bluuebunny/crossref_metadata_2025 huggingface dataset:
A Three Degree of Freedom Lumped Parameter Model of Whole Body Vibration Along the Spine in the Rat
Authors: Jaumard Nicolas V. , Baig Hassam A. , Guarino Benjamin B. , Winkelstein Beth A.
Published: January 2014

Whole body vibration (WBV) can induce a host of pathologies, including muscle fatigue and neck and low back pain [1,2]. A new model of WBV in the rat has been developed to define relationships between WBV exposures, kinematics, and behavioral sensitivity (i.e. pain) [3]. Although in vivo studies provide valuable associations between biomechanics and physiology, they are not able to fully define the mechanical loading of specific spinal regions and/or the tissues that may undergo injurious loading or deformation. Mathematical models of seated humans and primates have been used to estimate spinal loads and design measures that mitigate them during WBV [4–6]. Although such models provide estimates of relative spinal motions, they have limited utility for relating potentially pathological effects of vibration-induced kinematics and kinetics since those models do not enable simultaneous evaluation of relevant spinal tissues with the potential for injury and pain generation. As such, the goal of this work was to develop and validate a three degree of freedom (3DOF) lumped-parameter model of the prone rat undergoing WBV directed along the long-axis of the spine. The model was constructed with dimensions of a generalized rat and model parameters optimized using kinematics over a range of frequencies. It was validated by comparing predicted and measured transmissibility and further used to predict spinal extension and compression, as well as acceleration, during WBV for frequencies known to produce resonance in the seated human and pain in the rat [3,7].
Generation of Grade Specific Finite Element Model of Lumbar Spines
Authors: Natarajan Raghu N. , Gorasia Jigar , Andersson Gunnar
Published: January 2014

The anatomy and biomechanics of the intervertebral motion segments is complex, and the development of degenerative motion segment disorders, which occur frequently, is poorly understood. When disc degeneration occurs at one level, whether treated or not, degeneration frequently develops at mobile segments above or below the degenerated or treated segments. After surgical treatment the process is referred to adjacent segment disc disease (ASDD), and the condition clinically called transition syndrome. We do not know at this time if the ASDD is caused by the neighboring degenerated disc or if they represent the natural progression of the lumbar degenerative processes. The development of ASDD is clinically problematic because it can cause pain and necessitate further surgical intervention. The development and severity of ASDD in disc degeneration is broadly believed to depend on a number of variables such as the severity of degeneration, the number of levels that are degenerated and the location of the degenerative disc. Thus it is important to understand how ASDD develops and progresses and how different variables that cause ASDD compare with reference to normal disc biomechanics. It is proposed to address this clinically relevant problem using poroelastic finite element models.
Finite Element Predictions of Cartilage Contact Mechanics in Hips With Retroverted Acetabula
Authors: Henak Corinne R. , Carruth Eric D. , Anderson Andrew E. , Harris Michael D. , Ellis Benjamin J. , Peters Christopher L. , Weiss Jeffrey A.
Published: January 2014

Acetabular retroversion, defined by the crossover sign (COS) on plain film radiographs, (Figure 1) is thought to cause early onset osteoarthritis (OA). When the COS is present, the anterior acetabular rim is lateral to the posterior acetabular rim proximally. As the rim progresses distally, the posterior rim crosses lateral to the anterior rim, creating the COS. Clinical studies have demonstrated that hips with OA have a higher incidence of acetabular retroversion than normal hips [1–3]. There are two possible mechanical links between acetabular retroversion and OA. First, decreased area in the posterior acetabulum may cause abnormally high cartilage contact stresses in the posterior acetabulum during activities of daily living. Alternatively, pincer femoroacetabular impingement may cause posterior damage via posterior subluxation [4–6]. Although clinical studies suggest that retroverted hips have altered cartilage mechanics, cartilage mechanics cannot be measured in-vivo. However, finite element (FE) modeling can be used to predict mechanics, and thereby identify possible mechanical mechanisms of OA development in patient populations. Therefore, the objective of this study was to compare cartilage contact mechanics between normal hips and hips with acetabular retroversion using a validated approach to subject-specific FE modeling [7].
Obstetrician Hand Pressures During Mock Deliveries
Authors: Schwartz Cynthia , Kieweg Sarah , Weiner Carl , Wilson Sara E.
Published: January 2014

During the delivery of a fetus, an obstetrician assists by applying gentle axial downward traction on the head until the shoulders clear the pubic bone followed by catching and supporting the delivered infant body. If the shoulders become lodged behind the maternal pelvis (shoulder dystocia), the physician may be required to perform additional maneuvers to free the shoulders (1,2). Of significant concern is the potential for injury of the fetus during this process. It is believed that hyperextension, misalignment of forces on the head, or excessive applied forces can result in injuries to the brachial plexus nerves running through the neck and shoulder resulting in temporary or permanent Erb’s of Klumpke’s palsies for the infant. It is important to recognize there are delivery forces that originate with uterine contractions and maternal val salvo. To better understand the forces exerted during delivery in order to prevent these injuries, our long-term research goal is to create a tool that can accurately quantify these forces to improve understanding of them and to create training tools for medical trainees. The research goal of this project was to examine what hand pressures are typical during this traction phase in a normal delivery and where they are applied on the hand of the obstetrician. A secondary research question was whether there are any differences between fully trained obstetricians and residents in these pressures.
Effects of Media Stirring and Presence of Nutrient Channels on Functional Properties of Large Engineered Cartilage Constructs
Authors: Cigan Alexander D. , Nims Robert J. , Albro Michael B. , Hung Clark T. , Ateshian Gerard A.
Published: January 2014

