Accepted Manuscripts

Technical Brief  
Keyvan Amini Khoiy, Anup Pant and Rouzbeh Amini
J Biomech Eng   doi: 10.1115/1.4040126
The tricuspid valve is a one-way valve on the pulmonary side of the heart, which prevents backflow of blood during ventricular contractions. Development of computational models of the tricuspid valve is important both in understanding the normal valvular function and in the development/improvement of surgical procedures and medical devices. A key step in the development of such models is quantification of the mechanical properties of the tricuspid valve leaflets. In this study, after examining previously measured five-loading-protocol biaxial stress-strain response of porcine tricuspid valves, a phenomenological constitutive framework was chosen to represent this response. The material constants were quantified for all three leaflets, which were shown to be highly anisotropic with average anisotropy indices of less than 0.5 (an anisotropy index value of 1 indicates a perfectly isotropic response, whereas a smaller value of the anisotropy index indicates an anisotropic response). To obtain mean values of material constants, stress-strain responses of the leaflet samples were averaged and then fitted to the constitutive model (average R^2 over 0.9). Since the sample thicknesses were not hugely different, averaging the data using the same tension levels and stress levels produced similar average material constants for each leaflet.
TOPICS: Simulation, Constitutive equations, Valves, Anisotropy, Stress, Mechanical properties, Blood, Tension, Medical devices, Surgery
Technical Brief  
Jacob Reeves, Nikolas Knowles, George S Athwal and James A. Johnson
J Biomech Eng   doi: 10.1115/1.4040122
Quantitative computed tomography (qCT) relies on calibrated bone mineral density data. If a calibration phantom is absent from the CT scan, post-hoc calibration becomes necessary. Scanning a calibration phantom after-the-fact and applying that calibration to uncalibrated scans has been used previously. Alternatively, density varies with CT settings; suggesting that it may be possible to predict the calibration terms using CT settings. This study compares a novel CT setting regression method for post-hoc calibration to standard and post-hoc phantom-only calibrations. Five cadaveric upper limbs were scanned at 11 combinations of peak tube voltage and current (80-140kV and 100-300mA) with two calibration phantoms. Density calibrations were performed for the cadaver scans, and scans of the phantoms alone. Stepwise linear regression determined if the calibration equation terms were predictable using peak tube voltage and current. Peak tube voltage, but not current, was significantly correlated with regression calibration terms. Calibration equation slope was significantly related to the type of phantom (p < 0.001), calibration method (p = 0.026), and peak tube voltage (p < 0.001), but not current (p = 1.000). The calibration equation vertical intercept was significantly related to the type of phantom (p < 0.001), and peak tube voltage (p = 0.006), but not calibration method (p = 0.682), or current (p = 0.822). Accordingly, regression can correlate peak tube voltage with density calibration terms. Suggesting that, while standard qCT calibration is preferable, regression calibration may be an acceptable post-hoc method when necessary.
TOPICS: Density, Bone, Calibration, Phantoms, Computerized tomography, Minerals
Ryan J. Pewowaruk, Jennifer Philip, Shivendra Tewari, Claire Chen, Mark Nyaeme, Zhijie Wang, Diana Tabima, Anthony Baker, Daniel Beard and Naomi Chesler
J Biomech Eng   doi: 10.1115/1.4040044
Right ventricular (RV) failure, which occurs in the setting of pressure overload, i.e. pulmonary hypertension (PH), is characterized by abnormalities in myofilament mechanics and energetic state. The effects of these cell level changes on organ level RV function are unknown. The primary aim of this study was to quantify the effects of metabolite concentrations as well as active and passive cardiac tissue mechanics on RV function using a multiscale model of the cardiovascular system. The model integrates metabolic environment, actin-myosin cross bridging, intracellular myofilament mechanics and extracellular tissue mechanics in a mechanistically realistic heart model coupled with a simple lumped parameter circulation. Three models of PH were simulated and compared to experiment. The model was able to capture a wide range of cardiovascular physiology and pathophysiology, from mild RV dysfunction to severe RV failure, as well as elevated RV afterload secondary to LV disease. Simulations predict that in response to pressure overload alone, the RV is able to maintain cardiac output and that alterations in RV active myofilament mechanics or RV energetic state are necessary to decrease cardiac output.
