bluuebunny/crossref_metadata_2025 huggingface dataset:
Changes in Vascular Viscoelasticity Caused by Smooth Muscle Cell Tone and Pressurization Frequency
Authors: DeWall Ryan J. , Chesler Naomi C.
Published: March 2014

The cushioning and conduit functions of large arteries allow the body to efficiently circulate blood and perfuse organs. These functions can be characterized by quantifying the viscoelastic properties of arteries. In this study, we investigated the effects of smooth muscle cell (SMC) tone and pressurization frequency on vascular viscoelasticity using an isolated, perfused vessel test. We tested mouse carotid arteries in control, dilated (via sodium nitroprusside) and constricted (via the thromboxane receptor analogue U46619) states at 0.1, 1, 3, and 5 Hz with a pulse pressure from 90 to 120 mmHg. Dose response experiments were first performed in order to determine the optimal vasoconstrictor concentration to be used in frequency response experiments. Our results showed that energy dissipation was significantly higher and elasticity was significantly lower for vasoconstricted arteries. We also found that frequency significantly changed both energy dissipation and elasticity as the frequency was increased from 0.1 to 5 Hz. These results provide insights into the changes in vascular viscoelasticity caused by SMC tone and pressurization frequency, which have implications for vascular function in vivo.
Simulations of Bioprosthetic Heart Valve Dynamics Using a Sharp Interface Method
Authors: Vigmostad Sarah C. , Jeffrey Brian D. , Krishnan Sreedevi , Udaykumar H. S. , Chandran K. B.
Published: March 2014

Bioprosthetic heart valves are valve replacements constructed from animal tissue. They are deformable and offer similar mechanical properties to their native counterpart. While tearing of these valves is frequently observed, it is still not fully understood, but may be the result of high induced bending and shear stresses in the valve leaflets[1].
A Scaled-Up Mechanical Prosthetic Heart Valve Model for High-Resolution Flow Field Measurements
Authors: Donohue Eilis M. , Heraty Kevin B. , Quinlan Nathan J.
Published: March 2014

Every year, over 250,000 patients undergo heart valve implantation [1]. Approximately 55% of implanted prosthetic heart valves (PHV) are mechanical. Patients must undergo lifelong anticoagulant medication in order to alleviate the risk of thrombus formation. In order to understand the complex fluid dynamics underpinning problems such as thrombosis, detailed high-resolution quantitative information on the flow field in PHVs is essential [2]. High-resolution data is also needed for the validation of Computational Fluid Dynamics (CFD) studies.
Effects of Hydrostatic Pressure on Meniscus Cell-Seeded PLLA Scaffolds
Authors: Gunja Najmuddin J. , Athanasiou Kyriacos A.
Published: March 2014

Cartilage explant studies have shown that mechanical stimuli increase extracellular matrix (ECM) expression and synthesis in vitro [1]. The use of hydrostatic pressure (HP), as a loading regimen, is of particular interest as it causes no cellular deformation. This may be useful in tissue engineering studies where scaffolds with limited mechanical integrity need to withstand intermittent loading conditions. Studies investigating the effect of HP on 3-D cultures of chondrocytes have met with modest success [2, 3]; however literature on meniscal fibrochondrocytes is lacking.
Validation of a Computational Musculoskeletal Model of the Elbow
Authors: Fisk Justin P. , Wayne Jennifer S.
Published: March 2014

Musculoskeletal computational modeling can be a powerful and useful tool to study joint behavior, examine muscle and ligament function, measure joint contact pressures, simulate injury, and analyze the biomechanical results of reconstructive procedures. Commonly, biomechanical models are based on either finite element analysis (FEA) or three-dimensional rigid body dynamics. While each approach has advantages for specific applications, rigid body dynamics algorithms are highly efficient [1], thus significantly reducing solution time. Many musculoskeletal models of the elbow have been developed [2, 3], but all have constrained the articulations to have particular degrees of freedom and ignored the effects of ligaments. An accurate and robust model without these limitations has potential as a clinical tool to predict the outcome of injuries and/or surgical procedures. This work develops and validates an accurate computational model of the elbow joint whereby joint kinematics are dictated by three-dimensional bony geometry contact, ligamentous constraints, and muscle loading.
A Novel Experimental Technique for Quantifying the Local Mechanical Environment of Skeletal Tissues
Authors: Palomares Kristy T. S. , Miller Gregory J. , Gerstenfeld Louis C. , Einhorn Thomas A. , Morgan Elise F.
Published: March 2014

A growing body of evidence indicates that mechanical cues modulate the development and repair of skeletal tissues by regulating gene expression and tissue differentiation.[1–3] Further understanding of how the mechanical environment modulates these biological processes could be applied to enhance skeletal repair following injury or disease. Bone healing provides an excellent in vivo system for investigating cellular responses to mechanical stimuli, due to the recruitment of pluripotent, mechano-sensitive, mesenchymal stem cells. For example, recent studies have shown that bending and/or shear motion applied to a healing bone defect can result in cartilage rather than bone formation.[4,5] However, while different global (i.e. organ level) mechanical stimuli are known to result in different healing outcomes, the specific local (i.e. tissue level) stimuli that promote different tissue fates have yet to be established. Finite element analyses can provide estimates of these local stimuli, yet these analyses require many assumptions regarding tissue material properties and boundary conditions. Our overall goal in this study was to develop an experimental technique for quantifying the distributions of local strains that develop in skeletal tissues during mechanical loading.
Measuring Moment Arms Using Closed-Loop Force Control With an Elbow Simulator
Authors: Kuxhaus Laurel , Schimoler Patrick J. , Vipperman Jeffrey S. , Flamm Angela M. , Budny Daniel , Baratz Mark E. , DeMeo Patrick J. , Miller Mark Carl
Published: March 2014

