bluuebunny/crossref_metadata_2025 huggingface dataset:
Anisotropic Modeling of Fibrous White Matter
Authors: Wright Rika M. , Ramesh K. T.
Published: March 2014

Traumatic brain injury (TBI) is a debilitating injury that affects more than 1.4 million people in the United States each year. Of the incidences of TBI, diffuse axonal injury (DAI) accounts for the second largest percentage of deaths. DAI is caused by inertial loads to the head, and it is characterized by damage to neurons. Despite the extensive research on DAI, the injury mechanisms associated with the pathology are still poorly understood. The crucial link between the inertial forces to the head at the macroscale and the resulting damage at the cellular level has yet to be explained. An integral step to understanding this coupling between mechanical forces and the functional damage of neurons is the development of an analytical model that accurately represents the mechanics of brain deformation under inertial loads. It has been noted in clinical and experimental studies that the most common injury location of DAI is within the deep white matter of the brain. Structures such as the splenium of the corpus callosum are cited as being highly susceptible to damage [1]. Although numerous brain tissue models have been proposed, few models account for the anisotropic nature of white matter in the brain. As a first step in developing an anisotropic model for white matter, the effect of the invariant terms in a strain energy function for white matter is analyzed.
Controlled Cyclic Stretching of Tissue Engineered Heart Valves: Effects on Mechanical Properties and ECM Organization
Authors: Syedain Zeeshan H. , Tranquillo Robert T.
Published: March 2014

Tissue engineering provides a means to create fully functional tissue-equivalents that can grow, repair and remodel in vivo. Our laboratory’s approach to fabricating artery- and heart valve-equivalents utilizes cell-seeded fibrin gels. However, even after 4–5 weeks of static incubation, the mechanical properties of these constructs are below those of native tissue. Previous studies in our laboratory have shown a significant role of mechanical stretching in improving properties of collagen-based tissue constructs (Isenberg and Tranquillo, 2003). We examined the effects of cyclic distention (CD) of cell-seeded fibrin-based tubular constructs (TC) and valve-equivalents (VE) after five weeks of culture. We used human dermal fibroblasts and porcine valve interstitial cells as the cell sources. Circumferential strain amplitudes from 2.5% to 15% were applied to evaluate the effects of CD on remodeling of the TC. We further hypothesized that during long-term conditioning, cells adapt to CD of constant strain amplitude, diminishing the remodeling into tissue. We tested this hypothesis by applying step-wise incremental CD (ICD) from 5%–15% strain amplitude and compared this group to a set of samples subject to CD of constant strain amplitude in this range. Based on the outcome of the cyclic distension study with tubular constructs, we applied CD to VE in a novel bioreactor.
Electrodeposited Micro Copper Bumps for Packaging Module of a Micro-Thermoelectric Cooler
Authors: Kardak Ajay A. , Podlaha-Murphy Elizabeth J. , Murphy Michael C. , Devireddy Ram V.
Published: March 2014

Flipchip assembly is the direct electrical connection of the device die on the substrates or circuit boards using conductive stud bumps. Stud bumps help in the reduction of the number of bond wires and weight, and improve performance. Ueno et al. [1] fabricated copper column bumps with a diameter of 75 μm, a height of 50 μm and a pitch of 200 μm. Ni/Au bumps were also fabricated using electroless plating method with a pitch of 50 μm [2]. Tomita et al. [3] successfully fabricated tip capped copper column bumps with a height of 5 μm that were spaced 100 μm apart. Lead free solder bumps have been fabricated using pure-tin (Sn), tin-bismuth (80wt%Sn:20wt%Bi), tin-copper (99.3wt%Sn:0.7wt%Cu), tin-silver (96.5wt%Sn:3.5wt%Ag), and tin-silver-copper (93.8wt%Sn:3.5wt%Ag:0.7wt%Cu) alloys with a diameter of 200 μm and a pitch of 400 μm [4]. Low cost gold bumps have also been fabricated on polymer substrates with dimensions of 40 μm in diameter, 41 μm in height and a pitch of 100μm [5]. More recently Chu et al. [6] have demonstrated the use of cylindrical indium solder bumps with 80 μm diameter for optical interconnect and microwave applications.
Col1 and Col2 Gene Expression During the Development of Murine Knee Joints
Authors: Chokalingam Kumar , Frede Chris , Florer Jane L. , Wenstrup Richard J. , Butler David L.
Published: March 2014

Recently, tissue engineers have turned to developmental biology to try and improve the repair of tendons and ligaments [1]. The premise is that understanding normal growth and development of tendons and ligaments might facilitate in later repair. Understanding these similarities in extracellular matrix gene expression and growth factor expression might allow tissue engineers to develop treatments to augment adult tendon and ligament healing.
Biomechanical Comparison of Abdominal Wall Hernia Repair Materials
Authors: Boguszewski Daniel V. , Dyment Nathaniel A. , Bailey Denis L. , Shearn Jason T. , Butler David L.
Published: March 2014

