bluuebunny/crossref_metadata_2025 huggingface dataset:
IA-FEMesh: An Interactive All Hexahedral Mesh Generator for Discrete Anatomic Closed Surfaces
Authors: Shivanna Kiran H. , Kallemeyn Nicole A. , Tadepalli Srinivas C. , DeVries Nicole A. , Magnotta Vincent A. , Grosland Nicole M.
Published: March 2014

The broad objective of our software, IA-FEMesh is to aid patient-specific finite element (FE) model development. Patient-specific models hold the potential to enable surgeons to plan care using objective analysis-based tools. Thus, they can better evaluate alternate surgical protocols and treatments, thereby contributing to improved surgical outcome. Our previous efforts were focused on projection techniques specific to the geometry under consideration [1]. The current meshing technique is the generalization of projection techniques that builds upon a multi-block approach, with considerable attention given to incorporating interactive tools to ease the model development process, thereby creating a user friendly approach to anatomic modeling.
The Mechanical Properties of Porcine Coronary Arteries Determined With a Mixed Experimental-Numerical Approach
Authors: van der Horst Arjen , van den Broek Chantal N. , Rutten Marcel C. M. , van de Vosse Frans N.
Published: March 2014

Mechanical characterization of the coronary arterial wall is important for several reasons. Mechanical factors play an important role in the development of atherosclerosis [1]. Atherosclerotic coronary arteries may be treated mechanically with interventions like PTCA and stent implantation, 1265000 PTCA procedures were performed in the United States in 2005 [2]. Furthermore, knowledge of the mechanical properties of the arterial wall is important for modeling of the coronary circulation and explaining its hemodynamics.
An Experimental Methodology for the Determination of the Viscoelastic Properties of the Vocal Fold at Human Phonation Frequencies
Authors: Palko Joel , Abramowitch Steven , Gilbert Thomas W.
Published: March 2014

The vocal folds are subjected to some of the largest magnitudes and frequencies of deformation of any tissue in the human body during normal voice production. Vocal fold scarring creates a functional deficit in this highly specific tissue that compromises the integrity of an individual’s voice. Scarring is the leading cause of dysphonia which often leads to a decreased quality of life, especially to those whose voice is an integral part of their profession.
A Framework for Fluid-Solid-Growth Modeling and its Application to Understanding the Enlargement of a Fusiform Aneurysm
Authors: Baek Seungik , Figueroa C. Alberto , Taylor Charles A. , Humphrey Jay D.
Published: March 2014

Blood vessels adapt in response to changes in their biomechanical and biochemical environment under various physiological and pathological conditions. While advances in computational hemodynamics and arterial wall mechanics have been spectacular, such advances have been achieved separately; there is, therefore, a pressing need for coupling biosolid and biofluid mechanics within a computationally efficient framework to study effects of fluid-solid interactions (FSI) in growth and remodeling (G&R) of the vessel wall. Toward this end, we built a fluid-solid-growth (FSG) modeling framework [1] that incorporates four separate advances by our groups: biomechanics of G&R [2], a coupled momentum method for FSI during a cardiac cycle [3], a theory of small on large for coupling G&R and FSI models [4], and improved approaches for modeling fluid boundary conditions in complex vascular systems [5]. Although the framework presented here is sufficiently general to apply to many different vascular adaptation problems, we first apply this framework to a fusiform aneurysm with a simple geometry.
Risk of Rupture in Abdominal Aortic Aneurysms and Vulnerable Plaques: A Patient Based Fluid Structure Interaction Approach
Authors: Bluestein Danny , Alemu Yared , Xenos Michalis , Rissland Peter , Sheriff Jawaad , Gruberg Luis , Einav Shmuel , Ricotta John J.
Published: March 2014

In this study we performed two separate fluid structure interaction (FSI) simulations. A patient-specific Abdominal Aortic Aneurysm (AAA) geometry, and coronary vulnerable plaque (VP) geometry in idealized and in patient based geometries reconstructed from intravascular (IVUS) measurements.

The patient specific AAA FSI simulations were carried out with both isotropic and anisotropic wall properties. An orthotropic material model was used to describe wall properties, closely approximating experimental results of AAA specimens [1]. The results predict larger deformations and stress values for the anisotropic material model as compared to the isotropic one. This difference indicates that the isotropic formulation may underestimate the risk of rupture. The ability to quantify stresses developing within the aneurysm wall based on FSI simulations will help clinicians to reach informed decisions in determining rupture risk of AAA and the need for surgical intervention.

