bluuebunny/crossref_metadata_2025 huggingface dataset:
Growth and Remodeling of Vein Graft in an Arterial Environment: Parameter Estimation and Sensitivity Analysis
Authors: Ramachandra Abhay B. , Sankaran Sethuraman , Humphrey Jay D. , Marsden Alison L.
Published: January 2014

In coronary artery disease, surgical revascularization using venous bypass grafts is performed to relieve symptoms and prolong life. Coronary bypass graft surgery is performed on approximately 500,000 people every year in the United States, with graft failure rates as high as 50% within 5 years. When a vein graft is implanted in the arterial system it adapts to the high flow rate and high pressure of the arterial environment by changing composition and geometry. Hemodynamics is known to play an active role in growth and remodeling of blood vessels but the complete underlying mechanism of vein graft failure is not well understood. Experiments required to understand this phenomenon can be resource and time intensive. In order to augment the existing knowledge and to guide design and interpretation of experiments that are needed to refine our understanding of vein graft growth and remodeling, computational models of vascular growth and remodeling are used to describe and predict the response of vein grafts to changes in hemodynamic loads. Computational models of growth and remodeling have numerous parameters, and even the inputs from experiments have uncertainties associated with them. There is therefore a need for a systematic approach to estimate the parameters included in growth and remodeling models and to evaluate sensitivity of the quantities of interest to parametric variations.
Biomechanical and Microstructural Response of Recurrent Laryngeal Nerve in Pigs
Authors: Williams Megan , Barkmeier-Kraemer Julie , Utzinger Urs , Vande Geest Jonathan
Published: January 2014

Tensile loading is a common physiological condition of peripheral nerves but can induce pathologic effects. Significant defects in nerve conduction have been reported for strains as low as ∼6% greater than the in situ strain [1]. In order to better understand the functional deficits resulting from tensile loading of nerve tissue, biomechanical testing is performed. The long-term goal of this research is to develop a constitutive and a computational model of the biomechanical properties of the “packaging,” or connective tissues of the recurrent laryngeal nerve (RLN) to investigate their role in the onset of unilateral vocal fold paralysis (UVP). The vocal folds are important for protection of the airway during swallowing, the regulation of breathing, and for voice production. Although surgery is most often linked to onset of UVP, the cause remains unknown in a large percentage of those with this disorder. Recent research has suggested that individuals with idiopathic UVP may have damage to the RLN at the level of the aortic arch related to a thoracic aneurysm. Our preliminary work has resulted in the conclusion that connective tissues of the RLN exhibit different biomechanical properties in the region of the aortic arch [2]. An aneurysm would impose increased stress and strain on the RLN where it is adjacent to the aorta resulting in impaired nerve function. The primary goal of this study is to identify the relationship between the biomechanical response of RLN tissue and how it response is governed by load dependent underlying extracellular matrix (collagen) organization. We hypothesize that regional differences exist in the microstructure and/or biomechanical response of the RLN and that these differences play a role in the onset of idiopathic UVP.
Misinterpretation of Stenosis Severity in the Presence of Serial Coronary Stenoses: An In-Vitro Study
Authors: D’Souza Gavin , Peelukhana Srikara V. , Banerjee Rupak K.
Published: January 2014

In patients with multiple stenoses in the same coronary artery, the severity of one stenosis influences the diagnosis of the serial stenosis. Currently used diagnostic end-point, Fractional Flow Reserve, FFR (ratio of distal to proximal pressure of a stenotic region), has a cut-off point of 0.75. A value of FFR < 0.75 leads to a clinical intervention. However, FFR may fail to account for multiple stenoses interactions and might lead to clinical misinterpretation of one serial stenosis severity. In order to assess the effect of one stenosis on the other serial stenosis, we tested three combinations of serial stenoses: 80%–64%, 80%–80% and 80%–90% area stenosis (AS) respectively, using an in-vitro experimental setup. The hyperemic flow decreased from 136.4 ml/min to 126.4 ml/min and further to 90.7 ml/min as downstream stenosis severity increased from 64% AS to 80% AS and further to 90% AS, respectively. More importantly, the individual FFR values of the upstream stenosis (80% AS) increased from 0.76 to 0.79 and further to 0.88 as the downstream stenosis increased from 64% AS to 80% AS and further to 90% AS, respectively. On the contrary, the combined FFR across both the stenosis was below the threshold value of 0.75. These results indicate that the presence of a downstream stenosis might lead to a clinical misinterpretation of the upstream stenosis severity and also the combined stenosis severity.
Retention and Transport of Hydrophobic and Hydrophilic Drug Surrogate Molecules in Coronary Arteries Measured Nondestructively With Photoacoustic Ultrasound
Authors: Keyes Joseph T. , Montilla Leonardo G. , Witte Russel S. , Vande Geest Jonathan P.
Published: January 2014

The design and implementation of local drug delivery mechanisms in cardiovascular applications provides a method by which localized action can occur without potentially problematic systemic effects. This has been especially relevant in the case of drug-eluting stents (DESs). It has been previously shown that the degree of chemical polarization can significantly change the degree of transport and the degree of vascular retention of drugs. Understanding how these differences occur in real-time, and nondestructively, can better help guide the design of such pharmaceuticals. Previous work by our laboratory has indicated differences in transport based on location within the coronary tree (Fig. 1) [1].
Finite Element Analysis of Fixed Medial Malleolar Fractures
Authors: Chande Ruchi D. , Owen John R. , Adelaar Robert S. , Wayne Jennifer S.
Published: January 2014