Complications following abdominal hernia repair include infection, mechanical failure, adhesion, and hernia recurrence [1,2]. Mesh materials require less revision surgery and reduce patient morbidity compared to when fascia is harvested [1,3]. Biologic meshes have lower infection rates and less adhesion than synthetic materials, but are more expensive [1]. In order to determine how these materials will function in vivo, it is important to simulate aspects of the actual conditions to which the material might be subjected after surgery. Previous studies have examined how different types of fascia, synthetic materials, and extracellular matrix materials responded to tests that mimic the in vivo state [3–6]. Suture retention testing has been used to compare the performance of human fascia versus possible substitutes [4]. Ball burst testing has been instrumental in understanding the biomechanical properties of different soft tissues and replacement materials by simulating biaxial forces associated with physiological loading conditions [5–7]. This objective of this was to determine which material might be most optimal for use in hernia repair. We hypothesize that biologic mesh materials will exhibit more optimal mechanical properties than synthetic materials when exposed to these test procedures.
A New Method to Diagnose Left Ventricular Dyssynchrony With Analysis of Heart Wall Thickening From Cardiac CT
Authors: Goette Matthew J. , Delfino Jana G. , Fornwalt Brandon K. , Oshinski John N.
Published: March 2014

Left ventricular (LV) dyssynchrony is a pathological condition in which segments of the myocardial wall contract at different times. This dyssynchrony results in a decreased LV ejection fraction (EF) and an increased level of mitral regurgitation. LV dyssynchrony has been linked to higher rates of morbidity, mortality, and arrhythmic susceptibility in patients with congestive heart failure. Cardiac resynchronization therapy (CRT) with biventricular pacemakers has benefited patients with drug-refractory heart failure and signs of ventricular dyssynchrony. Patients are currently selected for CRT therapy if they have a prolonged QRS complex (> 120 msec) on a surface electrocardiogram as well as an EF of less than 35%. However, recent data suggests that these criteria are insufficient, as 30% of patients do not respond to CRT treatments.
The Mechanical Behaviour of Endovascular Gianturco Stents Measured In Vitro
Authors: Johnston Clifton R. , Lee Kogan , Flewitt Jacqueline , Moore Randy , Thornton Gail M. , Dobson Gary M.
Published: March 2014

Endovascular stents are used to treat aneurysms, dissections and acute traumatic disruptions of the thoracic aorta. While stents are certainly a much less invasive treatment option, the behaviour of stents in the aorta is still not well understood. Gianturco stents ranging from 8mm to 44mm in diameter were tested and found to exhibit nonlinear force-displacement relationships. The effect of stent length and the common clinical practice of overlapping two stents were also tested. It was found that stent pressure was proportional to stent length and that a small stent overlap resulted in a doubling of the stent force.
Comparison of the Duration of Diabetes and PSSD Measurements
Authors: Vines Robert S. , Marica Rucsandra R. , Vo Ha V.
Published: March 2014

In the U.S. there are roughly 15 million diabetics with 10 million of them having mild to severe forms of nerve damage. Almost 4.5 million diabetics suffer from nerve damage in the feet [1]. Early detection of neuropathy is paramount to preventing further damage to the affected limb(s). Neuropathy is a leading factor in amputations, which can be avoided or reduced if neuropathy is detected early and limb care is promoted.
Parameter Estimation of the Mechanical Behavior of the Artery Using a Nonlinear Least Square Method With a Noise Model
Authors: Zeinali Shahrokh , Choi Jongeun , Baek Seungik
Published: March 2014

Although it is well known that blood vessels adapt and remodel in response to various biomechanical stimuli, quantifying changes in constitutive relation corresponding to environmental changes is still challenging. Especially, when the dimension of blood vessel is small, the uncertainties in experimental measurements become significant and make it difficult to precisely estimate parameters of constitutive relations for mechanical behavior of the blood vessel. Hence without considering measurement error in displacement, a conventional nonlinear least square (NLS) method results in a biased parameter estimation. In this paper, we propose a new parameter estimation method to eliminate such bias error and provide more accurate estimated parameters for a constitutive relation using a weighted nonlinear least square (WNLS) method with a noise model. We first applied the proposed technique to a set of synthesized data with computer generated white noises and compared the fitting results to those of the NLS method without the noise model. We also applied our method to experimental data sets from mechanical tests of rabbit basilar and mouse carotid arteries and studied parameter sensitivity of the constitutive model.
Effective Gait Modification Strategies for Offloading the Medial Compartment of the Knee
Authors: Fregly Benjamin J. , D’Lima Darryl D. , Colwell Clifford W.
Published: March 2014

Gait modification is a conservative, non-invasive treatment option for patients with medial compartment knee osteoarthritis. If proven effective for offloading the medial compartment, it may provide one of the few treatment options with disease modifying potential. Furthermore, it could fill an important therapeutic “hole” for patients in their 40’s and 50’s who no longer achieve sufficient pain relief through pharmacological means and yet are too young to receive a total knee replacement. A variety of gait modifications have been proposed for offloading the medial compartment, including toeing out [1], walking more slowly or with decreased stride length [2], walking with increased medial-lateral trunk sway [3], using lateral heel wedges [4], or walking with medialized knees [5]. These modifications have been proposed primarily based on their ability to reduce the external knee adduction torque. While this external measure is highly correlated with medial compartment contact force [6], the acid test is to demonstrate experimentally that a gait modification reduces medial contact force directly.
Osmotic Effects on the Dynamic Shear Properties of Meniscal Fibrocartilage
Authors: Ho Patricia H. , Nguyen An M. , Levenston Marc E.
Published: March 2014

