bluuebunny/crossref_metadata_2025 huggingface dataset:
Pulsating Fluid Flows Undergoing Transitions Between Laminar, Transitional, and Turbulent Regimes
Authors: Abraham John P. , Sparrow Eph M. , Lovik Ryan D.
Published: July 2013

The two major fluid flow systems of the human body, blood circulation and respiration, experience timewise pulsations. The variations of the fluid velocity during a pulsation/respiration cycle give rise to transitions in the flow regime during the course of a cycle. At the lowest fluid velocity encountered in the cycle, it is likely that the flow is laminar. As the velocity increases, the laminar regime may transist into a regime called transitional intermittent. Further increases in velocity may lead either to the fully developed intermittent regime or to the fully developed turbulent regime. Once the velocity attains a maximum and begins to decrease, the process of laminarization may be initiated wherein a succession of flow regimes may occur in opposite order to that described in the foregoing.

The current capabilities of numerical simulation are limited to a single, user-specified flow regime, either laminar or turbulent. Consequently, the successive spontaneous flow regime transitions encountered in human-body fluid flows have been heretofore beyond the reach of biomedical investigators. Indeed, a thoroughgoing literature review failed to unearth any biomedical-oriented publications in which flow regime transitions have been taken into account.

The present investigation is aimed at applying, for the first time, a flow transition model previously developed for steady flows to unsteady flows. The flows to be considered are timewise periodic, with amplitudes, periods, and mean values appropriate to blood flows in large arteries. Special consideration will be given to the magnitudes of the wall shear stresses that are created by such flows, since the accumulation of plaque depends decisively on the shear. The work will also take account of variations in the flow geometry.
High Resolution 3D Reconstruction of an Atherosclorotic Plaque by a Combination of Histology and 3D Ultrasound
Authors: Choudhury Ahsan , Luppi Michael , Hopkins Warren , Gao Hao , Das Saroj , Kill Ian , Pinelli Michele , Long Quan
Published: July 2013

The sudden rupture of a vulnerable arterial plaque is a major cause of cerebral ischemic attack. Triggering of sudden rupture is a result of unfavourable plaque morphology, and is also a result of local stress concentration acting on the plaque. Computational stress analysis on a realistic plaque model is an important tool to assess the vulnerability of plaque rupture. However, the accuracy of the stress analysis is heavily dependent on the accuracy of the 3D reconstruction of the plaque geometry. The derivation of accurate vessel geometries from medical imaging has proved to be difficult due to limited image spatial resolution (at about 0.3mm in-plane) and the lack of contrast between the plaque components.
The Effects of Loading Rate and Duration on Mitigation of Osteopenia by Dynamic Muscle Stimulation
Authors: Qin Yi-Xian , Lam Hoyan , Malbari Murtaza
Published: July 2013

Musculoskeletal adaptations to aging and disuse environment have significant physiological effects on skeletal health, i.e., osteopenia and bone loss. Osteoporosis often occurs together with muscle loss. Such musculoskeletal complications cause severe physiologic changes and have been proposed the synergistic effects of muscle function and bone adaptation. The role of mechanobiology in the skeletal tissue may be closely related to load-induced transductive signals, e.g., bone fluid flow, which is proposed to be a critical mediator of bone and muscle adaptation. The skeletal muscle may serve as a muscle pump that may mediate bone mechanotransduction via modulation of intramedullary pressure. Muscular stimulation (MS) is proposed to be used to simultaneously treat both muscle and bone loss. Indeed, our recent data have demonstrated that high frequency, short duration stimulation can inhibit bone loss and muscle atrophy. Although 10 min dynamic loading can effectively attenuate bone loss, it cannot totally recover disuse osteopenia. The optimal parameters required for such treatment are unclear. Studies have separately investigated the optimal signal parameters for bone or muscle. Insertion of recovery periods during high frequency stimulations to extend the loading cycles have shown potential to reduce muscle atrophy by minimizing fatigue and mimicking physiologic contractions, and demonstrated enhancement of bone remodeling. The overall hypothesis for this study is that dynamic MS can enhance anabolic activity in bone, and inhibit bone loss in a functional disuse condition. Combined high frequency and sufficient loading cycle may be able to completely mitigate bone loss induced by disuse osteopenia.
Assessment of Structure Distortion of Paraffin Wax Histology Section of Human Carotid Atherosclerotic Plaque Specimen
Authors: Luppi Michael , Gao Hao , Choudhury Ahsan , Hopkins Warren , Das Saroj , Pinelli Michele , Long Quan
Published: July 2013

Paraffin wax histology analysis is treated as a golden standard to verify biological tissue microstructure. To generate a histology section, the tissue is subject to a sequence of dehydration processes to remove water from the tissue and replace it by wax to maintain the internal tissue structure. This process normally generates significant shrinkage in the specimen [1], adding uncertainties on quantifying region sizes based on histology sections, such as the area of lipid region, fibrous cap thickness (FCT) in human arterial plaque specimens.
Circumferential Residual Stress Distribution and Its Influence in a Diseased Carotid Artery
Authors: Pocaterra Massimo , Gao Hao , Das Saroj , Pinelli Michele , Long Quan
Published: July 2013

