bluuebunny/crossref_metadata_2025 huggingface dataset:
Development of a Quantitative Mechanical Test of Atherosclerotic Plaque Stability
Authors: Wang Ying , Ning Jinfeng , Sutton Michael A. , Lessner Susan M.
Published: July 2013

Atherosclerotic plaque rupture is the main cause of myocardial infarction, coronary thrombosis and stroke. Current clinical observations suggest that an advanced plaque features a thin, collagen-rich fibrous cap infiltrated by macrophages, overlying a large lipid core rich in lipid-laden macrophages. However, due to relatively poor understanding of mechanisms associated with plaque rupture, there is no quantitative standard for plaque stability estimation.
The Interplay Between Biomechanical and Biochemical Factors Regulates Lumen Formation and Navigation of Endothelial Cell Sprouts
Authors: Shamloo Amir , Heilshorn Sarah C.
Published: July 2013

Angiogenesis is the process of forming new blood vessels that originate from pre-existing vessels. In early angiogenesis stages, endothelial cells (ECs) migrate from the lumen of developed blood vessels into the surrounding extracellular matrix (ECM). Through the coordinated actions of migration and proliferation, these ECs organize into tubular capillary-like structures called sprouts. In this study, 3D EC sprout formation was examined using a microfluidic device that enabled the separate and simultaneous tuning of biomechanical and biochemical stimuli (Fig. 1). While previous investigations have been performed on each of these factors individually1, 2, more recent studies have identified a critical interplay between the simultaneous effects of these two factors3. For example, we previously studied 2D EC chemotaxis in response to vascular endothelial growth factor (VEGF) gradients in the absence of biomechanical stimulation.4 In developing a model that enables precise specification of biochemical and biomechanical cues, we utilized a protocol that enables ECs to undergo a transition from the 2D to 3D culture environment mimicking angiogenic sprouting. Here we quantified the relative importance and combined consequences of discrete changes in matrix density, growth factor concentration, and growth factor gradient steepness during the stages of early sprout initiation, sprout elongation, sprout navigation, and lumen formation.
Are Pure Lateral Chest Deflections a Hallmark for Side Airbag Boundary Condition?
Authors: Hallman Jason J. , Yoganandan Narayan , Pintar Frank A.
Published: July 2013

For thoracic and abdominal injury risk during blunt lateral impact, deformation (deflection) has been identified as an injury metric. With stationary biological test subjects, this metric has been obtained uniaxially from depth-limited impactors [1] and from post-experiment digitization of videography [2]. In sled experiments, deflection has been measured by videography of innovative marker sets [3] and by chestband transducers [4]. With the chestband, resistive strain gage time traces are recorded and reconstructed into closed contours representing the thoracic or abdominal circumference in the transverse plane. The resulting contours reveal thoracoabdominal deformation patterns in two dimensions. These patterns are important for side airbag interactions as they induce complex posterolateral deformations [5].
Model of Silorane Composite for Bone Stabilization Application
Authors: Melander Jennifer R. , Weiler Rachel A. , Miller Bradley D. , Kilway Kathleen V. , Eick J. David
Published: July 2013

Improvements in body armor and battlefield medical care have resulted in an increase in survival rates but also an increase in survivable battlefield extremity injuries (Covey 2002; Covey 2006; Owens, Kragh et al. 2007). It is well known that these traumatic extremity injuries require adequate stabilization to achieve an optimal healing outcome. Extremity fractures also affect a large proportion of the civilian population. In 2005, 5.7 million Americans suffered an injury resulting in bone fracture (CDC/NCHS). Transport of these domestically injured individuals to medical facilities also requires stabilization to avoid further injury.
Three-Dimensional Simulation of In Vitro Angiogenesis: Effects of Extracellular Matrix Structure and Density
Authors: Edgar Lowell Taylor , Guilkey James E. , Underwood Clayton J. , Baggett Brenda , Utzinger Urs , Weiss Jeffrey A.
Published: July 2013