TOPICS: Pressure, Simulation, Biological tissues, Engineering simulation, Cardiovascular system, Diseases, Failure, Physiology
Megan L Bland, Craig McNally and Steven Rowson
J Biomech Eng   doi: 10.1115/1.4040019
Cycling is a leading cause of sport-related head injuries in the U.S. Although bicycle helmets must comply with standards limiting head acceleration in severe impacts, helmets are not evaluated under more common, concussive-level impacts, and limited data are available indicating which helmets offer superior protection. Further, standards evaluate normal impacts, while real-world cyclist head impacts are oblique - involving normal and tangential velocities. The objective of this study was to investigate differences in protective capabilities of ten helmet models under common real-world accident conditions. Oblique impacts were evaluated through drop tests onto an angled anvil at common cyclist head impact velocities and locations. Linear and rotational accelerations were evaluated and related to concussion risk, which was then correlated with design parameters. Significant differences were observed in linear and rotational accelerations between models, producing concussion risks spanning >50% within single impact configurations. Risk differences were more attributable to linear acceleration, as rotational varied less between models. At the temporal location, shell thickness, vent configuration, and radius of curvature were found to influence helmet effective stiffness. This should be optimized to reduce impact kinematics. At the frontal, helmet rim location, liner thickness tapered off for some helmets, likely due to lack of standards testing at this location. This is a frequently impacted location for cyclists, suggesting that the standards testable area should be expanded to include the rim. These results can inform manufacturers, standards bodies, and consumers alike, aiding the development of improved bicycle helmet safety.
TOPICS: Bicycles, Risk, Shells, Sports, Stiffness, Vents, Wounds, Kinematics, Safety, Accidents, Design, Testing
Carmen Ridao-Fernández, Joaquin Ojeda and Gema Chamorro-Moriana
J Biomech Eng   doi: 10.1115/1.4040020
The main objective was to analyze the changes in the spatial and temporal step parameters during a dual-task: walking with a forearm crutch to partially unload the body weight of the subject. The secondary objective was to determine the influence of the use of the crutch with the dominant or non-dominant hand in the essential gait parameters. Seven healthy subjects performed gait without crutches (GWC) and unilateral assisted gait (UAG) with the crutch carried out by dominant hand (DC) and non-dominant hand (NDC). Gait was recorded using a Vicon System; the GCH System 2.0 and the GCH Control Software 1.0 controlled the loads. The variables were: step length, step period, velocity, step width and step angle. The Wilcoxon signed-rank test compared GWC and UAG while also analyzing the parameters measured for both legs with DC and NDC in general and in each subject. Wilcoxon test only found significant differences in 1 of the 15 general comparisons between both legs. In the analysis by subject, step length, step period and velocity showed significant differences between GWC and UAG. These parameters obtained less differences in DC. The effect of a forearm crutch on UAG caused a reduction in step length and velocity, and an increase in step period. However, it did not entail changes in step angle and step width. UAG was more effective when the dominant hand carried the crutch. The unloading of 10% body weight produced an assisted gait which closely matched GWC.
