bluuebunny/crossref_metadata_2025 huggingface dataset:
Differences in Shear Stress, Residence Time and Estimates of Hemolysis Between Different Ventricular Assist Devices
Authors: Fraser Katharine H. , Zhang Tao , Griffith Bartley P. , Wu Zhongjun J.
Published: July 2013

Cardiovascular disease is the leading cause of mortality globally. Among various forms of cardiovascular disease, heart failure (HF) affects 5.7 million patients in the United States1. Despite optimal treatment, some patients still do not improve and the available therapies fail to control their symptoms; for them, cardiac transplantation may be the only option. However, only around 2200 transplants are performed in the US each year1, or only about 6% of the estimated 35,000 US patients who would benefit actually receive a heart. To address the need to support the circulation in patients with end-stage HF a wide variety of mechanical circulatory support devices (MCSDs) have been developed over the past four decades.
Influence of Humeral Version and Deltoid Tension on Glenohumeral Kinematics After Reverse Total Shoulder Arthroplasty
Authors: Henninger Heath B. , Barg Alexej , Tashjian Robert Z. , Burks Robert T. , Bachus Kent N. , Anderson Andrew E.
Published: July 2013

Reverse total shoulder arthroplasty (rTSA) is used to improve pain and function in arthritic, rotator cuff deficient shoulders. Surgical intervention is considered successful if range of motion and stability of the joint is maximized and force to abduct the arm is minimized. Implant hardware positioning may affect these outcome measures.
A Continuous Method to Quantify Stress-Strain Behavior of Biologic Materials
Authors: Kuxhaus Laurel , Weisenbach Charles A. , Miller Mark Carl , Tanaka Martin L.
Published: July 2013

Mathematical models of biologic structures such as the knee, spine, and hand provide opportunities to better understand complex interactions and to simulate treatment outcomes. Accurate estimates of the material properties of biologic soft tissues are critical to the fidelity of biomechanical models. Biologic soft tissues have a nonlinear mechanical behavior characterized by an exponential toe region, described with σ = A(eBε −1) followed by a linear elastic region [1]. This has been used to describe the stress-strain properties of many soft tissues [2–4]. Using these traditional models, the two curves are independently fit to a separate set of data points. Thus, it is possible that the two portions of the modeled stress-strain curves do not necessarily exhibit both C0 and C1 continuity, and would not accurately represent a real material.
Modeling of Patient-Specific Fontan Physiology From MRI Images for CFD Testing of a Cavopulmonary Assist Device
Authors: DeGan Jonathan , Kennington Jeffrey , Anupindi Kameswararao , Shetty Dinesh , Chen Jun , Rodefeld Mark , Frankel Steven
Published: July 2013

Single ventricle heart disease is a congenital condition characterized by the inoperability of one ventricle of an infant’s heart. Those suffering from this condition face a series of palliative surgeries called the Fontan procedure, which bypasses the non-functional ventricle by creating a total cavopulmonary connection, or TCPC. This TCPC forms from the anastomosis of the superior and inferior vena cavae (SVC, IVC) to the left and right pulmonary arteries (LPA, RPA), thus allowing systemic blood flow to bypass the heart and flow passively to the lungs. The Fontan procedure creates this junction with three surgeries separated by months or years.
Flow Analysis in Upper Airway for an OSA Subject Before and After Surgery
Authors: Liu Y. , Ye J. Y. , Liu Y. X. , Luo H. Y.
Published: July 2013

Obstructive sleep apnea (OSA) is very common and can strike anyone at any age, even children. Yet still because of the lack of awareness by the public and healthcare professionals, the majority remain undiagnosed and therefore untreated, despite the fact that this serious disorder can have significant consequences. Untreated, sleep apnea can cause high blood pressure and other cardiovascular disease, memory problems, weight gain, impotency, and headaches [1]. OSA is caused by a blockage of the airway, usually when the soft tissue in the rear of the throat collapses and closes during sleep. With apnea event, the brain briefly arouses people with sleep apnea in order for them to resume breathing, but consequently sleep is extremely fragmented and of poor quality. Several surgical techniques may be used for OSA, and these include: uvulopalatopharngeoplasty (UP3), tonsillectomy and pharyngoplasty, uvulopalatal flap, laser and radiofrequency assisted uvulopalatal surgeries. The surgery involves removing the uvula and some of the surrounding soft palate. The idea behind the upper airway surgery is to eliminate the area of obstruction or to widen the airway so it does not occlude completely. However, the success rate is limited; for example, the UP3 helps in around 50% who have the surgery and in others it does not help at all or it helps only partially [2]. The post-operative complications after surgery are often the result of a dilemma during the operation of how much tissue to resect: too little is ineffective, yet too much may leave a patient with speech impedance and palatal stenosis, which can make OSA worse [3]. Therefore, accurate prediction of tissue reduction for this treatment is urgently needed.
Predicting and Controlling Solute Release From a Bioactive Degradable Interference Screw for ACL Reconstruction
Authors: Augustin Jephte , Wootton David , Lelkes Peter , Zhou Jack
Published: July 2013

