bluuebunny/crossref_metadata_2025 huggingface dataset:
Design of an Experimental Mock Circulatory System for the Fontan Circulation
Authors: Chiulli John A. , Conover Timothy A. , Figliola Richard S. , Hsia Tain-Yen
Published: July 2013

Each year, a small fraction of children are born with univentricular hearts, causing the lethal blue baby syndrome. Several preliminary operations are required to buy time until the child’s blood vessels grow to sufficient size. Once the child reaches an age of 3–5 years, the blood vessels have grown enough for the Stage 3 Fontan operation, in which the superior and inferior vena cavae are coupled directly to the pulmonary arteries in a cruciform junction [2,3]. After this operation, the heart is only pumping blood to the systemic circulation. Only residual pressure in the systemic veins and intrathoracic pressure change with respiration drive the flow into the lungs [5]. This circulation decreases the load on the heart, allowing the patients to survive with normal blood oxygen levels. This circulation decreases the load on the heart, allowing the patients to survive into their 20s and 30s. An aim of this study is to develop an experimental model of the Fontan circulation that can be readily adapted to simulate patient specific anatomies so as to assist in potential surgical decisions. Of interest is the study of chronic venous hypertension, a result of the Fontan circulation having no heart “vacuum” at the end of the vena cavae; it is known to cause liver failure. We also intend to examine the hypothesis of Hsia et al. [6] that decreasing sub-diaphragmatic venous flow reversal will improve functional outcome of the Fontan.
Mechanical Properties Along the Branching Site of the Abdominal Aorta and Iliac Arteries
Authors: Oltean Alina , Barocas Victor H.
Published: July 2013

There is a great interest in studying arteries due to the prevalence of arterial diseases such as atherosclerosis and aneurysms, but much of the focus has been on straight arteries [1,2]. As arteries branch off, the fiber alignment and thickness of the arterial wall change. Smooth muscle cells orient helically in straight segments while multiple orientations have been seen at the branching region. As a result, straight segments of arteries vary mechanically from branched segments [2]. This study focused on the structural and mechanical properties of arteries at branching sites to observe the effect of the structural changes at bifurcations on mechanical behavior.
A Relationship Between Pressure Fields and Flow Patterns During Left Ventricular Diastolic Dysfunction Using 2D Phase Contrast MRI
Authors: Charonko John J. , Kumar Rahul , Stewart Kelley , Little William C. , Vlachos Pavlos P.
Published: July 2013

Left Ventricular Diastolic Dysfunction (LVDD) is a disease in which the heart is unable to properly fill the left ventricle before the systolic contraction pushes the blood out of the chamber into the rest of the body [1]. It is frequently characterized by elevated filling pressures within the heart. Over 70 million people in the United States with high blood pressure are at risk for LVDD [2], and numerous studies have shown a link between LVDD and heart failure. However, due to compensatory mechanisms early stage dysfunction can be difficult to diagnose.
A Comparison of the Performance of Hexahedral and Tetrahedral Elements in Finite Element Models of the Foot
Authors: Tadepalli Srinivas C. , Erdemir Ahmet , Cavanagh Peter R.
Published: July 2013

Characterization of the contact pressure patterns under the foot provides significant insight into pathological conditions such as diabetic peripheral neuropathy [1]. The finite element method (FEM) is widely used in foot biomechanics for predictive simulations of plantar pressures in barefoot and shod conditions [2–6]. In the analysis of the foot, mesh generation accounts for most of the labor in model development, due to the complex structure of the foot including highly partitioned, embedded, and branching geometries. In FEM, hexahedral elements are preferred over tetrahedral elements because of their superior performance in terms of convergence and accuracy of the solution [7]. This becomes more apparent as the convergence behavior of the simulations are hindered by large deformation, material incompressibility, and contact with friction, mechanical features which are commonly seen in foot biomechanics. Unfortunately, unlike tetrahedral meshing which is highly automated [8], hexahedral mesh generation is a time consuming process requiring considerable operator intervention. Despite their reputed advantages, the relative performance of tetrahedral meshes in foot models has not been well established; to our knowledge, there has not been a comprehensive study comparing the performance of hexahedral and tetrahedral elements when material and geometric nonlinearity are included combined with material incompressibility and shear force loading conditions. Hence, the objective of the present study was to evaluate various types of meshes that can be used to model the interaction of a bone-soft tissue construct and rigid floor complex under compressive and shear loading in a heel-pad analog model.
FEM Numerical Model Comparison of Skin Thermal Damage Models to Experimental Results
Authors: Pearce John A.
Published: July 2013

Prediction of the threshold of skin burns from radio frequency (RF) current is clinically relevant. The classical studies on skin burns in the 1940s and 1950s [1–3] continue to be the most often cited and utilized framework. In the early 1980s an experimental study of radio frequency (RF) current [4] utilized circular disk electrodes applied to pig skin to create skin burns. A preliminary model of one of the more severe burn experiments has been described [5]. The objective of this study was to inspect the threshold skin damage experiment [3] and apply a recent model for micro-vascular disruption [6].
Early Remodeling Strain Levels Can Predict the Progression of Remodeling of the Left Ventricle Post Myocardial Infarction
Authors: Engel Emily , Wu Zhongjun J. , Griffith Bartley P.
Published: July 2013

