bluuebunny/crossref_metadata_2025 huggingface dataset:
Finite Element Study of Conformity of Flow Diverter With Intracranial Aneurysmal Vasculatures
Authors: Ma Ding , Xiang Jianping , Siddiqui Adnan , Natarajan Sabareesh , Meng Hui
Published: July 2013

Endovascular stents in the last decade have been extensively used in intracranial aneurysm (IA) management. Stenting procedure is normally performed with the placement of spring coils inside the aneurysm, where stent will serve as a mechanical scaffold to help anchor the packed coils. Although coiling holds relatively lower morbidity and mortality rate than traditional treatment, its applications to wide-necked IAs, IAs with large fusiform shapes, and thin-walled IAs are still problematic due to the difficulty of securing the coils in the first two scenarios and the vascular susceptibility to coil damage in the last situation. Recent flow diverter concept however offers a potential alternative to address these challenging cases with only stent (flow diverter) being implanted. A flow diverter stent usually has relatively high metal surface coverage rate (∼80%) so that it can significantly divert blood flow from going inside the aneurysm, causing the decreased flow in IA and subsequently the thrombogenic cascade in favor of occluding the lesion. Meanwhile, a new flow conduit across IA orifice is expected to form based on endothelial cell re-pavement on the inner surface of the stent. It is thus of academic and clinical importance to further examine the mechanisms involved with flow diverter to better understand the procedure and improve the treatment outcome. Since the straightening of vessel by stent and incomplete apposition between stent filaments and arterial wall could both induce complications, current study applies a developed finite element method (FEM) workflow to evaluate the conformity of a CoCr alloy flow diverter (Pipeline™ Embolization Device as PED by ev3, MN, USA) to patient specific IA geometries.
A Pneumatic Vibrator Created Using Rapid Prototyping Technology for the fMRI Environment
Authors: Soltys Joseph , Wilson Sara
Published: July 2013

Functional Magnetic Resonance Imaging (fMRI) promises to grant motor control researchers opportunities to more directly explore neuromotor system dynamics including the role of proprioception. The effects of vibration on proprioception have been well documented including changes in perceived muscle length and lengthening velocity and altered muscle spindle organ firing [1–4]. As such, the combination of vibration of the muscle-tendon with fMRI of the brain can be used to better understand how proprioceptive signals are managed in the brain. However, the strength of the magnetic environment of the fMRI does not easily allow for traditional vibration technologies, such as a DC motor with offset mass, to be used to create the necessary vibratory stimulus to perturb the proprioceptive system. Several researchers have nonetheless successfully designed and implemented various vibration devices to probe the brain in the fMRI environment [5–7].
Multiscale Mechanical Models for Understanding Microstructural Damage in Fibrous Tissues
Authors: Sander Edward A. , Hadi Mohammad F. , Barocas Victor H.
Published: July 2013

The mechanical behavior of tissues is critically dependent on the organization and composition of the extracellular matrix (ECM). In many tissues, the primary load-bearing component is fibrillar collagen, which is arranged into larger fiber bundles or fibrous networks depending on the specific tissue. This microstructural arrangement distributes and accommodates tissue-level loading and allows the tissue to function mechanically. Consequently, when collagen fibers are damaged, either through injury or disease, the distribution of load within the tissue changes, which can alter cell activity, mechanical behavior, and tissue function. This damage process underlies many physical ailments, but it remains poorly understood in part because of the difficulty relating macroscopic load to microsctructural alterations. To understand better local fiber failure and accompanying global restructuring, we have incorporated fiber damage from excessive force into our multiscale-modeling framework [1,2].
Biomechanical Analysis of Embryonic Atrioventricular Valvulogenesis
Authors: Buskohl Philip R. , Gould Russell A. , Butcher Jonathan T.
Published: July 2013

Heart valve development is directed by a complex interaction of molecular and mechanical cues[1]. Both molecular and mechanical based approaches are needed to clarify these relationships. Many technologies exist for the former, but the short length scale and super-compliant material properties of embryonic valve tissue make conventional mechanical testing techniques ineffective. The pipette aspiration technique has been a useful tool in cell mechanics[2] and has recently been applied to adult valve leaflets[3]. Geometric effects of thin, planar tissues however compromise the utility of aspiration based measurements. Herein, we utilize pipette aspiration and a novel uni-axial micro-tensile testing apparatus to quantify the biomechanical evolution of avian embryonic heart valves. We then relate biomechanical stiffening to changes in underlying structural composition.
Maternal Childbirth Injury Alters Vaginal Smooth Muscle Contractility
Authors: Jallah Zegbeh C. , Skoczylas Laura , Stein Suzan , Yoshimura Naoki , Moalli Pamela , Abramowitch Steven D.
Published: July 2013

