bluuebunny/crossref_metadata_2025 huggingface dataset:
Channel Geometry Effects on Red Blood Cell Dynamics and the Resulting ATP Release
Authors: Forsyth Alison M. , Owrutsky Philip D. , Wan Jiandi , Stone Howard A.
Published: July 2013

In shear flow, red blood cells (RBCs) exhibit a variety of dynamic behaviors such as translation, tumbling, swinging, and tank-treading. The physiological consequences of these dynamic behaviors, however, are unknown. For example, how different cell dynamics, be it translation, tumbling, or tank-treading relate to ATP release and how these dynamics are altered by pathological geometries such as constrictions and plaque formations at asymmetric bifurcations are not known. Using microfluidic channels to mimic pathological geometries and RBCs with attached carboxylate beads, to follow any relevant motion, we are able to quantify the dynamical response of red cells to specific pathological geometries with in vitro models. Further, by using an ATP-luciferase enzymatic reaction we set out to determine if there is a functional difference, via chemical release, in cell behaviors. Previously, we correlated RBC deformation and ATP release (Wan et al, PNAS 2008) which in vivo is known to stimulate nitric oxide production, leading to vasodilation. High-speed video and a probability-based cell tracking algorithm make it possible to study large numbers of cells. Preliminary experiments have shown that when cells enter a constriction, there are increased instances of tumbling along constriction wall, while cells more central in the constriction are aligned and deformed by the entrance flow. The relation between the observed cell behaviors and resulting ATP release will be reported.
Characterization of Fiber Organization in Rat Corneo-Scleral Shells Using Small Angle Light Scattering
Authors: Ethier C. Ross , Dahlmann Annegret , Vijay Sauparnika , Khaw Peng T. , Girard Michaël J. A.
Published: July 2013

Glaucoma is the second most common cause of blindness worldwide. It is associated with structural damage and a progressive loss of nerve cells — which transmit visual information from the retina to the brain — within the optic nerve head (ONH) at the posterior eye. Glaucoma was once thought to occur only in eyes with elevated intraocular pressure (IOP) and, to date, lowering IOP is the only clinical treatment proven to be beneficial for slowing its progression. However, the success rate of such therapy is only about 50% and multiple lines of evidence now indicate that IOP is not the only important risk factor in the disease since glaucoma can develop at either normal or elevated IOP without distinct etiology.
Intercellular Calcium Wave Propagation in Linear and Circuit-Like Bone Cell Networks
Authors: Lu X. Lucas , Huo Bo , Baik Andrew D. , Guo X. Edward
Published: July 2013

Intracellular calcium ([Ca2+]i) transients in response to mechanical stimulation can be propagated to neighboring cells in bone cell networks, which provides an essential mechanism for cell-cell communication in bone. Transfer of intracellular second messengers (e.g., IP3 and Ca2+) through gap junction pores and the diffusion of extracellular ATP to activate membrane receptors have long been conjectured as the two major pathways for intercellular Ca2+ wave propagation [1]. In this study, by comparing the calcium wave in open-end linear and looped circuit-like cell chains, the roles of gap junction intercellular communication (GJIC) and extracellular ATP diffusion in calcium wave propagation in bone cell networks were examined. The results were further confirmed with pathway-inhibitor studies performed on linear cell chains.
Fracture Mechanisms in Bovine Aorta
Authors: Haslach Henry W. , Chung Jonathan , Molotsky Aviva
Published: July 2013

Rupture of vascular tissue in the circulatory system under non-impact loading is involved in potentially life threatening events such as Marfan’s syndrome or rupture of small renal veins during shock wave lithotripsy. The rupture mechanisms are not well-understood. The complexity of the artery wall precludes the use of rupture theories invented for metals or for fibered composites with a homogeneous matrix. Artery tissue is composed of ground material, smooth muscle cells, elastin and collagen. The collagen fibers, which are generally circumferentially oriented, are the load carrying material after large deformations. Clark and Glagov [1] propose that the media of an elastic artery is built of musculo-elastic fascicles made up of a layer of circumferentially oriented SMC that lie parallel and between two elastin lamellae. Between the elastin sheets of adjacent elements are interspersed collagen fiber bundles.
Two Layer Fluid Stress Analysis During Airway Closure
Authors: Tai Cheng-feng , Halpern David , Grotberg James B.
Published: July 2013

There are several mechanisms which may cause airway closure in the lung. In this paper, we focus on airway closure due to the capillary instability [1]. In Gauglitz and Radke’s study [2], they showed that once the ratio of film thickness to tube radius is larger than 0.12, airway closure could occur. The induced interfacial deformation creates a driving pressure which forces more liquid into a growing bulge. The interface will then deform rapidly towards the end of the closure process due to the presence of large curvatures, which create strong driving pressures and will eventually lead to the formation of a liquid plug. Due to the velocity and pressure gradients in the liquid film caused by the instability, stresses, including normal and shear stresses on the airway wall, will be induced. The epithelial cells on the inner wall of the airway may be injured by these induced stresses. The purpose of this study is to measure the stresses on airway numerically and determine if the magnitude of the stresses are sufficient to injure the epithelial cells.
Histology and Trabecular Architecture of the Brain for Modeling of Subarachnoid Space
Authors: Saboori Parisa , Sadegh Ali
Published: July 2013