The meniscus plays an important role in many biomechanical functions of the knee, including shock absorption, load distribution, and joint lubrication. The ability to perform these functions is determined by the interactions of the major tissue constituents (water, proteoglycan, and collagen), although these interactions have not been as thoroughly studied in fibrocartilage as those in other soft tissues. In articular cartilage, electrochemical interactions between negatively charged glycosaminoglycan (GAG) side chains of proteoglycans and the interstitial fluid generate an osmotic swelling pressure that contributes to the compressive stiffness [1], and proteoglycan degradation dramatically decreases compressive and shear moduli [2]. Although the concentration of proteoglycan in the meniscus is substantially lower (<1%) than that in articular cartilage, aggrecan degradation also greatly decreases the compressive and shear moduli of meniscal fibrocartilage [3]. The proteoglycan distribution in meniscal fibrocartilage is macroscopically heterogeneous [4] and is concentrated in the secondary matrix surrounding the circumferential collagen bundles, and the extent to which osmotic interactions explain the influence on fibrocartilage material properties is unknown. Altering the osmotic strength of the bathing solution supplies a means to control osmotic interactions between the GAGs and the environment without degrading the tissue matrix. The objective of this study was to examine the effects of an altered osmotic environment on the dynamic shear modulus of meniscal tissue.
Influence of Non-Newtonian Models on Simulation of Aneurysm Hemodynamics
Authors: Rossmann Jenn , Fisher Carolyn
Published: March 2014

Aneurysm rupture rates are often associated with factors such as size, location, and patient specific risks such as age and health. However, the actual physiological causes of the pathogenesis, enlargement, and rupture are unclear. Many studies have shown aneurysm formation to be mechanically mediated. Hemodynamic forces such as wall shear stress (WSS), pressure, and flow patterns have been examined as causes for aneurysm development and eventual rupture [1]. Geometric factors such as the aneurysm size, shape, and aspect ratio may also be important in predicting rupture [2,3].
Parametric Stent Design Using pyFormex
Authors: Mortier Peter , De Beule Matthieu , Van Loo Denis , Verdonck Pascal , Verhegghe Benedict
Published: March 2014

Stenting is the most commonly used medical procedure to restore blood flow in stenotic arteries. During this endovascular intervention, a small tube-like structure is implanted in the narrowed section of the diseased artery. The vast majority of stents are crimped (i.e. plastically deformed) on a folded balloon (balloon expandable stents). After insertion through a small incision in the femoral or radial artery using a catheter, the balloon is inflated and the stent deploys. Following to the expansion, the balloon is deflated and retracted and from then on, the stent acts as a mechanical scaffold for the enlarged lumen.
In Situ Bioengineering of Arterial Vein Grafts
Authors: El-Kurdi Mohammed S. , Morelli Brian C. , Hong Yi , Wagner William R. , Vorp David A.
Published: March 2014

The autogenous saphenous vein remains the graft of choice for both coronary (500,000 annually in the US)1 or peripheral (80,000 annually)2 arterial bypass procedures. Failure of arterial vein grafts (AVGs) remains a major problem, and patients with failed grafts will die or require re-operation. Intimal hyperplasia (IH) accounts for 20% to 40% of all AVG failures3. It is believed that this adverse pathological response by AVGs is largely due to their abrupt exposure to the significantly elevated circumferential wall stress (CWS) associated with the arterial system4. We believe that if an AVG is given an ample opportunity to adapt and remodel to the stresses of its new environment, cellular injury may be reduced, thus limiting the initiating mechanisms of IH. The goal of this work was to develop a new mechanical conditioning paradigm, in the form of a peri-adventitially placed, biodegradable polymer wrap, to safely and functionally “arterialize” AVGs in situ. The electrospun polymer wrap was tuned so that as it degraded over a desired period of time, the mechanical support offered by it was reduced gradually, and hence the vein was exposed to slowly increasing levels of CWS in situ.
Shear Stress Modulates Plaque Composition in Human Coronary Arteries In Vivo
Authors: Gijsen Frank , Wentzel Jolanda , Schuurbiers Johan , Mastik Frits , Schaar Johannes , Serruys Patrick , van der Steen Anton
Published: March 2014

It is well established that atherosclerotic plaques generally develop in low shear stress regions, including curved arterial segments and bifurcations1. Once these plaques intrude into the lumen, the shear stress they are exposed to alters with hitherto unknown consequences. We hypothesize that in the more advanced stages of the disease, shear stress has an important impact on plaque composition in such a way that high shear stress enhances plaque vulnerability through its biological impact on the endothelium2. We investigated this hypothesis previously by studying the relationship between shear stress and strain, a marker for plaque composition, in human coronary arteries3. In this study, we will extend that study by investigating how shear stress influences changes of strain, and thus plaque composition, over a period of 6 months.
Evaluation of Fixation Stability for MIS Friendly Cemented Tibial Trays Using Finite Element Method: Cement Bonding Condition, Stem Geometry and Tray Stiffness
Authors: Fang Zhibin , Son Yang W. , Pendleton John E. , Levine Danny L. , Johnson Todd S.
Published: March 2014

Due to smaller incision and soft tissue sparing techniques, minimally invasive surgery (MIS) in total knee arthroplasty (TKA) has benefited many patients in terms of shortened hospital stays and quicker recoveries when compared to traditional TKA surgery [1]. A traditional TKA surgery generally requires an 8″ incision while MIS can be performed with a 3–5″ incision. To accommodate the smaller incision used in MIS TKA, MIS friendly tibial tray designs have shorter stems or use modular stem extensions as compared to traditional stemmed tibial tray designs. One of the design considerations is that the shorter stem may compromise the tibial tray’s fixation stability especially for Posterior Stabilized (PS) loading scenarios in which the tibial tray may be subjected to large anterior/posterior (A/P) load through the engagement of the tibial insert and the femoral component and cause tipping of the tray.
Experimental Validation of a Tibiofemoral Model for Analyzing Joint Force Distribution
Authors: Miller Emily J. , Reimer Rose F. , Haut Donahue Tammy L. , Kaufman Kenton R.
Published: March 2014