In search of a complete understanding of a joint’s function, one must understand both the anatomic parameters and how the brain controls the joint’s actuation. Accurate measurements of anatomical parameters are critical to non-linear biomechanical modeling and control and also to a clinical understanding of orthopaedic reconstruction. Likewise, new frontiers in the study of neuromuscular control contribute to our understanding of joint structure and function. One approach to study joint function is to use a joint simulator to actuate cadaver limbs. Towards the goals of understanding and improving human elbow joint control, a physiologic elbow joint simulator was previously constructed in our laboratory. It is the first elbow simulator to operate completely under closed-loop control. The closed-loop force control used to study joint mechanics permits measurement of moment arms in cadaveric elbow specimens. We hypothesized that the approach yields comparable results to previously-reported moment arm values.[1]
Fabrication and Properties of Collagen Fibers With Increased Surface Areas for Enhanced Fiber-Matrix Interactions
Authors: Finkbiner J. J. , Harrigan K. L. , Dee K. C. , Livesay G. A.
Published: March 2014

Collagen plays an important structural role in many natural tissues, such as ligaments and tendons. Due to its ubiquity in the human body and its commercial availability, biomaterials using collagen gel as a scaffold for an extracellular matrix are being developed as alternative treatments for soft tissue injuries [1]. The use of collagen fibers as a matrix in cell-seeded collagen gels has been shown to limit contraction of the gels as well as increase scaffold permeability and cell viability [2,3]. Additionally, it has been found that dehydration of collagen fibers increases fiber strength [4]. Therefore, investigating the effect of changing fiber shape to increase fiber surface and gel/fiber interaction is important.
The Effects of Pressure and Shear on Capillary Closure in the Microstructure of Skeletal Muscles: Computational Studies
Authors: Linder-Ganz Eran , Gefen Amit
Published: March 2014

Deep tissue injury (DTI) is a serious and potentially deadly type of pressure ulcers, which initiate in deep muscle tissue under bony prominences of immobilized patients, and progress outwards towards the skin with no clear visual indications of the injury at the surface of the body. It had been suggested that DTI appear in muscle tissue first, due to the dense capillary vasculature in skeletal muscles which is susceptible to obstruction and occlusion by mechanical forces [1–3]. Though mechanical forces may cause capillaries to collapse and thus induce ischemic conditions in adjacent muscle cells [2], some investigators stipulated that ischemia alone cannot explain the etiology of DTI, and so, other mechanisms, particularly excessive cellular deformations must be involved [1]. We hypothesize that physiological levels of stresses and strains in muscle tissue under bony prominences — even when muscles are highly loaded as during sitting — do not cause complete closure of muscle capillaries, and therefore, do not cause an acute ischemia in muscles. If this is indeed the case, then ischemia cannot be the only factor contributing to DTI onset. In order to test our hypothesis, we developed a finite element (FE) model of the microstructure of skeletal muscle, at the level of muscle fascicles, and employed the model to determine the stress and strain levels required for causing partial and complete closure of capillaries.
Hyaline Characteristics of Mechanically Induced Cartilaginous Tissues
Authors: Palomares Kristy T. S. , Einhorn Thomas A. , Gerstenfeld Louis C. , Morgan Elise F.
Published: March 2014

The mechanical properties of hyaline cartilage depend heavily on tissue structure and biochemical composition. Glycosaminoglycans (GAGs) and collagen fibrils are the key extracellular matrix components of hyaline cartilage that bestow compressive and tensile stiffness, respectively.[1–2] In articular cartilage, a decline in GAG content and collagen organization with injury or with diseases such as osteoarthritis is intimately linked with a decline in mechanical function.[3] In tissue-engineered cartilage and articular cartilage explants, mechanical loading in vitro results in increased aggrecan mRNA expression, GAG content, and increased stiffness.[4–6] These findings suggest that mechanical loading could be applied in vivo to promote cartilage repair via modulation of gene expression, tissue structure, and tissue composition. We have previously developed an in vivo model of skeletal repair in which application of a controlled bending motion to a healing osteotomy gap results in formation of cartilage within the gap.[6] Using this model, we sought to characterize the biochemical composition and collagen structure of the mechanically induced cartilaginous tissue. The objectives of this study were: 1) to quantify the total GAG content and aggrecan mRNA expression; and 2) to characterize the collagen fiber orientation.
Optimal Estimation of Dynamically Consistent Kinematics and Kinetics for Forward Dynamic Simulations
Authors: Remy Christian D. , Thelen Darryl G.
Published: March 2014