Cartilage tissue engineering is a promising approach for the replacement of degraded joint cartilage in osteoarthritis (OA) patients. Current strategies employ smaller constructs (∼20 mm 2), however OA generally does not become symptomatic until defects reach ≥ 5 cm 2. Therefore, small constructs may not ultimately be clinically relevant for treatment of OA. Attempts to scale up construct size are met with challenges, as inhomogeneous properties develop as a result of poor nutrient availability at the construct center due to cellular consumption at the periphery [1]. Previously, the incorporation of ∅1 mm nutrient channels in large (∅10 mm) constructs was found to improve Young’s modulus (E Y) and glycosaminoglycan (GAG) content and reproduce their native values [2]. Rotational mixing has been shown to improve properties of micro-channeled constructs [3]. As a major goal of our research is to optimize channel size and arrangement to improve the quality of large engineered cartilage constructs, it is essential to develop a simple but effective method for convecting media through channeled constructs. Therefore, this study seeks to compare the functional properties of large constructs that are subjected to different types of media stirring, by rocking or orbital motion, and to determine whether either of these conditions favors the quality of constructs with nutrient channels.
Effect of Vascular Convexity on Diffusive Delivery of Blood-Borne Substances in Normal and Tumor Tissues
Authors: Baish James
Published: January 2014

Blood-borne substances such as oxygen, nutrients, drugs and particles arrive at targeted tissues through a multi-step process that begins with convection along the blood vessels and then movement from the blood vessels to the surrounding tissues by convection through the cellular interstices or molecular diffusion. Interstitial convection may be important in the margins of tumors where highly permeable blood vessels encounter high transmural pressures, but otherwise, transport from the blood vessels to the tissues progresses primarily by diffusion.
Air Muscle Powered Ankle Foot Orthotic
Authors: Couper Nathan , Day Robert , Renahan Patrick , Streeter Patrick , DeBartolo Elizabeth
Published: January 2014

Foot drop, a disorder that affects millions of people worldwide, is a broad term used to describe a neurological or muscular-skeletal condition that restricts an individual’s ability to dorsiflex — raise — their foot about the ankle joint. Common causes of foot drop are stroke, ALS (Lou Gehrig’s disease), MS, and injury. Unassisted, an individual with foot drop will have difficulty walking as the affected foot easily catches on obstacles. Foot drop causes clients to drag their toes on each step, greatly increasing the risk of a trip or fall.
A Novel Bio-Microelectromechanical System for In Vivo Diagnostic Monitoring of Fracture Healing
Authors: McGilvray Kirk , Demir Hilmi Volkan , Unal Emre , Puttlitz Christian
Published: January 2014

The ability to detect a normal from aberrant bone healing cascade during the acute fracture fixation period (1–3 weeks post trauma) is critically important to insure a favorable clinical outcome for many complex fracture cases. Radiographic evaluations do not have the inherent fidelity to make qualitative predictions during the acute healing phase. Early detection of an atypical healing profile would allow for revision strategies to be employed without the need for expensive and undesirable follow-up surgeries. In an effort to address the critical need to diagnose the course of bone fracture healing in the vitally important early healing phase, our research group has developed a radio frequency (RF) strain sensor that takes advantages of the recent advances in meta-materials and micro-electo-mechanical systems (MEMS) technology. Our MEMS sensor is biocompatible (bioMEMS), inductively powered and monitors the surface strains on implanted hardware [1, 2]. Another novel feature of this new sensor is that it does not require an internal-external physical connection to sense and transmit in vivo biological data. The essence of the sensor’s design is that straining the integrated RF bioMEMS circuit results in a shift in its resonant frequency (ResF). Through telemetric detection of this ResF shift, it is possible to longitudinally monitor the temporal changes in hardware strain. It is well understood that that as proper fracture healing progresses (i.e. increasingly stable tissue(s) stabilizing the fracture sight) that the load/strain born by orthopaedic implant diminishes. Therefore, telemetric measurements of our bioMEMS system (i.e. hardware load/strain) provide direct insight into the degree of fracture stabilization and healing.
Role of Glycosaminoglycans in the Mechanical Behavior of the Posterior Sclera
Authors: Murienne Barbara J. , Nguyen C. Thao D.
Published: January 2014

Changes in sclera mechanical properties have been shown to play an important role in ocular diseases such as glaucoma 1,2,3 and myopia 4,5. In both diseases, those changes in mechanical behavior were observed along with changes in proteoglycan (PG) and associated glycosaminoglycan (GAG) levels, which have been shown to significantly influence the viscoelastic behavior of other tissues 6.
Mechanical Response of Tissue Constructs Fabricated From Self-Adhering Cellularized Microcarriers
Authors: Gabr Mohamed , Zhou Boran , Klatt Sandy , Shazly Tarek , Lessner Susan M. , Argraves W. Scott
Published: January 2014