Mathematical models are non-invasive tools used for analyzing biomechanical conditions. Various models of the knee using the finite element analysis technique [1–6] and rigid body spring model (RBSM) [7] have been developed to predict pressure distribution in articulating joints, although the RBSM is considered the simplest of the modeling techniques, while still effectively predicting load distribution. These models can be used to study altered joint loading, which causes a degeneration of the articular cartilage, in order to gain an understanding of the etiology of osteoarthritis (OA). The purpose of this study is to develop a subject-specific analytical knee model using the RBSM approach that incorporates subject-specific geometry, joint health, and loading patterns to predict tibiofemoral load distributions.
Feasibility of Portable Acoustic Emission Approach for Prognosis of Stress Fractures
Authors: Agcaoglu Serife , Kaul Vikas , Akkus Ozan
Published: March 2014

Repetitive mechanical loading induces microscale damage in bone to accumulate and may lead to stress fractures [1]. People with weakened bones due to disuse or disease, or, healthy people who have excessive exercise regimes (soldiers and athletes) experience these fractures [2]. Stress fractures interrupt training, reduce fitness and may even lead to discharge from the military in certain occasions [3]. Therefore, early prognosis and prevention of stress fractures would be desirable. Currently, following methods are being used for diagnosis: plain radiography, computed tomography (CT), bone scintigraphy and magnetic resonance imaging (MRI). The sensitivity of plain radiography is very low, 15–35% [4]. CT is less sensitive than radiography except some very special and rare cases of stress fractures [5]. Among these diagnostic methods, scintigraphy and MRI are more sensitive. However, the former lacks specificity because it may confound infections, tumors, bone infarctions, periostisis and osteonecrosis [2,5]. Furthermore, it is radioactive [5]. MRI has immense economical and logistical limitations [6].
Large Eddy Simulation of Flow Through a Stenosed Pipe
Authors: Gårdhagen Roland , Lantz Jonas , Carlsson Fredrik , Karlsson Matts
Published: March 2014

A majority of all deaths in the developed world are related to atherosclerosis, i.e. obstruction of blood vessels caused by growth of the vessel wall. Hemodynamic phenomena, especially wall shear stress, are since several decades thought to influence the risk to develop atherosclerosis; hence simulation of blood flow, either in order to elucidate the relation between the hemodynamic and disease initiation or to study the flow pattern, is an area of intense research [1,2].
Mechanical Stimulation Induced Elastogenesis in Collagenous Scaffolds Seeded With Bladder Smooth Muscle Cells
Authors: Long Rebecca A. , Ivanova Julia S. , Parekh Aron , Sacks Michael S.
Published: March 2014

The most successful approaches to tissue engineering the urinary bladder utilize biodegradable scaffolds seeded with autologous cells. Although this technique has proven successful in increasing bladder capacity, problems remain with lack of proper tissue organization post-implantation, impairing the bladder’s ability to maintain its full function. Small intestinal submucosa (SIS) has been utilized previously to engineer the urinary bladder wall with and without cell seeding.
Atomistic Simulation of Pore Formation in Lipid Bilayers in the Presence of Dimethylsulfoxide: Further Evidence for Entropic Driven Pore Formation
Authors: Alapati Raghava , Moldovan Dorel , Devireddy Ram
Published: March 2014

In a recent study, Moldovan et al [1] have demonstrated that in the presence of 11.3 mol% dimethylsulfoxide (DMSO) a pore can nucleate and grow spontaneously in a lipid bilayer even in the absence of an externally applied stresses or electric field. The authors rationalized the spontaneous pore nucleation, in the absence of any external driving force, by considering the combined effect of the entropy of pore shape fluctuation and the significant decrease of the bilayer line tension in the presence of DMSO. Building on the classical nucleation theory developed three decades ago by Lister [2] the authors propose a new formulation for the bilayer free energy that incorporates the pore shape configurational entropy. According to this study, in the presence of DMSO, the pore nucleates spontaneously and grows provided the bilayer line tension decreases below a threshold value, λ. In this study we report our recent simulation results on the effect of DMSO concentration on both bilayer line tension and bilayer structural stability with respect to pore nucleation. The lipid bilayer systems investigated in this study by molecular dynamics (MD) consists of 96 molecules (48 in each leaflet) of dimyristoylphosphatidylcholine (DMPC) immersed in DMSO-water solutions at various concentrations. In all MD simulations reported the bilayer systems were followed over 100 ns. Our simulations results indicate the existence of a critical DMSO concentration below which there are no pores nucleated in the lipid bilayers. Our findings corroborate and complement the entropy-based pore nucleation model proposed earlier by Moldovan et al. [1].
Simulation of Nano- and Micro-Indentation Behavior of Bone via a Plastic-Damage Model
Authors: Zhang Jingzhou , Ovaert Timothy
Published: March 2014

