bluuebunny/crossref_metadata_2025 huggingface dataset:
Wall Shear Stress Fluctuations due to Flow Instability in Intracranial Aneurysms
Authors: Baek Hyoungsu , Jayaraman Mahesh V. , Richardson Peter D. , Karniadakis George Em
Published: July 2013

Experimental studies of an impingement area inside aneurysms showed that loss of smooth muscle cells and degenerative remodeling of vessel walls occur at the region of high wall shear stress (WSS) and WSS gradient where the flow accelerates [1]. Also, a more sensitive response of endothelial cells to turbulent oscillatory shear rather than to laminar and steady shear has been demonstrated experimentally [2]. Therefore, it seems imperative to understand the spatio-temporal behavior of WSS vectors in the impingement (stagnation) locations. To this end, we investigate systematically the oscillatory behavior of WSS vectors inside aneurysms and the flow instability due to the presence of an aneurysm in the internal carotid arteries (ICA), more specifically, at the posterior communicating artery (PCoA) origin.
Validation of Magnetic Resonance Elastography by Dynamic Shear Testing in the Shear Wave Regime
Authors: Okamoto Ruth J. , Clayton Erik H. , Wilson Kate S. , Bayly Philip V.
Published: July 2013

Magnetic resonance elastography (MRE) is a novel experimental technique for probing the dynamic shear modulus of soft biological tissue non-invasively and in vivo. MRE utilizes a standard MRI scanner to acquire images of propagating shear waves through a specimen that is subject to external harmonic mechanical actuation; commonly at frequencies in excess of 200Hz. At steady state, the wavelength of the propagating shear wave can be used to estimate the shear modulus of the tissue. Dynamic shear testing (DST) is also used to characterize soft biomaterials. Thin samples of the material are subject to oscillatory shear strains. Shear force is measured, and converted to shear stress — analysis of this data of a range of frequencies gives a complex shear modulus. The data analysis method assumes that the shear displacement is linear and shear strain is constant through the thickness of the sample. In soft tissues, very thin samples are typically used to avoid inertial effects at higher frequencies. As the thickness of the sample decreases, it is more difficult to cut samples of uniform thickness and to maintain structural integrity of the sample. Thus in practice, measurements of brain tissue properties using DST without inertial correction are limited to low frequencies. In this work, we bridge the frequency regimes of DST and MRE by testing thick samples using DST over a range of frequencies that generates a shear wave in the sample, with a corresponding peak in the measured shear force. The frequency and magnitude of this peak give additional information about the complex shear modulus of the material being tested, and these DST results are interpreted using a finite element (FE) model of the sample. Using this method, we can obtain an estimate of shear modulus in an intermediate frequency regime between that of standard DST and MRE.
Modelling Normal Pressure Hydrocephalus as a ‘Two-Hit’ Disease Using Multiple-Network Poroelastic Theory
Authors: Tully Brett , Ventikos Yiannis
Published: July 2013

The evolution of many cerebral diseases such as Alzheimer’s and Parkinson’s Disease, Hydrocephalus, Cerebral Oedema, Stroke, and Tumour are strongly correlated to a change in the transport properties of fluid in the brain. This research proposes a novel application of Multiple-Network Poroelastic Theory (MPET) to investigate cerebral hydrodynamics through a detailed investigation of multiscalar, spatio-temporal transport of fluid between the cerebral blood, cerebrospinal fluid (CSF) and brain parenchyma. Specifically, MPET is used to interrogate the clinical markers of Normal Pressure Hydrocephalus (NPH).
Test to Fracture of Cardiac Lead Coils in Unidirectional Bending Fatigue
Authors: Campbell Michael P. , Johnson Byron E.
Published: July 2013

Transvenous cardiac leads are a key element of implanted pacing and defibrillation systems, providing the electrical connection between a programmable generator and the heart. Along their pathway, these thin flexible structures are subjected to cyclic in-vivo motion and deformation resulting from patient cardiac contraction, respiration, and arm motion. Medical imaging techniques such as biplane fluoroscopy have shown the in-vivo deformation to be primarily unidirectional cyclic bending.1,2
Improvement of Root Canal Disinfection Protocol Using Er;Cr:YSGG Laser: Theoretical Study of Temperature Distribution in Human Dentin
Authors: Gill Jennifer , Salloum Maher , Zhu Liang
Published: July 2013

There has been a great deal of interest regarding the use of Er;Cr;YSGG laser heating to disinfect human root canal, prior to a root canal procedure. Current disinfection procedures rely on irrigant solutions, such as sodium hypochlorite, which are applied to the canal prior to filling. However, prior experimentation has shown that bacteria are capable of penetrating into the dentin tubules as far as 800 μm, measured laterally from the root canal surface [Haapasalo and Orstavik 1987; Kakoli et al., 2009]. Further studies have proven that irrigants are incapable of destroying bacteria within deep dentin tubules, despite their ability to kill approximately 98% of the bacteria within the canal.
Thermally Reversible Hydrogel Sheets for Adult Stem Cell Culture
Authors: Thirumala Sreedhar , Devireddy Ram V.
Published: July 2013