The process of angiogenesis is regulated by both chemical and mechanical signaling. While the role of chemical factors such as vascular endothelial growth factor (VEGF) during angiogenesis has been extensively studied, the influence of the mechanostructural environment on new vessel generation has received significantly less attention. During angiogenesis, endothelial cells in the existing vasculature detach and migrate out into the surrounding extracellular matrix (ECM), forming tubular structures that eventually mature into new blood vessels. This process is modulated by the structure and composition of the ECM [1]. The ECM is then remodeled by endothelial cells in the elongating neovessel tip, resulting in matrix condensation and changes in fiber orientation [2]. The mechanism as to how angiogenic vasculature and the ECM influence each other is poorly understood.
Control of Active Above-Knee Prostheses Through Electromyography
Authors: Wu Sai-Kit , Waycaster Garrett , Shen Xiangrong
Published: July 2013

This paper describes a new electromyography (EMG) based control approach for powered above-knee prostheses. In the proposed control approach, the EMG signals are utilized as the direct control commands to the prosthesis, and thus enable the volitional control by the wearer, not only for locomotive functions, but for arbitrary motion as well. To better integrate the AK prosthesis into the rest of the human body, the control approach incorporates a human motor control mechanism-inspired ‘active-passive’ model, which combines an active control component that reflects the wearer’s motion intention, with a passive control component that implements the controllable impedance critical to the safe and stable interaction with the environment. The effectiveness of the proposed control approach was demonstrated through the experimental results for arbitrary free swing and level walking.
Comparison of Two Piano Playing Methods Using Motion Capture
Authors: Kelley Jace D. , Benoit Heather D. , White Joel D. , Abbott-Kirk Jane , Garner Brian A. , Skurla Carolyn P.
Published: July 2013

A motion capture study was performed to quantify differences between two piano playing methods. Reflective markers were placed on the hands, arms, and torsos of 10 pianists. Cameras positioned around the pianist captured and recorded the motion of the markers for post-processing analysis.
Outside-In vs. Inside-Out: Contrasting Patterns of Compressive Deformation in Cartilage and Meniscus
Authors: Lai Janice H. , Levenston Marc E.
Published: July 2013

The superficial zones of articular cartilage and meniscus are structurally distinct from the rest of the tissue. In cartilage, the superficial zone is characterized by a relatively low proteoglycan content and a relatively high content of fine collagen fibrils oriented parallel to the articular surface [1], resulting in a low compressive modulus at the surface [2, 3]. In meniscus, the superficial zone is characterized by a fine mesh of randomly oriented collagen fibrils [1] while the interior of the tissue consists of bundles of circumferentially oriented collagen I fibers surrounded by a secondary network containing multiple collagen types and proteoglycans [4]. As relatively little is known about the depth-varying mechanical properties of the meniscus, this study aimed to characterize the depth-dependent response of cartilage and meniscal tissue to compression by comparing the two-dimensional strain fields of site-matched tissue pairs.
Role of Hemodynamics in Initiation of Aneurysmal Remodeling
Authors: Meng Hui , Natarajan Sabareesh K. , Metaxa Eleni , Tremmel Markus , Gao Ling , Mandelbaum Max , Xiang Jianping , Liaw Nicholaws , Swartz Dan , Siddiqui Adnan , Mocco J. , Kolega John
Published: July 2013

Hemodynamic insult has long been speculated to be a key factor in intracranial aneurysm (IA) formation,1 but the specifics of hemodynamic insult contributing to this process are not understood. Despite other risk factors, IAs are predominantly found at locations associated with unique hemodynamic stress such as at the apices of arterial bifurcations or outer curves, prominent in high wall shear stress (WSS) and wall shear stress gradients (WSSG).2 Furthermore, it appears that increased flow at these locations is required to trigger the initiation of aneurysmal remodeling.3 We have previously shown that increasing flow in the rabbit basilar artery (BA), secondary to common carotid artery (CCA) ligation, resulted in nascent aneurysm development at the basilar terminus (BT).4 However, it is unclear if certain hemodynamic stress thresholds must be exceeded to trigger aneurysmal remodeling, and whether sustained insult is necessary.
Particle Image Velocimetry Flow Measurements About a Vena Cava Filter
Authors: Navitsky Michael A. , Nanna Jason C. , Pearson Joseph J. , Scanlon Matthew P. , Lynch Frank C. , Shontz Suzanne M. , Manning Keefe B.
Published: July 2013

