bluuebunny/crossref_metadata_2025 huggingface dataset:
Cyclic Pressure and Angiotensin II Influence the Biomechanical Properties of Aortic Valves
Authors: Myles Valtresa , Liao Jun , Warnock James N.
Published: July 2013

Hypertension is a known risk factor for aortic valve stenosis. The elevated blood pressure increases the transvalvular load and can elicit inflammation and extra-cellular matrix (ECM) remodeling. Elevated cyclic pressure and the vasoactive agent angiotensin II (Ang II) have both been shown to promote collagen synthesis, one of the early hallmarks of aortic sclerosis [1,2]. In the current study, it was hypothesized that the increased collagen production induced by either elevated pressure conditions or the presence of Ang II would affect the mechanical properties of the tissue by increasing stiffness.
Modeling Study Incorporating Depth-Dependent Transverse Reinforcement due to Variation in Collagen Lamellae Interweaving in Corneal Tissue
Authors: Ziegler Kimberly A. , Nguyen Thao D.
Published: July 2013

The cornea is crucial for maintaining refraction and focusing ability of the eye. Small alterations in mechanical behavior of the tissue can cause changes in curvature and structure of the cornea, having adverse affects on visual acuity. Since the corneal stroma makes up 90% of corneal thickness and contains a majority of the tissue’s collagen content, it is considered the dominant contributor to the tissue’s mechanical strength and stiffness, which originates from a complex fiber-reinforced structure [1]. It has been shown that collagen lamellae (comprised of type I collagen fibrils) within a dense, proteoglycan-rich matrix, are highly interwoven in the anterior third of the cornea and the degree of interweaving decreases significantly through the thickness with relatively no interweaving observed in the posterior third [1]. The interwoven structure also varies within the plane of the tissue, gradually increasing from a planar arrangement in the central cornea to a highly interwoven arrangement near the limbus [2].
Upper Body Kinematics of Relaxed Volunteers, Braced Volunteers, Hybrid III ATD, and PMHS in Low-Speed Frontal Sled Tests
Authors: Beeman Stephanie M. , Kemper Andrew R. , Madigan Michael L. , Duma Stefan M.
Published: July 2013

Human occupant responses in motor vehicle collisions (MVCs) are commonly predicted and evaluated in a laboratory using surrogates including human volunteers, anthropomorphic test devices (ATDs), and post mortem human surrogates (PMHSs) [1]. The ultimate goal of these surrogates is to demonstrate a similar response to humans in MVCs that can be used to evaluate human tolerance and enhance vehicle design and safety. The distinguishing attribute of human volunteers that non-human surrogates do not currently possess is the combination of identical human anthropometry, anatomy, and physiologic response of the target population, including resting muscle tone and active bracing capabilities. All human volunteer laboratory testing must be performed at sub-injurious levels due to ethical constraints, while non-human surrogates can be used to examine injurious or traumatic events. Given the capabilities and shortcomings of each surrogate in automobile safety research, performing matched tests with these surrogates can aid in the understanding of the biomechanical response of humans in an impact environment, leading to improvements in ATD design and increased efficacy of safety devices. Therefore, the purpose of this study was to investigate volunteer, ATD, and PMHS occupant kinematic responses in matched low-speed frontal sled tests.
Association of Wall Stress of Human Intracranial Saccular Aneurysm With Coil Packing Density After Coil Embolization
Authors: Pichamuthu Joseph E. , Tsamis Alkiviadis , Jankowitz Brian T. , Vorp David A.
Published: July 2013

Coil embolization has become a widely accepted endovascular procedure for intracranial aneurysms, as an alternative to surgical clipping [1,2]. This procedure involves treating an aneurysm from the inside out, whereby metallic coils are placed into the aneurysm to induce thrombosis of the lumen and eliminate the risk of rupture and hemorrhage. Successful endosaccular packing mainly depends on the morphological features and size of the aneurysm, and the relationship of the aneurysm to the cerebral arteries.
Numerical Study of Epithelial Deformation During Vaginal Application of a Viscoelastic Gel Using a Fluid-Structure Interaction Model
Authors: Hu Bin , Kieweg Sarah L.
Published: July 2013

This paper is one of the components of our research on how to optimize polymeric anti-HIV gels, microbicides [1]. Microbicides are delivered to the vaginal epithelium to protect it from HIV and other sexually transmitted infections. Microbicides may provide a physical barrier amplifying the normal vaginal defenses, as well as destroy the pathogens chemically or inhibit viral infection. Microbicides are a promising solution to provide a low-cost, female-controlled method for protection against HIV and other sexually transmitted pathogens.
Estimated Muscle Loads During Squat Exercise in Microgravity Conditions
Authors: Fregly Christopher D. , Kim Brandon T. , Li Zhao , De Witt John K. , Fregly Benjamin J.
Published: July 2013

Loss of muscle mass in microgravity is one of the primary factors limiting long-term space flight [1]. NASA researchers have developed a number of exercise devices to address this problem. The most recent is the Advanced Resistive Exercise Device (ARED) [2], which is currently used by astronauts on the International Space Station (ISS) to emulate typical free-weight exercises in microgravity. ARED exercise on the ISS is intended to reproduce Earth-level muscle loads, but the actual muscle loads produced remain unknown as they cannot currently be measured directly.
Healthy vs Diseased Transport and Mixing in the Human Left Ventricle
Authors: Hendabadi Sahar , del Alamo Juan C. , Shadden Shawn C.
Published: July 2013