Understanding how soft tissues behave in response to mechanical loading is essential in the field of biomechanics. Therefore, when a new tissue construct is fabricated, it is necessary to characterize its mechanical response using an appropriate test to quantify the material properties while minimizing error and artifact. To fully understand the behavior of the tissue construct, one should then be able to describe the behavior using a mechanical model.
Numerical Modeling of the Flow in Cerebral Aneurysms Can Predict Thrombus Deposition Regions Following Vascular Interventions
Authors: Rayz V. L. , Acevedo-Bolton G. , Lawton M. T. , Halbach V. , Leach J. R. , Saloner D.
Published: January 2014

Giant intracranial aneurysms present a grave danger of hemorrhage, cerebral compression, and thromboembolism. Fusiform aneurysms present a particular challenge for interventional treatment since these lesions cannot be completely removed from the circulation by clipping or coiling without sacrificing flow to the distal vasculature. In some cases, these lesions can be treated by interventions eliminating pathological hemodynamics, such as indirect aneurysm occlusion or deployment of a flow diverter stent (FDS). The first approach consists of proximal occlusion, distal occlusion, or trapping, sometimes performed with a bypass supplying flow from collateral circulation. In the second approach, a flow diverter device is used to reconstruct the parent vessel geometry and redirect the flow away from the aneurysmal sac. This is achieved due to the denser struts of an FDS relative to a standard stent, which provide resistance to the flow across its walls. Both interventional approaches often result in thrombus deposition (TD) in the aneurysm sac that is considered protective. Despite their advantages, these treatments introduce complications related to thrombotic occlusion of vital perforators or branch arteries. A virtual model, that could predict TD regions that result from flow alteration could help evaluate various treatment options. In addition to biochemical factors, an important role in the TD process may be played by hemodynamics. Previous studies demonstrated that flow regions with elevated TD potential are characterized by low velocities and near-wall shear stresses as well as increased flow residence time [1, 2]. The current study extends this patient-specific CFD methodology to predict TD regions following vascular interventions, such as proximal vessel occlusion and FDS deployment.
Effect of Asymmetry on Finite Element Model of Cervical Spine
Authors: Zafarparandeh Iman , Erbulut Deniz , Lazoglu Ismail , Ozer Fahir
Published: January 2014

The cervical region of spinal column has been known as a frequent site of injuries. The major causes of injuries are vehicle accidents and sports. Clinical instability is known as one of the important topics in cervical spine research. It clarifies the relation between the mechanical dysfunction of the spine and the neurologic dysfunction and pain. From the clinical point of view, if the spinal segment exhibits abnormal large increase in rotational or translational displacements under physiological load, it is considered as unstable. There are different biomechanical models available to understand the underlying mechanisms of injury and dysfunction. Finite element (FE) models have been used as a strong tool to provide the basic insights into the workings of the cervical spine system. Furthermore, they have been clinically useful in the development of the definition of clinical instability and of diagnostic guidelines [1].
Increasing the Removal Efficiency of CPAs by the Dilution-Concentration Method: Adaptive Optimization of Diluent Flow Rates
Authors: Qiao Heyuan , Ding Weiping , Sun Sijie , Zhao Gang , Gao Dayong
Published: January 2014

A dilution-concentration method for removing cryoprotective agents from cryopreserved blood was proposed in our previous work. In this study, the method was optimized adaptively by adjusting diluent flow rates. In the optimization, the diluent flow rate was set to vary with time, the tendency of which was designed to automatically minimize the washing time whereas the volume maximum of red blood cells was guaranteed below the upper tolerance limit. The results show that the optimized diluent flow rate decreases firstly and then increases rapidly. By doing so, the washing time is reduced by about 50%. In practice, the optimization strategy presented here will be very useful in the rapid preparation of cryopreserved blood for clinical use.
An Interdisciplinary Capstone Experience Involving Engineering and Business Students and a Manufacturing Rotation
Authors: Eberhardt Alan W. , Dobbs Joel H.
Published: January 2014

The Department of Biomedical Engineering (BME) at the University of Alabama at Birmingham (UAB) has a rich history of teaching critical and integrative thinking and design skills throughout the curriculum, culminating in a year-long senior capstone design experience. The capstone includes clinical rotations and shadowing in the early stages of the design sequence — participating medical faculty enhance student exposure to biomedical device ideation, which promotes the virtues of team-based experiential learning activities that teach critical thinking and integrate new knowledge with prior learning.
An Uncoupled Multi-Scale CFD Approach to Cell Motion in the Human Left Coronary Artery: Relation to Plaque Progression
Authors: Suo Jin , McDaniel Michael , Eshtehardi Parham , Samady Habib , Giddens Don
Published: January 2014