Pelvic organ prolapse (POP) is a multifactorial disorder, characterized by the descent of the pelvic organs into the vaginal canal. POP is associated with decreased quality of life, and even depression, yet 50% of women over the age of fifty are living with this disorder. The estimated direct cost for POP surgeries is over one billion dollars annually, in the United States alone. This rather exorbitant figure includes the cost of surgery performed for symptom management, but does not include strategies which address the underlying cause of the disorder. It is not surprising then, that within a few years over 10% of repairs will require a second procedure. Thus, more studies are needed to understand the pathophysiology of POP.
In Vivo Contact Mechanics of the Distal Radioulnar Joint of the Normal Wrist Compared to Scapholunate Injury and Surgical Repair
Authors: Varre Mathew S. , Lee Sang-Pil , McIff Terence E. , Toby E. Bruce , Fischer Kenneth J.
Published: July 2013

The distal radioulnar joint (DRUJ) is a joint of the wrist which allows forearm rotation and force transmission in the upper limb while preserving stability independent of flexion and extension of the forearm and wrist. The DRUJ is a frequently injured joint in the body. Conditions affecting the joint could be positive ulnar variance (Ulnar Impaction Syndrome) or negative ulnar variance (ulnar impingement), which may be congenital or may result from a poorly reduced distal radius fracture or both bone forearm fracture. The DRUJ is also adversely affected by other injuries near the joint. In fact, a significant correlation has been found between negative ulnar variance and scapholunate dissociation [1, 2, 3]. While this could be a predisposing factor, the associate also leads to the question of whether or not scapholunate dissociation may cause changes in the radioulnar joint mechanics. Altered joint mechanics are highly associated with onset of secondary osteoarthritis. An understanding of in vivo distal radioulnar joint contact mechanics in the normal and pathological wrist could help physicians make better clinical recommendations and improve treatment for the primary injury and avoid DRUJ pathology. Successful treatment may possibly reduce risk of or prevent the onset of osteoarthritis.
Development of a Finite Element Model for Porcine Scalp
Authors: Ryland Stephanie , Patnaik Sourav , Prabhu Rajkumar , Horstemeyer M. F. , Liao Jun , Williams Lakiesha N.
Published: July 2013

According to the Center for Disease Control and Prevention, head injuries account for 44% of all injury related deaths in the United States. Predictive head injury indicators are being used in car crash evaluations, forensic science investigations, and in research as an alternative to expensive, unpractical, and sometimes unethical animal or human experimentation [1]. The purpose of the present work is to characterize the structural and mechanical properties of the multilayer scalp and create a preliminary FEA model based on our findings. A longer term goal is to develop a high fidelity Finite Element (FE) model of human head.
Hemodynamic Changes in the Left Atrium due to Atrial Fibrillation
Authors: Funamoto Kenichi , Koizumi Ryo , Hayase Toshiyuki , Shibata Muneichi , Yambe Tomoyuki
Published: July 2013

The left atrium (LA), which connects four pulmonary veins (PVs) to the left ventricle (LV), has a characteristic shape called the left atrial appendage (LAA) under the left PV. Atrial fibrillation (AF) is a heart disease, by which irregular electrical signals with high-frequency contraction (> 400 bpm) occur in the LA. Although AF itself is not fatal, it may cause thrombus formation, resulting to cerebral infarction. In this study, hemodynamics in the LA with/without AF was investigated by means of fluid-structure interaction simulation.
Shock Wave as a Mechanism of Injury in Soft Tissues
Authors: Laksari Kaveh , Darvish Kurosh , Sadeghipour Keyanoush
Published: July 2013

The aim of this study is to investigate the propagation of shock waves and self-preserving waves in soft tissues such as aorta and brain as a mechanism of injury in high rate loading conditions as seen in blunt trauma and blast-induced trauma (BIT). It is shown that such phenomena can only be seen in nonlinear viscoelastic materials and the existing linear and quasi-linear models predict only decaying waves. Based on the results of this study, it is shown that when studying such high-rate loading conditions as in a blast, it is critical to consider the discontinuities predicted in strain and stress in certain realistic initial conditions to accurately determine the extent of soft tissue injuries.
Vascular Injury and Cortical Deformation in a Model of Brain Contusion
Authors: Yeoh Stewart , Mathur Vishwas , Monson Kenneth L.
Published: July 2013

Traumatic brain injury (TBI) is a leading cause of death and disability, affecting 1.7 million Americans annually, 50,000 of whom die [1]. Victims who survive the initial injury often suffer debilitating neurologic deficits. The total annual cost of TBI in the United States has been estimated at $60 billion [2]. While damage to brain tissue is of primary concern in TBI, nearly all head trauma includes some element of vascular injury or dysfunction [3], putting neural tissue uninjured in the primary event at subsequent risk. Contusion, which includes injury to both brain and vessel tissue in the cortex, is considered the hallmark of head injury, but little is known about the specific mechanisms of vascular injury in contusion. Previous efforts to elucidate mechanisms and thresholds for contusion, including inanimate gel, animal, and computational models [e.g. 4–7], have defined bulk tissue deformations that are associated with contusion, but the relationship to vascular injury is not clear. In order to address this question, our laboratory is studying acute disruption of the blood-brain barrier using a controlled cortical impact (CCI) mouse model. The objective of this study was to compare acute vascular injury in CCI with cortical mechanics predicted by a computational model of the experiment. This comparison is then discussed in the context of results from isolated vessels testing in our laboratory.
Modelling of Magnetic Targeting of Therapeutic Nanoparticles in a Two Phase Microvessel Flow
Authors: Ecker Tobias , Rylander Christopher G.
Published: July 2013