The progressive replacement of metallic implants by polymeric implants, although advantageous in many ways, is posing new medical challenges. In the case of anterior cruciate ligament (ACL) reconstruction, polymeric interference screws take a really long time to fully degrade, occasionally up to 3 years. Furthermore, they leave voids at the site of insertion after they degrade between the ligament and the surrounding bone tissue [2].
Preliminary In Vitro Estimates of Intra-Aneurysmal Void Sizes After Endovascular Coiling
Authors: Lieber B. B. , Sadasivan C. , Fiorella D. J. , Woo H. H. , Brownstein J. , Patel B. , Dholakia R. , Elhammady M. S. , Farhat H. , Aziz-Sultan M. A.
Published: July 2013

Endovascular coiling has become a well-established treatment method for cerebral aneurysms. The primary drawback of the technique is aneurysm recanalization requiring periodic angiographic follow-ups and possible aneurysm re-treatment. A recent review [1] estimates that 20% of treated aneurysms re-canalize and that half of those aneurysms (10%) are re-treated. Aneurysm recanalization is, in turn, largely caused by compaction of the coil mass due to hemodynamic impingement forces every cardiac cycle. Currently, the only quantitative measure used to characterize effectiveness of the treatment is the aneurysm packing density (ratio of total volume of coils inserted into the aneurysm and the volume of the aneurysm). Lower packing densities have been correlated with higher coil compaction rates [2], so aneurysms are generally coiled to maximal packing. A wider aneurysm neck is also correlated with higher coil-compaction rates. Coiling in such wide-neck aneurysms is performed either with the support of a balloon that is removed post-coiling or with the support of an intracranial stent that is implanted. Such assist devices also improve aneurysm packing densities [3].
In Silico Molecular Modeling of Collagen Crosslink Loading
Authors: Bourne Jonathan W. , Torzilli Peter A.
Published: July 2013

Collagens strengthen tissues throughout the body and are generally resistant to degradation, except by a small number of collagenolytic enzymes. As structural proteins, collagens often experience mechanical forces in vivo including expansion and contraction of blood vessels, tension on tendons and ligaments, and compression of cartilage.
Validation of Respiratory Resistance Measurements
Authors: Pan James , Saltos Andrew , Smith Dan , Johnson Arthur , Vossoughi Jafar
Published: July 2013

The airflow perturbation device (APD) has been developed as a portable, easy to use, and rapid-response instrument for noninvasively measuring respiratory resistance in humans. However, the APD has limited data validating it against established techniques; moreover, a method does not exist to standardize resistance measurement outputs between APD units. This study proposes a system that simulates the normal range of human breathing to validate the APD with the clinically accepted impulse oscillometry technique. Two respiratory resistance ranges were tested. The validation system consisted of a sinusoidal flow generator with ten standardized resistance configurations that were shown to represent a total range of resistances from 0.7000–9.4475 cmH2O·L−1·s−1. Impulse oscillometry (IOS) measurements and APD measurements of the calibration system were recorded and compared at a constant volumetric flow rate of 0.150 L·s−1. Both IOS and the APD consistently failed to estimate nominal resistance accurately. However, a strong second-order relationship was observed between APD measurements and IOS measurements (R2 = 0.997). Because of their comparability to IOS measurements, APD measurements are shown to be valid representations of respiratory resistance in a standard pneumatic model.
Longitudinal Image Based Study of Cerebral Aneurysms: Growth, Contacts and Hemodynamics During Aneurysmal Progression
Authors: Cebral Juan R. , Sforza Daniel , Tateshima Satoshi , Vinuela Fernando , Putman Christopher
Published: July 2013

Improving current procedures for the evaluation and treatment of cerebral aneurysms requires a better understanding of the underlying mechanisms governing their formation, progression and rupture. It is generally accepted that these mechanisms are multi-factorial, involving: hemodynamics, wall biomechanics and mechano-biology, and contacts with peri-aneurysmal structures [1]. However, little is known about the relative importance and interactions of these factors. The broad objective of our research is to investigate the mechanisms of aneurysm progression by studying cerebral aneurysms that are followed longitudinally in time with non-invasive 3D imaging. In this context, the goal of this paper is to highlight the importance of considering possible contacts between the aneurysm and peri-aneurysmal structures and studying their effects on the aneurysm evolution. For this purpose, we present a computational analysis of a growing aneurysm in contact with bones at the base of the skull.
Multiscale Modeling of the Blood Circulation in the Human Liver Using Vascular Corrosion Casting and Micro-CT Imaging Techniques
Authors: Debbaut Charlotte , Monbaliu Diethard , Casteleyn Christophe , Cornillie Pieter , Van Loo Denis , Van Hoorebeke Luc , Simoens Paul , Pirenne Jacques , Segers Patrick
Published: July 2013

Numerical models to analyze blood flow may be important for a better understanding of organ hemodynamics and (dys)function (e.g. in organ transplant research), and diagnostic techniques (e.g. contrast-enhanced MRI to characterize tumors). Existing models of (liver) vascular trees are predominantly based on idealized models using fractional calculus to describe bifurcating branching patterns. In contrast, we previously developed an electrical analog model of the human hepatic circulation, based on measured data of the macrocirculation and extrapolated data of the microcirculation [1]. Furthermore, the microcirculation is usually modeled as a porous medium [2].
Roles of Elastin, Muscle Contractility and Collagenous Stiffening in Aortic Aging: A Thick-Walled Multi-Layered Model
Authors: Valentín A. , Humphrey J. D. , Holzapfel G. A.
Published: July 2013