The ankle joint, comprised of the distal ends of the tibia and fibula as well as talus, is key in permitting movement of the foot and restricting excessive motion during weight-bearing activities. Medial ankle injury occurs as a result of pronation-abduction or pronation-external rotation loading scenarios in which avulsion of the medial malleolus or rupture of the deltoid ligament can result if the force is sufficient [1]. If left untreated, the joint may experience more severe conditions like osteoarthritis [2]. To avoid such consequences, medial ankle injuries — specifically bony injuries — are treated with open reduction and internal fixation via the use of plates, screws, wires, or some combination thereof [1, 3–4]. In this investigation, the mechanical performance of two such devices was compared by creating a 3-dimensional model of an earlier cadaveric study [5], validating the model against the cadaveric data via finite element analysis (FEA), and comparing regions of high stress to regions of experimental failure.
Optimal Constitutive Parameters and Subject Specific Variability: An Application to the Aortic Sinuses
Authors: Flamini Vittoria , Griffith Boyce E.
Published: January 2014

Advanced analyses of soft biological tissues have shown substantial subject-specific variability in mechanical properties [1]. Such variability is also easily observed at a geometrical or morphological level, and has been reported also in mechanical tests on biological tissue samples [1, 2]. While there is wide interest in reproducing accurate geometries for subject-specific modeling, constitutive parameters for mechanical models often use averaged data from mechanical tests [3]. Outliers are typically neglected, and only the ‘mean’ tissue behavior is considered. However, due to an increased interest in using multi-scale and finite element (FE) models for medical device testing and surgical planning [4], understanding of the variability of the outlier tests becomes increasingly important. In particular, by using detailed mechanistic constitutive models, it might be possible to classify the different mechanical behaviors observed on the basis of the changes in the constitutive parameters. This process could lead to the definition of a library of different ‘healthy’ or ‘diseased’ constitutive parameters to be used in computational analyses.
Nonlinear Dynamic Behaviour of the Intervertebral Disc
Authors: Marini Giacomo , Huber Gerd , Ferguson Stephen J.
Published: January 2014

The intervertebral disc, like many collagen-based tissues, has a mechanical response which is highly nonlinear (1). This characteristic is due to both the arrangement and composition of the tissue constituents of the disc (2). Over the past decades several studies have reported the nonlinear response of the disc for different loading scenarios. In particular, past studies were focused on the quasi-static and low frequency (< 10Hz) response to pure and combined cyclic loading, such as axial compression, shear, flexion/extension moment (3–6). The information provided by these studies has been applied in several fields, from the validation of numerical models to the development of disc prostheses. However, such loading conditions are only partially representative of the in-situ load that the intervertebral disc normally experiences. High frequency dynamics stimuli, such as that experienced while driving a car on a rough surface or driving heavy industrial machinery, are also important. It is well known that long-term exposure to vibrational loading is detrimental to normal disc metabolism (7,8). Despite its relevance only a few studies have investigated the dynamic response of the disc to high frequency vibration (9,10) with sometimes different outcomes. In particular, no study has shown an asymmetric, nonlinear dynamic behavior of the system, even though it is evident in quasi-static testing — the well-known tension / compression asymmetry. This aspect is somehow neglected when building rigid body models of the upper body for impact simulation where a Kelvin-Voigt model with linear stiffness is normally used. The aim of this experimental study was therefore to investigate the nonlinear dynamic response of the intervertebral disc to high frequency loadings, taking different pre-loads and displacement amplitude into account.
Contributions of Proteoglycans to the Biotransport and Electrical Properties of Articular Cartilage: An Experimental Study
Authors: Gao Xin , Meng Lingtu , Huang Chun-Yuh C. , Gu Weiyong
Published: January 2014

Proteoglycans (PGs) are one of the major components in the extracellular matrix (ECM) of cartilage, and are negatively charged due to the charged groups attached to their backbone (i.e., fixed charge groups). PGs play substantial roles in the mechanical, biotransport and electrical events within the tissue.3,7 More specifically, swelling pressure generated by the interaction between fixed charge groups and ionic interstitial fluid enhances cartilage’s capacity of load-bearing. In addition, biotransport properties (e.g., hydraulic permeability) and electrical properties (e.g., electrical conductivity) have been shown to be affected by water content (i.e., porosity) and fixed charge density (FCD).2–4 The alteration of proteoglycan content will affect the tissue FCD and water content, which could cause the changes in biomechanical, biotransport and electrical properties of the cartilage. The relationship between the PG content and biomechanical properties has been widely studied,6,8 but the knowledge on the effects of PG content on biotransport and electrical properties is limited.1 It is not clear whether the dependences of biotransport and electrical properties on PG content are mainly due to electric effects through the FCD associated with PGs or due to hindrance effects related to the effective pore size (i.e., water content) of the tissue. Therefore, the objectives of this study were (1) to investigate the effects of PG content on cartilage biotransport and electrical properties, (2) to analyze whether these effects are caused by changes of water content or FCD.
Mechanical and Electrical Stimulation Induces Calcium-Sensitive Mechanical Properties of Myoblast Derived Engineered Fibers
Authors: Mason Andrew K. , Koppes Ryan A. , Swank Douglas M. , Corr David T.
Published: January 2014

