine algorithm to analyze the activity at multiple force sensors of a mat while the subject was lying in supine position on the mat and undertaking natural, rhythmic respiration. The algorithm monitored the subset of active sensors to detect potential respiratory cycles. The similarity of the timing of the detected cycles between different sensors was used to determine the overall pattern of respiratory activity for the subject. Reliable detection of timing for respiratory cycles would be useful for detection of sleep apnea events.

Commentary by Dr. Valentin Fuster
2017;():V003T04A012. doi:10.1115/IMECE2017-72571.

A detailed and experimentally verified methodology is outlined on how to properly process a long tibia bone starting from computed tomography (CT) scans to finite element modeling (FEM). For pre-processing of the bone, CT scan in the form of Digital Imaging and Communications in Medicine (DICOM) files are segmented using Mimics. Next comes assigning gray value Hounsfield Units (HU) of the bone constituents into their cortical and cancellous regions. To have the FEM model arrives at the same mass of that measured experimentally, it was found that cut-off density, cut-off HU, and the utilized number of sub-materials must be considered as varying parameters. The values of these parameters had to be adjusted to properly demarcate cancellous regions from those of the cortical resulting in heterogeneous medium. Next, prior to generating the FEM mesh from the generated 3D model, volume and surface meshes had to be produced. In order to validate the methodology, the modal frequencies of a long tibia bone were experimentally measured. The FEM values of the properly processed CT scans compared favorably with those found experimentally.

Commentary by Dr. Valentin Fuster

Biomedical and Biotechnology Engineering: Computational Modeling in Biomedical Applications

2017;():V003T04A013. doi:10.1115/IMECE2017-70187.

Verification of numerical results with experimental data is an important aspect of any in silico study. In the case of the upper respiratory system, the air flow is often turbulent, which highlights the importance of validating an accurate turbulence model for numerical simulations. Patient specific CT based upper airway models were used for computational fluid dynamics (CFD) analyses of the upper respiratory system and the results were compared with the corresponding experimental results. Detailed CFD simulations were conducted using the STAR-CCM+ software to investigate the most appropriate numerical approach in accurately predicting flow characteristics in the upper respiratory system. Large Eddy Simulations (LES) and Reynolds-Averaged Navier-Stokes (RANS) equations with k-ε, and k-ω turbulence models were investigated.

The experiments include simulating inspiratory-expiratory flow with particle injection at the intake. A stereolithographic (SL) system (3-D system Projet 6000HD), with a resolution of 0.001–0.002 inches per inch of part and VisiJet SL Clear material, was used for fabricating the experimental model. The outlet of the model was connected to a manifold, with subsequent connection to a piston-cylinder system where a computer-controlled motor was used to simulate the normal breathing flow conditions. Investigations of flow characteristics within the upper airway were performed with a 2-D µPIV system from Intelligent Laser Applications (ILA for micro particle image velocimetry) which includes a high power green LED light source with an effective area of 100×100 mm, and a pulsing system (LPS controller). Matlab software was used for the post processing of PIV images.

The LES results displayed more detailed transient flow characteristics than the RANS results for both turbulence models. At the early time steps, the numerical results of the average velocity from all three methods were nearly identical. However, further downstream, where obstructions and strong velocity gradients exist, results differ with a larger velocity gradient near the wall for the LES simulation. Comparing the numerical and experimental results, due to seeding limitations, the experimental results did not display detailed low speed flow characteristics and thus, the shear stress and turbulence quantities were less than the corresponding CFD results. Further experiments are currently in progress to improve the experimental results and to better assess the transient numerical and experimental results.

Commentary by Dr. Valentin Fuster
2017;():V003T04A014. doi:10.1115/IMECE2017-70340.

Insulator-based dielectrophoresis (iDEP) is known as a powerful technique for separation and manipulation of bioparticles, using arrays of insulating posts and external electrical field. In this research, we utilized numerical simulation to study, in detail, the Joule heating which is one the most important phenomena in iDEP technique specially related to bioparticles separation and manipulation in physiological samples. Although Joule heating has been observed in both electrode-based and insulator dielectrophoresis, its effect is more significant in iDEP since higher electric potentials are required in this technology. As a result of the external electrical field, the temperature gradients would create conductivity, permittivity, viscosity and density local gradients in the solution, and consequently cause bulk fluid forces and fluid motion, known as electrothermal flow (ET). These flow circulations can cause unpredicted behavior of the device and even cause problems due to clogging. Moreover, the temperature rise due to the Joule heating could threaten the cell viability. In this study, we are going to develop a robust numerical model for predicting the flow behavior in the existence of external electric field and determining the temperature and velocity profile which can determine the cell viability and clogging problem in iDEP microdevices. The developed numerical tool was used based on the properties of circulating tumor cells (CTCs) and White blood cells (WBCs) and their separation.

Commentary by Dr. Valentin Fuster
2017;():V003T04A015. doi:10.1115/IMECE2017-70345.

Energy absorption and dissipation are characteristics that can be used to protect and extend the useful life of many systems. Two new models of shock absorption structures are proposed. These are based on honeycomb cell patterns with inherent negative stiffness, in theory enabling a large amplification of their damping and recoverability capabilities within a limited space.

A 2D finite element analysis (FEA) is carried on as a first approach for testing this concept. The reduction of kinetic energy of a falling block above the structure is taken as the main indicator of energy absorption.

After some verifications 3D models are developed and tested analogously. Numerical results are obtained with polyethylene (PE) material properties, looking forward for development of future applications in biomechanics.

Commentary by Dr. Valentin Fuster
2017;():V003T04A016. doi:10.1115/IMECE2017-70402.

A pressure drop and its oscillations occurring in the arteriovenous fistula due to sudden changes in the velocity vector direction or the transitional or turbulent flow, related to its complicated geometry, can exert a significant impact on the blood vessel wall behaviour. On the other hand, the pressure drop cannot be precisely measured in vivo with non-invasive measurement methods.

The aim of this study is to assess the pressure drop with numerical and experimental methods in the patient-specific fistula model taking into account a pulsating nature of the flow and the elasticity of blood vessel walls. An additional target is to find a correlation between these two methods.

FSI and in vitro simulations of the blood flow were performed for a patient-specific model of the fistula. Basic geometrical data of the correctly functioning mature fistula were obtained with angio-computed tomography. Those data were applied to develop a spatial CAD model of the fistula, which allowed for creating a virtual model for computer simulations and an analogous in vitro model made with rapid prototyping techniques. The material used to build the in vitro model is characterised by mechanical properties similar to the arterial tissue. A non-stationary computer simulation was carried out with an ANSYS software package, keeping as many flow similarities to the experiments carried out on the test stand as possible, and where the blood mimicking fluid was a water solution of glycerine. During the experiments, the static pressure was measured downstream and upstream of the anastomosis with precise pressure transducers.

The pressure drop was determined with the numerical and experimental methods, which take into account the elasticity of blood vessels. This is a novel approach, since most of similar studies were conducted on the assumption of rigid blood vessel walls. The obtained results show that the pressure drop within the fistula is not so high as reported in the literature, which is correlated with the precision of measurement methods and the fact that a large portion of the fluid energy is accumulated by the elastic walls.

Commentary by Dr. Valentin Fuster
2017;():V003T04A017. doi:10.1115/IMECE2017-70555.

The blockage of arteries in the human vertebrobasilar system (VBS) usually results in major disability or death. It has been widely seen that atherosclerotic stenosis occurs at locations with a low wall shear stress or a high oscillatory shear index. This study investigates the potential of developing arteriostenosis due to smoking in the human VBS at 3 different ages. For this purpose, the VBS has been modeled for smoking/nonsmoking subjects that are 20, 50, and 70 years of age. The governing equations were discretized and solved by a finite volume-based software (ANSYS Fluent v15.0). Five potential locations for stenosis were determined along the VBS. The quantified risks of stenosis were found for smoking and nonsmoking groups, indicating that the locations prone to stenosis are at a higher risk in smoking subjects. The stenosis probability increases around vertebrobasilar junction point (VBJ) and along the right vertebral artery in the 50 and 70-year-old smoker subjects, respectively. Also, the results suggested that the area around the VBJ is at higher risk levels for stenosis at different ages for both smoking and nonsmoking subjects.

Commentary by Dr. Valentin Fuster
2017;():V003T04A018. doi:10.1115/IMECE2017-70675.

Total Hip Arthroplasty (THA) is an orthopaedic procedure that is available to reduce pain and restore the functionality of hip joints. THA has been successfully implemented for the last 40 years. However, after more than 40 years of design and implementation, premature loosening of the femoral stem still occurs due to the stress shielding. Stress shielding can be reduced by using implants with lower stiffness. This however, could increase the micromotion and interface debonding between the stem and femur bone. The aim of this study is to investigate stress and micromotion distribution across the length of the stem and to develop a bone in growth simulation model. To achieve this, a bone growth mechano-regulation algorithm based on deviatoric strain was applied to study the tissue differentiation process. The initial outcome of the study indicates that the stiffness of the implant should not be uniform rather graded from the distal to proximal and lateral to medial directions of the implant. With such graded stiffness, bone growth density was possible across the entire length of the stem, hence reducing aseptic loosening due to stress shielding.

Topics: Stress , Bone , Stiffness
Commentary by Dr. Valentin Fuster
2017;():V003T04A019. doi:10.1115/IMECE2017-70841.

Objective: The aim of this study was to design a novel radiofrequency (RF) electrode for larger and more round ablation volumes and its ability to achieve the complete ablation of liver tumors (> 3 cm in diameter) using finite element method. Methods: A new RF expandable electrode comprising three parts (i.e., insulated shaft, changing shaft, and hooks) was designed. Two modes of this new electrode (i.e., monopolar expandable electrode (MEE) and hybrid expandable electrode (HEE)) and a commercial expandable electrode (CEE) were investigated using liver tissue with and without liver tumor. A temperature-controlled radiofrequency ablation (RFA) protocol with a target temperature of 95 °C and an ablation time of 15 minutes was used in this study. Both the volume and shape of the ablation zone were studied for all RF electrodes. A large liver tumor with the diameter of 3.5 cm was used to evaluate the effectiveness on the complete ablation of the new designed electrode. Results: In the first scenario (without liver tumor), the ablation volumes of CEE, HEE, and MEE were 9.96 cm3, 41.0 cm3, and 46.14 cm3, respectively. The values of sphericity index (SI) of CEE, HEE, and MEE were 0.36, 0.94, and 0.98, respectively. The best performance was achieved by the MEE electrode. In the second scenario (with liver tumor), the ablation volumes of MEE and CEE were 67.56 cm3 and 20.62 cm3, respectively. Also, a rounder ablation volume was generated by MEE compared to CEE (SI: 0.98 vs 0.55). Conclusion: This study concludes that compared with CEE, both MEE and HEE are able to get larger and more round ablation volumes due to the larger electrode-tissue interface and more round shape of hooks; compared with HEE, MEE is better to get a larger and rounder ablation volume; MEE is able to ablate a large liver tumor (i.e., 3.5 cm in diameter) completely.

Commentary by Dr. Valentin Fuster
2017;():V003T04A020. doi:10.1115/IMECE2017-70850.

Cardiovascular Diseases, the common name for various Heart Diseases, are responsible for nearly 17.3 million deaths annually and remain the leading global cause of death in the world. It is estimated that this number will grow to more than 23.6 million by 2030, with almost 80% of all cases taking place in low and middle income countries. Surgical treatment of these diseases involves the use of blood-wetted devices, whose relatively recent development has given rise to numerous possibilities for design improvements. However, blood can be damaged when flowing through these devices due to the lack of biocompatibility of surrounding walls, thermal and osmotic effects and most prominently, due to the excessive exposure of blood cells to shear stress for prolonged periods of time. This extended exposure may lead to a rupture of membrane of red blood cells, resulting in a release of hemoglobin into the blood plasma, in a process called hemolysis. Moreover, exposure of platelets to high shear stresses can increase the likelihood of thrombosis. Therefore, regions of high shear stress and residence time of blood cells must be considered thoroughly during the design of blood-contacting devices. Though laboratory tests are vital for design improvements, in-vitro experiments have proven to be costly, time-intensive and ethically controversial. On the other hand, simulating blood behavior using Computational Fluid Dynamics (CFD) is considered to be an inexpensive and promising tool to help predicting blood damage in complex flows. Nevertheless, current state-of-the-art CFD models of blood flow to predict hemolysis are still far from being fully reliable and accurate for design purposes. Previous work have demonstrated that prediction of hemolysis can be dramatically improved when using a multiphase (i.e., phases are plasma, red blood cells and platelets) model of the blood instead of assuming the blood as a homogeneous mixture. Nonetheless, the accurate determination of how the cells segregate becomes the critical issue in reaching a truthful prediction of blood damage. Therefore, the attempt of this study is to develop and validate a numerical model based on Granular Kinetic Theory (GKT) for solid phases (i.e., cells treated as particles) that provides an improved prediction of blood cells segregation within the flow in a microtube. Simulations were based on finite volume method using Eulerian-Eulerian modeling for treatment of three-phase (liquid-red blood cells and platelets) flow including the GKT to deal with viscous properties of the solid phases. GKT proved to be a good model to predict particle concentration and pressure drop by taking into account the contribution of collisional, kinetic and frictional effects in the stress tensor of the segregated solid phases. Preliminary results show that the improved segregated model leads to a better prediction of spatial distribution of blood cells. Simulations were performed using ANSYS FLUENT platform.

Commentary by Dr. Valentin Fuster
2017;():V003T04A021. doi:10.1115/IMECE2017-70946.

