bluuebunny/crossref_metadata_2025 huggingface dataset:
A Longitudinal Assessment of Wall Shear Stress Variation on Arteriovenous Fistula Maturation
Authors: Jaghargh Ehsan Rajabi , Roy-Chaudhury Prabir , Succop Paul , Banerjee Rupak K.
Published: July 2013

Arteriovenous (AV) fistula is the most preferred form of vascular access for end-stage renal disease patients. Acute changes in hemodynamics and in particular wall shear stress (WSS) immediately after fistula placement are followed by the dilation of the vasculature luminal area to recover the normal physiological condition before surgery. However, vasodilation in AV fistula is not well understood and thus, the major goal of this study is to assess the longitudinal effect of wall shear stress on fistula maturation. Six AV fistulae with curved (n = 3) and straight (n = 3) configurations are created between the femoral artery and vein of three Yorkshire pigs. Anatomical configuration and flow measurements are performed at 2D (D: days), 7D, and 28D post-surgery. It is shown that fistulae with relatively higher baseline axial WSS may result in better maturation as compared to the ones with lower levels of baseline axial WSS. This finding is novel and hasn’t been reported in previous studies. Moreover, it is found that the longitudinal variation of WSS is also of high importance in prediction of the maturation of AV fistula. Fistulae whose mean axial WSS decreases over time achieve larger mean area, and therefore, favorable remodeling, while an increasing trend of axial WSS is detrimental to fistulae maturation. Also, it is found that curved fistula as compared to the straight configuration results in larger luminal area over time and thus, is the preferred form of AV fistula.
The Effect of Patellar Orientation on the Stiffness of the Porcine Femur-Medial Patellofemoral Ligament-Patella Complex
Authors: Kim Kwang E. , Hsu Shanlin , Fisher Matthew B. , Woo Savio L-Y.
Published: July 2013

Patellar dislocation has an incidence of 5.8 per 100,000 per year in the US, and this number increases by five-fold for adolescents 1. Conservative management has been the preferred treatment, but recent follow-up studies have revealed a high redislocation rate. Similar outcomes were also found following primary repair of the medial patellofemoral ligament (MPFL) 2. As a result, replacement with soft tissue autografts has gained attention for recurrent patellar dislocations in recent years 2, 3. As such, the selection of an appropriate graft tissue will need the knowledge of the biomechanical properties of the FMPC, particularly its stiffness for the performance of the graft.
High-Order Large Eddy Simulation of Flow in Idealized and Patient-Specific Total Cavopulmonary Connections
Authors: Anupindi Kameswararao , Frankel Steven , Chen Jun , Shetty Dinesh , Kennington Jeffrey , DeGan Jonathan , Rodefeld Mark D.
Published: July 2013

The Fontan procedure is used in pediatric situations in which infants have complex congenital heart disease or a single effective ventricle. This procedure by-passes right heart by connecting the left and right pulmonary arteries (LPA/RPA) to the superior and inferior vena cavae (SVC/IVC). The resulting reconstructed anatomy is called total cavopulmonary connection or TCPC. Knowledge of fluid dynamics in TCPC helps in optimizing the connection itself for reduced resistance as well as aids in designing cavopulmonary assist devices like viscous impeller pump (VIP) [1].
Quantifying the Structural and Mechanical Changes in Elastase Degraded Arteries as an In Vitro Model of Aortic Aneurysm
Authors: Chow Ming-Jay , Mondonedo Jarred Raymund , Zhang Katherine Yanhang
Published: July 2013

Common characteristics of aortic aneurysm include loss of elastin/smooth muscle cells, increase in fibrillary collagen, and increase in artery diameter [5]. Because of the high mortality rate of aneurysm rupture, it is desirable to be able to predict when a patient should have surgery to repair the dilated tissue. Current clinical practices involve predicting aneurysm rupture based on artery expansion rate and diameter. However, other parameters such as wall stiffness and peak wall stress may offer better predictions as to when an aneurysm will fail [8]. Previous studies have investigated the differences in elastin and collagen content of abdominal aortic tissue with and without abdominal aortic aneurysm (AAA) [1]. In another study, human aortic aneurysm tissue was tested in a biaxial tensile tester and the resulting stress strain curves were fitted using Fung type exponential strain energy function [7]. More extensive modeling of aneurysm tissue has been done by modifying the Holzapfel model to incorporate a parameter that characterizes the tissue weakening before the failure of the inner elastic laminae, ground matrix, or collagen fibers themselves [6]. Previous studies have found compositional and mechanical differences between aneurysm and healthy tissue. In addition, good structurally based models for arteries that are developing aneurysm exist but these are mostly theoretical [6]. In order to improve aneurysm rupture prediction techniques, a better understanding of how structural changes affect the mechanical properties of the artery is necessary.
The Effects of Apertures on Internal Pressure Measured During Shock Wave Exposure
Authors: Dal Cengio Leonardi Alessandra , Bir Cynthia , Ritzel Dave , VandeVord Pamela
Published: July 2013