The risk of rupture of vulnerable plaques was studied in both idealized and patient specific geometries using FSI simulations. The idealized model included vessel wall, fibrous cap, and a lipid core. Regions susceptible to failure and the contribution of the various components were studied. The upstream side of the vulnerable plaque fibrous cap had the highest stresses. The presence of a calcified spot embedded within the fibrous cap proper was studied, and was demonstrated to enhance stresses within the fibrous cap, significantly contributing to its risk of rupture.
Multi-Body Dynamic Simulation of the Meniscus in a Computational Knee Model
Authors: Kia Mohammad , Guess Trent M.
Published: March 2014

The menisci have an important multifunctional role in the human knee. They protect the joint articular cartilage (by acting as a buffer between femoral and tibial surfaces while loading), provide joint lubrication, and increase joint stability (by providing congruity between femoral and tibial articular surfaces) [1]. The menisci also effectively distribute contact forces over the articular surfaces by increasing the contact surface of the joint [2].
An Elaborate Data Set for Mechanical Characterization of the Foot
Authors: Sirimamilla Pavana , Erdemir Ahmet , van den Bogert Antonie J. , Halloran Jason P.
Published: March 2014

Experimental testing of cadaver specimens is a useful means to quantify structural and material response of tissue and passive joint properties against applied loading[1,4]. Very often, specific material response (i.e., stress-strain behavior of a ligament or plantar tissue) has been the goal of experimental testing and is accomplished with uniaxial and/or biaxial tests of prepared tissue specimens with uniform geometries[2,5]. Material properties can then be calculated directly and if testing data involves individual sets of multiple loading modes (e.g. compression only, shear only, volumetric) an accurate representation of the global response of the specimen may be possible. In foot biomechanics, however, it is practically impossible to perform isolated mechanical testing in this manner. The structural response, therefore the stiffness characteristics, of the foot have been quantified, usually using a dominant loading mode: e.g., whole foot compression [6], heel pad indentation [3]. This approach ignores the complexity of most in vivo loading conditions, in which whole foot deformation involves interactions between compression, shear (e.g. heel pad) and tension (e.g. ligaments). Therefore, the purpose of this study was to quantify the mechanical response of a cadaver foot specimen subjected to compression and anterior-posterior (AP) shear loading of isolated heel and forefoot regions as well as whole foot compression. Results from the experimental tests represent a novel methodology to quantify a complete structural biomechanical response. Combined with medical imaging, followed by inverse finite element (FE) analysis, the data may also serve for material characterization of foot tissue.
Strain-Dependent TGF Beta-1 Synthesis and Activation by Aortic Valve Interstitial Cells
Authors: Merryman W. David , Nilo Michael P. , Murphy-Ullrich Joanne E.
Published: March 2014

Aortic valve (AV) sclerosis is identified by irregular thickening and decreased compliance of the leaflets causing impaired cardiac function and increased mortality with age. Both mechanical and molecular factors are thought to be important in the pathogenesis of AV sclerosis. The structural integrity of the AV leaflet extracellular matrix (ECM) is maintained by the resident fibroblast AV interstitial cells (AVICs). With increasing age and loss of compliance in the aorta, a stress transfer may occur in the AV leaflets that likely subjects the AVICs to increasing strains in the circumferential direction [1].
Response of Porcine Carotid Arteries to Independent Control of Medial Tensile Stresses and Shear Stress
Authors: Rachev Alexander , Dominguez Zachary , Vito Raymond
Published: March 2014

Remodeling plays an important role in normal arterial physiology and in the genesis and progression of vascular pathologies. Arteries respond to changes in their global mechanical environment, characterized by blood flow rate, arterial pressure, and longitudinal stretch by changing geometry, structure and composition. Remodeling results from altered vascular cell activity caused by perturbed local stresses and strains and, in general, tends to restore the local mechanical parameters to their baseline values. To date, experimental investigations in vivo and in organ culture have focused on remodeling responses initiated by controlled sustained changes in one global mechanical parameter while keeping the others at baseline values.
Proliferation and Fiber Formation of Human Dermal Fibroblasts on Patterned Differentially Adherent Substrates
Authors: Schiele Nathan R. , Chrisey Douglas B. , Corr David T.
Published: March 2014

Fibroblast cells are crucial in the human body for maintenance of the extracellular matrix, including synthesizing macromolecules like collagen, and they play a critical role in wound healing of soft tissues such as skin [1]. Directing fibroblast growth is an important step in tissue engineering where the focus has gone from a top-down approach of homogeneously introducing cells into a pre-formed scaffold to a bottom-up approach in which the tissue construct is built on a cell-by-cell basis with ability to manipulate specific cell environments through location, proximity, and geometry. The ability to direct cell proliferation to encourage organized tissue formation can provide tissue engineers a means of controlling the architectural and mechanical properties of soft tissue scaffolds. This approach to functional tissue engineering represents a novel direction for the development of replacement tissues. Previous attempts of directed growth have proven successful with C2C12 mouse myoblast cells. Using laser micromachined channels in agarose hydrogel lined with a basement membrane matrix, myoblast cells were guided to align and produce myotubes [2]. The objective of the current study was to apply similar principals to direct fibroblast cell growth and proliferation, ultimately leading to their growth into three-dimensional fibers, on differentially adherent substrates. Channels (widths ranging from 60 μm to 200 μm) were laser micromachined in agarose gel to explore an optimal geometry for cellular proliferation and fiber formation. The fibroblast cells used range in size from roughly 20–30 μm. Thus, the width of each channel was chosen to explore which multiple of cell width would allow for directional alignment parallel to the channel and subsequent fiber growth. The ability to direct fibroblast cells to align and produce fibers through manipulation of their environment is critical to our laboratory’s ongoing efforts to develop three-dimensional customized tissue replacement constructs to be used in many soft tissue applications such as ligament and skin grafts.
Effects of Sedimentation on Particle Deposition in the Lung Alveoli
Authors: Somani Imshaan , Whitten Jonathan , Hyun Sinjae , Kim Chong S.
Published: March 2014