Magnetic particle targeting is a new approach in cancer drug administration which aims to reduce side effects, increase healing rate and reduce treatment time. For this purpose a therapeutic agent is equipped with a magnetizable membrane and administered intravenously. A rare earth magnet can then be used to target cancerous tissue in proximity of the blood vessel.
The Collagen Fiber Kinematics in the Anteroinferior Glenohumeral Capsule Are Not Affine-Predicted
Authors: Voycheck Carrie A. , McMahon Patrick J. , Debski Richard E.
Published: July 2013

Glenohumeral dislocation is a significant clinical problem and often results in injury to the anteroinferior (anterior band of the inferior glenohumeral ligament (AB-IGHL) and axillary pouch) glenohumeral capsule. [1] However, clinical exams to diagnose capsular injuries are not reliable [2] and poor patient outcome still exists following repair procedures. [3] Validated finite element models of the glenohumeral capsule may be able to improve diagnostic and repair techniques; however, improving the accuracy of these models requires adequate constitutive models to describe capsule behavior. The collagen fibers in the anteroinferior capsule are randomly oriented [4], thus the material behavior of the glenohumeral capsule has been described using isotropic models. [5,6] A structural model consisting of an isotropic matrix embedded with randomly aligned collagen fibers proved to better predict the complex capsule behavior than an isotropic phenomenological model [7] indicating that structural models may improve the accuracy of finite element models of the glenohumeral joint. Many structural models make the affine assumption (local fiber kinematics follow global tissue deformation) however an approach to account for non-affine fiber kinematics in structural models has been recently developed [8]. Evaluating the affine assumption for the capsule would aid in developing an adequate constitutive model. Therefore, the objective of this work was to assess the affine assumption of fiber kinematics in the anteroinferior glenohumeral capsule by comparing experimentally measured preferred fiber directions to the affine-predicted fiber directions.
Using Robotic Testing System to Investigate ACL Reconstructions in Restoring the Normal Knee Joint Biomechanics: Experience at Harvard Medical School
Authors: Li Guoan , Gadikota Hemanth R. , Gill Thomas J.
Published: July 2013

Rupture of the anterior cruciate ligament (ACL) is a debilitating injury associated with various complications such as joint instability, meniscal injury and chronically may lead to osteoarthritis. ACL is believed to be the primary restraint to anterior translation and axial rotation. However, few studies have investigated the alterations to the other degrees of freedom kinematics due to ACL deficiency. ACL reconstruction has been widely accepted to be the standard of care for patients who sustain an ACL rupture to minimize the risk of the complications mentioned above. Widely practiced surgical techniques have yet to prove their efficacy in comprehensively restoring the normal knee joint function. Sub-optimal performance of the conventional single bundle ACL reconstruction has sparked a renewed interest in anatomical reconstruction and alterations to the conventional techniques.
Biomechanical Testing of the Compressive Strength of Various Distal Locking Screw Options for Intramedullary Nails in the Treatment of Tibia Fractures
Authors: Xavier Fred , Goldwyn Elan , Hayes Westley T. , Carrer Alexandra , Berdichevsky Max , Gaines Evan , Goldman Ariel T. , Saha Subrata
Published: July 2013

Treatment of distal third tibia fractures remains challenging. New intramedullary nails provide torsional stability by using distal interlocking screws. In this study we attempted to determine the most biomechanically stable number and configuration of distal locking screws. The distal part of human cadaveric tibia bones was nailed using a tibial nail (Stryker T2). Distal locking was performed in three different configurations: (a) Group I: 2 screws in the medio-lateral (ML) direction, (b) Group II: 1 ML screw and 1 Screw in the antero-posterior (AP) direction, and (c) Group III: 2 ML screws and 1 AP screw. The specimens were then mounted onto a mechanical testing machine (Instron) and tested in compression. The load carrying capacity of the samples from Group III with these locking screws was higher than Group I & II, although this difference was not statistically significant.
Characterizing the Ex-Vivo Properties of Prolapse Meshes
Authors: Feola Andrew J. , Barone William R. , Shepherd Jon , Moalli Pam , Abramowitch Steven
Published: July 2013

Pelvic organ prolapse is a common condition that affects roughly 30–40% of women in their lifetime (1). Although not all women become symptomatic, 225,000 to 280,000 require surgery for prolapse each year (1). Prolapse occurs when the vagina can no longer support the pelvic organs. Thus, many urogynecological procedures use synthetic meshes to restore the supportive capacity of the vagina. However, a significant underreported proportion of women undergoing mesh procedures require a procedure to remove surgically placed mesh due to pain, exposure, erosion, and dyspareunia (2). It is suspected that these complications are related to mesh structural properties. However, since there are a wide variety of mesh products in use with little known about their properties before and after implantation, identifying the role of mesh in surgical failure has been difficult.
Oscillation of Wall Shear Stress in Growing Intracranial Aneurysms: A Case Study
Authors: Sugiyama Shin-ichiro , Takahashi Akira , Tominaga Teiji
Published: July 2013