Damage results in a loss of material continuity, which distinguishes it from other types of material degradation. The loss of continuity can have an adverse effect on mechanical properties, and may be manifested in the form of cracks and/or voids. Bone tissue, as a composite material, contains voids and other non-homogeneities that are naturally occurring and distinct from damage. However, when subjected to mechanical loading, such as indentation, further damage accumulation may occur. Figure 1 shows a cross-section of a bovine cortical bone specimen after high-load conical indentation to a depth of 300 μm, resulting in a large permanently deformed region. Nanoindentation, using a Berkovich tip at 10 mN maximum load, was then performed at numerous locations within three defined damage “zones”. Zone 1 is adjacent to the bottom of the indent, defined at 25% of the maximum indent depth. Zones 2 and 3 extend further away, both scaled as a function of the indentation depth, d. Figure 2 shows the variation in Young’s modulus in the three damage zones, averaged over approximately 25 indents per zone. The data suggest that local changes in mechanical properties may occur as a result of compaction of voids or cracks. The purpose of this work, therefore, is to investigate the application of a plastic-damage model for simulation of bone nano- and micro-scale indentation behavior.
Growth and Remodeling of Arterial Tissue
Authors: Machyshyn Ihor , Bovendeerd Peter , van de Ven Fons , Rongen Peter , van de Vosse Frans
Published: March 2014

Living tissues continuously undergo growth, i.e. a change in mass, and remodeling, i.e. reorganization or renovation. Modeling both growth and remodeling (G&R) of the vascular tissue is aimed to provide insight into the adaptation of the tissue, in the healthy and diseased state, and upon surgical intervention. An important aspect is the description of remodeling of collagen fiber direction. Whereas a phenomenological approach for that is suggested in [2], in this study we adopt an approach towards more microstructural approach, along the model in [1].
Effects of Compression on Glucose Consumption in Intervertebral Disc
Authors: Huang Chun-Yuh , Gu Wei Yong
Published: March 2014

Nutrition supply is a concern for the health of avascular cartilaginous tissues such as intervertebral disc (IVD). Maintaining tissue integrity relies on cellular biosynthesis of extracellular matrix, which is an energy demanding process [1]. In the IVD, energy is mainly generated through glycolysis (i.e., glucose consumption). Metabolism of nutrients (e.g., oxygen and glucose) within the IVD depends on local concentrations of nutrients, and coupling effects between nutrient level and metabolic rate [2,3]. Our previous theoretical study had developed a new theoretical formulation by incorporating the metabolic rates of solutes into the mechano-electrochemical mixture theory [4,5]. By using this new theoretical model, the distribution of oxygen and lactate can be predicted within the IVD under static and dynamics compressions [4]. However, the effect of compression on glucose consumption in the IVD has not been studied. The objective of this study was to examine the effects of compression on glucose consumption in the IVD under static and dynamic unconfined compression numerically.
Modeling Heat Shock Protein Expression While Wearing a Therapeutic Heat Wrap
Authors: Song Alfred S. , Diller Kenneth R.
Published: March 2014

Hyperthermia mediated repair of injured tissues is attributed to increased blood perfusion and mass transport. A complimentary mechanism of healing may exist where heat shock proteins (HSPs) are over expressed due to local hyperthermia. HSPs are able to stabilize the tertiary structure of nascent proteins and to help re-fold denatured proteins. In this report, we created a temperature model that characterizes the temperature distribution in the dermis, subcutaneous fat, and muscle tissues due to the application a heat source as a commercially marketed heat wrap. The temperature evolution due to the heat wrap was calculated by applying the finite difference version of Pennes’ bioheat equation to the back of a subject consisting of a composite, semi-infinite system geometry. The temperature model included the factors of metabolic heat generation and blood perfusion. The HSP expression was modeled via interpolation of experimental constitutive data. The results show that the over expression of HSPs in the target tissue area likely contribute to the efficacy of the heat wrap.
Response of Normal Canine Prostate Tissue to Thermal Therapy
Authors: Khoshnevis Sepideh , Diller Kenneth R.
Published: March 2014

The goal of this study was to evaluate post-thermal stress cell survival in canine prostatic epithelial and stromal cells. Epithelial and stromal cells isolated from canine prostate were exposed to thermal stress using a water bath. Post-thermal stress cell viability was measured by flow cytometry and analyzed using FlowJo software. An ongoing analysis also measures Heat Shock Protein expression for the same stress protocols.
Collagen Content and Stiffness Affect the Biomechanical Response of Collagen Gels to Acupuncture In Vitro
Authors: Julias Margaret , Edgar Lowell T. , Shreiber David I. , Buettner Helen M.
Published: March 2014

Acupuncture is an ancient therapy that has been clinically proven for treating pain and nausea [1], though by unknown mechanisms. Recent in vivo and ex vivo studies demonstrate that acupuncture generates changes in the local tissue biomechanical environment, which may have been overlooked in previous neurophysiological studies [2].
Age-Related Changes in Scleral Material Properties of the Monkey Eye
Authors: Girard Michaël J. A. , Suh Jun-Kyo F. , Bottlang Michael , Burgoyne Claude F. , Downs J. Crawford
Published: March 2014

The sclera is the outer shell and principal load-bearing tissue of the eye, which consists primarily of avascular lamellae of collagen fibers. Ninety percent of the collagen fibers in the sclera are Type I, which provide the eye with necessary mechanical strength to sustain intraocular pressure (IOP). In the posterior sclera, there is a fenestrated canal, called the optic nerve head (ONH), through which the retinal ganglion cell axons pass transmitting visual signals from the retina to the brain. The opening of the ONH is structurally supported by a fenestrated connective tissue called the lamina cribrosa.
A CFD Computational Model for the Optimization of Transport Phenomena in a Rotating Hollow Fiber Bioreactor for Artificial Liver
Authors: Consolo Filippo , Caronna Marco , Montevecchi Franco M. , Fiore Gianfranco B. , Redaelli Alberto
Published: March 2014