Subarachnoid space (SAS) plays an important role in transferring and or damping the impact load or angular acceleration to the brain (Zoghi Sadegh 2009). Previous investigations have over simplified the complex architecture of the trabeculae of SAS and employed soft solid materials. The goal of this study is to investigate the histology, architecture and mechanotransduction of subarachnoid space and in particular the trabeculae. The results of this study facilitate future modeling of the brain and thereby better understanding of the TBI.
The Effects of Biaxial Preconditioning on Failure of Acelluluar Collagen Gels
Authors: Dean Ryan M. , Sander Edward A. , Barocas Victor H.
Published: July 2013

Due to collagen’s importance as an extracellular matrix (ECM) structural protein, it has often been used as a scaffold material for engineered or model tissue [1]. In order to correctly generate new tissues, the scaffolding must mimic the native ECM. The mechanical properties are crucial not only as a structural support but also to allow for cell differentiation [1]. Preconditioning is a processing technique where a sample of soft tissue material is subjected to cyclical strain. As a result, the fibers align in accordance with the direction of preconditioning [2]. Such realignment alters the mechanical properties of the tissue. In order to design more effective tissue engineering scaffolds, it is important to characterize the effects of preconditioning on the damage and failure of collagen constructs. This study attempts to understand how preconditioning alters the stresses, strains, and failure of a sample when it is subjected to a load in different orientations.
A Validated Finite Element Model of Force in Active and Passive Skeletal Muscle
Authors: Morrow Duane A. , Haut Donahue Tammy L. , Odegard Gregory M. , Kaufman Kenton R.
Published: July 2013

A fully 3D, continuum mechanics based model of skeletal muscle, validated against experimental force data, can be used to computationally solve for individual muscle forces. A constitutive formulation, representing muscle as a transversely isotropic, hyperelastic, and isovolumetric material [1] has been implemented in a finite element model (FEM) of passive skeletal muscle and validated against experimental tension measurements [2]. Of further interest is an expanded formulation that will allow for the addition of muscle activation levels on the overall skeletal muscle force generation. The purpose of this study was to expand the FEA model to include muscle activation and validate it with tests of active skeletal muscle tissue at varied lengths.
Identification of Atheroprone Morphological Features in Wall Shear Stress Waveforms in Carotid Bifurcations: A CFD-Based Integrated Approach
Authors: Gallo D. , Di Benedetto G. , Gaetano L. , Massai D. , Antiga L. , Ponzini R. , Deriu M. A. , Redaelli A. , Morbiducci U.
Published: July 2013

Vascular endothelial cells functions are modulated by shear stress at vessel wall. The presence of “abnormal” blood flow patterns can give rise to local variations from physiological wall shear stress (WSS) time histories. These variations might be risk factors that increase a vessel’s atherosusceptibility.
Mitigation of Bone Loss by Dynamic Hydraulic Pressure Stimulation in a Rat Disuse Model
Authors: Hu M. , Cheng J. , Ferreri S. , Serra-Hsu F. , Lin W. , Qin Y. X.
Published: July 2013

Osteoporosis is a skeletal disease resulting in diminished bone mass and altered bone microstructure, which leads to more fragile bones that have higher risk of fractures[1]. Approximately 44 million people have been diagnosed for osteoporosis nationwide[2]. It also causes nearly 1.5 million fractures annually. In order to prevent from such bone loss and to enhance bone quality, effective clinical treatments, e.g. using non-pharmacological approach, are in great need.
A New Fluorescence Photobleaching Method for Determining Solute Diffusive-Reactive Properties in Biological Tissues
Authors: Travascio Francesco , Gu Wei Yong
Published: July 2013

Knowledge of solute transport in biological tissues is fundamental in order to understand cell nutrition and biosynthetic activity, and to design and fabricate tissue engineered constructs.
Less Diffuse Damage was Observed in Osteogenesis Imperfecta Mice Femurs Than Wild-Type Controls
Authors: Dong X. Neil , Zoghi Mahyar , Ran Qitao , Wang Xiaodu
Published: July 2013

Accumulation of microdamage contributes to the deterioration of bone quality with aging among the elderly [1]. Microdamage formation in bone is dependent on its ultrastructural constituents. At the ultrastructural level, bone is a fiber-reinforced composite material in which mineral crystals are responsible for its stiffness and collagen fibrils offer its toughness [2]. Using animal models with distinct mineralization levels (BL6 and C3H mice), a previous study has demonstrated that highly mineralized bone tend to form linear microcracks whereas less mineralized bone is more likely to have diffuse damage [3]. To our knowledge, however, the effect of collagen phase on the microdamage formation of bone has not been well studied. Less collagen content [4] and smaller diameter [5] of collagen fibrils have been observed in bone with osteogenesis imperfecta (OI) disease, a mutation of a single nucleotide deletion in proα2(I) collagen gene. The oim mouse model has been widely used as animal models to study osteogenesis imperfecta disease. Consequently, the objective of current study was to determine the influence of collage phase alterations on microdamage formation in bone using oim mice.
The Effect of the Tibiofemoral Contact Path Centroid Location on TKR Contact Forces
Authors: Lundberg Hannah J. , Wimmer Markus A.
Published: July 2013

