Accepted Manuscripts

Sergio Ruiz de Galarreta, Aitor Cazon, Raúl Antón and Ender A. Finol
J Biomech Eng   doi: 10.1115/1.4036826
The maximum diameter criterion is the most important factor when predicting risk of rupture of abdominal aortic aneurysms (AAA). An elevated wall stress has also been linked to a high risk of aneurysm rupture, yet is an uncommon clinical practice to compute AAA wall stress. The purpose of this study is to assess whether other characteristics of the AAA geometry are statistically correlated with wall stress. Using in-house segmentation and meshing algorithms, thirty patient-specific AAA models were generated for finite element analysis. These models were subsequently used to estimate wall stress and maximum diameter, and to evaluate the spatial distributions of wall thickness, cross-sectional diameter, mean curvature, and Gaussian curvature. Data analysis consisted of statistical correlations of the aforementioned geometry metrics with wall stress for the thirty AAA inner and outer wall surfaces. In addition, a linear regression analysis was performed with all the AAA wall surfaces to quantify the relationship of the geometric indices with wall stress. These analyses indicated that while all geometry metrics have statistically significant correlations with wall stress, the local mean curvature (LMC) exhibits the highest average Pearson’s correlation coefficient for both inner and outer wall surfaces. The linear regression analysis revealed coefficients of determination for the outer and inner wall surfaces of 0.712 and 0.516, respectively, with LMC having the largest effect on the linear regression equation with wall stress. This work underscores the importance of evaluating AAA mean wall curvature as a potential surrogate for wall stress.
TOPICS: Stress, Aneurysms, Geometry, Regression analysis, Rupture, Exterior walls, Risk, Algorithms, Finite element analysis, Wall thickness, Image segmentation
Haofei Liu and Wei Sun
J Biomech Eng   doi: 10.1115/1.4036829
Objective stress rates are often used in commercial finite element (FE) programs. However, deriving a consistent tangent modulus tensor (also known as elasticity tensor or material Jacobian) associated with the objective stress rates is challenging when complex material models are utilized. In this paper, an approximation method for the tangent modulus tensor associated with the Green-Naghdi rate of the Kirchhoff stress is employed to simplify the evaluation process. The effectiveness of the approach is demonstrated through the implementation of two user-defined fiber-reinforced hyperelastic material models. Comparisons between the approximation method and the closed-form analytical method demonstrate that the former can simplify the material Jacobian evaluation with satisfactory accuracy while retaining its computational efficiency. Moreover, since the approximation method is independent of material models, it can facilitate the implementation of complex material models in FE analysis using shell/membrane elements in ABAQUS.
TOPICS: Elasticity, Tensors, Approximation, Stress, Finite element analysis, Fibers, Membranes, Shells
Ferris M. Pfeiffer, Rachel Bauer, Steve Borgelt, Suzanne Burgoyne, Sheila Grant, Heather Hunt, Jennie Pardoe and David Schmidt
J Biomech Eng   doi: 10.1115/1.4036793
The creative process is fun, complex, and sometimes frustrating, but it is critical to the future of our nation and progress in science, technology, engineering, mathematics, as well as other fields. Thus, we set out to see if implementing methods of active learning typical to the theatre department could impact the creativity of senior capstone design students in the Bioengineering department. Senior Bioengineering capstone design students were allowed to self-select into groups. Prior to the beginning of coursework, all students completed a validated survey measuring engineering design self-efficacy. The control and experimental groups both received standard instruction, but in addition the experimental group received one hour per week of creativity training developed by a theatre professor. Following the semester, the students again completed the self-efficacy survey. The surveys were examined to identify differences in the initial and final self-efficacy in the experimental and control groups over the course of the semester. An analysis of variance was used to compare the experimental and control groups with p<0.05 considered significant. Students in the experimental group reported more than a two-fold (4.8 (C) vs 10.9 (E)) increase of confidence. Additionally, students in the experimental group were more motivated and less anxious when engaging in engineering design following the semester of creativity instruction. The results of this pilot study indicate there is significant potential to improve engineering students’ creative self-efficacy through the implementation of a “curriculum of creativity” which is developed using theatre methods.