Residual stresses are present in a variety of biological tissues, such as the arteries [1]. It is believed that residual stress tends to make stress distribution more uniform throughout normal arterial wall [2]. However, the influence of residual stress in a diseased artery remains unclear. The aim of this study is to investigate the circumferential residual stress in a diseased carotid artery (atherosclerotic plaque) and its influence on the stress distribution under normal blood pressure loading. To achieve a more realistic stress analysis, an anisotropic non-linear material properties based on ANSYS™ framework with parameter constants, obtained according to Gasser et al [3], was used for all simulations in the study.
Stress Analysis on Human Arterial Plaques by Fluid Structure Interactions: Multi-Case Study
Authors: Gao Hao , Long Quan , Graves Martin , Gillard Jonathan H. , Li Zhi-Yong
Published: July 2013

Atherosclerotic plaque rupture has been extensively considered as the leading cause of death in the world. It is believed that high stress within plaque can be an important factor which can trigger the rupture of the plaque. High resolution multi-spectral magnetic resonance imaging (MRI) has allowed the plaque components (arterial wall, lipids, and fibrous cap) to be visualized in vivo [1]. The patient specific finite element model can be generated from the image data to perform stress analysis and provide critical information on understanding plaque rupture mechanisms [2]. The present work is to apply the procedure to a total of 14 patients (S1 ∼ S14), to study the stress distributions on carotid artery plaque reconstructed from multi-spectral magnetic resonance images, and the possible relationships between stress and plaque burdens.
3D Finite Element Modeling of the Biceps Femoris Muscle
Authors: Rehorn Michael R. , Blemker Silvia S.
Published: July 2013

Hamstring strain injury is a significant problem for many athletes [1]. Muscle-tendon (MT) length changes and activation patterns during the sprinting cycle likely contribute to the high risk of injury. It has been suggested that injury may occur during the late swing phase of the sprinting cycle when the hamstring fibers experience activated muscle lengthening [2]. Of the hamstrings muscles, the biceps femoris longhead (BFLH) is the most commonly injured, with the injury most frequently localized along the proximal muscle-tendon junction [3]. We hypothesize that the injuries are localized in this region because it is also the area of highest localized strains.
Stress Analysis of Carotid Atheroma in Transient Ischemic Attack Patients
Authors: Gao Hao , Long Quan , Graves Martin , Gillard Jonathan H. , Li Zhi-Yong
Published: July 2013

Rupture of atherosclerotic plaque is a major cause of mortality. Plaque stress analysis, based on patient-specific multi-sequence in vivo magnetic resonance images (MRI), can provide critical information for the understanding of plaque rupture and could eventually lead to plaque rupture prediction [1].
Determination of the Contact Areas in the Patello-Femoral and Tibio-Femoral Joints During Deep Knee Flexion
Authors: Hauser Ethan W. , Hefzy Mohamed Samir , Blessinger Brian
Published: July 2013

There are many daily activities that require deep knee flexion, such as squatting and kneeling. As the knee moves into deep flexion, the contact characteristics of the knee change substantially. Contact area is inversely related to stress, as area decreases, stress increase. Increased stress levels are associated with cartilage degeneration. An understanding of deep knee flexion kinematics, contact area, and stress has not been fully reached. The primary objective of this study is to determine the contact areas in the knee joint during deep knee flexion by experimental methods and to verify these results with a computer model developed in-house to determine contact areas based on the indirect method used by Hefzy [1].
The Mechanical Behavior of Engineered Hydrogels
Authors: Earnshaw Audrey L. , Roberts Justine J. , Nicodemus Garret D. , Bryant Stephanie J. , Ferguson Virginia L.
Published: July 2013

Agarose and poly(ethylene-glycol) (PEG) are commonly used as scaffolds for cell and tissue engineering applications [1]. Agarose is a natural biomaterial that is thought to be inert [2] and permits growing cells and tissues in a three-dimensional suspension [3]. Gels synthesized from photoreactive poly(ethylene glycol) (PEG) macromonomers are well suited as cell carriers because they can be rapidly photopolymerized in vivo by a chain radical polymerization that is not toxic to cells, including chondrocytes. This paper explores the differences in mechanical behavior between agarose, a physically cross-linked hydrogel, and PEG, a chemically cross-linked hydrogel, to set the foundation for choosing hydrogel properties and chemistries for a desired tissue engineering application.
Inter-Subject Variability in Ground Reaction Force - Walking Speed Relationship Is Related to Different Motion of the Center of Mass
Authors: Boyer Katherine , Rylander Jonathan , Andriacchi Thomas , Beaupre Gary
Published: July 2013

Walking programs provide an attractive intervention to address the preservation of bone mass in the aging population. Research suggests one in three women and one in five men over 50 will experience fractures due to osteoporosis [1,2]. Bone is a mechanically modulated tissue and thus, training programs that prescribe physical activities that dynamically load the skeleton through either muscle contractions (strength training) or locomotion (walking/running) would be expected to have a positive influence on bone mineral density (BMD) preservation. However, attempts to implement activity programs in populations at risk for developing osteoporosis to accrue or simply preserve bone mass have had limited success [3] due to a variable response between subjects. It has been suggested that the failure of these programs to significantly influence bone mass or density may be due to individual differences in the loads generated by the prescribed exercise regimes and/or the knowledge of specific types, intensities and volumes needed for effective osteogenic exercise. Walking, a simple, common activity, presents an interesting opportunity to examine the potential for individual differences in the style of walking to explain the variability in individual results to training programs designed to preserve bone density.
Electromagnetic Field Mediates Capillary-Like Network Formation via MAPK/ERK Signaling Cascade
Authors: Sheikh Abdul Q. , Kogan Andrei , Narmoneva Daria A.
Published: July 2013

