Accepted Manuscripts

Brett / S Klosterhoff, Keat Ghee Ong, Laxminarayanan Krishnan, Kevin Hetzendorfer, Young-Hui Chang, Mark G. Allen, Robert Guldberg and Nick J Willett
J Biomech Eng   doi: 10.1115/1.4037937
Bone development, maintenance, and regeneration are remarkably sensitive to mechanical cues. Consequently, mechanical stimulation has long been sought as a putative target to promote endogenous healing after fracture. Given the transient nature of bone repair, tissue-level mechanical cues evolve rapidly over time after injury and are challenging to measure non-invasively. The objective of this work was to develop and characterize an implantable strain sensor for non-invasive monitoring of axial strain across a rodent femoral defect during functional activity. Herein, we present the design, characterization, and in vivo demonstration of the device's capabilities for quantitatively interrogating physiological dynamic strains during bone regeneration. Ex vivo experimental characterization of the device showed that it possessed promising sensitivity, signal resolution, and electromechanical stability for in vivo applications. The digital telemetry minimized power consumption, enabling extended intermittent data collection. Devices were implanted in a rat 6 mm femoral segmental defect model and after three days, data were acquired wirelessly during ambulation and synchronized to corresponding radiographic videos, validating the ability of the sensor to non-invasively measure strain in real-time. Together, these data indicate the sensor is a promising technology to quantify tissue mechanics in a specimen specific manner, facilitating more detailed investigations into the role of the mechanical environment in dynamic bone healing and remodeling processes.
Nathaniel T. Pickle, Alena Grabowski, Jana Jeffers and Anne Silverman
J Biomech Eng   doi: 10.1115/1.4037938
Sloped walking is challenging for individuals with transtibial amputation due to the functional loss of the ankle plantarflexors. Prostheses that generate ankle power may restore this lost function. The purpose of this study was to use musculoskeletal modeling and simulation to quantify the mechanical power delivered to body segments by passive and powered prostheses and the remaining muscles in the amputated and intact legs during sloped walking. We generated walking simulations from experimental kinematic and kinetic data on slopes of 0, ±3° and ±6° in eight people with a transtibial amputation using powered and passive prostheses and eight non-amputees. Consistent with our hypothesis, the amputated leg hamstrings in individuals with amputation generated more power to both legs on uphill slopes compared to non-amputees, which may have implications for fatigue or overuse injuries. The amputated leg knee extensors delivered less power to the trunk on downhill slopes (effect size=1.35, p=0.02), which may be due to muscle weakness or socket instability. The power delivered to the trunk from the powered and passive prostheses was not significantly different (p>0.05), However, using the powered prosthesis on uphill slopes reduced the contributions from the amputated leg hamstrings in all segments (effect size=0.46, p=0.003), suggesting that added ankle power reduces the need for the hamstrings to compensate for lost ankle muscle function. Neither prosthesis replaced gastrocnemius function to absorb power from the trunk and deliver it to the leg on all slopes.
Jeremy D Eekhoff, Fei Fang, Lindsey G Kahan, M.G. Espinosa, Austin J Cocciolone, Jessica E. Wagenseil, Robert P Mecham and Spencer P Lake
J Biomech Eng   doi: 10.1115/1.4037932
Elastic fibers are present in low quantities in tendon, where they are located both within fascicles near tenocytes and more broadly in the interfascicular matrix. While elastic fibers have long been known to be significant in the mechanics of elastin-rich tissue (i.e. vasculature, skin, lungs), recent studies have suggested a mechanical role for elastic fibers in tendons that is dependent on specific tendon function. However, the exact contribution of elastin to properties of different types of tendons (e.g., positional, energy-storing) remains unknown. Therefore, this study purposed to evaluate the role of elastin in the mechanical properties and collagen alignment of functionally distinct supraspinatus tendons (SSTs) and Achilles tendons (ATs) from elastin haploinsufficient (HET) and wild type (WT) mice. Despite the significant decrease in elastin in HET tendons, a slight increase in linear stiffness of both tendons was the only significant mechanical effect of elastin haploinsufficiency. Additionally, there were significant changes in collagen nanostructure and subtle alteration to collagen alignment in the AT but not the SST. Hence, elastin may play only a minor role in tendon mechanical properties. Alternatively, larger changes to tendon mechanics may have been mitigated by developmental compensation of HET tendons and/or the role of elastic fibers may be less prominent in smaller mouse tendons compared to the larger bovine and human tendons evaluated in previous studies. Further research will be necessary to fully elucidate the influence of various elastic fiber components on structure-function relationships in functionally distinct tendons.