Micron sizes grooves can control the cell settlement on the implant surface or be used to direct tissue generation at the implant/bone interface. The effect of shape, size and the type of material of the microgrooves on the mechanical stimulus transfer from the implant to bone at physiological loading is not known yet. Therefore, this study evaluated both experimentally and numerically the effect of surface modification on a titanium implant to the load transfer characteristics from implant to bone for examining stress shielding parameters. This study measured the effect of micron grooves on titanium to the mechanical stability of titanium using a rabbit model. This study also developed a finite element model based on the in vivo test model to examine the stress shielding parameters. The results showed that the mean values of fracture strength were significantly higher for grooved titanium samples (1.32±0.45 MPa, n = 3) compared to control samples (without any groove) (0.22±0.16 MPa, n = 6) (P < 0.05). The load-displacement graph from the pull out tension tests was used to measure the frictional coefficient between Ti and bone from the FEA model. It was found from the FEA model that the average co-efficient of friction between titanium and bone was 0.50. Maximum equivalent stress along the interface of microgrooves on titanium was higher from groove area in compare to the non-groove area because of the change of the geometry along the groove. The microgrooves in the model have a significant effect on the stress transfer parameter between implant and adjoining bone. The unequal load sharing due to micro-grooving causes an increase in stiffness of the adjacent bone to the implant.

Topics: Stress , Titanium
Commentary by Dr. Valentin Fuster
2017;():V003T04A022. doi:10.1115/IMECE2017-71224.

Recently, the observation technology of micro structure has made great progress, and then collagen fiber orientation of meniscus can be measured accurately. This makes it possible to evaluate the stress in knee joint by considering the collagen fiber orientations at the micro scale. In this study, we developed visco-isotropic/anisotropic hyperelastic constitutive equations (Iso-VHE/Aniso-VHE) for menisci, which can reflect the initial collagen fiber orientations and their deformation induced rotations. Subsequently, we constructed a finite element (FE) model of normal human knee joint by using the magnetic resonance (MR) tomography images. The FE analysis with the proposed constitutive equations and FE model clarifies the reinforcement effect of collagen fibers on mechanical characteristics of knee joint.

Our computational prediction clarified that the stress concentration occurred on the contact parts of articular cartilages of femur and tibia, which met the tendency of the experimental results. Furthermore, the maximum compressive stresses evaluated by Aniso-VHE always showed a lower value as compared with Iso-VHE. This suggested that the anisotropy of meniscal collagen fibers relieved the stress concentration and lowered the maximum value. Therefore, our proposed FE analysis was proved to have a potential to reveal the functions of meniscus and knee joint.

Commentary by Dr. Valentin Fuster
2017;():V003T04A023. doi:10.1115/IMECE2017-71432.

The objective of this study was to computationally investigate the flow mechanics and the near-wall hemodynamics associated with the different take-off angles in the left coronary artery of the human heart. It is hypothesized that increasing the take-off angles of the left coronary artery will significantly increase or decrease the likelihood of plaque (atherosclerosis) buildup in the left coronary artery bifurcations. Specifically, this study quantified the effects of the varying take-off angles on the branches along the left anterior descending (LAD) of the left coronary artery using computational fluid dynamics (CFD) simulations. The study compared five test cases of the different take off-angles of the left coronary artery (LCA) and four different branch angles between the LAD and the left circumflex (LCx). It also considered the branch angles of the coronary artery downstream the LAD. The LCA inlet boundary conditions was set as a pulsatile mass flow inlet and flow split ratios were set for the outlets boundary conditions. The nature of blood pulsatile flow characteristic was accounted for and the properties of blood which include the density (1,050 kg/m3) and dynamic viscosity (0.0046 Pa-s) were obtained from previous research.

The results from the simulations are compared using established scales for the parameters evaluated. The parameters evaluated were: (i) Oscillatory Shear Index (OSI); which quantifies the extent in which the blood flow changes direction during a cardiac cycle (ii) Time Average Wall Shear Stress (TAWSS); which quantifies the average shear stress experienced by the wall of the artery and (iii) Relative Residence Time (RRT); which quantifies how long blood spends in a location along the artery during blood flow. These parameters are used to predict the likelihood of blood clots, atherosclerosis, endothelial damage, plaque formation, and aneurysm in the blood vessels. The data from the simulations were analyzed using functional macros to quantify and generate threshold values for the parameters.

Commentary by Dr. Valentin Fuster
2017;():V003T04A024. doi:10.1115/IMECE2017-71442.

The objective of this study was to assess the effects structural features of endovascular stent-grafts used to repair abdominal aortic aneurysms (AAA) have on the flow mechanics and near-wall hemodynamics using Computational Fluid Dynamics (CFD) simulations. This research compared two test case model representations: 1) a stent graft that included the wire struts in the graft walls, and 2) a stent graft that excluded the struts in the computational mesh. The two computer-aided design models were created to represent a bifurcated stent graft in the abdominal aorta, with the stent beginning in the thoracic region of the aorta and branching into the common iliac arteries. The geometries were imported as surface meshes into a commercially available CFD solver. Both models account for viscous pulsatile blood flow of the cardiac cycle using blood properties gathered from previous research. Results of the two simulations were compared by using established metrics, including oscillating shear index (OSI), time average wall shear stress (TAWSS), and relative residence time (RRT), all of which are used to predict the likelihood of clot formation, endothelial damage, and device failure. Scalar and vector scenes allow for visualization, and data was exported for quantifying threshold results of the parameters. Due to the expense of stent grafts and the risks involved with clinical trial, CFD modeling is becoming more prominent in endovascular repair of aneurysms. The overarching goal of this study is to enhance current models of stent grafts, which can potentially be used to complement clinical trial for stent graft development.

Commentary by Dr. Valentin Fuster
2017;():V003T04A025. doi:10.1115/IMECE2017-71713.

Anterior cervical decompression and fusion (ACDF) is a surgical procedure typically utilized in cervical spine disc herniation to alleviate spinal cord compression. There have been several implants used in ACDF surgeries [6,11]. Common implants include standalone cages that insert in the intervertebral space (zero-profile) and cages with an anterior cervical plate and screws that connects the adjacent vertebral bodies. The anterior cervical plate and screw placement has been the preferred method due to increase in fusion rate, reduced graft subsidence, and overall improved lordotic alignment [1]. Multiple studies have shown that standalone cages like the zero-profile result in higher incidence of failure and cage subsidence [16, 17, 18, 10, 19, 20]. This study aims to evaluate the mechanical stress induced by a zero-profile construct throughout the spine as a means to understand device risk and predict mechanical failure.

There are specific levels within the cervical spine that fail more often if adjacent levels are fused. When the level above the construct fails, it tends to be a process of subsidence and collapses of the above vertebral body onto the construct. This can be due to poor bone quality, or failure of bone growth to induce bony fusion between the two levels adjacent to the construct. Conversely, levels below the construct do not subside, but have an increased chance for disc herniation, requiring re-operation and extension of the fusion. The interaction of these levels and implanted cages remains poorly understood from a mechanical standpoint, and even less so in instances of multilevel ACDF [2].

Our computational model geometry included a zero-profile construct placed at a single level, followed by the application of physiological loading to the vertebral column. Parametric studies that probe various load magnitudes predict that resultant stress fields are concentrated at the level above the construct. High stresses immediately above the construct suggest an increased likelihood for subsidence in comparison to the levels below, which is in concert with clinical findings. Interestingly, the levels below the contrast experienced minimal stress shielding in comparison to referent normal simulations. Additional studies examined multidirectional forces that mimic flexion and extension of the cervical spine, with qualitatively similar findings of elevated stress above the construct. This model enables mechanical assessment of cervical spine instrumentation and provides a framework for understanding multilevel ACDF and predicting the performance of new cages/approaches to stabilize the spine.

Commentary by Dr. Valentin Fuster
2017;():V003T04A026. doi:10.1115/IMECE2017-71734.

Analysis of the electrical properties of a biological cell can provide useful information about its characteristic features, such as the intracellular composition, charge distribution and composition changes in cell membrane, as well as the extracellular environment. Electrical impedance spectroscopy of a cell suspension can be used to extract an average measure of the electrical properties of single cells. In sickle cell disease, the disease state of a sickle red blood cell is closely related to the intracellular hemoglobin composition and concentration. This study presents an electrical impedance measurement of sickle cell suspension with normal red blood cells as control. Electrical impedance spectra of cell suspensions are obtained in the range of 1000 Hz to 1MHz. Based on Maxwell’s mixture theory, average values of membrane capacitance and cytoplasm resistance of single cells are extracted for both normal and sickle blood samples. Comparing to traditional parallel-plate setup for cell suspension subjected to frequency sweep, this method requires low quantity of blood specimens and can be potentially valuable for patients that are already anemic.

Commentary by Dr. Valentin Fuster
2017;():V003T04A027. doi:10.1115/IMECE2017-71907.

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 corrosion induced pits of a titanium-alloy modular implant in cement-less total hip arthroplasty was numerically investigated. The effect of pit geometry parameters — cylindrical, conical, and hemispherical dimple are compared and discussed in terms of taper performance.

Commentary by Dr. Valentin Fuster
2017;():V003T04A028. doi:10.1115/IMECE2017-72013.

Despite new improvements in coronary artery stents, there is still great concern over the failure and lifecycle of stents in patients. In this work, we explore different models of existing stents fabricated using shape memory alloy and analyze them from the mechanical failure point of view and finally propose a novel double helix stent model for coronary arteries inspired from the structure of DNA. We conducted several simulations of the model under different conditions. The experiments are conducted using hyper elastic silicone rubber mimicking the human coronary arteries and the sample stent model made of super elastic NiTi shape memory material.

Commentary by Dr. Valentin Fuster
2017;():V003T04A029. doi:10.1115/IMECE2017-72146.

Stent deployment has been widely used to treat narrowed coronary artery. Its acute outcome in terms of stent under expansion and malapposition depends on the extent and shape of calcifications. However, no clear understanding as to how to quantify or categorize the impact of calcification. We have conducted ex vivo stenting characterized by the optical coherence tomography (OCT). The goal of this work is to capture the ex vivo stent deployment and quantify the effect of calcium morphology on the stenting. A three dimensional model of calcified plaque was reconstructed from ex vivo OCT images. The crimping, balloon expansion and recoil process of the Express stent were characterized. Three cross-sections with different calcium percentages were chosen to evaluated the effect of the calcium in terms of stress/strain, lumen gains and malapposition. Results will be used to the pre-surgical planning.

Commentary by Dr. Valentin Fuster
2017;():V003T04A030. doi:10.1115/IMECE2017-72201.

Background Surgical knots are one of several structures which can fail during surgical repair. However, there is no universal agreement on the superiority (best/safest) of one particular surgical knot technique. Tensile testing of repaired soft tissue has been used to assess the efficacy of surgical knot tying techniques, however, few computational models exist. The purpose of this study was to create a validated biomechanical model to evaluate the effect of knot configuration on the mechanical performance of surgical sutures.

Methods Two sutures were tested experimentally to find the mechanical properties and strength. Single throw knots were also tested for strength. Finite element models were constructed of each configuration and correlation was established.

Results The finite element results are quantitatively and qualitatively consistent with experimental findings. The FE model stress concentrations are also consistent with published strength reductions. Model and experimental results are presented using as-manufactured No. 2 FiberWire as well as its core and jacket constituents separately.

Clinical Relevance This paper describes a model which can evaluate the effect of knot topology on the mechanics of surgical suture. In the future, the model may be used to evaluate the mechanical differences between surgical techniques and suture materials. The findings may impact choices for suture and knot types selected for soft tissue repairs.

Commentary by Dr. Valentin Fuster
2017;():V003T04A031. doi:10.1115/IMECE2017-72671.

Magnetic seizure therapy (MST) is currently on trial as an alternative to Electro-convulsive therapy (ECT) to treat patients suffering from treatment resistant depression (TRD). This paper is concerned with developing a deeper understanding of the mechanics behind MST by employing finite element analysis (FEA) of brain. To this end, a model that consists of concentric spherical layers that represent a realistic anatomical head model has been employed. Simulations performed via COMSOL Multi-physics helped identify the dimensions and coil types for the MST device as well as the angular probing orientations. Largest induced current due to the externally imposed magnetic field was found in the cerebrospinal fluid (CSF), which act as a barrier to induce current in the gray matter. Different copper coil configurations were experimented with namely the cap coil, stacked coil and the multi-stacked coil. These studies are envisaged to provide a quantitative approach to virtually simulate the MST procedure and hence enhance the benefits clinical trials that are currently underway.

Commentary by Dr. Valentin Fuster

Biomedical and Biotechnology Engineering: Damage Biomechanics

2017;():V003T04A032. doi:10.1115/IMECE2017-70281.

This work lies within an overall effort to improve, as well as quantify, the uncertainty of traumatic brain injury (TBI) prediction for blast loading. Detailed finite element (FE) modeling of the human head currently provides the only viable means to quantify the mechanical response within the brain during a blast loading event. Unfortunately, the exact linkages between loading patterns, tissue mechanical response, and injury/physiological effects are still quite unknown; however, the exceedance of specified threshold values based on direct and derived measures of stress, strain, pressure, and acceleration within the brain have been shown to be useful injury criteria. The utility of these threshold values is somewhat mitigated by the fact that preliminary parametric studies focusing on varying head morphology and the material properties of FE head model components have shown significant variation in the predicted injury response, indicating that the exact relationship between model geometry, material properties, and mechanics-based injury response metrics has not yet been established.

Identifying an appropriate constitutive model form and optimal parameter values for biological tissues is an enormous challenge hindered by large epistemic uncertainties. Available experimental data sets frequently offer valuable but limited information due to the many vagaries associated with the testing of biomaterials, such as testing on different species, e.g., porcine and bovine specimens, testing with inapplicable strain rates, and having too little data. The parameters of hyperelastic, hyper-viscoelastic, and viscoelastic constitutive models, which are commonly utilized for modeling these biological tissues, can be fit to an aggregation of experimental data through a constrained optimization formulation. Specifically, this study considers fitting data from biomaterials to Ogden’s model of hyperelasticity. The goodness of fit of the optimization is limited by the appropriateness of the model forms as well as limited, and at times contradictory, data. In order to properly account for these uncertainties, a Bayesian approach is adopted for model calibration and posterior distributions are therefore produced for each model parameter.