A simple non-invasive method of cell retrieval using Methylcellulose (MC) coated Tissue Culture Poly-Styrone (TCPS) dishes was developed to allow the creation of single and multilayered adult stem cell sheet constructs while preserving the cell-cell and the cell–extracellular matrices. The optimal combination of MC-water-salt was found to be 12 to 14% of MC (mol. wt. of 15,000) in water with 0.5x PBS (∼150 mOsm). This solution exhibited a gel formation temperature of ∼32°C. The addition (evenly spread) of 200μl of 2mg/ml bovine collagen type -I (pH adjusted to 7.5) over the MC coated surface at 37°C, significantly improved the adult stem cell (ASC) adhesion and proliferation on the hydrogel system.
A Virtual Hemodialyzer Design Project for First-Year Engineers: An Epistemic Game Approach
Authors: Chesler Naomi C. , Bagley Elizabeth , Breckenfeld Eric , West Devin , Shaffer David Williamson
Published: July 2013

Engineering institutions nationwide are pursuing first-year engineering design courses to attract and retain nontraditional students. However, these courses often have high enrollment rates and can be resource intensive. Virtual design projects offer a potential solution to the physical resources requirements but often result in an overly constrained design space, creating uninteresting or non-challenging design problems. We are developing a design problem within a novel virtual environment (i.e., a game) that provides first-year engineering undergraduates with a more authentic engineering design experience and a more complete and accurate understanding of the engineering profession. The design problem presented challenges students to incorporate carbon nanotubes and chemical surfactants into a hemodialysis ultrafiltration unit. Our approach seeks to provide students with experience in the skills, knowledge, values, identity, and epistemology of the engineering profession, which is the epistemic frame of the profession. The virtual environment also provides a uniquely comprehensive platform for assessing the students’ epistemic frame development over time. We anticipate that this approach will be highly engaging to first-year undergraduate engineering students and will help engineering instructors understand how engineers-in-training learn to become engineers.
Detection of Skin Cancer Using Transient/Thermal Imaging
Authors: Çetingül Müge Pirtini , Alani Rhoda M. , Herman Cila
Published: July 2013

The incidence of melanoma in the United States has been increasing dramatically over the past several years [1] with melanoma currently being the sixth most common cancer in the United States. At present, there are no systemic agents available that significantly extend the lifespan of patients with advanced disease and improved survival relies solely on early detection and adequate surgical management [2]. The need to improve the diagnostic accuracy and sensitivity for skin cancer while increasing biopsy efficiency yields to the implementation of imaging technologies in dermatology. Current in-vivo imaging tools in use including digital photography (total cutaneous imaging or imaging of individual lesions), and dermoscopy are highly subjective and without broadly applicable standards or quantitative criteria.
Regulation of Stretch-Induced Mechanotransduction by Cytoskeletal Tension
Authors: Hsu Hui-Ju , Locke Andrea K. , Vanderzyl Susan Q. , Lee Chin-Fu , Kaunas Roland
Published: July 2013

Cytoskeletal tension enables cells to adhere, spread, contract, and migrate. In adherent, non-muscle cells such as endothelial cells and fibroblasts, tension is generated by actomyosin stress fibers applying traction forces to cell-matrix adhesions. Tension extends stress fibers beyond their unloaded lengths and cells maintain a preferred level of fiber strain that depends on actomyosin activity (Lu 2008). Stretching the matrix upon which cells adhere perturbs the cell-matrix traction forces and cells respond by actively re-establishing the pre-existing level of force (Gavara 2006). Sudden large increases or decreases in strain result in rapid stress fiber disassembly and reassembly (Lu 2008), suggesting that perturbing fiber strain from a preferred level stimulates stress fiber turnover.
Probing Dynamic Responses of the Extracellular Matrix to Coupled Mechanical and Chemical Inputs
Authors: Steward Robert L. , Cheng Chao-Min , LeDuc Philip R.
Published: July 2013

The extracellular matrix (ECM) is an important cellular component that provides structural support for cells that form the various connective tissues in the body and has been linked to various important cellular processes. One major, ubiquitously expressed ECM protein, fibronectin (FN) has been well documented to play an important role in the ECM, but most studies have investigated FN and its assembly and structural organization mainly through chemical stimulation. The ECM though likely experiences multiple modes of stimulation such as mechanical and chemical inputs. Since cells and the ECM may experience mechanical and chemical stimulation, we examined how NIH 3T3 fibroblasts altered their ECM in response to applied mechanical and chemical stimulation. Mechanical stimulation revealed an increase in FN matrix formation and secretion as reflected by immunofluorescence as well as FN localization around the cell periphery. Coupling of mechanical stimulation with chemical stimulation via inhibition of Rho activity revealed the same behavior as cells exposed purely to mechanical stimulation. This study is among the first to show the effect of coupled modes of stimulation on the ECM and show a purely mechanics-induced stimulation of ECM formation. These results have implications in a variety of fields including mechanotransduction, biophysics and bioengineering.
Pulsed Heat Shocks to Enhance Collagen Production of Human Dermal Fibroblasts in Ex-Vivo Skin
Authors: Dams S. D. , de Liefde M. , Nuijs A. M. , Oomens C. W. J. , Baaijens F. P. T.
Published: July 2013