Abnormal angiogenesis (formation of capillaries) plays an important role in the impaired diabetic wound healing and has emerged as a new target area for therapeutic interventions. Pulsed magnetic field therapy, which was initially used for healing of bone fractures, has been recently introduced as a potential therapy to treat diabetic and chronic wounds [1], although the mechanisms responsible for improved healing are still unclear. Electromagnetic fields (EMF) have been shown to act as a directional cues in cellular responses such as migration and activations of several signal transduction cascades [2]. Recent literature delineates an important role of GHz EMF (i.e., with an oscillation period of a fraction of a nanosecond) in inducing rapid and sustained phosphorylation of mitrogen-activated kinase and extracellular-signal-regulated kinase (MAPK/ERK) [3]. Recent studies have also implicated MAP kinase in mediating the phosphorylation of Connexin-43 (Cx43) that accompanies regulation of cell-cell communication via connexin gap junctions [4]. Importantly, both MAPK/ERK pathway and Cx43 signaling are involved in the process of angiogenesis [5,6]. Therefore, the goal of this study was to test the hypothesis that high-frequency (7.5GHz) EMFs promote angiogenesis in vitro via MAPK/ERK and/or Cx43 signaling. We used a custom-built EMF exposure setup and a self-assembling peptide nanoscaffold as a controlled angiogenic microenvironment [7] to quantify the effect of EMF on capillary formation and underlying cellular responses.
Synchronous Dynamic In-Vivo Deformation of the Mitral Valve Leaflet and Annulus
Authors: Eckert Chad E. , Gorman Joseph H. , Gorman Robert C. , Sacks Michael S.
Published: July 2013

Improvements in mitral valve (MV) treatments are dependent on a complete understanding of the function, mechanical properties, and underlying mechanobiological responses of the MV. While finite element analyses have provided insight into the cooperative interactions of MV components [1], a lack of quantitative information on the dynamic MV boundary conditions and synchronous leaflet deformation limits present modeling efforts [2]. In this work, we utilized high fidelity transducers implanted in the ovine MV annulus and anterior leaflet to quantify the complete 3D MV kinematics in synchrony. Additionally, effects of systolic blood pressure (SBP) variations on annular and leaflet deformation were investigated.
Corrosion of Metallic Endovascular Stents and Analyses of Wear Debris in Tissues
Authors: Halwani Dina O. , Anderson Peter G. , Brott Brigitta C. , Anayiotos Andreas S. , Lemons Jack E.
Published: July 2013

Corrosion resistance of metallic alloys commonly used in the manufacture of endovascular stents has been determined through in-vitro tests; however, limited information is available regarding the biostability of stent surfaces and their interaction with vascular tissue following implantation. As technology improves, stents are increasingly deployed in complex anatomy and higher risk locations. They are frequently implanted overlapping other stents, either deployed during the same procedure or to treat a recurrent lesion. In addition, with several alloys available for stents such as stainless steel (SS), nickel-titanium (NiTi), cobalt-chromium (CoCr), cobalt-chromium with a tantalum core (CoCr-Ta) and tantalum (Ta); there is an increasing likelihood of overlapping stents of different materials.
Validation of Intra-Operative Measurement Apparatus to Determine the Stiffness Properties of Spinal Motion Segments
Authors: Reutlinger Christoph , Gédet Philippe , Kowal Jens , Rudolph Tobias , Burger Jürgen , Hasler Carol , Büchler Philippe
Published: July 2013

The load-displacement behavior of spinal motion segments is commonly determined from in-vitro experiments on cadaveric spines. However, clinically, it is often desirable to quantify the patient specific biomechanical properties of the spine in-vivo. Load-displacement measurement requires direct access to the appropriate anatomy, which is typically available in spinal surgeries that aim to correct lumbar spinal instability or scoliosis. We propose an approach to measure the spinal load-displacement behavior for use during these surgeries.
An EMG-Driven Forward Dynamics Model to Simulate Stance Phase of Gait
Authors: Shao Qi , Manal Kurt , Buchanan Thomas S.
Published: July 2013

Simulations based on forward dynamics have been used to identify the biomechanical mechanisms how human movement is generated. They used either net joint torques [1] or muscle forces [2, 3, 4] as actuators to drive forward simulation. However, very few models used EMG-based patterns to define muscle excitations [4] or were actually driven by EMGs. Muscle activation patterns vary from subject to subject and from movement to movement, and the activations depend on the control task, sometimes quite different even for the same joint angle and joint torque [5]. Using EMG as input can account for subjects’ different muscle activation patterns and help revealing the neuromuscular control strategies.
Biomechanical Effects of Chiropractic-Based Distraction Therapy on the Behavior of Healthy and Degenerated Cervical Discs: A Finite Element Model Analysis
Authors: Hussain Mozammil , Gay Ralph E. , An Kai-Nan , Tepe Rodger
Published: July 2013