Commentary by Dr. Valentin Fuster
2017;():V003T04A033. doi:10.1115/IMECE2017-70413.

Conflicts in the Gulf have exposed warfighters to injury by means of improvised explosive device (IED) detonation beneath armored military vehicles, commonly referred to as underbody blast (UBB). Together with the pelvis, injuries to the foot-ankle-leg number among those most commonly sustained by warfighters in the event of a UBB. Multiple biomechanical tests are currently being conducted in order to develop injury thresholds and risk functions for warfighters subjected to these vertical loads. In a previous study of 38 foot-ankle-leg complexes tested under automotive and UBB load rates, a distribution of injuries was produced. High-speed x-ray video and post-test CT, Statscan (Lodox, Johannesburg, South Africa), and dissection were performed to document injuries. It is, however, difficult to thoroughly remove soft tissue and cartilage from the calcaneus and talus without inducing damage that could be mistaken as a test-induced injury. For this test series, Dermestidae macerated 31 tali and 18 calcanei revealing 12 and 4 injuries, respectively, that were previously undiagnosed through more traditional techniques. Logistic regressions were produced to quantify the significance of the findings. The pre- and post-maceration regressions predicted a 50% injury risk of 6626N and 4228N, respectively, or a 44% difference in mean.

Topics: Wounds
Commentary by Dr. Valentin Fuster
2017;():V003T04A034. doi:10.1115/IMECE2017-70610.

Traumatic brain injury (TBI) is one of the most common injuries to service members in recent conflicts. Computational models can offer insights in understanding the underlying mechanism of brain injury, which lead to the crucial development of effective personal protective equipment designed to prevent or mitigate the TBI.

Historically many computational models were developed for the brain injury study. However, these models use relatively coarse mesh with a less detailed head anatomy. Many models consider the head only and thus cannot properly model the real scenario, i.e., accidental fall, blunt impact or blast loading. A whole-body finite element model can represent the real scenario but is very expensive to use.

By combining the high-fidelity human head model with an articulated human body model, we developed the computational multi-fidelity human models to investigate the blunt- and blast-related TBI efficiently. A high-fidelity computational head model was generated from the high resolution image data to accurately reproduce the complex musculoskeletal and tissue structure of the head. The fast-running articulated human body model is based on the multi-body dynamics and was used to reconstruct the accidental falls. By utilizing the kinematics and force and moment at the joint of the articulated human body model, we can realistically simulate the blunt impact and assess the brain injury using the high-fidelity head model.

Topics: Modeling , Wounds
Commentary by Dr. Valentin Fuster
2017;():V003T04A035. doi:10.1115/IMECE2017-70611.

Current understanding of blast induced traumatic brain injury (TBI) mechanisms is incomplete and limits the development of protective and therapeutic measures. Animal testing has been used as a surrogate for human testing. The correlation of animals to human responses is not well understood with a limited set of experimental data, because of ethical concerns and cost of live animal tests. The validated computational animal models can be used to supplement and improve the granularity of available data at a significantly reduced cost.

A whole-body porcine high-fidelity computational model was developed based on the image data. The hyper-viscoelastic model was used for soft tissues to capture the rate dependence and large strain nonlinearity of the material. The shock wave interaction with a porcine subject in a shock tube was simulated using computational fluid dynamics (CFD) models, via a combination of 1-D, 2-D and 3-D numerical techniques. The shock wave loads were applied to the exterior of the porcine finite element (FE) model to simulate the pressure wave transmission through the body and capture its biomechanical response. The CFD and FE problems are solved using the explicit Eulerian and Lagrangian solvers, respectively, in the DoD Open Source code CoBi.

The computational models were validated by comparing the simulation results with experimental data at specific instrumented locations. The predicted brain tissue stress-strain fields were used to determine the areas susceptible to blast induced TBI by using published mechanical injury thresholds. The validated porcine model can be used to better understand TBI and how injury in animals corresponds to injury in humans. The coupled Eurlerian and Lagrangian approaches developed in this paper can be extended to other simulations to improve the solution accuracy.

Commentary by Dr. Valentin Fuster
2017;():V003T04A036. doi:10.1115/IMECE2017-70619.

The effects of combat helmet pad suspension components on explosive device ballistic impact on the helmet shell are determined for four helmet geometric designs with and without pad suspension systems. Finite element analysis of a flat panel test article is used to generate back face deflection (BFD) data as a function of impact obliquity to be input into a computer aided design (CAD) software application. The CAD software is used to evaluate omni-directional ballistic impacts to the helmet using one dimensional equations of motion. The BFD and acceleration results of the CAD software analysis are used to determine a head injury criteria and abbreviated injury score (AIS). The AIS is related to ten focal and diffuse head injuries from trauma literature. The attenuation of helmet back face deflections and projectile deceleration for over-pad impacts compared to between-pad impacts translates into reduced injury predictions. The analysis quantifies these effects and helps to define the helmet trade space, facilitate prototyping, and support helmet design optimization.

Topics: Brain , Wounds , Warfare
Commentary by Dr. Valentin Fuster
2017;():V003T04A037. doi:10.1115/IMECE2017-70624.

The purpose of this study is to build a risk model to predict the probability of Traumatic Brain Injury (TBI). The focus is on the occurrence of one of TBI outcomes, Diffuse Axonal Injury (DAI), due to car crashes. This goal is achieved by developing a multilevel framework, which includes vehicle crash Finite Element (FE) simulations with a dummy along with FE simulations of the brain using loading conditions derived from the crash simulations. The framework is used to propagate uncertainties and obtain probabilities of DAI based on certain injury criteria such as Cumulative Strain Damage Measure (CSDM). The risk model is constructed from a support vector machine classifier, adaptive sampling, and Monte-Carlo simulations. In contrast to previous risk models, it includes the uncertainty of explicit parameters such as impact conditions (e.g., velocity, impact angle), and material properties of the brain model. This risk model can provide, for instance, the probability of DAI for a given assumed velocity.

Commentary by Dr. Valentin Fuster
2017;():V003T04A038. doi:10.1115/IMECE2017-70650.

In addition to the direct mechanical damage that takes place during a ballistic injury, the formation of the temporary wound cavity creates a suction effect capable of introducing debris, particles, and bacteria from the environment into the wound track. This introduction of bacterial contamination into the wound can give rise to infections which may delay healing or result in more serious problems. Various authors have conducted controlled ballistics experiments placing bacterial contamination on the surface of ballistics gelatin targets to study the effect of parameters such as projectile caliber and speed on the distribution of bacteria along the permanent cavity. The results reported in the literature showed that bacteria were present along the entire surrogate wound track. Understanding the contribution that the formation of the temporary cavity has on the number and distribution of bacteria along the surrogate wound requires the development of experiments to visualize the flow of air during the transient phase of target deformation and the use of numerical simulations to predict variables associated with the flow of air, like pressure-time histories along the projectile path, that cannot be directly measured during experiments.

This paper discusses the development of a finite element model using ANSYS Autodyn for the simulation of a small caliber projectile traveling at moderate speeds penetrating a soft tissue surrogate target made of ballistics gelatin. The model uses a Coupled Eulerian-Lagrangian formulation and discretization scheme, which allows for the analysis of not only the deformation of the solid bodies, but also of the flow of air into the wound track. For model validation, the numerical results are compared to spatial data extracted from high speed video recorded during experiments matching key model parameters. Comparisons of the numerical and experimental results indicate that the model is providing reasonable results for the deformations and overall air flow. The predicted pressure dynamics within the simulated wound track clearly suggest that areas of partial vacuum exist within the cavity, which is consistent with the suction effect mentioned by several researchers.

Topics: Air flow , Wounds
Commentary by Dr. Valentin Fuster
2017;():V003T04A039. doi:10.1115/IMECE2017-70796.

Viscoelasticity of the nerve root may play a significant role in biomechanical stability of the spine. To date, however, relatively few studies have been conducted to characterize and elucidate this complex mechanical behavior. Thus, a series of tensile stress relaxation tests with a ramp-hold phase was performed using fiber bundles isolated from the nerve roots. In addition, the current study presents the application of a curve fitting technique, i.e., a stress relaxation response of the fiber bundles was theoretically predicted based on the measured data obtained at moderate to sub-traumatic loading conditions. To do that, a least squares optimization method was employed, and we revealed that this technique is applicable to reasonably predict even an instantaneous “elastic” response as well as subsequent slow stress decay of the neural fiber bundles. The resultant fitted coefficients also suggested that the viscoelastic tensile behavior of the nerve root is mainly dominated by the long-term time constants (100–1000 s) rather than the short-term time constants (0.1–1 s). Since a mathematical human body model is a powerful tool to investigate injury mechanisms involving high-contact sports and traffic accidents, our results will be useful in predicting potential spinal injuries and alleviating mechanical damage of the nerve roots, while preventing neck/low back pain due to such traumatic events.

Topics: Fibers
Commentary by Dr. Valentin Fuster
2017;():V003T04A040. doi:10.1115/IMECE2017-71007.

As the strongest of the meningeal tissues, the spinal dura mater plays an important role in the overall behavior of the spinal cord-meningeal complex (SCM). It follows that the accumulation of damage affects the dura mater’s ability to protect the cord from excessive mechanical loads. Unfortunately, current computational investigations of spinal cord injury etiology typically do not include post-yield behavior. Therefore, a more detailed description of the material behavior of the spinal dura mater, including characterization of damage accumulation, is required to comprehensively study spinal cord injuries.

Continuum mechanics-based viscoelastic damage theories have been previously applied to other biological tissues, however the current work is the first to report damage accumulation modeling in a SCM tissue. Longitudinal samples of ovine cervical dura mater were tensioned-to-failure at one of three strain rates (quasi-static, 0.05/sec, and 0.3/sec). The resulting stress-strain data were fit to a hyperelastic continuum damage model to characterize the strain-rate dependent sub-failure and failure behavior. The results show that the damage behavior of the fibrous and matrix components of the dura mater are strain-rate dependent, with distinct behaviors when exposed to strain-rates above that experienced during normal voluntary neck motion suggesting the possible existence of a protective mechanism.

Topics: Modeling , Damage
Commentary by Dr. Valentin Fuster
2017;():V003T04A041. doi:10.1115/IMECE2017-71511.

In this study, quasi-static compression and dynamic impact experiments were conducted on helmet pads. Various layers of the foam pad: comfort, stiff and bilayer were tested to characterize their material response. In the compression tests, a piston compressed foam samples at constant velocity. The samples were tested under confined and unconfined conditions. In the dynamic impact experiments, the foam samples were impacted by a rigid projectile. Both the time histories of the force applied to the foam samples and the sample displacement were recorded to calculate the engineering strain and stress in the foam samples. The material stiffness in the impact tests was found to be several times that of the quasi-static tests.

Commentary by Dr. Valentin Fuster
2017;():V003T04A042. doi:10.1115/IMECE2017-71528.

Quasi-static compression and dynamic impact experiments were conducted on comfort and stiff foam material used in the helmet pads. The time histories of displacement and total force applied to the foam were measured, from which the engineering stress-strain curves were calculated. At high rate, the material did not reach equilibrium and the calculated stress-strain curves may not represent the actual stress-strain response. Numerical models were developed in LS-DYNA to calibrate a material model for the comfort and stiff foams. The rate-dependent foam material response was captured reasonably well in the model.

Commentary by Dr. Valentin Fuster
2017;():V003T04A043. doi:10.1115/IMECE2017-71826.

Panicum Miliaceum (common millet) is an ancient crop and spread widely across the world. The high survivability and adaptability of this species is attributed to the unique structure of the seedcoat. Recently, it was found the seedcoat has a fascinating complex microstructure with star-shaped epidermis cells, articulated together via wavy suture interfaces, to form a compact jigsaw puzzle-like layer. To explore the damage initiation and evolution during quasi-static uniaxial compression, finite element simulations were performed for full seeds, and single seedcoat and kernels. A parametric study was conducted for the seedcoat and kernel to explore the relationship between material properties and damage. The material properties of the seedcoat and kernel were obtained by nanoindentation testing. A Hashin progressive damage material model was used to capture damage evolution of the seedcoat, combined with a damage plasticity model for the kernel. The simulation results show the capabilities in modeling the damage of seeds.

Topics: Compression , Damage
Commentary by Dr. Valentin Fuster

Biomedical and Biotechnology Engineering: Dynamics and Control of Biomechanical Systems

2017;():V003T04A044. doi:10.1115/IMECE2017-70982.

This work investigates the human leg muscle and ligaments forces during a drop-landing exercise. An inverse dynamics 2-D model of human leg is used on this ballistic task in order to predict these forces. The model consists of three bony structures, namely femur, tibia, and patella. The joints of the model are the knee joint and the hip joint. The ligamentous structure of the knee includes the two cruciate ligaments, Anterior Cruciate Ligament (ACL) and the Posterior Cruciate Ligament (PCL), and the two collateral ligaments, Lateral Collateral Ligament (LCL) and Medial Collateral Ligament (MCL). The system of muscles of the system includes muscle such as quadriceps, hamstrings, gastrocnemius are included in the model. Experimental data used show a maximum of 100 degrees of flexion angle and ground reaction forces up to 4 times the body weight. The inverse dynamics 2-D model consists of an objective function to minimize the muscle forces, and a set of constraints consisting of equality constraints which are the dynamics equations of the bony structures, and inequality constraints in which all muscle forces must be positive. All muscle forces show a pattern in which they reach large magnitudes at the beginning of landing, decreasing as the subject end the exercise with a standing position.