Hemodynamics is thought to influence the initiation, growth, and rupture of intracranial aneurysms. While there seems to be general consensus that high wall shear stress results in the initiation of intracranial aneurysms, the hemodynamic conditions that drive the development of aneurysms after initiation are still not completely elucidated. High wall shear stress has been postulated to account for aneurismal progression from the distal neck where flow impinges, whereas low wall shear stress has been associated with aneurysm growth in the dome.1
On the Mechanical Behavior of Healthy and Aneurysmal Abdominal Aorta
Authors: Ferruzzi J. , Enevoldsen M. S. , Humphrey J. D.
Published: July 2013

Abdominal aortic aneurysm (AAA) is a pathological condition of the infrarenal aorta characterized by a local dilatation of the arterial wall. The main histopathologic features of an AAA are smooth muscle cell death and loss of elastin. The biomechanical behavior of AAAs has been widely studied to determine the rupture potential according to the principles of material failure. However, most prior approaches are limited by the use of data from uniaxial tensile testing and by the assumption of material isotropy, leading to inaccurate characterization of the 3D multiaxial mechanical response of the aneurysmal tissue. To date, the best data available on the behavior of human abdominal aorta (AA) and AAA to planar biaxial testing are the ones reported by Vande Geest et al. [1,2]. In a recent work [3], we considered a structurally motivated four-fiber family strain energy function (SEF) [4] to capture the biaxial behavior of the human AA and AAA from Vande Geest et al. [1,2]. We showed that this constitutive relation fits human data better than prior models and most importantly it captures the stiffening of the arterial wall related to both aging and aneurysmal development. These changes in mechanical behavior are mirrored by changes in the best-fit values of the parameters, with a progressive decrease of the isotropic part attributed to elastin and a parallel increase in values associated with the families of collagen fibers.
A Model for Ligament Fibroblast Migration Into Provisional Matrix
Authors: Cheng Yu-Chen , Chao Pen-Hsiu Grace
Published: July 2013

Many strategies have been proposed to enhance the healing capability of the anterior cruciate ligament (ACL). A novel treatment option, called enhanced primary repair, places a provisional matrix at the tear site to promote cell infiltration of the wound and aims to reestablish the structure-function relationship of the ACL [1]. This approach of guided tissue regeneration offers great potential benefits of retaining the complex native tissue matrix structure, innervation, and vascularization as compared with grafts. A major aspect of this procedure is enhancing ligament fibroblast infiltration into the matrix material and promoting matrix synthesis. We have previously demonstrated that applied electric fields (EFs) enhance knee ligament fibroblast migration, alignment, and collagen gene expressions on planar substrates [2]. In the current study, we developed a new system to simulate cell infiltration from the tissue to a provisional collagen matrix. An EF was applied across the construct to investigate its effects of on ACL fibroblast migration into the provisional matrix.
Modeling Arterial Wall Transport for Drug-Eluting Stents
Authors: Bozsak Franz , Chomaz Jean-Marc , Martinelli Fulvio , Barakat Abdul I.
Published: July 2013

Drug-eluting stents (DES) are very commonly used for treating coronary atherosclerotic lesions. Despite the broad effectiveness of DES, ∼5% of treated patients experience complications including in-stent restenosis and late-stent thrombosis. The occurrence of these complications depends on various factors including the concentration of the eluted drug in the arterial wall and the rate of arterial re-endothelialization. Drug concentration in the arterial wall needs to be sufficiently high to be efficacious while remaining sufficiently low to avoid compromising wall stability (leading to stent malapposition). Furthermore, because drugs used in DES modulate proliferation rates of not only smooth muscle cells but also endothelial cells, the drug concentration affects re-endothelialization rates. Drug concentration in the arterial wall is determined by the transport and metabolism of the drug and may also be affected by the flow field in the lumen of the stented vessel. In the present study, we develop a computational model of drug transport in the arterial wall. Previous models have typically treated the arterial wall as a homogeneous porous medium [1] and have often ignored drug reaction with cells in the arterial wall [2]. In the present study, we have developed a model that incorporates the multi-layer structure of the arterial wall and have compared its predictions for the distribution of an eluted drug within the arterial wall with those of the single-layer homogeneous wall model.
Association of Mechanical Properties and Collagen Content With Valve Morphology in Ascending Thoracic Aortic Aneurysmal Tissue
Authors: Pichamuthu Joseph E. , Phillippi Julie A. , Cleary Deborah A. , Chew Douglas W. , Hempel John , Gleason Thomas G. , Vorp David A.
Published: July 2013

Bicuspid aortic valve (BAV) is the most common congenital heart malformation occurring in 1–2% of the population with a high rate of morbidity [1]. There is a significantly higher rate of dilation of the aortic root in adults with a BAV when compared to the normal population and this condition is often associated with ascending thoracic aortic aneurysm (ATAA). ATAA is characterized as an enlargement of the aorta to twice its normal diameter. If left untreated, ATAA can lead to aortic dissection or rupture. Therefore, ATAA is recommended for prophylactic surgery when its diameter reaches about 5.5 cm. However, in certain high-risk cases, such as patients with BAV, ATAA may rupture when its diameter is less than 5.5 cm. Since ATAA dissection and rupture are biomechanical phenomena, better mechanical models are needed to more accurately predict these events over the predictive capability of diameter alone.
Determination of Representative Pressure, Velocity and Flow Rate Waveforms in a Human Hepatic Artery System Afflicted With Metastatic Tumors
Authors: Basciano Christopher A. , Kleinstreuer Clement , Kennedy Andrew S.
Published: July 2013