TOPICS: Engineering design, Students, Creativity, Design, Bioengineering, Engineering students, Engineering teachers, Engineering mathematics
Kristen L. Billiar and Eric Kennedy
J Biomech Eng   doi: 10.1115/1.4036697
TOPICS: Biomechanics, Education
Lauren M. Mangano Drenkard, Meghan E. Kupratis, Katie Li, Louis C. Gerstenfeld and Elise F. Morgan
J Biomech Eng   doi: 10.1115/1.4036686
Injury to the growth plate is associated with growth disturbances, most notably premature cessation of growth. The goal of this study was to identify spatial changes in the structure and composition of the growth plate in response to injury to provide a foundation for developing therapies that minimize the consequences for skeletal development. We used contrast-enhanced micro-computed tomography (CECT) and histological analyses of a murine model of growth plate injury to quantify changes in the cartilaginous and osseous tissue of the growth plate. To distinguish between local and global changes, the growth plate was divided into regions of interest near to and far from the injury site. We noted increased thickness and CECT attenuation (a measure correlated with glycosaminoglycan content) near the injury, and increased tissue mineral density of bone bridges within the injury site, compared to outside the injury site and contralateral growth plates. Furthermore, we noted disruption of the normal zonal organization of the physis. The height of the hypertrophic zone was increased at the injury site, and the relative height of the proliferative zone was decreased across the entire injured growth plate. These results indicate that growth plate injury leads to localized disruption of cellular activity and of endochondral ossification. These local changes in tissue structure and composition may contribute to the observed retardation in femur growth. In particular, the changes in proliferative and hypertrophic zone heights seen following injury may impact growth and could be targeted when developing therapies for growth plate injury.
TOPICS: Wounds, Biological tissues, Patient treatment, Minerals, Bone, Plates (structures), Density, Bridges (Structures)
Technical Brief  
Michelle A Cruz, Steven McAnany, Nikita Gupta, Rose Long, Phillip R Nasser, David Eglin, Andrew Hecht, Svenja Illien-junger and James C Iatridis
J Biomech Eng   doi: 10.1115/1.4036623
Annulus fibrosus (AF) defects from intervertebral disc herniation and degeneration are highly correlated with back pain. Genipin crosslinked fibrin hydrogel (FibGen) is an injectable, space-filling AF sealant that was optimized to match AF shear properties and partially restored disc biomechanics. This study enhanced mechanical behaviors of FibGen to more closely match AF compressive, tensile and shear properties by adjusting genipin crosslink density and by creating a composite formulation by adding Poly(D,L-lactide-co-glycolide) (PDLGA). This study also evaluated effects of thrombin concentration and injection technique on gelation kinetics and adhesive strength. Increasing FibGen genipin concentration from 1 to 36mg/mL significantly increased adhesive strength (~5-35kPa), shear moduli (~10-110kPa) and compressive moduli (~25-150kPa) with concentration-dependent effects, and spanning native AF properties. Adding PDLGA to FibGen altered the material microstructure on electron microscopy and nearly tripled adhesive strength, but did not increase tensile moduli which remained nearly 5x below native AF, and had a small increase in shear moduli and significantly decreased compressive moduli. Increased thrombin concentration decreased gelation rate to <5 minutes and injection methods providing a structural FibGen cap increased pushout strength by ~40%. We conclude that FibGen is highly modifiable with tunable mechanical properties that can be formulated to be compatible with human AF compressive and shear properties and gelation kinetics and injection techniques compatible with clinical discectomy procedures. However, further innovations, perhaps with more efficient fiber reinforcement will be required to enable FibGen to match AF tensile properties.