TOPICS: Weight (Mass), Stress, Computer software
Sonia Kartha, Ben Bulka, Nick S. Stiansen, Harrison Troche and Beth A. Winkelstein
J Biomech Eng   doi: 10.1115/1.4040023
Although repetitive loading of ligamentous and joint tissues even within physiologic ranges of motion has been implicated in the development of pain and joint instability, the injury mechanisms are not well-known. A single facet joint distraction at magnitudes simulating physiologic strains is insufficient to induce pain; yet, it is hypothesized that repeated loading at physiologic strains may cause pain via altered biomechanical responses in the facet capsular ligament. This study evaluated if repeated loading of the facet at physiologic nonpainful strains alters the capsular ligament’s mechanical response and induces pain. Male rats underwent either two nonpainful facet joint distractions or sham surgeries each separated by two days. Pain was measured before the procedure and for 7 days; capsular mechanics were measured during each distraction and under tissue failure. Spinal glial activation was also assessed to probe potential pathophysiologic mechanisms responsible for pain. Capsular displacement significantly increased (p=0.019) and capsular stiffness decreased (p=0.008) during the second distraction compared to the first. Pain was induced after the second distraction and was sustained at day 7 (p<0.048). Repeated loading weakened the capsular ligament with, lower vertebral displacement (p=0.041) and peak force (p=0.014) at tissue rupture. Spinal glial activation was also induced after repeated loading. Together, these mechanical, physiological and neurological findings demonstrate repeated loading of the facet joint even within physiologic ranges of motion can induce pain, spinal inflammation and alter capsular mechanics similar to a more injurious loading exposure.
TOPICS: Biomechanics, Biological tissues, Surgery, Displacement, Failure, Probes, Rupture, Stiffness, Physiology, Injury mechanisms, Nervous system
Calvin Kuo, Jake A. Sganga, Michael G. Fanton and David Camarillo
J Biomech Eng   doi: 10.1115/1.4039987
Wearable sensors embedded with inertial measurement units have become commonplace for the measurement of head impact biomechanics, but individual systems often suffer from a lack of measurement fidelity. While some researchers have focused on developing highly accurate, single sensor systems, we have taken a parallel approach in investigating optimal estimation techniques with multiple noisy sensors. In this work, we present a novel sensor network methodology that utilizes multiple skin patch sensors arranged on the head, and combines their data to obtain a more accurate estimate than any individual sensor in the network. Our methodology visually localizes subject-specific sensor transformations, and based on rigid body assumptions, applies estimation algorithms to obtain a minimum mean squared error estimate. During mild soccer headers, individual skin patch sensors had over 100% error in peak angular velocity magnitude, angular acceleration magnitude, and linear acceleration magnitude. However, when properly networked using our visual localization and estimation methodology, we obtained kinematic estimates with median errors below 20%. While we demonstrate this methodology with skin patch sensors in mild soccer head impacts, the formulation can be generally applied to any dynamic scenario, such as measurement of cadaver head impact dynamics using arbitrarily placed sensors.
TOPICS: Measurement units and standards, Kinematics, Sensors, Errors, Skin, Sensor networks, Dynamics (Mechanics), Biomechanics, Algorithms
Raghu N. Natarajan, Kei Watanabe and Kazuhiro Hasegawa
J Biomech Eng   doi: 10.1115/1.4039989
Purpose. Examine the biomechanical effect of material properties, geometric variables and anchoring arrangements in a segmental pedicle screw with connecting rods spanning the entire lumbar spine using finite element models. This will help (1) to determine the variables with the greatest effect on spine kinematics and stresses in instrumentation, (2) to compare the multi-directional stability of the spinal instrumentation and (3) to determine less-rigid fixation systems that may reduce adjacent segment disc disease. Methods. A lumbar spine finite element model was used to analyze the biomechanical effects of different materials used for spinal rods (TNTZ or Ti or CoCr), varying diameters of the screws and rods (5 mm and 6 mm), and different fixation techniques (multi-level or intermittent). Results. The results based on the range of motion and stress distribution in the rods and screws revealed that differences in properties and variations in geometry of the screw-rod moderately affect the biomechanics of the spine. Further the spinal screw-rod system was least stable under the lateral bending mode. Stress analyses of the screws and rods revealed that the caudal section of the posterior spinal instrumentation was more susceptible to fatigue failure. Although CoCr screws and rods provided the greatest spinal stabilization, these constructs were susceptible to fatigue failure. Conclusion. The findings of the present study suggest that a posterior instrumentation system with a 5-mm screw-rod diameter made of Ti or TNTZ is advantageous over CoCr instrumentation system.