Detailed knowledge of in vivo knee contact forces and the contribution from muscles, ligaments, and other soft-tissues to knee joint function are essential for evaluating total knee replacement (TKR) designs. We have recently developed a mathematical model for calculating knee joint contact forces using parametric methodology (Lundberg et al., 2009). The numerical model calculates a “solution space” of three-dimensional contact forces for both the medial and lateral compartments of the tibial plateau. The solution spaces are physiologically meaningful, and represent the result of balancing the external moments and forces by different strategies.
Design and Fabrication of an In-Vitro Torque Device
Authors: Banks Andrew
Published: July 2013

A theory for adolescent idiopathic scoliosis was proposed by Dr. Stokes [1] in which a lateral spinal curvature produces asymmetrical loading of the skeletally immature spine, which in turn causes asymmetrical growth and therefore progressive wedging deformity. There have been many studies performed to evaluate the effect of compression-tension loading on wedging of the spine. Despite all these studies, only [2] investigated the effect of torque on segmented bodies, but did not incorporate independent torque control. The goal of this project was to design a torque device that allows controlled torque to be applied to segmented bodies and to validate the design through in-vitro testing.
Study of Folding in Endovascular Grafts due to Oversizing
Authors: Lin Kathleen , Raghavan Madhavan L.
Published: July 2013

Endovascular grafts (EVG) are stent grafts implanted percutaneously to repair aortic aneurysms. The primary source of fixation of the EVG is the friction from radial forces generated by graft over-sizing. Although a 10–20% over-sizing is common, it may range from 0 to 45% [1]. A clinical study on patient outcomes noted high migration rates when oversizing was greater than 30%. A recent in vitro study of barbed EVGs by our group found that greater than 30% oversizing results in decreased fixation strength quantified by the force needed to pullout the graft from the aorta [2]. In that study, based on anecdotal visual observation, we hypothesized that grafts with excessive oversizing may be folding, resulting in poor fixation strength. In this study, we ranked the level of folding noted in EVGs with varying oversizing in order to test that hypothesis.
Employing Topological Equivalence in Biomechanics
Authors: Tanaka Martin L. , Ross Shane D.
Published: July 2013

By its very nature, biomedical engineering is interdisciplinary, often combining tools and techniques originally developed for engineered systems and applying them to biological problems. Often techniques developed to solve one problem may be used to solve a very different problem. One useful concept from the field of mathematics is topological equivalence. Two dynamical systems are “topologically equivalent” if the phase portraits are qualitatively similar. That is, one portrait can be obtained from the other by a continuous transformation (Figure 1).
A Semi-Empirical Elastic-Plastic-Visco-Damage Constitutive Model of Cortical Bone
Authors: Luo Qing , Leng Huijie , Acuna Rae , Dong Xuanliang , Rong Qiguo , Wang Xiaodu
Published: July 2013

Bone quality can be characterized by toughness of bone which quantifies the energy required for failure. As much of the toughness of bone occurs after yielding, elucidating the underlying mechanism of post-yield behavior of bone is critical for further development of clinical strategies to predict and prevent age and disease related bone fractures. However, the underlying mechanism of the post-yield behavior of cortical bone is so far poorly understood, which makes it difficult to establish physically sound constitutive models for cortical bone that could accurately predict the mechanical behavior of the tissue. The absence of the constitutive equations has significantly hindered the application of bone mechanics in solving biomedical problems. Besides, an accurate constitutive model is always required in numerical modeling and simulating the mechanical behavior of bone under different loading conditions. Based on the experimental results obtained in our lab, the objective of this study was to develop and verify a constitutive model of cortical bone under compression, which accounted for damage accumulation, plastic deformation and viscoelastic properties.
Optimal Position for the Artifical Patella During Resurfacing to Decrease Stress and Avoid Pre-Prosthetic Patellar Fracture
Authors: Choi Kwang Won , Amirouche Farid , Gonzalez Mark H. , Goldstein Wayne
Published: July 2013

Total knee arthroplasty (TKA) is known to be an excellent solution to patients experiencing considerable pain at the joint and difficulty flexing and extending their knee. Unfortunately, after surgery, cases of peri-prosthetic patellar fracture are possible. The prevalence of this fracture ranges from 0.11% to 21.4% for the over 400,000 TKAs that are conducted in the United States every year and therefore, patellar fracture can become a serious concern. The factors that lead to this are several and many researchers are still investigating this problem. This research shows that the position of the surgically inserted artificial patella, also referred to as the patellar button, influences occurrence of patellar fractures and attempts to derive the ideal position for the button to reduce the risk of patellar fracture.
Design of Biomorphic Polymeric Heart Valve Prosthes by Means of FEM Modeling
Authors: Zaffora Adriano , Stasiak Joanna , Moggridge Geoff D. , Costantino Maria Laura , Fumero Roberto
Published: July 2013

Severe stenotic or insufficient native heart valves (nHV) must be substituted with artificial heart valve prostheses (aHV) to prevent heart failure. Nowadays, surgeons can implant two types of aHVs: mechanical aHV or bioprosthetic aHV. Mechanical aHVs, which are built up from synthetic hard materials, assure good reliability but require daily anticoagulant treatment to avoid blood cells damage. On the contrary, bioprosthetic aHVs, which are made from animal or human tissues, display better hemocompatibility but significant risk of failure due to tissue degradation. Despite current development in manufacturing of valve prostheses, long-term clinical applications claim for new generation of aHVs able to meet reliability and effectiveness requirements [2].
Parametric Analysis of Eustachian Tube Function Using Fully Coupled Fluid-Structure Interaction Models
Authors: Sheer Francis J. , Ghadiali Samir N.
Published: July 2013