Skeletal muscle loss, through injuries, myopathies, and interventional medicine, presents major challenges in physiological function and clinical interventions [1]. Autologous tissue transplantation necessitates tissue loss from the donor site, and autologous grafts do not attain the strength of the original tissue. Exogenous tissue grafting faces similar strength issues, as well as the added challenge of immunorejection [2,3]. In vitro skeletal muscle tissue engineering holds promise for addressing these issues. However, these tissues have not yet shown proper dynamic response when compared to physiological muscle [2]. Mechanical and electrical stimulation have shown promise in improving construct properties [4], but mainly limited to 2D and scaffold-based constructs.
Simulation Based Development and Analysis of Helmet-to-Helmet Collision
Authors: Ladner Ian , Johnson Kyle , Horstemeyer M. F. , Williams L. N. , Liao J. , Prabhu R.
Published: January 2014

In 2003, a study was conducted to analyze brain-related fatalities in American football. From 1945–1999 a total of 497 fatalities were brain injury-related. Majority of the injuries, 61%, occurred during the football game, and “75% of these were high school players.” The number of high school students was more than 13 times greater than the number of college and professional players combined [1]. While millions of high school students will never make it to the next lever; collegiate and professional players have brought the attention needed to the make advances in the field of helmet design. Further, a study conducted by Bartsch et al. showed that the 20 th and 21 st century football helmet and the “leatherhead” helmets are very similar in their concussion-resistant and shock-mitigating capabilities [2]. In the past few decades, improvements in the helmet design have not addressed shock wave mitigation but rather focused on the strength, durability, and “looks” of the helmet. A major issue stems from the lack of thorough knowledge of the biomechanics and physics of traumatic brain injury (TBI) due to helmet-to-helmet contacts. The current study proposes to an in-depth finite element analysis (FEA) of the helmet-to-helmet collision. The finite element (FE) model consists of a human head clad with helmet with simulations being performed using ABAQUS/Explicit [3]. Here, Helmet-to-helmet impacts will be analyzed to develop a new head injury metric that captures the locational and history effects of the impending shock wave due to collision.
Measuring Elbow Stiffness at Two Muscle Contraction Levels
Authors: Zeng Sisi , Kuxhaus Laurel , Robinson Charles J.
Published: January 2014

The elbow joint is critical for positioning the hand to carry out activities of daily living. Deficits in elbow joint range of motion, torque production capabilities, or alterations in elbow joint stiffness affect the ability to successfully carry out feeding, grooming, and other essential activities [1]. Thus quantifying elbow joint stiffness is desirable. Quantifying elbow joint stiffness could help diagnose, monitor and rehabilitate elbow impairments if its relationship to them is known. Ultimately, accurate measurements of joint stiffness can also impact the design of artificial limbs and human motor system control and simulation. The long-term research goal is to quantify how elbow stiffness changes with elbow joint flexion angles, movement speeds, muscle contraction, and injury or disease. The immediate goal was to validate that a recently-modified Stiffness Tester measures elbow stiffness values within the range of those previously reported. The expectation was that muscle contraction level and joint position would influence the elbow stiffness values.
Fabrication of Tissue-Engineered Cartilage Grafts With Anatomic Surface Contours for Repair of Large Focal Defects
Authors: Roach Brendan L. , Tan Andrea R. , Stoker Aaron M. , Cook James L. , Yeager Keith J. , Ateshian Gerard A. , Hung Clark T.
Published: January 2014

Articular cartilage exhibits a poor healing response to injury that necessitates surgical intervention to repair or replace damaged tissue. Treatment options, however, are dependent on the location and size of the defect site. For small focal defects (<2 cm 2), microfracture is the primary method of treatment [8] despite the production of biologically inferior cartilage. For lesions greater than 10 cm 2 where the articular cartilage loss and morphology of the condyle is distorted, a fresh osteoarticular allograft is most likely to succeed [3], while posing a significant surgical challenge related to the technical demands in restoring congruency of the articular surface (i.e., attaining a flush fit of the graft with the surrounding host cartilage tissue). This requires matching of the donor joint size to provide grafts with similar anatomical surface contours. As there is insufficient supply of suitable cartilage grafts to meet the clinical demand, the development of tissue engineered osteochondral grafts would have significant clinical impact for treatment of cartilage lesions and eventually entire articular surfaces.
Binding and Release Kinetics of Glycosaminoglycans and Collagen in Engineered Cartilage Under TGF-β Supplementation
Authors: Nims Robert J. , Cigan Alexander D. , Albro Michael B. , Hung Clark T. , Ateshian Gerard A.
Published: January 2014

Cartilage tissue engineering (CTE) is a strategy of great interest and promise for the replacement of osteoarthritic (OA) cartilage. In CTE, chondrocytes are used to synthesize cartilage matrix products (predominantly glycosaminoglycans (GAG) and type II collagen). The aim for CTE is to develop engineered constructs with mechanical properties and biochemical composition comparable to native tissue, to reproduce its functional properties.
Degradation Behavior of Nanostructured Stent Materials Using Cold Spray
Authors: Barua R. , Mongrain R. , Aydin H. , Yue S. , Bertrand O. F. , Frost D. L.
Published: January 2014