Many neck pain complaints are associated with degenerated discs in cervical spine. Disc degeneration (DD) consists of cascading stages of events with complex changes in disc tissue properties. This results in deterioration of the ability of the disc to perform its function normally. Several biomechanical and biochemical changes occur in the disc with degeneration. Increase in motion segment stiffness and peak stresses in the posterior annulus are some of the gross changes that occur in the disc with degeneration.
Analysis of Natural Knee Rollback Using Lowest Point Method
Authors: Komosa Mark C. , West James E. , Mane Amit M. , Reeve Amber N. , Clary Chadd W. , Maletsky Lorin P.
Published: July 2013

During knee flexion and extension the ACL and PCL help to coordinate the movement and rotation of the knee by constraining the sliding and rolling motions at the joint. In the natural knee the femur pivots about the medial condyle and the femur tends to roll back on the tibia with increasing flexion [1]. The purpose of this study was to observe if and how rollback occurs in the natural knee using the lowest point (LP) method, and to understand how anterior-posterior (AP) motion is related to flexion angle in the natural knee. A better understanding of natural knee femoral rollback will influence future design of total knee arthroplasties.
Fabrication of Cartilage-Bone Specimens for Cartilage Wear Testing
Authors: McGann Megan E. , Wagner Diane R.
Published: July 2013

Experimental techniques to repair focal defects in articular cartilage involve replacing a small area of damaged cartilage with an artificial implant. An important consideration with these devices is the potential for cartilage to wear against the implant surface. To evaluate these implants and to screen for optimal materials and finishes, a method to quickly and accurately predict in vivo cartilage wear is required. Although pin-on-disc wear testers are frequently used to evaluate the wear of engineering materials, and multi-station test machines are available commercially for rapid testing, they have not often been used to test cartilage wear.
Influence of Heart Rate and Area Stenosis on Coronary Diagnostic Parameters in a Porcine Model
Authors: Kolli Kranthi Kumar , Peelukhana Srikara V. , Effat Mohamed , Helmy Tarek , Leesar Massoud , Schneeberger Eric W. , Hand Dwight , Gottliebson William , Banerjee Rupak K.
Published: July 2013

Several parameters have been proposed to assess the physiologic significance of coronary lesions invasively. The purpose of the present study is to determine the effect of heart rate and percentage area stenosis on Fractional Flow Reserve (FFR), which is the ratio of mean pressure distal to stenosis over the mean proximal (aortic) pressure and Pressure Drop Coefficient (CDP), ratio of trans-stenotic pressure gradient to distal dynamic pressure. In-vivo experiments were performed on three Yorkshire pigs, to achieve the objective. It was found that increase in heart rate does have a significant effect on the coronary diagnostic parameters with increase in area stenosis.
Feasibility Study for Applying Irreversible Electroporation to the Treatment of Breast Cancer
Authors: Neal Robert E. , Singh Ravi , Torti Suzy , Davalos Rafael V.
Published: July 2013

Non-thermal irreversible electroporation (IRE) is a new, minimally invasive, localized tissue ablation technique [1]. The procedure uses electrodes to deliver short-length, high voltage electric pulses to destabilize a cell membrane, leading to the creation of nanopores. When the pulses are strong enough, the cell cannot repair the damage and dies [2]. It has been shown that substantial volumes of tissue and cutaneous tumors may be ablated in a non-thermal manner using irreversible electroporation [1, 3]. In addition, this procedure may be predicted by numerical modeling, promotes an immune response, leaves the extracellular matrix intact, does not affect nerves, may be monitored in real-time, and preserves tissue vasculature [2–5].
Cellular Strain Assessment Tool (CSAT): Precision Controlled Cyclic Uniaxial Tensile Loading
Authors: Yung Yu Ching , Vandenburgh Herman , Mooney David J.
Published: July 2013

Cells throughout our body are exposed to various forms of mechanical stimuli[1, 2]. To examine effects of mechanical cyclic strain on vascular cells, several types of strain devices have been developed, and the methods of force application range from use of dynamic indenters[3] to vacuum pressures (both positive[4] or negative[5, 6]) to stretch the bottom surface of the elastic substrate to which the cells are cultured. A number of custom uniaxial strain devices have been developed to examine cells that are normally exposed to lateral stresses[7–11]. However, a limitation to most uniaxial strain devices is that they can only accommodate a limited number of samples[8–12] at one time. Most devices also lack a platform to perform consistent clamping and loading of samples, which can significantly alter substrate strain[8, 9, 13] and ultimately, introduce large variations between experiments. Here we present a computer controlled precision strain application system composed of a custom multi-well uniaxial Cellular Strain Assessment Tool (CSAT) (Figure 1), a microscope adaptable mini CSAT, and custom elastomeric polydimethylsiloxane (PDMS) plates. The effect of cyclic tensile strain on the migration of endothelial cells was also analyzed in this study. Human umbilical vein endothelial cells (HUVECs), cultured in 2D directly on elastomeric polydimethylsiloxane (PDMS) substrates were exposed to cyclic tensile strain at physiologic levels, and demonstrated to enhance EC migration.
Utah bioDesign: An Asynchronous Approach to Team Based Learning
Authors: Parikh Monir K. , Hitchcock Robert W.
Published: July 2013