Forward dynamic simulation provides a powerful framework for characterizing in vivo loads, for investigating the muscular coordination of movement, and for predicting changes in movement due to injury, impairment or surgical intervention. However, the computational challenge of generating simulations has greatly limited the use and application of dynamic models. Traditional approaches use optimization to determine a set of input trajectories (e.g. muscle forces or joint torques) that drive a model to track experimental motion and force measurements [1,2]. Optimization is needed, in part, to resolve dynamic inconsistencies between measured kinematics and ground reactions. Large scale dynamic optimization problems of this type are inherently difficult to solve, often necessitating model simplifications. It has previously been shown that dynamic inconsistencies can be efficiently resolved on a per-frame basis by enforcing whole-body dynamic constraints [3,4]. However, forward simulations cannot be generated from such data since integration of the accelerations will not re-produce measured velocities and positions.
The Response of Tissue Engineered Cartilage to the Temporal Application of Transforming and Insulin-Like Growth Factors
Authors: O’Conor Christopher J. , Ng Kenneth W. , Kugler Lindsay E. , Ateshian Gerard A. , Hung Clark T.
Published: March 2014

Agarose has been used as an experimental scaffold for cartilage tissue engineering research due to its biocompatibility with chondrocytes, support of cartilage tissue development, and ability to transmit mechanical stimuli [1–3]. Tissue engineering studies have demonstrated that the temporal application of transforming growth factor (TGF) β3 for only 2 weeks elicits rapid tissue development that results in mechanical properties approaching native values [4]. However, it is not known whether this response to a 2-week exposure to growth factors is unique to TGF-β3. Therefore, the present study characterizes the response of tissue engineered cartilage to the temporal application of the anabolic growth factors TGF-β1, TGF-β3, and insulin-like growth factor I (IGF-I).
Image Based Simulation of Pulmonary Airflow Using Multi-Level Voxel Modeling
Authors: Imai Yohsuke , Miki Takahito , Nakamura Masanori , Ishikawa Takuji , Wada Shigeo , Yamaguchi Takami
Published: March 2014

Chronic Obstructive Pulmonary Disease (COPD) refers to a group of diseases that are characterized by airflow obstruction. Currently, COPD is the fourth leading cause of death worldwide, but fluid dynamics in airways of COPD patients has not been well understood. Multi-slice Computer Tomography (CT) images provide three-dimensional realistic geometry of patient airways. Computational Fluid Dynamics (CFD) analysis using the patient-specific geometry will greatly help the understanding of the mechanism of COPD. However, few studies have performed such a patient-specific pulmonary airflow simulation. Our aim is to develop a patient-specific CFD method applicable to multi-scale airways, involving trachea, bronchi, bronchioles, and alveoli. We propose a CFD method using multi-level voxel modeling of airway geometry, in which voxel size in a local domain is adaptively refined or coarsened to the local flow scale.
Measuring the Biaxial Stress-Strain Characteristics of Human Sclera
Authors: Olesen C. G. , Tertinegg I. , Eilaghi A. , Brodland G. W. , Horst C. , Veldhuis J. H. , Flanagan J. G. , Ethier C. R.
Published: March 2014

Glaucoma is a common ocular disease that causes irreversible loss of vision. Elevated intraocular pressure (IOP) is the primary risk factor for developing glaucoma. It is believed that increased IOP causes mechanical strain on the glial cells that support the retinal ganglion cell axons and thereby causes ganglion cell apoptosis [1,2]. This damage occurs in the optic nerve head (ONH) region of the eye, and is important for understanding ONH biomechanics.
Effect of Stent Design Parameters on Fluid and Structural Mechanics in Coronary Arteries
Authors: Geiger Shannon B. , Golay Mark P. , Harless Benjamin G. , Holzgang Brice A. , Pugh David R. , Stanhope Rawley J. , Wolfe Patricia S. , Satyaprakash Karri , Pierrakos Olga , Vlachos Pavlos
Published: March 2014

As undergraduates at Virginia Polytechnic Institute and State University, our senior design team has been developing new arterial stent designs using computational, experimental and flow characterizations. Coronary artery stenting has become a popular alternative to bypass surgery due to its relatively low cost and short recovery time. There are approximately one million of these procedures performed each year. At the beginning of 2006, drug eluting stents (DES) accounted for 90% of stenting procedures; this number dropped below 75% by the end of 2006. The initial popularity of DES was due to their effective reduction in restenosis compared to the first generation of stents, bare-metal stents. Recently, the makers of DES have agreed that, compared with bare-metal stents, there is a small, but significant increase in the rate of stent thrombosis for both the Cypher (Johnson & Johnson) and Taxus (Boston Scientific) stents, beginning about 12 months after implantation [1].
Time Resolved DPIV Analysis of Pulsatile Flow in Symmetric Stenotic Arteries: A Comparison Between Arterial and Coronary Flow
Authors: Karri Satyaprakash Babu , Ali Etebari , Vlachos Pavlos
Published: March 2014

The presence of stenoses in the vasculature is responsible for significant alterations in the blood flow patterns. The flow within the stenosis is characterized by regions of high shear rates and flow separation, and downstream of stenosis recirculation region is formed, with low wall shear stresses (WSS) and large residence time[1,2. Flow in a symmetric stenosis is characterized by a central jet region with axisymmetrically separated flow surrounding it. A shear layer is formed between the jet and the recirculation region, which may be responsible for platelet activation [3,4] Wall shear stresses as high as 1500 to 3000 dynes/cm2 have been predicted at the throat of the stenosis in coronary flow models. A thorough characterization of these phenomenon is important because of the established relationship between the hemodynamics and vascular pathology. [3,4]
The Effect of Embolic Protection Filters on Distal Embolization and Slow Flow Condition in Carotid Artery Stenting
Authors: Siewiorek Gail M. , Finol Ender A.
Published: March 2014