Very late stent thrombosis (ST) stent fracture (SF) increases restenosis rate of permanent drug eluting stents (DES). In fact, permanent stents after arterial remodeling (change of artery dimensions during atherosclerosis) process becomes a supportive part inside our body and this idea lead us to develop biodegradable stents which support till arterial remodeling and progressively degrade thereafter. In this research, cold gas dynamic spray technique, simply referred to as cold spray is introduced to spray micro particles on metallic plane and cylindrical substrate. Reference material for permanent stent, stainless steel, 316L is mixed with pure iron in different proportions to induce microgalvanic corrosion effect on as sprayed specimens. Although annealed 316L coatings indicate better ultimate strength, porosity and ductility, their degradation study signifies their poor degradability in Hank’s physiological solution. In contrast to that, immersion and potentiodynamic polarization tests under Hank’s physiological solution indicate that corrosion rate of as sprayed composite increases as amount of iron increases. More iron particles release more iron ions and increases corrosion rate in hanks solution.
Age Dependent and Anisotropic Material Properties of Immature Porcine Sclera
Authors: Saffioti Jami M. , Coats Brittany
Published: January 2014

Current finite element (FE) models of the pediatric eye are based on adult material properties [2,3]. To date, there are no data characterizing the age dependent material properties of ocular tissues. The sclera is a major load bearing tissue and an essential component to most computational models of the eye. In preparation for the development of a pediatric FE model, age-dependent and anisotropic properties of sclera were evaluated in newborn (3–5 days) and toddler (4 weeks) pigs. Data from this study will guide future testing protocols for human pediatric specimens.
Wall Shear Stress and Intraluminal Thrombus Changes in Abdominal Aortic Aneurysms: Study With Longitudinal Patients
Authors: Zambrano B. , Jaberi F. , Lee W. , Baek S.
Published: January 2014

Abdominal Aortic Aneurysm (AAA), a focal enlargement of the abdominal aorta is an ongoing process that can be affected by many parameters. Among these parameters, hemodynamics and intraluminal thrombus layer (ILT) play important roles on AAA growth. It is widely accepted that hemodynamic forces (normal and shear forces) have a profound impact on the mechano-homeostasis of the arterial wall and its vascular remodeling. The role of ILT, however, remains controversial. Some studies suggest that ILT may be beneficial by shieling the weak aneurysm wall, whereas others claim that the presence of ILT can lead to immune responses that increase protease breakdown of collagen and elastin, adversely affecting wall strength. ILT is formed by the deposition of blood clots called thrombus. Thrombus formation is achieved through different mechanisms, but all research agrees that shear fluid forces are one of the key parameters for the formation and development of ILT. There are few studies to date that use these three parameters to assess the evolution of AAAs growth. Here, we explore the relation between wall shear stress (WSS), ILT and AAA expansion using longitudinal CT images from follow-up studies from 3 patients (a total of 8 scans). We used geometrical models of AAAs segmented from patient images to estimate outer surface displacement, ILT, and tissue thickness. Additionally, we used fluid dynamic data to estimate wall shear stress at peak systolic. These parameters were then used to investigate possible relationships with each other.
Musculoskeletal Model During Treadmill Gait
Authors: Kia Mohammad , Guess Trent M. , Stylianou Antonis P.
Published: January 2014

Detailed knowledge of joint kinematics and loading is essential for improving the design and surgical outcomes of total knee replacements as well as tissue engineering applications. Dynamic loading is a contributing factor in the development of joint osteoarthritis and in total knee replacement wear. Dynamic computational models in which muscle, ligament, and joint loads are predicted concurrently would be ideal clinical tools for surgery planning and for implant design. An important obstacle in clinical applications of computational models is validation of the estimated in-vivo loads.
Assessment of the Vascular and Trabecular Microstructures Using Micro Computed Tomography, Vascular Network Perfusion, and Image Registration Techniques
Authors: Tseng Wei-Ju , Zhu Hainan , Huh Beom Kang , de Bakker Chantal , Luo Shiming , Tang Juyu , Qin Ling , Liu X. Sherry
Published: January 2014

Bone is a dynamic organ that constantly undergoes remodeling throughout one’s life. The remodeling process is required to repair damaged bone tissue and more importantly, to regulate calcium and phosphate homeostasis through the osteocytic network in conjunction with the microvascular network within bone marrow. Recently, techniques combining micro computed tomography (μCT) imaging with vascular network perfusion were developed to allow for 3-D visualization of the bone vascular network structure [1]. However, simultaneous visualization of the trabecular and vascular microstructures using standard μCT remains challenging, and thus the precise relationships between blood vessel formation and trabecular remodeling, as well as the impact of these relationships on metabolic bone diseases such as osteoporosis, remain unclear.
Engineered Microvessels Subjected to Interstitial Flow
Authors: Morin Kristen T. , Dries-Devlin Jessica L. , Tranquillo Robert T.
Published: January 2014