TOPICS: Tendons, Fibers, Mechanical properties, Biological tissues, Lung, Skin, Stiffness, Air traffic control
Adnan Morshed and Prashanta Dutta
J Biomech Eng   doi: 10.1115/1.4037915
Availability of essential species like oxygen is critical in shaping the dynamics of tumor growth. When the intracellular oxygen level falls below normal, it initiates major cascades in cellular dynamics leading to tumor cell survival. In a cellular block with cells growing away from the blood vessel, the scenario can be aggravated for the cells further inside the block. In this study, the dynamics of intracellular species inside a colony of tumor cells are investigated by varying the cell block thickness and cell types in a microfluidic cell culture device. The oxygen transport across the cell block is modeled through diffusion, while ascorbate transport from the extracellular medium is addressed by a concentration dependent uptake model. The extracellular and intracellular descriptions were coupled through the consumption and traffic of species . Our model shows that the onset of hypoxia is possible in HeLa cell within minutes depending on the cell location, although the nutrient supply inside the channel is maintained in normoxic levels. This eventually leads to total oxygen deprivation inside the cell block in the extreme case, representing the development of a necrotic core. The numerical model reveals that species concentration and hypoxic response are different for HeLa and HelaS3 cells. Results also indicate that the long-term hypoxic response from a microfluidic cellular block stays within 5% of the values of a tissue with the basal layer. The hybrid model can be very useful in designing microfluidic experiments to satisfactorily predict the tissue level response in cancer research.
TOPICS: Microfluidics, Biological tissues, Oxygen, Dynamics (Mechanics), Tumors, Diffusion (Physics), Computer simulation, Traffic, Blood vessels, Design, Cancer
Afshin Anssari-Benam and Andrea Bucchi
J Biomech Eng   doi: 10.1115/1.4037916
This paper is concerned with proposing a suitable structurally-motivated strain energy function for modelling the deformation of the elastin network within the aortic valve (AV) tissue. The AV elastin network is the main non-collagenous load-bearing component of the valve matrix and therefore, within the context of continuum-based modelling of the AV, it essentially serves as the contribution of the 'isotropic matrix'. To date, such function has mainly been considered as either a generic neo-Hookean term or a general exponential function. In this paper, we take advantage of the established structural analogy between the network of elastin chains and the freely jointed molecular chain networks, and customise a structurally-motivated function on this basis. The ensuing stress-strain (force-stretch) relationships are thus derived and fitted to the experimental data points reported by Vesely (1998) for intact AV elastin network specimens under uniaxial tension. The fitting results are then compared with those of the neo-Hookean and the general exponential models, as well as the Arruda-Boyce model as the gold standard of the network chain models. It is shown that the neo-Hookean function is entirely inadequate for modelling the AV elastin network, while the parameters estimated by the Arruda-Boyce model are not mathematically and structurally valid. Since the general exponential function is purely phenomenological, we conclude that our proposed strain energy function may be the preferred choice for modelling the behaviour of the AV elastin network, and thereby the 'isotropic matrix'.