Over one million patients are affected with left ventricular (LV) injury annually after sustaining a myocardial infarction (MI). In order to compensate for the loss in pumping function, the heart undergoes changes meant to maintain homeostasis. This process actually leads to a remodeling process that is initially compensatory and later becomes maladaptive. Remodeling after MI often involves loss of contractility and hypertrophy of the LV in response to increased loading conditions. Some patients are able to recover with the use of medicine and surgical intervention. However, others experience a progression of the remodeling process which leads to LV dysfunction and heart failure as the heart becomes more spherical and loses its ability to effectively contract. [1]
Dynamic Tensile Loading Improves the Mechanical Properties of MSC-Laden Aligned Nanofibrous Scaffolds
Authors: Baker Brendon M. , Shah Roshan P. , Mauck Robert L.
Published: July 2013

Fibrocartilaginous tissues such as the meniscus and annulus fibrosus serve critical load-bearing roles, relying on arrays of highly organized collagen fibers to resist tensile loads experienced with normal physiologic activities [1]. As these specialized structures are often injured, there exists great demand for engineered tissues for repair or replacement. Towards recreating the structural and mechanical features of these anisotropic tissues in vitro, we fabricate scaffolds composed of co-aligned, ultra-fine biodegradable polymer fibers. These 3D micro-patterns direct mesenchymal stem cell (MSC) orientation and the subsequent formation of organized extracellular matrix (ECM) [2]. As this cell-produced matrix continually develops with time in culture, the mechanical properties of the construct gradually increase. In previous studies aimed at engineering human meniscus tissue, constructs achieved moduli of ∼40MPa after 10 weeks of culture, representing a two-fold increase in the starting properties of the scaffold [3]. Despite this demonstrable increase, this value remains well below that of the native tissue. As mechanical forces are essential to the maintenance of musculoskeletal tissues, this work examined the effect of cyclic tensile loading on MSC-laden nanofibrous constructs to enhance their in vitro maturation. We hypothesized that this loading modality would modulate the transcriptional behavior of seeded MSCs, spur the deposition of collagen-rich matrix, and lead to additional improvements in construct mechanical properties.
Investigation of the Relationship Between Color M-Mode Early Diastolic Propagation Velocity and Left Ventricular Adverse Pressure Gradients
Authors: Stewart Kelley C. , Kumar Rahul , Charonko John J. , Vlachos Pavlos P. , Little William C.
Published: July 2013

Left ventricular diastolic dysfunction (LVDD) and diastolic heart failure are conditions that affect the filling dynamics of the heart and affect 36% of patients diagnosed with congestive heart failure [1]. Although this condition is very prevalent, it currently remains difficult to diagnose due to inherent atrio-ventricular compensatory mechanisms including increased heart rate, increased left ventricular (LV) contractility, and increased left atrial pressure (LA). A greater comprehension of the governing flow physics in the left ventricle throughout the introduction of the heart’s compensatory mechanisms has great potential to substantially increase the understanding of the progression of diastolic dysfunction and in turn advance the diagnostic techniques.
Priming of Synovium-Derived Mesenchymal Stem Cells for Cartilage Tissue Engineering
Authors: Gunja Najmuddin , Fong Jason , Tan Andrea , Moy Man-Yu , Xu Duo , O’Connell Grace , Bulinski J. Chloe , Ateshian Gerard A. , Hung Clark T.
Published: July 2013

The clinical potential of stem cells has driven forward efforts toward their optimization for tissue engineering applications. The intimal layer of the synovium is composed of two cell types, macrophages and fibroblast-like cells. The fibroblast-like cells, often referred to as synovial-derived mesenchymal stem cells (sMSCs), have the capability to differentiate down a chondrogenic lineage1. In addition, in vivo tests have shown that synovial cells may be recruited from the synovial membrane to aid in the repair of articular cartilage defects2.
High Fidelity Computational Model of Bone Remodeling Cellular Mechanisms
Authors: Penninger Charles L. , Tovar Andrés , Niebur Glen L. , Renaud John E.
Published: July 2013

One of the most intriguing aspects of bone is its ability to grow, repair damage, adapt to mechanical loads, and maintain mineral homeostasis [1]. It is generally accepted that bone adaptation occurs in response to the mechanical demands of our daily activities; moreover, strain and microdamage have been implicated as potential stimuli that regulate bone remodeling [2]. Computational models have been used to simulate remodeling in an attempt to better understand the metabolic activities which possess the key information of how this process is carried out [3]. At present, the connection between the cellular activity of remodeling and the applied mechanical stimuli is not fully understood. Only a few mathematical models have been formulated to characterize the remolding process in terms of the cellular mechanisms that occur [4,5].
Functional Grading of PLGA Nanofiber Scaffolds for Tendon-to-Bone Insertion Tissue Engineering
Authors: Lipner J. , Li X. , Liu Y. X. , Mangano M. , Xie J. , Genin G. M. , Xia Y. , Thomopoulos S.
Published: July 2013