Evolving geometry, composition and mechanical properties in the aging aorta, resulting in part from elastin degradation, decreased smooth muscle tone, and altered rates of turnover of fibrillar collagen, contribute to many cardiovascular diseases. Constrained mixture models permit us to account for individual mass kinetics of structurally significant constituents as well as their individual deposition stretches and mechanical properties and predict salient facets of arterial growth and remodeling (G&R). Thick-walled models can also predict evolving retraction lengths, opening angles, and internal stress distributions. Employing a thick-walled, multi-layered constrained mixture model, we suggest that a coupled loss of elastin and vasoactive function are fundamental mechanisms by which aortic aging occurs. The model predicts that gradual losses of elastin and vasoactivity drive complex G&R sequences and differential growth. The model also suggests that collagenous stiffening, although typically regarded as harmful, can play a role in preventing the development and/or enlargement of abdominal aortic aneurysms.
Determination of In Vivo Ankle Ligament Strains During External Rotation of the Foot
Authors: Wei Feng , Braman Jerrod E. , Weaver Brian T. , Haut Roger C.
Published: July 2013

Numerous studies have been conducted to evaluate the properties of shoe-surface interface conditions on natural grass and synthetic turfs [2,7,9]. It is suggested that ankle injuries are related to the torque generated in the joint. Recently, our laboratory has developed a surrogate ankle [10] for use with a rotational traction measurement apparatus on various surfaces [9]. External rotation, commonly thought as the mechanism of a high ankle sprain in football, is applied to the surrogate foot and the resistive torque is measured. The study suggests that synthetic turfs generate higher ankle torques than natural grasses, therefore implying a high injury risk on turfs. One disadvantage of these studies is that only artificial devices are used to represent the ankle. Consequently, it is not possible to determine ligament strains, which is crucial in determining ankle injury.
Influence of Decorin and Biglycan on Tensile Viscoelastic Properties in Knockout Mice
Authors: Dourte LeAnn M. , Pathmanathan Lydia , Iozzo Renato V. , Soslowsky Louis J.
Published: July 2013

Tendons have a complex, viscoelastic mechanical behavior that depends on their composition and structure. Understanding these structure-function relationships may help elucidate important differences in the varying functional behaviors of specific tendons as well as guide targeted treatment modalities and tissue engineered constructs. The tendon extracellular matrix (ECM) can be described as a biocomposite material consisting of collagen fibers surrounded by an extrafibrillar matrix. Many studies have focused on the role of the fibers on the tensile properties of tendon; however, fibers alone do not completely explain the viscoelastic and non-linear response of tendon. The interactions of small leucine-rich proteoglycans (SLRPs) with other ECM molecules, such as collagen fibrils, as well as their association with water suggest that SLRPs may play a role in tendon viscoelasticity. Some studies have assessed the role of SLRPs or glycosaminoglycans in the mechanical response of tendon, but few have explored their role in more sophisticated viscoelastic properties. Therefore, the objective of this study was to evaluate the viscoelastic response of the patellar tendon in two different SLRP knockout mice compared to wildtype. We hypothesized that the absence of SLRPs would lead to a stiffer dynamic tissue response compared to wildtype.
Left Ventricular Vortex Ring Dynamics and Their Association to Early Diastolic Filling
Authors: Stewart Kelley C. , Charonko John J. , Ohara Takahiro , Little William C. , Vlachos Pavlos P.
Published: July 2013

Diastolic dysfunction is the impairment of the filling in the left ventricle. Patients with left ventricular diastolic dysfunction (LVDD) lose the ability to adjust left ventricular filling properties without increasing left atrial pressure [1]. Although LVDD is very prevalent, it currently remains difficult to diagnose due to inherent atrioventricular compensatory mechanisms including increased heart rate, increased left ventricular (LV) contractility, and increased left atrial (LA) pressure. Although variations within the early diastolic filling velocity have been previously observed [2], the physical mechanism for the deceleration of the early filling wave is not understood.
Effects of Freezing-Induced Cell-Fluid-Matrix Interactions on Cells and Extracellular Matrix of Engineered Tissues
Authors: Teo Ka Yaw , Dutton J. Craig , Grinnell Frederick , Han Bumsoo
Published: July 2013

Long-term cryopreservation of functional engineered tissues (ETs) is a key enabling technology for tissue engineering and regenerative medicine. However, a limited understanding of tissue-level biophysical phenomena during freeze/thaw (F/T) and their effects on cells and ECM microstructure poses significant challenges for i) preserving tissue functionality, and ii) controlling highly tissue-type dependent cryopreservation outcomes.
Insights Into the Molecular Mechanisms of Actin Dynamics: A Multiscale Modeling Approach
Authors: Bidone Tamara C. , Deriu Marco A. , Di Benedetto Giacomo , Massai Diana , Morbiducci Umberto
Published: July 2013