TOPICS: Adhesives, Maintenance, Materials properties, Annulus, Intervertebral discs, Shear strength, Shear modulus, Discectomies, Tensile strength, Hydrogels, Mechanical properties, Mechanical behavior, Disks, Electron microscopy, Sealants, Biomechanics, Fibers, Density, Composite materials
Marco A. Marra, Michael S. Andersen, Michael Damsgaard, Bart F.J.M. Koopman, Dennis Janssen and Nico Verdonschot
J Biomech Eng   doi: 10.1115/1.4036605
Knowing the forces in the human body is of great clinical interest and musculoskeletal models are the most commonly used tool to estimate them in vivo. Unfortunately, the process of computing muscle, joint contact and ligament forces simultaneously is computationally highly demanding. The goal of this study was to develop a fast surrogate model of the tibiofemoral (TF) contact in a total knee replacement (TKR) model and apply it to force-dependent kinematic simulations of activities of daily living (ADLs). Multiple domains were populated with sample points from the reference TKR contact model, based on reference simulations and design-of-experiments. Artificial neural networks learned the relationship between TF pose and loads from the medial and lateral sides of the implant. Normal and right-turn gait, rising-from-a-chair, and a squat were simulated using both surrogate and reference contact models. Compared to the reference contact model, the surrogate contact model predicted TF forces with a root-mean-square error (RMSE) lower than 10 N and TF moments lower than 0.3 Nm over all simulated activities. Secondary knee kinematics were predicted with RMSE lower than 0.2 mm and 0.2 degrees. Simulations that used the surrogate contact model ran on average three times faster than those using the reference model, allowing the simulation of a full gait cycle in 4.5 min. This modeling approach proved fast and accurate enough to perform extensive parametric analyses, such as simulating subject-specific variations and surgical-related factors in TKR.
TOPICS: Simulation, Knee joint prostheses, Engineering simulation, Kinematics, Stress, Modeling, Surgery, Artificial neural networks, Cycles, Errors, Experimental design, Muscle, Musculoskeletal system, Knee
Sofia Brandão, Marco Parente, Thuane Huyer Da Roza, Elisabete Silva, Isabel Maria Ramos, Teresa Mascarenhas and Renato Manuel Natal Jorge
J Biomech Eng   doi: 10.1115/1.4036606
Midurethral slings are used to correct urethral hypermobility in female stress urinary incontinence, defined as the complaint of involuntary urine leakage when the intra-abdominal pressure is increased. Structural and thermal features influence their mechanical properties, which may explain postoperative complications, e.g., erosion, urethral obstruction. We studied the effect of the mesh stiffness on urethral mobility at Valsalva maneuver, under impairment of the supporting structures (levator ani and/or ligaments), by using a numerical model. For that purpose, we modeled a sling with “lower” vs. “higher” stiffness, and evaluated the mobility of the bladder and urethra, that of the urethrovesical junction (the a-angle), and the force exerted at the fixation of the sling. The effect of impaired levator ani or pubourethral ligaments alone on the organs displacement and a-angle opening was similar, showing their important role together on urethral stabilization. When the levator ani and all the ligaments were simulated as impaired, the descent of the bladder and urethra went up to 25.02mm, that of the bladder neck was 14.57mm, and the a-angle was 129.7°, in the range of what was found in women with SUI. Both meshes allowed returning to normal positioning, although at the cost of higher force exerted by the mesh with “higher” stiffness (3.4N against 2.3N), which can relate to tissue erosion. This finite element analysis allowed mimicking the biomechanical response of the pelvic structures in response to changing a material property of the midurethral synthetic mesh.
TOPICS: Finite element analysis, Stiffness, Mechanical admittance, Erosion, Leakage, Displacement, Junctions, Pressure, Computer simulation, Stress, Biomechanics, Materials properties, Mechanical properties, Biological tissues
Wanchuan Xie, Weston M. Lewis, Jared Kaser, C. Ross Welch, Pengbo Li, Carl A. Nelson, Vishal Kothari and Benjamin S. Terry
J Biomech Eng   doi: 10.1115/1.4036607
We have proposed a long-term, non-invasive, non-restrictive method of delivering and implanting a biosensor within the body via a swallowable implantation capsule robot (ICR). The design and preliminary validation of the ICR's primary subsystem—the sensor deployment system—is discussed and evidence is provided for major design choices. The purpose of the sensor deployment system is to adhere a small biosensor to the mucosa of the intestine long-term, and the modality was inspired by tapeworms and other organisms that employ a strategy of mechanical adhesion to soft tissue via the combined use of hooks or needles and suckers. Testing was performed to refine the design of the suction and needle attachment as well as the sensor ejection features of the ICR. An experiment was conducted in which needle sharpness, needle length, and vacuum volume were varied, and no statistically significant difference was observed. Finally, preliminary testing, coupled with prior work within a live porcine model, provided evidence that this is a promising approach for implanting a biosensor within the small intestine.