Blast-induced neurotrauma with no overt damage to the skull has been identified as a condition suffered by military personnel serving in Iraq and Afghanistan (Glasser 2007). Symptoms of mild blast neurotrauma include alterations in cognitive functions (memory, language, problem-solving-skills) and in emotional behavior (mood swings, depression, anxiety, emotional outbursts) (Okie 2005). Despite the improvements in helmets and body armors, many veterans returning from the war front are being diagnosed with mild blast-neurotrauma (Warden 2006). Little is known of the means by which brain injury results from exposure to blast where there is no evident physical damage to the head. This study looks at possible mechanisms of brain injury related to blast by examining how pressure transmission occurs within a skull/brain surrogate system. Investigations were carried out to resolve the variables affecting skull dynamics and their effect on pressure imparted to the brain. Testing assessed internal pressure profiles as a function of ambient overpressure, orientation of the sample to shock-front exposure, and the presence of apertures.
Monte Carlo Simulation of Enhanced Laser Absorption in Tumors With Gold Nanorod Injection
Authors: Chen Yonghui , Ma Ronghui , Zhu Liang
Published: July 2013

The employment of gold nanoshells or nanorods in photothermal emerges as a promising technology in treatment of cancers in the past several years [1–4]. Gold nanoshells consist of a solid dielectric core nanoparticle (∼100 nm) coated by a thin gold shell (∼10 nm). Gold nanorods are usually small with a size of ∼10 nm and an aspect ratio of approximately four. By varying the size ratio, the nanostructures can be tuned to have strong absorption and scattering to a specific near infrared (NIR) laser at ∼800 nm. The enhancement in laser energy absorption is several orders of magnitude compared to some traditional dyes [1]. The laser energy absorbed in an area congregating by the nanostructures is transferred to the surrounding tissue by heat conduction. The nanostructures in tumors not only enables targeted delivery of laser energy, but also maximally concentrates a majority of the laser energy to the tumor region.
Development of a Lower Extremity Model for Finite Element Analysis at Blast Condition
Authors: Bertucci Robbin , Liao Jun , Williams Lakiesha
Published: July 2013

Explosions are the leading cause of death on the battlefield [1]. These explosives generate shock waves which stimulate large accelerations and deformations. The resulting loads pose serious threats to military and civilians. Since lower extremities are in direct contact with the ground, the lower extremities are commonly injured during explosions [2]. These injuries could be seriously fatal. Although experimental studies have been performed to advance these understandings [2], limited progress has been made in computational analysis of shock waves on the lower extremity.
Flexural Rigidity of Intact Chlamydomonas Flagella Measured With an Optical Trap
Authors: Okamoto R. J. , Ying J. , Lewis B. L. , Ranz E. C. , Shao J.-Y. , Dutcher S. K. , Bayly P. V.
Published: July 2013

Flagella and cilia are thin, active organelles protruding from cells that are used to propel the cell or move fluid. The flagellated alga Chlamydomonas reinhardtii is a uni-cellular model organism well-suited for the study of flagellar and cilia mechanics.
High Frequency Electroporation for Cancer Therapy
Authors: Arena Christopher B. , Sano Michael B. , Rylander Marissa Nichole , Davalos Rafael V.
Published: July 2013

Electroporation is a non-linear biophysical mechanism in which the application of an external pulsed electric field leads to an increase in the permeability of cellular membranes. The extent of electroporation is attributed to the induced buildup of charge across the membrane, and consequently, transmembrane potential (TMP). Increasing the TMP has been described to produce various permeabilizing effects, wherein the formation of hydrophilic, aqueous pores becomes energetically favorable [1]. If the pulse parameters are tuned such that the membrane defects are only temporary, and the cell remains viable, the process is termed reversible electroporation. As a cancer therapy, reversible electroporation has been employed to increase the cellular uptake of chemotherapeutic drugs. Irreversible electroporation (IRE) results when membrane defects are permanent, leading to cell death. Recently, IRE has been recognized as an independent means to destroy tumors without the use of adjuvant drugs and prior to the onset of thermal injury [2].
Structural Simulation of a Mouse-Specific Abdominal Aorta
Authors: Bols Joris , Trachet Bram , Degroote Joris , De Santis Gianluca , Mortier Peter , Verhegghe Benedict , Segers Patrick , Vierendeels Jan
Published: July 2013

In the last years there is an increasing interest in patient-specific simulations of the fluid-structure interaction in aortic aneurysms, a.o. to better understand the growth and development of the aneurysm and to support diagnosis through assessment of its rupture potential. In order to verify these simulations, validation is an important and difficult task. Given ethical constraints, the slow time course of the disease in humans and the absence of true baseline data in a healthy aorta, these studies are difficult to perform in humans. This is particularly true for aneurysm rupture research, as rupture will normally be prevented by surgery and access to post-mortem tissue is not always possible. In order to overcome these problems an AAA mouse model can be used [1].
Correlation Between Plaque Composition and Shear Stress Using Three-Dimensional Reconstructed Histology and Computational Fluid Dynamics of Diseased Human Carotid Arteries
Authors: van der Heiden Kim , Groen Harald C. , Speelman Lambert , van der Lugt Aad , van der Steen Anton F. W. , Niessen Wiro , Gijsen Frank J. H. , Wentzel Jolanda J.
Published: July 2013

Wall shear stress (WSS) has been shown to play a crucial role in atherosclerotic plaque formation and progression. Moreover, some recent studies suggest that WSS is also involved in determining plaque composition (Cheng et al., 2006) and plaque destabilization in advanced atherosclerosis (Groen et al., 2007). More detailed studies on the relationship between WSS and plaque composition are needed to confirm those relationships.
Collagen-Agarose Co-Gels as a Model for Collagen-Matrix Interaction in Soft Tissue
Authors: Lake Spencer P. , Doggett Sadie , Barocas Victor H.
Published: July 2013