The University of Utah offers a two semester capstone biomedical engineering design course (bioDesign) where products are developed and prototyped using the guidance of FDA Design Control mandates. During the two semesters, students are required to develop a project plan, marketing requirements, specifications, test plan, results and working prototype. Additionally, design reviews are regularly held in order to provide student teams with constructive feedback from clinicians, coaches, and course instructors. To foster a rich environment for innovation and to better instruct students in problem based learning, we partner student teams with design ideas that have been conceptualized by clinical advisors. This collaboration creates high value relationships maximizing the students’ learning experience while exposing them to best practices. This course offers unique challenges to the students; they must balance the creativity and innovation of design work with the documentation and regulations mandated by the FDA and other regulatory agencies. Since the inception of this course, we have identified various problems with student learning. Over the past 25 years, educators have begun to understand the importance of hands-on, interactive learning experiences in the undergraduate engineering curriculum [1,2]. Therefore, by overcoming the teaching and learning issues associated with this program, we hope to develop a course that empowers student teams to become effective, innovative engineers.
Fiberoptic Microneedle Probes for Tissue Penetration
Authors: Kosoglu Mehmet A. , Rylander Christopher G.
Published: July 2013

Medical diagnostic imaging and therapeutic applications using lasers such as Optical Coherence Tomography (OCT) and laser hyperthermia therapy have limited success due to the lack of penetration depth of light into in vivo tissues. Light can only travel a few millimeters into tissue before the effects of scattering and absorption attenuate it to unuseful levels.
Mechanical Stimulation Enhances the Production of BMP-2 in Ossifying Rat Bone Marrow Organ Cultures
Authors: Gurkan Umut A. , Krueger Adam , Akkus Ozan
Published: July 2013

Bone marrow is a reservoir of mesenchymal stem cells and osteoprogenitors. It was previously shown [1, 2] and we have recently verified that in vitro cultures of bone marrow undergo osteogenesis without addition of osteoinductive stimulants. We hypothesized that the in vitro ossifying bone marrow organ culture system can be used as a model to investigate the dynamics of the osteogenesis process and its mechanoresponsiveness in terms of expression of key osteoinductive factors. The outcomes of these studies can be used to develop more effective tissue engineered substitutes for bone regeneration by the utilization of multiple osteogenic factors with complex/sequential delivery mechanisms.
Surface Temperature Response to Millimeter Wave Exposure as an Indicator of Skin Blood Flow
Authors: Zirlott Carmen D. , Nelson David A.
Published: July 2013

The aim of this research project is to test the feasibility of using low-power radio frequency (RF) radiation operating in the millimeter wave (MMW) range and non-contact infrared temperature acquisition to measure skin blood-flow rates. MMW is the band of the electromagnetic spectrum from 30 to 300 GHZ. It has been shown that millimeter waves will cause a local temperature rise in the skin, without the harmful effects of ionizing radiation [1]. Skin blood flow is a physiological variable that is essential in the assessment of many diseases, such as diabetes, and can also be the determining factor in many other heat-related body functions (i.e. hot flashes in menopausal women) and malfunctions (i.e. heat stroke) [2]. However, there is currently no non-invasive and non-contact means of measuring actual skin blood flow rates in a patient. During this research, millimeter waves at 35 GHz are being used to superficially heat the skin tissues of a rabbit ear. Simultaneous, non-contacting measurement of skin surface temperature could allow the inference of the rate of blood flow to the tissue, based on observed relationships between surface temperature and skin perfusion rates during MMW irradiation at 35 GHz [1, 3].
Hydrodynamics and Semi-Flexible Filament Behavior
Authors: Chandran Preethi L. , Mofrad Mohammad R. K.
Published: July 2013

In this paper we simulate the effect of hydrodynamic interaction on the Brownian dynamics of semiflexible filaments. Semiflexible filaments are those whose entropy-driven bending fluctuations are resisted by the elastic bending stiffness. Semiflexible filaments make up the structural scaffold of cell and tissue matrix, and understanding their dynamic behavior is necessary for studying force transmission and remodeling in cells and tissue matrix. Hydrodynamic interaction refers to force on filament mediated through the local solvent flow around it. The local solvent flow is induced by the motion of the filament itself. Dynamic studies of semiflexible filaments tend to assume a uniform friction coefficient at every point on the filament. However Lagamarsino et al [1] showed that even for a filament in uniform translation, most of the drag is localized at the filament ends, which increases the tendency of the filament to bend and rotate even under a uniform driving force. In this paper we explore how the combined effect of non-uniform friction coefficient due to hydrodynamic screening and the non-uniform local solvent flow due to the filament fluctuations affects its Brownian dynamics.
A Novel Bioreactor for Tissue Engineered Heart Valves Based on Controlled Cyclic Stretching
Authors: Syedain Zeeshan H. , Tranquillo Robert T.
Published: July 2013