The near wall motion and residence time of cells that participate in atherosclerosis is an important factor in the development and progression of atherosclerotic lesions. Attachment of leukocytes and monocytes depends upon a complex biological milieu, including expression of adhesion molecules and receptors at cell surfaces, but biomechanical forces also come into play in the local microenvironment. Cell attachment to the endothelium begins with rolling at the surface and can consummate in firm adhesion. These phenomena are influenced by flow-induced forces and moments acting on the cell in proximity to the endothelium. The initial rolling condition and capture process are related to the local shear flow, and there have been extensive investigations — both theoretical and experimental — of these phenomena for various cell types [1–3]. In most studies, steady flow and analytical methods based on Stokes equations were widely used, since the Reynolds numbers are extremely low. In our study, we focus on relating simulated cell motion to conditions in the region of an atherosclerotic plaque in an effort to assist in the interpretation of concurrent investigations of plaque development and progression in human coronary arteries. Thus, our studies are not designed to address fundamental questions of the biology of cell attachment but rather are aimed at elucidation of clinical observations. An inherent challenge is the fact that the length scales of interest vary from sub-micron to millimeters, a range ∼ 104–105 that presents a significant computational task if tackled directly. Hence, various schemes have been employed to address this multi-scale computational problem. Our approach here is intended to decouple the macro (∼ sub-mm) and micro (∼ sub-μm) flows in an effort to achieve computational simplicity, yet preserve accuracy, and thus to concentrate on relevance to flow in the human coronary arteries.
Spatial Actin Structure Does Not Correlate With Nuclear Organization
Authors: Wen Shin-Min , Chao Pen-hsiu Grace
Published: January 2014

Cells in situ exhibit a great variety of morphologies that intimately relates to phenotypic controls. Cell morphology regulates cytoskeletal organization, which in turn influences nuclear shape and organization [1–4]. The actomyosin cytoskeleton is connected to a structure known as the linker of nucleoskeleton and cytoskeleton (LINC) complex located on the nuclear membrane. LINC is believed to transmit deformation of the actin cytoskeleton into the nucleus and nucleoskeleton, change nuclear shape as well as chromatin conformation, and modulate gene expression [5, 6]. Khatau and coworkers reported a structure of apical actin dome, called the actin cap, that controls nuclear deformation through LINC [7]. In addition, actin stress fibers hves been shown to compress the nucleus laterally and increase chromatin condensation [4]. Based on these findings, we hypothesize that there is a spatial correlation between the actin cytoskeleton and chromatin density. In the current study, we investigated the role of actin cytoskeleton in nuclear deformation with respect to the z-axis. We found no spatial relationships between actin structure and nuclear deformation or chromatin condensation, suggesting that the actomyosin cytoskeleton acts globally to influence nuclear structure and additional structural components may contribute to the actin-nucleus mechanical coupling.
Estimating Individual Joint Contributions to Recorded Upper Extremity Movements Using OpenSim
Authors: Honert Eric , Powell Bethany , Goehler Craig M.
Published: January 2014

A multitude of tasks are performed every day with minimal direct thought on how to orient the arm. While there have been many studies concerning upper extremity motion, there has been relatively little research reported in the area of how individual joint contributions vary between different upper extremity tasks. Such studies are necessary in order to accurately recreate dynamic motions of the arm using mechanical devices, e.g. prosthetic limbs. One difficulty in directly measuring these individual joint contributions in physical experiments is that most tasks are multi-joint movements and the limb segments influence each other causing passive interactive torques [1]. In order to quantify the individual joint contributions, it is beneficial to examine recorded arm movements within a simulation environment such as OpenSim [2].
Theoretical Simulation of Temperature Elevations in a Joint Wear Simulator During Rotations
Authors: Chamani Alireza , Mehta Hitesh P. , McDermott Martin K. , Attaluri Anilchandra , Zhang Tina , Jammula Siri , Topoleski L. D. Timmie , Zhu Liang
Published: January 2014

Artificial joints are the most successful long-term treatment for arthritis. Artificial joints have improved the quality of life for millions of patients; however, one of their major limitations is that failure of the device requires a surgical revision. A wear simulator is a valuable tool for testing the long term wear behavior of artificial joints and developing optimal designs before they are implanted in clinical settings. One of the issues related to artificial joint wear is potential temperature elevations caused by friction between articulating components, which affects not only the lubricant in-between, but also induces heat conduction through the components of the simulator. It has been suggested that the temperature elevations, if sufficient, may roughen the component interface, therefore leading to increases in wear. 1–2
Applying Polynomial Chaos Expansions to Evaluate the Effect of Tissue Non-Homogeneous Properties in Biotransport
Authors: Salloum Maher , Ma Ronghui , Zhu Liang
Published: January 2014

Modeling drug transport in tissues has recently gained a lot of attention in the bioengineering community due its vast areas of applications [1]. Such injections often employ a positive pressure infusion directly in the target tissue. It is often referred to as convection enhanced delivery. There are several studies that addressed this problem in the literature. These studies rely on mathematical models of flow in porous media (Darcy, Brinkman...) and are successful in accounting for the existence of capillaries, tissue metabolism, etc. However, these models rely on the assumption that the tissue properties (e.g. permeability) are uniform inside tumors. MicroCT imaging following nanofluid infusion often reveals highly irregular distributions due to the spatial heterogeneity of the tissue [2].
Translational Research in High-Intensity Therapeutic Ultrasound: Novel Techniques for Pre-Clinical Testing
Authors: Myers Matthew R. , Hariharan Prasanna , Banerjee Rupak K.
Published: January 2014