Deposition of inhaled particles in the lung is one of the key factors for assessing toxic effects of airborne pollutant particles on one hand and for evaluating efficacy of inhalant pharmaceutical aerosols on the other side. Due to the geometric complexity and time-dependency of respiratory tracks, the correct prediction of the particle transport and deposition in the lung airway has been studied with experimental and computational approaches. The human alveolar duct, which connects the alveoli to the bronchioles of the lung, is recently the subject of interest within mathematical modeling because of its implications to drug delivery and ingestion of pollutants. Series of computational approaches have been performed to model the entire lung using 1-dimensional and “trumpet” model analyses [1,2]. Although these models represent with reasonable approximation of the regional particle deposition characteristics, they do not account for the local intricacy of particle transport and deposition in the acinus region, consisting of the alveolar duct and alveoli.
Comparison of Three Material Models to Predict the Time-Dependent Deformation of a Single Cell Under Micropipette Aspiration
Authors: Zhao Ruogang , Wyss Kristine , Simmons Craig A.
Published: March 2014

Micropipette aspiration is an experimental technique that is used widely to measure the mechanical properties of single cells [1]. The viscoelastic properties of the probed cell are often estimated by fitting experimental data to a three-parameter standard linear solid (SLS) half-space model (e.g., [1]). However, this analytical model does not account for the large strains that can occur with micropipette aspiration. This limitation has motivated the development of numerical methods to interpret the experimental data. For example, Zhou [2] implemented a material model combining a hyperelastic neo-Hookean material and a viscoelastic SLS material in an axisymmetric finite element (FE) model to simulate large strain micropipette aspiration of a suspended cell. The time-dependent creep deformation of cells has also been described by power-law rheology [3]; this material model has been applied to micropipette aspiration of nuclei [4], but not whole cells.
Mechanical Stimulation Improves Muscle-Derived Stem Cell Transplantation for Cardiac Repair
Authors: Cassino Theresa R. , Okada Masaho , Drowley Lauren , Huard Johnny , LeDuc Philip R.
Published: March 2014

Muscle-derived stem cells (MDSCs) have been successfully transplanted into both skeletal (1) and cardiac muscle (2) of dystrophin-deficient (mdx) mice, and show potential for improving cardiac and skeletal dysfunction in diseases like Duchenne muscular dystrophy (DMD). Our previous study explored the regeneration of dystrophin-expressing myocytes following MDSC transplantation into environments with distinct blood flow and chemical/mechanical stimulation attributes. After MDSC transplantation within left ventricular myocardium and gastrocnemius (GN) muscles of the same mdx mice, significantly more dystrophin-positive fibers were found within the myocardium than in the GN. We hypothesized that the differences in mechanical loading of the two environments influenced the transplantation and explored whether using MDSCs exposed to mechanical stimulation prior to transplantation could improve transplantation. Our study shows increased engraftment into the heart and GN muscle for cells pretreated with mechanical stretch for 24 hours. This increase was significant for transplantation into the heart. These studies have implications in a variety of applications including mechanotransduction, stem cell biology, and Duchenne muscular dystrophy.
Role of Nanofibrous Scaffold Geometry in Cellular Adhesion
Authors: Chen Ming , Michaud Heather , Lovett Michael L. , Kaplan David L. , Bhowmick Sankha
Published: March 2014

The goal of this study was to investigate the kinetics of NIH 3T3 fibroblast cell adhesion and their actin cytoskeleton organization on different geometry electrospun polycaprolactone nanofibrous scaffolds. Cell adhesion kinetics was measured by MTS assay. Cells on beaded scaffolds, which are not uniform fibrous scaffolds, showed the lowest adhesion rate and the smallest cytoskeleoton organization in all experiments. For uniform fiber scaffolds, cell adhesion rate was a function of scaffold specific surface area (SSA). Cell adhesion rate increased with increasing SSA when scaffold SSA was higher than 7.13 μm−1. Cell adhesion in high serum concentration culture medium was higher than in low serum concentration medium for all scaffolds. Results indicate that from 0–5% serum concentrations, cell adhesion at 4 or 8 hours were not significantly different between different geometry scaffolds. F-actin maximum projected area was quantified to indicate mature cell adhesion. Results indicate higher area for cells cultured in high serum concentration medium on 18.79 μm−1 (SSA) scaffolds, and had higher values when cultured for 8 hrs compared to 24 hrs. 10% serum concentration and 18.79 μm−1 (SSA) scaffolds are considered to be an optimum combination for enhanced cell adhesion.
A Hydrodynamic Efficiency Parameter as a Novel Left Ventricular Diastolic Dysfunction Diagnostic Metric
Authors: Stewart Kelley C. , Kumar Rahul , Charonko John J. , Vlachos Pavlos P. , Little William C.
Published: March 2014

Numerous studies have shown that cardiac diastolic dysfunction and diastolic filling play a critical role in dictating overall cardiac health and demonstrated that the filling wave propagation speed is a significant index of the severity of diastolic dysfunction [1, 2]. However, the governing flow physics underlying the relationship between propagation speed and diastolic dysfunction are poorly understood. More importantly, currently there is no reliable metric to allow clinicians the ability to diagnose cardiac dysfunction on the basis of the wave filling speed.
The Role of Knee Extensor Strength in Balance-Restoring Step Initiation and Execution
Authors: King Gregory W. , Luchies Carl W.
Published: March 2014