TOPICS: Deformation, Modeling, Valves, Chain, Stress, Bearings, Biological tissues, Fittings, Tension
Review Article  
Hafizur Rahman, Eric Currier, Marshall Johnson, Rick Goding, Amy J. Wagoner Johnson and Mariana Kersh
J Biomech Eng   doi: 10.1115/1.4037917
Rotator cuff tears are one of the primary causes of shoulder pain and dysfunction in the upper extremity accounting over 4.5 million physician visits per year with 250,000 rotator cuff repairs being performed annually in the United States. While the tear is often considered an injury to a specific tendon/tendons and consequently treated as such, there are secondary effects of rotator cuff tears that may have significant consequences for shoulder function. Specifically, rotator cuff tears have been shown to affect the joint cartilage, bone, the ligaments, as well as the remaining intact tendons of the shoulder joint. Injuries associated with the upper extremities account for the largest percent of workplace injuries. Unfortunately, the variable success rate related to rotator cuff tears motivates the need for a better understanding of the biomechanical consequences associated with the shoulder injuries. Understanding the timing of the injury and the secondary anatomic consequences that are likely to have occurred are also of great importance in treatment planning because the approach to the treatment algorithm is influenced by the functional and anatomic state of the rotator cuff and the shoulder complex in general. In this review, we summarized the contribution of rotator cuff tears to joint stability in terms of both primary (injured tendon) and secondary (remaining tissues) consequences including anatomic changes in the tissues surrounding the affected tendon/tendons.
TOPICS: Biological tissues, Wounds, Tendons, Accounting, Cartilage, Bone, Stability, Maintenance, Biomechanics, Algorithms
Review Article  
Zachary Abraham, Emma Hawley, Daniel Hayosh, Victoria Webster-Wood and Ozan Akkus
J Biomech Eng   doi: 10.1115/1.4037886
Motor proteins play critical roles in the normal function of cells and proper development of organisms. Among motor proteins, failings in the normal function of two types of proteins, kinesin and dynein, have been shown to lead many pathologies, including neurodegenerative diseases and cancers. As such, it is critical for researchers to understand the underlying mechanics and behaviors of these proteins, not only to shed light on how failures may lead to disease, but also to guide research towards novel treatment and nanoengineering solutions. To this end, many experimental techniques have been developed to measure the force and motility capabilities of these proteins. This review will: a) discuss such techniques, specifically microscopy, atomic force microscopy, optical trapping, and magnetic tweezers, and, b) the resulting nanomechanical properties of motor protein functions such as stalling force, velocity and dependence on ATP concentrations will be comparatively discussed. Additionally, this review will highlight the clinical importance of these proteins. Furthermore, as the understanding of the structure and function of motor proteins improves, novel applications are emerging in the field. Specifically, researchers have begun to modify the structure of existing proteins, thereby engineering novel elements to alter and improve native motor protein function, or even allow the motor proteins to perform entirely new tasks as parts of nanomachines. Kinesin and dynein are vital elements for the proper function of cells. While many exciting experiments have shed light on their function, mechanics, and applications, additional research is needed to completely understand their behavior.
TOPICS: Atomic force microscopy, Engines, Motors, Molecular machines, Microscopy, Cancer, Diseases, Failure, Proteins, Nanoengineering
Pouya Youssefi, Alberto Gomez, Christopher Arthurs, Rajan Sharma, Marjan Jahangiri and Alberto Figueroa
J Biomech Eng   doi: 10.1115/1.4037857
Background-Computational fluid dynamics (CFD) provides a non-invasive method to functionally assess aortic hemodynamics. The thoracic aorta has an anatomically complex inlet comprising of the aortic valve, which is highly prone to different morphologies and pathologies. We investigated the effect of using patient-specific inflow velocity profiles compared to idealised profiles based on the patient's flow waveform. Methods-A healthy 31yo with a normally functioning tricuspid aortic valve (subject A), and a 52yo with a bicuspid aortic valve, aortic valvular stenosis and dilated ascending aorta (subject B) were studied. Subjects underwent MR angiography to image and reconstruct 3D geometric models of the thoracic aorta. Flow-MRI was acquired above the aortic valve and used to extract the patient-specific velocity profiles. Results-Subject B's eccentric asymmetrical inflow profile led to highly complex velocity patterns which were not replicated by the idealised velocity profiles. Despite having identical flow rates, the idealised inflow profiles displayed significantly different peak and radial velocities. Subject A's results showed some similarity between patient-specific and parabolic inflow profiles, however other parameters such as Flow-asymmetry were significantly different. Conclusion-Idealised inflow velocity profiles significantly alter velocity patterns and produce inaccurate hemodynamic assessments in the thoracic aorta. The complex structure of the aortic valve and its predisposition to pathological change means the inflow into the thoracic aorta can be highly variable. CFD analysis of the thoracic aorta needs to utilise fully patient-specific inflow boundary conditions in order to produce truly meaningful results.