The tissue-engineered heart valve (TEHV) is considered a promising alternative for valve replacement, especially in pediatric patients. To date, most TEHVs have been cultured in pulse-flow bioreactors to generate mechanical loads and deformations leading to tissue growth (1, 2). Our approach has been to apply controlled mechanical stretching to induce tissue growth (3). In this study, a novel controlled cyclic stretch bioreactor is presented to enhance functional properties of TEHVs.
Guiding Stem Cell Differentiation Into Neural Lineages With Tunable Collagen Biomaterials
Authors: Monteiro Gary A. , Shreiber David I.
Published: July 2013

The long-term objective of this research is to develop tunable collagen-based biomaterial scaffolds for directed stem cell differentiation into neural lineages to aid in CNS diseases and trauma. Type I collagen is a ubiquitous protein that provides mechanostructural and ligand-induced biochemical cues to cells that attach to the protein via integrin receptors. Previous studies have demonstrated that the mechanical properties of a substrate or tissue can be an important regulator of stem cell differentiation. For example, the mechanical properties polyacrylamide gels can be tuned to induce neural differentiation from stem cells [1, 2]. Mesenchymal stem cells (MSCs) cultured on ployacrylamide gels with low elastic modulus (0.1–1 kPa) resulted in a neural like population. MSCs on 10-fold stiffer matrices that mimic striated muscle elasticity (Emuscle ∼8–17 kPa) lead to spindle-shaped cells similar in shape to myoblasts. Still stiffer gels (25–40 kPa) resulted in osetoblast differentiation. Based on these observations, collagen gels may provide an ideal material for differentiation into neural lineages because of their low compliance.
3D Structural Information of Soft Tissues Using Small Angle Light Scattering
Authors: Gaitan Diana M. , Schmidt David E. , Chew Douglas W. , Vorp David A. , Sacks Michael S.
Published: July 2013

Small angle light scattering (SALS) is a extensively utilized technique for the rapid quantification of the organization and structure of native fibrous soft tissues. In the present work, we developed a method to extend serial histological sections to obtain 3D distribution architectural information. This technique allows for rapid quantification and study of general trends of architectural information over large volume or areas of tissue and is beneficial to study highly heterogeneous tissue where changes in architecture, due to pathologies or stress may induce complex regional changes. An important clinical example is learning the degree of organization of abdominal aortic aneurysm (AAA) tissue. When studying the organization trend in histological sections of AAA tissue, conclusions from the SALS 2D images cannot be drawn due to the high variability of organization from section to section. This is common to diseased tissues due to the altered structure that is otherwise organized in healthy tissue.
Coupling the Haemodynamic Environment to the Evolution of Cerebral Aneurysms
Authors: Watton Paul N. , Ventikos Yiannis , Holzapfel Gerhard A.
Published: July 2013

Cerebral aneurysms are thought to be present in 2–5% of the general population. Most aneurysms remain asymptomatic and of those that are detected, the risk of rupture is relatively low, i.e. 0.1–1% per year. However, very high morbidity and mortality rates are associated with an aneurysm that does rupture (30–50%). Consequently, elective repair of an aneurysm at high risk of rupture may be deemed appropriate. Unfortunately, interventional procedures are themselves not without risk and have morbidity rates of up to 6%. Moreover, it is difficult to quantify the risk of rupture on a patient specific basis: more sophisticated diagnostic criteria are required. Computational models of aneurysm evolution aim to improve the understanding of the aetiology of the disease. The ultimate aim is to predict future evolution and rupture.
Longitudinal Residual Strains in Coronary Arteries
Authors: Wang Ruoya , Gleason Rudy L.
Published: July 2013

Constitutive formulation is fundamental to the study of vascular mechanics. A robust and accurate constitutive model can aid in the design of tissue engineered grafts or provide insights for growth and remodeling studies. Strains in constitutive model are defined with reference to a stress-free configuration. Therefore, identifying the appropriate stress-free configuration is important and has been the focus of many studies. Fung [1] and Vaishnav and Vossoughi [2] independently presented evidence showing that the traction-free state of a blood vessel is not stress-free due to the presence of residual strains. These residual strains are evident when a vessel ring in the unloaded state opens up into a sector in response to a radial cut. Chuong and Fung [3] proposed quantifying these residual strains by measuring the opening angle of the sector. The opening angle is defined as the angle between two lines which join at the midpoint of the inner wall extending to the tips of the inner wall at the location of the radial cut as shown in Figure 1. This technique has now become the canonical method for measuring residual strains in blood vessels. It is believed that this single radial cut can relieve a majority of the vessel’s residual stress [4].
Confocal Microscopy and Image Processing Techniques for Online Monitoring of Engineered Tissue
Authors: Lasher Richard A. , Sachse Frank B. , Hitchcock Robert W.
Published: July 2013

Evaluation of engineered tissue is often limited to endpoint analyses, such as characterizing histology, gene expression and solutes [1]. Most of these applied analysis approaches are based on immunochemistry procedures that require excision, fixation and sectioning of the tissue as well as cell membrane perforation and labeling of proteins [2]. These analyses are time-consuming, do not facilitate high throughput processing and do not allow for online monitoring of engineered tissue. Because of these limitations, there is a need for online, high throughput monitoring techniques to evaluate engineered tissue. In this work, we introduce an approach for microscopic imaging and online analysis of living engineered tissue. The approach is based on application of a non-toxic dye specific for the extracellular space and subsequent interrogation by in vivo confocal microcopy. We hypothesized that the approach will allow for online characterization of cell structure.
Effects of Nonuniform Vessel Wall Properties in Fluid-Structure Interaction Simulations
Authors: Martin K. Heath , Hyun Sinjae
Published: July 2013