Connective soft tissues have complex mechanical properties that are determined by their collagen fiber network and surrounding non-fibrillar material. The mechanical role of non-fibrillar material and the nature of its interaction with the collagen network remain poorly understood, in part because of the lack of a simple experimental model system to examine and quantify these properties. The development of a simple but representational experimental system will allow for greater insight into the interaction between fibers and the non-fibrillar matrix. Reconstituted Type I collagen gels are an attractive model tissue for exploring micro- and macroscale relationships between constituents (e.g., [1–2]), but standard collagen gels lack the non-fibrillar components (i.e., proteoglycan, minor collagens, etc.) present in native tissue. A recent study [3] added low quantities of agarose to collagen gels, which dramatically increased the shear storage modulus with minimal changes to the collagen fiber network. In this study, we suggest that collagen-agarose co-gels can serve as a model system to investigate the mechanical role of non-fibrillar ECM. Even though agarose is relatively compliant at low concentrations, and collagen fibers are very stiff in tension, we hypothesized that the presence of agarose in co-gels would have a pronounced effect on structural response and mechanical behavior in tensile loading. Therefore, the objective of this study was to examine the properties of collagen-agarose co-gels to understand better the nature of, and the relationships between, the collagen fiber network and non-fibrillar matrix of simplified tissue analogs.
In Vivo Three-Dimensional Analysis of the Facet Joint Surface Center
Authors: Ishihara Y. , Espinoza Orías A. A. , An H. S. , Simon P. , Andersson G. B. , Inoue N.
Published: July 2013

Facet joints are considered to play important roles in controlling spinal segmental motion and load transmission. It has been reported that 15–45% of low back pain is caused by facet joint diseases (1). Numerous studies on facet joint orientation have been reported in the literature; however, data on facet joint position is limited. Since the so-called “three-joint complex” is comprised of an intervertebral disc and two facet joints, it is important to determine the spatial relationship among these components to understand motion segment kinematics. Three-dimensional (3D) location of the facet joint may also provide important information for the studies on lumbar canal stenosis and spondylolisthesis. There has been no study, to our knowledge, to evaluate 3D position of the facet joint within the spine. The aim of this study was to determine accurately the facet joint position by using a subject-based computed tomography (CT) model and 3D measurement techniques, and analyze level, gender, ages and effects.
Stereoscopic Motion Tracking System
Authors: Calderon A. , Dembele M. , Hossain B. , Noor Y. , Ovsiew S.
Published: July 2013

The “National Institute of Neurological Disorders and Stroke” defines Cerebral Palsy as a neurological disorder that affects body movement and muscle coordination. This condition usually appears at birth or during the first three years of life [3]. Treatment for children with Cerebral Palsy is extensive and can include any or all of the following: physical/occupational therapy, speech therapy, medicine, surgery, and orthopedic devices. Physical therapy involves having the child perform several repetitions of a set of exercises that will target the specific muscle group that needs to be worked on. A technique that has recently been employed in physical therapy is the use of video games [2], this allows the therapist to have the child perform similar sets of exercises while at the same time motivate and entertain the child.
An In Vitro Model to Quantify the Effects of Fluid Shear Stress on Lymphatic Pump Function
Authors: Kornuta Jeffrey A. , Korneva Arina , Dixon J. Brandon
Published: July 2013

Nearly all tissues are supported by the lymphatic system for a variety of functions, including the regulation of fluid balance, the removal of particulate matter from the interstitium, as well as the transport of fat from the intestine to the blood, among others. Despite these important functions, very little is known about the particular mechanisms through which the lymphatics fulfill these roles. Lymphedema, a chronic disease characterized by an inability of the lymphatics to maintain tissue homeostasis and estimated to affect over 130 million people worldwide, can result in serious clinical problems for which there are very few beneficial cures or therapies [1]. While fluid stagnation is the primary clinical manifestation of the disease, severe lymphedema is often correlated with tissue remodeling and the gross accumulation of lipid [1]. Given these symptoms, one must consider the breakdown in the lymphatic response to mechanical load (i.e. fluid balance) in order to understand the progression of the disease.
Evaluation of Wrist Cartilage With and Without Scapholunate Ligament Injury in Pre and Post Operation Subjects
Authors: Sturgeon Dannica L. , Lee Sang-Pil , McIff Terence E. , Toby E. Bruce , Fischer Kenneth J.
Published: July 2013

Hand and wrist injuries commonly occur and can be debilitating. Scapholunate dissociation generally requires surgery, and if left untreated, can lead to scapholunate advanced collapse (SLAC wrist) and associated osteoarthritis [1]. The overall goal of this research is to make a positive impact on the assessment and treatment of wrist injuries and on prevention of osteoarthritis as a result of injury.
Non-Destructive Real-Time Imaging of Cell Seeded Tissue Engineered Scaffolds
Authors: Whited Bryce M. , Hofmann Matthias C. , Rylander Chris G. , Goldstein Aaron S. , Freeman Joseph W. , Furth Mark , Soker Shay , Wang Ge , Xu Yong , Rylander Marissa N.
Published: July 2013