Deep vein thrombosis (DVT) is a medical condition in which blood clots form in the lower extremities, often times the right leg, or pelvis region. These blood clots are formed through a variety of circumstances including: injury to the vessel wall, decreased blood supply, or increased clotting factors. Complications from DVT often arise when the blood clot breaks free forming a pulmonary embolism (PE). The incidence of such an occurrence is over 600,000 cases per year in the United States. If the PE is allowed to travel through the vascular system, occlusion of the pulmonary arteries and death may result. There are over 200,000 deaths attributed to this cause every year in the United States.
Possible Mechanism of Blast-Induced Neuronal Damage in Hippocampus May Explain Cognitive Deficits
Authors: Sajja Sujith V. , Galloway Matthew P. , Ghoddoussi Farhad , Dhananjeyan T. , Kespel Andrea , VandeVord Pamela
Published: July 2013

Traumatic brain injury due to blast exposure is quickly becoming the most frequently seen injury in today’s battlefields. Alterations in cognitive function, such as attention, memory, language and problem solving skills appear to occur as a result of blast-induced TBI. Furthermore, behavioral symptoms such as mood changes, depression, anxiety, impulsiveness and emotional outbursts are associated with blast-induced TBI (Okie et al, 2005). Observed overlaps between symptoms of post-traumatic stress disorder (PTSD) and TBI confound the differential diagnosis. Thus, soldiers with blast-induced TBI may be substantially under-diagnosed after exposure to blast waves. Animal models of blast-induced TBI are underdeveloped and there is a vital need for blast exposure biomarkers to help effectively diagnosis blast-induced TBI. In this study, we have investigated the mechanisms that underlie cognitive impairment of blast-induced neurotrauma. We have studied the cascade of neurochemical changes within the hippocampus of blast-exposed animals using 1H-Magnetic Resonance Spectroscopy (1HMRS). Furthermore, we examined changes in TBI protein markers using Western blotting and immunohistochemistry. Results suggest that exposure to blast waves has a significant effect on the hippocampus.
Finite Element Analysis of the Influence of Cement Viscosity on Cement Mantle in Total Knee Arthroplasty
Authors: Rohrs Eric , Paliwal Manish , Allan D. Gordon
Published: July 2013

Aseptic loosening of the tibial implant is one of the major reasons of failure in Total Knee Arthroplasty (TKA). The cement viscosity at the time of application to the bone influences the cement penetration and stability of the prosthesis. Four cements of different viscosities and set times were selected for analysis (Simplex-P, DePuy-2, Palacos, and Endurance). Finite element analysis was used to model cement flow and cement mantle resulting from a surgically implanted tibial plate into sawbone open cell blocks simulating tibial cancellous bone (Pacific Research, WA). Frictional stress, pressure, sliding distance, and total stress at the bone-cement-stem interface were studied at the contact interfaces, which may contribute towards construct stability. Palacos had the maximum interface pressure, sliding distance, and total stress, while DePuy-2 displayed the lowest total stress and sliding distance at interface. Simulated flow profile correlated well with the cemented constructs’ radiographic profiles.
A New Scheme for Soft Tissue Artifact Compensation in Human Motion Analysis
Authors: Gao Bo , Banks Scott , Zheng Nigel
Published: July 2013

Skin marker-based stereophotogrammetry provides a non-invasive and radiation-free approach in human motion analysis. It has been widely used to study the normal function and pathological conditions of human musculoskeletal system. One major limitation of this technique is usually referred to as soft tissue artifact (STA), which is defined as the relative movement between skin markers and the underlying bone. Much effort has been devoted to developing techniques for STA compensation and better motion analysis accuracy. However, the problem has not yet been solved satisfactorily.
Misinterpretation of the Functional Severity of Coronary Stenosis Due To Variability in Arterial Wall Compliance
Authors: Konala Bhaskar Chandra , Das Ashish , Effat Mohamed , Imran Arif , Banerjee Rupak K.
Published: July 2013