TOPICS: Robots, Design, Biosensors, needles, Sensors, Testing, Vacuum, Suction, Soft tissues, Adhesion
Fei Fang and Spencer P. Lake
J Biomech Eng   doi: 10.1115/1.4036602
Proteoglycans (PGs) have been reported to be broadly distributed within many soft tissues and, among other roles, often contribute to mechanical properties. Although PGs were once assumed to help support load in tendon, numerous studies have found no changes to tensile mechanics after PG depletion. Since PGs are known to help sustain non-tensile loading in other tissues (e.g., compressive forces in cartilage), we hypothesized that PGs might help support non-tensile loading in the human supraspinatus tendon (SST), a commonly injured tendon which functions in a complex multiaxial loading environment. Therefore, the objective of this study was to determine whether PGs contribute to the response of SST to shear loading, specifically in terms of multiscale mechanical properties and mechanisms of microscale matrix deformation. Results showed that ChABC treatment successfully digested PGs in SST samples while not disrupting collagen fibers. Peak and equilibrium shear stresses decreased only slightly after ChABC treatment and were not significantly different from pre-treatment values. Reduced stress ratios were computed and shown to be slightly greater after ChABC treatment compared to PBS incubation without enzyme, suggesting that these relatively small changes in stress values were not due strictly to tissue swelling. Microscale deformations were also not different after treatment. This study demonstrates that PGs possibly play a minor role in contributing to the mechanical behavior of tendon in shear, but are not a key tissue constituent to regulate shear mechanics.
TOPICS: Shear (Mechanics), Tendons, Biological tissues, Stress, Deformation, Mechanical properties, Microscale devices, Enzymes, Soft tissues, Cartilage, Shear stress, Mechanical behavior, Fibers, Equilibrium (Physics)
Julia C. Quindlen, Burak Güçlü, Eric A. Schepis and Victor H. Barocas
J Biomech Eng   doi: 10.1115/1.4036603
The Pacinian corpuscle (PC) is a cutaneous mechanoreceptor that senses low-amplitude, high-frequency vibrations. The PC contains a nerve fiber surrounded by alternating layers of solid lamellae and interlamellar fluid, and this structure is hypothesized to contribute to the PC's role as a band-pass filter for vibrations. In this study, we sought to evaluate the relationship between the PC's material and geometric parameters and its response to vibration. We used a spherical finite-element mechanical model based on shell theory and lubrication theory to model the PC's outer core. Specifically, we analyzed the effect of the following structural properties on the PC's frequency sensitivity: lamellar modulus (E), lamellar thickness (h), fluid viscosity (µ), PC outer radius (Ro), and number of lamellae (N). The frequency of peak strain amplification (henceforth “peak frequency”) and frequency range over which strain amplification occurred (henceforth “bandwidth”) increased with lamellar modulus or lamellar thickness, and decreased with an increase in fluid viscosity and radius. All five structural parameters were combined into expressions for the relationship between the parameters and peak frequency or bandwidth. Although further work is needed to understand how mechanical variability contributes to functional variability in PCs and how factors such as PC eccentricity also affect PC behavior, this study provides two simple expressions that can be used to predict the impact of structural or material changes with aging or disease on the frequency response of the PC.
TOPICS: Fluids, Fibers, Viscosity, Mechanical properties, Finite element analysis, Vibration, Diseases, Filters, Frequency response, Shells, Lubrication theory, Dynamic light scattering
Mohammadreza Khani, Tao Xing, Christina Gibbs, John Oshinski, Gregory R. Stewart, Jillynne R. Zeller and Bryn A. Martin
J Biomech Eng   doi: 10.1115/1.4036608
A detailed quantification and understanding of cerebrospinal fluid (CSF) dynamics may improve detection and treatment of central nervous system (CNS) diseases and help optimize CSF system-based delivery of CNS therapeutics. This study presents a computational fluid dynamics (CFD) model that utilizes a non-uniform moving boundary approach to accurately reproduce the non-uniform distribution of CSF flow along the spinal subarachnoid space (SAS) of a single cynomolgus monkey. A magnetic resonance imaging (MRI) protocol was developed and applied to quantify subject-specific CSF space geometry and flow and define the CFD domain and boundary conditions. An algorithm was implemented to reproduce the axial distribution of unsteady CSF flow by non-uniform deformation of the dura surface. Results showed that maximum difference between the MRI measurements and CFD simulation of CSF flow rates was <3.6%. CSF flow along the entire spine was laminar with a peak Reynold's number of ~150 and average Womersley number of ~5.4. Maximum CSF flow rate was present at the C4-C5 vertebral level. Deformation of the dura ranged up to a maximum of 134 µm. Geometric analysis indicated that total spinal CSF space volume was ~8.7 ml. Average hydraulic diameter, wetted perimeter and SAS area was 2.9 mm, 37.3 mm and 27.24 mm2, respectively. CSF pulse wave velocity along the spine was quantified to be 1.2 m/s.