Otitis Media (OM) is the most commonly diagnosed childhood illness and has health care related cost of four billion dollars annually. [1] The onset of OM has been directly related to Eustachian Tube (ET) dysfunction. The ET has three main physiological functions, and when these functions are compromised, middle ear (ME) disorders arise. It is also known that specific populations of patients, such as those with cranio-facial abnormalities, such as a cleft palate, have a 100% onset rate of OM. Even though ET dysfunction has been related to OM, the underlying reasons for ET dysfunction in certain populations remains unknown. To gain an understanding of this system, we use fully coupled fluid-structure interaction (FSI) models of the ET based on geometries reconstructed from histological images. Using these models in systematic parameter variation studies allows us to identify which parameters of the ET can cause dysfunction. Using healthy adult subjects as a model for a well-functioning ET, we determined ET function to be sensitive to changes in TVP muscle force.
Force Depression in the Drosophila Jump Muscle
Authors: Koppes Ryan A. , Swank Douglas M. , Corr David T.
Published: July 2013

The depression of isometric force after active shortening, termed force depression (FD), is a well-accepted characteristic of skeletal muscle that has been demonstrated in both whole muscle [1,3] and single-fiber preparations [1,2]. Although this history-dependent behavior has been observed experimentally for over 70 years, its underlying mechanism(s) remain unknown. Drosophila melangastor, commonly known as the fruit fly, is a well established, comprehensively understood, and genetically manipulable animal model. Furthermore, Drosophila have proved to be an accurate model species for studying muscle mechanics, and the Tergal Depressor of the Trochanter (TDT), or jump muscle, has most precisely resembled the mechanics of mammalian skeletal muscle [4]. Due to the structural and phenomenological similarities of the TDT muscle to skeletal muscle, in addition to the potential use of genetic mutations in fly models, it is extremely advantageous to investigate the presence of history dependent phenomenon in the TDT. If such phenomena are present, further investigation utilizing different myosin and actin isoforms to study the underlying mechanism(s) could produce new insight into this history-dependent phenomenon, otherwise impossible to elucidate using current experimental models. Thus, it is the goal of this study to determine the presence and degree of FD in the TDT muscle of wild type Drosophila.
Computer Controlled Device to Independently Control Flow Waveform Parameters During Organ Culture and Biomechanical Testing of Mouse Carotid Arteries
Authors: Gazes Seth , Caulk Alexander , Gleason Rudolph L.
Published: July 2013

Understanding the mechanisms of cardiovascular disease progression is essential in developing novel therapies to combat this disease that contributes to 1 in 3 deaths in the United States every year. Endothelial dysfunction and its effects on vessel growth and remodeling are key factors in the progression and localization of atherosclerosis. Much of our understanding in this area has come from in-vivo and in-vitro experiments. However, perfused organ culture systems provide an alternative approach[1]. Organ culture systems can provide a more controlled mechanical, neural, and hormonal environment compared to in-vivo models. This study focused on furthering development of an organ culture model for mouse arteries by introducing a novel device to produce flow waveforms at the high frequencies and low mean flows seen in the mouse model.
Interstitial Flow and Effects on Tumor Cell Migration
Authors: Polacheck William , Kamm Roger
Published: July 2013

Interstitial flow is the convective transport of fluid through tissue extracellular matrix. This creeping fluid flow has been shown to be important in regulating the development, function, and pathology of tissues. Furthermore, interstitial flow has been shown to affect the morphology and migration of cells such as fibroblasts, cancer cells, endothelial cells, and mesenchymal stem cells (1). Chary and Jain used fluorescence recovery after photobleaching to directly observe fluid flow in the tissue interstitium and determined typical flow velocities are on the order of 0.1–2.0μm/s (2). Interstitial flow is particularly important in driving transport in tumor tissues, as neoplastic tissue is often characterized by increased interstitial pressure (3).
Probing Cytoskeletal Mechanics Using Biochemical Inhibitors
Authors: Pryse Kenneth M. , Abney Teresa M. , Genin Guy M. , Elson Elliot L.
Published: July 2013

Quantifying the mechanics of the cytoskeletons of living cells is important for understanding several physiologic and pathologic cellular functions, such as wound healing and cellular migration in cancer. Our laboratory develops three-dimensional tissue constructs for assaying cytoskeletal mechanics in controlled conditions. These tissue constructs consist of defined components such as chick embryo fibroblasts and reconstituted rat tail collagen; fibroblasts remodel the collagen extracellular matrix (ECM) and develop a structural environment representative of that which would exist in a natural tissue.