Effect of arterial wall compliance on the invasive coronary diagnostic parameters for various severities of coronary stenoses was assessed. The Mooney-Rivlin model was used to define the non-linear properties of the arterial wall and the plaque regions. The non-Newtonian viscosity of blood was modeled using the Carreau model. A finite element method was employed to solve the pulsatile fluid (blood)-structure (arterial wall) interaction (FSI) equations. Variability in the diagnostic parameter values can occur near the cut-off value due to change in compliance of stenotic arteries between the range of 84% and 89% area stenosis. This may lead to misdiagnosis and might wrongly lead to postponement of coronary intervention.
Fracture Patterns on the Infant Porcine Skull Following Severe Blunt Impact
Authors: Powell Brian J. , Passalacqua Nicholas V. , Baumer Timothy G. , Fenton Todd W. , Haut Roger C.
Published: July 2013

There is a 1 in 3 chance of abuse in a case where a child less than 18 months has a skull fracture [1]. The most commonly fractured site on the skull is the parietal bone, however it is currently difficult to establish the causation of injury based on the characteristics of the injury [2]. Thus, injury biomechanics are often utilized in the investigation of suspected child abuse cases [3]. Computer simulations, test dummies, and animal models are all used as aids in the assessment of skull fracture causation. For a given impact situation, a number of variables can control the pattern of skull fracture. A study by Baumer et. al assessed the effects of interface and age using an infant porcine skull model, specifically looking at the location of fracture initiation on the parietal bone [4]. This study showed that in low energy impacts fracture initiation occurs at the bone-suture boundary. Also, a deformable interface caused more fracture than a rigid interface for very young subjects. The current study was conducted to assess the effects of higher energy impacts on the patterns of fracture in this model.
Numerical Study on Diastolic Left Ventricular Hemodynamics Using Motion Models of Mitral Valve With/Without Edge-to-Edge Repair
Authors: Hu Yingying , Shi Liang , Parameswaran Siva , Smirnov Sergey A. , He Zhaoming
Published: July 2013

Edge-to-edge repair (ETER) is a newly developed technique to correct such mitral valve (MV) malfunctions as regurgitation [1,2]. This technique changes MV geometric configuration by suturing the anterior and posterior leaflets at central or commissural edges, and consequently alters MV and left ventricle (LV) dynamics. For instance, stress in the MV elevated due to ETER may cause leaflets tearing near suture. Little has been known about shear stress on the MV and LV walls under MV ETER conditions, where high shear stress might cause platelet activation or hemolysis [3]. When ETER is done at the central leaflet edges, it generates two MV orifices, leads to two deflected jets, and completely changes vortices in the LV. ETER also reduces the orifice area, and increases jet velocity and transmitral pressure [1,2,4]. Flow patterns in the LV and ETER effects on the LV and MV functions have not been understood well.
Empirical Modeling the Effect of Hsp90 Inhibition on Cytokines Associated With Impaired Biotransport of Apoptotic Debris
Authors: Shimp Samuel K. , Reilly Christopher M. , Rylander Marissa Nichole
Published: July 2013