Most previous research on engineered microvessels has been in isotropic systems;1–3 however, aligned microvessels would be advantageous both in terms of mimicking alignment in native tissue (e.g. myocardium4), and in terms of establishing efficient perfusion of the microvessels, as alignment creates natural inlet and outlet sides.
A 3D Microfluidic Tumor Construct to Determine Transport and Photothermal Properties of Single Walled Nanohorns
Authors: DeWitt Matthew , Buchanan Cara , Pekkanen Allison , Rylander M. Nichole
Published: January 2014

Photothermal therapy is a cancer treatment that utilizes light energy to deposit specific amounts of heat to effectively kill cells in a specified tumor region. While Hyperthermia has been widely used for centuries as a treatment option for a variety of diseases, Localized Hyperthermia, as seen in photothermal therapies, has seen a rapid increase in use as a cancer treatment due to its non-invasive nature, low cost, simplicity, and reduced complications as compared to other currently available resection options [1]. The inclusion of nanoparticles that are capable of intense absorption in a specific wavelength band allows for higher selectivity of this thermal dose based upon the location of the delivered nanoparticles through both the additional absorption of laser energy, which gets deposited as heat, in the desired location containing the photoabsorbers and by lowering the amount of energy or power of the laser necessary to affect the region of interest, thus lowering the energy applied to the non-desired thermal damage region.
Temperature Dependent Reversible Self Assembly of Methacrylated Collagen Gels
Authors: Drzewiecki Kathryn , Gaudet Ian , Pike Douglas , Branch Jonathan , Nanda Vikas , Shreiber David
Published: January 2014

Hydrogel-based tissue engineering scaffolds can allow tissues to repair and regenerate by providing a 3D environment similar to soft tissue. Type I collagen has the ability to assemble into a fibrillar gel at physiological temperature and pH, while promoting cell adhesion and growth. Our lab has modified type I collagen by covalently adding methacrylate groups to lysine residues to create collagen methacrylamide (CMA). This biomaterial, like collagen, maintains the ability to self-assemble, and can then be photocrosslinked with long-wave UV light and a water-soluble photoinitiator, which allows extensive spatiotemporal control of mechanical and biochemical properties [1]. In characterizing CMA and developing it for other applications, we discovered an interesting property. Unlike type I collagen hydrogels, which maintain a stable fibrillar network during cooling and freezing, CMA will spontaneously disassemble at temperatures less than 10°C. In this paper, we discuss the temperature-dependent rheological properties of CMA as well as the nature of its molecular and supramolecular structure in comparison to collagen.
Effect of Walking Speed on Angular Stiffness and Roll-Over Shape of the Intact and Prosthetic Feet of Transtibial Amputees
Authors: Roland Michelle , Adamczyk Peter G. , Hahn Michael E.
Published: January 2014

The calculated roll-over shape and respective radius of intact and prosthetic feet has been shown to be a useful measure of lower limb function during walking [1–2]. Hansen et al [3] reported that the roll-over radius, R, is constant over a range of speeds for the intact foot-ankle system. It may be assumed that the prosthetic foot R would also be constant with increased walking speed. Similarly, the angular stiffness of prosthetic feet is not likely to change with walking speed, as the material stiffness remains unchanged. However, the effective angular stiffness of the intact ankle may increase with the plantar flexor moment during the stance phase of gait, which typically increases in magnitude with walking speed.
Head Rotation Effects on the Flow and Hemodynamics of the Human Carotid Bifurcation
Authors: Aristokleous Nicolas , Papaharilaou Yannis , Seimenis Ioannis , Georgiou Georgios C. , Brott Brigitta C. , Anayiotos Andreas S.
Published: January 2014

The use of realistic anatomic human carotid artery bifurcation (CB) models with a realistic blood waveform leads to physiologically relevant numerical simulations. To study the effects of head posture on the geometry and hemodynamics of the CB, Magnetic resonance imaging (MRI) was used on six healthy volunteers in two different head postures: 1) the supine neutral (N) and 2) the prone with rightward head rotation (P) up to 80°. Geometric differences with posture change in both the left (LCA) and right (RCA) carotid arteries were reported before [1]. The blood velocity waveform for each individual was obtained using phase-contrast MRI (PCMRI) at five diameters upstream of CB. Results have shown that peak systolic blood flow rate is reduced, in the prone position for both RCA and LCA in all six volunteers. To investigate the effects of the reduced peak systolic flow on the hemodynamics of the CB, numerical simulations were performed for a volunteer that exhibited the most geometric changes for the prone position in comparison to the other five based on specific geometric parameters [1, 2]. For the two investigated head postures the observed measured input waveforms were used.
A Model of Glomerular Mesangial Transport in Health and Disease
Authors: Hunt Sarah , Segal Yoav , Dorfman Kevin D. , Barocas Victor H.
Published: January 2014

Transport in the kidney is critically important in normal function and in disease. Solute transport occurs in many locations within the kidney, including convection within the capillaries, filtration across the basement membrane, and convection/diffusion within the mesangium (Figure 1). Models of transport in the kidney have traditionally focused on ultrafiltration [1], which is the predominant pathway for fluid and solutes passing into the urinary space. However, the mesangium is often the site of the first symptoms in disease [2], suggesting that mesangial transport is significant, at least in some cases.
Tissue Hydration Influences Bursting Pressure of Fused Arteries
Authors: Cezo James D. , Anderson Nicholas , Kramer Eric , Taylor Kenneth D. , Rentschler Mark E. , Ferguson Virginia L.
Published: January 2014