Strokes are the third leading cause of death in the United States today. Carotid artery stenting (CAS) used in conjunction with a cerebral protection device (CPD) is a current alternative treatment for severe carotid artery disease. A type of CPD, an embolic protection filter (EPF), has received attention recently due to its allowance of distal perfusion during use. This investigation studied the effects of four EPFs (Spider RX, FilterWire EZ, RX Accunet, Emboshield) on both pressure gradient and flow rate in the internal carotid artery (ICA) in vitro. Dyed polymer microspheres larger than the pore size of the devices tested were injected into the ICA of a 70% stenosed carotid artery model. The percentage of particles missed was calculated. None of the devices tested were able to completely prevent embolization. Emboshield had the least desirable performance (missing 35.4% of particles) while Spider RX had the best (missing 0.06%). A decrease in flow rate and an increase in pressure drop were seen after the device was filled with particles. From these results, it is inferred that improper wall apposition is the primary cause for inadequate capture efficiency rates, which may lead to an increase in distal embolization and stroke.
Design and Evaluation of an Adaptive Ground Contact Model
Authors: Remy Christian D. , Thelen Darryl G.
Published: March 2014

Ground reaction forces are the driving element of human gait. They are — in the form of forceplate measures — included in virtually all inverse dynamic analyses. While it is possible to base forward dynamic analyses on such measurements, it is preferable to model the foot-floor interactions such that simulations can be performed independent of experimental data. Such a representation then facilitates the use of simulations to predict how movement would change in response to an impairment or intervention.
Rheological Properties of Extracellular Matrix Derived Gels
Authors: Freytes Donald O. , Kolman Samuel , Velankar Sachin S. , Badylak Stephen F.
Published: March 2014

Bioscaffolds composed of extracellular matrix (ECM) have been used for the repair of a variety of tissues often leading to tissue-specific constructive remodeling [1]. ECM scaffolds are typically prepared by decellularization of tissues and are composed of the structural proteins (e.g. collagen) and functional proteins (e.g. growth factors) that characterize the native ECM. However, for certain applications, the use of ECM scaffolds can be limited by the native two-dimensional sheet form in which they are harvested.
Noninvasive Blood Perfusion Measurement on the Liver of an Anesthetized Rat
Authors: Ricketts Patricia L. , Mudaliar Ashvinikumar V. , Ellis Brent E. , Diller Thomas E. , Scott Elaine P. , Lanz Otto I.
Published: March 2014

Blood perfusion is the local, non-directional blood flow through living tissue. It is measured as the volumetric flow rate of blood per volume of tissue and a large range of perfusion values have been reported for human tissue (i.e. 0.002–0.5 ml/ml/s). This large range is thought to be due to measurement sensitivity, environmental factors, and tissue type and location.
Dynamic Hydrostatic Pressurization Differentially Regulates Extracellular Matrix Elaboration by Bovine Inner and Outer Annulus Fibrosus Cells Seeded on 3-D Polymer Scaffolds
Authors: Reza Anna T. , Nicoll Steven B.
Published: March 2014

Current surgical treatments for intervertebral disc (IVD) degeneration result in decreased mobility of the spine [1]. A tissue engineering approach may provide an alternative that restores both IVD structure and function. The IVD is comprised of three distinct regions: the outer annulus fibrosus (OA), inner annulus fibrosus (IA), and the nucleus pulposus (NP). Each of the cell populations within these regions possess unique phenotypic properties that are greatly influenced by environmental factors, such as the surrounding 3-D extracellular matrix (ECM) and mechanical loading (i.e., hydrostatic pressurization) [2]. As such, both the 3-D scaffold and in vitro culture conditions may have marked effects on the development of tissue-engineered IVD constructs. Although the influence of mechanical loading on IVD cells and explants has been investigated, no prior studies have examined the impact of hydrostatic pressurization on OA and IA cells in 3-D culture. Therefore, the objective of this study was to determine the effects of dynamic hydrostatic pressurization on OA and IA cells seeded on 3-D fibrous poly(glycolic acid)-poly(L-lactic acid) (PGA-PLLA) scaffolds. We hypothesized that the application of hydrostatic pressure would promote increased production of type II collagen and chondroitin sulfate proteoglycan in both OA- and IA-seeded constructs.
Load Down-Regulates TNF-Alpha Induced Cartilage Degradation in Part Through NF-KB and P38 Pathways
Authors: Wolfe Valerie M. , Park Seonghun , Tomic Marjana , Torzilli Peter A. , Chen C. T. Christopher
Published: March 2014

Pro-inflammatory cytokines, such as interleukin-1 (IL-1) and tumor necrosis factor (TNF), can induce cartilage degradation after acute injury or in inflammatory diseases [1,2,3,7]. The degradative events are coordinated through the elevation and activation of two classes of enzymes, namely matrix metalloproteinases (MMPs) and aggrecanases (ADAMTS-4 and −5) [1,6]. Prior studies suggested that pro-inflammatory responses induced by IL-1β can be inhibited by tensile load [2] and more recently by cyclic compression [8]. It is, however, not clear whether load affects other cytokines, such as TNF-α. TNF-α is known to bind its receptor (TNFR1) to cause a cascade that ends with degradation of an inhibitor, IκBα, and release of the transcription factor NF-κB [3]. The actions of TNF-α are also known to be affected by at least three NF-κB independent pathways including the p38, ERK, and JNK pathways [4]. The objective of this study was to determine whether cyclic compression could affect TNF-α induced cartilage degradation and to determine the roles of p38, ERK, and JNK pathways in TNF-induced cartilage degradation. We hypothesized that cyclic loading would inhibit the degradative effects caused by TNF-α.
Flow Alteration Through Nasal Passages Due to Turbinectomy
Authors: Learned Amanda , Savilonis Brian , Miczek Sarah , Wexler David , Kimbell Julia
Published: March 2014