A rising therapy for liver tumor treatment is the local delivery of Yttrium-90 (90Y) radiation via the injection of radioactive microspheres into the hepatic arteries. The elevated arterial blood flow supplying the liver tumor(s) hopefully directs the microspheres towards tumor cells rather than healthy liver tissue. While limited in precise control of the microspheres, the therapy has been shown to have positive response rates on tumors that are nonresponsive to chemotherapy or are disqualified for surgical resection or ablation. Thus, research studies seeking to improve clinical 90Y-microsphere therapy are crucial to advancing radiation oncologists’ ability to effectively treat the increasing number of patients afflicted with liver tumors1,2.
Simulation of Stress Fiber Remodeling and Mixed-Mode Focal Adhesion Assembly During Cell Spreading and for Cells Adhered to Elastic Substrates
Authors: Ronan William , Deshpande Vikram S. , McMeeking Robert M. , McGarry J. Patrick
Published: July 2013

Cell spreading is governed by two cooperative cellular processes: the association of binding proteins to form focal adhesions, and the active remodeling of the actin cytoskeleton as the cell spreads [1]. The interaction between these two processes is poorly understood, and previous computational models have only examined each process in isolation. Previous studies have established that cells possess the ability to sense and react to their physical environment, for example cells seeded on substrates of varying stiffness exhibit a different cytoskeletal response [2,3].
Smoothed Particle Hydrodynamics Simulation of Flow Through a Bileaflet Mechanical Heart Valve: Advantages and Prospects
Authors: Shahriari Shahrokh , Maleki Hoda , Hassan Ibrahim , Kadem Lyes
Published: July 2013

A numerical simulation of pulsatile flow through a bileaflet mechanical heart valve is presented using smoothed particle hydrodynamics (SPH), a meshfree particle method. In SPH, the flow is modeled using fluid particles moving within the domain in which there is no mesh generation process and the conservation of mass is satisfied automatically. SPH showed a good capability to capture the main hemodynamic trend. The particle based nature of SPH allows also blood particle tracking, an important component in order to analysis the level of hemolysis induced by bileaflet mechanical heart valves.
Novel Robotic System for Joint Mechanical Tests Using Velocity-Impedance Control
Authors: Fujie Hiromichi , Yagi Hitoshi
Published: July 2013

The first study as regard with the application of robotic technology to the field of joint biomechaics was reported more than 20 years ago1). Since then, a variety of studies have employed commercially available articulated manipulators for the joint biomechanical studies1–4). However, such articulated manipulators are generally poor at stiffness and precision although they were basically designed to achieve high speeds of motion while performing tasks in a large work space. To solve the problem, we have previously developed a robotic system consisting of a custom-made 6-degree of freedom (6-DOF) manipulator and a universal force-moment sensor (UFS)5). Referring to the robotic system, the present study was aimed to develop a novel robotic system of rigid body/structure that allows a high-rate displacement/force control of the knee using a velocity-impedance control.
Nitric Oxide Transport in Lymphatic Vessels
Authors: Wilson John T. , Dahlin Rebecca L. , Gasheva Olga , Zawieja David C. , Moore James E.
Published: July 2013

The lymphatic system plays a vital role in maintaining proper physiological function in the body. Its removal of proteins and other particulate matter from the tissue spaces is particularly important for the body’s prevention of extracellular edema [1]. After fluid is absorbed by the initial lymphatics, it is transported to lymph nodes where filtration occurs. In addition, the lymphatic system serves as a common pathway of initial metastases to regional lymph nodes for certain types of cancers [2]. Thus, the characterization of mass transport in the lymphatic system could lead to unprecedented insight into the treatment of such pathologies.
Modeling of Tissue Fatigue Damage in Bio-Prosthetic Heart Valve
Authors: Martin Caitlin , Sun Wei
Published: July 2013

Bio-prosthetic heart valves (BHVs) with leaflets made of glutaraldehyde-treated bovine pericardium (GLBP), have been used extensively to replace diseased heart valves. BHVs display superior hemodynamics to mechanical valves and eliminate the need for anticoagulant therapy; however, they exhibit poor durability resulting from in vivo degradation and fatigue damage of the leaflets.
Pulsatile Hemodynamics of the Fontan Connection: A Tri-Modal Investigation
Authors: Haggerty Christopher M. , de Zélicourt Diane A. , Kanter Jessica R. , Sundareswaran Kartik S. , Fogel Mark A. , Yoganathan Ajit P.
Published: July 2013

To evaluate the qualitative impact and computational accuracy of pulsatile flow through the total cavopulmonary connection (TCPC), multiple patient-specific models were studied using computational, experimental, and imaging techniques and the multi-modality results compared. Agreement with regard to both qualitative behavior and quantitative velocity measures was very convincing, which robustly demonstrates the precision of our various investigational methods.
On the Mechanics of Microtubule Filaments
Authors: Mehrbod Mehrdad , Mofrad Mohammad R. K.
Published: July 2013