The use of tissue engineered scaffolds in combination with progenitor cells has emerged as a promising strategy to restore or replace tissues damaged by disease or trauma. In addition to being biocompatible and exhibiting appropriate mechanical properties, scaffolds must be designed to sustain cell attachment, proliferation, and differentiation to ultimately produce the desired tissue once implanted in the patient [1]. Conventional techniques used to assess successful scaffold design include cell viability stains, DNA assays, and histological sectioning/staining. While significant information can be gained from using these methodologies, they are destructive to the sample and only provide snapshots of scaffold and cell development at a limited number of time points. Consequently, key temporal and spatial information relating to tissue regeneration in the scaffold is lost utilizing these techniques. Thus, the ability to non-destructively monitor cell viability, proliferation, and differentiation in real-time is of great importance for scaffold design and tissue engineering [2].
An Experimental Study of the Effects Anatomical Variations Have on Collateral Flows Within the Circle of Willis
Authors: Fahy Paul , Delassus Patrick , O’Flynn Padraig , Morris Liam
Published: July 2013

The circle of Willis (CoW) is a complex arterial network comprising of major cerebral arteries that converge to form a pentagonal arrangement as shown in Figure 1(A). This arterial network supplies oxygen-enriched blood to the brain. An incomplete CoW can exist in up to 50% of cases [1]. These missing vessels can be accommodated by the collateral flow feature within the CoW configuration. In certain circumstances, anatomical variations within the CoW can result in undesirable flow patterns [2–3]. It is unclear from the literature what effects these variations can have on blood flow collision paths within a complete CoW.
Assessment of Cardiac Function During Mechanical Circulatory Support: A Simulation Study
Authors: Ferreira Antonio , Wang Yajuan , Gorcsan John , Antaki James F.
Published: July 2013

Ventricular Assist Devices (VADs) have emerged as the standard of care for advanced heart failure (HF) patients, requiring mechanical circulatory support [1]. Regardless of the intended use, a small — yet significant — portion of implanted patients exhibits signs of recovery of the left ventricular function [2].
Bidirectional Oscillatory Shear Stress Increases Pro-Atherogenic Gene Expressions (I-CAM1, E-Selectin and IL-6) in Endothelial Cells
Authors: Chakraborty Amlan , Jala Venkatakrishna R. , Chakraborty Sutirtha , Berson R. Eric , Sharp M. Keith , Haribabu Bodduluri
Published: July 2013

Wall shear stress (WSS) plays a key role in altering intracellular pathways and gene expression of endothelial cells, and has significant impacts on atherosclerotic plaque development (1–3). Further, the atherogenic regulators Leukotriene B4 (LTB4) and Lipopolysaccharide (LPS) have significant impacts on the pathophysiology of many inflammatory diseases. This study investigates the effects of oscillatory shear directionality on pro-atherogenic gene expression (I-CAM, E-Selectin, and IL-6) in the presence of LTB4 and LPS. An orbital shaker was used to expose the endothelial cells to oscillatory shear in culture dishes, and Computational fluid dynamics (CFD) was applied to quantify the shear stress on the bottom of the orbiting dish. Directionality of oscillatory shear was characterized by a newly developed hemodynamic parameter — Directional oscillatory shear index (DOSI), which was demonstrated in a previous study to significantly impact cell morphology (4). Results showed that DOSI significantly altered gene expression. Therefore, directionality of shear modulates atherosclerotic gene expression in vitro and thus, may influence the formation of atherosclerotic plaque in vivo.
Self-Assembling Peptide Nanofibers for MMP Delivery and Cardiac Regeneration in Diabetes
Authors: Hurley Jennifer R. , Sheikh Abdul Q. , Beckenhaupt Meredith , Ingram Cameron , Mutchler Andrew , Narmoneva Daria A.
Published: July 2013

Diabetes is a serious problem in the United States, afflicting 7.8% of the population with annual medical costs estimated at $116B in 2007 (1). Diabetic cardiomyopathy (DCM) is a cardiovascular complication of diabetes resulting in pathological alterations to the myocardium including circulatory defects, impaired heart muscle contraction, and progressive fibrosis. Cardiac fibrosis is associated with an imbalance between the deposition of the extracellular matrix (ECM) proteins by cardiac fibroblasts and the ECM proteolytic degradation via matrix metalloproteinases (MMPs). Recent studies have demonstrated that in the diabetic heart, expression and activity of MMP-2 are reduced, resulting in increased collagen accumulation and cardiac dysfunction (2). These observations suggest that a MMP-related mechanism may contribute to cardiac fibrosis, and that it may be attenuated through stimulation of native MMP-2 expression or delivery of exogenous MMP-2. Therefore, reduced MMP-2 activity in DCM may represent a novel target for therapeutic treatment (3). To achieve this, a special proteolytically-stable delivery scaffold would be needed, because native ECM is rapidly degraded by MMPs. The goal of this study is to determine if self-assembling peptide nanofibers can be used for long-term (several weeks) MMP delivery and enhancement of cardiac remodeling. This study tests the hypothesis that increased MMP-2 concentration (native or exogenous) in the nanofiber environment will promote matrix remodeling in diabetic cardiac fibroblasts in vitro.
The Effects of a Functionally Graded Cellular Structure on Impact Properties of a Hip Joint: A Finite Element Study
Authors: Kara T. , Takak S. , Ali M. , Hoffman J.
Published: July 2013