Well-known characteristics of aging skin are the development of fine lines and wrinkles, but also changes in skin tone, skin texture, thickness and moisture content [1, 2]. Rejuvenation of the skin aims at reversing the signs of aging and can be established in the epidermis as well as in the dermis. Aged dermis for that matter has a degenerated collagen matrix. To regenerate this matrix, fibroblasts need to be stimulated into synthesizing new collagen. Among the rejuvenation methods used the non-ablative techniques are gaining popularity. These methods produce dermal remodeling without obvious epidermal injury using a thermal approach. The generation of heat would cause collagen injury and contraction followed by collagen synthesis [2, 3]. However, little research on physiological evidence can be found in contemporary literature. In this study, the effects of heat shocks of different temperatures on the expression of procollagen type 1and type 3 of human dermal fibroblasts in ex-vivo skin are investigated.
Towards Non-Invasive Pressure Assessment
Authors: Bijnens Nathalie , Beulen Bart , Brands Peter , Rutten Marcel , van de Vosse Frans
Published: July 2013

In clinical practice, ultrasound is frequently applied to non-invasively assess blood velocity, blood volume flow and blood vessel wall properties such as vessel wall thickness and vessel diameter waveforms. To convert these properties into relevant biomechanical properties that are related to cardiovascular disease (CVD), such as elastic modulus and compliance of the vessel wall, local pressure has to be assessed simultaneously with vessel wall thickness and vessel diameter waveforms. Additionally, accurate estimates of vascular impedance (transfer function between pressure and blood flow) can be a valuable tool for the estimation of the condition of the vessel, e.g., to diagnose stenosis. Studies of arterial impedance in humans, however, are hampered by the lack of reliable non-invasive techniques to simultaneously record pressure and flow locally as a function of time. Local pressure assessment together with flow has great potential for improving the ability to diagnose and monitor CVD.
Generalized Anisotropic Inverse Mechanics: Mechanical Anisotropy Correlates With Structural Anisotropy in Collagen Based Tissue Equivalents
Authors: Raghupathy Ramesh , Lake Spencer P. , Sander Edward A. , Barocas Victor H.
Published: July 2013

Few elastographic methods handle both anisotropy and inhomogeneity. Much of the focus has been on inhomogeneous materials that are locally isotropic. However, most load-bearing tissues (heart, ligament, blood vessels) are highly anisotropic, and the underlying structure is distinct and essential for function. With disease or damage, this structure is altered, and hence the potential for an elastographic tool that identifies regional changes in anisotropy is high. In this study we present a generalized anisotropic inverse mechanics (GAIM) method that is applicable to soft tissues and demonstrate its performance on tissue equivalents which serve as a convenient test case due to their inhomogeneity and the ease of pre-specifying the fiber alignment pattern.
Supercritical Carbon Dioxide Sterilization Minimally Affects Human Allograft Skin Morphology and Biomechanics
Authors: Shaw Joshua , Au Liemin , Hull Barbara , Hunter Shawn
Published: July 2013

Skin-based products are currently used to treat numerous acute and chronic injuries. Allograft skin typically used for burn treatment is recovered aseptically and either cryopreserved or provided fresh shortly after procurement in order to maintain viability for engraftment. Such skin is also further processed in a variety of ways, including decellularization and lyophilization, to create biologic dressings and skin substitutes. Although allograft skin is vigorously screened and disinfected to prevent pathogen transmission it is seldom terminally sterilized, which may be of concern when it is used for patients who are immunocompromised. Thus, the overall goal of this work is to develop a sterile, skin-based biomaterial for potential use as a matrix for tissue regeneration.
Biomechanical Determinants of Plaque Rupture
Authors: Akyildiz Ali Cagdas , Speelman Lambert , Wentzel Jolanda , van der Steen Anton , Gijsen Frank
Published: July 2013

Atherosclerosis is an important cardiovascular disease in which plaque build up occurs in a vessel. The rupture of the cap that covers the plaque of a coronary artery is the underlying cause of the majority of fatal acute myocardial infarctions and sudden coronary deaths [1].
A Mathematical Model of Blood Circulation in the Liver Lobule
Authors: Bonfiglio Andrea , Leungchavaphongse Kritsada , Repetto Rodolfo , Siggers Jennifer H.
Published: July 2013

The liver has a specialized circulation. It is supplied by two main vessels: the hepatic portal vein, carrying nutrient-rich deoxygenated blood, and the hepatic artery, carrying oxygenated blood. The hepatic portal vein supplies up to 80% of the blood. Within the liver, both the portal vein and the hepatic artery undergo a series of successive bifurcations, which end at the portal tracts. Each portal tract contains three vessels: a portal vein, an artery and a bile duct. Blood drains out from the portal tracts into the sinusoidal space and from there into the central veins. The central veins, after a series of converging bifurcations, end at the hepatic veins, which carry blood out of the liver. The sinusoidal space consists of a network of tortuous, interconnected channels called sinusoids. One of the most common and widely accepted descriptions of the primitive units of the liver is the “classic lobule”. A diagram of an idealized arrangement of liver lobules is shown in Figure 1. Each lobule has the shape of a hexagonal prism with a portal tract running along each of the parallel edges and a central vein on the central axis. The remainder of the space is made up of sinusoids.
Investigation of Fiber Wear in a Woven Composite Using Atomic Force Microscopy
Authors: Giordano Michael , Schmid Steven
Published: July 2013