It has become increasingly clear that the dynamics of the left ventricle (LV) plays a major role in dictating overall cardiac health. Phase-contrast magnetic resonance imaging (PCMRI) and Doppler-ultrasound echocardiography can measure flow characteristics inside the human left ventricle in vivo, including diagnostic data useful for evaluating pathological conditions such as cardiomyopathies. Studying these flow patterns is a potential avenue for heart failure diagnosis. Traditional studies based on Eulerian measures computed from instantaneous velocity data, e.g. streamlines, vorticity, Q-criterion, etc., can be insufficient or unreliable to fully understand unsteady blood flow behavior. We used the Finite-Time Lyapunov Exponent (FTLE) approach to compute Lagrangian coherent structures (LCS) to gain insight into how blood is transported inside the LV. LCS can be thought of as special moving boundaries in the flow that partition regions with different dynamics, and whose coordinated motion organizes transport and mixing.
Microposts With Embedded Nanowires to Control Substrate Stiffness
Authors: Bielawski Kevin S. , Sniadecki Nathan J.
Published: July 2013

Cells can sense the stiffness of their substrate and respond through mechanotransduction pathways that lead to changes in cell contractility1. Studies to measure the mechanical response of cells have been primarily performed on passive substrates that do not change stiffness as a cell matures. This paper presents a novel substrate that has local regions of higher stiffness. In the current setup, polymer microposts are stiffened with nickel nanowires in random locations. An experiment was run with cells seeded onto the posts which resulted in a promising trend of an increase in cell force per post as the percentage of stiff posts seen by the cell increased.
Computational Simulations of Ocular Blast Loading and Prediction of Eye Injury Risk
Authors: Stitzel Joel D. , Weaver Ashley A.
Published: July 2013

Ocular injury from blast loading is associated with severe ocular morbidity and visual impairment [1]. Improvised explosive devices are a common cause of ocular injury and were responsible for 51% of ocular war injuries in a study by Mader et al [2].
Developing a Model for Mass Transport of Nitric Oxide in the Lymphatic System
Authors: Wilson John T. , Jafarnejad Mohammad , Walsh Peter , Zawieja David C. , Kaunas Roland , Moore James E.
Published: July 2013

The lymphatic system plays a vital role in maintaining fluid homeostasis. It is responsible for the uptake and return of large particulates and extravasated proteins from interstitial spaces to the venous system. Its dysfunction could result in extracellular edema [1]. It also plays an important role in the immune system and is often the route of metastasis for certain types of cancers.
A Computational Model of Fibroblast Growth Factor-2 Binding to Isolated and Intact Cell Surface Receptors: Effects of Fibroblast Growth Factor-2 Concentration, Flow and Delivery Mode
Authors: Patel Nisha S. , Clyne Alisa Morss
Published: July 2013

Fibroblast growth factor-2 (FGF2) plays an important role in both healthy vascular cell functions and pathogenesis in cancer, atherosclerosis and reduced perfusion in diabetes (1–4). FGF2 therapy and targeted drug delivery have great potential in the treatment of such diseases, but have had little clinical success. FGF2 binding kinetics to heparan sulfate proteoglycan (HSPG) and fibroblast growth factor receptors (FGFR) have been largely studied under static conditions (5), however FGF2 binding to endothelial cells occurs physiologically under fluid flow conditions. Understanding complex FGF2 binding kinetics would enable the development of new anti- and pro-angiogenic therapeutics. We developed a computational model of FGF2 binding to FGFR and HSPG with flow to investigate the effect of fluid flow and FGF2 delivery mode on FGF2 binding to isolated or combined binding sites.
A Robust Method to Characterize Vertebral Geometry In Vivo
Authors: Kao T. H. , Espinoza Orías A. A. , Andersson G. B. J. , An H. S. , Inoue N.
Published: July 2013

Wolff’s law postulates that bone will grow in the direction principal stress, as an effect of adaptation to this loading environment, and therefore will adjust their shape to prevent physiological imbalance. Altered geometry can be a mark of disease progression and degeneration just like a biomarker. For functional reasons, the vertebral body as a bone is not immune to these changes in geometry. Previous work in the literature has documented vertebral body geometry characteristics with age [1], its contribution to lordosis changes [2] and detected some asymmetric features [3]. These few descriptions available in the literature are limited due to their planar approach (radiography or individual CT slice cuts) [1, 2] or use of manual metrology devices that are subject to operator error, which might compromise its repeatability [3]. Based on the Wolff’s law premise, the hypothesis for this study is that a known alteration — spinal degeneration — of the spine configuration (lordosis) will also have an effect on the shape of the vertebral bodies. A common byproduct of spinal degeneration is also the presence of osteophytes in the intervertebral junction. To the best of the authors’ knowledge, no study has attempted to characterize hypothetical changes in vertebral geometry as in a population of low back pain symptomatic/ asymptomatic volunteers in vivo. The aim of this study is to prove said hypothesis by applying an accurate imaging technique that is insensitive to osteophytes and able to measure the vertebral body using subject-specific CT-based 3D models.
A Biomechanical Model of the Thumb That Effectively Replicates Endpoint Forces Produced by Human Subjects and Measured in Anatomical Specimens
Authors: Wohlman Sarah J. , Murray Wendy M.
Published: July 2013