A stepping response is often used to restore balance following a fall. Using laboratory-induced balance perturbations, various researchers have reported age-related alterations in balance recovery step characteristics including earlier step liftoff time [1; 2], shorter step length [1; 3], and longer step duration [2]. Such age-related changes in the step response may be related to older adults’ reduced strength reserve, which is prominent in the lower extremities [4] and therefore likely plays an important role in balance recovery.
Non-Intrusive ECG Measurement on Vehicle Steering Wheel and Driver Seat
Authors: Hu Shan , Yu Xun
Published: March 2014

Driver drowsiness is one of the major causes of deadly traffic accidents. Continuous monitoring of drivers’ drowsiness thus is of great importance for preventing drowsiness-caused accidents. Previous psychophysiological studies have shown that heart rate variability (HRV) has established differences between waking and sleep stages [1, 2]. This offers a way to detect driver’s drowsiness by analyzing HRV, which is typically measured and analyzed from electrocardiogram (ECG) signal. Although ECG measurement techniques are well developed, most of them involve electrode contacts on chest or head. Wiring and discomfort problems inherent in those techniques prevent implementing them on cars. To address these problems, we make full use of the environment settings in a car to develop two non-intrusive real-time ECG measurement methods for drivers.
Low Endurance Testing of a Spinous Process Spacer
Authors: DiAngelo Denis J. , Sander Elizabeth J. , Zufelt Nephi A. , Kelly Brian P. , Foley Kevin T.
Published: March 2014

Lumbar neurogenic claudication secondary to spinal stenosis causes narrowing of the spinal canal that contributes to extremity lower back pain. Lumbar extension, as seen in standing and walking, exacerbates symptoms by decreasing the foraminal height, width, and area, whereas flexion, as seen in sitting, improves symptoms by increasing the cross-sectional area of the foramen. Interspinous process devices have been developed to treat symptomatic lumbar stenosis [1]. The device is placed between the spinous processes and serves to limit the amount of extension that can occur beyond a neutral alignment. The objective of this study was to perform low endurance cyclic tests on the In-Space spinous process spacer (Synthes Spine) to assess fixation and containment in a human cadaveric spine model in vitro. The device was cyclically tested under an alternating sequence of combined loading conditions using a new protocol developed on a robotic based spinal testing system (Spine Robot).
Microfluidic Generation of Adhesion Gradients Through 3D Collagen Gels: Implications for Neural Tissue Engineering
Authors: Sundararaghavan Harini G. , Monteiro Gary A. , Shreiber David I.
Published: March 2014

During development, neurites are directed by gradients of attractive and repulsive soluble (chemotactic) cues and substrate-bound adhesive (haptotactic) cues. Many of these cues have been extensively researched in vitro, and incorporated into strategies for nerve and spinal cord regeneration, primarily to improve the regenerative environment. To enhance and direct growth, we have developed a system to create 1D gradients of adhesion through a 3D collagen gel using microfluidics. We test our system using collagen grafted with bioactive peptide sequences, IKVAV and YIGSR, from laminin — an extra-cellular matrix (ECM) protein known to strongly influence neurite outgrowth [1, 2]. Gradients are established from 0.14 mg/ml–0, and 0.07 mg/ml–0 of each peptide and tested using chick dorsal root ganglia (DRG). Neurite growth is evaluated 5 days after gradient formation. Neurites show increased growth in the gradient system when compared to control and biased growth up the gradient of peptides. These results demonstrate that neurite growth can be enhanced and directed by controlled, immobilized, haptotactic gradients through 3D scaffolds, and suggest that including these gradients in regenerative therapies may accelerate nerve and spinal cord regeneration.
Effects of Glenoid Prosthesis Design Variables on Glenoid Bone Remodeling: A Finite Element Based Simulation and Validation Study
Authors: Sharma Gulshan B. , Robertson Douglas D. , Smolinski Patrick J. , Debski Richard E. , McMahon Patrick J.
Published: March 2014

Finite element (FE) analysis has been used to improve glenoid prosthesis design. One of the major complications of shoulder arthroplasty has been glenoid prosthesis loosening. Design improvements are needed to increase their longevity [1]. Current FE analyses have used static or non-linear solutions to compare design variations with respect to stresses in the glenoid bone and prosthesis [2, 3]. Previous numerical models have not incorporated Wolff’s Law of adaptive bone remodeling to simulate normal glenoid bone remodeling or remodeling in response to implanted glenoid prostheses. Of the numerous remodeling simulation theories available in the literature, this study controlled internal structure remodeling using bone strain-energy. In order to design longer lasting glenoid prosthesis bone remodeling behavior due to various prosthesis fixation geometries and materials needs to be considered.
Non-Planar Shape of the Mitral Annulus Reduces Systolic Strain on the Posterior Leaflet by Increasing Leaflet Curvature
Authors: Padala Muralidhar , Sacks Michael S. , Yoganathan Ajit P.
Published: March 2014