A number of cartilage replacement materials have been suggested including woven materials because of their similar mechanical properties compared to natural tissue [1]. However, the wear performance of woven materials has not been optimized, nor systematically analyzed to date. This paper focuses upon fiber-fiber interactions within a three-dimensional woven material using an atomic force microscope (AFM) to directly simulate abrasive wear events.
Comparison of Analytical and Finite Element Implementation of Exponential Constitutive Models for Valve Tissue Under Micropipette Aspiration
Authors: Zhao Ruogang , Sider Krista Lynn , Simmons Craig A.
Published: July 2013

Micropipette aspiration (MA) has been widely used to measure the biomechanical properties of cells and biomaterials [1]. Typically a linear elastic half-space model is used to fit the experimental load-deformation data [1]. However, load-deformation relationships for most biological tissues are highly nonlinear, suggesting alternative constitutive models are necessary. In the case of aortic heart valve tissue, exponential-type constitutive models have been found to fit the biaxial stress-strain behavior well [2]. Based on these studies, Butcher et al. used an exponential constitutive model to characterize the response of chicken embryonic valve (atrioventricular cushion) under MA [3]. To do so, they implemented an analytical exponential constitutive model [2] and directly related the stress and strain to the experimentally measured pressure and aspiration length. This allowed the authors to fit the tissue MA data without accounting for the complexities of the boundary conditions and multicomponent strain field inherent in MA. However, it is unclear whether the material parameters estimated using this approach are different from those estimated by solving the more complex boundary value problem, which presumably more faithfully simulates the physical process of tissue aspiration.
A Biomechanical Model for Augmented Human Rotator Cuff Repairs
Authors: Aurora Amit , Gatica Jorge E. , van den Bogert Antonie J. , McCarron Jesse A. , Derwin Kathleen A.
Published: July 2013

Rotator cuff tears affect 40% or more of those over age 60 and are a common cause of pain and disability. Surgical repairs have high failure rates that range from 20 to 90%. Hence, natural and synthetic scaffolds are being developed to mechanically augment tendon repairs and to biologically enhance the intrinsic healing potential of the patient. When used as an augmentation device, scaffolds are believed to provide some degree of load sharing in a manner that decreases the likelihood of tendon re-tear. While significant advances are being made in the development of scaffolds, no studies have investigated the degree of load sharing provided by a scaffold used for rotator cuff repair augmentation. Furthermore, the manner in which loads on an augmented rotator cuff repair are distributed amongst the various components of the repair is not known, nor is the relative biomechanical importance of the various components of the repair. To answer these questions, the objectives of this study are to (1) develop quasi-static analytical models of simplified rotator cuff repairs, (2) validate the models by comparing the predicted model force to experimental measurements of force for human rotator cuff repairs, and (3) use the models to predict the degree of load sharing provided by a scaffold used for rotator cuff repair augmentation.
Morphological Differences Between Normal and Diseased Coronary Arteries
Authors: Ryans Jason , Dewitt Sarah E. , Fratino Anthony L. , Marko Kristin , Hyun Sinjae , Qian Zhen , Voros Szilard
Published: July 2013

Coronary artery disease (CAD) including heart attack has been extensively recognized as a dominant health problem in the developed as well as developing countries. According to statistics from the American Heart Association, the latest year for which data is available, CAD were responsible for more than 40% of all deaths and was the largest single cause of death in the United States. In 2002, the direct costs of this disease were estimated around 200 billion dollars.
Condylar Contact During Normal Walking and Lateral Trunk Sway Gait: an EMG-Driven Modeling Approach to Estimate Articular Loading
Authors: Manal Kurt , Innocenti Bernardo , Labey Luc , Buchanan Thomas S.
Published: July 2013

The knee adduction moment has a characteristic double hump pattern with the first peak generally larger than the second. Recently, Mundermann showed that walking with a lateral trunk sway can reduce the 1st peak moment [1]. One might expect from this finding that there would be a decrease in medial compartment loading. This however may be too simplistic a view. Fregly et al. showed that a decrease in knee adduction moment does not guarantee a decrease in medial contact [2]. Moreover, the relationship between net joint moments and loading is not straightforward, especially when agonist/antagonist muscles are co-activated as occurs in patients with pathology. Computational methods can benefit by accounting for subject specific neuromuscular activation patterns while taking into account subject specific dynamics when predicting articular loading. In this paper we outline our EMG-driven modeling approach to predict articular loading during trunk sway for a patient with a force measuring instrumented knee implant. We hypothesized that walking with a lateral trunk sway would: (a) decrease medial contact force, and (b) increase contact force in the lateral compartment.
Localizing Damage in the Cervical Facet Capsular Ligament With Image-Based Multiscale Models
Authors: Sander Edward A. , Quinn Kyle P. , Winkelstein Beth A. , Barocas Victor H.
Published: July 2013