Our protocol for quantifying the microscale mechanics of the proteins that comprise the cytoskeleton involves mechanical testing of a tissue construct first in a bath that contains nutrition medium to support the active physiologic functioning of the cells, and next in the presence of inhibitors that selectively eliminate specific cytoskeletal structures. By solving an inverse homogenization problem, the mechanical functioning of these proteins at the cellular level can be estimated. Here, we present a combination of mechanical testing and imaging results to quantify the effects of specific inhibitors on cytoskeletal and extracellular matrix form and function.
Shear Stress Exposure Measurements on the Motionless Fluid Diode Valve in the Pulmonary Position
Authors: Camp Tiffany , Figliola Richard S. , Conover Timothy A. , Hsia T.-Y.
Published: July 2013

Pulmonary insufficiency is one of the consequences of congenital heart disease, and currently no permanent solution exists. The concept of a motionless diode valve to regulate the pulmonary circulation has been proposed and previously studied. The diode valve has shown the ability to regulate flow with levels of regurgitation and pressure gradient that are acceptable within the pulmonary circulation [1].
The Dominant Mechanical Interaction Between the Brain and Skull In Vivo: Is Sliding Arrested at Key Points of Brain-Skull Tethering?
Authors: Abney Teresa M. , Feng Y. Aaron , Pless Robert , Okamoto Ruth J. , Genin Guy M. , Bayly Philip V.
Published: July 2013

The relationship between skull acceleration and brain injury is not well understood, in large part because of the challenge of visualizing the brain’s mechanical response in vivo. This difficulty also complicates the validation of computational mechanics predictions.

Our dynamic magnetic resonance (MR) imaging suggests an important role for the attachments between brain and skull. Here, we present an MRI-based method for identifying the dominant modes of brain displacement relative to the skull during angular acceleration of the head, and apply it to study brain/skull interactions in live volunteers. The approach was to estimate dynamic intracranial displacement fields from a sequence of tagged MR images of the brain and skull, then identify dominant displacement modes using principal component (PC) analysis. After verifying the method through analysis of a simulated 2-D vibrating plate and MR images of a cylindrical gel phantom, the method was applied to show that the dominant mode of brain/skull interaction is one of sliding arrested by brain/skull meninges in a few specific regions.
The Importance of Posterior Muscle Strength and Facet Contact in Preventing Lumbar Disc Herniation During Forward Bending
Authors: Rundell S. A. , Isaza J. , Day J. S. , Guillory S. , Newberry W. N. , Kurtz S. M.
Published: July 2013

During forward bending, a combination of compression, anterior shear, and flexion moment is applied to the lumbar spine due to upper body weight. A combination of posterior muscle and ligament forces must be generated in order to prevent excessive motion and restore upright posture. It is generally believed that forward bending to 90 degrees while maintaining a straight or extended lumbar spine is biomechanically favorable compared to lifting with a rounded back [1]. A simple biomechanical model of the lumbar spine during bending in which the vertical force from upper body weight is balanced with posterior muscle and ligament tension would result in similar levels of compression of the disc regardless of the bending modality. However, this model does not take into consideration the facets. A study involving professional class weightlifters showed that subjects would increase the lordosis in their lumbar spines prior to executing a deadlift maneuver [2]. The authors suggest several possible advantages for why the lifters increased the lordosis including muscle control and geometric advantages, but do not indicate the potential for increased facet engagement. During forward bending the lumbar spine will be exposed to anterior shear forces, which will cause the facets to engage [3]. Posterior muscle activation occurring during facet engagement may generate a fulcrum, which has the potential to reduce the compression experienced by the disc. Therefore, the objective of the current study was to simulate forward bending with a previously validated finite element model of L4-L5 and determine if increasing posterior muscle force results in a reduction in disc pressure. We hypothesized that posterior muscle activation during forward bending would increase facet contact and reduce intradiscal pressure and nucleus extrusion forces thereby minimizing the contribution to progressive disc herniation.
Transport of Insulin-Like Growth Factor 1 in Intervertebral Disc: Effect of Binding Interactions and Inhomogeneous Distribution of Binding Proteins in Annulus Fibrosus and Nucleus Pulposus
Authors: Travascio Francesco , Huang Chun Yuh , Gu Wei Yong
Published: July 2013

The intervertebral disc (IVD), being the largest avascular structure in human body, receives nourishment from the vascular network present near its periannular surface and at cartilage endplates (CEPs). It is believed that insufficient nutritional supply is a major cause for disc degeneration [1]. Understanding the mechanisms of solute transport in IVD is crucial for elucidating the etiology of disc degeneration, and to develop strategies for tissue repair (in vivo), and tissue engineering (in vitro). Transport in IVD is complex and involves a series of electromechanical, chemical, and biological coupled events. This study focused on the implications of solute-tissue reversible binding reactions on transport phenomena in the disc. A two dimensional (2D) finite element model was developed to predict diffusive-reactive transport in IVD. The numerical model was used to simulate transport of insulin-like growth factor 1 (IGF-1) in IVD, in the presence of binding interactions between IGF-1 and IGF-binding proteins (IGFBP-3) located on the extracellular matrix (ECM) of the disc.
Tensile and Compression Response of Agarose Gel at Various Strain Rates
Authors: Liu Quinli , Subhash Ghatu , Moore David
Published: July 2013