Stress concentrations often develop at the interfaces of dissimilar materials. Effective attachments can be achieved by incorporating functional gradients in mechanical properties to avoid damaging stress concentrations. Interfaces between biologic materials utilize these gradients to produce robust damage-resistant attachments. For example, the attachment of dissimilar materials, tendon (modulus of ∼200MPa) and bone (modulus of ∼20GPa), is required to transmit force from muscles to the skeleton. This tendon-to-bone attachment is achieved through a linear gradient in mineral content and changes in collagen orientation [1].
Modeling Inter-Lamellar Interactions in Angle-Ply Nanofibrous Biologic Laminates for Annulus Fibrosus Tissue Engineering
Authors: Nerurkar Nandan L. , Mauck Robert L. , Elliott Dawn M.
Published: July 2013

Function of the annulus fibrosus (AF) of the intervertebral disc is predicated on a high degree of structural organization over multiple length scales. Recently, we have employed aligned electrospun scaffolds to engineer nanofibrous biologic laminates that replicate the form and function of the AF [1]. Further, we determined that interlamellar shearing — a direct consequence of the +/−30° angle-ply architecture — plays an important role in reinforcing the tensile response of these materials (Fig. 1). Although we have utilized fiber-reinforced continuum models to characterize the evolving mechanics of single-lamellar AF constructs with in vitro culture [2, 3], these models are not capable of capturing the interlamellar interactions observed in bi-lamellar constructs. Indeed, continuum models of the native AF typically do not account for the organization of fiber populations into discrete, alternating planes of alignment, and so these models, too, do not account for inter-lamellar shearing interactions [4–6]. Therefore, in the present work we propose a novel constitutive model for the reinforcing role of interlamellar shearing during uniaxial extension of angle-ply biologic laminates and employ this model to evaluate the functional evolution of bilayers for AF tissue engineering.
The Orientation Distribution of Apatite Crystals Accounts for Variability in the Elastic Anisotropy of Human Cortical Bone Tissue
Authors: Deuerling Justin M. , Roeder Ryan K.
Published: July 2013

Elastic constants for cortical bone tissue have been correlated with the apparent tissue density, mineral density, and tissue porosity [1–4], but the little data that exists has indicated a weak or no relationship between these structural parameters and the elastic anisotropy [4,5]. A micromechanical model accounting for seven structural parameters across multiple length scales identified the bone mineral orientation distribution to be the most significant structural parameter governing the elastic anisotropy of cortical bone [6].
In Vitro Simulation of Flow Diverter Induced Clotting in Aneurysms Using Rennet Activated Milk Flow
Authors: Sadasivan Chander , Schmidtman Jessica M. , Woo Henry H. , Fiorella David J. , Lieber Baruch B.
Published: July 2013

Flow diverters are currently being evaluated in patients with cerebral aneurysms. Blood cells (such as platelets) contact the device mesh as they enter the aneurysm and pro-coagulant factors released by these activated cells accumulate within the aneurysm because of the intra-aneurismal flow stasis created by the device. The efficacy of any flow diverter is thus related to the rate at which blood coagulation factors accumulate within the aneurysm and get converted to thrombus.
Modified Poly (N-Isopropylacrylamide) Hydrogels for Drug Delivery
Authors: Fu Guoguang , Soboyejo Winston
Published: July 2013

Thermo-responsive hydrogel can change their swelling behavior and drug release characteristics in response to environmental temperature [1–5]. Poly(N-isopropylacrylamide) (PNIPA) hydrogel undergoes a phase transition when the temperatue is lower than a lower critical solution temperature (LCST) of ∼32°C in aqueous solution [8], and drug release profiles in PNIPA hydrogel can be controlled by the alternation of their solution temperatures.
Detection of Fatigue Microdamage in Whole Rat Femora Using Contrast-Enhanced Micro-Computed Tomography
Authors: Turnbull Travis L. , Roeder Ryan K.
Published: July 2013

Microdamage in bone tissue results from repetitive mechanical loading, and the accumulation of microdamage has been implicated with increased fracture susceptibility, including stress fractures in active individuals and fragility fractures in the elderly [1–3]. Conventional methods used to detect microdamage in bone are limited to thin histological sections, which are inherently invasive, destructive, tedious and two-dimensional [3]. A non-destructive, three-dimensional (3-D) method would enable correlation of the spatial location and accumulation of microdamage with variations in the mechanical loading and morphology of whole bones.
Alteration of Fibroblast Cell Behavior due to Contraction of Substrate
Authors: Chippada Uday , Jiang Xue , Previtera Michelle , Schloss Rene , Yurke Bernard , Firestein Bonnie L. , Langrana Noshir A.
Published: July 2013

Many researchers have utilized hydrogels as substrates for cell attachment. The stiffness of these substrates has been found to influence the cellular behavior such as morphology, proliferation, growth and differentiation. Lo et al. deformed polyacrylamide substrates with a blunted microneedle and observed the movement of NIH 3T3 fibroblasts. In both pulling and pushing, the cells reversed their direction and moved away from the needle. This shows that cellular behavior is also affected by stretching the underlying substrates. In a previous study, Lin et al. have demonstrated the ability to contract DNA-crosslinked polyacrylamide hydrogels (‘DNA gels’ in short) by addition of crosslinks. Jiang et al. have utilized these DNA gels as substrates to observe the cellular responses of L929 and GFP fibroblasts to both static and dynamic substrate compliances.
Traumatic Brain Injury: Coupled Experiment/Finite Element Simulation on High Rate Mechanical Response of Porcine Brain
Authors: Prabhu Raj , Horstemeyer Mark , McCollum Michael , Whittington Wilburn , Bouvard Jean-Luc , Sherburn Jesse , Williams Lakiesha , Marin Esteban , Liao Jun
Published: July 2013