TOPICS: Flow (Dynamics), Simulation, Computational fluid dynamics, Magnetic resonance imaging, Deformation, Waves, Algorithms, Boundary-value problems, Diseases, Geometry, Cerebrospinal fluid, Nervous system, Dynamics (Mechanics)
Anita Singh
J Biomech Eng   doi: 10.1115/1.4036604
Demand of biomedical engineers is rising exponentially to meet the needs of healthcare industry. Current training of bioengineers follows the traditional and dominant model of theory-focused curricula. However, the unmet needs of the healthcare industry warrant newer skill sets in these engineers where translational training strategies such as solving real world problems can be incorporated to the existing biomedical engineering education through active, adaptive and experiential learning. In this paper we report our findings of active and adaptive project based learning approach through a simulation lab visit that served as a clinical immersion experience for students enrolled in a senior-level Biomechanics undergraduate course. In this team-based learning activity, students identified an unmet need in the simulation mannequin and offered a biomechanics related solution to overcome the problem. Surveys assessed student perceptions of the activity and learning experience. While students, across three cohorts, felt challenged to solve a real-world problem identified during the simulation lab visit, they felt more confident in utilizing knowledge learned in the biomechanics course and self-directed research indicating that the active and experiential learning approach fostered their technical knowledge and life-long learning skills while exposing them to the components of adaptive learning and innovation.
TOPICS: Biomechanics, Teaching, Students, Simulation, Health care, Teams, Biomedical engineering, Engineers, Biomedical engineers, Education, Undergraduate students, Innovation
Arnold D. Gomez, Huashan Zou, Megan E. Bowen, Xiaoqing Liu, Edward W. Hsu and Stephen H. McKellar
J Biomech Eng   doi: 10.1115/1.4036485
Right ventricular failure (RVF) is a lethal condition in diverse pathologies. Pressure overload is the most common etiology of RVF, but our understanding of the tissue structure remodeling and other biomechanical factors involved in RVF is limited. Some remodeling patterns are interpreted as compensatory mechanisms including myocyte hypertrophy, extracellular fibrosis, and changes in fiber orientation. However, the specific implications of these changes, especially in relation to clinically observable measurements, are difficult to investigate experimentally. In this computational study, we hypothesized that, with other variables constant, fiber orientation alteration provides a quantifiable and distinct compensatory mechanism during RV pressure overload. Numerical models were constructed using a rabbit model of chronic pressure overload RVF based on intraventricular pressure measurements, CINE magnetic resonance imaging (MRI), and diffusion tensor MRI (DT-MRI). Biventricular simulations were conducted under normotensive and hypertensive boundary conditions using variations in RV wall thickness, tissue stiffness, and fiber orientation to investigate their effect on RV pump function. Our results show that a longitudinally aligned myocardial fiber orientation contributed to an increase in RV ejection fraction (RVEF). This effect was more pronounced in response to pressure overload. Likewise, models with longitudinally aligned fiber orientation required a lesser contractility for maintaining a target RVEF against elevated pressures. In addition to increased wall thickness and material stiffness (diastolic compensation), systolic mechanisms in the forms of myocardial fiber realignment and changes in contractility are likely involved in the overall compensatory responses to pressure overload.