Internal structure plays a significant role in controlling airflow behavior through a nasal passageway. In cases of hypertrophy, swelling of membranes due to chronic sinusitis or allergy, or deviated septum, the anatomical nasal structures known as turbinates are considered to over-restrict airflow. Turbinectomy is a commonly performed surgical procedure that removes or reduces turbinate bulk, opening up the passages. In practice, this surgery enables patients to breathe more comfortably without relying on medications developed to relieve nasal congestion. However, there has been little investigation into fluid dynamic changes caused by this procedure.
Using Mechanical Environment to Enhance Stem Cell Transplantation in Muscle Regeneration
Authors: Cassino Theresa R. , Okada Masaho , Drowley Lauren M. , Feduska Joseph , Huard Johnny , LeDuc Philip R.
Published: March 2014

Muscle-derived stem cell (MDSC) transplantation has shown potential as a therapy for cardiac and skeletal muscle dysfunction in diseases such as Duchenne muscular dystrophy (DMD). In this study we explore mechanical environment and its effects on MDSCs engraftment into cardiac and skeletal muscle in mdx mice and neoangiogenesis within the engraftment area. We first looked at transplantation of the same number of MDSCs into the heart and gastrocnemius (GN) muscle of dystrophic mice and the resulting dystrophin expression. We then explored neoangiogenesis within the engraftments through quantification of CD31 positive microvessels. This study is important to aid in determining the in vivo environmental factors leading to large graft size which may aid in determining optimum transplantation conditions for muscle repair.
A 3d Histomorphometric Method for Analyses of Skeletal Tissue Mechanobiology
Authors: Gleason Ryan E. , Palomares Kristy T. S. , Einhorn Thomas A. , Gerstenfeld Louis C. , Morgan Elise F.
Published: March 2014

Skeletal repair and regeneration involve a dynamic interplay of biological processes that result in spatially and temporally varying patterns of tissue formation and remodeling. For example, during bone fracture healing the cartilaginous callus that is formed initially in the fracture site is subsequently mineralized and remodeled to restore the original form and function to the injured bone. During much of this healing process, the fracture callus is comprised of a heterogeneous mixture of cartilage, fibrocartilage, multipotent mesenchymal tissue, and bone. Adding to this complexity, mechanical stimuli are known to influence the rate and type of tissues formed during skeletal healing [1]. Given the growing body of evidence that controlled mechanical stimulation may be used to enhance healing, it is of substantial interest to elucidate relationships between the distributions of local stresses and strains that develop within the healing region and the distribution of tissue types that form. While histomorphometry is a well established approach for characterizing the latter, it has historically been limited to analyses of a small number of two-dimensional sections of tissue. Such 2D sampling may be inadequate for quantitative characterization of the irregular geometry and heterogeneous composition of healing tissues. In this study, we report on a 3D histomorphometric method and apply this method to an in vivo model of skeletal repair [2] in which a bending stimulus delivered to a healing bone defect results in the formation of predominantly cartilage tissue, rather than bone.
The Anisotropy and Tension/Compression Behavior of Human Cervical Tissue
Authors: Myers Kristin M. , Paskaleva Anastassia , House Michael , Socrate Simona
Published: March 2014

The cervix plays a crucial role in maintaining a healthy pregnancy, acting as a mechanical barrier to hold the fetus inside the uterus during gestation. Altered mechanical properties of the cervical tissue are suspected to play an important role in spontaneous preterm birth. However, not much is known about the mechanical properties of human cervical tissue and the etiology of spontaneous preterm birth.
Effects of Arterial Geometry on Inflow Rate Into Cerebral Aneurysms on Curved Arteries
Authors: Imai Yohsuke , Sato Kodai , Ishikawa Takuji , Yamaguchi Takami
Published: March 2014

Pathobiological studies have demonstrated that atherosclerotic lesions have been found on the wall of saccular cerebral aneurysms [1]. We propose a hypothesis that some of these aneurysms are prevented from rupturing due to the atherosclerotic lesions. It has been presented that mass transport of biochemical species such as LDL and ATP, has some important roles in the development of atherosclerosis. A variety of Computational Fluid Dynamics (CFD) studies of the mass transport has been performed for arteries [2, 3], few studies have however, done for aneurysms.
Comparison of 2-D Fiber Network Orientation Measurement Methods
Authors: Sander Edward A. , Barocas Victor H.
Published: March 2014

The mechanical properties of most soft tissues are dependent on the underlying network of collagen fibers, proteoglycans, and other extracellular matrix components [1]. Similarly, the properties of in vitro tissue analogs, often created from collagen or fibrin gels, are also dependent on the organization of the biopolymers within [2]. In both materials, the overall mechanical response is inherently multi-scale and dynamic. To understand the interplay between scales a satisfactory description of the microstructure must be obtained that is both tractable for modeling purposes and faithful to the essential physics of the tissue.
Development and Response of Materially-Nonlinear, Multi-Layer Synthetic Models of the Human Vocal Folds
Authors: Drechsel James S. , Munger Jacob B. , Pulsipher Allyson A. , Thomson Scott L.
Published: March 2014