Actin dynamics, which is at the basis of many fundamental cellular processes as cell migration [1], is governed by the self-assembly and disassembly of actin monomers (G-actin) that, in turn, are determined by the kinetics of ATP hydrolysis and by the local concentrations of Mg2+ and Ca2+ [2]. During cell migration, interactions of the actin filaments (F-actin) with different nucleotide-cation complexes induce local topological rearrangements, because the filament building G-actins undergo conformational shifts between multiple equilibrium states separated by low-energy barriers. For example, the structural rearrangements of the DNase-I binding loop (residues 38–52) in subdomain 2 are driven by ATP hydrolysis and the changes in the conformation of subdomain 4 are induced by the presence of a tightly-bound Mg2+ or Ca2+ ion (Figure 1a). These conformational shifts alter the cross-linking between monomers, varying the contact surfaces among adjacent inter- and intrasubdomains of G-actin, and reflect on the overall properties of F-actin.
Oscillatory Fluid Flow Affects the Osteogenic Differentiation of Human Bone Marrow Stromal Cells in a Primary Cilium Dependent Manner
Authors: Hoey David A. , Jacobs Christopher R.
Published: July 2013

Osteoporosis is a debilitating bone disease which occurs in part when bone marrow stromal cells (BMSCs) fail to produce sufficient numbers of osteoblasts to counteract bone resorption by osteoclasts. The majority of research to date has described chemically induced differentiation of BMSCs but a key regulator of stromal cell differentiation is physical loading. BMSCs experience both hydrostatic pressure and fluid flow within the marrow cavity and such modes of loading have been shown to significantly alter gene expression in vitro [1,2]. In particular, the effect of oscillatory fluid flow (OFF) induced shear stress results in the upregulation of osteogenic genes in preosteoblastic cells; however the effect of this mode of loading is not well characterized in human MSCs (hMSCs) [3].
On the Importance of Assumptions for Bulk Flow in Hemodynamic Models of the Carotid Bifurcation
Authors: Morbiducci Umberto , Massai Diana , Gallo Diego , Ponzini Raffaele , Deriu Marco A. , Redaelli Alberto
Published: July 2013

It is widely accepted that the local hemodynamics in the arterial system affects the atherogenic process. In particular the hemodynamic environment at the carotid artery bifurcation has been widely studied due to its predilection for atherosclerosis. Much effort has been spent in the past on image-based CFD carotid bifurcation models to assess the sensitivity to several assumptions of wall shear stress (WSS)-based parameters as indicators of abnormal flow. This luminal-surface-oriented approach was historically driven by histological observations on samples of the vessel wall. The consequence for this was that the reduction of the complexity of 4D flow fields focused mainly on WSS. However, few studies have provided adequate insights into the influence of these assumptions in order to confidently model the 4D hemodynamics within the bifurcation. Only recently the interest in the role played by the bulk flow in the development of the arterial disease has grown dramatically. This is the consequence of the emerging awareness that arterial hemodynamics, being an intricate process that involves interaction, reconnection and continuous re-organization of structures, could play a primary role in the regulation of mass transfer, and of its athero-protective/susceptible effect. Earlier works [1] pointed out the existence of a relationship between helical/vortical flow patterns and transport processes that could affect blood-vessel wall interaction, and might cause alterations in the residence time of atherogenic particles involved in the initiation of inflammatory response. Recently we introduced robust quantitative descriptors of bulk flow that can “reduce” the inherent complexity associated with 4D flow fields in arteries [1]. Here we present a study on the impact of assumptions on blood rheology and outflow boundary conditions (BCs) on bulk flow features within healthy carotid bifurcations, by using 4D flow descriptors. The final goal is to provide adequate insights not only to complement and to integrate, but also to extend with a quantitative characterization of the bulk flow the description currently adopted to classify altered hemodynamics.
Model Based Surface Design to Incorporate the Effect of Soluble Cues
Authors: Chan C. , Baek S.
Published: July 2013

Many disease states such as obesity and Type 2 diabetes are polygenic and involve multiple organs with inter-related metabolic and vascular abnormalities, and furthermore are risk factors for other diseases such as nonalcoholic steatohepatitis (NASH), cardiovascular or Alzheimer’s diseases. Tissue engineering is attempting to address these diseases from the perspective of developing “spare” or “replacement” parts. Cell and tissue engineering integrates cellular and molecular biology with the principles and methods of chemical and mechanical engineering to develop biological substitutes that can restore, maintain, or control tissue function.
Hemodynamic Compromise During Carotid Angioplasty and Stenting
Authors: Lynch A. G. , Walsh M. T.
Published: July 2013

Modern surgical treatment of arterial disease is moving towards minimally invasive procedures, as the benefits are numerous. However, one area that is resisting this trend is the treatment of carotid artery disease. For the past number of decades carotid endarterectomy surgery has been referred to as the “gold standard” in the treatment of carotid artery disease. However, in recent year’s carotid angioplasty and stenting (CAS) has emerged to challenge carotid endarterectomy surgery (CES) as a viable alternative for the prevention of strokes. However uptake of this procedure has been hindered due to the peri-operative complications associated with the treatment. During this procedure blood flow in one of the internal carotid arteries supplying blood to the brain is interrupted for a period of time. However, it has been shown that not all patients can accommodate this interruption. Qureshi et al. suggests that ischemic neurological deficits occur in 3 to 13% of patients as a result of hemodynamic compromise.
An Automated Histologic System for 3D Histomorphometry of the Mouse Knee
Authors: Murienne Barbara J. , Girard Michael J. , Loerup Lise , Boussommier-Calleja Alexandra , Shefelbine Sandra J. , Marenzana Massimo , Ethier C. Ross
Published: July 2013