Topics: Muscle , Knee
Commentary by Dr. Valentin Fuster
2017;():V003T04A045. doi:10.1115/IMECE2017-70988.

Knee joint biomechanics for various ambulatory exercises was investigated using inverse dynamics in OpenSim, a computational platform for accelerated biomechanics research. A motion capture system was used to collect kinematic and kinetic information during walking, squatting, and the one-legged squat. Pre-processing of the data was accomplished using a MATLAB toolbox. Subsequent modeling, simulation, and analysis was performed in OpenSim. Loading in the cruciate ligaments and select muscles were the primary focus for the analysis. The accuracy of the results is compared with other available work in the literature. The impact, limitations, technology, and novelty were also reviewed in the scope of this work.

Commentary by Dr. Valentin Fuster
2017;():V003T04A046. doi:10.1115/IMECE2017-71143.

This project aims to create an electronically powered and controlled knee brace to aid stroke victims with partial paralysis with their leg muscle rehabilitation process. The newly designed assistive bionic joint takes the functionality of the existing assistive knee braces to the next level by incorporating a control algorithm that uses sensor signals gathered from the patient’s leg muscles. Electromyography (EMG) is used for gathering impulse signals from electrodes placed on key muscles as inputs for the device. The action of each major leg muscle is replicated using a set of fluidic muscles that mimic the functionality of the actual leg muscles. A microcontroller is used to interpret sensor data and adjust the contraction length of the muscles, thereby providing the wearer with augmented strength and mobility. Initial testing of a proof-of-concept prototype has led to finite control over muscle contraction length based on sensor data and has a response time of 280ms from full extension to contraction. Further testing of the brace assembly, fluidic muscles and control system is conducted and the results indicate a 600ms response time due to a step input. This personalized, powered brace has many implications for the enrichment of muscle rehabilitation such as higher patient morale, more muscle activity, and shortened recovery times.

Topics: Bionics , Design , Muscle
Commentary by Dr. Valentin Fuster
2017;():V003T04A047. doi:10.1115/IMECE2017-71301.

We have been investigating how to use microorganisms for bio-micromachines. In this paper, we investigated the motion control property of Paramecium in the vertical plane to prepare the real 3-dimensional motion control. First, we developed a motion control pool for the vertical set up. Basically, the controllability of Paramecium in the vertical plane is not so different to the controllability in the horizontal plane. We can control paramecium very stably for over 100 laps along the star-shaped target route by using this newly made experimental pool. The controllability was improved with the progression of making a circuit. It may relate to the dropping of the swimming speed. The swimming trace, however, showed the peculiarity that related to the vertical movements. The swimming speed of the downward direction is higher than that of the upward direction. The overrun on the downward route was larger than that on the upward route in the vertical plane. It was caused by the difference of the swimming speed on each of routes. Therefore, we developed a new motion control algorithm to decrease this overrun. In our former algorithm, the change timing of the target point was decided by the previous change timing and the previous turning point. In the new algorithm, we change this adjusting method to refer the same target point of the past laps using smoothing value calculated by the integral of the equal ratio attenuation. By using this adjustment method, we succeeded to decrease the overrun. We also investigated the transportability of the object by using motion controlled paramecium in the vertical pool. We found that paramecia often cause their avoiding reaction when they hit object made of hard material. In the case of the object made of soft material, paramecia can push more often and more easily. Therefore, we decided to change the target object from hard plastic to soft gel. We succeeded to transport and drop a gel oval sphere to the target place by manually controlled paramecium in the vertical plane pool.

Commentary by Dr. Valentin Fuster
2017;():V003T04A048. doi:10.1115/IMECE2017-72386.

Geometry consistent spatio-temporal measurements of the experimental acceleration of olive tree branches were analyzed with advanced POD tools in an effort to gain knowledge on the mechanics-dynamics of this bio-mechanical structure. To pave the way for understanding the dynamics of this system, both the typical olive tree as a whole and its typical branch are approached as interacting soft-stiff continuum mechanical systems. The POD analysis reveals that the impact response is a nonlinear vibration with very fast dissipation. The POD modal amplitudes are nonlinear vibrations of continuous, broadband frequency spectrum. Initially they exhibit regular phases of nonlinear slow dissipation-and-amplification followed by irregular, fast dissipation-and-amplification phases. Sequentially applied impacts at the branch soft area results in a complete detachment of the fruit. The POD analysis reveals that this occurs because the response is highly localized in the soft area where the impact is applied and thus it transfers its momentum to the fruits. The work is supplemented with analysis of field measurements of the acceleration dynamics of orchard olive tree branches excited by harvesting devices generating combing clouds of impulsive forces aimed at detaching the olive fruit by momentum transfer.

Commentary by Dr. Valentin Fuster

Biomedical and Biotechnology Engineering: General Biomedical and Biotechnology Applications

2017;():V003T04A049. doi:10.1115/IMECE2017-70086.

This report discusses the design problem of developing an air-based cooling system for an infantry soldier. The background explores the different designs that already exist as well as specific parts and materials that will be essential to the design process. Currently, liquid-based cooling systems are the most explored types of cooling devices. However, there are specific downsides to this type of cooling device. As opposed to an air-based system, water requires more energy to be cooled, and therefore more battery power. The liquid-based system is also relatively bulky and heavy due to battery size and the water that runs through the system. With air-based cooling systems, efficient cooling is possible. An air-based cooling system was tested in a laboratory and field environment. In a humid environment, a desiccant attachment can improve the cooling device’s effectiveness. The cooling design effectively reduces the wearer’s core body temperature through evaporative cooling. The design evaporates a significant amount of sweat from wearer’s back and torso. While the prototype can be improved, evaporative cooling is an effective cooling solution for Soldiers.

Topics: Cooling , Soldiers
Commentary by Dr. Valentin Fuster
2017;():V003T04A050. doi:10.1115/IMECE2017-70193.

In silico study of the relationships between flow conditions, arterial surface shear stress, and pressure was investigated in a patient with pulmonary arterial hypertension (PAH), using multi-detector Computed Tomography Angiography (CTA) images and Computational Fluid Dynamics (CFD). The CTA images were converted into 3D models and transferred to CFD software for simulations, allowing for patient-specific comparisons between in silico results with clinical right heart catheterization pressure data. The simulations were performed using two different methods of outlet boundary conditions: zero traction and lumped parameter model (LPM) methods. Outlet pressures were set to a constant value in zero traction method, which can produce flow characteristics solely based on the segmented distal arteries, while the lumped parameter model used a three-element Windkessel lumped model to represent the distal vasculature by accounting for resistance, compliance, and impedance of the vasculature. Considering existing limitations with both approaches, it was found that the lumped parameter Windkessel outlet boundary condition provides a better correlation with the clinical RHC pressure results than the zero traction constant pressure outlet boundary condition.

Commentary by Dr. Valentin Fuster
2017;():V003T04A051. doi:10.1115/IMECE2017-70285.

Motion capture is a common technology used to measure human motion. One key aspect to collecting an ample amount of accurate data is maximizing the motion capture volume. This maximization is typically gone by a trial and error method. The purpose of this study was to develop a better method to determine the camera placement to maximize the captured volume. Two active marker scanners were methodically placed at various locations around a circle centered on a forceplate. The scanner placements of optimal coverage were defined as the position of the scanners when the area of overlap between the two scanners was maximum and the area of uncovered walkway at a minimum. The optimal placement of the scanners occurred when one scanner was placed at (−1.718, 2.459) meters with respect to the forceplate origin and the other positioned at (0.7691, −2.9) meters. Although these dimensions are specific to the constraints and walkway of our lab, the method can be adapted to any lab size. This setup is crucial to establish so accurate, un-occluded marker data can be collected in future studies.

Topics: Dimensions , Errors
Commentary by Dr. Valentin Fuster
2017;():V003T04A052. doi:10.1115/IMECE2017-70578.

In this paper, a flexible microfluidic-based sensor is investigated for monitoring the bending and tilting of a metal bar for miniature access pectus excavatum repair (MAPER). Built on a polyethylene terephthalate (PET) substrate, the sensor contains a polydimethylsiloxane (PDMS) microstructure embedded with an electrolyte-enabled 5×1 resistive transducer array. One end of the metal bar is fixed and the sensor is attached to different locations of the bar. The other end of the metal bar is connected to a 5-lb weight for controlling the bending of the bar. Manually holding and releasing the weight bends the metal bar, which translates to strain in the PET substrate and consequently causes resistance changes in the transducer array. Upon the same amount of bending, resistance change of the sensor varies with the location of the sensor on the metal bar, due to the bending (or strain) variation along its length. Tilting of the metal bar relative to a rigid object (i.e., sternum) introduces force acting on the microstructure of the sensor, and thus gives rise to resistance changes in the transducer array. As a result, this sensor shows the potential of being used in MAPER to minimize tissue injury in vivo application.

Commentary by Dr. Valentin Fuster
2017;():V003T04A053. doi:10.1115/IMECE2017-70740.

In this paper, we propose analytical and numerical experiments to investigate the feasibility of a wireless photonic sensor for measuring the intraocular pressure (IOP). The sensing element is a polymeric cavity embedded into a thin layer of biocompatible material integrated to a soft contact lens. The sensor concept is based on the morphology dependent resonance (MDR) phenomenon. Changes in the eye pressure perturb the micro-cavity morphology, leading to a shift in the optical modes. The IOP is measured by monitoring the shift of optical resonances. The sensor-light coupling is made through the evanescent field by using an optical prism. Therefore, the sensor can be powered and monitored wirelessly by using frustrated total internal reflection (FTIR) of a polymeric dielectric cavity. Usually, micro-optical cavities exhibit a very high quality factor Q; thus, sensors based on MDR phenomenon exhibit high resolution. Therefore, by recording tiny variations of IOP is possible to gain more knowledge about the start, comportment, and evolution of glaucoma disease.

Commentary by Dr. Valentin Fuster
2017;():V003T04A054. doi:10.1115/IMECE2017-70810.

The aim of this study was to analyze five factors that are responsible for the ablation volume and maximum temperature during the procedure of irreversible electroporation (IRE). The five factors used in this study were the pulse strength (U), the electrode diameter (B), the distance between the electrode and the center (D), the electrode length (L), and the number of electrodes (N). A validated finite element model of IRE was built to collect the data of the ablation volume and maximum temperature generated in a liver tissue. Twenty-five experiments were performed, in which the ablation volume and maximum temperature were taken as response variables. The five factors with ranges were analyzed to investigate their impacts on the ablation volume and maximum temperature, respectively, using analysis of variance (ANOVA). Response surface method (RSM) was used to optimize the five factors for the maximum ablation volume without thermal damage (the maximum temperature ≤ 50 °C). U, and L were found with significant impacts on the ablation volume (P < 0.001, and P = 0.009, respectively) while the same conclusion was not found for B, D and N (P = 0.886, P = 0.075 and P = 0.279, respectively). Furthermore, U, D, and N had the significant impacts on the maximum temperature with P < 0.001, P < 0.001, and P = 0.003, respectively while same conclusion was not found for B and L (P = 0.720 and P = 0.051, respectively). The maximum ablation volume of 2952.9960 mm3 without thermal damage can be obtained by using the following set of factors: U = 2362.2384 V, B = 1.4889 mm, D = 7 mm, L = 4.5659 mm, and N = 3. The study concludes that both B and N have insignificant impacts (P = 0.886, and P = 0.279, respectively) on the ablation volume; U has the most significant impact (P < 0.001) on the ablation volume; electrode configuration and pulse strength in IRE can be optimized for the maximum ablation volume without thermal damage using response surface method.

Commentary by Dr. Valentin Fuster
2017;():V003T04A055. doi:10.1115/IMECE2017-70901.

Lower limb deficiencies and below knee amputations are the most common form of deficiency that may arise from disease or trauma, and returning a patient close to a normal quality-of-life requires prosthetics, which can be quite challenging. Children present even further difficulty to prosthetists and physicians than adults. Although the underlying prosthetic principles for adults are the same for children, additional considerations must be made for practicality, such as downsizing while maintaining its degree of complexity, and frequent appointments to account for the rapid growth of an adolescent. This review article will evaluate the current state-of-the-art in the field of transtibial-amputee prosthetics, review the insurance coverage a typical family would face, and suggest potential improvements to children’s biomimetic prostheses that aid in reducing the frequency of health care provider intervention.

Commentary by Dr. Valentin Fuster
2017;():V003T04A056. doi:10.1115/IMECE2017-71027.

This work focuses on the research related to enabling individuals with speech impairment to use speech-to-text software to recognize and dictate their speech. Automatic Speech Recognition (ASR) tends to be a challenging problem for researchers because of the wide range of speech variability. Some of the variabilities include different accents, pronunciations, speeds, volumes, etc. It is very difficult to train an end-to-end speech recognition model on data with speech impediment due to the lack of large enough datasets, and the difficulty of generalizing a speech disorder pattern on all users with speech impediments. This work highlights the different techniques used in deep learning to achieve ASR and how it can be modified to recognize and dictate speech from individuals with speech impediments.

Commentary by Dr. Valentin Fuster
2017;():V003T04A057. doi:10.1115/IMECE2017-71063.

Most stroke victims undergo muscular disorders leading to weakening of muscles and inability to perform normal hand activities. An exoskeleton device is therefore needed to aid in performing basic hand movements to improve the quality of life of the victims. Most of the available devices in literature are controlled using electrical motors with a rigid structure and complex design. This paper discusses the design and performance of an inexpensive and lightweight 3D printed orthotic device featuring a wrist mechanism. The design is simple and utilizes twisted and coiled polymeric (TCP) muscles which are easy to fabricate using a silver coated nylon 6, 6 threads. The device facilitates the movement of all the three joints of the human finger namely, distal interphalangeal joint (DIP), proximal interphalangeal joint (PIP) and the metacarpophalangeal joint (MCP). Experiments were performed using a custom-made hand which was 3D printed and casted using silicone rubber with a shore hardness 10 (Ecoflex® 010) to resemble an actual human hand. The results showed the range of motion achieved with the device, grasping and pinching of various objects with assistive efforts using TCP muscles and demonstrated the capability of the device to achieve flexion and extension of the fingers mimicking the human finger movements.