Current biomechanical models of the thumb do not replicate either the maximum pinch forces produced via coordinated muscle actions by human subjects [1] or the magnitudes of the forces produced by individual muscles as quantified in cadaveric specimens [2]. However, compared to the literature, these models either underestimate the forces produced by human subjects [1] or overestimate the magnitudes quantified in cadaveric specimens [3, 4]. Specifically, the model developed by Valero-Cuevas et al (2003) was reported to be four times weaker than the endpoint forces produced during maximum effort by human subjects experimentally [1]. In contrast, Towles et al., (2008) reported simulated endpoint forces substantially greater than the forces produced by individual muscles in cadaveric experiments for six of nine muscles studied. [3]. Similarly, Goehler and Murray (2010) simulated the endpoint forces produced by individual extrinsic muscles and reported results that were approximately 60% larger than the forces measured in cadavers [4].
Glycated Collagen Decreases Urokinase Plasminogen Activator (uPA) Activity in Endothelial Cells
Authors: Mathew Justin G. , Morss Clyne Alisa
Published: July 2013

Angiogenesis is the growth of new blood vessels from pre-existing vessels. Reduced angiogenesis contributes to morbidity and mortality in diabetic patients, since it leads to improper wound healing and reduced blood flow to vital organs (Martin, 2003). Extracellular matrix (ECM) degradation is an initial step in angiogenesis, and the plasminogen system is a driving force behind this degradation.
Computational Modelling of Optogenetics in Cardiac Cells
Authors: Wong Jonathan , Abilez Oscar , Kuhl Ellen
Published: July 2013

Channelrhodopsin-2 (ChR2) is a light-activated ion channel that can allow scientists to electrically activate cells via optical stimulation. Using a combination of existing computational electrophysiological and mechanical cardiac cell models with a novel ChR2 ion channel model, we created a model for ChR2-transduced cardiac myocytes. We implemented this model into a commonly available finite element platform and simulated both the single cell and the tissue electromechanical response. Our simulations show that it is possible to stimulate cardiac tissue optically with ChR2-transduced cells.
Calcium Signaling of Chondrocytes Under Osmotic Stress and Mechanical Stimulation
Authors: Li Wen , Park Miri , Kirn-Safran Catherine , Wang Liyun , Lu X. Lucas
Published: July 2013

Chondrocytes play a critical role in cartilage remodeling by mediating the biosynthesis, organization, and modification of extracellular matrix (ECM) [1]. Previous studies showed that chondrocytes are highly sensitive to the surrounding mechanical and osmotic environments [2]. However, how these signals are perceived and transduced by chondrocytes remains unclear. One of the earliest responses of chondrocytes to stimuli is a transient oscillation in intracellular Ca2+ concentration ([Ca2+]i) [3]. The major objective of this study was to investigate and compare the Ca2+ signaling of chondrocytes, including both primary cells and chondrogenic cell line, under mechanical stimulus [4] and osmotic stress. The roles of seven essential pathways in Ca2+ signaling were further examined using pharmacological inhibitors.
Neurovascular 3D: A Virtual Interface for Creating Aneurysms in a Population-Average Intracranial Arterial Network Model
Authors: Berkowitz Benjamin , Raghavan Madhavan L.
Published: July 2013

The head and neck vasculature is a multi-arterial network that includes the Circle of Willis and numerous afferent and efferent vessels. After diagnosis, an intracranial aneurysm’s location within this vasculature has important implications for the management of the patient — to treat or not, treatment modality and approach, potential for complications, etc. Location can also have important implications for large population research studies designed to test hypotheses on risk factors for growth and rupture such as that by the International study of unruptured intracranial aneurysms (ISUIA). Currently, aneurysm location is communicated by vessel names among healthcare professionals (e.g., between a neuroradiologist and an interventionalist) and at best using codes among research personnel. But this may not do full justice to all aspects of aneurysm location. For instance, information such as proximity to the syphon of the internal carotid artery (ICA) or the orientation at a vessel junction (e.g., is the aneurysm along or opposite to the branching vessel) may be of importance, but rarely recorded in objective ways in the clinic or in the lab. The objective of this study was to develop a software interface (Neurovascular 3D) for recording the characteristics of patients’ aneurysms for use in large-scale scientific studies, and for efficient communication among clinical personnel about the aneurysm’s location and baseline characteristics. Capabilities in the interface would need to include the ability to record precisely within an idealized 3D model, the location, orientation, size and some aspects of aneurysm shape, as well as the ability to review and edit their created models in real time.
Effects of Collagen Microstructure on the Transport Properties of Vascularized Engineered Tissues
Authors: Park Seungman , Whittington Catherine , Yoder Mervin C. , Voytik-Harbin Sherry , Han Bumsoo
Published: July 2013

When vascular perfusion is compromised within the body, a number of physiological phenomena can occur, including the progression of disease states (e.g. peripheral vascular disease), impaired wound healing, and organ/tissue transplant failure. Therefore, there is a need for an engineered tissue construct that promotes therapeutic vasculogenesis by enhancing the formation of functional, stabilized vessel networks that have the ability to integrate with the host vasculature. In order to restore tissue structure and function, a matrix-based delivery system, which combines a biopolymer and endothelial precursor cells, is necessary to ensure the localization and guidance of vessel formation and stabilization.
Dextran and PEG Coating Reduced Nanoparticle Toxicity to Cells
Authors: Yu Miao , Clyne Alisa Morss
Published: July 2013