Osteoarthritis (OA) is a degenerative joint disease that is a leading cause of adult pain and disability in Western countries1. Clinically, several structural features of the joint are important in diagnosis, prognosis and evaluation of treatment efficacy, e.g. cartilage volume, homogeneity and joint space narrowing2,3. In animal models of OA, structural features such as bone defects and cartilage changes are commonly investigated using histomorphometry, a technique that uses stereological point counting and manual tracing of regions of interest to extract 3-dimensional (3D) geometrical properties from 2D histology slides. This is time-consuming and subject to inter-observer variations, hence limiting precision 4,5. Therefore, a technique for rapidly imaging joint structures in 3D at high resolution, including articular cartilage and subchondral bone, is currently needed in pre-clinical OA research.
Improved Simulation of Heel Contact During Normal Walking
Authors: Mahboobin Arash , Cham Rakié , Piazza Stephen J.
Published: July 2013

Causes of slips and falls involve the interaction of complex environmental and human factors [1]. While experimental studies have been useful to identify biomechanical variables that may impact slipping severity, it is unclear how these factors interact. Relying on experiments alone to acquire this knowledge and establishing cause-effect relationships in complex dynamic systems is difficult. Computational modeling and forward dynamics simulations of walking and slipping are needed to meet these research needs.
A Robust Real-Time Control Algorithm for Whole-Body Running
Authors: Zhou Xianlian , Przekwas Andrzej
Published: July 2013

Dynamic simulations of human movement are becoming increasingly important in biomechanics, computer animation, clinical and military applications. It complements experimental approaches by providing capabilities not generally offered by the experimental approaches. Nonetheless, the dynamic simulation of human movement remains one of great challenges in biomechanics due to the high-mobility of the human body and the redundancy of body control. Over past decades, various methods have been developed to simulate human motion.
A Surface-to-Surface Contact Model for Multibody Dynamics Modelling of the Human Hip
Authors: Stops Adam , Wilcox Ruth , Jin Zhongmin
Published: July 2013

Typically, MultiBody Dynamics (MBD) simulations of the human hip use 3 degrees of freedom to represent joint constraints. Consequently, typical MBD simulations omit the important characteristic of cartilage deformation. This paper presents a novel development of a surface-to-surface contact model that allows for an improved understanding of joint mechanics during dynamic activities such as walking. The contact model uses bilateral constraints, whereby the cartilage mechanical properties are derived from Finite Element (FE) and experimental investigations. Future developments will use this new technique for modeling the hip in order to help clinicians understand how movement sequences may cause severe deformations, and so clinicians can then advise patients to avoid activities that increase the risk of wear and degeneration.
Finite Element Implementation of Neutral Solute Transport in Porous Biological Soft Tissues Under Finite Deformation
Authors: Ateshian Gerard A. , Albro Michael B. , Maas Steve , Weiss Jeffrey A.
Published: July 2013

The physiological function of biological tissues and cells is critically dependent on the transport of various solutes, such as nutrients, cytokines, hormones, and waste products. Transport in such media may be significantly hindered by the porous solid matrix, which may impart anisotropic transport properties to the solutes. Furthermore, large deformations of soft tissues and cells may significantly alter these transport properties due to concomitant alterations in pore volume and structure. Another potential influence of the porous solid matrix is steric volume exclusion resulting from the ratio of solute size and pore size distribution. This steric effect implies that solute concentration inside a tissue or cell may be less than the concentration in a surrounding bath, and this limit on solubility may be exacerbated under finite deformation due to changes in pore volume. Finally, the osmotic pressurization of the interstitial fluid may deviate from ideal physico-chemical behavior and this deviation may be dependent on the state of strain in the solid matrix. Therefore, a finite element framework that can accommodate solid-solute momentum exchanges, strain-induced anisotropy in transport properties and solubility, and strain-dependent non-ideal osmotic response, can provide an important modeling tool in the biomechanics of soft tissues and cells.
Evaluation of the Biofidelity of the HIII and MIL-Lx Lower Leg Surrogates Under Axial Impact Loading
Authors: Quenneville Cheryl E. , Dunning Cynthia E.
Published: July 2013

Impact loading of the lower legs can occur during a range of events such as car crashes, parachute landings, or anti-vehicular (AV) landmine blasts. This rapid, high-force loading can lead to debilitating injuries and long-term impairment. For military applications, the current lower leg injury standard is a maximum axial force of 5.4 kN, measured using a standard 50th percentile male Anthropomorphic Test Device (ATD) [1,2]. For an ATD leg to be an appropriate tool for assessing injury risk, it must have an impact response similar to that of the natural human leg.
Airway Closure With Two Liquid Layers
Authors: Tai Cheng-feng , Halpern David , Grotberg James B.
Published: July 2013