The mitral valve annulus is a dynamic structure that changes in its shape during the cardiac cycle. It changes from a flat shape during diastole to a non-planar saddle shape during systole, which has been confirmed in animals and humans using various techniques. However a teleologic reason for nature’s selection of this shape and its role in mitral valve mechanics are poorly understood. Recent studies from our laboratory indicate that mitral annular saddle optimizes the force distribution on the valve components that could potentially affect valve function and mechanics. The objective of this study is to provide a quantitative and mechanistic insight into the synergy between the non-planar mitral annular shape and posterior leaflet mechanics. The posterior leaflet was specifically selected as most mitral valve surgeries require placement of suture lines in this region, which fail in more than 40% of the patients due to high strains in this region.
Effects of External Loading on the Morphology of the Yielded Regions in Trabecular Bone Predicted by FEA
Authors: Shi Xiutao , Wang Xiang , Niebur Glen L.
Published: March 2014

Osteoporosis is an age-related skeletal condition characterized by low bone mineral density and deterioration of the trabecular architecture leading to increased susceptibility to fracture [1]. Wolff hypothesized that trabecular architecture adapts to have its principal material axes aligned with the principal loading directions. Regions of experimentally labeled trabecular microdamage correspond to areas of high stress and strain calculated from FEA [2]. Studying the morphology of numerically predicted regions of tissue level yielding might provide insight into the role of trabecular architecture in the strength of trabecular bone.
On the Bidirectional Viscoelastic Behavior of the Human Achilles Tendon
Authors: Komolafe Oluseeni A. , Doehring Todd C.
Published: March 2014

Soft tissues such as tendons and ligaments are made up of groups of collagen fascicles surrounded by a sheath of epitenon. The friction between these structural fibers and their surrounding ground substance has been suggested to be the main contributor to the observed viscoelastic response of the tissue[1]. During normal daily activities such as walking, climbing stairs or jumping, these tissues are subjected to alternating loading and unloading conditions. Depending on the load and tissue orientation, this alternating loading condition may not be uniformly applied over the entire volume of the tissue. In some instances, certain fiber bundles are in tension (loaded) while others might be unloading. Hence, the development of accurate predictive models requires characterization of not only the loading behavior, but also the unloading behavior. To our knowledge, there are few models that specifically address the unloading behavior of the tissue.
An Infusion and Pressure System to Measure Hydraulic Conductivity at a Microscale Level
Authors: Saaibi Ana M. , Sarntinoranont Malisa
Published: March 2014

In studies on nervous tissues, researchers have investigated the relationship between tracer distributions, infusion pressure, flow rate, and tissue properties to optimize and implement infusion techniques [1]. Intratumoral infusion studies have also measured pressure gradients in vitro and determined how drug delivery depends on intrinsic tissue structures [2]. Measuring pressure gradients allows for the calculation of tissue transport properties such as hydraulic conductivity. This property is necessary for modeling extracellular flow and convective transport through tissues. However, it remains a challenge to measure in vivo pressure gradients due to difficulties in measuring small changes in pressure over short distances and the invasive nature of these experiments. Porous media models of infusion predict exponential decay of the pressure profile in tissues [3], but experimental studies to validate these results in biological tissue or hydrogels are lacking. In this study, we measured the pressure within a hydrogel at different distances from an infusion source. The measured pressure gradient was used to estimate hydraulic conductivity of the hydrogel. Eventually, the developed infusion-pressure testing system may be used to characterize hydraulic conductivity of biological tissues.
Determination of Optical Absorption Coefficient of Thermally Coagulated Blood Using Photoacoustic Analysis
Authors: Viator John A. , Holan Scott H. , Spradling Emily , Talbert Robert J.
Published: March 2014

Determination of the optical properties of thermally coagulated blood is becoming more important as the use of laser based methods to diagnose burn wounds has increased [1–3]. Knowledge of all optical properties within an inhomogeneous tissue sample, such as a burn wound, in combination with response of that tissue to laser light, allows for the identification of a specific chromophore, such as thermally coagulated blood, within the whole tissue sample. This is important for burn wound diagnosis because the boundary between the necrotic tissue layer, containing thermally coagulated blood, must be distinguished from the underlying viable tissue layer, which contains whole, viable blood[4]. Although the optical properties of whole blood have been studied extensively[5], there is a lack of research devoted to the study of the optical properties of thermally coagulated blood.
Computational Simulation of a MEMS-Based Microactuator for Tissue Engineering Applications
Authors: Keyes Joseph , Junkin Michael , Wong Pak Kin , Vande Geest Jonathan P.
Published: March 2014

The relationship between the 3D microstructure of tissue-engineered constructs (TECs) and their resulting mechanical and biological function is critical in providing TECs with clinically meaningful mechanical properties in reasonable incubation times. We hypothesize that the next generation of TECs must incorporate a controllable and optimized microstructure (and resulting mechanical properties) if they are to mechanically and biologically mimic tissue function. While the development of a robustly engineered tissue replacement will undoubtedly require simultaneous biochemical and biomechanical stimulation, this paper will focus on the development of a device to impose localized micro-mechanical stimulation.
Smart Molecules: Organization and Morphology of the Self-Assembled Collagen Fibrils Formed From a Solution of Densly Packed Collagen Monomers
Authors: Saeidi Nima , Ruberti Jeffrey W.
Published: March 2014