Iron oxide nanoparticles are of interest for drug delivery, since they can be targeted using a magnetic field. However, prior to using nanoparticles in vivo, they must be shown as relatively non-toxic to cells. We and others have shown that bare iron oxide nanoparticles are readily taken up by cells, where they catalyze production of highly toxic reactive oxygen species (ROS). This oxidative stress disrupts the cell cytoskeleton and alters cell mechanics. [1] Iron oxide nanoparticles under current development for in vivo biomedical applications are often coated with a polysaccharide (eg. dextran) or a polymer (eg. polyethylene glycol, PEG). Both the size and the surface coating of nanoparticle may play an important role in cell toxicity.
Alterations in the Microstructure of the Anterior Mitral Valve Leaflet Under Physiological Stress
Authors: Carruthers Christopher A. , Good Bryan , D’Amore Antonio , Liao Jun , Amini Rouzbeh , Watkins Simon C. , Sacks Michael S.
Published: July 2013

An improved understanding of mitral valve (MV) function remains an important goal for determining mechanisms underlying valve disease and for developing novel therapies. Critical to heart valve tissue homeostasis is the valvular interstitial cells (VICs), which reside in the interstitium and maintain the extracellular matrix (ECM) through both protein synthesis and enzymatic degradation [1]. There is scant quantitative experimental data on the alterations of the MV fiber network reorganization as a function of load, which is critical for implementation of computational strategies that attempt to link this meso-micro scale phenomenon. The observed large scale deformations experienced by VICs could be implicated in mechanotransduction [2], i.e., translation of mechanical stimuli into biochemical signals. Consequently, our goal was to quantitatively characterize the MV microstructure as a function of physiological loads, including localized 3D VIC deformations and relate it to the fiber network.
Optimization of Engineered Ovine Pulmonary Heart Valve Leaflet Tissue Shape for Single Leaflet Replacement
Authors: Fan Rong , Sacks Michael S. , Bayoumi Ahmed , Mayer John E. , Hobson Christopher M. , Wagner William R.
Published: July 2013

Pulmonary valve (PV) replacement surgery is a treatment option for patients with a congenitally defective pulmonary outflow track. While a tissue engineered approach offers many potential advantages, develop of such a valve involves a complex process of optimization. As an intermediate step, we have used a single leaflet replacement surgical model to further our understanding of the in-vivo remodeling process. A critical step is to determine the deformed shape of the replacement PV leaflet under transvalvular pressure. Key factors in this process are: the scaffold anisotropic mechanical properties, optimal thickness, and the exact initial leaflet shape. We have used electrospun poly (ester urethane) ureas (ES-PEUU) scaffolds since they exhibit mechanical properties very similar to the native PV. In this work we present a design framework of the optimal leaflet shape determination utilizing a single sheet of ES-PEUU for single leaflet replacement surgery via finite element (FE) simulation. The mechanical properties of ES-PEUU scaffold for leaflet replacement were obtained from biaxial in-plane tension experiments. Generalized Fung-type hyperelastic constitutive model [1] was implemented into a commercial FE software package to simulate the deformation of ES-PEUU scaffolds under pressure. By perturbing the initial shape of leaflet and simulating its quasi-static deformation under PV diastolic loading, the optimal shape of unloaded leaflet was determined by comparing the deformed shape of leaflet obtained from FE simulation of TEPV with the one from microCT scan of a native ovine PV. In-vitro test of PV after single leaflet replacement was also conducted to validate the developed method.
Determining the Natural Head Posture for Extant Animal Species Using Line-of-Sight From the Eyesocket and Optical Foramen
Authors: Tobaben Eric J. , Martin Larry D. , Fischer Kenneth J.
Published: July 2013

Understanding natural head posture in animals is improtant in interpreting their biomechanics and behavior. For extinct animals, natural posture cannot be directly determined from the fossil record. There have been few prior studies of animal line of sight and head posture. Most line of sight studies have focused on the breadth of binocular vision versus panoramic vision in relation to behavior (predator type or grazer, for instance) or the animals typical environment (open or cluttered) [1]. For head posture some have studied changes in cognition or the environment or related aspects like the eyeball orientation as head posture changes [2]. Still others have focused on the areas of the brain that control 3D head position [3]. However, none of these studies address a method to determine the natural head posture or angle. While there currently is no definitive way to determine natural head angle in extinct animals, it seems reasonable to assume that the natural head posture would place the line of sight in the horizontal plane for most species. Therefore, we hypothesized that the opening for the optical (the optical foremen) and the eye socket structure itself can be used to accurately determine the natural head posture for a large portion of extant and extinct animal species. Specifically, if the skull is oriented such that the plane of sight (the plane common to both lines of sight) is horizontal, then the skull will be in the natural posture. If this hypothesis is shown to be valid, it will provide naturalists a reliable tool to determine the natural head posture (head angle) of extinct animals. The objective of this study was to test the above hypothesis on animals in the Felidae (cats).
Mechanical Loading Reduces Chondrocyte Death After Single Impact Trauma: Porcine Knee Model
Authors: Vernon Lauren L. , Wilensky David G. , Wang Chong , Kaplan Lee D. , Huang Chun-Yuh C.
Published: July 2013