There are several mechanisms which may cause airway closure in the lung. In this paper, we focus on airway closure due to the capillary instability [1]. In Gauglitz and Radke’s study [2], they showed that once the ratio of film thickness to tube radius is larger than 0.12, airway closure could occur. The induced interfacial deformation creates a driving pressure which forces more liquid into a growing bulge. The interface will then deform rapidly towards the end of the closure process due to the presence of large curvatures, which create strong driving pressures and will eventually lead to the formation of a liquid plug. Due to the instability, stresses, including normal and shear stresses on the airway wall, will be induced. The epithelial cells on the inner wall of the airway may be injured by these induced stresses. The purpose of this study is to calculate the wall stresses for a two-layer system and determine if the magnitude of the stresses are sufficient to injure the epithelial cells.
Functionalization of Electrospun Poly (Caprolactone) to Achieve Enhanced Cell Attachment
Authors: Jassal Manisha , Regis Shawn M. , Bhowmick Sankha
Published: July 2013

The covalent immobilization of various compounds onto functionalized polymer surfaces has been an area of interest to the researchers in the past decade. Methods that can be used to alter the surface properties of materials to improve performance, biocompatibility or to achieve certain desired effects are a key to continued development of these materials [1]. The artificial scaffolds trying to mimic the architecture of natural human tissues at nanoscale may lead to successful implants within the body [2]. Among various nano-scaled materials, nano fibers produced by electrospinning process offer advantages as comparatively low cost, production of continuous fibers, feasibility of complex and seamless three dimensional shapes and many more. In the present work, polycaprolactone nanofibers were generated by electrospinning process and the scaffolds were functionalized in two different ways i.e. by amination followed by subsequent RGD immobilization and hydrolysis. Thereafter, fibroblast cells behavior was studied on functionalized scaffolds.
Electrophysiological Investigation of Hydrostatic Pressure Mechanotransduction by Urothelial Cell Lines
Authors: Champaigne Kevin D. , Jenderny Sarette N. , Nagatomi Jiro
Published: July 2013

The urothelium is the epithelial lining of the ureters, urinary bladder, and urethra. Recent discoveries have suggested that in addition to providing a barrier function to urine, the urothelium actively participates in sensory functions related to thermal, chemical, and mechanical stimuli, and releases chemical signals in response[1]. In addition to a sensitivity to cell membrane stretch caused by wall tension upon bladder filling, in vitro studies by our group have shown that urothelial cells may be sensitive to hydrostatic pressure directly without requiring membrane stretching [2]. Specifically, primary cultures of rat bladder urothelial cells exposed to 10 cmH2O pressure on rigid substrates released significantly greater amounts of ATP compared to the baseline control without exposure to pressure. Moreover, this ATP response by rat urothelial cells to pressure was inhibited by pre-treatment of cells with ruthenium red, a non-specific antagonist of transient receptor potential (TRP) channels, suggesting a potential involvement of these channels in pressure mechanotransduction. Further understanding of the mechanisms, however, is needed to improve treatment of bladder dysfunction such as overactive bladder.
How Far Cells Can Feel: Effects of ECM Fibers
Authors: Ma Xiaoyue , Weber Maureen , Stevenson Mark , Ghadiali Samir N. , Gooch Keith J. , Hart Richard T.
Published: July 2013

A rapidly growing body of literature suggests that the passive mechanical environment (i.e., the local mechanical setting and material properties) impacts the formation of multi-cellular structures and cell function, proliferation, migration, and differentiation [1]. Computational modeling and experimental studies suggest that cells grown on top of polyacrylamide (PA) gels are responsive to their pericellular mechanical environment but not to features more than several tens of microns away from the cell [2]. In contrast to cells on PA gel, cells grown on biological polymer gels (e.g. fibrin, collagen, etc.) appear to respond to their mechanical environment and can sense several hundreds of microns in distance [3].
Age Related Variation in BMD and Trabecular Architecture Differs Between the Proximal Femur and Calcaneus in Men
Authors: Isaksson Hanna , Prantner Viktoria , Jurvelin Jukka S.
Published: July 2013

Fragility fractures due to degradation of the bone tissue during aging or development of osteoporosis are responsible for significant morbidity and mortality in elderly patients. A variety of factors contribute to the overall resistance of bones to fracture, e.g. the bone quality. Traditionally, bone mineral density (BMD) as assessed by the dual energy x-ray absorptiometry (DXA) is the gold standard for osteoporosis diagnostics 1. However, BMD alone is insufficient to explain fracture risk in patients 2. Additional characterization of bone structural parameters may provide more insight into the predictive capacity of BMD with respect to bone structural parameters. Further, as various skeletal sites are used to assess bone status, differences in structural characteristics of skeletal sites should be addressed.
Comparisons of the Joint Responses to Surgical Transection and Traumatic Rupture of the ACL in a Rabbit Model
Authors: Meyer Eric G. , Isaac Daniel I. , Haut Donahue Tammy L. , Déjardin Loïc M. , Haut Roger C.
Published: July 2013