TOPICS: Hemodynamics, Aorta, Inflow, Valves, Flow (Dynamics), Computational fluid dynamics, Magnetic resonance imaging, Boundary-value problems, Fluid dynamics
Jason M Szafron, Christopher Breuer, Yadong Wang and Jay Humphrey
J Biomech Eng   doi: 10.1115/1.4037856
Continuing advances in the fabrication of scaffolds for tissue engineered vascular grafts is greatly expanding the scope of potential designs. Increasing recognition of the importance of local biomechanical cues for cell-mediated neotissue formation, neovessel growth, and subsequent remodeling is similarly influencing the design process. This study examines directly the potential effects of different combinations of key geometric and material properties of polymeric scaffolds on the initial mechanical state of an implanted graft into which cells are seeded or migrate. Toward this end, we developed a bilayered computational model that accounts for layer-specific thickness and stiffness, as well as the potential to be residually stressed during fabrication or to swell during implantation. We found that, for realistic ranges of parameter values, the circumferential stress that would be presented to seeded or infiltrating cells is typically much lower than ideal, often by an order of magnitude. Indeed, accounting for layer-specific intrinsic swelling resulting from hydrophilicity or residual stresses not relieved via annealing revealed potentially large compressive stresses, which could lead to unintended cell phenotypes and associated maladaptive growth or, in extreme cases, graft failure. Metrics of global hemodynamics were also found to be inversely related to markers of a favorable local mechanobiological environment, suggesting a tradeoff in designs that seek mechanical homeostasis at a single scale. These findings highlight the importance of the initial mechanical state in tissue engineering scaffold design and the utility of computational modeling in reducing the experimental search space for future graft development and testing.
TOPICS: Biological tissues, Design, Stress, Manufacturing, Residual stresses, Computer simulation, Annealing, Biomechanics, Materials properties, Testing, Compressive stress, Failure, Hemodynamics, Hydrophilicity, Stiffness, Tissue scaffolds, Hoop stress, Tradeoffs, Accounting
Benjamin Werbner, Minhao Zhou and Grace O'Connell
J Biomech Eng   doi: 10.1115/1.4037855
Tears in the annulus fibrosus (AF) of the intervertebral disc can result in herniation of the nucleus pulposus and progressive disc degeneration. Understanding AF failure mechanics is particularly important as research moves towards developing biological repair strategies for herniated discs. Unfortunately, failure mechanics of fiber-reinforced tissues, particularly those with fibers oriented off-axis from the applied load, is not well understood. Therefore, the objective of this study was to investigate the effectiveness of mid-length notch geometries in producing repeatable and consistent tissue failure within the gauge region of AF mechanical test specimens. Finite element models (FEMs) representing several notch geometries were created to predict the location of bulk tissue failure using a local strain-based criterion. FEM results were then validated by experimentally testing a sub-set of the modeled specimen geometries. Mechanical testing data agreed well with model predictions (~90% agreement), validating the predictive power of the model. Two of the modified dog-bone geometries ('Half' and 'Quarter') effectively ensured tissue failure at the mid-length for specimens oriented along the circumferential-axial and circumferential-radial directions. The variance of mechanical properties measured was significantly lower for notched samples that failed at the mid-length, suggesting that mid-length notch geometries result in more consistent and reliable data. In addition, the approach developed in this study provides a framework for evaluating failure properties of other fiber-reinforced tissues, such as tendons and meniscus.