Tissue fusion is a complex thermally driven reaction which, through the application of heat and pressure, bonds the extracellular matrix (ECM) of neighboring tissues together. While the mechanism of this reaction is unknown, several theories do exist. Collagen is largely thought to be responsible for the formation of the fusion bond [1–3]. During tissue fusion, as the tissue temperature is elevated (> 100 °C) [4–5], collagen denatures and water is forcibly evaporated out of the tissue [6–11]. Collagen in arterial tissue is comprised of a tightly wound triple helix held in place by crosslinking. Upon denaturation, the crosslinks are broken and the helix unwinds [6–8]. It is theorized that under applied heat and pressure the denatured molecules tangling with adjacent molecules [1], crosslinking to neighboring molecules [2], or a combination of these two mechanisms are responsible for the formation of the tissue fusion bond [3]. Water is also present in the ECM which can be classified as free or bound. Free water is able to diffuse and move freely around the ECM. Bound water is held to ECM proteins through dipole interactions. During tissue fusion, the water is forcibly removed and these charged sites which interact with water are now able to interact with adjacent molecules. These charged sites would not exist if not for the removal of water from the ECM. The goal of this study is to elucidate the importance of water in the formation of the tissue fusion bond.
Mineral Morphology at the Tendon-to-Bone Interface Observed via High Energy X-Ray Diffraction
Authors: Deymier-Black Alix C. , Schwartz Andrea G. , Cai Zhonghou , Genin Guy M. , Thomopoulos Stavros
Published: January 2014

Tough, graded interfaces are a broadly conserved feature of biological attachment of two dissimilar materials, but the mechanisms by which toughening occurs are not fully known. In biological systems, graded structures are commonly found in the attachments of materials with very different properties such as bone, which is very stiff, and tendon, which is compliant 1. Previous research has shown that the interface between these two materials is composed mostly of collagen, proteoglycans, and carbonated apatite crystals (mineral). Our working hypothesis is that gradients in mineral content and collagen orientation combine to provide a compliant energy absorbing region between the tendon and bone 1.
A Novel Device for the Microindentation of Soft Biomaterials With Application to Aortic Valve Leaflets
Authors: Doyle Matthew G. , Chehade Moussa , Simmons Craig A.
Published: January 2014

Microscale mechanical properties of soft biomaterials, such as heart valves, are of interest to researchers studying the effects of matrix mechanical properties on cell function. Measurements at the microscale, on the order of 1–500 μm, are representative of the mechanical properties experienced by the cells in their environment (1). In contrast, other methods like conventional tensile/compression testing and atomic force microscopy provide macroscale and nanoscale properties, respectively, that do not reflect the local micromechanical environment at the cellular scale.
Simulation and Analysis of a Flow Profile and Reaction Rate Within a 3D Microfluidic Cell Culture Array
Authors: Ahmed A. H. Rezwanuddin , Dereli Korkut Zeynep , Akaydin H. Dogus , Wang Sihong
Published: January 2014

Microfluidic devices deliver the promise of high throughput data output over conventional cell cultures with significantly smaller sample sizes[1]. The 3D microenvironment of sample cells provides with a more relevant analog to the realistic nature of cells over 2D cultures[2]. A microfluidic device of three layers to emulate the blood vessel, the basal membrane, and aggregates of tumor cells was developed using microfabrication technologies with Polydimethylsiloxane (PDMS) [3]. Such a 3D separation of the different layers is necessary in order to understand the dynamics of tumor cells with respect to drug responses[4]. In this study, we examine the flow patterns and transport issues in the 3D layered microfluidic device that mimicks the tumor microenvironment.
Identification of the Toughness Properties of Mitral Valve Leaflets
Authors: Javid Farhad , Shahmansouri Nastaran , Amabili Marco , Mongrain Rosaire , Pasini Damiano , Angeles Jorge
Published: January 2014

Suturing a prosthetic ring to the mitral valve is one of the main challenges in percutaneous mitral valve annuloplasty. Novel self-anchoring fasteners developed for minimally invasive surgery may easily tear the tissue and cause their failure. Identification of the fracture toughness of the mitral valve tissue is an important step towards the optimization of these novel fasteners to minimize their deleterious effects on the surrounding tissue. Moreover, the study of rupture mechanism of the heart valve tissue can provide interesting information on the developing process of congenital mitral regurgitation due to the cleft mitral valve.
Lower Limb Amputee Recovery Response to an Imposed Mediolateral Error in Foot Placement
Authors: Segal Ava D. , Klute Glenn K.
Published: January 2014

Lower limb amputees exhibit increased foot placement variability during gait [1–3] in part due to the lack of ankle musculature that reduces their ability to shift the prosthetic limb center of pressure (COP) [4]. In spite of compensating with a wider step width compared to non-amputees [2,3], amputees are still 20% more likely to fall compared to age-matched norms [5]. Since mediolateral (ML) balance is critical for successful ambulation and contingent on accurate ML foot placement [6,7], we chose to study how an error in ML foot placement affects amputee balance to gain a better understanding of the biomechanic strategies amputees employ to compensate for their lack of ankle musculature.
High-Density Surface EMG Biofeedback From the Trapezius for Real-Time Postural Correction
Authors: Gaffney Brecca M. , Maluf Katrina S. , Davidson Bradley S.
Published: January 2014