Load-bearing tissues owe their mechanical properties to the presence of highly-organized arrays of collagen fibrils. Aligned lamellae in cornea and aligned fascicles in tendon are the best examples of collagen fibrillar organization at the macroscopic level. The process by which collagen is organized in the extracellular matrix (ECM) is still unclear. But it is generally thought to be facilitated locally via “fibripositors” or cell surface “crypts”. According to this theory, fibroblasts create bounded “compartments” in the ECM through which they deposit organized groups of fibrils (in the form of lamellae in the cornea and in the form of fascicles in the tendon) [1, 2]. An alternative hypothesis proposed by Marie Giraud-Guille suggests that fibroblasts concentrate collagen monomers to form cholesteric liquid crystalline patterns that resemble those found in collagenous matrices in vivo [3–8]. Such organization has been demonstrated in vitro using extracted collagen monomers. However, the data presented in these studies focuses principally on the alignment of the collagen molecules and not on the organization and resulting morphology of condensed collagen fibrils. Considering that matrix mechanical properties in vivo are the result of the fibrillar alignment and not the alignment of individual molecules, further investigation of cholesterically organized condensed fibrils and their morphology is necessary.
Mechanics of Embryonic Head Fold Morphogenesis
Authors: Varner Victor D. , Voronov Dmitry A. , Taber Larry A.
Published: March 2014

Head fold morphogenesis constitutes the first discernible epithelial folding event in the embryonic development of the chick. It arises at Hamburger and Hamilton (HH) stage 6 (approximately 24 hours into a 21-day incubation period) and establishes the anterior extent of the embryo [1]. At this stage, the embryonic blastoderm is composed of three germ layers (endoderm, mesoderm, and ectoderm), which are organized into a flat layered sheet that overlies the fibrous vitelline membrane (VM). Within this blastodermal sheet, a crescent-shaped head fold develops just anterior to the elongating notochord, spanning across the embryonic midline at the rostral end of neural plate. At the crest of this fold, the bilateral precardiac plates fuse in a cranial to caudal direction and give rise to the primitive heart tube and foregut [2, 3]. An understanding of head fold morphogenesis may thus offer insight into how embryonic tissues are arranged to make ready for proper cardiac formation.
Development of a Dynamic Knee Simulator
Authors: Dauster Andrew , Hefzy Mohamed Samir , Hauser Ethan , Nowicki Philip
Published: March 2014

Dynamic knee simulators use muscle analogs to incite motion at the knee joint [1–5]. There is a great variation between simulators in choice of powering of muscle analog systems, what movements are fixed, controlled, or unconstrained, as well as whether or not the system is open or closed kinetic chain. The objective of this work is to develop a portable dynamic knee simulator that allows simulation of knee joint motions when it is maximally flexed during a large range of activities involving the lower limb in both a vertical (e.g. deep squat) as well an horizontal position (e.g. rowing).
Influence of Mechanical Load on the Degradation of Corneal Collagen
Authors: Zareian Ramin , Church Kelli P. , Ruberti Jeffrey W.
Published: March 2014

Collagen is one of the most important structural proteins in vertebrate animals. Over 25 different types of collagen have been identified, but type I collagen is the most abundant fibril forming collagen and contributes to the structural performance numerous connective tissues including ligaments, tendons and cornea [1]. In addition to collagen self-assembly, collagen degradation is an important step in the development, remodeling, homeostasis and pathology of load-bearing ECM. Matrix Metalloproteinase (MMP) types I and VIII, bacterial collagenase and cathepsin are the best known enzymes capable of directly degrading the collagen triple helix [2, 3]. Several researchers have hypothesized that straining collagen fibrils makes them less susceptible to enzymatic degradation [4, 5]. This concept, which we refer to as “strain-stabilization” has important implications for our understanding of collagen as an engineering material.
Cartilage Deformation Measured by MRI Image Segmentation Validates MRI-Based Modeling Results
Authors: Fischer Kenneth J. , Waller Alexander J. , Bilgen Mehmet , Toby E. Bruce , Kunz Manuela , McIff Terence E. , Eckstein Felix
Published: March 2014

The onset of arthritis is clearly associated with abnormal joint kinematics and contact pressures [1]. Yet our understanding of in vivo joint mechanics is still limited. In order to elucidate the relationship between joint mechanics and arthritis we must increase our knowledge of normal contact pressure distributions that help maintain healthy cartilage and abnormal contact pressure distributions that lead to arthritis. MRI-based modeling is a non-invasive means of determining joint mechanics in vivo, by combining information from MRI scans of joints with and without active functional loading.
Using Computational Fluid Dynamics to Design and Optimize a Novel Endovascular Procedure for Carotid Stenosis Repair
Authors: Yeh Victoria , Figueroa C. Alberto , Les Andrea , Ho Jacqueline P. , Dalman Ronald , Taylor Charles A.
Published: March 2014

The carotid arteries, located in both sides of the neck, are critical to supplying oxygenated blood to the brain. Over time, atherosclerotic plaque may accumulate in these vessels, causing them to narrow, which results in a reduced cerebral blood supply. This condition is known as carotid artery stenosis. In addition, small pieces of this plaque may become dislodged and travel to the brain, resulting in a stroke. Seven hundred thousand Americans suffer a stroke in the United States each year, and 150,000 cases are fatal, making it the third leading cause of death in the United States.
Tensile Material Properties of Skeletal Muscle Tissue in Longitudinal and Transverse Directions
Authors: Morrow Duane A. , Haut Donahue Tammy L. , Odegard Gregory M. , Kaufman Kenton R.
Published: March 2014