Aneurysms are a disease that plagues mankind. Clinicians are in a difficult position when trying to gauge what action, if any, needs to be taken after a patient is found to have an aneurysm. Increasingly, doctors rely on computer simulations to determine the transient 3-D hemodynamics within the aneurysm sac. Specifically, ongoing research is being conducted to characterize aneurysms in order to develop criteria which predict high-risk factors leading to aneurysm rupture, using patient-specific geometries [1–4].
Establishing an Animal Model for the Evaluation of Vaginal Meshes
Authors: Feola Andrew J. , Jones Keisha , Alperin Marianna , Duerr Robbie , Moalli Pam A. , Abramowitch Steven
Published: July 2013

Roughly three million women in the United States give birth vaginally each year [1]. Clinically, the vagina undergoes pronounced adaptations up to the time of delivery, presumably to afford passage of the fetus [2]. Our group has suggested that if these adaptations are not sufficient or if fetus size is too large, an injury to the vagina or its supportive tissues will likely result. Vaginal injury at the time of delivery occurs quite frequently and research examining the levator ani muscle, the major muscular component of the pelvic floor, revealed injury in up to 20% of women who have given birth vaginally [3]. Therefore, vaginal birth is considered one of the greatest risk factors for pelvic floor disorders (i.e. urinary dysfunction and pelvic organ prolapse) later in life.
The Role of Agarose Mechanical Response on the Matrix Synthesis of Nucleus Pulposus Cells: A Pilot Study
Authors: Tasci Arzu , Ettinger Ladina , Ferguson Stephen , Büchler Philippe
Published: July 2013

Low back pain is the most common spinal disorder and its main cause is intervertebral disc (IVD) degeneration. IVD has a major role of withstanding loads generated in the spine during daily activities. However, it has a limited capacity for self-repair. Since it has an avascular structure, the pathways it uses for regeneration is quite complex and not yet well understood. The mechanical stimulation studies on the cell seeded constructs revealed that cells regulate their biosynthetic activity with cyclic loading [1,2]. The mechanical properties of the scaffold might play an important role in the transmission of mechanical signals to the embedded cells. The objective of this study is to investigate the effect of agarose concentration on the amount of extracellular matrix synthesis in IVD cell seeded constructs under static culture and cyclic loading conditions.
A Pin-to-Hole Spark Discharge Plasma Generates Nitric Oxide and Can Be Safely Applied to an Endothelial Cell Monolayer
Authors: Graham Drew A. , Dobrynin Danil V. , Fridman Alexander , Friedman Gary , Clyne Alisa Morss
Published: July 2013

Endothelial cells line all blood vessels and regulate many homeostatic functions (e.g. platelet aggregation, vascular tone, vascular cell proliferation, leukocyte adhesion) by production of the signaling molecule nitric oxide (NO). NO bioavailability and thus endothelial cell function are compromised in many chronic disease states, including diabetes mellitus and its associated micro- and macrovascular complications (e.g. impaired wound healing and atherosclerosis, respectively) [1]. In the specific case of diabetic wound healing, application of exogenous NO to the diseased tissue may help restore critical NO-mediated processes and could positively impact healing and overall patient health [2]. We have developed a novel pin-to-hole spark discharge plasma device that generates NO and can be applied to cultured endothelial cells with minimal cell injury or death. We propose that this plasma device represents a promising novel method for topical NO application.
Collagen Fiber Structure Correlates With Mechanical Environment in Healing Myocardial Infarcts
Authors: Fomovsky Gregory M. , Holmes Jeffrey W.
Published: July 2013

Mechanics of healing myocardial infarcts are an important determinant of ventricular function. Large collagen fibers are the major contributors to the mechanical properties of healing scar. It has been suggested that an anisotropic structure, as observed in healing pig scars, may help preserve ventricular function, and that the alignment of collagen fibers could be guided by the regional mechanical environment in the infarct — in pig scars the alignment of collagen fibers was in the direction of greatest stretch [1]. By contrast, in the standard rat model of infarction we found that scars are structurally and mechanically isotropic at all time points in healing [2].
Microstructurally Motivated Constitutive Models for Mouse Arteries
Authors: Hansen Laura , Wan William , Gleason Rudolph
Published: July 2013

Vascular remodeling occurs as cells sense changes in their mechanical environment. Thus, quantifying the cells’ local environment in terms of stress and strain distributions is an important aspect in studies of vascular remodeling. Knowledge of the constitutive behavior of vessel will allow the local stresses and strains to be calculated given applied loads and geometry. The goal of this study is to determine material parameters for several constitutive models by fitting biaxial testing data from mouse carotid arteries cultured under different axial loading conditions [1].
Effects of Muscle Moment Arm Variation on Performance During the Acceleration Phase of Sprinting: A Computer Simulation Study
Authors: Piazza Stephen J.
Published: July 2013