Traumatic Brain Injury (TBI), due to recursive concussions, is prevalent in professional sports. Martland was first to report neuropathological conditions related to recursive TBI in professional boxing; while Omalu et al. were the first to report similar neuropathogical conditions, in NFL professionals [1, 2]. Both Martland and Omalu et al. reported long-term neurodegeneration leading to dementia and Alzheimer’s disease [1, 2]. Professional athletes with recursive TBI were observed to have developed speech difficulties, memory lapses, Parkinsons’s-like syndrome with drooling, tremors, and emotional volatility. Although clinical and experimental studies have been carried out to advance the understanding of pathophysiological mechanisms following TBI, limited progress has been made in understanding the effect of stress waves on the neuropathology of TBI using Finite Element Analysis (FEA).
Effect of Patellar Component Alignment in Total Knee Arthroplasty on Patellar Tracking During In Vitro Simulated Squat
Authors: Komosa Mark C. , Mane Amit M. , Maletsky Lorin P.
Published: July 2013

Abnormal patellar tracking is one of the major causes of anterior knee pain and revision surgery after total knee arthroplasty (TKA)1. Patellar tracking after TKA results from several factors including component design, tissue balancing during TKA, shifting of the joint line, and alignment of the patellar and femoral prosthetic components, all of which can lead to anterior knee pain2. The purpose of this study was to observe in vitro the relationship between altered patellar tracking after TKA during a simulated squat activity and the alignment of the patellar component during TKA.
A Nonlinear Finite Element Inverse Approach to Characterize the Material Properties of Tracheal Cartilage: Preliminary Study
Authors: Murphy Colm , Kelliher Denis , Davenport John
Published: July 2013

Tracheal cartilage is a form of hyaline cartilage. Mature hyaline cartilage is classified by miniature aggregations of chondrocytes implanted in an amorphous matrix of ground substance reinforced by collagen fibres designated as collagen type II. The adjacent layer, the perichondrium, consists of collagen fibers and spindle-shaped cells which are similar to fibroblasts. It has been determined that collagen is a nonlinear material[1], and consequently, tracheal cartilage is also nonlinear. Previous research on tracheal cartilage has treated the material as both linear and nonlinear[2].
Rheology of Synovial Fluid From Patients With Osteoarthritis and the Effects of Viscosupplements on the Rheology of Synovial Fluid
Authors: Bhuanantanondh Petcharatana , Grecov Dana , Kwok Ezra
Published: July 2013

Osteoarthritis (OA) is the most common joint disorder associated with aging. It is a degenerative joint disease that is characterized by the breakdown of articular cartilage resulting in joint pain and stiffness. Articular cartilage and synovial fluid are closely linked in providing lubrication, and protective barrier between the ends of the bones. Therefore, damage to articular cartilage may result in modification in rheological properties of the synovial fluid and eventually will have an effect on the performance of the joint. In a diseased joint, the composition of the synovial fluid is changed resulting in deterioration of rheological properties. Synovial fluid becomes less viscous and therefore less effective in lubrication [6].
Experimental Wall Shear Estimation as a Means of Predicting Thrombus Formation Within a 50cc Penn State Blood Pump
Authors: Nanna Jason C. , Topper Stephen R. , Yang Ning , Roszelle Breigh N. , Deutsch Steven , Manning Keefe B.
Published: July 2013

The use of ventricular assist devices (VADs) as a means of cardiac support for patients with diminished heart function has been investigated since the 1960s [1]. While VAD therapy has had success in assisting the failing heart, thrombus formation within these devices is one of various complications that still limit its long term use. Research has shown that thrombus deposition in VADs is a function of the underlying fluid mechanics within these devices. Areas of flow stasis, high blood residence time, and wall shear rates under 500 s−1 are important flow characteristics driving thrombosis [2].
Use of Extracellular Matrix Bioscaffolds to Enhance ACL Healing: A Multidisciplinary Approach in a Goat Model
Authors: Fisher Matthew B. , Jung Ho-Joong , Liang Rui , Kim Kwang , McMahon Patrick J. , Woo Savio L.-Y.
Published: July 2013

Due to the poor healing potential of the anterior cruciate ligament (ACL) of the knee, surgical reconstruction using soft tissue replacement grafts is performed to restore knee stability and function. However, the surgery has serious complications including a high incidence of donor site morbidity and the development of osteoarthritis in the long-term. Recently, functional tissue engineering approaches to heal an injured ACL using biological stimulation via growth factors and bioscaffolds have yielded some positive clinical and laboratory results. As the healing process for the ACL is slow, additional suture repair of the ACL has been needed to provide initial joint stability and to reduce the risk of injury to neighboring tissues.
The Use of a Cellular Strain Injury Criterion and Diffusion Tensor Imaging in a Computational Model of Traumatic Brain Injury
Authors: Wright Rika M. , Ramesh K. T.
Published: July 2013