TOPICS: Testing, Annulus, Failure, Biological tissues, Fibers, Disks, Finite element model, Mechanical testing, Tendons, Intervertebral discs, Bone, Gages, Maintenance, Stress, Mechanical properties
Joshua T. Green, Rena F. Hale, Jerome Hausselle and Roger V. Gonzalez
J Biomech Eng   doi: 10.1115/1.4037853
Advancements in computational musculoskeletal biomechanics are constrained by a lack of experimental measurement under real-time physiological loading conditions. This paper presents the design, configuration, capabilities, accuracy, and repeatability of The University of Texas at El Paso Joint Load Simulator (UTJLS) by testing four cadaver knee specimens with 47 real-time tests including heel and toe squat maneuvers with and without musculotendon forces. The UTJLS is a musculoskeletal simulator consisting of two robotic manipulators and eight musculotendon actuators. Sensors include eight tension load cells, two force/torque systems, nine absolute encoders, and eight incremental encoders. A custom control system determines command output for position, force, and hybrid control and collects data at 2000 Hz. Controller configuration performed forward-dynamic control for all knee degrees of freedom except knee flexion. Actuator placement and specimen potting techniques uniquely replicate muscle paths. Accuracy and repeatability standard deviations across specimen during squat simulations were equal or less than 8 N and 5 N for musculotendon actuators, 30 N and 13 N for linear ground reaction forces, and 4.4 N m and 1.9 N m for ground reaction moments. The UTJLS is the first of its design type. Controller flexibility and physical design supports axis constraint to match traditional testing rigs, absolute motion, and synchronous real-time simulation of multiplanar kinematics, ground reaction forces, and musculotendon forces. System degrees of freedom, range of motion, and speed support future testing of faster maneuvers, various joints, and kinetic chains of two connected joints.
TOPICS: Kinematics, Torque, Sensors, Control systems, Control equipment, Simulation, Stress, Degrees of freedom, Actuators, Chain, Design, Testing, Manipulators, Muscle, Tension, Physiology, Musculoskeletal soft tissue mechanics, Hybrid control, Musculoskeletal system, Knee
Costin D. Untaroiu, Wansoo Pak, Yunzhu Meng, Jeremy M. Schap, Bharath Koya and F. Scott Gayzik
J Biomech Eng   doi: 10.1115/1.4037854
Pedestrians represent one of the most vulnerable road users and comprise nearly 22% the road crash related fatalities in the world. Therefore, protection of pedestrians in car-to-pedestrian collisions (CPC) has recently generated increased attention with regulations involving three subsystem tests. The development of a finite element (FE) pedestrian model could provide a complementary component that characterizes the whole-body response of vehicle-pedestrian interactions and assesses the pedestrian injuries. The main goal of this study was to develop and to validate a simplified full body FE model corresponding to a 50th male pedestrian in standing posture (M50-PS). The FE model mesh and defined material properties are based on a 50th percentile male occupant model. The lower limb-pelvis and lumbar spine regions of the human model were validated against the post-mortem human surrogate (PMHS) test data recorded in four-point lateral knee bending tests, pelvic\abdomen\shoulder\thoracic impact tests, and lumbar spine bending tests. Then, a pedestrian-to-vehicle impact simulation was performed using the whole pedestrian model and the results were compared to corresponding PMHS tests. Overall, the simulation results showed that lower leg response is mostly within boundaries of PMHS corridors. In addition, the model shows the capability to predict the most common lower extremity injuries observed in pedestrian accidents. Generally, the validated pedestrian model may be used by safety researchers in the design of front ends of new vehicles in order to increase pedestrian protection.