Topics: Muscle , Orthotics
Commentary by Dr. Valentin Fuster
2017;():V003T04A058. doi:10.1115/IMECE2017-71066.

In orthopedics, the current internal fixations often use screws or intramedullary rods that obstruct bone material. In this paper, an internal implant was modelled as a hollow cylindrical sector made of a functionally graded material (FGM), which will hold bone in place with less obstruction of bone surface. Functionally graded implant was considered as an inhomogeneous composite structure, with continuously compositional variation from a ceramic at the outer diameter to a metal at the inner diameter. The buckling behavior of the implant was numerically analyzed using a finite element analysis software (ANSYS), and the structural stability of the implant was assessed. The buckling critical loads were calculated for different fixation lengths, cross sectional areas, and different sector angles. These critical loads were then compared with the critical loads of an FGM hollow cylinder with the same cross sectional area. Results showed that the critical load of the hollow cylindrical sector was ∼ 63%, ∼ 70%, and ∼ 73% of the hollow cylinder for different fixation lengths, cross sectional areas, and sector angles, respectively. Further investigations are warranted to study the relation between the composition profile and the implant stability, which can lead to batter internal fixation solutions.

Commentary by Dr. Valentin Fuster
2017;():V003T04A059. doi:10.1115/IMECE2017-71299.

In this paper, potentials of accumulative roll bonding (ARB) severe plastic deformation (SPD) method to process effective nickel titanium alloys for biomedical application is presented. Effective material properties of biomedical NiTi alloys, including ultra-fine grain microstructure, functional, mechanical, wear and corrosion resistance were highlighted and discussed. Performance and challenges of other SPD methods in the literature have been reviewed and compared to that of ARB. Existing challenges, advantages and recommendation of using ARB to process NiTi alloys with desired properties for biomedical applications are given.

Commentary by Dr. Valentin Fuster
2017;():V003T04A060. doi:10.1115/IMECE2017-71693.

There is an increased risk of melanoma in adulthood when a child (pre-puberty) has been exposed to high levels of ultraviolet radiation (UVR). It has also been hypothesized that the childhood body air (vellus hair) plays a role in the increased incidence of melanoma later in life. This is attributed to the fact that the vellus hair has properties and physiology which encourage the transmission of harmful energy into the follicle of the hair and ultimately cause damage to the stem cells in residence there. Later in life these damaged stem cells become involved in the generation of melanomas in the epidermis.

It has been debated whether the UVR or the heat generated by it is the main contributor to melanoma occurrence. This research is the first step in investigating this phenomenon by focusing on the contribution of changes in thermal characteristics on the incidence of melanoma. To test the hypothesis that child hair can transmit energy more easily than adult hair the transient electro-thermal technique is used to determine the thermal diffusivity of the hair. This involved subjecting platinum coated hair samples to a current pulse and measuring the subsequent voltage response in the sample. Results show that the child hair has a thermal diffusivity around two times higher than adult hair, thus supporting the hypothesis. Further research will be needed, in particular, quantifying the optical transmission characteristics of child hair compared to adult hair.

Commentary by Dr. Valentin Fuster
2017;():V003T04A061. doi:10.1115/IMECE2017-71911.

Detecting humans and objects during walking has been a very difficult problem for people with visual impairment. To safely avoid collision with any object or human and to navigate from one location to another, it is significant to know how far and what kind of obstacle the user is facing. In recent years, many researches have shown that providing different vibration stimulation can be very useful to convey important information to the user. In this paper, we present our stereovision system with high definition camera to detect and identify humans and obstacles in real time and compare it with a modified version of existing wearable haptic belt that uses high-performance Ultrasonic sensors. The aim of this paper is to present the practicability of stereovision system over cane and assistive technology such as vibrotactile belt.

The study is based on two assistive technologies. The first one consists of the vibrotactile belt connected to ultrasonic sensors and an accelerometer which returns user movement & speed information to the microcontroller. The microcontroller initiates expressive vibrotactile stimulation based on sensor data. Data gathered from this technology will be used as the baseline data for comparison with our stereovision system. Second, we present a novel approach to detect the type of obstacle using object recognition algorithm and the best approach to avoid it using the stereovision feedback. Data gathered from this technology with be comparted against the baseline data from the vibrotactile belt. In addition, we present the results of the comparative study which shows that stereovision system has plethora of advantages over vibrotactile belt.

Commentary by Dr. Valentin Fuster
2017;():V003T04A062. doi:10.1115/IMECE2017-72115.

In lower limb amputees, the comfort and fit of the prosthesis determine whether the user wears or not the prosthesis, fact on which a successful rehabilitation depends. The prosthetic fit is highly related with the relative motion between the socket and the residual limb (i.e., displacement). Displacement has been measured in static and dynamic position and between several surfaces such as skin-socket, liner-socket, bone-socket using various instruments. Marker-based optical tracking system is one of the most recent instruments used for measuring displacement between the socket and the residual limb that solves many of the constraints faced by other measurement instruments. Two options have been reported on the literature for using this instrument: transparent test socket with 2D marker and definite socket with cavities and 3D marker, both facing different limitations. The objective of this study is to evaluate these two options using Marker-based optical tracking system in order to give recommendations and contribute to the use of this method on future research.

Two sockets were used for the study: a transparent socket and a definite socket with and without cavities. Six trials were performed using both sockets with three types of markers located inside the socket: 2D circular, 3D hemisphere and 3D sphere. VICON motion capture system was used to detect the visibility of the markers at knee flexion angles (0° to 30°).

The results showed that all markers were visible from 15° to 30° knee flexion in all trials. The 2D marker presented difficulty of detection on knee angles from 0° to 10°, especially on the final socket without cavities. 3D hemisphere marker was seen almost all along the knee angles. 3D-sphere marker was visible in all positions, but the relatively large size of these markers may not be adequate to measure displacement.

Using the definite socket with the 2D circular and 3D hemisphere markers could be a good option to measure displacement between the residual limb and socket. Using this socket will be closer to reality than doing it on the transparent one. Additionally, the size of the 3D-hemisphere is relatively small, it may not drastically change the behavior between surfaces and as it is a 3D marker it can be better seen by the cameras.

Further tests should be done with patients walking all along the path in order to assess if the markers visibility is the same on static and dynamic trials.

Topics: Displacement
Commentary by Dr. Valentin Fuster
2017;():V003T04A063. doi:10.1115/IMECE2017-72360.

To reduce the development time-line of stent grafts, this project focuses on software tools that will automate and simplify execution of Computational Fluid Design (CFD) simulations on a High Performance Computing (HPC) platform, as well as postprocessing CFD results. This program is a Java-based Graphical User Interface (GUI), which enables the end user to automatically calculate and visualize the CFD results. Its portability and design allow for ease of use across multiple workstations. A visual element is included to reconstruct simulation images into other video formats. In addition, Scripting languages, such as Perl and R, were used to indicate the appropriate allocation of resources within an HPC environment. Each simulation would receive the optimal assets for each test conducted, and potentially need less time to perform. The projected outcome is to allow the user to compute data and quickly produce results for predicting the flow mechanics and near-wall hemodynamics of endovascular stent grafts in the design process.

Commentary by Dr. Valentin Fuster
2017;():V003T04A064. doi:10.1115/IMECE2017-72606.

In this present study, the nano finishing of stainless steel 316L (SS316L) was obtained by means of magneto rheological abrasive flow finishing (MRAFF) process by varying the amount of current to the electromagnet. The MRAFF process is an advanced machining process in which the metal removal process is effectively controlled by means of the rheological property of the magneto rheological abrasive (MRA) fluid. After the finishing process, the surface roughness profiles and parameter were obtained with the help of Talysurf coherence correlation interferometer (CCI). Stainless steel 316L sample surfaces obtained by means of MRAFF process with different nano roughness values are utilized to study its biocompatibility by an in vitro study to examine the cell viability, proliferation of a fibroblast cell line (NIH-3T3) by means of MTT assay. The optical density (OD) values were utilized to determine the amount of viable cells. The cell proliferations studies were conducted and observed for 1, 3 and 7 days of incubation period with respect to the absorbance value of the samples. The protein adsorption studies are also made by using bicinchoninic acid assay (BCA) kit. The characters of biocompatibility are correlated with the nano scale surface roughness parameters of the SS316L samples.

Commentary by Dr. Valentin Fuster

Biomedical and Biotechnology Engineering: Musculoskeletal and Sports Biomechanics

2017;():V003T04A065. doi:10.1115/IMECE2017-70730.

A realization of how specific exercises relate to balance performance is important for a wide demographic of individuals. Maintaining active and healthy living is particularly important for balance-impaired individuals (e.g., otherwise healthy individuals recovering from injury, fall-prone elderly, and stroke survivors) whom are interested in improving their balance for function in daily life. However, balance performance is also important for persons that are unimpaired (e.g., athletes). How balance performance may be improved as a result of, and in relation to, various athletic activities and exercises is a common question. Further, how certain activities can be used to prevent injury is an ultimate goal. Our objective was to compare standing balance in 3 unimpaired groups (i.e., female track & female tennis collegiate athletes and female non-athletes).

To assess static balance, participants performed stance variations increasing in difficulty-level, utilizing a wide or tandem stance (increasing or decreasing support base) and eyes-open or eyes-closed (limiting or providing visual cues), while standing on a forceplate walkway. Through the recorded ground reaction forceplate-based, center-of-pressure (COP) position time series, we extracted velocity and displacement parameters that aided in identifying differences between the above groups.

Our general findings were that anterior-posterior (AP, or front-to-back) COP displacement and velocity measures for female track athletes were unchanged relative to the (baseline) female non-athletes. However, mediolateral (ML, or side-to-side) measures, which have previously been shown to be associated with fall-risk, showed observable differences in displacement and velocity parameters, particularly for the female track athletes. Specifically, the female track athletes were better able to control their ML COP velocity in eyes-closed, wide, and eyes-open tandem conditions compared to non-athletes. However, tennis athletes had difficulty balancing in situations where eyes were closed (vision eliminated) and feet were tandem (base-of-support decreased) which was made apparent by the increases in all AP and ML COP-derived parameters. We interpreted this finding as the female tennis athletes were trained to rely heavily on visual cues (e.g., hand-eye or eye-body coordination), and also their balance may be more focused on maintaining their center-of-mass stability and body orientation, as opposed to COP per se.

Our study lends new insights as to how various types of athletic activities, and reliance on vision in athletes, impacts balance performance in un-impaired females.

Commentary by Dr. Valentin Fuster
2017;():V003T04A066. doi:10.1115/IMECE2017-70754.

Design of an optimally safe football helmet system requires an awareness and evaluation of the factors and variables that can adversely affect the impact attenuating performance of energy absorbing (EA) pad materials needed to minimize transmission of linear and rotational forces applied to the head so that risk of head injury is reduced. For instance, player head sweating can induce high temperatures and moisture within a helmet system (i.e. a Hot-Wet condition) which can result in degradation of helmet EA capacity and cause increased measures of head injury risk levels, which are often used for comparative evaluation of helmet designs.

In this study, a “multivariable” experimental method was utilized to demonstrate an efficient means for assessment and comparison of currently representative adult and youth football helmet system designs when subjected to a range of variables that included, among other factors: temperature-moisture effects; impact energy; and, repeat impacts. Both quasi-static (QS) compression testing of commonly used EA materials and dynamic impact testing of full helmet systems were conducted and the results are presented in Tables and graphic form.

The EA pad types that were QS tested included: Thermoplastic-Polyurethane (TPU) “waffle shaped” EA pad configurations; load rate sensitive “Gel” foam padding; and, dual and single density elastomeric foam padding. Dynamic helmet repeat impact tests were conducted by using a pendulum impact test device where various helmet designs were mounted to a Hybrid-III head and neck system and impacted against a non-yielding surface at energy levels of 108J and 130J after being subjected to ambient and Hot-Wet conditions.

The QS tests showed that a short Hot-Wet soak time of only a few hours’ noticeably diminished EA levels. Also, the dynamic full helmet system testing demonstrated that the “Hot-Wet” condition tended to degrade helmet impact attenuation performance such that, depending on the size and type of EA material provided in the crush zone, head injury risk measures tended to increase. Finally, examples of the use and benefits of a “multivariable” experimental method for helmet injury risk assessment, not reported on previously, are provided.

Topics: Temperature , Wounds , Risk
Commentary by Dr. Valentin Fuster
2017;():V003T04A067. doi:10.1115/IMECE2017-70905.

Traumatic brain injury (TBI) is an intracranial injury caused by impacts or angular accelerations of the head such as a violent blow, a bump, a projectile, or even a blast. TBI is a major problem that accounts for over 1.4 million emergency room visits in US. Thus, it is important to understand and predict the occurrence of TBI. Previous studies have shown that the interaction between the subarachnoid space (SAS) trabeculae and the cerebrospinal fluid (CSF) plays an important role in damping the effect of impacts and reducing the brain injuries. However, the influence of sulci parameters and sulci trabeculae in impact induced TBI is still unexplored. A few studies have shown that inclusion of sulci in brain models alters the brain injuries conclusions, even though those models do not take into account the trabecular tissue present in the sulci.