High Intensity Therapeutic Ultrasound (HITU) is an emerging field that shows considerable promise for noninvasively performing medical procedures such as tumor and fibroid ablation, clot destruction, vessel cauterization. Owing to the potential of sensor damage by the intense acoustic field, traditional methods of pre-clinical testing ultrasound devices, such as hydrophone scanning, are problematic with HITU devices. New techniques for performing pre-clinical testing of HITU devices are desirable in order to expedite commercialization. This paper discusses two methods currently being developed for noninvasively determining the intensity fields produced by HITU transducers.
Multiscale Modeling of Flow Induced Thrombogenicity Using Dissipative Particle Dynamics and Coarse Grained Molecular Dynamics
Authors: Zhang Peng , Sheriff Jawaad , Soares João S. , Gao Chao , Pothapragada Seetha , Zhang Na , Deng Yuefan , Bluestein Danny
Published: January 2014

The coagulation cascade of blood may be initiated by flow induced platelet activation, which prompts clot formation in prosthetic cardiovascular devices and arterial disease processes. While platelet activation may be induced by biochemical agonists, shear stresses arising from pathological flow patterns enhance the propensity of platelets to activate and initiate the intrinsic pathway of coagulation, leading to thrombosis. Upon activation platelets undergo complex biochemical and morphological changes: organelles are centralized, membrane glycoproteins undergo conformational changes, and adhesive pseudopods are extended. Activated platelets polymerize fibrinogen into a fibrin network that enmeshes red blood cells. Activated platelets also cross-talk and aggregate to form thrombi. Current numerical simulations to model this complex process mostly treat blood as a continuum and solve the Navier-Stokes equations governing blood flow, coupled with diffusion-convection-reaction equations. It requires various complex constitutive relations or simplifying assumptions, and is limited to μm level scales. However, molecular mechanisms governing platelet shape change upon activation and their effect on rheological properties can be in the nm level scales. To address this challenge, a multiscale approach which departs from continuum approaches, may offer an effective means to bridge the gap between macroscopic flow and cellular scales. Coarse Grained Molecular dynamics (CGMD) and discrete/dissipative particle dynamics (DPD) methods have been employed in recent years to simulate complex processes at the molecular scales, and various viscous fluids at low-to-high Reynolds numbers at mesoscopic scales. Such particle methods possess important properties at the mesoscopic scale: complex fluids with heterogeneous particles can be modeled, allowing the simulation of processes which are otherwise very difficult to solve by continuum approaches. It is becoming a powerful tool for simulating complex blood flow, red blood cells interactions, and platelet-mediated thrombosis involving platelet activation, aggregation, and adhesion.
Development of a Biomechanical Model Producing Proximal Pedicle Pullout of Long Fusion Spinal Constructs
Authors: Martin Audrey , Wanberg Peter , Leasure Jeremi , Buckley Jenni , Kondrashov Dimitriy , Ames Christopher
Published: January 2014

Proximal pedicle screw pullout is a common clinical occurrence for long fusion constructs. Recently, novel spinal hardware and surgical techniques have been in development to alleviate this complication [1]. However, there is currently no biomechanical model to simulate this mode of failure in vitro to adequately evaluate these strategies in a rigorous laboratory setting. Standard pure moment loading and range of motion testing are not equipped to reproduce this failure modality [2] and a vast majority of such outcomes have merely been observed clinically [3]. It is hypothesized that a combination of anterior-posterior (AP) shear and compressive force is required to induce screw pullout with clinically similar fatigue patterns. The goal of this preliminary study is the development of such a biomechanical model to simulate clinically observed proximal pedicle screw failure.
In Vivo Biomechanics of Thumb Carpometacarpal Joint: A Preliminary Study of Gender Differences
Authors: Zheng Qi , Lee Phil , McIff Terence E. , Toby E. Bruce , Fischer Kenneth J.
Published: January 2014

The thumb carpometacarpal joint, which is also known as the trapeziometacarpal (TMC) joint, is an essential load bearing joint subject to repetitive functional loading. The unique double saddle articular surfaces allow complex thumb movement, but also provide bony constraint. The TMC joint is the second most common hand joint affected by osteoarthritis (OA) [1]. Prior studies suggest that TMC OA prevalence in females is much higher than that in males [1], though there hasn’t been any conclusive explanation for etiology or gender difference. Better understanding of TMC joint mechanics will provide insights regarding OA development at this joint and possible variations due to gender differences. Better knowledge of the etiology will help to improve prevention and treatment. Extensive studies have been done based on cadaveric models [2]; while there have been very few in vivo studies on TMC joint mechanics. Therefore, the objective of this study is to quantitatively compare in vivo contact mechanics of TMC joint of males and females.
Four Week Durability of Combined RF Ablation and Cryo-Anchoring Treatment for Mitral Valve Prolapse
Authors: Boronyak Steven M. , Merryman W. David
Published: January 2014