TOPICS: Fibers, Pressure, Magnetic resonance imaging, Stiffness, Wall thickness, Biological tissues, Engineering simulation, Pumps, Diffusion (Physics), Pressure measurement, Computer simulation, Simulation, Biomechanics, Tensors, Boundary-value problems, Failure
Chelsey L. Dunham, Ryan M. Castile, Aaron M. Chamberlain, Leesa M. Galatz and Spencer P. Lake
J Biomech Eng   doi: 10.1115/1.4036472
The elbow joint is highly susceptible to joint contracture, and treating elbow contracture is a challenging clinical problem. Previously, we established an animal model to study elbow contracture that exhibited features similar to the human condition including persistent decreased range of motion (ROM) in flexion-extension and increased capsule thickness/adhesions. The objective of this study was to mechanically quantify pronation-supination in different injury models to determine if significant differences compared to control or contralateral persist long-term in our animal elbow contracture model. After surgically inducing soft tissue damage in the elbow, Injury I (anterior capsulotomy) and Injury II (anterior capsulotomy with lateral collateral ligament transection), limbs were immobilized for six weeks (IM). Animals were evaluated after the IM period or following an additional six-weeks of free mobilization (FM). Total ROM for pronation-supination was significantly decreased compared to the uninjured contralateral limb for both IM and FM, although not different from control limbs. Specifically, for both IM and FM, total ROM for Injury I and Injury II were significantly decreased by ~20% compared to contralateral. Correlations of measurements from flexion-extension and pronation-supination divulged that FM did not affect these motions in the same way, demonstrating that joint motions need to be studied/treated separately. Overall, injured limbs exhibited persistent motion loss in pronation-supination when comparing side-to-side differences, similar to human post-traumatic joint contracture. Future work will use this animal model to study how elbow periarticular soft tissues contribute to contracture.
TOPICS: Surgery, Wounds, Soft tissues, Damage
Kerianne E. Steucke, Zaw Win, Taylor R. Stemler, Emily E. Walsh, Jennifer L. Hall and Patrick W. Alford
J Biomech Eng   doi: 10.1115/1.4036454
Cardiovascular disease can alter the mechanical environment of the vascular system, leading to mechano-adaptive growth and remodeling. Predictive models of arterial mechano-adaptation could improve patient treatments and outcomes in cardiovascular disease. Vessel-scale mechano-adaptation includes remodeling of both the cells and extracellular matrix. Here, we aimed to experimentally measure and characterize a phenomenological mechano-adaptation law for vascular smooth muscle cells (VSMCs) within an artery. To do this, we developed a highly controlled and reproducible system for applying a chronic step-change in strain to individual VSMCs with in vivo like architecture, and tracked the temporal cellular stress evolution. We found that a simple linear growth law was able to capture the dynamic stress evolution of VSMCs in response to this mechanical perturbation. These results provide an initial framework for development of clinically relevant models of vascular remodeling that include VSMC adaptation.
TOPICS: Muscle, Stress, Cardiovascular system, Diseases, Performance, Patient treatment, Vessels
Zaw Win, Justin M Buksa, Kerianne E Steucke, G.W. Gant Luxton, Victor H Barocas and Patrick W Alford
J Biomech Eng   doi: 10.1115/1.4036440
The stress in a cell due to extracellular mechanical stimulus is determined by its mechanical properties, and the structural organization of many adherent cells suggests that their properties are anisotropic. This anisotropy may significantly influence the cells' mechanotransductive response to complex loads, and has important implications for development of accurate models of tissue biomechanics. Standard methods for measuring cellular mechanics report linear moduli that cannot capture large-deformation anisotropic properties, which in a continuum mechanics framework are best described by a strain energy density function (SED). In tissues, the SED is most robustly measured using biaxial testing. Here, we describe a cellular micro-biaxial stretching (CµBS) method that modifies this tissue-scale approach to measure the anisotropic elastic behavior of individual vascular smooth muscle cells (VSMCs) with native-like cytoarchitecture. Using CµBS, we reveal that VSMCs are highly anisotropic under large deformations. We then characterize a Holzapfel-Gasser-Ogden type SED for individual VSMCs and find that architecture-dependent properties of the cells can be robustly described using a formulation solely based on the organization of their actin cytoskeleton. These results suggest that cellular anisotropy should be considered when developing biomechanical models, and could play an important role in cellular mechano-adaptation.