In this study, to obtain a perspective of the morphology and architecture of the sulci trabeculae at the frontal lobe of the brain, Human cadaver brain of an 87 year old male was used. For the first experiment, several sulci from the frontal lobe were sectioned and measured to find the average sulci depth, using the image processing software called ‘ImageJ’. This experiment was followed by the Scanning Electron Microscopy (SEM) study on the samples prepared from the frontal lobe. Indeed, numerous images were taken at various magnifications to find different trabecular morphology and architecture in the sulci.

The results from the experimental studies were used in our numerical analyses. To do so, the validated global 3D FE model of the human head and neck, created at The City College of New York, were impacted by a rigid barrier on the forehead. The pressure time history, beneath the skull, was calculated during and after the impact. Moreover, a local 3D FE model has been created, having the meninges and the brain with sulci, including the trabeculae and the CSF. The depth of the sulci and the architecture of the trabeculae have been inspired by the imaging and SEM studies. Indeed, the top surface of the local model was subjected to the pressure loading condition obtained from the global model. The results of the finite element simulations reveal that the interaction between the trabeculae and the CSF inside the sulci, would affect and reduce the movement and displacement of gyri and sulci’s walls when the forehead of the head is impacted by an elastic barrier.

Commentary by Dr. Valentin Fuster
2017;():V003T04A068. doi:10.1115/IMECE2017-70950.

Individuals with Down syndrome (DS) use a different motor gait strategy than healthy people. This study aims at analyzing plane walking differences between two groups of normally developed (ND) subjects and subjects with DS in terms of the generated mechanical power and work in the joints of the lower limb. Thirty-nine adults including two groups of 21 subjects with DS (age: 21.6 ± 7 years (mean ± SD)) and 18 ND subjects (age: 25.1 ± 2.4 years) participated in this study. Gait data and ground reaction forces were acquired using a quantitative movement analysis system composed of an optoelectronic motion analyzer (Elite2002, BTS) with eight infrared cameras, and two force platforms mounted in the middle of walkway. Mechanical power and work exchanges were computed during the stance phase by dedicated software, and then compared between the two groups (significance level: p-value = 0.05). Results showed that the mechanical power at the ankle joint was significantly larger in ND subjects compared to subjects with DS (0.084 ± 0.015 vs 0.027 ± 0.010 W/kg). The mechanical work of the ankle joint and the knee joint was significantly lower in ND compared to DS (0.015 ± 0.013 vs 0.028 ± 0.008 kJ/kg.m, and 0.066 ± 0.031 vs 0.109 ± 0.023 kJ/kg.m, respectively). For both groups, the mechanical work done by knee was less than that performed at the ankle and hip level, which might indicate that the knee muscles mainly absorb the energy, rather than generate it. Our results suggest that the subjects with DS walk with a different motor strategy than normal subjects in terms of mechanical power and work in the joints of the lower extremity. Further investigations are warranted to study the relation between these parameters and gait strategy in subjects with DS, which can lead to better rehabilitative strategies.

Commentary by Dr. Valentin Fuster
2017;():V003T04A069. doi:10.1115/IMECE2017-70957.

A tissue engineered intervertebral disc (IVD) anchor the circumference and top/bottom sides of nucleus pulposus (NP) implants with annulus fibrosus and endplates. The proper anchorage of a NP implant to annulus fibrosus and endplates is possible by enclosing the NP by electrospun fiber mesh that mimics the surrounding structures. The biomechanical performance of silicone based NP can be improved if electrospun fiber mesh can secure all sides of silicone NP. However, it is unknown whether silicone surrounded by an electrospun nanofiber matrix can better restore the biomechanical functions of the disc in compare to intact, IVD made with silicone only, and, IVD made with silicone anchored all sides by nanofiber. This study compared the compressive and viscoelastic properties of a silicone and electrospun nanofiber anchored silicone discs (ENAS) under compression and shear with the same properties of human NP. This study developed a nonlinear finite element model (FEM) for the intact and ENAS implanted human lumbar vertebra segments. The compression test results show that ENAS disc compressive modulus (87.47 ± 7.56 kPa, n = 3) is significantly higher in compare to silicone gel (38.75 ± 2.15 kPa, n = 3) and the value is within the range of the compressive modulus of human NP (64.9 ± 44.1 kPa). The rheological test results show that ENAS disc compressive modulus (16 ∼ 40 kPa) is significantly higher in compare to silicone gel (0.10 ∼ 0.16 kPa) and the value is within the range of the compressive modulus of human NP (7 ∼ 20 kPa). These results confirm the suitability of ENAS disc over silicone as NP implant. A finite element model has been developed based on the ENAS properties. The FEA results showed that ENAS can restore better the biomechanical motions of a lumbar vertebra segments in compare to silicone NP.

Commentary by Dr. Valentin Fuster
2017;():V003T04A070. doi:10.1115/IMECE2017-71743.

Injuries to the growth plate of the humerus can occur in children during motor vehicle accidents. These injuries can then lead to growth abnormalities and musculoskeletal issues as the child develops. This research was conducted to analyze and develop a solution to musculoskeletal strain caused by uneven weight distribution inherent in a case of upper limb length discrepancy. The issue is an imbalance due to the growth of a shorter humerus in the individual’s right upper limb (RUL) as the result of a prior surgery on the individual’s right humeral growth plate. This shortened RUL weighs less than the left upper limb (LUL). This effectively lowers the mass moment of inertia of the RUL, thus lowering the balancing moment on the torso. When the individual sprints during physical exercise, there is an imbalance in rotational momentum that is created between the two arms. This imbalance in momentum requires that the opposing lower limb of the shorter RUL, the individual’s left lower limb, drives harder, leading to eventual failure in the hip flexor. In order to solve this biomechanical problem, kinematic equations were developed to model the motion of a sprinter. These equations model the motions of the hands, torso, and legs. In particular, the model defines the influence of the imbalance of the upper limbs’ motion on the lower limbs’ motion, which results in a forward rotation of the torso while sprinting. To balance the rotational momentum of the upper limbs, a counter-acting weight was attached to the wrist of the RUL, minimizing the effects on the lower limb musculature. Hence, the left lower limb would not have to overcompensate for the shorter RUL’s lack of momentum. The equations were then reconfigured to account for the counterweight, and the effect was observed and analyzed. A simulation predicted an angle of tilt of up to 5.7° in the sagittal plane from the vertical. The force required to rotate the body to the normal position was 18N. This force was determined to cause a twist of 10.0° in the transverse plane from the frontal plane. While this study was conducted on an individual with a shortened right upper limb secondary to a surgical procedure, study results can readily be generalized to individuals with shortening of either upper limb secondary to other traumatic events, such as motor vehicle accidents.

Topics: Weight (Mass) , Damage
Commentary by Dr. Valentin Fuster
2017;():V003T04A071. doi:10.1115/IMECE2017-71964.

After the introduction of Title IX, a federal law prohibiting discrimination based on gender, the number of women involved in high school and collegiate level sports has significantly increased. Increasing the number of female athletes has a direct correlation with the amount of injuries experienced by these women. One of the most common injuries to female athletes is a sprain or a tear in the Anterior Cruciate Ligament (ACL) located in the knee. The ACL is one of the main components in the stabilization of the knee. A strain or tear to the ACL causes everyday life to be impacted significantly. ACL injuries are not only debilitating, but are expensive and have long term effects including arthritis.

Women have an increased chance of injuring their ACL for three main reasons: anatomical, hormonal, and biomedical. Statistically, women have wider hips and weaker inner thigh muscles than men. Additionally, women experience changes in hormonal imbalance which contributes to their cyclic changes in ligament strength. Lastly, knees can experience a bio-medical condition known as valgus. The presence of extreme valgus typically indicates a high risk of future ACL injury due to the increased stress on the ligament. Due to these factors, this study involved designing three prophylactic braces to be used as part of a training program to help strengthen the muscles surrounding the knee.

Topics: Knee
Commentary by Dr. Valentin Fuster

Biomedical and Biotechnology Engineering: Symposium on Biomedical Devices

2017;():V003T04A072. doi:10.1115/IMECE2017-70227.

The development of wearable equipment is posing new challenges to traditional sensors. Currently, it is important to reduce sensor size and improve sensor sensitivity so that data could be collected without interfering users’ common behavior. This article illustrates a new method for real time plantar force measurement. By paralleling planar inductive sensing coils with capacitors to form a LC resonant circuit and monitoring the change of resonant frequency or inductance, the occurrence of heel-strike and toe-off could be detected, because the change of the clearances between foot and insole triggers the simultaneous alternation of coil inductance. We conducted experiments on two different types of coils and compared them with force sensitive resistor (FSR). It is found that the Pearson correlation coefficients of these two coils’ inductance with the output voltage of FSR conversion circuit are −0.9780 and −0.7788, respectively. With smaller size and less expensive than traditional resistive sensors, this new sensing system could precisely reflect different gaits of walkers when tested in realistic situations.

Commentary by Dr. Valentin Fuster
2017;():V003T04A073. doi:10.1115/IMECE2017-70535.

Many industries, such as the biotechnology, food, and beauty industries, require noninvasive methods for quantifying material stiffness. One such method is the indentation test, which is particularly useful in evaluating the mechanical characteristics of soft materials. However, it is difficult to identify mechanical characteristics of the distinct layers of layered materials such as human skin due to their physical integration with one another. There is particular interest in evaluating the softness of the stratum corneum (the outermost layer of skin) in the cosmetics industry, where the effect of cosmetics should be restricted to this outermost layer. The purpose of this study was to develop a method to determine the elasticities and thicknesses of discrete layers in a layered material by using an indentation test. This paper discusses the results of this indentation test derived via the finite element method (FEM). Here, the finite element (FE) model is constructed by a layered structure of flat surfaces with given Young’s moduli. The FEM results suggest the existence of a law among the elasticities and layer thicknesses of a layered material.

Commentary by Dr. Valentin Fuster
2017;():V003T04A074. doi:10.1115/IMECE2017-70546.

The incidence rate of breast cancer for women in Japan is increasing each year. The three main methods of screening for breast cancer are finger palpation, mammography and breast ultrasound. These methods must be improved to decrease the incidence rate. This involves the development of personal, easy-to-use devices that facilitate cancer diagnosis. This study evaluates an indentation device developed to imitate traditional finger palpation and identify the position of the tumor inside the breast. The identification procedure is based on the extended Hertzian contact theory, which was developed to evaluate the elasticity of a thin specimen. In this extended theory, the thickness effect of the specimen is represented by a thickness parameter, and the position can be identified by the analysis of the effect. The procedure is verified by using FEM for ideal inclusion model in soft object, and the accurateness of the identification is discussed for the development. In the verification, some difference in the identified position between the condition and the result of FEM is observed with the difference of the identified elasticity of the object. It was reported that the approximation of accurate elasticity could affect the accuracy of position identification. Subsequently, the identification accuracy of Young’s modulus and thickness of specimen is discussed considering the problem of inclusion. Using the proposed approach, high accuracy can be observed in the range of 5 mm to 15 mm; however, a greater level of accuracy in identification remains to be achieved in other ranges. Thus, it is concluded that identification is possible using the extended Hertzian contact theory; however, for accurate identification of cancer position in a breast, the theory requires further modification.

Commentary by Dr. Valentin Fuster
2017;():V003T04A075. doi:10.1115/IMECE2017-70724.

For the several millions of vestibular loss sufferers nationwide, daily-living is severely affected in that common everyday tasks, such as getting out of bed at night, maintaining balance on a moving bus, or walking on an uneven surface, may cause loss of stability leading to falls and injury. Aside from loss of balance, blurred vision and vertigo (perceived spinning sensation) are also extremely debilitating in vestibular impaired individuals. For the investigation of implants and prostheses that are being developed towards implementation in humans, non-human primates are a key component.

The purpose of our study was to implement a distinctive balance platform-system to investigate postural responses for moderate to severe vestibular loss and invasive vestibular prosthesis-assisted non-human primates (rhesus monkeys) for test balance conditions of various task-difficulty levels. Although the need for vestibular rehabilitative solutions is apparent, postural responses for a broad range of peripheral vestibular function, and for various stationary and moving support conditions, have not been systematically investigated.

The measurement system used in this research was unique in that it allowed us to conduct animal experiments, not investigated previously; such experiments are necessary towards the development on an invasive vestibular prosthesis to be used in humans suffering from vestibular loss. Our platform-system facilitated the study of rhesus monkey posture for stationary support surface conditions (i.e., quiet stance and head turns; more versus fewer footplate cues and large versus small base-of-support) and for dynamic support surface conditions (i.e., pseudorandom roll-tilts of the support surface). Further, the platform-system was used to systematically study postural responses that will serve as baseline measures for future vestibular-focused human and non-human primate posture studies.

Topics: Prostheses
Commentary by Dr. Valentin Fuster
2017;():V003T04A076. doi:10.1115/IMECE2017-71568.

The human ankle is crucial to mobility as it counteracts the forces and moments created during walking. Around 85% of the 1.7 million people in the United States living with limb loss are transtibial (below knee) and transfemoral (above knee) amputees who are missing their ankle and require a prosthetic. This paper presents the Compliant and Articulating Prosthetic Ankle (CAPA) foot, a solution that uses torsional springs to store and release energy at three different locations on the mechanism, assisting in forward motion. The CAPA foot utilizes 3D printing and allows for the full ankle range of motion in the sagittal plane. Testing was performed with the CAPA foot on the Computer Assisted Rehabilitation Environment on an able-bodied person wearing a prosthetic simulator. Compared to the conventional non-articulating Solid Ankle Cushioned Heel foot, the CAPA foot is shown to better mimic the ground reaction forces and ankle angles of a healthy gait.

Commentary by Dr. Valentin Fuster
2017;():V003T04A077. doi:10.1115/IMECE2017-71621.