Hip implants have successfully been employed since the 1900’s. With the development of the total hip arthroplasty (THA) in 1960 by Sir John Charnley (Mohamed N. Rahaman, 2007), Since then the development of wear resistant materials has been extensive and improved the life time of hip prosthesis. (V. Banchet, 2007) THA wholly reconstructs the hip joint and enables joint kinematics. Components include an acetabulum liner and cup and femoral head and neck. Common combinations included metal on plastic, metal on metal, and ceramic on ceramic head and cup compnents.
Bone Biomechanical Behavior in Adult Mice is Regulated by Osteoblast Gi Signaling in a Sex- and Site-Specific Manner
Authors: Fields Aaron J. , Millard Susan M. , Bailey Jeannie F. , O’Carroll Dylan , Lotz Jeffrey C. , Nissenson Robert A.
Published: July 2013

Osteoporosis decreases bone strength owing to loss of bone mass and deterioration in bone microstructure. The maintenance of bone mass and microstructure depends, at least in part, on the signaling and function of osteoblasts. For example, Gi-coupled signaling by G-protein coupled receptors endogenous to osteoblasts has been shown to restrict cortical and trabecular bone formation in female mice [1,2]. This suggests that inhibiting Gi-coupled signaling in osteoblasts may be an effective strategy for the development of anabolic osteoporosis therapies. However, it remains unclear whether inhibiting Gi-coupled signaling improves bone biomechanical behavior. Thus, the objectives of this study were to: 1) quantify the effect of Gi-coupled signaling on bone strength and bone stiffness; and 2) determine the effects of this signaling mechanism on cortical and trabecular microstructure and on the relationship between mechanical behavior and microstructure.
Material Properties of the Developing Bone-Cartilage Interface in the Human Fetal Spine
Authors: Paietta Rachel C. , Burger Evalina , Ferguson Virginia L.
Published: July 2013

Treatment of disc degeneration and subsequent device interfacing in the spine are limited by a poor understanding of the mechanics of the bone-cartilage interface between vertebral bodies (VB) and the intervertebral disc (IVD). Additionally, tissue engineering strategies are under investigation despite a lack of information on the structure of the developing interface and mechanical properties during endochondral ossification. Fetal tissue provides an initial reference to study the developing mineralization patterns and mechanical property gradient at the transition between mineralized and soft tissues. Through nanoindentation, quantitative back scattered electron microscopy (qBSE) (Ferguson 2003) and energy-dispersive X-ray spectroscopy (EDX), it is possible to study mineralized tissue formation from both mechanical and compositional perspectives at scales relevant to the mechanics of the interface.
Stress State Dependence of Human Placenta Mechanical Behavior
Authors: Weed Benjamin , Borazjani Ali , Patnaik Sourav , Prabhu Rajkumar , Franz Thomas , Horstemeyer M. F. , Williams Lakiesha , Liao Jun
Published: July 2013

Maternal trauma affects 5–8% of all pregnancies and is the leading nonobstetric cause of maternal death in the United States [1]. The most common cause of trauma is motor vehicle accident (MVA) and the most common pathology is abruptio placentae, detachment of the placenta from uterus, which leads to serious maternal and fetal consequences [2].
Microstructure Motivated Growth and Remodeling of the Lamina Cribrosa in Early Glaucoma
Authors: Grytz Rafael , Sigal Ian A. , Ruberti Jeffrey W. , Downs J. Crawford
Published: July 2013

Glaucoma is a leading cause of blindness in the world and is due to the loss of retinal ganglion cell axons. These axons deteriorate in a region in the posterior pole of the eye known as the optic nerve head (ONH). The axons pass through the lamina cribrosa (LC) as they exit the eye at the ONH. The LC is characterized by a porous, connective tissue structure composed of laminar beams. The function of the LC is unclear, but is believed to include providing mechanical support to the axons as they transition from inside the pressurized globe to the lower pressure orbital space. Early experimental glaucoma studies have shown that the LC remodels into a thicker, more posterior structure which incorporates more connective tissue after chronic IOP elevation [1,2]. The process by which this occurs is unknown. These structural changes are assumed to play an important role in the pathophysiology of the ocular disease glaucoma, where elevated IOP is known to be the most relevant risk factor.
How Do Cells Sense Substrate Stiffness? Effects of Substrate Elasticity and Thickness on the Behavior of Rat Aortic Smooth Muscle Cells
Authors: Matsumoto Takeo , Matsui Norihiro , Ishiguro Mai , Nagayama Kazuaki
Published: July 2013

There has been growing evidence that elasticity of substrate has significant effects on cells on it. For example, smooth muscle cells (SMCs) on elastic substrate increase their adhesion area as the substrate gets stiffer [1]. SMCs on substrate with elasticity gradient move to stiffer region [2]. Even differentiation of mesenchymal stem cells depends on substrate elasticity [3]. Thus, it is crucial to investigate how cells sense substrate elasticity to understand mechanical aspects of cell biology.
Hemodynamics of Elastase-Induced Aneurysms in Rabbit: A New High Flow Bifurcation Model
Authors: Zeng Zijing , Kallmes David F. , Ding Yong Hong , Kadirvel Ramanathan , Lewis Debra A. , Dai D. , Robertson Anne M.
Published: July 2013