Long-term participation in vigorous physical activity increases the risk of acute and chronic injuries to the knee. Two specific types of injury strongly associated with subsequent knee osteoarthritis (OA) are cruciate ligament damage and meniscal tears. Many clinical studies have discussed the high frequency of noncontact ACL injuries, for example, from jump landings. Axial compressive loading of the knee during landing from a jump can generate approximately 6–8 times bodyweight. With the tibial plateau having an inherent posterior slope of 10–15°, these loads can produce an anterior shift of the tibia during jump landings that result in isolated rupture of the anterior cruciate ligament (ACL) in the laboratory.1 These studies have shown acute damages in the articular cartilage and underlying subchondral and trabecular bone in the human cadaver joint.2 Clinically, in over 80% of ACL injury cases, characteristic osteochondral lesions occur in the posterolateral aspect of the tibia and/or anterolateral aspect of the lateral femoral condyle, potentially due to these levels of joint compressive loads.3
A Novel Approach in Assessing the Effects on Hemodynamics of Topology Preserving Shape Changes of Image Based Arterial Structures
Authors: Papaharilaou Yannis , Seimenis Ioannis , Anayiotos Andreas
Published: July 2013

Advances in medical imaging technology have allowed the extraction of 3D anatomic information non-invasively in vivo. This information has been used to reconstruct the anatomy of interest and obtain a realistic model of the 3D geometry. Such models provide a parametric shape description which allows for the quantitative comparison of inter or intra individual variability of topologically similar anatomic structures. However, the uncertainty associated with the imaging and reconstruction processes involved in generating these models limits the spatial information that can be accurately resolved utilizing this approach. This, within the context of arterial structures, limits the accuracy of the data obtained from flow simulations using these models. However, the primary effects on the hemodynamics of topology preserving changes in the geometry of arterial structures, such as those occurring due to changes in body posture associated with normal daily activity, could be resolved if the small scale surface features are separated from the strong shape features that characterize the topology. Here we develop geometric tools and methods to achieve this and apply them to assess the influence of head posture on carotid artery hemodynamics [1].
Geometric and Hemodynamic Evaluation of 3-Dimensional Reconstruction Techniques for the Assessment of Coronary Artery Wall Shear Stress in the Setting of Clinical Disease Progression
Authors: Timmins Lucas H. , Suo Jin , Eshtehardi Parham , Dhawan Saurabh S. , McDaniel Michael C. , Oshinski John N. , Samady Habib , Giddens Don P.
Published: July 2013

Myocardial infarction and sudden cardiac death are usually due to the rapid progression of previously non-flow limiting atherosclerotic plaques that transform to an unstable (i.e., vulnerable) phenotype. Despite considerable advances in medical therapies and treatment modalities for coronary artery disease (CAD), there is no accurate method to predict the site of abrupt lesion progression that can lead to an acute coronary event. Wall shear stress (WSS) has not only been implicated in the development of CAD, but also in its rapid progression [1]. Recent data from our laboratory indicates significant plaque progression in areas of low WSS (<10 dynes/cm2), plaque regression in regions of physiologic WSS (10–25 dynes/cm2), and phenotypic transformation towards an unstable lesion in regions of high WSS (>25 dynes/cm2) [2].
Substrate Dependence of Mechanical Response of Neurons and Astrocytes
Authors: Bernick Kristin B. , Socrate Simona
Published: July 2013

The response of neural cells to mechanical cues is a critical component of the innate neuroprotective cascade aimed at minimizing the consequences of traumatic brain injury (TBI). Reactive gliosis and the formation of glial scars around the lesion site are among the processes triggered by TBI where mechanical stimuli play a central role. It is well established that the mechanical properties of the microenvironment influence phenotype and morphology in most cell types. It has been shown that astrocytes change morphology [1] and cytoskeletal content [2] when grown on substrates of varying stiffness, and that mechanically injured astrocyte cultures show alterations in cell stiffness [3]. Accurate estimates of the mechanical properties of central nervous system (CNS) cells in their in-vivo conditions are needed to develop multiscale models of TBI. Lu et al found astrocytes to be softer than neurons under small deformations [4]. In recent studies, we investigated the response of neurons to large strains and at different loading rates in order to develop single cell models capable of simulating cell deformations in regimes relevant for TBI conditions [5]. However, these studies have been conducted on cells cultured on hard substrates, and the measured cell properties might differ from their in-vivo counterparts due to the aforementioned effects. Here, in order to investigate the effects of substrate stiffness on the cell mechanical properties, we used atomic force microscopy (AFM) and confocal imaging techniques to characterize the response of primary neurons and astrocytes cultured on polyacrylamide (PAA) gels of varying composition. The use of artificial gels minimizes confounding effects associated with biopolymer gels (both protein-based and polysaccharide-based) where specific receptor bindings may trigger additional biochemical responses [1].
Influence of Plaque Geometry on Peak Cap Stresses
Authors: Akyildiz A. C. , Speelman L. , Nieuwstadt H. , Wentzel J. , van der Steen A. , Gijsen F.
Published: July 2013

Atherosclerosis is an important cardiovascular disease in which plaque build up occurs in vessels. Plaques with thin cap and thick necrotic core are defined as vulnerable plaques. Rupture of the cap of a vulnerable plaque in a coronary artery is the underlying cause of the majority of acute myocardial infarctions and sudden coronary deaths [1].
What is the Pumping Mechanism Behind Embryonic Hearts?
Authors: Maes Frédéric , Chaudhry Bill , Van Ransbeeck Peter , Verdonck Pascal
Published: July 2013