Since Blix noted that force varies with muscle length [1], many investigators have worked to characterize the passive length-tension properties of skeletal muscle in the tissue’s fiber direction [2]. However, few reports have examined the properties of muscle in either transverse extension or in longitudinal shear [3–4]. Material properties in these three directions are needed to fully characterize computational models, which generally describe muscle as being transversely isotropic, hyperelastic, and isovolumetric [3–6]. Further, previous studies reporting tri-planar material properties indicate that muscle tissue is stiffer in the transverse direction compared to the longitudinal direction [3–4]. This counters conventional notions of transversely isotropic materials, which are generally stiffer in the fiber direction.
Electroosmotic Injection and Chemical Kinetics in Micro Reactors
Authors: Arumbuliyur Comandur Kaushik , Bhagat Ali Asgar S. , Dasgupta Subhashish , Papautsky Ian , Banerjee Rupak K.
Published: March 2014

The study of fluid flow in microchannels is of significant interest due to its application in a wide area of fields ranging from microscale flow injection, cooling of microchips, fuel vaporizer and micro reactors for chemical and biological systems. Design of effective electrokinetic micro reactors requires in-depth understanding of the electrokinetic phenomena and bulk reactions of species in the micro reactor. Although electrokinetic flows are popularly used for applications in the field of capillary electrophoresis (CE) [1], the phenomena of electroosmosis can be conveniently used for bulk transport and mixing of reagents. Electroosmosis occurs when the electrical double layer (EDL) near a solid-liquid interface is created by an external electric field. The uniqueness of electroosmotic flow (EOF) is characterized by plug velocity profile having uniform flow. Devasenathipathy et al. [2] showed that EOF offers a number of significant advantages over conventional pressure driven flow like reduced sample diffusion and controlled sample movement.
Controlled Waveform Chemical Stimulus of Cellular Subdomains for System Identification
Authors: Kuczenski Brandon , Messner William C. , LeDuc Philip R.
Published: March 2014

The dynamic behavior of cells is a subject of extensive investigation. Current attempts to model and describe cell behavior show similarity to traditional engineering models of dynamic systems, often making use of the same vocabulary and principles (e.g. amplification, feedback, regulation, instability). A significant difference between biological dynamic systems and engineered ones is that the latter often feature a designed compensator whose dynamic behavior modulates the dynamic response of the system through closed-loop feedback control. In biological systems, by contrast, the feedback is often implicit, and the investigator has no direct control over modulations which are internal to the system. Although disruptive techniques like synthetic siRNA [1] or genetic modification can certainly change cellular behavior, in some cases it is desirable to probe the dynamics of cellular processes without changing their essential operation, or without substantial delay between applying a perturbation and observing its effects.
Experimental and Theoretical Study of Bovine Aorta and its Elastin
Authors: Zou Yu , Zhang Katherine Yanhang
Published: March 2014

Blood vessels are complex organs with hierarchical ultrastructures. Different kinds of structural supporting fibers, such as collagen and elastin fibers, are cross-linked in a three-dimensional manner to provide stiffness of the tissue. Elastin networks endow blood vessels critical mechanical properties, and are essential to accommodate deformations encountered during physiological functions. Many Pathological conditions involve significant changes in elastin. Therefore it is important to fully characterize and understand the mechanical properties of aorta and its elastin networks. Here we studied, both experimentally and theoretically, the mechanical responses of bovine aorta and its elastin under biaxial loading.
Time-Resolved Study of Laser-Induced Bubbles and Shockwaves in Agar Gel Tissue Phantoms
Authors: Pérez-Gutiérrez Francisco , Evans Rodger , Camacho-López Santiago , Aguilar Guillermo
Published: March 2014

Laser-tissue interactions have been extensively used in a number of biomedical treatments. However, the high optical absorption in tissue and the use of relatively long laser pulses or, in many cases, cw laser exposure, frequently results in excessive laser-heating producing undesirable collateral damage. Short pulsed lasers are one of the most precise tools for delivering energy and can allow for the greatest finesse [1]. Laser pulses with duration of only a few nanoseconds, and as short as a few hundreds of femtoseconds, seem to be a good alternative to minimize or even suppress laser-heating undesirable effects [2].
Instrument and Method for Visualizing and Characterizing Gravity-Induced Flow of Gels in an Environment Simulating Aspects of the Vaginal Lumen
Authors: Kheyfets Vitaly O. , Kieweg Sarah L.
Published: March 2014

Developing a mechanism capable of protecting the vaginal or rectal epithelium from sexually transmitted pathogens can be an effective tool in the prevention of HIV infection [1]. One such tool can come in the form of a microbicide gel, which provides a physical barrier and acts as a delivery vehicle for its active ingredient [1]. In order for the microbicide to be an effective barrier and delivery vehicle, it must have the capability to coat the epithelium for a specific amount of time and sustain its structural integrity under the influence of gravity and other perturbation forces. In addition, to be used as a drug delivery vehicle the microbicide must serve the following functions: coat the surface completely without leaving any of the surface exposed, stay on the surface while influenced by external forces such as gravity and squeezing, and must be able to contain potent concentrations of one or more active microbicidal ingredients.
Noncontact Determination of the Mechanical Properties of the Human Vocal Folds
Authors: Deguchi Shinji , Kawashima Kazutaka
Published: March 2014