Quantitative understanding of cell mechanics has challenged biological scientists during the past couple of decades. one of the promising attempts towards mechanical modeling of the cytoskeleton has been the “tensegrity” cytoskeletal model, which simplifies the complex network of cytoskeletal filaments as a structure merely composed of compression-bearing elements (hinge-ended struts) and tensile members (cables). This discrete model can interestingly explain many experimental observations in cell mechanics. However, evidence suggests that the simplicity of this model may undermine the accuracy of its predictions [1–2]. Continuum mechanics predicts that a free, simply-supported beam tends to buckle in the first mode of buckling and that is the case for an in vitro loading of a single microtubule. However, in vivo imaging of microtubules indicates that the buckling mostly occurs in higher modes. This buckling mode switch takes place mostly because of lateral support of microtubules via their connections to actin and intermediate filaments, which themselves are tensile members of the tensegrity cytoskeleton model. Since these loads are exerted throughout the microtubule length, they introduce a considerable amount of microtubule bending behavior. The objective of this paper is to explore the influence of this flexural behavior on the accuracy of the tensegrity model, given the model’s underlying assumption that “every single member bears solely either tensile or compressive behavior”.
Calcific Nodule Morphogenesis by Aortic Valve Interstitial Cells: Synergism of Applied Strain and TGF-β1
Authors: Chen Joseph , Fisher Charles I. , Sewell-Loftin M. K. , Merryman W. David
Published: July 2013

Calcific Aortic Valve Disease (CAVD) is the third most common cause of cardiovascular disease, affecting nearly 5 million people in the United States alone. It is now the most common form of acquired valvular disease in industrialized countries and will likely affect more individuals in the coming years as the prevalence increases with life expectancy. It is known that the progression of CAVD is closely related to the behavior of aortic valve interstitial cells (AVICs); however the cellular mechanobiological mechanisms leading to dysfunction remain unclear. Generally, CAVD is characterized by the formation of calcified AVIC aggregates with an apoptotic core. These aggregates increase the leaflet stiffness and impede normal valve function. Multiple studies have investigated the effects of various biochemical cues on this process, such as transformation growth factor β1 (TGF-β1), on the regulation of nodule formation [1]. Additionally, Yip et al revealed that matrix stiffness controls nodule formation in vitro, with stiffer substrates promoting apoptotic nodule formation, while compliant substrates generated nodules containing cells with osteoblast markers [2]. This suggests that matrix stiffness is involved in the regulatory mechanisms of nodule formation and may initiate different types of nodule formation (i.e. osteogenic vs. dystrophic). In the current study, we examined the synergistic role of strain and TGF-β1 in the generation of calcified nodules AVICs.
Engineered Model of the Intestine Suggests Active Transport of Lipid by Lymphatics
Authors: Faulkner M. F. , Dixon J. Brandon
Published: July 2013

The lymphatic system has long been thought of as little more than a series of passive ducts as they serve to return fluid and proteins from interstitial spaces back to the blood, provide a route for immune cell trafficking, and transport dietary lipid from the intestine to the blood. Recent evidence has revealed that the lymphatics play an active role in lipid trafficking, and alterations in this function have been correlated with the presence of lymphatic diseases (Dixon, 2010). Here we describe the use of a two-cell, tissue engineered model to explore mechanisms of lipid transport across lymphatic endothelial cells (LEC). Previously this model was demonstrated to recapitulate essential features of the intestinal-lacteal interface with in the mammalian gut (Dixon et al., 2009). With our model we demonstrate, not only that lipid transport across the lymphatics is transcellular and ATP dependent, but also, this mechanism of transport utilizes the molecular motors dynein and kinesin.
Incomplete Fibers Affect Disc Biomechanics Higher Than the Fibers With Laxity: A Finite Element Model Analysis
Authors: Hussain Mozammil
Published: July 2013

Disc morphological disruptions — incomplete length and laxity in annular fibers — affect the behavior of the disc tissues in different ways. These changes in fibers alter the main function of the disc — inter-segmental load transfer along the spine — by affecting the surrounding extracellular disc tissue matrix. Tissues surrounding the altered fibers experience variations in stress distributions and the biomechanical reasoning behind variations in stress patterns may be multifactorial. While incomplete fibers are found in both healthy and aged discs with higher occurrences in the later ones [1], laxity in fibers is a progressive degenerative property [2]. How much the fiber incompleteness relative to the laxity in fibers contributes to the disc biomechanics remains to be clearly quantified?
2D Spatial Analysis of Chondrocyte Distribution: Implications for Identifying Representative Volume Elements for Multiscale Knee Modeling
Authors: Bennetts Craig , Chokhandre Snehal , Erdemir Ahmet
Published: July 2013