TOPICS: Biomechanics, Finite element model, Lumbar spine, Screws, Rods, Instrumentation, Fatigue failure, Spinal pedicle screws, Spine mechanics, Disks, Diseases, Geometry, Stress, Kinematics, Stability, Stress analysis (Engineering), Stress concentration, Materials properties
Technical Brief  
Stephen A. Schwaner, Alison M. Kight, Robert N. Perry, Marta Pazos, Hongli Yang, Elaine C. Johnson, John C. Morrison, Claude F. Burgoyne and C. Ross Ethier
J Biomech Eng   doi: 10.1115/1.4039998
Glaucoma is the leading cause of irreversible blindness and involves the death of retinal ganglion cells (RGCs). Although biomechanics likely contributes to axonal injury within the optic nerve head (ONH), leading to RGC death, the pathways by which this occurs are not well understood. While rat models of glaucoma are well-suited for mechanistic studies, the anatomy of the rat ONH is different from the human, and the resulting differences in biomechanics have not been characterized. The aim of this study is to describe a methodology for building individual-specific finite element (FE) models of rat optic nerve heads. This method was used to build three rat ONH FE models and compute the biomechanical environment within these ONHs. Initial results show that rat ONH strains are larger and more asymmetric than those seen in human ONH modeling studies. This method provides a framework for building additional models of normotensive and glaucomatous rat ONHs. Comparing model strain patterns with patterns of cellular response seen in studies using rat glaucoma models will help us to learn more about the link between biomechanics and glaucomatous cell death, which in turn may drive development of novel therapies for glaucoma.
TOPICS: Modeling, Biomechanics, Finite element analysis, Finite element model, Patient treatment, Wounds, Anatomy
Eoin McEvoy, Gerhard A. Holzapfel and Patrick McGarry
J Biomech Eng   doi: 10.1115/1.4039947
While the anisotropic behaviour of the complex composite myocardial tissue has been well characterized in recent years, the compressibility of the tissue has not been rigorously investigated to date. In the first part of this study we present experimental evidence that passive excised porcine myocardium exhibits volume change. Under tensile loading of a cylindrical specimen, a volume change of 4.1±1.95% is observed at a peak stretch of 1.3. Confined compression experiments also demonstrate significant volume change in the tissue (loading applied up to a volumetric strain of 10%). In order to simulate the multi-axial passive behaviour of the myocardium a nonlinear volumetric hyperelastic component is combined with the well-established Holzapfel-Ogden anisotropic hyperelastic component for myocardium fibres. This framework is shown to describe the experimentally observed behaviour of porcine and human tissues under shear and biaxial loading conditions. In the second part of the study a representative volumetric element (RVE) of myocardium tissue is constructed to parse the contribution of the tissue vasculature to observed volume change under confined compression loading. Simulations of the myocardium microstructure suggest that the vasculature cannot fully account for the experimentally measured volume change. Additionally, the RVE is subjected to six modes of shear loading to investigate the influence of micro-scale fibre alignment and dispersion on tissue-scale mechanical behaviour.
TOPICS: Compressibility, Anisotropy, Modeling, Experimental analysis, Myocardium, Biological tissues, Fibers, Compression, Shear (Mechanics), Simulation, Composite materials, Engineering simulation, Mechanical behavior, Microscale devices
Hamza Atcha, Chase Davis, Nicholas R Sullivan, Tim D. Smith, Sara Anis, Waleed Z. Dahbour, Zachery R Robinson, Anna Grosberg and Wendy Liu
J Biomech Eng   doi: 10.1115/1.4039949
Mechanical cues play a critical role in regulating the behavior of many cell types, particularly those that experience substantial mechanical stress within tissues. Devices that impart mechanical stimulation to cells in vitro have been instrumental in helping to develop a better understanding of how cells respond to mechanical forces. However, these devices often have constraints, such as cost and limited functional capabilities, that restrict their use in research or educational environments. Here, we describe a low-cost method to fabricate a uniaxial cell stretcher that would enable widespread use, and facilitate engineering design and mechanobiology education for undergraduate students. The device is capable of producing consistent and reliable strain profiles through the use of a servo motor, gear, and gear rack system. The servo motor can be programmed to output various waveforms at specific frequencies and stretch amplitudes by controlling the degree of rotation, speed, and acceleration of the servo gear. Furthermore, the stretchable membranes are easy to fabricate and can be customized, allowing for greater flexibility in culture well size. We used the custom-built stretching device to uniaxially strain macrophages and cardiomyocytes, and found that both cell types displayed functional and cell shape changes that were consistent with previous studies using commercially available systems. Overall, this uniaxial cell stretcher provides a more cost-effective alternative to study the effects of mechanical stretch on cells, and can therefore be widely used in research and educational environments to broaden the study and pedagogy of cell mechanobiology.