The human vocal folds are responsible for sound production during normal speech, and a study of their flow-induced vibrations can lead to improved prevention and treatment of voice disorders. However, studying the vocal folds in vivo or using excised larynges has several disadvantages. Therefore, alternatives exist using either synthetic (physical) and/or computational vocal fold models. In order to be physiologically relevant, the behavior and properties of these models must reasonably match those of the human vocal folds.
The Role of Proteoglycans on Residual Stresses in the Aorta
Authors: Azeloglu Evren U. , Albro Michael B. , Thimmappa Vikrum A. , Haggart Charles R. , Ng Kenneth W. , Ateshian Gerard A. , Costa Kevin D.
Published: March 2014

Arteries exhibit significant residual stresses, most notably demonstrated by the tendency of rings of arterial wall to open when cut radially [1, 2]. Residual stresses play an important role in the identification of appropriate reference configurations, and hence the definition of stresses and strains in the tissue; they are also important in vascular growth, remodeling and disease [3–5]. Though it has been suggested that elastin appears to be primarily responsible for residual stresses in arteries [6], no explicit mechanism has been described to date which can explain how these residual stresses might be induced, and why they might vary along the length of arteries such as the aorta.
Muscle Mechanical Work Adaptations With Increasing Walking Speed
Authors: Neptune Richard R. , Sasaki Kotaro , Kautz Steven A.
Published: March 2014

Recent modeling studies of walking at self-selected speeds have identified how individual muscles work in synergy to satisfy the task demands including body support, forward propulsion and swing initiation (e.g. [1, 6]). These analyses revealed that young adults walking at a self-selected speed utilize a distribution of hip and knee extensor muscle force in early stance and ankle plantar flexor and rectus femoris force in late stance to provide support and forward propulsion [6]. However, how these muscles’ putative contributions to these functional tasks change with walking speed is not well understood. Intuitively, increasing walking speed would necessitate an increase in activity for muscles that contribute to forward propulsion. However, increasing walking speed is also associated with longer stride lengths (e.g., [2]), which may require increased activity from those muscles contributing to swing initiation, and increased activity from those muscles contributing to vertical support because the vertical excursion of the body’s center of mass increases.
Development of a System for Application of Dynamic Mechanical Compression on Intervertebral Discs in Organ Culture and Investigation of Load Magnitude Effects
Authors: Korecki Casey L. , MacLean Jeffrey J. , Iatridis James C.
Published: March 2014

In vivo studies on the intervertebral disc (IVD) indicate that the magnitude, frequency, and duration of applied compression loading results in alterations in mRNA expression, composition, and annulus fibrosus structure [1]. In vivo models typically use small animal models or small sample sizes that make it difficult to evaluate multiple dependent variables on the same tissue. In this study, it was considered a priority to utilize a large animal model to investigate the effects of magnitude of compression loading on interacting dependent variable measurements of disc cell viability, biosynthesis, composition, structure, and biomechanics. A bovine IVD organ culture system was used because it provides control over mechanical and chemical boundary conditions while maintaining viable cells and normal cell-matrix interactions. To date, there are no studies investigating the response of the IVD in organ culture to dynamic mechanical loading.
Measurement of Coronary Artery Wall Strain In Situ Using IVUS
Authors: Liang Yun , Zhu Hui , Friedman Morton H.
Published: March 2014

Atherosclerotic plaque rupture is the leading cause of mortality in cardiovascular diseases. Studying biomechanics of plaque provides important insights into its vulnerability, since a plaque behaves consistently with its underlying contents. Arterial wall strain in response to luminal pressure change is such a measurable quantity. Intravascular ultrasound (IVUS) imaging is a wildly available clinical technique providing real time cross-sectional images of the vessel wall and plaque morphometry. IVUS elastography has been used to measure the radial strain through correlation analysis of the IVUS radiofrequency (RF) signals. We have developed a strain estimation method based on IVUS image registration. Our method has the ability to overcome nonlinear tissue deformation and measure 2D strain.
Durability Test Method for Patella Implants
Authors: Kirkpatrick L. , Borgstede L. , Johnson T. , Mason J.
Published: March 2014

Modeling and testing of the patello-femoral joint (PFJ) presents challenges in simulating the appropriate loading and kinematics. Walking is an activity of lower demand for patella performance. Higher demands occur during higher flexion activities such as stair ascending/descending, chair rising, and squatting. High patellofemoral joint reaction forces (PFJR) have been shown to begin around 60° of tibiofemoral flexion and remain high (2.5 × BW to 3.35 × BW) until approximately 110° of tibiofemoral (TF) flexion, at which point contact with soft tissue will tend to off-load the knee joint. Therefore, the flexion range of highest load for the patella is considered to be between 60° and 110° of TF flexion.
Photonic Crystal Sensors for the Rapid Detection of Myocardial Ischemia
Authors: Baca Justin T. , Finegold David N. , Asher Sanford A.
Published: March 2014