Facial paralysis affects hundreds of thousands of people each year; a common result of infection, trauma, stroke, and Bell’s palsy, among others. Achieving facial prosthetics that are lightweight, comfortable, aesthetically pleasing, energy efficient, and that allow human-like facial motion is a challenge. This study focuses on examining the feasibility of the use of a shape memory alloy as a means of low-power artificial muscles. Nitinol is a shape memory alloy (SMA) that can recover up to four percent of its original length when exposed to either a large enough change in temperature which can be controlled via electrical current or a stress. In this work, human eyelid muscles are replicated using Nitinol embedded in silicon. Silicone is used due to its elasticity, texture, flexibility, compatibility and ease of manufacturing. A mold is created based on human facial geometry around the orbital using a 3D printer. Based on average human eyelid dimensions, as well as the contraction properties of the Nitinol wire, an elliptical equation is used determine the length of wire required to completely close the eyelid from an open position. Temperature change of the system is controlled by modulating current through the resistive Nitinol wire. The contraction and expansion times of the eyelids are measured. The circuit is then optimized so that response times mimicked that of the human eyelid. Finally, based on the amount of times the average human blinks, the average daily power consumption is calculated. Future directions including miniaturization of the control system, bonding between SMA wires and silicone, and energy management are discussed.

Commentary by Dr. Valentin Fuster
2017;():V003T04A078. doi:10.1115/IMECE2017-71883.

This paper presents the design and analysis of a portable forearm exoskeleton designed for rehabilitation and assistive purposes (FE.RAP). The design uses a direct-drive mechanism to actuate three degrees of freedom (DOFs) of the wrist, including: (1) wrist flexion and extension, (2) wrist radial and ulnar deviation, and (3) forearm supination and pronation. In recent decades, automated at-home recovery therapies have emerged as popular alternatives to hospital-based rehabilitation. Often in the case of lower arm rehabilitation, however, existing exoskeletons are not practical to use as home rehabilitation devices due to being non-transportable, bulky in size, and heavy in weight. In addition, compact sized exoskeletons often lack sufficient DOFs to mirror the natural movements of the hand. This paper proposes a design that addresses the drawbacks of current exoskeletons. The FE.RAP is designed to be portable and lightweight, while maintaining sufficient DOFs to help patients recover the range of motion needed by the wrist and forearm to support activities of daily living (ADL). Along with the design, the paper presents an analysis used to optimize the workspace for each DOF of the system. A kinematic analysis is performed to validate and compare the workspace of the system, as well as the coupling relationship between the DOFs, to that of the human hand and wrist. Finally, the torque required to support most ADLs is determined using static and dynamic analyses.

Commentary by Dr. Valentin Fuster
2017;():V003T04A079. doi:10.1115/IMECE2017-71961.

This paper investigates how crutch tip designs affect the user’s gait. Five Kinetic Crutch Tips (KCT), each with different durometers (i.e., stiffnesses) along with one carbon fiber reinforced nylon 3D printed KCT and one Standard Rubber Tip were tested. The first experiment examined eight healthy subjects to determine the assistive horizontal force generated and crutch angle range. The second experiment eliminates the human factor and uses a weighted crutch in free fall to investigate transitional angles between forward and backward motions. It was found that the KCT had a larger transitional angle than the Standard Rubber Tip. This increases the assistive forward forces of the crutch due to the surface kinetic shape of KCTs; however, the total angle of different crutch tips remains the same when used by the subjects. The assistive forces were present for the longest amount of time for the highest durometer KCT.

Commentary by Dr. Valentin Fuster
2017;():V003T04A080. doi:10.1115/IMECE2017-72219.

Modern design and manufacturing engineering technologies have greatly improved the way in which modern craniofacial implants are designed and fabricated. However, few efforts have been made in order to optimize their design. While the weight of polymer-based implants (e.g. PMMA implants) may not affect the patient’s comfort, the higher weight of metal-based implants (e.g. titanium implants), could greatly affect the patient’s comfort, causing in some cases nuisances and imbalance problems. Thus, the optimization of the implant becomes relevant in order to guarantee its structural stiffness but with a reduced weight.

In this paper, the design and structural optimization of customized craniofacial implants based on the use of modern engineering technologies is presented. The aim is to introduce an engineering methodology for the design and optimization of customized craniofacial implants. The methodology starts from the patient’s medical images, obtained from a computerized tomography (CT), which are processed to reconstruct the digital 3D model. Next, the geometrical design of the implant is carried out in a computer aided design (CAD) system using the patient’s 3D model. Then, the structural analysis of the implant is performed using the Finite Element Method (FEM) and considering a quasi-static load. The topology optimization of the implant is made using the Solid Isotropic Material Penalization (SIMP) method. Finally, the optimized customized implant is fabricated in an additive manufacturing (AM) system. A case study of a craniofacial implant is presented and the results reveal that the proposed methodology is an effective approach to design and optimize craniofacial implants.

Commentary by Dr. Valentin Fuster

Biomedical and Biotechnology Engineering: Symposium on MechanoBiology

2017;():V003T04A081. doi:10.1115/IMECE2017-70781.

The dynamic behavior of a woven Dacron graft, currently used in thoracic aortic reconstructions in the case of aneurysm or dissection, has been experimentally investigated for the first time.

Dacron grafts are widely used in cardiovascular surgery to replace segments of diseased large blood vessels; however, scarce data are available about their durability. The dynamic modeling of such prostheses may fill this gap and may provide guidelines for the study of human aortic segments as well. Dynamic phenomena such as vibrations are being included among the most likely causes of important aortic pathologies, such as dissections and consequent ruptures. The compatibility of the dynamic behavior of Dacron grafts and human arteries seems a characteristic worthy of experimental investigation as well. For this reason, a cylindrical Dacron graft has been subjected to fixed boundary conditions and to a physiological value of static axial pre-stretch. A constant internal pressure, equal to the average value of the physiologic blood pressure, was exerted by a liquid mixture of suitable viscosity and density. A three-dimensional quasi-linear viscoelastic model was fitted onto the Dacron fabric by means of dedicated traction and relaxation tests. Forced linear and large-amplitude vibrations were imposed and measured. An identification tool recently developed by this research group is being used to study the change of the equivalent modal damping ratio with vibration amplitude during nonlinear vibrations. Furthermore, an ongoing study is revealing a dependence of dissipation on frequency that is coherent to the most common model for biological materials adopted by the medical community.

Commentary by Dr. Valentin Fuster
2017;():V003T04A082. doi:10.1115/IMECE2017-72451.

Static and dynamic analysis of a circular cylindrical shell that models a segment of human aorta is carried out in this study. The shell is assumed to have three hyperelastic layers with residual stresses. Material data and residual stresses are taken from the literature from human toracic descending aorta. The material model is the Holzapfel-Gasser-Ogden (HGO). Dissipation is modelled by viscoelasticity. The dynamic load is given by a pulsating pressure reproducing the physiological pressure during the heart beating. The inertial effect of the contained blood fluid is taken into account. Under the static pressure, the initially soft shell becomes much stiffer, which is a common feature of soft biological tissues. The nonlinear dynamics is not particularly complicated, due to the significant damping.

Commentary by Dr. Valentin Fuster

Biomedical and Biotechnology Engineering: Tissue and Biomaterials: Modelling, Synthesis, Fabrication and Characterization

2017;():V003T04A083. doi:10.1115/IMECE2017-70005.

The 64 codons of the genetic code determine which amino acids are linked into a sequence to produce protein synthesis. Some of the codons specify the same amino acid by using only the first two letters of their codon triplet to do so, thus rendering their 3rd base irrelevant. Crick called this the wobble hypothesis, and a more complete understanding of the reading process could someday lead to a drug that can repair a misreading or to the creation of synthetic ribosomes capable of healthy protein synthesis. A step towards this goal is to apply mathematical logic to the 64 codons so that experimental results can be reproduced and to answer the specific question, how can the nucleotides in the three base positions be interpreted using mathematical code? Here it is shown that a mathematical formula derived from fluid mechanics predicts which codons in the dictionary will encode using their 3rd bases and which ones will not.

Commentary by Dr. Valentin Fuster
2017;():V003T04A084. doi:10.1115/IMECE2017-70376.

A 3D finite element model to predict the stress state and tear propagation on the human aorta is presented. The human aorta is modeled as a three-layered hyperelastic cylindrical shell with a radial tear in the intima layer and circumferential tear in the media layer. The ultimate strength and fracture energy required for the onset of crack propagation is obtained from the literature and used as an input to the simulations. The effect of depth and length of the tear on the critical pressure show that the critical pressure decreases when tear length and depth increase. The variation of von Mises stress on the aortic layers due to crack propagation is investigated. This study will provide additional insight into the mechanics of aortic dissection (AD) with the possibility of being used in designing new clinical protocols.

Commentary by Dr. Valentin Fuster
2017;():V003T04A085. doi:10.1115/IMECE2017-70601.

This paper reports on a numerical study on how the elasticity of soft tissue measured by a Compression-Relaxation (C-R) testing method via a two-dimensional (2D) distributed-deflection sensor varies with the tissue parameters (i.e., elasticity, thickness and in-plane dimension). The 2D sensor entails a polydimethylsiloxane (PDMS) micro structure embedded with a 3×3 sensing-plate/transducer array deposited on a Pyrex substrate. By moving the 2D sensor against a soft tissue region with a pre-defined compression pattern, the average deflection-depth slope of the deflections of the sensing-plate array versus the compression depth of the testing tissue is measured, and is translated to the measured tissue elasticity via a 1D theoretical model. Since the measured tissue elasticity arises from the tissue-sensor interaction, a numerical model, which includes the 2D sensor and a soft tissue underneath, is created in COMSOL to investigate the sensitivity of the measured tissue elasticity to tissue parameters including tissue thickness, in-plane dimension and elasticity. The numerical results reveal that the theoretical model causes a 20% overestimate on the inherent tissue elasticity in the range of 25kPa∼200kPa. The measured tissue elasticity does not vary with tissue thickness when tissue thickness is above 6mm. However, a relatively thin tissue leads to higher measured tissue elasticity. As long as the tissue in-plane dimension is larger than the sensor in-plane dimension, the measured tissue elasticity is insensitive to the tissue in-plane dimension.

Commentary by Dr. Valentin Fuster
2017;():V003T04A086. doi:10.1115/IMECE2017-70878.

Recently, the electromagnetic stimulation method to enhance a nerve axonal extension has been attracting a great attention in the nerve regeneration. In this study, we design and fabricate a new 3D bio-reactor, which can implement uniform AC magnetic field (ACMF) stimulation on PC12 cells. We observe the morphology of PC12 cells using the multi photon microscope and evaluate effectiveness of uniform ACMF stimulation of the nerve axonal extension and the neural network generation.

Firstly, a uniform ACMF stimulation bio-reactor was designed by using the pole piece structure. We searched an optimum structure using the magnetic field finite element analyses to obtain a uniform magnetic flux density in the culture region. Secondly, a chamber for 3D culture of PC12 cells was fabricated. PC12 cells were disseminated into a collagen gel which poured in the chamber. We evaluated the effects of uniform ACMF stimulation to enhance the nerve axonal extension. In our bio-reactor, an increase in axonal extension length and number of dendrites was observed under ACMF stimulation after 7 days culture. Finally, it was concluded that our uniform ACMF stimulation bio-reactor is an effective tool for the nerve axonal extension and the neural network generation.

Commentary by Dr. Valentin Fuster
2017;():V003T04A087. doi:10.1115/IMECE2017-70933.

It has been found from our previous studies that the time of curing of high viscous polymethylmethacrylate (HV-PMMA) cement influences the shear strength of titanium (Ti) implant/ HV-PMMA cement samples during pull out static tests, although the reason for the influence is not understood yet. This study hypothesizes that time of curing of cement influences the strength and hardness of the cement adjacent to the implant, which resulted in the variability of the shear strength between Ti and cement. To test this hypothesis, this study conducted ASTM standard three point bend (3PB) test on a HV-PMMA cement to measure the flexural strength of HV-PMMA cement that was cured for 10 and 60 minutes. In addition, this study conducted pull out tension tests on Ti/ HV-PMMA cement to measure the shear strength between Ti and HV-PMMA cement that was cured for 10 and 60 minutes. The hardness of the HV-PMMA cement at the adjacent to Ti was measured using a Rockwell R hardness test scale. Two groups of samples were produced for each type of experiments by varying the curing times: 10 and 60 minutes. The cement during the liquid phase poured into a custom made mold to create the 3PB cylindrical samples. For the pull out tension tests on Ti/cement samples, the Ti implant was fastened at the top gripper and a custom made holder that has a hole was fastened at the bottom gripper of universal mechanical test system. Cement was poured in to the gap between implant and holder. The cement was cured for an hour. This study found that the curing time significantly increases the values of bending, shear and hardness properties (p<0.05). The study concludes that the variability of the shear strength between Ti and cement depends on the strength and hardness of the cement adjacent to the implant.

Commentary by Dr. Valentin Fuster
2017;():V003T04A088. doi:10.1115/IMECE2017-71795.

Tracking of movement under water is still in its infancy. Difficulties include the designing experimental systems that are able to account for the distortion of dense media and the electrical insulation of the experimental apparatus. We propose a simple and inexpensive underwater system which combines the use of GoPro cameras and camera space manipulation (CSM) algorithms for the tracking of movements under water. A comparison of the GoPro cameras to standard computer vision cameras was performed to verify the effect of fisheye lens distortion on linear and non-linear CSM algorithm. Finally, calibration under water was performed using a linear CSM algorithm obtaining errors comparable with measurements obtained by standard cameras outside of water.

Topics: Calibration
Commentary by Dr. Valentin Fuster
2017;():V003T04A089. doi:10.1115/IMECE2017-72018.