With the increase in the number of soldiers sustaining traumatic brain injury from military incidents and the recent attention on sports related traumatic brain injury, there has been a focused effort to develop preventative and treatment methods for traumatic brain injury (TBI). Traumatic brain injury is caused by mechanical loading to the head, such as from impacts, sudden accelerations, or blast loading, and the pathology can range from focal damage in the brain to widespread diffuse injury [1]. In this study, we investigate the injury mechanisms of diffuse axonal injury (DAI), which accounts for the second largest percentage of deaths due to brain trauma [2]. DAI is caused by sudden inertial loads to the head, and it is characterized by damage to neural axons. Despite the extensive research on DAI, the coupling between the mechanical loading to the head and the damage at the cellular level is still poorly understood. Unlike previous computational models that use macroscopic stress and strain measures to determine injury, a cellular injury criterion is used in this work as numerous studies have shown that cellular strain can be related to the functional damage of neurons. The effectiveness of using this cellular injury criterion to predict damage in a finite element model of DAI is investigated.
The Effects of Geometry and Static Boundary Conditions on Microvessel Outgrowth in a 3D Model of Angiogenesis
Authors: Underwood Clayton J. , Krishnan Laxminarayanan , Edgar Lowell T. , Maas Steve , Hoying James B. , Weiss Jeffrey A.
Published: July 2013

We reported previously that, in addition to mechanical strain, a constrained boundary condition alone can alter the organization of microvessel outgrowth during in vitro angiogenesis [1]. After 6 days of culture in vitro, microvessels aligned parallel to the long axis of rectangular 3D collagen gels that had constrained edges on the ends. However, unconstrained cultures did not show any alignment of microvessels. The ability to direct microvessel outgrowth during angiogenesis has significant implications for engineering prevascularized grafts and tissues in vitro, therefore an understanding of this process is important. Since there is direct relationship between the ability of endothelial cells to contract 3D gels and matrix stiffness [2], we hypothesize that some constrained boundary conditions will increase the apparent matrix stiffness and in turn will limit gel contraction, prevent microvessel alignment, and reduce microvessel outgrowth. The objective of this study was to compare microvessel growth and alignment under several different static boundary conditions.
The Role of Thrombin, Fibrinogen, and Fibronectin on Platelet Clot Retraction Forces Analyzed Using Microposts
Authors: Liang Xin M. , Gao Dayong , Sniadecki Nathan J.
Published: July 2013

When a blood vessel is damaged, platelets aggregate together to form a thrombus that seals vascular leakage and promotes healing. The process of thrombosis involves activation of platelets by soluble ligands, adhesion to the wound site, change in shape from a discoidal to a stellate structure, and the attachment of additional platelets onto the nascent clot through adhesive ligand bridges. Once formed, a clot will undergo a retraction in volume that packs platelets together and allows blood flow to recommence. Much attention has been paid to the early phases of thrombosis — adhesion and aggregation — but the process of clot retraction is vital to stabilizing the clot.
Assessment of Energy Loss due to Pulmonary Valve Insufficiency in Tetralogy of Fallot Physiology Using Patient Specific Geometry
Authors: Das Ashish , Gottliebson William , Karve Madhra , Banerjee Rupak K.
Published: July 2013

Right ventricular (RV) enlargement and pulmonary valve insufficiency (PI) are well-known, unavoidable long term sequelae encountered by patients who undergo tetralogy of Fallot (TOF) surgery. Energy losses in the pulmonary artery (PA) of TOF and normal subjects was calculated using patient specific geometry and pressure and flow data to develop quantifiable clinical diagnostic parameters. The TOF subject shows 35% higher energy losses than our normal subject.
Mechanical Properties of the Rat Brain: Effect of Age and Anatomical Region
Authors: Elkin Benjamin S. , Morrison Barclay
Published: July 2013

Of the 1.5 million traumatic brain injuries (TBI) every year, about 250,000 require hospitalization and result in 50,000 deaths[1]. Outcome after TBI is strongly dependent on age[2, 3]. Because there is no pharmacological treatment for the head injured patient, prevention of TBI is paramount. By gaining an in depth understanding of injury biomechanics, it may be possible to design more effective protection either in the form of helmets or automotive safety systems. To this end, finite element models are frequently employed to understand the induced brain deformation due to injurious loading scenarios[4].
Estimation of the Stresses Applied on Aneurysm Wall by the Expansion of Shape Memory Polymer Foam
Authors: Hwang Wonjun , Singhal Pooja , Maitland Duncan J.
Published: July 2013

SMP foams have been proposed for an improved treatment of aneurysms over the currently used Guglielmi Detachable Coils (GDC) [1]. With the recent FDA approval of first SMP medical device in March 2009 by FDA, this procedure has a high potential of being used in aneurysm treatment in humans [2].
Simulating Axonal Stretch During Traumatic Brain Injury Events
Authors: Dollé Jean-Pierre , Barminko Jeffrey , Schloss Rene , Yarmush Martin L.
Published: July 2013