TOPICS: Accidents, Finite element model, Vehicles, Roads, Wounds, Lumbar spine, Knee, Simulation results, Impact testing, Regulations, Design, Finite element analysis, Safety, Simulation, Collisions (Physics), Materials properties
Hongyan Yuan, Bahador Marzban and Kevin Kit Parker
J Biomech Eng   doi: 10.1115/1.4037795
The mechanisms underlying the spatial organization of self-assembled myofibrils in cardiac tissues remain incompletely understood. By modeling cells as elastic solids under active cytoskeletal contraction, we found a good correlation between the predicted maximal principal stress directions and the in vitro myofibril orientations in individual cardiomyocytes. This implies that actomyosin fibers tend to assemble along the maximal tensile stress directions. By considering the dynamics of focal adhesion and myofibril formation in the model, we showed that the different patterns of myofibril organizations in mature versus immature cardiomyocytes can be explained as the consequence of the different levels of force-dependent remodeling of focal adhesions. Further we applied the mechanics model to cell pairs and showed that the myofibril organizations can be regulated by a combination of multiple factors including cell shape, cell-substrate adhesions, and cell-cell adhesions. This mechanics model can guide the rational design in cardiac tissue engineering where recapitulating in vivo myofibril organizations is crucial to the contractile function of the heart.
TOPICS: Stress, Biological tissues, Design, Modeling, Self-assembly, Shapes, Tension, Tissue engineering, Dynamics (Mechanics), Solids, Adhesion, Fibers
Review Article  
Kevin D. Dorfman
J Biomech Eng   doi: 10.1115/1.4037790
The development of bright bis-intercalating dyes for DNA in the 1990s, most notably YOYO-1, revolutionized the field of polymer physics in the ensuing years. These dyes, in conjunction with modern molecular biology techniques, permit the facile observation of polymer dynamics via fluorescence microscopy, and thus direct tests of different theories of polymer dynamics. At the same time, they have played a key role in advancing an emerging next-generation method known as genome mapping in nanochannels. The effect of intercalation on the bending energy of DNA, as embodied by a change in its statistical segment length (or, alternatively, its persistence length) has been the subject of significant controversy. The precise value of the statistical segment length is critical for the proper interpretation of polymer physics experiments, and controls the phenomena underlying the aforementioned genomics technology. In this Perspective, we briefly review the model of DNA as a wormlike chain and a trio of methods (light scattering, optical or magnetic tweezers, and atomic force microscopy) that have been used to determine the statistical segment length of DNA. We then outline the disagreement in the literature over the role of bis-intercalation on the bending energy of DNA, and how a multi-scale biomechanical approach could provide an important model for this scientifically and technologically relevant problem.
TOPICS: Physics, Biomechanics, Modeling, Polymers, DNA, Dynamics (Mechanics), Fluorescence, Atomic force microscopy, Light scattering, Physics experiments, Chain, Biology, Microscopy
Technical Brief  
Allen H. Hoffman, Zhongzhao Teng, Jie Zheng, Zheyang Wu, Pamela Woodard, Kristen Billiar, Liang Wang and Dalin Tang
J Biomech Eng   doi: 10.1115/1.4037794
Introduction. Arteries can be considered as layered composite material. Experimental data on the stiffness of human atherosclerotic carotid arteries and their media and adventitia layers is very limited. This study used uniaxial tests to determine the stiffness (tangent modulus) of human carotid artery sections containing AHA type II and III lesions. Methods. Axial and circumferential oriented adventitia, media and full thickness specimens were prepared from 6 human carotid arteries (total tissue strips: 71). Each artery yielded 12 specimens with 2 specimens in each of the following 6 categories; axial full thickness, axial adventitia, axial media, circumferential full thickness, circumferential adventitia and circumferential media. Uniaxial testing was performed using Inspec 2200 controlled by software developed using LabVIEW. Results. The mean stiffness of the adventitia was 3,570±667 and 2,960±331 kPa in the axial and circumferential directions respectively, while the corresponding values for the media were 1,070±186 and 1,800±384 kPa. The adventitia was significantly stiffer than the media in both the axial (p=0.003) and circumferential (p=0.010) directions. The stiffness of the full thickness specimens was nearly identical in the axial (1,540±186) and circumferential (1,530±389 kPa) directions. The differences in axial and circumferential stiffness of media and adventitia were not statistically significant.