Mechanical properties of the vocal folds (such as stiffness or viscoelastic properties) play an essential role in phonation. They affect not only voice quality but also onset threshold of vocal fold self-excited oscillation, a sound source of voice [1]. Many experimental data on the mechanical properties have been reported so far, in which in vitro [2] or in vivo measurement techniques [3] were employed. In vitro measurements give us detailed information on the mechanical properties, yet it would be required to consider possible loss of freshness of the specimen. Meanwhile, current in vivo measurement methods utilize a thin probe to deform the vocal fold tissue located at the back of the throat and hence need technical skills for the surveyor to successfully obtain its loading-deformation relationship.
Peripheral Nerve Strain: A Comparison of Strain Measuring Techniques
Authors: Johnson Joshua E. , Fischer Kenneth J. , McIff Terence E.
Published: March 2014

The main function of the nervous system is to serve the body’s control center and communications network. Each nerve consists of various elements that possess distinct anatomic and physiological properties which allow them to perform their intended roles and function as a unit. Studies have shown the endoneurium, perineurium and epineurium, comprising the successive layers of intraneural connective tissue surrounding nerve fibers, to exhibit different properties [1, 2]. It is therefore important to take this into consideration when investigating mechanical properties of nerves.
An Inverse Finite Element Method for Estimating Elastic Coefficients of Anisotropic and Inhomogeneous Materials
Authors: Raghupathy Ramesh , Barocas Victor H.
Published: March 2014

Elastography, the imaging of soft tissues on the basis of elastic modulus has been actively studied in the recent years. Since cancerous tissue is often stiffer than normal tissue [1] its response to mechanical stimuli is considerably different. Hence information about the mechanical properties of cancers and tumors can be potentially extracted from imaging. This inverse problem of estimating mechanical properties from imaging and displacement data holds promise for applications in medical diagnostics.
Quantifying the Microstructure of Human Sclera Using Small Angle Light Scattering
Authors: Eskinazi Amanda E. , Vande Geest Jonathan P.
Published: March 2014

The role of mechanical forces in the progression of glaucoma has been suggested to be critical, especially in the region of the lamina cribrosa and optic nerve head [1,2]. However, little is known regarding the quantitative mapping of collagen fiber architecture around the scleral globe. Several experimental investigations into the biomechanical response of ocular tissue from animals [3–5] have been performed while comparatively less information is available for the response of human ocular tissue.
Hyaluronic Acid Macromer Concentration Influences Functional MSC Chondrogenesis in Photocrosslinked MSC-Laden Hydrogels
Authors: Erikson Isaac E. , Chung Cindy , Burdick Jason A. , Mauck Robert L.
Published: March 2014

Intrinsic repair of articular cartilage is poor, and so numerous tissue engineering strategies have been developed for producing functional cartilage replacements. Photopolymerizable methacrylated hyaluronic acid (MeHA) hydrogels have been developed as a potential hydrogel that possesses the distinct advantage of being biologically relevant as well as easily modified to generate a range of hydrogel properties [1]. To date, optimization of this hydrogel has been carried out by adjusting macromer molecular weight, concentration, and extent of methacrylation. Recent studies using MeHA hydrogels with auricular chondrocytes have shown that adjustments in these parameters can have significant impact on cell viability and construct maturation. [1, 2].
A Fluid-Structure Interaction Model for 3D Heart Valve Dynamics
Authors: Vigmostad Sarah C. , Udaykumar H. S. , Lu Jia , Sacks Michael S. , Chandran K. B.
Published: March 2014

Bioprosthetic heart valves are valve replacements constructed from animal tissue. Although they are geometrically similar to native aortic valves and offer comparable hemodynamic characteristics in their function, they have limited operational life, often requiring replacement 10–15 years after implantation. Though much is still unknown about bioprosthetic heart valve failure, it is generally accepted that this failure is to some extent due to structural decomposition. Although the mechanism for degradation is not clearly understood, it has been observed that these regions of failure are typically in locations where the leaflet undergoes large flexion and high compressive and tensile stresses [1]. An understanding of bioprosthetic heart valve failure necessitates detailed quantitative information on the complex motion of and the stresses on the leaflets particularly during the opening and closing phases and their relationship to structural failure.
Correlation Between 3D Computational Prediction of Mechanical Function and Simulated Physical Weightbearing in the Cadaveric Lower Leg
Authors: Iaquinto Joseph M. , Wayne Jennifer S.
Published: March 2014

The foot is an intricate three dimensional complex that requires insight into both superficial and deep structures to understand mechanical function. Palpation and clinical tests assist with superficial treatment while radiography is invaluable for interior features. Computational modeling has obtained the capacity to predict mechanical function of diarthrodial joints, with a recent model developed of the lower leg [1]. The aim of this work was to extend the predictive capabilities of the lower leg model to simulate stance weightbearing. Comparisons were made to measurements taken from weightbearing loads applied to the cadaveric limb.