An intracranial aneurysm (IA) is a pathological condition of cerebral arteries characterized by local enlargements of the arterial wall, typically into a saccular shape. Rupture of the aneurysm sac can result in devastating cerebral hemorrhage. Hemodynamic factors are believed to play an important role in initiation, development and rupture of IAs [1–3]. However, the coupling between hemodynamics and aneurysm pathophysiology is complex and remains poorly understood. Patient specific diagnostics regarding risk of rupture can be substantially advanced by improving our understanding of the in-vivo response of the aneurysm wall to intra-saccular hemodynamic stresses. A mechanism for fundamental studies of the impact of chronically altered WSS on the intact vascular wall is provided by animal models. However, cerebral aneurysms have not been shown to occur naturally in animals. Thus, a number of animal models have been created for studying aneurysm pathogenesis including those in mice, rats, rabbits, canines, swine and primates. To make meaningful use of these models, it is important to evaluate their relevance to human biomechanics and pathophysiology.
Influence of Zona Pellucida Area Expansion Stiffness on the Passive Response of Oocytes to Osmotic Loading
Authors: Oungoulian Sevan R. , Chan Kelvin , Barritt Jason , McDonald Casey A. , Copperman Alan B. , Elad David , Ateshian Gerard A.
Published: July 2013

The zona pellucida (ZP) is a thick glycoprotein shell surrounding the mammalian egg cell (oocyte) that regulates spermatozoa access during fertilization and protects the zygote during early embryonic development [1]. Hardening of the zona pellucida over the cell fertilization cycle is a well-recognized phenomenon and has been investigated using contact methods to measure shear and bending elasticity from indentation and micropipette aspiration [2, 3]. However, the area elasticity of the ZP, which provides resistance to cell swelling under variable osmotic environments, has not yet been reported. A recently devised theoretical model [4] suggests that the ZP area expansion modulus may be determined through non-contact hypo-osmotic loading of the oocyte. If successful, this method may be suited for implementation by practicing fertility health professionals during routine manipulation.
Level- and Region-Specific Properties of Young Human Lumbar Annulus
Authors: Stemper Brian D. , Yoganandan Narayan , Shender Barry S. , Paskoff Glenn R. , Pintar Frank A. , Baisden Jamie L.
Published: July 2013

The objective of this study was to determine the material properties of the human lumbar intervertebral disc annulus as a function of anatomical region and spinal level. Samples from minimally or nondegenerated spines were extracted from young post mortem human subjects and tested in tension. Statistically significant differences were found based on anatomical region. Trends appear to indicate spinal level dependency, although additional samples are required to attain statistical significance. It is possible to use finite element models incorporating these region- and level-specific properties to quantify internal load-sharing and delineate the mechanism of disorders such as herniation.
Simulated Deployment of Percutaneous Transvenous Mitral Annuloplasty Device Into Human Coronary Sinus Vessel
Authors: Pham Thuy M. , Wang Qian , DeHerrera Milton , Sun Wei
Published: July 2013

Functional mitral regurgitation (MR) is the consequence of left ventricular dysfunction occurring after ischemic heart disease and often has poor prognosis. Surgical repair and replacement of the mitral valve are currently being used to treat severe functional MR However, the technique carries high mortality rate [1] and is not suitable for patients with comorbidities and advanced age [2]. Recently, a new non-surgical intervention, percutaneous transvenous mitral annuloplasty (PTMA), is emerging as an attractive endovascular alternative that is less invasive, less recovery time, and cost effective. The device is delivered percutaneously into the coronary sinus (CS) vessel and once embedded, it contracts and shortens the septo-lateral distance of the mitral annulus, hence improve MR. However, despite of its feasibility, current clinical trials reported severe adverse events, such as device fracture [3]. The biomechanical interaction between the CS wall and the stent plays a critical role in the outcome of the deployment and the device performance. In this study, we proposed to analyze this interaction by developing Finite Element (FE) models of the CS vessel and the PTMA anchors and analyzing the peak stresses, strains, interaction forces (shear, normal) after the deployment of the proximal and distal anchors into a realistic patient-specific CS model.
A Method to Delineate Irreversible Electroporation From Thermal Damage Validated Ex Vivo With Real-Time Temperature
Authors: Garcia Paulo A. , Rossmeisl John H. , Ellis Thomas L. , Davalos Rafael V.
Published: July 2013

Irreversible electroporation (IRE) is a new non-thermal focal tissue ablation technique that uses low-energy electric pulses to destabilize cell membranes, thus achieving tissue death [1]. The procedure is minimally invasive and is performed through small electrodes inserted into the tissue with pulse delivery of about one minute. The pulses create an electric field that induces an increase in the resting transmembrane potential (TMP) of the cells [1]. Depending on the magnitude of the induced TMP, the electric pulses can have no effect, transiently increase membrane permeability, or cause cell death [1]. Our group has confirmed the safety of the procedure in brain with three experimental dogs [2]. We also treated a canine patient with IRE and radiation therapy for a non-resectable, high-grade glioma, resulting in complete remission of the tumor at four months [3].
Tibiofemoral Kinematics of the Knee During the Stance Phase of Gait After ACL Deficiency
Authors: Chen Chih-Hui , Li Jing-Sheng , Hosseini Ali , Gadikota Hemanth Reddy , Kozanek Michal , Gill Thomas J. , Li Guoan
Published: July 2013