Traumatic Brain Injuries (TBI) affect up to 1.5 million people annually within the United States with as many as 250,000 being hospitalized and 50,000 dying [1]. TBI events occur when the brain experiences a sudden trauma such as a rapid deceleration of the brain that typically occurs during motor vehicle accidents. During rapid deceleration events, the brain is subjected to high inertial forces that can result in a shearing or elongation of axons that is commonly known as Diffuse Axonal Injury (DAI) [2,3].
Mass Transfer of LDL Based on Wall Shear Stress From FSI Simulation in Atherosclerotic Human Carotid Artery
Authors: Kim Sungho , Giddens Don P.
Published: July 2013

Wall shear stress (WSS) distribution and low density lipoprotein (LDL) mass flux are simulated using a fluid-structure interaction (FSI) approach. T2 weighted black blood MRI images of a human left carotid artery are used for the arterial model construction, and the boundary conditions for FSI simulation are derived from phase contrast (PC) MR data. The endothelium is treated as a shear stress dependent, three pathways pore model for LDL particles. The computational results demonstrate that the region distal to an atherosclerotic plaque in the internal carotid artery experiences both low WSS and high mass and volume flux, which are hypothesized to be essential factors in progression of atherosclerosis.
Differential Gene Expression of Endothelial Cells Under High Wall Shear Stress and Spatial Gradients
Authors: Dolan Jennifer , Liu Song , Meng Hui , Kolega John
Published: July 2013

In both human and animal models, cerebral aneurysms tend to develop at the apices of bifurcations in the cerebral vasculature. Due to the focal nature of aneurysm development it has long been speculated that hemodynamics are an important factor in aneurysm susceptibility. The local hemodynamics of bifurcations are complex, being characterized by flow impingement causing a high frictional force on the vessel wall known as wall shear stress (WSS) and significant flow acceleration or deceleration, manifested as the positive or negative spatial gradient of WSS (WSSG). In vivo studies have recently identified that aneurysm initiation occurs at areas of the vessel wall that experience a combination of both high WSS and positive WSSG [1,2]
Muscle Forces May Explain Paradoxical Knee Loads During Different Gait Patterns
Authors: Walter Jonathan P. , D’Lima Darryl D. , Fregly Benjamin J.
Published: July 2013

Medial compartment knee osteoarthritis is a common clinical disorder [1] in which the articular cartilage in the medial compartment progressively deteriorates. To slow disease progression without surgical intervention, researchers have proposed gait modifications to offload the medial compartment. Since knee medial contact force (MCF) cannot be measured non-invasively in vivo, researchers have identified the external knee adduction moment (KAM) as a surrogate measure that is easy to calculate [2]. A common assumption has been that reducing the peak KAM will result in a corresponding reduction in peak MCF. While the magnitude of the peak KAM has been correlated with disease severity and rate of disease progression [3,4], it is not clear that reduction of this external load via gait modification will always result in a decrease in internal MCF.
Evaluation of Cerebral Aneurysm Stent Performance in a Subject-Specific Computational Model
Authors: Gundert Timothy J. , LaDisa John F.
Published: July 2013

Rupture of cerebral aneurysms is the second leading cause of stroke in the United States [1]. Altered hemodynamics is thought to play a role in the progression and subsequent rupture of aneurysms. Blood flow into an aneurysm can be occluded by surgically clipping the aneurysm or using endovascular devices, such as stents or coils. In saccular aneurysms, coiling alone may be a sufficient method of inducing flow stagnation in the aneurysm, causing thrombosis and preventing rupture. When treating wide-necked aneurysms, stenting is often used in conjunction with coiling to prevent the migration of coils. Many investigators have studied the ability of a stent-only treatment to favorably alter flow in aneurysms [2, 3].
A Method for Developing MRI-Based Finite Element Models of the Left Ventricle With Mitral Valve and Chordae Tendineae
Authors: Wenk Jonathan F. , Zhang Zhihong , Cheng Guangming , Malhotra Deepak , Acevedo-Bolton Gabriel , Burger Mike , Suzuki Takamaro , Saloner David A. , Wallace Arthur W. , Guccione Julius M. , Ratcliffe Mark B.
Published: July 2013

Ischemic mitral regurgitation (MR) affects 1.2 to 2.1 million patients in the United States, with more than 400,000 patients having moderate-to-severe MR [1]. As a consequence of left ventricular remodeling after postero-basal myocardial infarction (MI), the posterior papillary muscle moves laterally. This causes both anterior and posterior mitral leaflets to be tethered, and type 3B Carpentier leaflet motion (restricted motion during systole) and ischemic MR to occur.
Shear and Friction in the Delamination of Human Chorioamnion
Authors: Briggs Brandi N. , Ferguson Virginia L.
Published: July 2013