TOPICS: Rotation, Servomechanisms, Stress, Servomotors, Engineering design, Biological tissues, Gears, Membranes, Shapes, Education, Undergraduate students
Dan Tudor Zaharie and Andrew Phillips
J Biomech Eng   doi: 10.1115/1.4039894
The pelvic construct is an important part of the body as it facilitates the transfer of upper body weight to the lower limb and protects a number of organs and vessels in the lower abdomen. In addition, the importance of the pelvis is highlighted by the large mortality rates associated with pelvic trauma. Although computational models of the pelvis have been used to assess its structure or behaviour under loading, no attempt has been made to develop a model using a structural mechanics approach as opposed to a continuum mechanics approach. This study presents a mesoscale structural model of the pelvic construct and the joints and ligaments associated with it. Shell elements were used to model cortical bone, while truss elements were used to model trabecular bone and the ligaments and joints. The finite element model was subjected to an iterative optimisation process based on a strain driven bone adaptation algorithm. The bone model was adapted to a number of common daily living activities (walking, stair ascent, stair descent, sit-to-stand and stand-to-sit) by applying onto it both joint and muscle loads derived using a musculoskeletal modelling framework. The cortical thickness distribution and trabecular architecture of the adapted model were compared qualitatively with computed tomography scans and models developed in previous studies showing good agreement. The developed structural model enables a number of applications such as fracture modelling, design and additive manufacturing of frangible surrogates.
TOPICS: Weight (Mass), Stairs, Structural analysis, Stress, Trusses (Building), Continuum mechanics, Fracture (Materials), Algorithms, Bone, Design, Fracture (Process), Modeling, Optimization, Structural mechanics, Computerized tomography, Finite element model, Muscle, Shells, Vessels, Additive manufacturing, Musculoskeletal system
Ziwen Fang, Allison N Ranslow, Patricia De Tomas, Allan Gunnarsson, Tusit Weerasooriya, Sikhanda Satapathy, Kimberly A. Thompson and Reuben Kraft
J Biomech Eng   doi: 10.1115/1.4039895
The development of a multiaxial failure criterion for trabecular skull bone has many clinical and biological implications. This failure criterion would allow for modeling of bone under daily loading scenarios that typically are multiaxial in nature. Some yield criteria have been developed to evaluate the failure of trabecular bone, but there is a little consensus among them. To help gain deeper understanding of multiaxial failure response of trabecular skull bone, we developed 30 microstructural finite element models of porous porcine skull bone and subjected them to multiaxial displacement loading simulations that spanned three-dimensional stress and strain space. High-resolution micro-computed tomography (microCT) scans of porcine trabecular bone were obtained and used to develop the meshes used for finite element simulations. In total, 376 unique multiaxial loading cases were simulated for each of the 30 microstructure models. Then, results from the total of 11,280 simulations were used to develop three-dimensional yield surfaces in strain space. The resulting yield surfaces capture both the geometric and material nonlinearities in the response that are characteristic of porous trabecular bone. From this study, we characterized the overall response of the microstructural failure response with an equation for a parallelepiped that describes the multiaxial failure behavior of porcine trabecular skull bone very well.