Percutaneous approaches to mitral valve (MV) repair have received a great deal of interest, as they avoid open-chest surgery and are often the only option for patients with significant co-morbidities [1]. One technique currently in development is a combined radiofrequency (RF) ablation and cryo-anchoring catheter, and we recently demonstrated that reduction of MV leaflet surface area due to RF ablation is feasible in the proximity of cryo-anchoring [2]. This reduction of enlarged, diseased MV leaflets is designed to improve leaflet coaptation and reduce mitral regurgitation. However, myocardial infarcts treated with RF ablation re-dilated in 20–30 days without the application of a retaining patch [3]. Additionally, joint capsular tissues treated with RF ablation reduced in stiffness and ultimate strength over the first six weeks before regaining strength and stiffness [4]. Re-dilation of MV tissues treated with combined RF ablation and cryo-anchoring would reverse the effects of the treatment strategy. Therefore, we hypothesized that excised porcine MV leaflets treated with combined RF ablation and cryo-anchoring would undergo little to no re-dilation over four weeks. Biaxial mechanical testing at 0 and 4 week time points and picrosirius red (PSR) staining was used to assess the degree of re-dilation and collagen morphological changes following 4 week bioreactor treatment of cyclic uniaxial tension.
Newly Synthesized RNA and Intranuclear Strain Measurements in Living Cells Maintained Within Native Tissue
Authors: Henderson Jonathan T. , Shannon Garrett , Veress Alexander I. , Neu Corey P.
Published: January 2014

The nucleus is a regulation center for cellular gene expression 1. Mechanical forces transfer to the nucleus directly and indirectly through cellular cytoskeletal structures and pathways 2, 3. The transmitted strains often cause nuclear deformation which is thought to trigger mechanosensitive gene expression within the nucleus 4. Protein dynamics inside the nucleus are additionally important for maintaining the nuclear structure and in facilitating gene expression at the transcription level 5. Probing spatiotemporal relationships between mechanical forces and localized gene expression (i.e. biophysical and biochemical factors) in the nuclei of cells is important in order to clarify variability observed in large and heterogeneous cell populations within complex tissues. This requires the development of innovative methods for intranuclear strain measurements of cells in situ, and the further capability to quantify associated biochemical responses. This abstract describes a method combining the simultaneous measurement of newly synthesized RNA with spatiotemporal intranuclear strain mapping in single cells embedded in native tissue.
A 3D Motion Phantom for Assessing the Accuracy and Precision of Dynamic Magnetic Resonance Measurement of In Vivo Knee Kinematics
Authors: Kaiser Jarred , Chaudhary Rajeev , Wieben Oliver , Kijowski Richard , Thelen Darryl
Published: January 2014

Measurement of in vivo knee kinematics can provide useful insight into disease, injury, and clinical treatment. Cartilage loading patterns are of particular interest while studying the progression of osteoarthritis [1]. However, inferring cartilage contact from skeletal kinematics requires high resolution volumetric models of cartilage surfaces and accurate skeletal positions and orientations. This is a challenging requirement at the knee, which exhibits substantial translation and non-sagittal rotation during normal activities such as gait [2]. We have recently introduced a novel 3D cine magnetic resonance (MR) imaging technique to measure in vivo tibiofemoral kinematics [3]. The purpose of this study was to develop a MR-compatible motion phantom that can generate repeatable 3D skeletal motion suitable for quantifying the accuracy and precision of kinematics derived from dynamic MRI.
Biaxial Response of Ovine Spinal Cord Dura Mater
Authors: Shetye Snehal S. , Puttlitz Christian M.
Published: January 2014

The dura mater plays a major functional role in the spinal cord-meningeal complex (SCM). Being the strongest structure of the meninges, it helps in sustaining the flow and pressure of the cerebral spinal fluid (CSF) in addition to protecting the spinal cord from external mechanical loading. Loss of integrity of the dura can result in subdural and epidural hematomas. Accidental damage of the dura during procedures such as lumbar puncture and epidural anesthesia can potentially result in post-dural-puncture headaches (PDPH).
Changes in Endplate Thickness and Apparent Density After Disc Herniation
Authors: Agarwal A. , Agarwal A. K. , Goel V. K.
Published: January 2014

Endplates play a major role in intervertebral disc (IVD) health, but the opposite could also be true with changes in IVD affecting the morphological features of endplates. We here hypothesize that changes in biomechanical environment due to disc herniation will change the thickness and apparent density of the endplates at the index level.
Stress and Material Property Estimation in the Intervertebral Disc From MRI-Based Finite Strains
Authors: Butz Kent D. , Chan Deva D. , Neu Corey P. , Nauman Eric A.
Published: January 2014

The ability to estimate stresses and material properties within the intervertebral disc (IVD) has potential to provide a greater level of understanding and insight in the study of disc degeneration as well as the development of effective intervention strategies. By integrating non-invasive MRI-based imaging methods with computational modeling, a more complete mechanical characterization of the IVD may be achieved, thereby eliminating the need to disturb the tissue or potentially alter the structure destructively.
Enhancement of Prediction for Hip Fractures Using Stochastic Assessment of Bone Mineral Density Distribution From DXA Images
Authors: Dong Xuanliang Neil , Cussen Patricia , Lowe Timothy , Di Paolo David , Ballard Joyce
Published: January 2014