Osteoarthritis often results from degenerative changes induced by trauma such as joint impact injuries sustained during athletics, combat, or motor vehicle accidents. Articular cartilage, avascular in nature, relies of synovial nutrition [1] and lacks sufficient regenerative capabilities [2]. Acute cartilage injuries have been shown to induce cell death [3, 4, 5], leading to reduced chondrocyte density and degenerative changes to the cartilage matrix composition; over time the tissue becomes compromised and loses its ability to maintain and restore itself. It has been demonstrated, that mechanical loading can affect local perfusion and diffusion through the matrix thereby altering the flow of nutrients and metabolites [2, 6]. Furthermore, mechanical loading modulates the chondrocyte biosynthesis of extracellular matrix that is required in the cartilage repair process. In this study, a two part in-vitro porcine knee model was utilized to investigate articular cartilage response immediately following a single impact injury under cyclic mechanical loading conditions.
Sex Differences in Right Ventricular-Vascular Coupling and Pulmonary Artery Impedance in Response to Chronic Hypoxia and Recovery
Authors: Liu Aiping , Tian Lian , Tabima Diana M. , Chesler Naomi C.
Published: July 2013

Pulmonary artery hypertension (PAH) is a female dominant disease (the female-to-male ratio is 4:1), characterized by small distal pulmonary arterial narrowing and large proximal arterial stiffening, which increase right ventricle (RV) afterload and ultimately lead to RV failure [1,2]. Our recent studies have shown that collagen accumulation induced by chronic hypoxia increases the stiffness of the large extralobar pulmonary arteries (PAs) [3], and affects pulmonary vascular impedance (PVZ) [4]. The role of collagen in the female predominance in developing PAH has not been explored to date.
Hydroxyapatite Scaffold Porosity, Bone Regeneration, and Vascularization Using an Adapted CAM Assay
Authors: Wagoner Johnson A. J. , Polak S. J.
Published: July 2013

Hydroxyapatite (HA) is used in a number of applications for bone restoration and implant fixation. Direct-write manufacturing methods enable the fabrication of HA scaffolds with precisely controlled macroporosity (>100μm) between scaffold struts, or rods, and microporosity (<20μm) within the rods [1]. The need for macroporosity for bone regeneration is well documented, though its specific influence on directing vascularization is not as well studied. Limited research has investigated the role of microporosity in bone regeneration or vascularization. This work aims to address these gaps.
Quantitative Mapping of Local Mechanical Properties of Living Cells at Near-Physiological Conditions Using Multi-Harmonic Atomic Force Microscopy
Authors: Cartagena Alexander , Wang Wen-Horng , Geahlen Robert L. , Raman Arvind
Published: July 2013

Measurements of local nanomechanical properties of living cells recently have become extremely important for the cellular biology and biomechanics communities [1]. The measurement of progressive variations in viscoelastic properties of living cells in their native physiological liquid environments can provide significant insight to the mechanistic processes underpinning morphogenesis, mechano-transduction, motility, metastasis, aging, etc. Atomic Force Microscopy (AFM) based biomechanical assays have the unique advantage of resolving/mapping spatially the local nanomechanical properties over the cell surface. However current methods using standard force-volume, force displacement curves [2–3] are very low resolution and low speed making them completely incompatible for biomechanical assays of living cells.
Effects of Hormone Therapy on Regional Surface Strain as a Function of Applied Strain in the Macaque Inferior Glenohumeral Ligament
Authors: Caldwell Jon-Michael E. , Cassilly Ryan T. , Bunting Haley A. , Ahmad Christopher S. , Bigliani Louis U. , Levine William N. , Gardner Thomas R.
Published: July 2013

Hormones such as estrogen are known to have an effect on the biomechanical properties of certain ligaments such as the anterior cruciate ligament in the knee; however, relatively little is known about its effect on the ligaments of the shoulder. The inferior glenohumeral ligament (IGHL) is a static stabilizer of the shoulder that prevents anterior translation of the humeral head. Alterations to the properties of this ligament can result in capsular stretching, increased laxity, and ultimately instability. The cynomolgus macaque (Macaca fascicularis) shares many hormonal similarities with humans including a 28-day menstrual cycle and is a commonly used model for hormone replacement therapy studies. This study uses the female cynomolgus monkey as a model of the human shoulder to determine if estrogen has an effect on the regional surface strain behavior of the inferior glenohumeral ligament.
Bioinspired Anti-Biofilm Surfaces Based on Topographical Cues
Authors: Kargar Mehdi , Saucke Jeff , Nain Amrinder S. , Behkam Bahareh
Published: July 2013

Adhesion of bacteria to surfaces is the starting point for formation of biofilms, which tend to be significantly less responsive to antibiotics and antimicrobial stressors, compared with planktonic bacteria. The physicochemical properties of natural anti-biofilm surfaces are being actively studied to develop bioinspired anti-biofilm strategies. It has been shown that –majority of natural anti-biofilm surfaces have well organized micro/nanoscale surfaces features [1]. The difficulties associated with the manufacturing of well-defined and controlled nano-textured surfaces and complexity of the behaviour of microorganisms interacting with engineered surfaces has limited rigorous quantitative study of the state of adhesion of fouling microorganisms to engineered surfaces. The work presented here aims to advance the current understanding of cell-textured surface interaction with the ultimate goal of developing an anti-biofilm design framework based on topographical cues.
Electric Field Stimulates Angiogenesis via Activation of MAPK/ERK Signaling in Microvascular Endothelial Cells
Authors: Sheikh Abdul Q. , Taghian Toloo , Kogan Andrei , Narmoneva Daria A.
Published: July 2013