Excessive soft tissue loading can produce pathophysiological changes in the absence of tissue failure or visible injury [1]. In these cases, strain has often been used as a metric to infer the location of damage and define tissue tolerances due to a lack of any other means to detect injury. A recent study of the human facet capsular ligament identified localized anomalous collagen fiber realignment prior to gross failure by correlating fiber alignment vectors derived from quantitative polarized light imaging [1]. The onset of anomalous fiber realignment was strongly associated with a decrease in tissue stiffness in that study, suggesting the occurrence of damage, but the location of this putative damage did not correspond to the location of maximum principal strain. The disconnect between maximum strain and the location of damage may be explained by the heterogeneous structural organization of the facet capsular ligament. By employing image-based multiscale computational models, which account for the local fiber alignment of the tissue, we hypothesized that estimates of the tissue stress field may predict the development of microstructural damage that occurs outside of the location of maximum strain. In this study, multi-scale fiber network models were compared to the experimentally-derived strain fields during facet capsular ligament loading up to the detection of anomalous fiber realignment to begin to understand the relationships between macroscopic tissue loading, collagen fiber reorganization, and the development of initial localized microstructural damage.
Evaluation of Synthetic Composite Tibias for Fracture Testing
Authors: Quenneville Cheryl E. , Greeley Gillian S. , Dunning Cynthia E.
Published: July 2013

Composite synthetic bones are widely used in orthopaedic research. They offer many advantages over post mortem human specimens, including low inter-specimen variability in both geometry and material properties, ready availability, and ease of handling, storage and disposal. Fourth generation models of Sawbones® (Pacific Research Laboratories, Inc., Vashon, WA, USA) are made using a short glass fiber reinforced epoxy resin injected around a core of rigid polyurethane foam. These composite bones have been previously validated to replicate natural bone response at a quasi-static rate [1].
Three-Dimensional Finite Element Analysis of Intervertebral Disc: Effects of In Vivo Loading Conditions and Endplate Calcification on Glucose Distributions
Authors: Jackson Alicia R. , Huang Chun-Yuh , Gu Wei Yong
Published: July 2013

Degeneration of the intervertebral disc (IVD) of the spine is a common condition which has been implicated as a factor leading to low back pain. Poor nutritional supply is believed to be a primary contributor to IVD degeneration. Because the disc is the largest avascular structure in the body, cells must rely on transport of important nutrients, such as glucose and oxygen, from the surrounding vasculature in order to maintain cell viability in the disc tissue. Due to difficulty in obtaining data in vivo, theoretical modeling is a useful tool to supplement experimental results and predict in vivo conditions.
Fluid-Structure Modeling of Lung Epithelial Cell Deformation During the Reopening of Compliant Airways
Authors: Chen Xiaodong , Ghadiali Samir
Published: July 2013

Acute respiratory distress syndrome (ARDS) is a severe lung disease caused by a variety of direct and indirect insults. During ARDS edema fluid accumulated in the lung inhibits gas exchange between air and blood. The main treatment for ARDS is mechanical ventilation. The ventilation of fluid filled lungs involves the propagation of microbubbles over a layer of epithelial cells as shown in Figure 1. Unfortunately, experimental studies [1,3] have demonstrated that the large shear and normal stress gradients generated by microbubbles cause significant cellular deformation and injury. As a result, the mortality rates for ARDS is high (∼30–40%).
Bone Remodeling Simulation Using Abaqus Subroutine USDFLD
Authors: Liu Xiangyi Cheryl , Govindarajan Sekar , Sett Subham
Published: July 2013

Numerical simulation of the adaptive process of bone tissue remodeling can be a useful tool for implant designers, analysts or physicians to achieve long term success of orthopedic implants. While several remodeling theories have been proposed for finite element analysis (FEA), their implementation often requires considerable expertise and can be time consuming. One of the leading bone remodeling algorithms is implemented with Abaqus non-linear FEA in a user-friendly manner, and its potential applications in total hip replacement design are demonstrated in this paper.
Synthesis and Characterization of Boundary Lubricant-Functionalized PVA Gels for Biotribological Applications
Authors: Blum Michelle M. , Ovaert Timothy C.
Published: July 2013

Hyaline cartilage is a material which exhibits ideal tribological properties by maintaining naturally low friction, leading to high wear resistance in articulating joints. When damage to hyaline cartilage occurs, due to diseases such as osteoarthritis or traumatic tissue injuries, tissue regeneration is limited due to cartilage’s avascular and aneural nature. The resulting bone-on-bone contact causes serious pain and limited mobility. Current treatment options are limited to total or partial joint replacements, which are not ideal procedures due to long term failure of components and osteolysis. A vastly improved material is desirable, which better mimics the structure and excellent tribological behavior of natural cartilage.
Vasculature Formation Using Three-Dimensional Cell Printing Technology
Authors: Lee Vivian , Dai Guohao
Published: July 2013

One of the major challenges in tissue engineering is vascularization which provides adequate supplies of oxygen and nutrients to cells within thick tissue-engineered constructs. Oxygen, nutrients and other molecules required for cell growth and survival can only diffuse to 150∼200 μm without proper vascular system. For this reason, thicker tissues have diffusion problems and cannot survive/proliferate well. To date, fabrications of relatively thin tissues such as skin and bladder, and cartilage tissues, which require low level of oxygen and nutrients, are reported. Obstacles in vascularization still exist for thick and complex tissue construct such as kidney, lung and heart (1). Overcoming this problem is a critical step to the clinical applications of tissue engineering (2).
3-Dimensional Ultrasound Elasticity Imaging for Quantitative Cardiac Mechanical Property Assessment: A Numerical Approach
Authors: Tripathy S. , Simon M. A. , Sacks M. S. , Brigham J. C. , Kim K.
Published: July 2013