Finite element analysis (FEA) of the knee including joint, tissue and cell representations can be used to predict chondrocyte stresses in the cartilage given the joint level loading. This is of clinical significance since excessive loading on the joint may cause elevated cartilage stresses, potentially inducing chondrocyte apoptosis [1]. However, the level of complexity of a model that fully represents all cells within the cartilage is prohibitive given the current state of computational technology if results are desired in a timely fashion.
Functional Dynamic In-Vivo Stresses of the Mitral Valve Anterior Leaflet
Authors: Amini Rouzbeh , Eckert Chad E. , Carruthers Christopher A. , Koomalsingh Kevin , Minakawa Mashito , Gorman Robert C. , Gorman Joseph H. , Sacks Michael S.
Published: July 2013

Although mitral valve (MV) repair surgeries are commonly performed, their long-term durability has not been completely satisfying. In most cases, failure was a result of disruption at the leaflet, chordae, or annular suture lines. These failure modes suggest excessive stress and the resulting tissue damage as etiologic factors. The purpose of this study was to develop a method to better estimate functional dynamic in-vivo stresses in the MV anterior leaflet (AL) midsection. The stress was computed from the dynamic in-vivo strain measured experimentally. Numerous in-vivo and in-vitro studies (e.g. [3, 4]) have been conducted to quantify MV dynamic strain. We used in-vivo strain data obtained from our well-established ovine model [4]. To calculate the in-vivo strain, we employed the actual unloaded state of the tissue as the reference frame, measured for the first time in this study. The AL stress was then computed using our nonlinear structural constitutive model [5].
The Congenital Bicuspid Aortic Valve Can Experience Fluid Shear Stresses Associated With Sclerosis
Authors: Yap Choon Hwai , Saikrishnan Neelakantan , Rathan Swetha , Tamilselvan Gowthami , Vasilyev Nikolay V. , Yoganathan Ajit P.
Published: July 2013

Aortic valve calcification is a degenerative disease with high prevalence, especially amongst the elderly, and is a major cause of morbidity and mortality. Ex vivo experiments has shown that aortic valve leaflets are sensitive to their mechanical environment in a magnitude dependent manner. Fluid shear stresses, specifically, has been shown to affect inflammatory and remodeling responses relevant to aortic valve calcification [1,2].
Shear Strain of Mineral Crystals Calculated Using Wide-Angle X-Ray Scattering (WAXS) Techniques
Authors: Giri Bijay , Dong X. Neil , Almer Jon D. , Wang Xiaodu
Published: July 2013

The post-yield properties of bone mainly provide the estimation of its toughness and are directly related to the composition and structure of the tissue at basic building unit. Combining the recently developed synchrotron X-ray scattering techniques with a novel progressive loading scheme [1], a recent study has evinced that the internal strain of mineral and collagen phases in bone varies significantly before and after yielding of the tissue [2]. The minerals as well as collagen fibrils in bone have random and preferred orientation distribution according to the location within a body. Such orientation distribution will have significant influence on the deformation mechanisms of bone. This study hence aims to develop a methodology to determine local strain tensors in the mineral phase aligned in different orientations. To do so, the deformation of different lattice planes within individual mineral crystals is taken in account using the full WAXS spectrum.
A Novel In Vitro Model for Irreversible Electroporation Based Cancer Therapies and Treatment Planning
Authors: Szot Christopher S. , Arena Christopher B. , Garcia Paulo A. , Davalos Rafael V. , Freeman Joseph W. , Rylander Marissa Nichole
Published: July 2013

Irreversible electroporation (IRE) is a minimally invasive, localized, non-thermal tissue ablation technique that has shown tremendous promise as an effective cancer therapy option. This procedure uses electrodes to apply a series of short-duration, high intensity electric pulses to a targeted tissue region. These pulses can produce irreversible structural changes in the cell membranes within the targeted region, generating a controllable range of cell death [1].
Fluid Shear Stress Characteristics of the Ventricular Surface Versus the Aortic Surface of the Aortic Valve: An In Vitro Study
Authors: Yap Choon Hwai , Saikrishnan Neelakantan , Tamilselvan Gowthami , Yoganathan Ajit P.
Published: July 2013

Aortic valve calcification is a degenerative disease with high prevalence, especially amongst the elderly, and is a major cause of morbidity and mortality. Ex vivo experiments has shown that aortic valve leaflets are sensitive to their mechanical environment in a magnitude dependent manner. Fluid shear stresses, specifically, has been shown to affect inflammatory and remodeling responses relevant to aortic valve calcification [1,2]. Consequently, it has been proposed that the phenomenon of diseased calcium nodules developing exclusively on the aortic surface as opposed to the ventricular surface is due to the exposure of the aortic surface to disturbed shear stresses, whereas undisturbed shear stresses on the ventricular surface do not trigger calcification [3,4]. Additionally, it has been observed that the non-coronary leaflet of the AV is more susceptible to calcification, which is hypothesized to be due to reduced shear stresses from the lack of diastolic coronary flow [5].
A Comparative Study of the Main Pulmonary Artery and Ascending Aorta Biomechanical Behavior
Authors: Fata Bahar , Galdi Elena , Sacks Michael S.
Published: July 2013