Hip fractures are among the most common types of osteoporotic fractures that affect one in three women and one in six men over the age of 50 [1]. It is well known that loss of bone mass, quantified by bone mineral density using Dual-energy X-ray Absorptiometry (DXA), is associated with the increasing risk of bone fractures. However, bone mineral density (BMD) alone cannot fully explain changes in fracture risks [2, 3]. In particular, BMD is not able to predict fracture risks for women with osteopenia, in which a BMD T-score is between −1.0 and −2.5. This suggests additional factors (i.e., bone quality) should be considered in predicting fracture risks [4].
Effects of Valve Geometry and Tissue Anisotropy on the Radial Stretch and Coaptation Area of Tissue-Engineered Heart Valves
Authors: Loerakker Sandra , Argento Giulia , Oomens Cees W. J. , Baaijens Frank P. T.
Published: January 2014

Tissue engineering represents a promising technique to overcome the limitations of the current valve prostheses, since it allows for synthesizing living, autologous valves that have the potential to grow and remodel in response to changing demands. However, one particular problem with tissue-engineered heart valves (TEHVs) is retraction of the valve leaflets (Fig. 1), which results in valvular insufficiency [1, 2]. As long-term regurgitation will lead to ventricular failure, this is a critical problem that needs to be solved before TEHVs can be used in clinical practice.
Determination of Layer and Region Specific Mechanical Properties of Intraluminal Thrombus (ILT): The Importance of Biaxial Tensile Testing
Authors: O’Leary S. , Kavanagh E. , Grace P. , McGloughlin T. , Doyle B.
Published: January 2014

Abdominal Aortic Aneurysm (AAA) is the gradual and irreversible local widening of the distal region of the aorta. If undetected or untreated the intramural stress can exceed the strength of the aneurysm wall causing the structure to rupture. Upon rupture, AAA has a 90% mortality rate. It has been hypothesized, and shown in some studies, that regions of elevated stress of the AAA wall may be linked to sites of AAA rupture. In order for Finite Element Analysis (FEA) to be successfully used as a clinical tool, to aid in AAA rupture prediction, it is crucial that the mechanics of both the AAA wall and intraluminal thrombus (ILT) are described accurately. At present it is unclear whether ILT increases or decreases the rupture risk of AAA. This may be due to the lack of available data which can accurately describe its behaviour in vivo. A recent review of AAA mechanics explains how ‘there have been limited studies on the mechanical properties of intraluminal thrombus’. Due to the recent popularity of endovascular aneurysm repair (EVAR) the opportunities to harvest and conduct mechanical tests on this tissue are rare. This study aims to further characterize ILT using both uniaxial and biaxial test methods and where possible determine the layer and region specific mechanical properties of this material.
Multi-Phase Blood Flow Modeling in Intracranial Aneurysms Considering Possible Transition to Turbulence
Authors: Berg P. , Abdelsamie A. , Yu H. , Janiga G. , Thévenin D.
Published: January 2014

According to the Dorland Medical Dictionary a cerebral aneurysm is an abnormal bulge or ballooning in a blood vessel supplying the brain. Aneurysms can rupture and bleed into the area between the brain and the surrounding membrane. A noticeable percentage of the human population, typically 2 to 5% depending on the country, harbors a cerebral aneurysm, but only about 0.1% of those aneurysms rupture annually [1].
Influence of Strain and Contact Guidance on Collagen Organization in Engineered Cardiovascular Tissues: Implications for In Situ Tissue Engineering
Authors: de Jonge Nicky , Argento Giulia , Baaijens Frank P. T. , Bouten Carlijn V. C.
Published: January 2014

Cardiovascular tissues have a prominent load-bearing function. Collagen fibers in the extracellular matrix provide strength to these tissues. In particular the content and organization of these fibers contribute to overall strength [1]. In case of changes in mechanical demand, collagen content and organization can be adapted; a process referred to as collagen remodeling. For the creation of engineered cardiovascular tissues knowledge about collagen remodeling is of utmost importance to produce tissues with load bearing function. In case of in situ tissue engineering (TE) collagen content and organization in the developing tissue can be influenced by local tissue strains as well as scaffold structure and degradation properties [2, 3].
Tensile Strength of the Aorta can be Estimated From Mechanical Parameters Which Depends on Degree of Intramural Collagen Fiber Alignment
Authors: Sugita Shukei , Matsumoto Takeo
Published: January 2014

Aortic aneurysms larger than a critical value, ∼50 mm for example, have high risk of rupture due to the Laplace’s law. However, aneurysms smaller than the critical diameter sometimes rupture (1, 2). Since intramural stress is relatively low in smaller aneurysms, their rupture indicates weakening of aneurysmal wall. For more reliable prediction of risk of aneurysm rupture, therefore, local strength of aneurysmal wall should be obtained.
Engineered Microtissues for Real-Time Characterization of Cardiomyocyte Function
Authors: van Spreeuwel Ariane C. C. , Bax Noortje A. M. , Foolen Jasper , Borochin M. A. , van der Schaft Daisy W. J. , Chen Chris S. , Bouten Carlijn V. C.
Published: January 2014