Agarose gel is a sea weed based gel used in biomedical applications. Therefore, determination of its constitutive response under a variety of loading conditions is a necessary prerequisite for successful application. In this manuscript, agarose gel specimens at various concentrations were prepared for testing under quasistatic tension, quasistatic compression, and dynamic compression. Different test techniques were adopted to extract the material response.
Experimental Induction of Lumbar Spine Compression-Flexion Injuries
Authors: Storvik Steven G. , Yoganandan Narayan , Pintar Frank A. , Stemper Brian D.
Published: July 2013

Biomechanical research was conducted to outline mechanisms of cervical and lumbar vertebral body burst and wedge fractures using spines obtained from post-mortem human subjects (PMHS) and animals [1–5]. These studies incorporated full columns [1, 2] or, more commonly, three-body vertebral segments [3–6]. The method of load application most often involved static specimen placement with dynamic load application to the superior fixation using a weight-drop method or an MTS piston. While these studies experimentally induced vertebral body burst fractures, as clinically demonstrated following abrupt and severe axial loading through the pelvis, fractures resulted from unrealistic experimental boundary conditions. For example, three-body vertebral segments remove effects of spinal curvature and weight-drop or piston load application to the cranial fixation does not replicate the acceleration-driven loading as applied to the base of the spine, wherein characteristics of the acceleration versus time pulse are important in injury type and severity. Therefore, the present study developed an experimental model to mimic real-world loading situations resulting in vertebral body burst and wedge fractures.
Quantification of the Biomechanical Differences in Wild-Type and Heterozygous TGF Beta2 Knockout Mice
Authors: Keyes Joseph T. , Borowicz Stacy , Utzinger Urs , Azhar Mohamad , Vande Geest Jonathan P.
Published: July 2013

The use of transgenic mice is an incredibly powerful tool in understanding the underlying etiology of disease. To understand the usefulness of specific transgenic mice, the systems of interest should be characterized. We have created TGFβ2-deficient mouse fetuses that develop widespread aortic and coronary artery aneurysms [1]. Several studies have pointed to a strong connection between elevated TGFβ signaling and aortic aneurysm [2]. In situ hybridization has shown that Tgfb2 and Tgfb3 are major ligands expressed in the aortic medial wall. Further reduction of TGFβ signaling by combining TGFβ2- and TGFβ3-deficient mice exacerbated cardiovascular aneurysms in TGFβ2/TGFβ3-doubly deficient embryos. In vitro cell culture experiments demonstrated an impaired ability of TGFβ2-deficient mouse embryonic fibroblasts to reorganize collagen. Previous data indicate reduced levels of TGFβ2 leading to a higher susceptibility to aortic aneurysm. We present here the macroscopic biomechanical characterization of the aorta of a transgenic mouse line showing this susceptibility and compare it to wild-type mice. We also present results comparing the microstructure between mouse lines.
Effect of Implant Shape and Material Properties on Stresses in the Glenoid Components of Total Shoulder Arthroplasties: A Finite Element Analysis
Authors: Zhang Jingzhou , Yongpravat Charlie , Dyrszka Marc D. , Levine William N. , Gardner Thomas R. , Ahmad Christopher S.
Published: July 2013

The geometry of the glenohumeral joint is osseous, naturally nonconforming and minimally constrained, thus the essential requirement of a glenohumeral prosthesis in total shoulder arthroplasty (TSA) is prevention of joint degeneration and glenoid loosening. A variety of glenoid prostheses have been developed. Nonconforming glenohumeral implants are common for TSA. However, the nonconforming shape increases the instability when the humeral head is in the central region, where motion frequently occurs. Conforming implants can increase joint stability, but the “rocking-horse” effect [1] caused by the conforming shape is thought to lead to high stresses and moments at the glenoid rim when the humeral head approaches the periphery during its range of motion. The hybrid design, with a conforming center and a nonconforming periphery, combines the advantages of both nonconforming and conforming implant geometries. It has been shown [2] that the peak stress generated in glenoid components during activities of daily living can be as high as 25 MPa, which exceeds the polyethylene yield strength of the glenoid component and can lead to wear and cold flow of the component. Polyethylene has also been shown to be viscoelastic [3]. Therefore, both elastic-plastic and viscoelastic-plastic models of the glenoid implant were used to determine how viscoelasticity affected stress in the implant. The effects of implant shape on the stresses in the center, transition, and superior zones for the three different glenoid implant shapes, as well as on the stress in the underlying cement and bone, were determined in this study.
Biomechanical Comparison of Contact Pressure in the Cervical Facet Joint During Bending Using a Probe and Pressure-Sensitive Paper
Authors: Jaumard Nicolas V. , Bauman Joel A. , Welch William C. , Winkelstein Beth A.
Published: July 2013

Non-physiologic loading of the facet joint is a potential cause of facet joint pain in the cervical spine [1]. When the local biomechanical environment of the facet joint is altered, like with trauma or after surgery [2], the cartilaginous articular surfaces of the facets can also be damaged. Defining articular contact pressure can provide a metric of altered joint mechanics and the local mechanical environment of the cartilage in the facet joint. However, accessing the articular surface to make such measurements without altering the overall mechanics of the joint remains a substantial challenge.
Effect of Continuous Supression of Heparan Sulfate on Arterial Endothelial Alignment and Gene Expression Under Several Shear Stress Waveforms
Authors: Wallace Charles S. , Friedman Morton H.
Published: July 2013