Electrospinning is a versatile technique to produce nano/micro fibers with controlled morphology in terms of fiber diameter, alignment etc. With multiple configurations including single axial, co-axial, tri-axial, and co-spinning, this method enables researchers to produce electrospun (ES) fibers with bioactive molecules encapsulated in order to mimic the extracellular matrix for tissue engineering applications. It is of great interest to understand and control the release rate of the bioactive molecules to examine the effects of bioactive molecules such as growth factors on cells. We developed a stochastic simulation method based on the Fick’s diffusion equation to model the diffusive behaviors of macromolecules encapsulated in electrospun fibers. This paper presents a detailed parametric study including 1) the effects of inherent random variation within the samples such as distribution of diameters, initial concentration, diffusion constants, and 2) the effects of volume of release medium. MATHEMATICA is used to carry out the simulations. The computed results are compared with experimental data in the literature.

Commentary by Dr. Valentin Fuster
2017;():V003T04A090. doi:10.1115/IMECE2017-72500.

Shape memory polymers (SMPs) have been developed as an emerging technology platform for biomedical applications in the past decades. In particular, SMPs are clinically essential for the development of novel medical devices to significantly improve long-term surgical outcomes. In this paper, we synthesized and characterized thermally-activated aliphatic urethane SMPs fabricated with nanocomposites for the design and development of biomedical devices. The thermal activation of shape memory function was investigated by direct thermal activation. Critical polymer properties, such as the glass transition temperature and shape memory function, have been tailored to desired applications, by adjusting the polymer composition. Carbon nanotubes were uniformly dispersed within the polymer during nanocomposite fabrication to significantly enhance the thermal and electrical properties. The synthesized SMPs and nanocomposites were characterized to understand their thermal and mechanical properties using dynamic mechanical analysis (DMA). Scanning electron microscopy was employed to evaluate the dispersion of carbon nanotubes in polymer matrix. The mechanical properties of SMPs and nanocomposites at temperature above their glass transition temperature were evaluated using dog-bone samples in a dual-column mechanical testing system and an environmental chamber. SMPs and nanocomposites will then be fabricated in the form of foam for the development of novel devices applicable to endovascular embolization of cerebral aneurysms.

Commentary by Dr. Valentin Fuster

Biomedical and Biotechnology Engineering: Vibration and Acoustics in Biomedical Applications

2017;():V003T04A091. doi:10.1115/IMECE2017-70745.

The misdiagnosis rate of epilepsy is said to keep high from 5% to 30% because of dependency upon an individual judgment by each medical doctor in diagnosis and a quantitative index seems necessary to manage diagnosis uncertainty. To detect some change appearing in brain waves, we focus on introducing a Duffing oscillator model, which could provide reasonably good predictions for the dynamics of neuronal groups. The aim of this paper is to discuss indexes for epilepsy diagnosis by representing characteristics of electroencephalogram (EEG) quantitatively using a Duffing oscillator model. The model parameters are directly identified to adapt the characteristics of the temporal EEG variation to dynamical properties of the model quantitatively. Therefore, in animal experiments, we obtained time histories of the EEG data changed from normal EEG to the epileptic EEG. As a result, it is found that the parameter values related to non-linearity are extremely reduced as the epileptic EEG progresses with time. On the other hand, the input signal strength in epileptic EEG is much bigger than that of normal as expected. Moreover, the directly identified exciting frequency and the eigenfrequency determined by the identified parameter exist in wider band than that of normal as the epileptic EEG progresses with time. The change of the EEG due to epileptic seizure could reflect on the model parameters and it is shown that the model parameters have the possibility to use as supporting index of diagnosis about epilepsy. As a result, the proposed method could be used to support the decline of misdiagnosis rate of epilepsy.

Commentary by Dr. Valentin Fuster
2017;():V003T04A092. doi:10.1115/IMECE2017-71161.

Where heterogeneous material considerations may yield more accurate estimates of long bones’ modal characteristics, homogeneous description has the advantage for yielding faster approximate solutions. In this study, modal frequencies of (bovine) long tibia bones are numerically estimated using the finite element method (FEM) using ANSYS starting from anatomically accurate CT scans and 3D models. Whole long bones are segmented into their cortical and cancellous constituents based on Hounsfield (HU) values. Bones’ cortical and cancellous constituents are first treated as heterogeneous material. Relative to stiffness-density relations, stiffness values are assigned for each element yielding a stiffness-graded structure. Modal frequencies are generated and values compared to those measured from dynamic experiments. Analysis was repeated where bone properties are homogenized by averaging the stiffness properties of bone constituents.

The resulting frequencies are compared with those of the heterogeneous stiffness-graded bones. As compared with measured experimental values of one control long bone, the heterogeneous material assumption returned good estimates of the frequency values in the CC plane with of +0.85 % for mode 1 and +10.66 % for mode 2. For homogeneous material assumption, underestimates were returned with error values of −13.25% and −0.13 % differences for mode 2. In the ML plane, heterogeneous material assumption returned good estimates of the frequency values with −8.89 % for mode 1 and + 1.01 % for mode 2. Homogeneous material assumption underestimated the frequency values with error of −20.52 % for mode 1 and −7.50 % for mode 2. Homogeneous simplifications yielded faster and more memory-efficient FEM runs with heterogeneous modal analysis requiring 1.5 more running time and twice the utilized memory.

Topics: Bone
Commentary by Dr. Valentin Fuster
2017;():V003T04A093. doi:10.1115/IMECE2017-71341.

During spaceflight, the loss of mechanical loads due to microgravity leads to rapid bone loss, where bone deteriorates at a rate of 1–2% per month, where some astronauts can lose as much as 20% of their skeletal mass in a single expedition [NASA, 2001]. In order to prevent muscle and bone loss, long-term space flight exercise regimes are strictly implemented [Shackleford, 2004]. Current research has demonstrated that mechanical vibrations can help to maintain or improve bone mass [Chan, 2013] and reduce adiposity [Chen, 2015, Sen, 2011] when signals are applied at the appropriate frequency and amplitude.

We have developed an acoustic sound chamber that can apply sound waves to stem cells grown in vitro. Characterization of the culture conditions inside the vibration chamber showed considerable variance across the culture plates where an applied acceleration of 0.6g varied at different spots in a 12-well tissue culture plate from as low as 0.47g to 0.78g. We believe the variance is caused by differences in the rigidity of the culture plates that makes the waves transmit inconsistently through the plastic. We hypothesized acoustic waves would induce osteogenic differentiation when applied to stem cells. We utilized pre-osteoblastic stem cells (MC3T3-E1-Subclone 4) to observe the effects of acoustic waves when applied at 0.3g and 0.6g, compared to non-vibrated controls. Cells were vibrated for 30 minutes a day for either 6 days (n = 24/group) or 12 days (n = 12/group). Cellular changes were characterized by assessing well-by-well cell number by a manual cell count and mineral content by Alizarin Red S staining. Differences between groups were determined using One-Way ANOVA with a post hoc test: Student’s t-test. To assess the effects of the variance across the culture plates, correlative analysis was conducted for well-by-well variation using Regression Analysis. Acoustically vibrated wells had 10x more cells after 6 days and showed more mineralization than non-vibrated wells at both 6 and 12 days. Acoustic waves have the ability to increase cell proliferation and can drive stem cell differentiation towards an osteoblastic lineage, this could lead to therapies that prevent bone loss during spaceflight.

Topics: Acoustics , Waves , Stem cells
Commentary by Dr. Valentin Fuster
2017;():V003T04A094. doi:10.1115/IMECE2017-71363.

It was reported that osteoblastic cells respond to mechanical vibration and generate the bone mass with a peak at a specific frequency like a resonance curve [1]. There seems to be an analogy between its cell response and the resonance of a cell as a mechanical system. This paper describes a novel method to measure the cellular modes of vibration of a cell and its calcium ion response under mechanical vibration, and the evaluation of the obtained results to clarify the mechanism of the cell mechanosensing. Nuclei and calcium ion in osteoblastic cells were visualized with fluorescent labelling. Mechanical vibration was applied to cells in a dish in the horizontal direction under a confocal laser scanning microscope by an exciter. Since the fluorescent intensity was very weak due to high frame rate to capture moving cells under Mechanical vibration, we used a high-speed and high-sensitive camera adjusting various conditions such as exposure time. We realized the spatial resolution of approximately 2 μm in the captured micrographs even under mechanical vibration using the experimental setup. As a result, the modes of vibration of nuclei was not obtained in this resolution. We found that the intracellular calcium ion concentration began to increase in a few seconds after mechanical vibration was applied. This experimental result indicates that applying mechanical vibration to cells can produce calcium signals as a second messenger by causing the entry of the ion.

Topics: Vibration
Commentary by Dr. Valentin Fuster
2017;():V003T04A095. doi:10.1115/IMECE2017-71573.

After experiencing a stroke, 80% of individuals face hemiparesis causing muscle weaknesses, paralysis, and lack of proprioception. This often induces difficulty to perform everyday functions such as balancing. The goal of this project is to determine if stroke-like balance can be induced in healthy individuals. The Proprioceptive Interference Apparatus (PIA) applies vibrations and transcutaneous electrical nerve stimulation (TENS) about the knee joint in different combinations both with and without visual feedback.

Ten subjects stood on one foot for periods of two minutes for each of the eight trial conditions. The root mean squared (RMS) of the position coordinates, the standard deviation of the forces, and the RMS of center of pressure coordinates were analyzed for each trial and subject. Analysis of the variation of position markers and forces showed a statistically significant difference between balance with visual feedback versus without. However, the use of PIA did not have any statistically significant difference on these measures.

Topics: Knee
Commentary by Dr. Valentin Fuster
2017;():V003T04A096. doi:10.1115/IMECE2017-72158.

Focal brain cooling has recently drawn attention as a less-invasive treatment for intractable epileptic patients. The objective of this study is to investigate the dependence of brain cooling rate on epileptic discharges (EDs) suppression with experiments using four epilepsy model rat. EDs were induced by Penicillin G in anesthetized rat, and cooled to 16 °C under four different time conditions (30, 60, 100 and 200 second, respectively). The ECoG obtained from the experiments were sorted into frequency band components which have physiological significance. The results of frequency analyses confirmed that the suppression of EDs have a cooling rate dependency, and power of four frequency bands (delta, theta, alpha and beta waves) in EDs are smaller when the cooling rate is slower. Our results suggested that slower cooling on brain surface can effectively suppress EDs and rapid brain cooling is not necessarily the best way. This finding implied that there are optimum cooling condition depending on the degree of EDs or epileptic symptoms.

Commentary by Dr. Valentin Fuster
2017;():V003T04A097. doi:10.1115/IMECE2017-72174.

Unlike x-ray, ultrasound imaging (USI) uses nonionizing acoustic radiation to detect tumors in various body organs, including breast. In the reconstructed images, a radiologist can distinguish between a tumor and a non-malignant cyst, which is highly valuable in making true-positive diagnoses. However, clinical data shows that the addition of ultrasound to mammography, as a separate but auxiliary imaging tool, can increase the false-positive rates [1]. Nonetheless, in a co-registered manner, when an ultrasound image is used as prior information for another breast imaging modality, USI has the potential to make diagnosis more accurate. Previously, we presented the early results of a near-field radar imaging (NRI) system, developed as an add-on unit to the Digital Breast Tomosynthesis to enhance its low radiological contrast. In this work, the early results of a bimodal, USI-NRI, imaging system is presented by adding an ultrasound sensor to our previous system. A simple experimental configuration was utilized for the purpose of proving the concept. The initial results of this study can open the way for safer (in terms of radiation) and more accurate breast imaging in future.

Commentary by Dr. Valentin Fuster
2017;():V003T04A098. doi:10.1115/IMECE2017-72211.

The maxillofacial surgery is a complex surgical procedure to correct facial malformations located in the head of the patient. A precise and reliable surgical planning is necessary for a successful maxillofacial surgical procedure. The experience and clinical practice of surgeons play a very important role during the surgical procedures. Modern Computer Aided Systems (CAS) have been developed in order to speed up the surgical planning process and to increase the accuracy and reliability of the surgical procedure. However, CAS systems have not been focused on their ability to train and to provide experience and clinical practice to novice surgeons or medical student. In this way CAS systems could be a potential tool to improve the skill of surgeons in order to decrease human errors in the maxillofacial treatment and surgical procedures.

This paper presents an investigation to evaluate the use of virtual reality and haptic systems as a training tool for maxillofacial surgeries, in particular osteotomies procedures. The aim is to evaluate the effect of virtual training on surgeon skills. Thus, a virtual osteotomy system has been developed and is presented. The system is based on an open source computer and programming resources, and makes use of haptic technologies to provide the users with the sense of touch. The virtual osteotomy procedures implemented are based on current surgical orthognathic surgery procedures. Free-form 3D manual cutting of bone is available in the system by means of the haptic device and the force feedback provided to the user, which increases the level of realism of the virtual procedure. The evaluation results show that the haptic-enabled virtual training of osteotomies increases the psychomotor skills of the practitioner, leading to an improved accuracy when carrying out the actual bone cut.

Topics: Haptics
Commentary by Dr. Valentin Fuster
2017;():V003T04A099. doi:10.1115/IMECE2017-72296.

Head concussion and neck injury are often induced by an accident even in a minor collision. In this study, a discrete model of masses, springs, and dampers are considered which represent the components of a vehicle-passenger system. The vehicle accounts for 5 degrees of freedom (DOF) whereas the passenger contributes an additional 5 DOF. Differential equations that express the dynamic forces and moments acting upon each mass are developed and then solved numerically using Runge-Kutta method. The results were used to validate the use of such a model to accurately represent real life crash situations. The primary responses of the model are the magnitudes of acceleration experienced by various sections of the model and their relative displacements in two-dimensional space. Analyses were conducted at varying crash velocities and also with different model configurations. It was found that the behavior of the model corresponds well to previous studies and also to what one would intuitively expect at actual collision scene.

Commentary by Dr. Valentin Fuster

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