Coronary Heart Disease is the leading cause of death in the United States and was responsible for approximately one of every five deaths in 2003 [1]. Unnecessary admissions to US Hospitals of patients with suspected Acute Coronary Syndrome (ACS) is estimated to cost about 12 billion dollars a year [2]. The earliest biochemical markers currently assayed do not appear in the blood for hours after the onset of chest pain; a rapid test for myocardial ischemia would help to expedite treatment and avoid unnecessary hospital admissions [3].
Dynamic Distraction of the Cervical Facet Joint Produces Higher Mechanical Allodynia than Quasistatic Distraction: Implications of Displacement Thresholds for Pain in Whiplash Loading
Authors: Dong Ling , Lee Kathryn E. , Winkelstein Beth A.
Published: March 2014

Chronic neck pain due to whiplash injury results in 10.2 million visits to ambulatory care settings annually in the United States [1]. During the whiplash kinematic, the cervical facet joint undergoes tensile loading at a strain rate of 500–1000%/s [2,3]. In addition, distraction of the facet joint and its capsule in animal models produces both firing of pain fibers in the capsule and persistent behavioral hypersensitivity (measured by mechanical allodynia) [4,5]. In vivo studies have demonstrated a dependence of pain symptoms on the magnitude of applied joint distraction, with some distraction magnitudes not producing any changes in physiologic outcomes or pain [5]. However, in those studies, joint loading was applied quasistatically, despite the dynamic nature of whiplash. While such work provides insight into mechanisms of facet-mediated neck pain and suggests that the magnitude of joint distraction may affect pain symptoms, those studies did not incorporate the dynamic effects necessary for modeling whiplash. It remains unclear whether dynamic loading of the cervical facet joint can induce behavioral hypersensitivity, and if so, whether the degree of behavioral sensitivity depends on the distraction magnitude. This pilot study compared the effects of dynamically and quasistatically applied facet joint loading on ligament kinematics and corresponding pain symptoms.
Using Triple-Density Bone Analog to Evaluate the Initial Fixation of a Cementless Tibial Implant
Authors: Son Yang W. , Fang Zhibin , Pendleton John E. , Levine Danny L. , Johnson Todd S.
Published: March 2014

To achieve stable initial fixation and longevity of a cementless tibial implant, low relative motion between implant and bone is vital. Although many studies have been conducted to evaluate the micromotion in-vivo and in-vitro, the methods have been either too complicated to repeat consistently or too simple to truly represent proximal tibial behavior. In this investigation, an experimental micromotion test method was developed to test a commercially available cementless tibial implant using a 3-layer bone analog simulating subchondral, trabecular, and cortical bone and the results compared with the micromotion measurement from a single density polyurethane foam. The results indicate that there is a significant difference in micromotion between the single density foam and the 3-layer bone analog when an applied tipping moment increases.
Fully Coupled vs. Partially Coupled Fluid-Structure Interaction Methods for Patient-Specific Abdominal Aortic Aneurysm Biomechanics
Authors: Scotti Christine M. , Finol Ender A.
Published: March 2014

Primary among the mechanical factors linked with abdominal aortic aneurysm (AAA) rupture is peak wall stress, frequently quantified as either the maximum principal or Von Mises stress exerted along the diseased arterial wall. Intraluminal pressure, as an impinging normal force on the wall, has been hypothesized as the dominant influence on this stress and thus the majority of numerical modeling studies of AAA mechanics have focused on static computational solid stress (CSS) predictions [1,2]. Unfortunately, retrospective studies comparing the magnitude of wall stress with the failure strength of the aneurysmal wall have yet to consistently predict the outcome for patient-specific AAAs [3,4]. Previous studies have shown that hemodynamics also plays a significant role in both the biological and mechanical factors that exist within AAAs. In the present investigation, partially and fully coupled fluid-structure interaction (p-FSI and f-FSI, respectively) computations of patient-specific AAA models are presented and compared to identify the effect of fluid flow in the biomechanical environment of these aneurysms.
Effect of Age and Frequency on Intervertebral Disc Cell Response to Dynamic Compression
Authors: Korecki Casey L. , Kuo Catherine K. , Tuan Rocky S. , Iatridis James C.
Published: March 2014

The intervertebral disc (IVD) is a unique orthopaedic tissue consisting of at least two cell types: fibroblast-like annulus fibrosus (AF) cells and chondrocyte-like nucleus pulposus (NP) cells. Culture of cells in 3D gel matrices (such as alginate or agarose), maintains the normal morphology and ECM molecule production of chondrocytes for extended periods of time and also allows the application of various forms of mechanical stimulation, such as hydrostatic or compressive loading. In vivo studies have shown IVD cells to be responsive to frequency, duration, and amplitude of mechanical load [1]. IVD literature on mechanobiology uses varying methodologies to apply dynamic loads (compression, hydrostatic forces), with different times of mechanical stimulation, differences in model systems (in vivo, tissue culture, cell culture), species, and ages, and an optimal loading protocol to stimulate extracellular matrix protein accumulation is unknown. The overall goal of this work is to evaluate the potential, and perhaps even feasibility, of mechanical stimulation for extracellular matrix (ECM) regeneration using intervertebral disc cells. Also of interest is whether cells from mature tissue are capable of serving as a potential cell source for future IVD regeneration [2,3].
Microvascular Oreintation During Angiogenesis: Effects of Mechanical Stretch and Boundary Conditions
Authors: Krishnan Laxminarayanan , Underwood Clayton J. , Maas Steve A. , Ellis Benjamin , Kode Tejas C. , Hoying James B. , Weiss Jeffrey A.
Published: March 2014