Numerous studies have demonstrated that ACL deficiency could lead to further meniscus tear and cartilage degeneration. The post-injury joint degeneration has been mainly attributed to altered joint kinematics caused by ACL deficiency. Therefore, understanding of the effect of ACL injuries on knee joint motion is critical for development of conservative treatment or surgical reconstruction of the ACL injured knees. However, few data have been reported on the influence of ACL deficiency on knee joint motion during gait [1,2] — the most commonly performed daily activities. The objective of this study was to determine the 6DOF kinematics of the knee after ACL injuries during gait on a treadmill and to compare the kinematics data to those measured from the intact contralateral side using a combined dual fluoroscopic imaging system (DFIS) and MR image technique [3,4]. We hypothesized that the 6DOF tibiofemoral kinematics of ACL-deficient knees would be altered even under low demand activities such as walking.
Geometric Analysis and Decomposition of Normal and Hypertensive Human Right Ventricle From Diagnostic Medical Imaging
Authors: Wu J. , Brigham J. C. , Simon M. A. , Kim K. , Sacks M. S.
Published: July 2013

Pulmonary hypertension (PH) is a cardio-pulmonary illness which affects all ages and racial populations, and induces significant changes to right ventricle (RV) shape and function. As such, the functional state of the RV is commonly thought to be a major determinant of symptoms and survival rates for PH. However, there has been little success to-date to identify clinically obtainable metrics of RV shape and deformation as a means to detect the onset and progression of PH. This difficulty is heightened by the complexity of RV shapes, which continues to confound basic and clinical scientists.
A Cadaveric Study: Is There a Correlation Between Clinical Tests for Anterior-Posterior Laxity and Rotary Instability?
Authors: Fucinaro Kaity H. , Denney Linda , Cyr Adam J. , Maletsky Lorin P.
Published: July 2013

Instability is not necessarily determined by knee laxity, yet passive clinical tests are included in the examination which determines the functional status of the knee. The current arthrokinematic findings and validated clinical tests support the definition of excessive sagittal plane and frontal-plane laxity; however it is unknown if these findings in a single plane predict rotary instability of the knee.
The Effects of High Porosity Stent Configurations on Cerebral Aneurysm Hemodynamics
Authors: Babiker Haithem , Ryan Justin , Gonzalez L. Fernando , Albuquerque Felipe , Collins Daniel , Elvikis Arius , Frakes David H.
Published: July 2013

Coil embolization is the most common endovascular treatment for cerebral aneurysms at many centers [1]. Nevertheless, the coiling of wide-neck aneurysms is a challenge. Incomplete filling of the aneurysmal sac due to coil configuration challenges and aneurysmal growth can often lead to recurrence. To assist treatment with coils, clinicians may deploy a high porosity stent in a staged process to act as a supporting bridge for coils. The stent is first deployed across the aneurysmal neck, and multiple coils are then deployed into the aneurysmal sac 6–8 weeks later [2]. Under certain circumstances, coil deployment is not possible and high porosity stents alone are used for treatment [2–3].
Abdominal Aortic Aneurysm Growth: The Association of Aortic Wall Mechanics and Geometry
Authors: Washington Christopher B. , Shum Judy , Muluk Satish C. , Finol Ender A.
Published: July 2013

In an effort to prevent rupture, patients with known AAA undergo periodic abdominal ultrasound or CT scan surveillance. When the aneurysm grows to a diameter of 5.0–5.5 cm or is shown to expand at a rate greater than 1 cm/yr, elective operative repair is undertaken. While this strategy certainly prevents a number of potentially catastrophic ruptures, AAA rupture can occur at sizes less than 5 cm. From a biomechanical standpoint, aneurysm rupture occurs when wall stress exceeds wall strength. By using non-invasive techniques, such as finite element analysis (FEA), wall stress can be estimated for patient specific AAA models, which can perhaps more carefully predict the rupture potential of a given aneurysm, regardless of size. FEA is a computational method that can be used to evaluate complicated structures such as aneurysms. To this end, it was reported earlier that AAA peak wall stress provides a better assessment of rupture risk than the commonly used maximum diameter criterion [1]. What has yet to be examined, however, is the relationship between wall stress and AAA geometry during aneurysm growth. Such finding has the potential for providing individualized predictions of AAA rupture potential during patient surveillance. The purpose of this study is to estimate peak wall stress for an AAA under surveillance and evaluate its potential correlation with geometric features characteristic of the aneurysm’s morphology.
Effect of In Vivo Physical Interaction of the Ascending Aorta and Main Pulmonary Artery on Postnatal Surface Growth Patterns in Ovine
Authors: Fata Bahar , Gottlieb Danielle , Mayer John E. , Sacks Michael S.
Published: July 2013

Congenital abnormalities of the main pulmonary artery (MPA) and ascending aorta (AA) often necessitate surgical repair or the use of a valved conduit replacement, requiring multiple re-interventions due to regurgitation or failure of the prosthetic conduit. In recent years there has been a growing interest in the development of a living autologous tissue graft that could address the critical need for growing substitutes in the repair of congenital cardiovascular defects [1]. Regardless of the particulars of the therapeutic approach, the detailed growth characteristics of the native artery is required to establish the baseline dimensional changes post-implantation. During normal embryogenesis the Truncus Arteriosus begins to split and form into the anterior pulmonary artery and the posterior aorta [2]. Due to their common embryologic origin from a single outflow tract, there are disease conditions that originate in one artery and eventually affect both arteries [3]. Therefore, the postnatal growth deformation of both the MPA and AA was computed to quantify the effects of the mechanical association of these two arteries.
Induced Intramedullary Pressure by Dynamic Hydraulic Stimulation and Its Potential in Attenuation of Bone Loss
Authors: Hu M. , Cheng J. , Ferreri S. , Serra-Hsu F. , Lin W. , Qin Y. X.
Published: July 2013