Different types of physiological amplitude (40–250 mV/mm) [1] electric fields (EFs) have been shown to influence a wide variety of biological systems [2] and have been used as a therapeutic tool for tissue repair [3]. There has been emerging evidence that certain types of EFs can promote angiogenesis and tissue vascularization [4]. Studies have shown that direct current EF and pulsed EF induced angiogenic responses including cell migration, VEGF release and cytoskeletal reorganization in human endothelial cells (HUVECs) [4, 5]. Similarly different types of EF induced the activation of intracellular MAPK pathways in several non-endothelial cell types. [6, 7]. However, the effect of EF with different modalities on endothelial angiogenic responses and the intracellular pathways remain unknown.
Simulation of Tissue Differentiation During Fracture Healing Within a Collagenous Scaffold Implanted in a Murine Tibia With an Oblique Fracture
Authors: Nasr Saghar , Duncan Neil A.
Published: July 2013

It is known that mechanical factors play a key role in bone formation and regulation of tissue regeneration during skeletal healing. However, the underlying mechanisms are not fully understood. Mechanical loads, such as cyclic compression, torsion and bending are key factors driving the differentiation of mesenchymal stem cells (MSCs). On the other hand, excessive mechanical loading may disrupt the process of healing and lead to non-unions and cell apoptosis. Therefore, effective positive mechanical factors are bounded by a range and frequency. A number of mechanoregulation algorithms have been developed by comparing tissue differentiation patterns under different loading regimes [1, 2, 3, 4]. The aim of this study was to predict the development of differentiated tissues in a closed fracture model treated with a stem cell seeded soft collagenous scaffold under load regimes of axial compression, bending and torsion. The long term goal is to improve our understanding of fracture healing in non-union fractures and develop stem cell based tissue engineering treatments.
CFD Challenge: Solutions Using the Commercial Finite Volume Solver, STAR-CD
Authors: Xiang Jianping , Meng Hui
Published: July 2013

The Meng group has nearly 10 years focused on the image-based CFD research, particularly as applied to cerebral aneurysm flows. For this Challenge, CFD simulations were performed by PhD student Jianping Xiang, using the commercial finite volume solver, STAR-CD.
CFD Challenge: Solutions Using a Finite Element Method Flow Solver Implemented in FEniCS
Authors: Valen-Sendstad Kristian , Steinman David A.
Published: July 2013

FEniCS is a finite element library for ‘automated, efficient solution of differential equations’ (www.fenicsproject.org). The focus has been to develop a high-level software interface that allows the user to type in the equations nearly as they are read. Recent development has involved extensions for parallel computing and building an efficient pipeline for patient specific blood flow simulations based on exporting meshes and boundary markers from Vascular Modelling Toolkit (VMTK, www.vmtk.org). The aim is therefore to evaluate the accuracy and efficiency of one of the developed computational fluid mechanics (CFD) solvers. The simulations were performed according to the given instructions and so that information is not repeated here.
Patterning Anisotropic Collagen Scaffolds for Tendon Insertion Regeneration
Authors: Caliari S. R. , Weisgerber D. W. , Hortensius R. A. , Kelkhoff D. O. , Ramirez M. A. , Harley B. A. C.
Published: July 2013

Tendons are connective tissues that transmit loads between bone and muscle. The biological solution to the problem of connecting relatively compliant tendon to stiffer (∼2 orders of magnitude) bone is a gradient interface zone ∼100μm wide. Over the tendon-bone-junction (TBJ) a linear transition takes place in the ECM inorganic:organic (mineral:collagen) ratio as well as mineral crystallinity from that of tendon to bone. While small TBJ injuries can heal via regeneration, severe defects undergo repair-mediated healing characterized by fibrocartilagenous scar tissue with inferior biomechanical and functional properties. Severe TBJ injuries are common in athletes, the elderly, and following severe craniofacial and extremity trauma. Many tendon injuries (i.e. supraspinatus injuries), particularly those associated with acute trauma, are prone to occur at the TBJ due to high levels of region-specific stress concentrations; rotator cuff tendons injuries, one of the most common TBJ injuries, exhibit re-tears at rates as high as 94%. The scale of such defects and current poor clinical results suggest the need for a biomaterial solution that can mimic the dynamic heterogeneities of the native insertion and tendon body to induce rapid, functional regeneration. Three-dimensional collagen-GAG (CG) scaffolds have been successfully used clinically to regenerate large soft tissue defects (skin, peripheral nerves); they act by mimicking the native extracellular matrix (ECM) of the damaged tissue to prevent wound contraction and scar tissue synthesis. However these scaffolds have not traditionally been used for orthopedics due to an inability to recapitulate two critical features of orthopedic tissues: multiscale structural complexity, biomechanical properties.
Stent Induced Changes to the Radius of Curvature of the Cerebrovasculature
Authors: King Robert M. , Chueh Juyu , van der Bom Imramsjah M. J. , Silva Christine F. , Wakhloo Ajay K. , Gounis Matthew J.
Published: July 2013