Over the last decades, many attempts have been made aimed at developing bioartificial systems able for providing temporary hepatic support to patients with liver failure [1].
Mechanism of Cerebral Aneurysm Bruits: Resonance of Parent Artery and Aneurysm
Authors: Jou L.-D. , Morsi H. , Mawad M. E.
Published: March 2014

Cerebral aneurysms have distinct sounds that peak at a frequency between 260–660Hz, very different from the spectrum without aneurysms [1]. While this phenomenon has been known for years, the exact cause of bruits is not known. Figure 1 shows the spectrums of sounds from a healthy subject and a 65-year-old patient with a 16mm aneurysm at the paraclinoid segment of the internal carotid artery using a digital electronic stethoscope. The healthy subject has a peak at 96Hz, and the spectrum for the aneurysm patient peaks at 403 Hz.
The Inferior Stability Provided by the Glenohumeral Capsule Increases With External Rotation in the Abducted Glenohumeral Joint
Authors: Drury Nicholas J. , Ellis Benjamin J. , McMahon Patrick J. , Weiss Jeffrey A. , Debski Richard E.
Published: March 2014

The shoulder is the most frequently dislocated major joint in the body, and the glenohumeral capsule is the primary stabilizer to the joint in positions of dislocation. Although the majority of dislocations occur in the anterior direction, multidirectional instability is common and usually occurs in the anterior and inferior directions. Clinicians have difficulty differentiating between multidirectional and unidirectional instability, and greater than 38% of post-operative recurrences may be due to misdiagnosis of the type of instability [1].
A Biphasic Hyperelastic Model for Analysis of Fluid Transport in Brain Tissue
Authors: Smith Joshua H. , García Jose Jaime
Published: March 2014

Poroelastic or biphasic models have been used to study hydrocephalus [1] and the fluid transport that occurs during positive pressure infusion, also called convection enhanced delivery [2,3]. Each of the studies is limited by the assumption of linear elasticity of the solid phase. Nonlinear stress-strain curves under finite deformations have been documented for brain tissue under tension [4] and compression [5]. The nonlinear variation of hydraulic conductivity with strain has also recently been taken into account [1,3] and this effect has been deemed to play an important role in both the mechanics of the tissue and the associated fluid transport.
Effect of Leaflet Anisotropy, Coaptation Curvature, and Stent Flexibility on the Stress Concentrations and In Vitro Function of Polymer Trileaflet Heart Valves
Authors: Gallocher Siobhain L. , Datye Amit , Wu Kuang-Hsi , Pinchuk Leonard , Schoephoerster Richard T.
Published: March 2014

Polymer trileaflet valves have been under investigation for the past 40–50 years in an attempt to produce a valve alternative that is both durable and non-thrombogenic. Most have met with limited success due to oxidative reactions and high dynamic stresses borne by the material [1]. With this knowledge, an oxidatively stable polyolefin, poly(styrene-b-isobutylene-b-styrene) (SIBS), was selected for the design of a fiber-reinforced polymer trileaflet heart valve. The hydrodynamic properties of prototype SIBS valves have been encouraging, but some valves failed prematurely as a result of insufficient durability during in vivo implantation in a sheep model or during accelerated in vitro fatigue.
Computer Modeling of Cardiovascular Stent Coating Damage
Authors: Hopkins Caroline G. , McHugh Peter E. , McGarry J. Patrick
Published: March 2014

In this paper computational simulations of stent coating debonding are presented. Finite element methods are implemented to model coating delamination during stent crimping, deployment and recoil. Gold, titanium and polymer coatings of differing thicknesses are explicitly modeled. The interfacial relationship between the stent surface and the coating during crimping and deployment is simulated using a cohesive zone model.
Zeta Potential of Silica Calcium Phosphate Nanocomposite: Effect of Material Composition and Medium pH
Authors: Aniket  , El-Ghannam Ahmed R.
Published: March 2014

Biodegradable ceramics have lately found exciting applications in orthopedic and maxillofacial surgeries as agents for bone repair, drug delivery vehicles and filling materials. A novel bioactive resorbable ceramic that demonstrated a superior mechanical properties, bioactivity and resorbability compared to traditional calcium phosphate ceramics or bioactive glass is bioactive silica-calcium phosphate nanocomposite (SCPC) [1, 2]. Previous studies have demonstrated that the enhanced bioactivity of SCPC is attributed to its nano structure as well as other physicochemical properties of the material [2]. Surface charge is one of the most important factors that control tissue and cell response to the implant material. Additionally, surface charge enhances the adsorption of biological molecules onto the material surface. The objective of the present work is to investigate the effect of SCPC composition and medium pH on the zeta potential and conductance of the material.
Discrimination of Vessel Wall Components of Abdominal Aortic Aneurysms by Multi-Contrast MRI
Authors: van Dam Evelyne , Rutten Marcel , van de Vosse Frans
Published: March 2014