During the prenatal period a state of physiologic pulmonary hypertension exists due to the equalization of pressures by the patent ductus arteriosus, resulting in similar wall thickness of the ascending aorta (AA) and main pulmonary artery (MPA). After birth, as the ductus arteriosus closes and pulmonary arterial pressure decreases, attenuation of medial smooth muscle occurs such that the ratio of medial thickness to external diameter decreases from about 25% in fetuses to less than 10% in infants 3 to 6 months of age. After the first year of life, thickness of the MPA is normally less than half that of the adjacent ascending aorta, although the diameters of the two great arteries remain the same relative to one another [1]. During homeostatic conditions, the total pulmonary and systemic blood flows are essentially identical. In spite of their comparable blood flow rate and common embryologic origin, the anatomic characteristics of these two segments of the cardiovascular system differ substantially [2]. Futhremore, both these arteries are affected by many congenital abnormalities and also are subject to hypertension. Knowledge of the normal biomechanical properties of these great arteries is important for surgical treamtment, angioplasty, and tissue engineering. It can also provide insight into the disease processes and is a prerequisite to the study of mechanical behavior during disease conditions. In this study we characterized the biaxial mechanical behavior of both arteries as a function of location, which has not been previously performed in the pulmonary trunk.
Parameter Correlation in Models of Hyperthermic Cell Death
Authors: Wright Neil T.
Published: July 2013

A number of mathematical models have been developed to predict the survival of cells after heating. Some of these models have been based on first principle arguments, while others have been empirically motivated. Some models have been inspired by analogs of damage to cells by ionizing radiation. Evidence exists for multiple targets leading to cell death, although precise definition of the pathways for the various temperature ranges and environmental conditions remains in question. For reviews of the cellular targets of heating, see [1], [2], or [3].
Irreversible Electroporation: An In Vivo Study Within the Dorsal Skin Fold Chamber
Authors: Qin Zhenpeng , Jiang Jing , Long Gary , Bischof John C.
Published: July 2013

Electroporation has been traditionally used to enhance molecular transport into cells (e.g. gene therapy) and through tissues (e.g. skin) by creating reversible pores with short electrical pulses [1]. Increasing the parameters (electrical field, pulse duration and number) can induce irreversible damage to the cells and tissue. Recently, irreversible electroporation (IRE) has been investigated as a new tumor ablation method [2]. The advantages of the IRE include the simple and fast procedure (train of μs pulses), sharp demarcation between treated and untreated regions, destruction of tumor cells while preserving the connective tissue, and minimal effect of immune response on treatment efficacy [3]. The unique interaction of electrical field with heterogeneous structures prevents damage to nerves, blood vessels and ducts [4]. IRE has been claimed to produce negligible thermal injury and protein denaturation typical to thermal ablation [5]. However, how each electroporation parameter in IRE affects tumor destruction and the possibility of heating remains to be studied in tumors vivo.
A Musculoskeletal Model With Prosthetic Knee During a Walk Cycle
Authors: Kia Mohammad , Guess Trent M.
Published: July 2013

Musculoskeletal models of movement typically use simplified representation of joints (i.e the knee joint as a hinge). This simplification can influence prediction of knee loading and muscle activation. Therefore, simulations that incorporate more realistic representation of knee structures, contact mechanics and muscle forces could increase our knowledge and understanding of joint and tissue loading during movement.
A Study on the Parameters Influencing Clearance of Mucus During Cough in a Model Trachea
Authors: Ragavan Anpalaki J. , Evrensel Cahit A. , Krumpe Peter
Published: July 2013

There are large numbers of physiological, material and geometrical parameters that influence the efficiency of clearance of mucus by cough in human airways. In this study the effect of ten independent variables on the displacement of simulated airway mucus in a rigid model trachea during cough is explored. This is the first attempt in combining these 10 parameters into a single non-dimensional group. Eight hundred (800) different combinations of these parameters are used to test its feasibility experimentally. All independent variables had variance inflation less than 10 indicating adequate independence among them. Although additional tests may be needed to confirm, the preliminary test results are promising.
Measurement of Intracellular Ice Formation and Water Transport During Freezing of Human Dermal Fibroblasts Using Differential Scanning Calorimetry
Authors: Mori Shoji , Choi Jeunghwan , Bischof John
Published: July 2013

In cryopreservation protocols maximum survivability is achieved when cooling occurs slowly enough to avoid Intracellular ice formation (IIF) yet fast enough to avoid solute effects injury (1). IIF plays a significant role in cell damage during cryopreservation. IIF has been extensively studied using cryomicroscopy. This technique is a useful tool to understand the dynamic processes during cooling, i.e. volume change of cells and IIF occurrence associated with temperature. However it has some limitations in being applied to biological systems. The central assumption in cryomicroscopy is that the projected two-dimensional area of the cell can be extrapolated to a spherical three-dimensional volume. While reasonable for spherical cell systems, this assumption is inappropriate for obtaining quantitative volumetric information in nonspherical cell systems. Differential scanning calorimetry (DSC), however, can be applied to nonspherical cell systems. Thus, DSC exotherms during freezing needed to be compared with cryomicroscopy observations in simple spherical cell systems. Several studies related to IIF using DSC havebeen reported (2)–(5). Most of them, however, discussed only IIF peaks and/or Extracellular ice formation (EIF). In order to predict the optimum cooling rate from DSC results, it is important to quantify not only IIF and EIF but also water transport (WT) during cooling at various cooling rates.