TOPICS: Stiffness, Atherosclerosis, Carotid arteries, Strips, Composite materials, Biological tissues, Testing, Computer software
Nicole Harper, Jason Wilken and Richard Neptune
J Biomech Eng   doi: 10.1115/1.4037791
Stair ascent is an activity of daily living and necessary for maintaining independence in community environments. One challenge to improving an individual's ability to ascend stairs is a limited understanding of how lower-limb muscles work in synergy to perform stair ascent. Through dynamic coupling muscles may perform multiple functions and require contributions from other muscles to perform a task successfully. The purpose of this study was to identify the functional roles of individual muscles during stair ascent and the mechanisms by which muscles work together to perform specific subtasks. A three-dimensional muscle-actuated simulation of stair ascent was generated to identify individual muscle contributions to the biomechanical subtasks of vertical propulsion, anteroposterior propulsion (forward propulsion and braking), mediolateral control and leg swing. The vasti and plantarflexors were the primary contributors to vertical propulsion during the first and second halves of stance, respectively, while gluteus maximus and hamstrings were the primary contributors to forward propulsion during the first and second halves of stance, respectively. The anterior and posterior components of gluteus medius were the primary contributors to medial control while vasti and hamstrings were the primary contributors to lateral control during the first and second halves of stance, respectively. To control leg swing, antagonistic muscles spanning the hip, knee and ankle joints distributed power from the leg to the remaining body segments. These results compliment previous studies analyzing stair ascent and provide further rationale for developing targeted rehabilitation strategies to address patient-specific deficits in stair ascent.
TOPICS: Stairs, Muscle, Propulsion, Biomechanics, Braking, Simulation, Knee
Nikhil Paliwal, Robert Damiano, Nicole Varble, Vincent Tutino, Zhongwang Dou, Adnan Siddiqui and Hui Meng
J Biomech Eng   doi: 10.1115/1.4037792
Computational fluid dynamics (CFD) is a promising tool to aid in clinical diagnoses of cardiovascular diseases. However, it uses assumptions that simplify the complexities of the real cardiovascular flow. Due to high-stakes in the clinical setting, it is critical to calculate the effect of these assumptions in the CFD simulation results. However, existing CFD validation approaches do not quantify error in the simulation results due to the CFD solver's modeling assumptions. Instead, they directly compare CFD simulation results against validation data. Thus, to quantify the accuracy of a CFD solver, we developed a validation methodology that calculates the CFD model error (arising from modeling assumptions). Our methodology identifies independent error sources in CFD and validation experiments, and calculates the model error by parsing out other sources of error inherent in simulation and experiments. To demonstrate the method, we simulated the flow field of a patient-specific intracranial aneurysm in the commercial CFD software STAR-CCM+. Particle image velocimetry provided validation datasets for the flow field on 2 orthogonal planes. The average model error in the STAR-CCM+ solver was 5.63%±5.49% along the intersecting validation line of the orthogonal planes. Furthermore, we demonstrated that our validation method is superior to existing validation approaches by applying 3 representative existing validation techniques to our CFD and experimental dataset, and comparing the validation results. Our validation methodology offers a streamlined workflow to extract the "true" accuracy of a CFD solver.