The chorioamnion (CA), or placental, membrane is the sac that surrounds the fetus in utero. It is comprised of two layers; the inner fibrous amnion, composed of mainly collagen, and the thick, cellular chorion. The CA membrane exhibits incredible toughness under tension, while still allowing the two layers to easily slide over one another1,2. The interface between the chorion and amnion consists of gyri (folds) and sulci (furrows)3, which enable the two layers to tightly interlock and facilitate the intact membrane’s resistance to tension. This complex structure also allows the two layers to expand during gestation without losing mechanical integrity. The gyrus and sulcus from one section are believed to uncouple, slide laterally, and then lock into their new position while the remaining membrane is unaffected by the motion3. SEM imaging of freeze-fractured CA has revealed a multitude of fine fibers connecting the two layers as illustrated in Figure 1. These are suggested to serve as “guy ropes”, which restrict the amount that the two layers could slide over one another3. Also of importance at this interface is the presence of hyaluronan, a glycosaminoglycan. The hyaluronan has been suggested to reduce the resistance between the two layers so that they may glide over one another more easily throughout gestation and with vigorous fetal movements1. The combination of the elaborate topography of the interface and the lubricating glycosaminoglycans present throughout this layer play a role in the mechanics of the interface between chorion and amnion.
Are Passaged Chondrocytes Phenotypically Similar to Meniscal Fibrochondrocytes?
Authors: Son Min-Sun , Levenston Marc E.
Published: July 2013

The knee menisci are heterogeneous fibrocartilages with regional variations in phenotype and extracellular matrix composition reflecting varying functional demands. The inner (compressive) region is generally described as closer to cartilage, with higher aggrecan and collagen II contents and rounded cells resembling articular chondrocytes1,2, while the outer (tensile) third of the meniscus is fibrous and vascularized with cells described as fibroblast-like. Some studies have suggested that passaged chondrocytes can be used as a source for engineering fibrocartilage due to their tendency to become more “fibrous”3,4. However, the characteristics of isolated and passaged cells have not been quantitatively compared to the behaviors of meniscal cells. In fact, despite a qualitative understanding of phenotypic variations within the meniscus and between meniscal cells and chondrocytes, no metrics have been identified to quantitatively distinguish fibrochondrocytes from chondrocytes. In this study, we evaluated the gene expression profiles of serially passaged chondrocytes in the context of the expression profiles of articular chondrocytes and meniscal fibrochondrocytes in native tissue isolated from different anatomical regions, with a focus on genes important to the production and regulation of the extracellular matrix.
Experimental and Computational Evaluation of Embolic Protection
Authors: Siewiorek Gail M. , Finol Ender A.
Published: July 2013

Carotid artery stenting (CAS), an endovascular treatment for severe carotid artery occlusive disease, is increasingly considered a complimentary procedure to carotid endarterectomy. One reason for the acceptance of CAS as a viable treatment alternative is cerebral protection devices (CPDs), which can reduce the embolic load in the cerebral vasculature. One particular type of CPD, distal protection filters (DPFs), are a popular choice due to their ability to allow distal perfusion peri-procedurally while filtering and removing plaque emboli from the body. This investigation studied one FDA-approved DPF, RX Accunet, using both in vitro and computational methods.
The Spatio-Temporal Structure of Force Variability in Static Grasp Suggests a Continually Active Neural Controller
Authors: Rácz Kornelius , Inouye Josh M. , Valero-Cuevas Francisco J.
Published: July 2013

Fingertip forces during simple and static tripod grasp exhibit a surprisingly rich dynamics [1]. Here we explore the hypothesis that, even for this apparently simple manipulation task, these fluctuations are shaped by a neural controller rather than by signal-dependent motor noise. We fed band-limited noise processes scaled to mean force level into a 21-muscle model of 3-finger grasp, and compare model output with experimental force recordings. We find that the spatial and spectral characteristics of simulated force fluctuations differed greatly from those observed in actual static tripod grasp. In light of current literature [2], we propose that a continually active neural controller is at work even for this simplest example of multifinger manipulation.
An Education Platform for Awareness and Prevention of Obesity Epidemic Among Children and Adolescents
Authors: Kazempour Majidreza M.
Published: July 2013

Obesity is now replacing undernutrition and infectious diseases as the leading cause of ill health. It is considered as one of the greatest medical challenges to health in the United States; over 65% of American adults are either overweight or obese leading to 320,000 deaths each year in the United States (Kopelman, 2005). The annual medical costs of obesity in the United States are enormous (Bhattacharya and Bundorf, 2009). Globally, according to the World Health Organization, there are more than one billion overweight adults, of which at least 300 million are clinically obese. A recent National Health and Nutrition Examination Survey (NHANES) data (2003–2006) has showed that for children aged 6–11 years and 12–19 years, the prevalence of overweight was 17.0% and 17.6%, respectively.
Accelerations of the Head During Soccer Ball Heading
Authors: Paris Anthony J. , Antonini Kyle R. , McFerran Brock Jennifer
Published: July 2013

The objective of this study was to investigate the accelerations of the head during soccer ball heading by introducing a prototype accelerometer-chip instrumented mouth guard. This mouth guard was evaluated for further use in head impact studies.
Modeling of the effects of charge transport on voltage-dependent photocurrent in ultrathin CdTe solar cells
Authors: Arnab Salman M. , Kabir M. Z.
Published: July 2013