Quantitative assessment of the cardiac tissue mechanical property or contractility is essential for the prognosis and treatment of various cardiac diseases such as myocardial infarction, pulmonary hypertension, and heart failure. Current evaluation methods are either invasive or limited, mainly due to complex 3-dimensional (3D) geometry and deformation of a heart. 2D imaging techniques assume erroneous planar geometry and deformations, while available 3D imaging techniques have limited functional assessment. Correlation-based 3D ultrasound (US) elasticity imaging (UEI) provides both anatomical and functional information such as mechanical property change of the cardiac walls, which is important for diagnosis and monitoring of the treatment. Using finite element (FE) techniques, one and two ellipsoid chamber cardiac mechanical models were developed, and combined with 3D US radio frequency (RF) data generation program. 3D UEI on the synthesized 3D US volume images were quantitatively analyzed and compared with 2D UEI.
Assessment of Bone Quality Associated With Loosely and Tightly Bound Water
Authors: Ni Qingwen , Nicolella Naniel P.
Published: July 2013

Previous studies have shown that the age-related increase in bone porosity results a decrease in bone strength, and porosity is related to the volume of mobile water in the pores. In addition, since water is also bound to collagen and mineral, changes in the amount of bound water will potentially affect the bone strength. It is known that the removal of the loosely bound water (via hydrogen bonding) requires less energy than the water molecules trapped inside collagen molecules, which in turn requires similar or less energy than water molecules bound to the surface charges of mineral apatite (more ionic in nature). Also, water that is imbedded in the lattice of hydroxyapatite (more covalent in nature) requires the highest energy to dislodge. However, there is no traditional method that can determine mobile and bound water, further for loosely and tightly bound ware accurately, non-destructively and non-invasively. Here, we propose that by using NMR Car-Purcell-Meiboom-Gill (CPMG) spin-spin relaxation measurement to determine the mobile water, and the NMR inversion T2-FID spectrum derived from NMR free induction decay (FID) measurements for estimating the bound and free water distribution. Furthermore, after comparison of the total water lost (weighing method) within tissue by using drying (free dry) on the air to the total mobile water lost measured by NMR CPMG method, then, the total loosely bound water lost can be estimated. Following this, the mechanical test will be used to evaluate the bone quality related to the tightly and loosely bound water within bone. This information can be used to further assessment of bone quality.
A Finite Element Analysis of the C2-C7 Sheep Spine
Authors: DeVries Nicole A. , Kallemeyn Nicole A. , Shivanna Kiran H. , Grosland Nicole M.
Published: July 2013

Due to the limited availability of human cadaveric specimens, sheep are often utilized for in vitro studies of various spinal disorders and surgical techniques. Understanding the similarities and differences between the human and sheep spine is crucial for constructing a valuable study and interpreting the results. Several studies have identified the anatomical similarities between the sheep and human spine; however these studies have been limited to quantifying the anatomic dimensions as opposed to the biomechanical responses [1–2]. Although anatomical similarities are important, biomechanical correspondence is imperative for studying the effects of disorders, surgical techniques, and implant designs. Studies by Wilke and colleagues [3] and Clarke et al. [4] have focused on experimental biomechanics of the sheep cervical functional spinal units (FSUs).
Assessing the Feasibility of a Nailing Operation for Bone Fracture Fixation Using a Cavity-Expansion Based Penetration Model
Authors: Prygoski Matthew P. , Schmid Steven R.
Published: July 2013

After a bone is fractured the two bone segments must be realigned and fixated so that proper healing can occur. It is beneficial and often necessary to also fixate any bone fragments that may have formed during the injury. Traditionally a fracture fixation plate must be inserted using bone screws to hold the bone segments together. Any additional fragments must be attached using screws, bone pins, or wires. Each fracture, especially when complex in nature, may require a unique set of hardware to achieve proper fixation. Proper planning by a skilled surgeon is usually necessary. Insertion of these implants may also be rather invasive since the devices must be inserted into incisions at least as large as the device itself. All of these factors increase the duration of the surgery.
Micro-Engineered Sythetical Extrocellular Metrix for Stem Cell Differentiation Study
Authors: Fu Jianping
Published: July 2013

We report the use of micromolded elastomeric micropost arrays to modulate substrate rigidity independently of effects on adhesive and other material surface properties. We demonstrate that micropost rigidity impacts cell morphology, focal adhesions, cytoskeletal contractility, and stem cell differentiation. Furthermore, these micropost arrays reveal that changes in cytoskeletal contractility can precede stem cell differentiation and be utilized as a non-destructive predictor for fate decisions at the single cell level.
Probing Multicellular Dynamics in Xenopus Laevis Embryonic Development Using a Mechanical Engineering Based Microfluidic Feedback Approach
Authors: Kim YongTae , Joshi Sagar D. , LeDuc Philip R. , Davidson Lance A. , Messner William C.
Published: July 2013