The literature suggests that endothelial cells (ECs) possess many molecules that have mechanosensor capabilities, such as intracellular junction proteins, G proteins, ion channels, integrins, and the glycocalyx [1]. The endothelial glycocalyx is located on the luminal surface of ECs and interacts with the passing blood, thus making it a strong mechanosensor candidate. The glycocalyx is a negatively charged gel layer ranging from 0.5 μm thick in capillaries to 4.5 μm thick in carotid arteries [2]. The glycocalyx consists primarily of sialic acids, chondroitin sulfate, hyaluronic acid, and heparan sulfate (HS). HS is the most abundant glycosaminoglycan within the glycocalyx, and it is one of the most studied molecules in this layer [3].
Simulation of Flow and Structural Dynamics in Human Upper Airways
Authors: Mylavarapu Goutham , Gutmark Ephraim , Mihaescu Mihai , Murugappan Shanmugam
Published: July 2013

Obstructive Sleep Apnea and Hypo Apnea Syndrome (OSAHS) is a respiratory disorder characterized by repeated episodes of partial or complete airway obstruction. OSAHS is also associated with decreased quality of life, decreased cardiovascular health, day-time sleepiness, and increased transportation accidents. Its high prevalence with as much as 4% of American population suffering from OSAHS also makes it an important health care issue[1]. Existing surgical treatments suffer from a moderate to high successful failure rates. Broader research on this respiratory disorder for a better understanding of the pathophysiology of human upper airway, to develop better diagnostic methods and treatment modalities is very much needed.
Multi-Stress Conditioning Can Synergisticly Enhance Production of Osteogenic Markers and Heat Shock Proteins
Authors: Chung Eunna , Rylander Marissa Nichole
Published: July 2013

Tissue regeneration can be enhanced by introduction of biochemical and mechanical cues. We investigated the effect of thermal and mechanical stress alone or in combination with growth factors (GFs) (BMP-2 and TGF-β1) on cell proliferation and induction of heat shock proteins and bone-related proteins by MC3T3-E1mouse preosteoblasts. Thermal and mechanical stress conditioning alone induced bone-related proteins such as osteocalcin (OCN), vascular endothelial growth factor (VEGF), osteoprotegerin (OPG), and osteopontin (OPN) and heat shock proteins (HSP27, HSP47, HSP70). Cell proliferation was increased by cyclic tension in combination with growth factors. Combined thermal and mechanical stress induced synergistic expression of HSPs and VEGF. Therefore, utilization of thermal and tensile stress conditioning can stimulate bone healing or regeneration.
Dissection Properties of Aneurysmal and Nonaneurysmal Human Ascending Thoracic Aorta: Preliminary Results
Authors: Pasta Salvatore , Philippi Julie A. , Gleason Thomas G. , Vorp David A.
Published: July 2013

Ascending thoracic aortic aneurysm (ATAA) is among the most devastating forms of cardiovascular disease, causing a significant mortality despite current medical and surgical treatments [1]. Moreover these therapies themselves are associated with great risk of mortality or morbidity, complicated by the advanced age of the typical patient, and high surgical costs. The mechanics of spontaneous aortic dissection is not fully understood. It is generally believed that aortic dissection initiates as an intimal tear in which a separation of wall layers produces the formation of a ‘false’ lumen. The dissection may propagate axially and/or circumferentially due to blood flow and pressure. Dissection may lead to several possible complications. For example, the septum between the false lumen and true lumen may fracture, resulting in embolism and ischemic damage. Another possibility is that the thinned and weakened residual outer aortic wall may fail, resulting in rapid blood loss and tamponade.
Mass-Spring vs. Finite Element Models of Anisotropic Heart Valves: Speed and Accuracy
Authors: Hammer Peter E. , Sacks Michael S. , del Nido Pedro J. , Howe Robert D.
Published: July 2013

Heat valve dysfunction can lead to heart failure and death, and surgery is the standard treatment. Valve repair surgery is performed under cardiopulmonary bypass making it difficult for the surgeon to know if a surgical modification will be effective when blood flow is restored. A surgical planning system has been proposed to improve surgical outcomes by allowing a surgeon to explore valve repair strategies on a computer model of a patient’s valve (1). Many groups have published computational models of heart valves based on the finite element (FE) method, but they are prohibitively slow for simulating valve mechanics in an interactive setting. Mass-spring (MS) networks have been used as an alternative to FE methods for modeling deformable bodies, trading off accuracy for speed.
Dose-Dependent Effects of Interleukin-1Alpha on Functional Degradation of Lateral and Medial Menisci
Authors: Ling Carrie H. , Lai Janice H. , Nishimuta James F. , Levenston Marc E.
Published: July 2013

Despite a growing recognition that meniscal degeneration often precedes cartilage degeneration in the development of knee osteoarthritis (OA), little is known about the role of meniscal degeneration in the onset and progression of knee OA. Even a mild degenerative lesion increases meniscal extrusion, implying changes in biomechanical function. Understanding the mechanisms of meniscal degeneration may enable the diagnosis and disease-modifying treatment of early knee OA, potentially preventing or slowing the progression of the disease. The roles of pro-inflammatory cytokines such as interleukin-1 (IL-1) in promoting cartilage matrix degradation and mediating inflammation in the progression of OA have been widely demonstrated [1,2]. Recent results from our group indicated that 20ng/ml hrIL-1α produced similar cell-mediated degradation and loss of mechanical properties in immature cartilage and meniscus, but progresses more rapidly in meniscus explants [3]. This study further explored the effects of IL-1α dosage and medial-lateral differences on the functional degradation of meniscal explants.
Blood Damage Induced by Cardiovascular Devices: High Resolution Measurements in a Scaled-Up Model Valve
Authors: Bellofiore Alessandro , Quinlan Nathan J.
Published: July 2013