Stent implantation has expanded the endovascular treatment of intracranial aneurysms to those with widenecks, that were previously unfavorable to coil embolization. Past studies have found that several mechanisms including stent-induced endothelization and hemodynamic changes due to alteration in vessel geometry may contribute to stable clot formation within the aneurysmal sac and aid in aneurismal healing [1,2]. Change in the angle of the parent arteries after stent-assisted coil embolization of anterior communicating artery (Acom) aneurysms has been measured on projection angiograms; however, use of 2D angiographic datasets to describe changes of vessel angle in 3D may result in significant error. The goal of this study was to quantitatively characterize the change in the radius of curvature (RC) of the parent artery induced by the implantation of an intracranial stent in 3D.
Targeted Loss of Proteoglycans Results in Changes of Frequency-Dependent Viscoelastic Behavior of the Intact Articular Cartilage
Authors: Tang Simon Y. , Alliston Tamara
Published: July 2013

Cartilage is a multi-phasic, viscoelastic material that derives its mechanical behavior of its primary constituents including collagen, proteoglycans, and water. The complex mechanical function of cartilage depends critically on the composition and balance of these constituents. We sought to determine the effects of proteoglycan loss on both the time- and frequency-dependent mechanical behavior of articular cartilage. Using cathepsin d, an enzyme that specifically cleaves proteoglycans, we assessed the in situ mechanical behavior of intact bovine articular cartilage before and after enzymatic digestion using microindentation over loading frequencies ranging between 0.5 hz to 20 hz. The loss of proteoglycans does not affect the elastic components of mechanical behavior (indentation modulus; p = 0.67), but have significant consequences on the viscoelastic components (tan δ; p<0.001). Moreover, the changes in the viscoelastic mechanical behavior are more pronounced at higher loading frequencies (p<0.001). Taken together, these results suggest that proteoglycans are critical for providing dynamic stability for the cartilage tissue.
Irreversible Electroporation Using the Vasculature of an Organ as Fluid Electrodes
Authors: Sano Michael B. , Arena Christopher B. , Garcia Paulo A. , Davalos Rafael V.
Published: July 2013

Electroporation is a non-linear biophysical process in which the application of pulsed electric fields leads to an increase in permeability of cells, presumably through the creation of nanoscale pores in the lipid bilayer [1]. At low pulsing energy, this permeability is reversible and cellular health and function is maintained. Once a critical electric field intensity threshold is surpassed the cell membrane is unable to recover and cell death is induced in a precise and controllable manner with sub-millimeter resolution [2]. This process is referred to as irreversible electroporation (IRE). IRE does not rely on thermal mechanisms and preserves the structure of the underlying extracellular matrix (ECM) as well as nerve conduits and bile ducts [3].
Non-Destructive, Dynamic Imaging of HSP70 Response to Nanoparticle Mediated Photothermal Therapy in a 3D Tumor Mimic
Authors: DeWitt Matthew , Whited Bryce , Hofmann Matthias C. , Lu Peng , Xu Yong , Rylander Marissa Nichole
Published: July 2013

Laser based photothermal therapy is a minimally invasive technique that relies on the absorption of energy by an irradiated tissue sample and results in the deposition of heat to destroy cancerous cells. The inclusion of nanoparticles that act as intense infrared absorbers allows for higher selectivity and additional absorption of laser energy into heat in the desired material. One promising carbonaceous nanoparticle is single walled carbon nanohorns (SWNHs) which have been demonstrated to be effective photoabsorbers [1].
Nanostructure-Enhanced Proliferative Therapy for Ligaments and Tendons
Authors: Ekwueme Emmanuel C. , Empson Yvonne M. , Freeman Joseph W.
Published: July 2013

In our general population, sprains and strains account for 5.7 million visits to emergency rooms in the United States each year1. A strain is an injury to the muscle or tendon due to overuse or trauma. A sprain is a damaged or torn ligament resulting from excessive force or motion having been applied to a joint. While a sprain can occur in any joint, the most common joints to be injured are the knees, ankles, and fingers. Not only must the initial injury be managed and considered, but it would also be very beneficial to have a therapy that prevents chronic joint instability. For those who experience an ankle sprain, for example, it is astounding that the majority are likely to suffer a recurrent injury in that joint2. When the injury results in a torn ligament or tendon, either from recurrent injury or serious initial trauma, ligament and tendon surgical replacement or repair are the only current options. It is estimated that between 100,000 and over 250,000 patients have anterior cruciate ligament (ACL) disruptions each year in the United States, with nearly 50,000 of these injuries requiring surgical reconstruction2. Anyone injured with sprains or strains would greatly benefit from a permanent, nonsurgical strengthening of the ligaments or tendons.
Effect of Different Fixation Techniques on Segmental Kinematics and Load Sharing of Lumbar Spine: A FEM Study
Authors: Kiapour A. , Kiapour A. M. , Serhan H. , Garfin S. , Allen T. , Goel V. K.
Published: July 2013