An analytical model is developed to study the current–voltage characteristics of CdTe thin film solar cells by incorporating exponential photon absorption, carrier trapping, carrier drift, and diffusion in the photon absorber layer. An analytical expression for the external voltage-dependent photocurrent is derived, considering partial depletion of the absorber layer at operating terminal voltage. The overall load current is calculated considering the actual solar spectrum and dark current components. The analytical model is verified by Taurus Medici simulation and published experimental results for different absorber layer thicknesses. A good agreement of the analytical and numerical models with experimental data is ensured by reducing carrier lifetimes in the thinner absorber layers. The hole lifetime is reduced drastically by decreasing the width of the absorber layer from 1.1 to 0.5 μm, and the cell efficiency depends critically on the transport properties of the holes. The results of this paper indicate that the improvement of the charge transport properties in submicron CdTe solar cells is extremely important to increase the power conversion efficiency.
Few layer graphene synthesized by filtered cathodic vacuum arc technique
Authors: Panwar Omvir Singh , Kumar Kesarwani Ajay , Dhakate Sanjay Rangnath , Singh Bhanu Pratap , Rakshit Rajib Kumar , Bisht Atul , Chockalingam Sreekumar
Published: July 2013

Filtered cathodic vacuum arc technique has been used to deposit amorphous carbon (a-C) films of varying thicknesses from 10 nm to 38 nm on catalytic nickel thin film grown on SiO2/Si substrates. Subsequently, a-C films were annealed in vacuum in the temperature range from 650 to 850 °C. Micro-Raman spectroscopic study in combination with optical microscopy and scanning electron microscopy has revealed few layer graphene formations with optical transmittance in the range 85%–88% with a-C films deposited with 10 nm and 18 nm thicknesses. The optimum temperature of annealing was observed to be 750 °C.
Comparison of head-related impulse response measurement approaches
Authors: Rothbucher Martin , Veprek Kajetan , Paukner Philipp , Habigt Tim , Diepold Klaus
Published: July 2013

The well-established static head-related transfer function (HRTF) measurement approaches using maximum length sequences and sine sweeps are compared with a recent HRTF estimation approach using normalized least mean square adaptive filters, which enables a continuous movement of the person to be measured during the recording of the excitation signal. By using continuous movement HRTF measurement, a huge amount of time for the individual HRTF estimation can be saved to create a dense HRTF database for headphone-based sound synthesis or applications such as crosstalk cancellation for loudspeaker-based sound synthesis. The different approaches are implemented and experimentally compared by objective and subjective evaluation.
The development of a modified spectral ripple test
Authors: Aronoff Justin M. , Landsberger David M.
Published: July 2013

Poor spectral resolution can be a limiting factor for hearing impaired listeners, particularly for complex listening tasks such as speech understanding in noise. Spectral ripple tests are commonly used to measure spectral resolution, but these tests contain a number of potential confounds that can make interpretation of the results difficult. To measure spectral resolution while avoiding those confounds, a modified spectral ripple test with dynamically changing ripples was created, referred to as the spectral-temporally modulated ripple test (SMRT). This paper describes the SMRT and provides evidence that it is sensitive to changes in spectral resolution.
A higher-order tangent linear parabolic-equation solution of three-dimensional sound propagation
Authors: Lin Ying-Tsong
Published: July 2013

A higher-order square-root operator splitting algorithm is employed to derive a tangent linear solution for the three-dimensional parabolic wave equation due to small variations of the sound speed in the medium. The solution shown in this paper unifies other solutions obtained from less accurate approximations. Examples of three-dimensional acoustic ducts are presented to demonstrate the accuracy of the solution. Future work on the applications of associated adjoint models for acoustic inversions is proposed and discussed.
Accuracy of a sequential approach to identify young febrile infants at low risk for invasive bacterial infection
Authors: Mintegi Santiago , Bressan Silvia , Gomez Borja , Da Dalt Liviana , Blázquez Daniel , Olaciregui Izaskun , de la Torre Mercedes , Palacios Miriam , Berlese Paola , Benito Javier
Published: July 2013

Introduction

Much effort has been put in the past years to create and assess accurate tools for the management of febrile infants. However, no optimal strategy has been so far identified. A sequential approach evaluating, first, the appearance of the infant, second, the age and result of the urinanalysis and, finally, the results of the blood biomarkers, including procalcitonin, may better identify low risk febrile infants suitable for outpatient management.

Objective

To assess the value of a sequential approach (‘step by step’) to febrile young infants in order to identify patients at a low risk for invasive bacterial infections (IBI) who are suitable for outpatient management and compare it with other previously described strategies such as the Rochester criteria and the Lab-score.

Methods

A retrospective comparison of three different approaches (step by step, Lab-score and Rochester criteria) was carried out in 1123 febrile infants less than 3 months of age attended in seven European paediatric emergency departments. IBI was defined as isolation of a bacterial pathogen from the blood or cerebrospinal fluid.

Results

Of the 1123 infants (IBI 48; 4.2%), 488 (43.4%) were classified as low-risk criteria according to the step by step approach (vs 693 (61.7%) with the Lab-score and 458 (40.7%) with the Rochester criteria). The prevalence of IBI in the low-risk criteria patients was 0.2% (95% CI 0% to 0.6%) using the step by step approach; 0.7% (95% CI 0.1% to 1.3%) using the Lab-score; and 1.1% (95% CI 0.1% to 2%) using the Rochester criteria. Using the step by step approach, one patient with IBI was not correctly classified (2.0%, 95% CI 0% to 6.12%) versus five using the Lab-score or Rochester criteria (10.4%, 95% CI 1.76% to 19.04%).

Conclusions

A sequential approach to young febrile infants based on clinical and laboratory parameters, including procalcitonin, identifies better patients more suitable for outpatient management.