TOPICS: Bone, Engineering simulation, Simulation, Failure, Finite element model, Stress, Resolution (Optics), Finite element analysis, Modeling, Displacement
Craig J. Goergen and Corey P. Neu
J Biomech Eng   doi: 10.1115/1.4039879
TOPICS: Engineering education
C.P.L. Paul, Kaj S. Emanuel, Idsart Kingma, Albert J. van der Veen, Roderick M. Holewijn, Pieter-Paul A. Vergroesen, Peter M. van de Ven, Margriet G. Mullender, Marco N. Helder and Theodoor H. Smit
J Biomech Eng   doi: 10.1115/1.4039890
Intervertebral disc (IVD) degeneration is described by loss of height and hydration. However, in the first stage of IVD degeneration this loss has not yet occurred. In the current study, we use an ex vivo degeneration model to quantify changes in the IVDs mechanical behavior. We assess whether these changes, characterized by stretched-exponential fitting, qualify as markers for early degeneration. Enzymatic degeneration of healthy lumbar caprine IVDs was induced by injecting 100uL of Chondroïtinase ABC (Cabc) into the nucleus. A no-intervention and PBS injected group were used as controls. IVDs were cultured in a bioreactor for 20 days under diurnal, simulated-physiological loading conditions. Disc deformation was continuously monitored. Changes in disc height recovery behavior were quantified using stretched-exponential fitting. Disc height, histological sections and water- and GAG-content measurements were used as gold standards for the degenerative state. Cabc injection caused significant GAG loss from the nucleus and had detrimental effects on poro-elastic mechanical properties of the IVDs. These were progressive over time, with a propensity towards more linear recovery behavior. On histological sections, both PBS en Cabc injected IVDs showed moderate degeneration. A small GAG loss yields significant changes in IVD recovery behavior, which were quantified with stretched-exponential fit parameters. Studies on early disc degeneration and biomaterial engineering for DDD could benefit from focusing on IVD biomechanical behavior rather than height, as marker for early disc degeneration.
TOPICS: Mechanical behavior, Intervertebral discs, Disks, Fittings, Water, Physiology, Bioreactors, Deformation, Biomaterials, Biomechanics, Mechanical properties
Rami M A Al-Dirini, Dermot O'Rourke, Daniel Huff, Saulo Martelli and Mark Taylor
J Biomech Eng   doi: 10.1115/1.4039824
Successful designs of total hip replacement (THR) need to be robust to surgical variation in sizing and positioning of the femoral stem. This study presents an automated method for comprehensive evaluation of the potential impact of surgical variability in sizing and positioning on the primary stability of a contemporary cementless femoral stem (Corail®, Depuy Synthes). A patient-specific finite element (FE) model of a femur was generated from computed-tomography (CT) images from a female donor. An automated algorithm was developed to span the plausible surgical envelope of implant positions constrained by the inner cortical boundary. The analysis was performed on four stem sizes: oversized, ideal (nominal) size and undersized by up to two stem sizes. For each size, Latin Hypercube sampling was used to generate models for 100 unique alignment scenarios. For each scenario, peak hip contact and muscle forces published for stair climbing were scaled to the donor's body weight and applied to the model. The risk of implant loosening was assessed by comparing the bone-implant micromotion/strains to thresholds (150µm and 7000µe) above which fibrous tissue is expected to prevail and the peri-prosthetic bone to yield, respectively. The risk of long-term loosening due to adverse bone resorption was assessed using bone adaptation theory. The range of implant positions generated effectively spanned the available intra-cortical space. The Corail® stem was found stable and robust to changes in size and position, with the majority of the bone-implant interface ...