Spatial and temporal regulation of chemical environments in and around cells or tissues for long time periods is important to understand multicellular signaling since the responses to chemical factors control the resulting coordinated events in development. Although progress has been made in command of single cell environments, both long-term and high-speed control of multicellular chemical environments in development is still challenging. We have developed a mechanical engineering based microfluidic feedback approach that allows long-term and high-speed manipulation of a laminar flow interface in a microfluidic channel. This approach enabled long-term spatiotemporal control of chemical conditions over Animal Cap (AC) explants during the gastrulation stage in Xenopus laevis embryonic development. We present the responses of the explants to periodic stimulation of steroid hormone dexamethasone (DEX) by tracking a hormone-activated nuclear-localizing green fluorescent protein tagged glucocorticoid receptor (nuc-GR-GFP). We believe that our approach will be useful in diverse areas including dynamic system and control in microfluidics, embryonic development, and spatiotemporally integrated biological responses.
Computational Model to Predict Oxygen Availability for Cells Cultured Under Flow Conditions
Authors: Kumar B. Karthik , Cassell James P. , Coger Robin N.
Published: July 2013

Tissue bioreactors are flow systems able to support cultured cells over time. Consequently the functionality of these in vivo systems require the cells to be provided with the required substrate, nutrient, and O2. When a bioreactor is used for liver support, the latter requirement is particularly critical since hepatocyte functionalities are highly dependent on O2 [1]. So for bioreactor designers, computational models would serve as a powerful tool for predicting O2 transport dynamics. In the current study, such a model is developed to predict the level of O2 available to hepatocytes dispersed within a porous collagen substrate, for varying flow conditions. This is carried out by intially verifying the model’s accuracy through experiments conducted using a customized flow device and then extending the model to clarify the sensitivity of O2 transport through the cellular space with respect to the flow conditions, the cells’ O2 consumption rates and dissolved O2 levels in the media.
Effect of Joint Center Location on In-Vivo Joint Contact Forces During Walking
Authors: Kim Yoon-Hyuk , Park Won-Man , Phuong Bui Thi Thanh
Published: July 2013

Estimation of in-vivo joint contact forces and muscle forces during walking is important in order to protect the knee joint from injury or provide adequate rehabilitation and exercise protocols [1]. Assessment of muscle forces can help to understand the neuro-muscular coordination related on neurological problems [2]. Accurate quantification of joint contact forces can help to characterize the contact phenomena of articular cartilage at the joint related on osteoarthritis and to improve the implant design for the longevity of joint arthroplasty [3].
A Phenomenological Model of Corrosion in Biodegradable Metallic Stents
Authors: Grogan J. , Leen S. , McHugh P.
Published: July 2013

Coronary stents are tiny scaffolds that are used in the treatment of heart disease. A new generation of metallic stents that dissolve in the body when no longer required have shown promise in a number of clinical applications. However, one of the primary challenges in developing such a stent is maintaining adequate control over the rate at which it dissolves. A model that is capable of representing corrosion induced material degradation in a finite element framework is being developed. Such a model will prove useful in predicting the lifetime of biodegradable metallic stents in vivo.
In Vitro Meniscus Integration Potential is Inversely Correlated With Tissue Maturation State
Authors: Ionescu Lara C. , Garcia Grant H. , Zachry Tiffany L. , Lee Gregory C. , Sennett Brian J. , Mauck Robert L.
Published: July 2013

Meniscal surgeries are amongst the most common procedures performed in orthopedics today. Clinical solutions are few and have limited success, and so partial meniscectomy is a common outcome. While tears are common in older patients, few young patients present with meniscus damage. It is unclear whether juvenile menisci are less susceptible to damage or more given to endogenous repair. Early in development, the menisci are well vascularized throughout their radial expanse, while in adults, vascularity is restricted to the peripheral rim of the tissue, near the synovial margin [1]. Tears in this vascular region often do heal in adults, while those in the avascular inner regions of the tissue do not [2]. This has led to the inference that vascularity is essential for meniscus healing and this manner of thinking has directed numerous repair strategies toward that end [3].
Pericyte-Based Human Tissue Engineered Vascular Grafts: In Vivo Feasibility Assessment
Authors: He Wei , Nieponice Alejandro , Soletti Lorenzo , Hong Yi , Gharaibeh Burhan , Crisan Mihaela , Peault Bruno , Huard Johnny , Wagner William R. , Vorp David A.
Published: July 2013

Although autologous vessel grafts are the gold standard for bypass procedures, they are limited by availability in many cases. Current synthetic grafts are not suitable for small-diameter (ID<6mm) vascular applications due to acute thrombosis. While a tissue-engineered vascular graft (TEVG), constructed by incorporating cells within a biodegradable scaffold, seems to be a possible solution to the challenge, its success greatly relies on an appropriate cell source and an efficient cellular delivery and carrier system. Terminally-differentiated vascular cells have poor self-renewal and expansion capabilities, exhibit phenotype switching in culture, and are difficult to harvest in necessary numbers, all of which represent limitations of their use in tissue engineering. Human adult mesenchymal stem cells (MSCs) exhibit multipotentiality and self-renewal capabilities, are more readily available, and therefore could overcome these limitations [1]. Pericytes closely encircle endothelial cells in capillaries. It has been shown that pericytes purified from multiple tissue types displayed multipotentiality, suggesting that they are developmental precursors of MSC [2].
Serotonin Antagonists Prevent Cytokine and Mechanical Activation of Aortic Valve Interstitial Cells
Authors: Hutcheson Joshua D. , Merryman W. David
Published: July 2013