Work-related chronic neck pain is a growing condition in the United States that accounts for 56% to 65% of all occupational disabling injuries [1]. Fifty-four percent of working adults suffer from chronic neck pain within any six-month period and 5% of working adults report that neck pain significantly inhibits daily activities [2]. These conditions have been linked to poor posture in the cervical spine and shoulder [3]. Poor cervical spine posture commonly includes simultaneous extension in the upper vertebrae (C1-C3) and flexion in lower vertebrae (C7-C4). This posture moves the head anterior to the torso and increases the load carried by the upper trapezius (UT) [4]. To maintain this posture, the UT is activated and elevates the scapula. Chronic activation of the UT has been correlated to chronic neck pain [5]. Although there is an apparent correlation between poor posture and neck pain, it is unclear whether neck pain causes poor posture or if poor posture causes neck pain.
Characterization of Near-Infrared Functional Lymphatic Imaging in the Rat Tail Model
Authors: Weiler Michael , Dixon J. Brandon
Published: January 2014

The lymphatic vasculature is present in nearly every tissue of the body to serve essential functions in fluid homeostasis, immune cell trafficking, and lipid transport, and it has been implicated in the progression of several diseases. Despite the critical roles that this system performs, very little is known about the lymphatic vasculature in comparison to the blood vasculature, which can be attributed, in part, to the difficulty associated with imaging lymphatic vessels. With the growing interest in studying lymphatics, near-infrared (NIR) imaging has emerged in the literature as a novel lymphatic imaging modality to simultaneously improve spatial resolution to visualize small initial lymphatics and increase temporal resolution to capture the dynamic lymphatic pump function responsible for fluid propulsion.
Supplementing Basic Graduate Level Courses With Conference-Based Research Communication Experiences
Authors: Bush Tamara Reid , Leitkam Sam , Gunn Craig
Published: January 2014

Two difficulties are commonly identified for early graduate-level students that hinder their growth in the academic community. First, students in graduate school engineering courses find the basic material difficult to relate to real-life problems. Second, early career graduate students have little practice at presenting research in a professional format (e.g. ASME conference).
In Vitro Nonlinear Viscoelastic Characterization of the Porcine Spinal Cord
Authors: Shetye Snehal S. , Troyer Kevin L. , Streijger Femke , Lee Jae , Kwon Brian K. , Cripton Peter , Puttlitz Christian M.
Published: January 2014

Approximately 12,400 new cases of spinal cord injuries (SCI) are reported in the United States every year. It has been estimated that the annual financial burden of SCI in the United States is approximately $7.736 billion. The mechanisms of mechanical damage to the spinal cord can be broadly classified into distraction, dislocation or contusion. Distraction injuries are predominantly caused by rapid acceleration-deceleration of the cervical spine. Vertebral burst fractures commonly result in contusion of the spinal cord and relative dislocation of adjacent vertebrae can inter-segmentally shear the spinal cord resulting in injury. Multiple studies have examined the quasi-static mechanical properties of the spinal cord [1–3]. However, considering that most spinal cord injuries occur during dynamic events with relatively high strain rates (ex: 10/s), alarmingly few studies have investigated the time-dependent mechanical characteristics of the spinal cord.
Platelet Activity of Coaxial Electrospun Scaffolds for Applications in Cardiovascular Tissue Engineering
Authors: Merkle Valerie M. , Hutchinson Marcus , Tran Phat L. , Sheriff Jawaad , Bluestein Danny , Wu Xiaoyi , Slepian Marvin J.
Published: January 2014

A biocompatible scaffold is vital to implant device design, tissue engineering, and drug delivery. Previous work has shown smooth muscle cell and human umbilical vascular endothelial cell viability, adhesion, proliferation, and migration on coaxially electrospun scaffolds. For vascular applications, these electrospun scaffolds need to be non-thrombogenic, while simultaneously not completely inhibiting the platelets role in hemostasis and augmenting angiogenesis.[1] Therefore, platelet activity on electrospun scaffolds needs to be assessed. In this study, we fabricated coaxial electrospun nanofibers in both 1:1 and 3:1 (gelatin:polyvinyl alcohol, volumetric flow ratios), as well as scaffolds composed of either gelatin or polyvinyl alcohol (PVA). Platelet deposition on the electrospun scaffolds was measured. Furthermore, the activity of human platelets on the electrospun scaffolds was assessed using a modified prothrombinase assay.[2]
Application of a Standard Quantitative Comparison Method to Assess a Full Body Finite Element Model in Frontal Impact
Authors: Vavalle Nicholas A. , Moreno Daniel P. , Stitzel Joel D. , Gayzik F. Scott
Published: January 2014