Fusion has been the gold standard for treatment of various disorders associated with the spine especially at intervertebral disc level. The surgical procedure for fusion often requires fixation of the anterior column of the defected segment with interbody fixation devices such as cages. Anterior (ALIF), transforaminal (TLIF) and lateral (LIF) lumbar interbody fusion are some of the most common techniques for segmental fixation. The unacceptably low fusion rate with the interbody cages, when used as standalone, has led to the practice of combining these devices with posterior instrumentation. The segmental kinematics, the load distribution on the vertebral endplate and on the components of the posterior instrumentation are the key biomechanical parameters which can help to evaluate the performance of interbody fixation techniques with posterior instrumentation. We conducted a finite element (FE) study to compare biomechanics of these fixation methods.
Effectiveness of Negative Pressure in Promoting Tissue Growth Into Porous Metal Implants
Authors: Lamping Jeffrey W. , Bubb Stephen K. , McIff Terence E.
Published: July 2013

Extremity War Injuries (EWI) with large open segmental and periarticular defects constitute a high volume and high morbidity challenge for the military trauma management system. Open segmental tibia and elbow fractures caused by Improvised Explosive Device (IED) wounds, are two examples of such injuries. Several problems occur when trying to repair such a wound. The large, gaping wounds make skin closure difficult. Infection is also a prevalent complication typically caused by debris contaminating the wound. Lastly, large amounts of damaged tissue including segmental bone defects make repair difficult.
Thermal Effects on Osteogenesis of Human Mesenchymal Stem Cells
Authors: Chen Jing , Wang Sihong
Published: July 2013

Intensive studies were reported on the osteogenesis of mesenchymal stem cells (MSC) using chemicals and mechanical loading. However, the maturity of differentiated osteoblasts is not same as that of isolated adult osteoblasts. Thermal treatment could be a missing factor in stem cell differentiation. It was reported that mild heat stimulated bone growth in animal experiments [1–2]. Thermal treatment is also used as a therapy to promote bone repair after injury [3]. In addition, hot shower daily is recommended to osteoarthritis patients. However, the mechanisms for the heat-induced osteogenesis are not completely known and the thermal regulation of human mesenchymal stem cells (hMSCs) differentiation is not well studied. In this study, the direct effects of mild heat shock (HS) on the differentiation of hMSCs into osteoblasts in self-assembling peptide hydrogel were investigated.
Integrin-Focal Adhesion Coupling and Substrate Stiffness Affect Smooth Muscle Alpha Actin Expression in Fibroblasts
Authors: Schroer Alison K. , Merryman W. David
Published: July 2013

Fibroblast cells play a key role in producing and maintaining connective tissue throughout the body. The ability of these cells to differentiate into a more active myofibroblastic phenotype is important during development and wound healing, but prolonged myofibroblast activation can lead to overproduction of extracellular matrix proteins and stiffening of the surrounding tissue. This stiffening can cause heightened differentiation of neighboring fibroblast through force transduction pathways and can lead to detrimental fibrotic pathologies in many organ systems. Atherosclerosis, interstitial lung disease, cirrhosis and heart valve disease are fibrotic diseases that cause significant cost and mortality in our society. Understanding the processes by which cells sense and respond to substrate stiffness is crucial to the treatment of connective tissue diseases. One primary indicator of the myofibroblastic phenotype is the production of α smooth muscle actin (αSMA) bundles called stress fibers which help transmit stress inside the cell and increases the contractility of the cells and their surrounding tissue [1].
Radial Compressive Properties of an Aortic Stent Graft
Authors: Schwarz Chaid , Raghavan Madhavan L.
Published: July 2013

The long-term fixation characteristics of stent grafts used to treat aortic aneurysms are likely related to the nature of its apposition to the aortic wall after deployment. But we only have a rudimentary understanding of the mechanisms involved and the factors that determine the nature of deployment of these implants. One factor that has been shown to be of particular relevance is oversizing — the % difference between the size of the graft to that of the aorta in which it is deployed (oversizing implies the former is larger) [1]. Other proposed factors include the angulation in the aortic neck and stent design. Naturally, issues of mechanics are central to this problem. Computational models of the mechanics involved, if developed with rigor, can be useful for gaining insights into the mechanisms involved and for interrogating the interactions among these multiple factors.
Development of a Multi-Phase Flow Model for Simulating Solid Particle Motion in the Stomach
Authors: Miyagawa Taimei , Imai Yohsuke , Kobayashi Ikuma , Ishikawa Takuji , Yamaguchi Takami
Published: July 2013

Functions of the stomach are storage, mixing and emptying of gastric contents. Among these functions, we focus on the gastric mixing. The stomach shows an antral contraction wave (ACW) that propagates from the proximal antrum to the pylorus. Previous studies using high-resolution concurrent manometry and magnetic resonance imaging (MRI) have suggested that the ACW plays an important role in the gastric mixing. However it is difficult to observe in vivo intragastric fluid motion in detail.
Capture of Magnetic Microspheres in Electrokinetic Flow for Application in Lab-on-Chip Devices
Authors: Das Debarun , Al-Rjoub Marwan , Yadav Jagjit S. , Banerjee Rupak K.
Published: July 2013

Isolation of bio-molecules, cells and pathogens for immunoassays is a critical component in micro total analysis systems (μTAS). Magnetophoretic technique is often used for separation of such target species, where magnetic beads tagged with specific antibodies against cell surface epitopes, are captured in the microfluidic device. In this study, a numerical model is developed for capture of beads under an external magnetic field in electrokinetically driven flow. The results indicate an increase in the number of beads captured when the magnetic field is higher and the flow is driven by lower electric fields.