Degenerative aortic valve disease (DAVD) is the most common heart valve pathology and is especially prevalent in the elderly population. Studies have shown that stenosis, the most severe form of DAVD, increases in prevalence from 0.7% in people between 18 and 44 years of age to over 13% of people over 75 years of age. Furthermore, early symptoms of DAVD have been detected in 29% of patients over 65 years of age. These symptoms are associated with a 50% increase in cardiovascular related morbidity and a similar increase in the risk of myocardial infarction [1]. Currently, aortic valve (AV) replacement surgery is the only method available to correct DAVD, and while these procedures have become less invasive, replacement valves are still rather expensive and do not function as well as native valves. Therefore, the development of a therapeutic that could prevent DAVD would greatly benefit many patients.
Characterizing the Biaxial Mechanical Properties of Vaginal Maternal Adaptations During Pregnancy
Authors: Tokar Stacy , Feola Andrew , Moalli Pamela A. , Abramowitch Steven
Published: July 2013

Pelvic organ prolapse impacts the lives of many women. Injury during vaginal delivery is considered to be one of the greatest risk factors for developing this disorder. In this study, we characterized vaginal adaptations during pregnancy in terms of changes in the mechanical behavior of virgin and mid-pregnant vaginas using a planar biaxial mechanical testing protocol to determine the change necessary to avoid maternal birth injury. The findings of this study show that the vagina is anisotropic and that the tissue becomes more distensible circumferentially by mid-pregnancy in the rodent model.
Reduction in Beam Positioning Error During HIFU Ablation Studies in Tissue Phantoms
Authors: Dasgupta Subhashish , Hariharan Prasanna , Myers Matthew R. , Banerjee Rupak K.
Published: July 2013

Measurements of high intensity focused ultrasound (HIFU) induced temperature rise using thermocouples in tissue phantoms are subject to several types of error which must be accounted for in order to accurately assess the thermal field and predict the outcome of clinical procedures. Thermocouple artifacts due to viscous heating is one source of error. A second source of error involves displacement of the beam relative to the targeted thermocouple junction, due to the difficulty in precisely positioning the very narrow beam. This paper presents an iterative method for removing inaccuracies due to positioning error from the measured temperature data. The refined data is used to quantify the effect of blood flow through large vessels on the efficacy of HIFU procedures. It was determined that blood flow cooling effect causes an order of magnitude decrease in thermal dose at the target within 2 mm of the blood vessel, potentially resulting in incomplete ablation of the tumor. The technique also reveals that thermocouple artifacts exist in significant proportions from about 0.5 to 2.2 times the computed temperature rise in the initial few seconds. The iterative method can aid in clinical procedure planning, especially in predicting the proper HIFU intensity and duration for complete destruction of tumors.
In Vitro Assessment of Rat Heart Force Generation: A Quantitative Approach for Predicting Outcomes From Pluripotent Stem Cell-Derived Therapy for Myocardial Infarction
Authors: Guillou Lionel , Abilez Oscar J. , Baugh Joshua , Billakanti Gyanesh , Zarins Christopher K. , Kuhl Ellen
Published: July 2013

Five million Americans currently suffer from heart failure, with 550,000 new cases diagnosed each year. The most common cause of heart failure is ischemic heart disease with an episode of acute myocardial infarction. Prognosis is poor with an annual mortality rate of 40% the first year, and 10% thereafter. Unfortunately, there is currently no medical therapy to stop or reverse the advancement of heart failure.
Relationship of Knee Articular Cartilage Thickness to Body Mass Index and Gait Mechanics
Authors: Blazek Katerina , Erhart Jennifer , Asay Jessica , Andriacchi Thomas
Published: July 2013

In longitudinal studies, obesity has been shown to be a major risk factor for knee osteoarthritis (OA) (Felson, 1988), but the cause of this increased prevalence is not yet clear. A common hypothesis is that obesity increases joint loads due to increased body mass, causing the articular cartilage to experience higher load and degenerate more quickly (Griffin, 2005). However, it has been shown that in healthy, normal-weight subjects, knee cartilage thickness increases in proportion to the loads applied during ambulation (Andriacchi, 2004). It is not known whether this same relationship also holds true for obese people who do not have OA. Because it is difficult to measure joint loads directly in vivo, the external adduction moment can be used as a surrogate measure of the relative load distribution between the medial and lateral compartments of the knee (Andriacchi 2004). If cartilage responds positively to load, a higher adduction moment will be correlated with thicker cartilage on the medial side and thinner cartilage in the lateral compartment. Similarly, average cartilage thickness should be proportional to body mass index. Therefore the purpose of this study was to examine the following hypotheses in a group of healthy-weight, overweight, and obese individuals: 1. Average cartilage thickness in both compartments is proportional to body mass index (BMI). 2. Average cartilage thickness in the lateral compartment is inversely proportional to the knee adduction moment. 3. Average cartilage thickness in the medial compartment is proportional to the knee adduction moment. 4. The ratio of medial to lateral cartilage thickness is proportional to the adduction moment.