Advanced human body finite element models (FEMs) are gaining popularity in the study of injury biomechanics [1, 2]. FEMs must be validated to ensure that model outputs correspond to experimentally-observed phenomena. During the validation process researchers often qualitatively compare the model response to a laboratory experiment. However, a more rigorous approach is to use quantitative methods. Often, these methods attempt to parse the error contributions of phase, magnitude, and a shape factor. The purpose of this study is to apply one such method for validation quantification, called the enhanced error assessment of response time histories (EEARTH), to a model that was recently developed. The EEARTH method is anticipated to be part of the forthcoming ISO standard (ISO/TC 22/SC 10/WG 4) on comparing model outcomes to experimental data. The subject of this study is the Global Human Body Models Consortium (GHBMC) 50 th percentile male seated model (M50). The mission statement of the consortium is to develop a set of biofidelic computational human body models to aid in the study injury biomechanics and safety system enhancement.
In Vitro Biocompatibility of Coaxial Electrospun Scaffolds for Cardiovascular Tissue Engineering
Authors: Merkle Valerie M. , Ammann Kaitlyn R. , DeCook Katrina J. , Tran Phat L. , Slepian Marvin J. , Wu Xiaoyi
Published: January 2014

Coaxial electrospinning is a novel technique that allows the fabrication of composite nanofibers in a core-shell structure. This technique can be used to optimize the biological properties of a natural polymer (i.e. gelatin) and the mechanical properties of a synthetic polymer (i.e. polyvinyl alcohol). In this study, we fabricated coaxial nanofibers of gelatin and polyvinyl alcohol (PVA) for use in cardiovascular tissue engineering. Cellular adhesion and proliferation of human umbilical endothelial cells (HUVEC) and smooth muscle cells (SMC) is determined on coaxial nanofibers fabricated from a 1:1 and 3:1 (gelatin:PVA volumetric flow rate ratios), as well as nanofibers composed solely of gelatin or PVA. In addition, cellular migration on the coaxial nanofibers, gelatin nanofibers, and PVA nanofibers is determined for both endothelial cells and smooth muscle cells.
Validation of an Open Source Framework for the Simulation of Blood Flow in Rigid and Deformable Vessels
Authors: Passerini T. , Quaini A. , Villa U. , Veneziani A. , Canic S.
Published: January 2014

Computational methods are the tool of choice for the study of physics phenomena in many fields of scientific endeavor. To guarantee the reliability of the results of computational analyses, it is crucial that mathematical models are validated and numerical methods are verified. A verified method is capable of correctly solving the problem equations, while a valid model is able to correctly describe the features of the problem (i.e. it uses the right equations). In this paper we: (i) verify and validate an open source computational fluid dynamics (CFD) framework for the solution of problems of interest in hemodynamics and (ii) provide a report on the methodology that we use, to make our experiences reproducible.
The Direction of Cyclic Stretch-Induced Cell and Stress Fiber Alignment Depends on Matrix Rigidity
Authors: Tondon Abhishek , Kaunas Roland
Published: January 2014

We have previously reported that stress fibers (SFs) in cells with normal contractility reorient perpendicular to the direction of cyclic stretch [1], while cells treated with inhibitors of myosin light-chain kinase (MLCK) or members of the Rho GTPase pathway oriented parallel to the direction of stretch [1, 2]. Our theoretical modeling predicts that myosin II acts as a tension sensor acting to maintain SF tension through sliding along actin filaments under low strain rates or promoting SF reorientation under high strain rates [3]. This model predicts that SFs on stiff elastic substrates are at an optimal level of tension and that cyclic stretching subjects these SFs to excessive loads in the direction of stretch, hence SFs preferentially orient away from the direction of stretch. On soft substrate, intracellular tension is expected to be much lower than on stiff substrates [4]. Consequently, we postulated that stretching cells on a soft substrate would induce cell and SF alignment parallel to the direction of stretch in a manner dependent on cell contractility.
On Unconfined Compression Response of the Porcine Corneal Stroma
Authors: Etebu Ebitimi , Hatami-Marbini Hamed
Published: January 2014

The corneal stroma constitutes about 90% of the corneal total thickness and is mainly responsible for its mechanical properties. The stroma is a highly ordered structure composed of mostly parallel to the surface stacks of 2 μm thick collagenous lamellae. The collagen fibrils have an almost uniform diameter and are arranged in a pseudohexagonal lattice structure. Under normal physiological conditions, the collagen fibrils are responsible for carrying the membrane tensile stresses caused by the intraocular pressure. It is believed that the interaction between the collagen fibrils and hydrophilic negatively charged proteoglycans are responsible for the stromal architecture as well as the compressive properties of the tissue. Up to date uniaxial strip testing method and biaxial pressure inflation experiments have widely been used to determine the mechanical parameters of the cornea. These experimental measurements often provide the necessary information for characterizing the tissue behavior in tension [1] [2, 3]. Nevertheless, the mechanical parameters of the cornea in compression have received less attention in the literature. Most of the previous studies are focused on describing the swelling pressure and hydration relations [4]. In this research work, we used unconfined compression experiments along with a biphasic model to measure the corneal parameters in compression. This method has been extensively used to explore the mechanical properties of similar hydrated tissues such as the articular cartilage [5]. Due to specific microstructure of the cornea, a transversely isotropic model was used to curve-fit the experimental data and to derive the in-plane modulus of the cornea. The predicted in-plane modulus was compared to the values reported in literature.