TOPICS: Biomechanics, Surgery, Robustness, Bone, Risk, Finite element analysis, Hip joint prostheses, Artificial limbs, Computerized tomography, Muscle, Algorithms, Biological tissues, Weight (Mass), Stability, Stairs
Pedro Garcia Carrascal, Javier Garcia, Jose Sierra Pallares, Francisco Castro Ruiz and Fernando Manuel Martín
J Biomech Eng   doi: 10.1115/1.4039676
In-stent restenosis ails many patients who have undergone stenting. When the stented artery is a bifurcation, the intervention is especially critical because of the complex stent geometry involved in these structures. Computational Fluid Dynamics (CFD) has demonstrated to be an effective approach when modelling blood flow behavior and understanding the mechanisms that underlie in-stent restenosis. These CFD models, however, require validation through experimental data in order to be reliable. It is with this purpose in mind that we performed Particle Image Velocimetry (PIV) measurements of velocity fields within flows through a simplified coronary bifurcation. Although the flow in this simplified bifurcation differs from the actual blood flow, it emulates the main fluid dynamic mechanisms found in hemodynamic flow. Experimental measurements for several stenting techniques under steady and unsteady flow conditions were performed. The test conditions were highly controlled and uncertainty was accurately predicted. The results obtained in this research consist of readily accessible, easy to emulate, detailed velocity fields and geometry. These results have been successfully used to validate our numerical model. This data can be used as a benchmark for further development of numerical CFD modelling through comparison of the main characteristics of the flow pattern.
TOPICS: Flow (Dynamics), Computer simulation, Bifurcation, Computational fluid dynamics, stents, Geometry, Modeling, Blood flow, Uncertainty, Fluids, Particulate matter, Hemodynamics, Unsteady flow
Review Article  
Andrea Acuna, Alycia Berman, Frederick Damen, Brett Myers, Amelia Adelsperger, Kelsey Bayer, Melissa Brindise, Brittani L Bungart, Alexander M Kiel, Rachel Morrison, Joseph Muskat, Kelsey Wasilczuk, Yi Wen, Jiacheng Zhang, Patrick Zito and Craig Goergen
J Biomech Eng   doi: 10.1115/1.4039678
Recent applications of Computational Fluid Dynamics (CFD) applied to the cardiovascular system have demonstrated its power in investigating the impact of hemodynamics on disease initiation, progression, and treatment outcomes. Flow metrics such as pressure distributions, wall shear stresses, and blood velocity profiles can be quantified to provide insight into observed pathologies, assist with surgical planning, or even predict disease progression. While numerous studies have performed simulations on clinical human patient data, it often lacks pre-diagnosis information and can be subject to large inter-subject variability, limiting the generalizability of findings. Thus, animal models are often used to identify and manipulate specific factors contributing to vascular disease because they provide a more controlled environment. In this review, we explore the use of CFD in animal models in recent studies to investigate the initiating mechanisms, progression, and intervention effects of various vascular diseases. The first section provides a brief overview of the CFD theory and tools that are commonly used to study blood flow. The following sections are separated by anatomical region, with the abdominal, thoracic, and cerebral areas specifically highlighted. We discuss the associated benefits and obstacles to performing CFD modeling in each location. Lastly, we highlight animal CFD studies focusing on common surgical treatments, including arteriovenous fistulas and pulmonary artery grafts. The studies included in this review demonstrate the value of combining CFD with animal imaging and should encourage further research to optimize and expand upon these techniques for the study of vascular disease.
TOPICS: Computational fluid dynamics, Diseases, Surgery, Cardiovascular system, Hemodynamics, Imaging, Blood flow, Pulmonary artery, Shear stress, Engineering simulation, Modeling, Performance, Pressure, Flow (Dynamics), Simulation, Blood
Technical Brief  
Nachiket M. kharalkar, Steven C. Bauserman and Jonathan W. Valvano
J Biomech Eng   doi: 10.1115/1.4026559
Effect of formalin fixation on thermal conductivity of the biological tissues is presented. A self-heated thermistor probe was used to measure the tissue thermal conductivity. The thermal conductivity of muscle and fatty tissue samples was measured before the formalin fixation and then 27 hours after formalin fixation. The results indicate that the formalin fixation does not cause a significant change in the tissue thermal conductivity of muscle and fatty tissues. In the clinical setting, tissues removed surgically are often fixed in formalin for subsequent pathological analysis. These results suggest that, in terms of thermal properties, it is equally appropriate to perform in vitro studies in either fresh tissue or formalin-fixed tissue.
TOPICS: Thermal conductivity, Biological tissues, Muscle, Probes, Surgery, Thermal properties

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