In this paper we describe the use of a scaled-up mechanical heart valve (MHV) model to measure flow at very high resolution and assess blood damage potential. A major goal in MHV design is to reduce the risk of mechanically induced thrombosis and hemolysis. Blood damage is triggered at the cellular level by several phenomena, including prolonged exposure to high shear stress and long residence in zones of flow recirculation [1] as well as turbulence [2]. To enhance the capability to understand and predict blood damage, it is necessary to comprehend the structure of the flow field at very small scales. Particle Image Velocimetry (PIV) has been used extensively to measure the flow field in MHVs [3]. However, the spatial resolution (defined as the distance between velocity measurement locations) of current PIV systems is coarse with respect to cellular scale. Temporal resolution can be increased to capture rapidly evolving transient features, but the price to pay is even poorer spatial resolution [4].
A Pneumatic Artificial Muscle Articulated Knee Prosthesis
Authors: Waycaster Garrett , Wu Sai-Kit , Shen Xiangrong
Published: July 2013

This paper describes the mechanical design and control approach for an above-knee (AK) prosthesis actuated by pneumatic artificial muscle. Pneumatic artificial muscle (PAM) affords great potential in prosthetics, since this type of actuator features a high power density, and similar characteristics to human muscles. However, there is no application of PAM in AK prosthetics in existing literature to the best knowledge of the authors. In this paper, a design of the prosthesis is presented, which provides sufficient actuation torque for the knee joint in energy consuming locomotive functions such as fast walking and stair climbing. The corresponding control approach is developed to mimic the human motor control in locomotive functions, which includes a lower-level equilibrium-point hypothesis-inspired motion controller, and a higher-level joint-behavior-based motion planner.
Extracting Appropriate Mathematical Expressions Defining Moment Arm Relationships Using Symbolic Regression
Authors: Kurse Manish U. , Schmidt Michael , Lipson Hod , Valero-Cuevas Francisco J.
Published: July 2013

Estimating tendon excursion-joint angle relationships that define moment arm variations is a critical part of biomechanical modeling. The conventional approach has been to assume a specific mathematical form for these relationships and use experimental data to regress the parameters of these assumed mathematical functions. In contrast, here we propose a novel method that uses symbolic regression to simultaneously determine both the appropriate topology, i.e. the form of the mathematical expression, and the parameter values that best fit the experimental data. We demonstrate this method with synthetic data generated using a known model of the human index finger. Cross validation with realistic noise levels shows that this method can extract the correct form and parameter values for nonlinear tendon excursion-joint angle relationships even in the presence of noise.
In Vitro Viscoelastic Flow Measurements of a Pediatric End-to-Side Anastomosis to the 12cc Penn State Ventricular Assist Device
Authors: Perone Michael V. , Yang Ning , Roszelle Breigh N. , Deutsch Steven , Manning Keefe B.
Published: July 2013

Congenital cardiovascular defects are the leading cause of infant mortality due to birth defects, accounting for 29% of all birth defect-related infant deaths [1]. Each year over 35,000 babies are born with heart defects in the United States. A quarter of these patients require invasive treatment [2]. Although transplantation has proven to be a viable option for recovery, it is limited by an inadequate supply of donor organs. The average wait time for a transplant in 2005 was 107 days, and without the availability of transplants, approximately 40% of infants in need of a cardiovascular transplant may die [3,4].
The Challenges of Developing a Pediatric Ventricular Assist Device From a Fluid Dynamics Perspective
Authors: Roszelle Breigh N. , Cooper Benjamin T. , Yang Ning , Deutsch Steven , Manning Keefe B.
Published: July 2013

As a medical device proves successful in adult patients, it is anticipated that a similar solution for pediatrics may be developed. However, in many cases this task has proved to be much more complex than simply scaling the device down for a miniature adult patient. Pediatric patients present a unique set of characteristics and constraints not seen in adults. These include a large range of sizes from infants to adolescents, the possible growth of the patient during use, possible anatomical deformities and a body that has not fully matured.
Biaxial Mechanical Testing of Single Annulus Fibrosus Layers
Authors: Rys J. P. , Ellingson A. M. , Nuckley D. J. , Barocas V. H.
Published: July 2013

The intervertebral disc (IVD), consisting of the inner nucleus pulposus and the outer annulus fibrosus, is subjected to multiaxial stress in vivo. The disc undergoes degenerative changes that account for impairment and disability in middle-aged and older individuals.4 In addition to age-related degeneration, the intervertebral disc is subject to the development of lesions due to partial displacement or rupture of the annulus fibrosus. Such occurrences, typically resulting from physical trauma, can yield disabling effects from impingement on spinal nerve structures. A greater understanding of the IVD and how it functions mechanically is crucial in prevention and repair of debilitating spinal disorders.