Elite sprinters are differentiated from merely good sprinters by their performance during the first 20 m of a 100 m race [1]. The impulse of the ground reaction force in the forward direction during the sprint start has been found to correlate negatively with overall race time indicating that the best sprinters are the ones who are able to accelerate rapidly at the start of a race. Many factors have been examined to determine the anatomical and physiological characteristics that contribute to sprinting ability, including muscle fiber type, muscle size, and muscle architecture parameters such as fascicle length and pennation angle. Joint structure has received less attention, although it has the potential to influence sprint performance in complex ways.
Real Time Observation and Quantification of Shear-Induced Collagen Self-Assembly
Authors: Saeidi Nima , Sander Edward , Ruberti Jeffrey
Published: July 2013

Collagen is the most abundant protein in the extracellular matrix (ECM) of vertebrates and is distributed widely throughout connective tissues. Fibrillar collagen is the principal load-bearing molecule in vertebrates (e.g. type I in tendon and ligament and type II in cartilage). Its inherent biocompatibility makes collagen an attractive scaffolding material candidate for tissue engineering. Although use of 2-D or 3-D collagen networks as a substrate for cell culturing have provided invaluable information about cell-ECM interactions, it has not been very successful in producing load-bearing tissue-engineered constructs. We attribute the fundamental problem to the use of disorganized collagen which may interfere with the ability of cells to generate organization. Several research groups have developed methods to produce organized layer(s) of collagen fibrils de novo (often with the intention of using them for guiding cell culture systems). Methods employed to influence collagen fibril organization during self-assembly include, electro-spinning [1], the use of strong magnetic fields [2–4], electrical gradients [5], flows through a microfluidic channel [6, 7], a combination of fluid flow and magnetic field [8], dip-pen nanolithography [9], cholesteric methods [10], and even freezing and thawing [11]. Although there has been some progress in controlling the alignment of collagen fibrils in vitro, there are many unknown factors which govern directed collagen self-assembly.
Cervical Posterior Fusion Rods Undergo Substantial Bending Deformations for Activities of Daily Living
Authors: Rodriguez J. P. , Scheer J. , Eguizabal J. , Buckley J. M. , McClellan T. , Deviren V. , Ames C.
Published: July 2013

Cervical corpectomy is a procedure most commonly indicated for resection of metastatic disease in the vertebra, access to the spinal cord tumors and inflammatory or infectious lesions.[1] Posterior occipitocervical instrumentation with rods and lateral mass screws has been shown to be a rigid fixation technique in this region [2] and, small diameter rods are thought to be lighter weight, less prominent and less likely to be associated with screw pullout.[3] Still, deformity imposed upon small diameter rods, by the weight of the head, the cervical spine, and spinal ligaments has yet to be quantified. Anecdotal observations show that the rods lose their lordotic curvature and patients fuse in a kyphotic curve making daily living more difficult. The goal of this study is to examine the mechanical behavior of these rods in situ under physiologic loading conditions reflective of activies of daily living.
Regulation of Tendon Tissue Engineered Construct Stiffness by Culture Time, Mesenchymal Stem Cells and Mechanical Stimulation
Authors: Jain Abhishek , Kinneberg Kirsten R. C. , Nirmalanandhan Victor S. , Shearn Jason T. , Powell Heather M. , Gooch Cynthia , Butler David L.
Published: July 2013

More than 57.2 million episodes of musculoskeletal injuries were recorded in 2004 in the United States, costing the US economy more than $254 billion [1, 2]. Approximately 45% of these are tendon, ligament and joint capsule related injuries [3]. Tissue engineering approaches have emerged as an attractive alternative to conventional and oftentimes ineffective treatment methods. Implanting MSC-seeded collagen tissue engineered constructs (TECs) in the central defects of patellar tendon (PT) has significantly improved repair biomechanics compared to natural healing as well as acellular repairs in the rabbit model [4, 5]. Mechanically stimulating these MSC-collagen TECs further improved repair outcome, and TEC stiffness at the time of surgery positively correlated with and predicted repair stiffness twelve weeks after surgery [6, 7]. Although these improvements were observed twelve weeks after surgery, repairs were still not strong enough to withstand forces that might arise during more strenuous activities.
Development of a Skull-T2 Finite Element Model for the Investigation of Subluxation-Based Upper Cervical Chiropractic Manipulation
Authors: Liu Xia , Potluri Tejaswy , Kulkarni Nikhil , Chinthakunta Suresh , Goel Vijay , Denton Keith , Palmer James
Published: July 2013

Chiropractors routinely manipulate cervical spines for treating neck pain and headaches. However, limited quantitative information is available about the mechanical response (e.g., displacement, ligament stress, load transfer) during a cervical spinal manipulation.
Techniques Beyond Range of Motion for Analyzing Spinal Instrumentation Utilizing a CT Based Specimen Specific Solid Model
Authors: Cheng Boyle C. , Cook Daniel J. , Jegapragasan Mithulan , Cuchanski Mathieu , Patwardhan Avinash
Published: July 2013

Motion preservation technology for the spine has specific design goals that differ dramatically from fixation technology. In order to accurately characterize motion preservation devices, new methods of biomechanical testing along with new metrics for comparison are needed. Devices designed to serve as an adjunct to fusion, i.e., spinal fixation instrumentation, have traditionally relied on arthrodesis to off load the implant over time as the fusion mass gains structural integrity. However, motion preservation devices are expected to function continuously for extended periods of time.