Systemic lupus erythematosus (SLE) is a chronic inflammatory autoimmune disorder that can affect nearly every organ in the body. A link has been established between abnormal biotransport of apoptotic cell debris and pathogenesis of SLE [1]. Lupus mice are hyper-responsive to immune stimulation and overproduce inflammatory mediators including IL-6, IL-12, and nitric oxide (NO) [2]. Extracellular expression and transport of inflammatory cytokines are thought to be involved with the inhibited clearance of cellular debris [1]. Hsp90 has a prominent role in folding and conformational regulation of several client proteins, including proteins involved with production of inflammatory mediators [3]. Hsp90 readily binds ATP at the amino (N-) terminal domain. This binding event causes a conformational change in Hsp90 making it “clamp down” on its client protein [3]. Geldanamycin (Geld) is a known inhibitor of Hsp90 that out competes ATP binding at the N-terminal. This prevents chaperone capability and ultimately leads to client protein deactivation, destabilization, and degradation [3]. Hsp90 inhibitors have been shown to suppress immune stimulated release of interleukin 6 (IL-6), IL-12, tumor necrosis factor alpha (TNF-α), and nitric oxide (NO) [4].
A Novel Approach Towards Modeling the Collagen Fibril Network for Use in Nonlinear Anisotropic Polyconvex Mixture Models of Articular Cartilage
Authors: Shirazi Reza , Vena Pasquale , Sah Robert L. , Klisch Stephen M.
Published: July 2013

Despite distinct mechanical functions, biological soft tissues have a common microstructure in which a ground matrix is reinforced by a collagen (COL) fibril network. The highly anisotropic, heterogeneous, and asymmetric material properties caused by the microstructural nature of the COL fibril network suggest the importance, as well as the challenges, of accurately modeling soft tissue biomechanics. For soft fibrous tissues with multiple constituents, mathematical distribution functions have represented dispersed and continuous (i.e. non-discrete) fibrils oriented in all directions depending on the type of (and anatomical location in) the tissue under investigation [1–2]. These types of continuous fibril models have been used recently for articular cartilage [3–5]. The strain energy of the COL fibril network is calculated based on the response of individual fibrils in tension in different directions and integrated over a unit sphere at a material point. The specific aims of the current study were to: 1. introduce a novel approach to modeling a continuous distribution of COL fibrils in soft tissues; 2. develop a strain energy function for the COL network based on the proposed distribution function of COL fibrils; 3. derive the stress and material elasticity tensors for the COL network that may be “pre-stressed” in a stress-free natural configuration of the tissue; 4. propose a special model that may be appropriate for immature tissue and establish its suitability for use in a polyconvex tissue strain energy function.
Designing a Therapeutic Mechanical Horse
Authors: Benoit Heather D. , Kelley Jace D. , White Joel D. , Garner Brian A.
Published: July 2013

Hippotherapy is a strategy that uses the movement of a horse to treat individuals with any of a variety of neuro-musculoskeletal disabilities including cerebral palsy, paralysis, traumatic brain injury, stroke and others. The patients’ overall treatment program includes time riding on a therapeutic horse under the direction of a physical therapist. The premise behind hippotherapy is that the movement of the horse drives the patients’ body, and particularly the hips, in a pattern that is similar to natural human movements such as healthy human gait [1][2][3][4]. The rhythmic motion of the riding surface engages and challenges the patient to actively anticipate, compensate, and adapt in order to maintain balance. Hippotherapy treatment is believed to help improve flexibility, strength, muscle symmetry, balance and postural control, and motor function [1][2][4][5][6].
Direct Visualization of the Initiation and Progression of Vertebral Fractures
Authors: Hussein Amira I. , Morgan Elise F.
Published: July 2013

Vertebral fractures are the hallmark of osteoporosis, yet the failure mechanisms involved in these fractures are not well understood. Failure patterns within whole vertebrae are typically estimated from finite element analyses or from images acquired after fracture has occurred. Experimental measurement of deformations sustained by vertebrae during injurious loading would enable direct visualization of vertebral failure mechanisms as well as the possibility of validating the results of numerical simulations of vertebral fracture. Time-lapsed micro-computed tomography (μCT) has been used previously to visualize failure processes in excised specimens of trabecular bone [1,2], and methods of digital volume correlation (DVC) can be applied to these types of image series to obtain quantitative information on the deformations that the bone undergoes [3]. However, application of DVC to whole bones has not been reported and involves additional challenges such as the irregular geometry of the volume and the large size of the sets of image data. The overall goal of this study was to develop a DVC-based method for quantifying deformations throughout entire vertebrae as these vertebrae are loaded to failure.
Multifilament Stainless Steel as a Core Suture Material in Flexor Tendon Repair
Authors: McDonald Erik , Fischer Jason , Buckley Jenni M. , Gordon Leonard
Published: July 2013