Rupture of an abdominal aortic aneurysm (AAA) is a major cause of death in the Western world. When the AAA is diagnosed timely, rupture can be prevented by conventional surgical or by endovascular repair. To date, the decision to operate is based on geometry alone, but it has already been suggested that wall stress would be a better predictor [2]. Patient specific computational models have been developed to calculate wall stress [2; 5; 9; 8; 10]. In these models, the AAA wall is assumed to be homogeneous. Patient-specific inhomogeneities such as atherosclerotic plaques and calcifications have large effects on the maximum wall stress and wall stress distribution [6; 7]. Histological examination is not feasible for determining wall composition of patients.
Local Mechanical Properties of Abdominal Aortic Aneurysms
Authors: van Dam Evelyne , Rutten Marcel , van de Vosse Frans
Published: March 2014

Rupture risk of abdominal aortic aneurysms (AAA) based on wall stress analysis may be superior to the currently used diameter-based rupture risk prediction [4; 5; 6; 7]. In patient specific computational models for wall stress analysis, the geometry of the aneurysm is obtained from CT or MR images. The wall thickness and mechanical properties are mostly assumed to be homogeneous. The pathological AAA vessel wall may contain collageneous areas, but also calcifications, cholesterol crystals and large amounts of fat cells. No research has yet focused yet on the differences in mechanical properties of the components present within the degrading AAA vessel wall.
Effects of Joint Congruency on the Response of a Tension-Compression Nonlinear Constitutive Model for Cartilage
Authors: Ellis Benjamin J. , Ateshian Gerard A. , Anderson Andrew E. , Canal Clare , Maas Steve A. , Weiss Jeffrey A.
Published: March 2014

Articular cartilage exhibits inhomogeneous, rate-dependent and tension-compression (TC) nonlinear material properties. It is a biphasic material (solid and fluid phases) and its solid phase is stiffer in tension than compression [1]. Despite this complex material behavior, elastic, incompressible material models can be used to predict the short-time loading response of cartilage [2]. To our knowledge, the use of an anisotropic incompressible material to represent cartilage in a finite element (FE) joint model has not been investigated and thus the importance of the TC nonlinearity in the analysis of 3D articular contact models is limited [3]. We have been investigating a TC nonlinear incompressible constitutive model to represent hip cartilage. The objective of this study was to assess the influence of TC nonlinearity on FE predictions of stress and strain as a function of congruency between two spherical cartilage layers. It was hypothesized that the TC nonlinear and neo-Hookean constitutive models would yield a similar response when the cartilage layers were nearly congruent, but as the congruency of the cartilage layers decreased the predicted response from the two materials would be different.
In Vivo Characterization of Transport Anisotropy in Rat Spinal Cord Using Diffusion Tensor Imaging
Authors: Chen Xiaoming , Astary Garrett W. , Mareci Thomas H. , Sarntinoranont Malisa
Published: March 2014

Biotransport in nervous tissues is complicated by the existence of neural fibers. These axonal fibers result in inhomogeneous and anisotropic extracellular transport, which complicates the prediction of local drug delivery such as convection-enhanced delivery [1]. Previous studies by our group [4] have shown that by using diffusion tensor imaging (DTI) [2, 3], anisotropic transport in rat spinal cord can be modeled using computational models, and consequently extracellular flows which influence drug transport can be well predicted. In previous studies, DTI-based models used data from an excised and fixed rat spinal cord. In the current study, we extend our DTI study to in vivo measures, and report the in vivo characterization of transport anisotropy in rat spinal cord. The MR imaging method is presented and the DTI data is discussed.
Can the Hip Joint be Modeled Accurately Using Simplified Geometry?
Authors: Anderson Andrew E. , Maas Steve A. , Ellis Benjamin J. , Weiss Jeffrey A.
Published: March 2014

Simplified analytical approaches to estimate hip joint contact pressures using perfectly spherical geometry have been described in the literature (rigid body spring models); however, estimations based on these simulations have not corresponded well with experimental in vitro data. Recent evidence from our laboratory suggests that finite element (FE) models of the hip joint that incorporate detailed geometry for cartilage and bone can predict cartilage pressures in good agreement with experimental data [1]. However, it is unknown whether this degree of model complexity is necessary. The objective of this study was to compare cartilage contact pressure predictions from FE models with varying degrees of simplicity to elucidate which aspects of hip morphology are required to obtain accurate predictions of cartilage contact pressure. Models based on 1) subject-specific (SS) geometry, 2) spheres, and 3) rotational conchoids were analyzed.
Fully Coupled Fluid-Structure Interaction Model of Active Eustachian Tube Function
Authors: Sheer Francis J. , Ghadiali Samir N.
Published: March 2014

The Eustachian Tube (ET) is a collapsible tube that connects the Middle Ear (ME) to the nasopharynx (NP). The ET is responsible for three primary functions: 1) regulation of ME pressure 2) protection of the ME from foreign pathogens and 3) drainage of fluid from the ME. [1] In healthy patients, the ET opens during swallowing because the surrounding tissue is deformed by muscle activity. If the ET fails to open, the ME develops painful sub-ambient pressure and fluid accumulates in the ME. ET dysfunction results in Otitis Media (OM), the most common ME disorder in children. The overall goal of our lab is to identify the mechanisms responsible for ET dysfunction and to develop novel treatments for OM that target the ET.
Cytokine Convection Affects Cancer Metastasis by a Shear Rate Dependent Mechanism
Authors: Hoskins Meghan H. , Liang Shile , Khanna Payal , Kunz Robert F. , Dong Cheng
Published: March 2014