Engineered cardiac tissue models become increasingly important for understanding normal and disease cardiac physiology [1]. Where clinical diagnostic tools usually measure overall function of the heart, cardiac tissue models make it possible to focus on single CMs and their microenvironment. The use of in-vitro cardiac disease models can give more insight in the functionality changes of CMs during disease and thereby speed up the development of new therapies. Therefore, we aim to develop a model for healthy and diseased myocardium to study the effect of diseased microenvironments on the mechanical performance of CMs. The platform consists of 3D engineered microtissues with matrix, CMs and fibroblasts (FBs) on an array of polydimethylsiloxane (PDMS) microposts and allows for real-time characterization of CMs and their surrounding matrix. The design was adapted from Legant et. al. [2] and enables us to measure inhomogeneous tissue forces which may occur if not all cells contract equally. Here we focus on optimization and validation of the platform to measure contraction forces and gain insight in CM mechanical functioning.
Numerical Simulation of Blood Flow in the Renal Arteries: Influence of the Ostium Flow Diverter
Authors: Albert Scott , Rossmann Jenn Stroud , Balaban Robert
Published: January 2014

The tendency of atherosclerotic plaques to develop at arterial branch points is likely due to both the hemodynamics and macromolecular environment associated with these branch points. Arterial branches experience flow separation, which results in regions of low shear stress[1–3], and contributes to longer residence times that may allow for deposition of pro-atherogenic material in the vessel wall [2]. In addition, low shear stress itself may provide cellular signals that alter the tissue microenvironment in favor of atherogenesis [3, e.g.].
Computational Modeling of Cell Orientation in 3D Micro-Constructs
Authors: Obbink-Huizer Christine , Oomens Cees W. J. , Loerakker Sandra , Foolen Jasper , Bouten Carlijn V. C. , Baaijens Frank P. T.
Published: January 2014

In many tissue engineering applications it is essential to understand how cells orient under the influence of their mechanical environment. In vitro engineered models are used to investigate the orientation of F-actin stress fibers inside cells. One such in vitro model [1] consists of a mixture of cells, collagen and matrigel, that is constrained by an array of silicone posts (Figure 1). We have recently developed a computational model to describe the orientation of stress fibers in response to their mechanical environment [2]. In the present study, this computational model is extended to 3D and used to simulate cell behavior in the mentioned in vitro model. This improves our understanding of how stress fibers orient in response to the mechanical environment and aids in optimizing the use of the in vitro model.
Elastin in the Arterial ECM: Interactions With Collagen and the Mechanical Properties After Elastin Degradation
Authors: Chow Ming-Jay , Turcotte Raphaël , Zhang Katherine Yanhang
Published: January 2014

Elastin and collagen are the main structural components in the extracellular matrix (ECM) that contribute to the anisotropic and hyperelastic passive mechanical behavior of elastic arteries. It is commonly accepted that the elastin fibers support most of the load at the onset of stretching while collagen fiber recruitment and the transition to collagen bearing the load occurs at higher pressures [1]. Various diseases lead to changes in the ECM, for example in aortic aneurysm there is reduced elastin, excess aged collagen, and fragmentation of the elastic lamellae [2]. Likewise hypertension has been shown to increase arterial collagen and wall thickness with increased stiffness [3]. Improving our knowledge of how the ECM structure affects the mechanical behavior of arteries can provide insights to disease progression and better treatment methods.
Fluid-Structure Interaction Modelling Predicts That Strain Transfer Through Focal Attachments of Osteoblast Cells are the Primary Mediators of Mechanical Stimulation Under Fluid Flow
Authors: Vaughan T. J. , Haugh M. G. , McNamara L. M.
Published: January 2014

Bone continuously adapts its internal structure to accommodate the functional demands of its mechanical environment. It has been proposed that indirect strain-induced flow of interstitial fluid surrounding bone cells may be the primary mediator of mechanical stimuli in-vivo [1]. Due to the practical difficulties in ascertaining whether interstitial fluid flow is indeed the primary mediator of mechanical stimuli in the in vivo environment, much of the evidence supporting this theory has been established through in vitro investigations that have observed cellular activity in response to fluid flow imposed by perfusion chambers [2]. While such in vitro experiments have identified key mechanisms involved in the mechanotransduction process, the exact mechanical stimulus being imparted to cells within a monolayer is unknown [3]. Furthermoreit is not clear whether the mechanical stimulation is comparable between different experimental systems or, more importantly, is representative of physiological loading conditions experienced by bone cells in vivo.
A Wearable Gait Monitor and Terrain Prediction System
Authors: Sullivan Christopher , DeBartolo Elizabeth , Lamkin-Kennard Kathleen
Published: January 2014

Nearly one million people in 2009 were discharged from the hospital with stroke as the primary diagnosis [1]. One of the many lasting side effects of a stroke can be foot drop, or an inability to dorsiflex the foot. In order to remedy this, many people wear an ankle-foot orthotic (AFO) post-stroke. Interviews with AFO users revealed that they frequently have difficulty walking on stairs and ramps, because the AFO limits the plantarflexion that is natural in navigating those ground types. An active AFO that adapts to changing ground terrain would provide a more natural gait pattern for these individuals, if it could be designed to respond appropriately to upcoming terrain. In order to respond to terrain, the device must first identify the terrain.

This paper outlines a system [2] that simultaneously predicts the type of terrain a user is approaching as they walk, and captures information about that user’s walking activity. Such a system can be used as the control system for an active orthotic or prosthetic device. Additionally, this system can be used as a stand-alone gait and terrain monitor to aid in rehabilitation monitoring in between patient visits with a clinician.