Bone loss is a critical health problem of astronauts in long-term space missions. A growing number of evidence has pointed out bone fluid flow as a critical regulator in mechanotransductive signaling and bone adaptation. Intramedullary pressure (ImP) is a key mediator for bone fluid flow initiation and it influences the osteogenic signals within the skeleton. The potential ImP-induced bone fluid flow then triggers bone adaptation [1]. Previous in vivo study has demonstrated that ImP induced by oscillatory electrical stimulations can effectively mitigate disuse osteopenia in a frequency-dependent manner in a disuse rat model [2, 3]. In order to develop the translational potentials of ImP, a non-invasive intervention with direct fluid flow coupling is necessary to develop new treatments for microgravity-induced osteopenia/osteoporosis.
Collagen Scaffold-Membrane Composites for Mimicking Orthopedic Interfaces
Authors: Harley Brendan A. C.
Published: July 2013

Tendons are specialized connective tissues that transmit load between bone and muscle, and whose microstructural and compositional features underlie their function. The biological solution to the problem of connecting relatively compliant tendon to stiffer (∼2 orders of magnitude) bone is a gradient interface zone ∼100μm wide. Over the tendon-bone-junction (TBJ) a linear transition takes place in the ECM inorganic:organic (mineral:collagen) ratio as well as mineral crystallinity from that of tendon to bone. While small TBJ injuries can heal via regeneration, severe defects undergo repair-mediated healing characterized by fibrocartilagenous scar tissue with inferior biomechanical and functional properties. Severe TBJ injuries are common in athletes, the elderly, and following severe craniofacial and extremity trauma. Many tendon injuries (i.e. supraspinatus injuries), particularly those associated with acute trauma, are prone to occur at the TBJ due to high levels of region-specific stress concentrations; rotator cuff tendons injuries, one of the most common TBJ injuries, exhibit re-tears at rates as high as 94%. The scale of such defects and current poor clinical results suggest the need for a biomaterial solution that can mimic the dynamic heterogeneities of the native insertion and tendon body to induce rapid, functional regeneration. Three-dimensional collagen-GAG (CG) scaffolds have been successfully used clinically to regenerate large soft tissue defects (skin, peripheral nerves); they act by mimicking the native extracellular matrix (ECM) of the damaged tissue to prevent wound contraction and scar tissue synthesis. However these scaffolds have not traditionally been used for orthopedics due to an inability to recapitulate two critical features of orthopedic tissues: multiscale structural complexity, biomechanical properties. While the multi-scale properties of tendon itself cannot be currently replicated, nature provides an alternative paradigm: core-shell composites. Plant stems combine a porous core with a dense shell to aid osmotic transport (core) while maintaining sufficient tensile/bending stiffness (shell); many bird beaks use core-shell designs to efficiently enhance compressive strength. Here we describe development of three biomaterial engineering approaches to create the next generation of regeneration templates for tendon insertion injuries: composite, spatially patterned CG biomaterials.
Interfacial polymer ferroelectric dipole induced electric field effect on the photovoltaic performance of organic solar cells
Authors: Rastogi Alok C.
Published: July 2013

Effect of a dipolar electrical field on the photovoltaic properties of polymer solar cell devices in the bulk heterojunction structure based on 1:1 blend of donor-regioregular poly(3-hexylthiophene), P3HT, and acceptor-phenyl-C61-butyric acid methyl ester, PCBM, polymer semiconductor material is studied. With a thin layer of poled ferroelectric P(VDF + TrFE) copolymer film having oriented dipoles inserted at the interface between poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate) (PEDOT:PSS) and the P3HT:PCBM composite layer, significant improvement in the short-circuit photocurrent and open circuit voltage was observed consistent with the increase in the poling voltage. Remnant polarization charge due to dipoles produces localized electric field of 300–700 V · μm−1. The presence of the electric field helps increase the charge transfer exciton dissociation rates at the P3HT (donor)–PCBM (acceptor) interfaces, reduces the exciton recombination probability and increases the carrier extraction yield resulting in the enhancement in the photocurrent. Solar cell device in a structure having a poled P(VDF + TrFE) copolymer film sandwiched between the two P3HT:PCBM composite layers shows only a marginal improvement in the photovoltaic properties. This is mainly attributed to shielding of dipolar field from free charge carries and the inferior nanoscale morphology of the P3HT:PCBM composite layer.
Time course of a perceptual enhancement effect for noise-masked speech in reverberant environments
Authors: Brandewie Eugene , Zahorik Pavel
Published: July 2013

Speech intelligibility has been shown to improve with prior exposure to a reverberant room environment [Brandewie and Zahorik (2010). J. Acoust. Soc. Am. 128, 291–299] with a spatially separated noise masker. Here, this speech enhancement effect was examined in multiple room environments using carrier phrases of varying lengths in order to control the amount of exposure. Speech intelligibility enhancement of between 5% and 18% was observed with as little as 850 ms of exposure, although the effect's time course varied considerably with reverberation and signal-to-noise ratio. In agreement with previous work, greater speech enhancement was found for reverberant environments compared to anechoic space.
Lucky VII? A Dual Role for Collagen in Wound Healing
Authors: Ghajar Cyrus M.
Published: July 2013

The extracellular matrix protein collagen VII creates a microenvironment ripe for proper wound healing.