TOPICS: Computational fluid dynamics, Aneurysms, Biomedicine, Errors, Simulation results, Flow (Dynamics), Modeling, Cardiovascular system, Computer software, Diseases, Particulate matter, Simulation, Workflow
Derrick Ross, Stephen Howell and Maury Hull
J Biomech Eng   doi: 10.1115/1.4037632
Knowledge of A-P tibial contact locations provides an objective assessment of the relative motion of the tibia on the femur following total knee arthroplasty, which can be used to compare the effects of different components, surgical techniques, and alignment goals on knee function in vivo. Both the closest point method and the penetration method have been used to calculate A-P tibial contact locations using 3D model-to-2D image registration. Because the errors in calculating the A-P tibial contact locations using these two methods are unknown, the primary purpose of this study was to determine these errors. The A-P tibial contact locations were calculated with the two methods and simultaneously measured with a tibial force sensor in ten fresh frozen cadaveric knee specimens with a total knee arthroplasty. Single-plane radiographs of the knee specimens were taken at 0°, 30°, 60°, and 90° of flexion in neutrally, internally, and externally rotated orientations. While the radiographs were exposed, reference A-P tibial contact locations were simultaneously collected using the tibial force sensor to be compared to the calculated A-P tibial contact locations. The overall root mean squared errors (RMSEs) in the A-P tibial contact location calculated with the closest point method, the penetration method with penetration, and penetration method without penetration were 5.5 mm, 3.6 mm, and 8.9 mm, respectively. The overall RMSE was lowest for the penetration method with
TOPICS: Errors, Image registration, Knee, Arthroplasty, Force sensors, Surgery
Yunfeng Liu, Ying-ying Fan, Hui-yue Dong and Jian-xing Zhang
J Biomech Eng   doi: 10.1115/1.4037633
Background: The method used in biomechanical modeling for finite element method (FEM) analysis needs to deliver accurate results. There are currently two solutions used in FEM modeling for biomedical model of human bone from CT images: one is based on a triangular mesh, and the other is based on the parametric surface model and is more popular in practice. Materials and methods: The outline and modeling procedures for the two solutions are compared and analyzed. Using a mandibular bone as an example, several key modeling steps are then discussed in detail, and the FEM calculation was conducted. Results: Numerical calculation results based on the models derived from the two methods, including stress, strain, and displacement, are compared and evaluated in relation to accuracy and validity. Moreover, a comprehensive comparison of the two solutions is listed. Conclusions: The parametric surface based method is more helpful when using powerful design tools in CAD software, but the triangular mesh based method is more robust and efficient.
TOPICS: Simulation, Biomechanics, Finite element analysis, Modeling, Bone, Finite element methods, Stress, Computer software, Displacement, Biomedicine, Computer-aided design, Design
Karthik Somasundaram, Anil Kalra, Don Sherman, Paul Begeman, King H. Yang and John M Cavanaugh
J Biomech Eng   doi: 10.1115/1.4037591
Anthropometric test devices (ATDs) such as Hybrid III dummy have been widely used in automotive crash tests to evaluate the risks of injury at different body regions. In recent years, researchers have started using automotive ATDs to study the high-speed vertical loading response caused by underbelly blast (UBB) impacts. This study analyzed the Hybrid III dummy responses to short-duration large magnitude vertical acceleration in a laboratory setup. Two unique test conditions were investigated using a horizontal sled system to simulate the UBB loading conditions. The biomechanical response in terms of the pelvis acceleration, chest acceleration, lumbar spine force, head accelerations and neck forces were measured. Subsequently, a series of finite element analyses (FEA) were performed to simulate the physical tests. The correlation between the Hybrid III test and numerical model was evaluated using the CORA version 3.6.1. The score for WSU FE model was 0.878 and 0.790 for loading condition 1 and 2, respectively in which 1.0 indicated a perfect correlation between the experiment and simulation response. With repetitive vertical impacts, the Hybrid III dummy pelvis showed a significant increase in the peak acceleration accompanied by rupture of the pelvis foam and flesh. The revised WSU Hybrid III model indicated high stress concentrations at the same location, providing a possible explanation for the material failure in actual Hybrid III tests.
TOPICS: Computer simulation, Simulation, Stress, Biomechanics, Finite element analysis, Failure, Finite element model, Traffic accidents, Rupture, Wounds, Lumbar spine

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