TOPICS: Density, Anisotropy, Spectral energy distribution, Biological tissues, Deformation, Stress, Biomechanics, Elasticity, Mechanical properties, Continuum mechanics, Cellular mechanics, Testing, Muscle
Alan W. Eberhardt, Shea Tillman, Brandon Kirkland and Brandon Sherrod
J Biomech Eng   doi: 10.1115/1.4036441
There exists a need for educational processes in which students gain experience with design and commercialization of medical devices. This manuscript describes the implementation of, and assessment results from, the first year offering of a “project course” sequence in a Master of Engineering (MEng) in Design and Commercialization at our institution. The three-semester course sequence focused on developing and applying hands-on skills that contribute to product development to address medical device needs found within our university hospital and local community. The first semester integrated computer aided drawing (CAD) as preparation for manufacturing of device-related components (hand machining, CNC, 3D printing and plastics molding), followed by an introduction to microcontrollers and printed circuit boards for associated electronics and control systems. In the second semester, the students applied these skills on a unified project, working together to construct and test multiple weighing scales for wheelchair users. In the final semester, the students applied Industrial Design concepts to four distinct device designs, including user and context reassessment, human factors (functional and aesthetic) design refinement, and advanced visualization for commercialization. Assessment results are described, along with lessons learned and plans for enhancement of the course sequence.
TOPICS: Medical devices, Innovation, Students, Design, Human factors, Visualization, Product development, Machining, Industrial design, Control systems, Manufacturing, Computer-aided engineering, Plastics molding, Computer-aided design, Electronics, Wheelchairs, Printed circuit boards, Computer numerical control machine tools, Additive manufacturing
Stephanie M. George and Zachary J. Domire
J Biomech Eng   doi: 10.1115/1.4036315
As the reliance on computational models to inform experiments and evaluate medical devices grows, the demand for students with modeling experience will grow. In this paper, we report on the three year experience of a National Science Foundation funded Research Experiences for Undergraduates (REU) based on the theme simulations, imaging, and modeling in biomechanics. While directly applicable to REU sites, our findings also apply to those creating other types of summer undergraduate research programs. The objective of the paper is to examine if a theme of simulations, imaging, and modeling will improve students' understanding of the important topic of modeling, provide an overall positive research experience, and provide an interdisciplinary experience. The structure of the program and evaluation plan are described. We report on the results from 25 students over three summers from 2014-2016. Overall, students reported significant gains in knowledge of modeling, the research process, and graduate school based on self-reported mastery levels and open-ended qualitative responses. This theme provides students with a skill set that is adaptable to other applications illustrating the interdisciplinary nature of modeling in biomechanics. Another advantage is that students may also be able to continue working on their project following the summer experience through network connections. In conclusion, we have described the successful implementation of the theme simulation, imaging, and modeling for an REU site and the overall positive response of the student participants.
TOPICS: Modeling, Imaging, Simulation, Biomechanics, Undergraduate research, Students, Undergraduate students, Medical devices
Christopher E. Korenczuk, Lauren E. Votava, Rohit Y. Dhume, Shannen B. Kizilski, George E. Brown, Rahul Narain and Victor H. Barocas
J Biomech Eng   doi: 10.1115/1.4036316
The von Mises (VM) stress is a common stress measure for finite-element models of tissue mechanics. The VM failure criterion, however, is inherently isotropic, and therefore may yield incorrect results for anisotropic tissues, and the relevance of the VM stress to anisotropic materials is not clear. We explored the application of a well-studied anisotropic failure criterion, the Tsai-Hill (TH) theory, to the mechanically anisotropic porcine aorta. Uniaxial dogbones were cut at different angles and stretched to failure. The tissue was anisotropic, with the circumferential failure stress nearly twice the axial (2.67 ± 0.67 MPa compared to 1.46 ± 0.59 MPa). The VM failure criterion did not capture the anisotropic tissue response, but the TH criterion fit the data well (R2 = 0.986). Shear lap samples were also tested to study the efficacy of each criterion in predicting tissue failure. 2D failure propagation simulations showed that the VM failure criterion did not capture the failure type, location, or propagation direction nearly as well as the TH criterion. Over the range of loading conditions and tissue geometries studied, we found that problematic results that arise when applying the VM failure criterion to an anisotropic tissue. In contrast, the TH failure criterion, though simplistic and clearly unable to capture all aspects of tissue failure, performed much better. Ultimately, isotropic failure criteria are not appropriate for anisotropic tissues, and the use of the VM stress as a metric of mechanical state should be reconsidered when dealing with anisotropic tissues.
TOPICS: Anisotropy, Biological tissues, Failure, Stress, Simulation, Shear (Mechanics), Finite element model, Aorta, Engineering simulation

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