Malignant melanoma is the most deadly form of skin cancer due to its propensity to spread, or metastasize. No current treatment exists that is effective against melanoma metastasis [1,2].
Aiding Vascular Trauma Detection in the Human Upper Extremities With Image-Based Models of Blood Flow
Authors: Wang Aaron S. , Liang David H. , Taylor Charles A.
Published: March 2014

In the hands of an experienced sonographer, a portable diagnostic ultrasound (US) allows for a quick and inexpensive diagnosis of vascular trauma in the field. However, trained sonographers are usually not available at trauma settings, such as in the battlefield. Recent studies by Luo 2007 [1] quantified ultrasound signatures of bleeding at the sites of vessel puncture, which can be used in automated algorithms for ultrasound diagnosis of suspected bleeding sites. However, trauma patients often have large areas of injury requiring extensive scanning to find the bleeding site. An algorithm that can first assess a vascular tree and localize suspicious branches for further examination or therapy would be useful. This study was focused on the upper extremity vascular tree. Specific goals of this study were to 1) demonstrate a physics-based model to characterize normal blood flow, and 2) evaluate its ability to detect vascular abnormalities by looking for flows that deviate from the model.
Investigation of Calcium Mechanotransduction by Quasi 3-D Microfiber Mechanical Stimulation of Cells
Authors: Ruder Warren C. , Pratt Erica D. , Sitti Metin , LeDuc Philip R. , Antaki James F.
Published: March 2014

Fibroblast cells mechanically interact with their environment through several mechanisms, including the formation of focal adhesion complexes (FACs) with adjacent ligands. A quasi-3D (Q3D) experimental device was devised to investigate chemo-mechanical stimulation of these cells. It employed a novel microscopic fixture featuring micropolymer arrays positioned just above a cellular monolayer, enabling mechanical stimulation through dorsal attachment to FACs. This protocol demonstrated the ability to preserve the normal stellate morphology of fibroblasts. Live-cell imaging during mechanical stimulation revealed robust calcium elevation in cells interacting with the Q3D device. This system provides a simple alternative to existing 3D culture methods yet allows dynamic, real-time mechanical probing of cells in a physiologically significant environment as compared to optical or magnetic tweezers.
Developing Computational Flow Models for the Lymphatic Vasculature
Authors: Rahbar Elaheh , Moore James E. , Zawieja David C. , Gashev Anatoliy A. , Cote Gerard L.
Published: March 2014

The lymphatic system performs many crucial body functions to ensure normal health. The lymphatics are responsible for fluid and protein balance, gathering approximately 4 liters/day of interstitial fluid and returning it to the venous system. As this fluid is filtered, undesirable elements such as tumor cells and foreign pathogens are normally destroyed in lymph nodes. This system also plays a part in serving as the primary transport mechanism for the immune system. Lymphedema, a debilitating disease for which there is no known cure, affects a large number of cancer patients who have undergone lymphadenectomy and also trauma victims. The lymphatic system is also the major transport route for metastases of various cancers.
Biodistribution of TNF-alpha Coated Gold Nanoparticles in an In Vivo Cancer Model
Authors: Goel Raghav , Shah Neha , Visaria Rachana , Paciotti Giulio F. , Bischof John C.
Published: March 2014

Over the past several years, there has been an increasing interest in the use of nanoparticles as a tool for treatment of cancer. We have shown tremendous augmentation and control (without toxicity) of both heat and cold-based thermal therapy for cancer treatment with a gold based nanodrug-CYT-6091 (Cytimmune Sciences, Inc.) [1–3]. To reach the full potential of these nanodrugs for both stand-alone solid cancer treatment and as adjuvant to thermal therapy, there is a need to understand the in vivo biodistribution and their short-term and long-term tissue interaction.
Interaction of Shear Stress, Myosin II, and Actin in Dynamic Modulation of Endothelial Cell Microrheology
Authors: Dangaria Jhanvi H. , Butler Peter J.
Published: March 2014

The endothelial cell (EC) cytoskeleton mediates several biological functions such as adhesion, migration, phagocytosis, cell division, and mechanosensitivity. These functions are carried out in part through dynamic cytoskeletal polymerization, modulation of crosslinking, and development of tension between intracellular organelles and the extracellular matrix via focal adhesion plaques. One important component of the cytoskeleton is actin which polymerizes into filaments and is thought to be prestressed by virtue of crosslinking proteins such as α-actinin, filamin and myosin II molecular motors. Additionally, actomyosin interaction has been hypothesized to act as a stress dissipation mechanism by virtue of dynamic crossbridging which facilitates actin diffusion through the polymer network of the cytoplasm (Humphrey et al., 2002).
The Role of Collagen in Pulmonary Hypertension-Induced Large Artery Stiffening
Authors: Ooi Chen Yen , Chesler Naomi C.
Published: March 2014

Hypoxic pulmonary hypertension (HPH) leads to stiffening of large pulmonary arteries, which affects right ventricular afterload. We hypothesized that vascular collagen accumulation is the major cause of large pulmonary artery (PA) stiffening in HPH. We tested this hypothesis with transgenic mice that produce collagen type I resistant to degradation (Col1a1R/R) and wild type littermate controls (Col1a1+/+) exposed to hypoxia and allowed to recover. Pressure-diameter testing on left PAs demonstrated that stiffness in control mice increased with hypoxia and decreased with recovery (p < 0.05). Preliminary tests in degradation-resistant mice suggest that PA stiffness decreases less with recovery than in controls. Quantitative measurements of vascular collagen content in right PAs are planned to develop statistical correlations between structure and function.