During this initial phase of the development the embryonic heart consist only of a contractile tube lacking valves. There has been recent debate as to how this valveless heart can generate uni-directional flow. Recently Forouhar et al. proposed a mechanism for the zebrafish embryo based on dynamic suction previously described as the Liebau effect [1]. Dynamic suction pumping is characterized by one stationary point of activation, inducing waves which then travel passively along the primitive heart tube. The passive waves create the blood flow. Peristalsis on the other hand is characterized by a series of adjacent contraction locations creating the appearance of a travelling wave along the wall. In this investigation we begin to determine how the embryonic vertebrate heart functions.
Multilayer Hybrid Construct for Vascular Tissue Engineering
Authors: Madhavan Krishna , Bonani Walter , Tan Wei
Published: July 2013

Vascular grafts are often used as blood vessel substitutes. Until now, synthetic materials have not matched the efficacy of native tissues, particularly in the applications of small-diameter vascular grafts (<6mm) such as bypass grafts for arthrosclerosis and vascular access graft for hemodialysis. There is a considerable need for alternatives to the autologous veins or arteries. Many patients do not have an autologous vessel suitable for use due to preexisting pathological conditions or previous surgical harvest. Recent developments in vascular tissue engineering demonstrate the possibility of a biodegradable graft material containing living cells to mimic the structure and function of native vessels. However, fabrication of biomimetic grafts is often time and labor intensive, and subsequently requires complicated storage. This demands technology advancements in producing vessel mimetic grafts, considering their availability in addition to efficacy. To this end, new approaches to constructing small-diameter grafts that are of immediate availability and capable of regenerating biomimetic blood vessels in vivo may address the unmet demand in this area. We have designed a novel multilayer vascular construct which is made up of a nanofibrous “intima-equivalent” with thrombus-resistant vessel lumen and a porous biopolymer matrix as “media-equivalent” to allow smooth muscle cells (SMC) from native artery to grow and remodel the tissue. In this study, various layering strategies have been explored. To evaluate the resultant multilayer construct, structural, biochemical and biomechanical characterizations, as well as cell assays and short-term animal studie have been performed.
Finite Element Predictions of Labrum and Cartilage Mechanics in Dysplastic Human Hips
Authors: Henak Corinne R. , Davis Ryan S. , Ellis Benjamin J. , Harris Michael D. , Anderson Andrew E. , Peters Christopher L. , Weiss Jeffrey A.
Published: July 2013

Acetabular dysplasia, characterized by a shallow acetabulum and decreased coverage of the femoral head (Figure 1), is thought to cause early osteoarthritis due to altered mechanical loading. Clinical observation of hypertrophic labra in dysplastic hips suggests that the labrum supports mechanical load (e.g., [1]). Simulations have predicted increased cartilage contact pressure and decreased contact area in dysplastic hips as potential causes of early osteoarthritis (e.g., [2]), but have been limited by the use of simplified geometry and the omission of the labrum. The objective of this study was to compare labrum and cartilage mechanics between normal and dysplastic hips using a validated approach to subject-specific finite element modeling of the hip.
A Weighted Objective Function Reduces Estimates of Medial and Lateral Knee Joint Contact Loads During Gait
Authors: Brandon S. C. E. , Thelen D. G. , Deluzio K. J.
Published: July 2013

Accurate prediction of knee joint contact loading during gait is important for understanding knee pathology and development of suitable clinical interventions. While many researchers have modeled the knee contact loads during level walking, these predictions have ranged from 3.4 [1] to 7 [2] times body weight. Validation of contact loads is difficult; the joint contact load depends not only on readily obtainable external kinematics and reaction forces, but also on the forces generated by muscle and other soft tissues. Recently, an instrumented tibial implant, capable of telemetrically reporting the six degree-of-freedom loading environment of the tibial plateau, was used to tune and validate an EMG-driven model of the lower extremity [3]. Recognizing the value of these in vivo data, and the limitations of existing knee models, these researchers devised the Grand Challenge Competitions to Predict In Vivo Knee Loads.
Characterization of αGal(−) ECM Bioscaffolds: An Indication for Application in Tissue Engineering
Authors: Liang Rui , Fisher Matthew B. , Yang Guoguang , Hall Christine , Woo Savio L-Y.
Published: July 2013

Extracellular matrix (ECM) bioscaffolds derived from animal sources, such as porcine small intestine submucosa (SIS) and urinary bladder matrix (UBM), have a successful history for application in clinical and/or experimental settings [1]. In our research center, we have demonstrated that the porcine SIS bioscaffolds could improve the morphological, biochemical, and biomechanical properties of healing ligaments and tendons in different animal models [2, 3].
A Multi-Directional Tribo-System: Testing the Wear of UHMWPE Under Sliding, Rolling, and Rotation
Authors: Patten Eli W. , Carney Matthew E. , Johnson Perry M. , Hong Timothy , Almaguer A. J. , Pruitt Lisa A.
Published: July 2013

A tribological testing system with up to four degrees of motion has been designed and built to simulate the wear of materials used in joint replacements. The machine is versatile enough to test simple pin-on-disk contact in planar sliding as well as ball-on-flat contact with more complex rotation and rolling motions. A wide range of materials, loads, and specimen configurations can be tested with this machine, making it a powerful tool for hypothesis-driven research. This tribosystem is robust, customizable, cost effective, and offers the first opportunity to investigate the fundamental wear mechanisms that arise from the four degrees of motion in total knee replacements. Basic design features, advantages, and preliminary validation will be discussed.