Mechanical forces affect the behavior of a variety of cell types including fibroblasts, chondrocytes, osteoblasts, smooth muscle cells, and endothelial cells. In vitro cellular orientation is primarily achieved through cell-generated mechanical forces or contact guidance. Endothelial cell (EC) cords align both normal to the stretch direction as well as along pre-tensioned collagen matrices. Confluent ECs orient parallel to grooved surfaces while tractional forces generated by ECs contract the matrix aligning collagen fibers, which in turn are considered a guiding scaffold. The influence of mechanical forces and boundary conditions on the growth and proliferation of microvessels during the process of angiogenesis is unknown. A better understanding of these interactions is essential both from a basic science standpoint as well as in the engineering of artificial vascularized matrices with specific orientation of vessels and endothelial cells. The objective of this study was to examine the role of internal and external mechanical forces in microvessel orientation during angiogenesis using an in vitro model of angiogenesis.
Multiscale Stress Analysis of Sheared and Focally-Adhered Endothelial Cells: Role of Subcellular Matrix Moduli in Focal Adhesion-Mediated Signaling
Authors: Butler Peter J. , Bhatnagar Amit , Ferko Michael
Published: March 2014

Focal adhesions (FAs) and their associated integrins are thought to act as mechanosensors and transducers of shear stress into intracellular biochemical signals. However, to date there exists no quantification of the magnitude of forces generated at integrin molecules in response to apically-applied fluid shear stress. Thus, we used finite element analysis of fluid dynamics and cellular stresses to compute FA stresses from solid models of focally-adhered endothelial cells. These models were developed from quantitative 3-D microscopy and total internal reflection fluorescence (TIRF) microscopy of calcein-stained endothelial cells. Extrusion coupling variables mapped stresses from the macroscale cell model to individual microscale 3-D models of FAs determined from quantitative TIRF. Included in the microscale FA model were moduli for subcellular matrix (SCM) (e.g. hyaluronan, hyaluronaic acid and other glycocalyx constituents) and extracellular matrix (ECM) (e.g. collagen, fibronectin). Integrin forces were estimated from assumed bonds densities and computed FA stresses. Maximal bond tension obtained from the simulation for a single integrin-extracellular matrix (ECM) bond was .1pN. Thus, it is unlikely that integrin-ECM bonds or chemical activities are appreciably affected by shear stress. The computational model, however, supports an alternative model of activation in and reorganization of FAs in which shear stress-induced forces cause the membrane to bend toward and away from the ECM immediately upstream and downstream of the FA, respectively. The simulation also suggests that the elasticity of the SCM plays an important role in modulating shear-induced FA reorganization. These results support a new model of endothelial cell activation by shear stress in which integrins and FAs participate in the directional biasing of force-induce signaling but do not initiate it.
Bone Formation and Inhibition of Bone Loss by Dynamic Muscle Stimulation With Altered Interstitial Fluid Pressure
Authors: Qin Yi-Xian , Lam Hoyan
Published: March 2014

Tissue-level mechanisms and functions, including bone strain and muscle, are the potential key players in bone physiology and adaptation [1,2,3]. However, the mechanisms are not yet fully understood. Exercise such as muscle contraction appears to increase blood flow to the skeletal tissues, i.e., bone and muscle. These evidences imply that bone fluid flow induced by muscle dynamics may be an important role in regulating fluid flow through coupling of muscle and bone via microvascular system.
Comparing the Kinematics of Lumbar Spine: Anatomic Facet Replacement System (AFRS™) vs. Rigid Fixation System
Authors: Mehta A. , Faizan A. , Kiapour A. , Jangra J. , Goel V. K. , Hoy B.
Published: March 2014

Problems associated with spinal fusion such as adjacent level degeneration and donor site pain have shifted the focus to motion preservation technologies. The Anatomic Facet Replacement System (AFRS™) (Facet Solutions, Inc., Logan, Utah) attempts to address posterior lumbar spine pathologies while preserving stability and natural biomechanics thereby mitigating any potential adjacent level effects resulting from the reduction or elimination of motion as seen in semi-constrained dynamic stabilization and fusion devices. The AFRS™ is comprised of a precision instrumentation set whose design is based upon a comprehensive CT morphology study of the facet joint. It utilizes traditional pedicle screw fixation of its superior and inferior facet implants and is manufactured from a wear resistant alloy called cobalt-chromium-molybdenum. An experimentally validated finite element model was used for the quantification of facet loads and stresses in various components of the facet replacement system and also in the model stabilized using a pedicle screw rigid rod fixation system.
Finite Element Modeling of Rollover Crash Tests With Hybrid III Dummies
Authors: Friedman Keith , Hutchinson John , Mihora Dennis
Published: March 2014

This paper reports on the finite element modeling of rollover crash tests with Hybrid III dummies. Finite element models of a vehicle design and the Hybrid III dummy were used to evaluate the subsystem under manufacturer created rollover conditions for a production and roll caged roof structure.

The objective of this study was to demonstrate the ability to reproduce the impact environment occurring in rollover crash tests. There are over 26,000 fatalities and serious injuries annually occurring in rollover accidents in the United States. Many of these are to restrained occupants and their head and spinal injuries have been associated with contact with the roof structure. To analyze the crash tests the effects of the system, finite element models were made of rollover crash tests that had been conducted using baseline and modified passenger vehicles and Hybrid III dummies using the defined impact conditions. Neck loads were utilized to validate the model against the test results. The results show that finite element modeling can reproduce the results from rollover crash tests.