Over the past decades flexor tendons have been repaired using many repair configurations and suture types. The result of the repair depends on the method of attachment of the suture to the tendon(1), as well as the characteristics of the suture material (2). Both the ultimate tensile strength of the repair and the force needed to produce a 2mm gap at the repair site are important(3). Ultimate tensile strength and gap formation depend on the number of strands crossing the repair site, the characteristics of the suture material(4,5), and the repair configuration to the tendon. Stiffer sutures allow less gap formation for the same applied force(5). The repair also depends on the knot holding ability of the suture, because sutures fail most frequently at the knots. This is either because the knots untie or the suture is weakened at these points. The ideal combination is a suture technique that provides a strong attachment to the tendon, with a suture that is strong and resists elongation. Combined with these features the method should also be relatively simple to perform, with suture that is manageable and easy to tie.
Effect of Vessel Stiffening and High Pulsatility Flow on Contractile Function and Proliferation of Small Arterial Cells
Authors: Scott Devon , Shandas Robin , Tan Wei
Published: July 2013

Recent studies have identified arterial stiffening as a predictor of some vascular diseases such as pulmonary hypertension, which is characterized by dysfunction of small arteries. Stiffening is shown to cause changes in blood flow, extending high pulsatile flow into small arteries that normally experience steady flow conditions (Chui 2004). However, few studies have investigated the mechanisms underlying the effects of arterial stiffening on vascular remodeling. We hypothesized that arterial stiffness effects dysfunction of downstream vascular endothelium and smooth muscle through changes in flow pulsatility. Previously we developed a flow system to study the influence of pulse flow waves, by modulating upstream stiffness, on downstream mimetic vascular cell co-culture. With this system, the present study examines contractile and proliferating protein expressions of smooth muscle cell (SMC) co-cultured with endothelial cell (EC). The endothelium, directly interfaces with the blood flow, and transduces mechanical signals to underlying SMC (Stegemann 2005). We recently showed that high pulsatile flow induced EC dysfunction. Therefore, we further asked whether high pulsatility flow would cause characteristic changes of small arterial SMC in the hypertension condition such as smooth muscle hyperplasia (increased cell proliferation) and hypertrophy (increased contractile proteins) (Voelkel 1997), and whether these changes would be mediated by EC dysfunction.
Early Cellular and Molecular Changes During Hemodynamic Initiation of Intracranial Aneurysms in a Rabbit Model
Authors: Gao Ling , Mandelbaum Max , Liaw Nicholas , Natarajan Sabareesh K. , Mocco J. , Siddiqui Adnan H. , Meng Hui , Kolega John
Published: July 2013

Hemodynamics constitutes a critical factor in the formation of intracranial aneurysms. However, little is known about how an intracranial arterial wall responds to a hemodynamic insult, and how that response contributes to aneurysm formation. Unlike straight arterial segments (which respond to increased flow by expansive remodeling) and sinuses opposing bifurcation apices (which harbor recirculation flows and are prone to atherosclerotic development), aneurysmal degeneration occurs on the apical side of the bifurcation in the immediate peri-apical region, where flow creates very high wall shear stress (WSS) and wall shear stress gradient (WSSG)1. This results in destructive aneurysmal remodeling, characterized by loss of the internal elastic lamina (IEL) and thinning of the media. It is unknown how the unique hemodynamic conditions of combined high WSS and positive WSSG elicit these morphological changes, how the vascular wall responds to such insult at the molecular level, and what molecular mechanisms are involved.
Development of Methodology to Assess the Effect of Stem Surface Finish on Implant Loosening
Authors: Hosein Yara K. , McLachlin Stewart D. , King Graham J. W. , Dunning Cynthia E.
Published: July 2013

Joint replacement surgery is a common orthopaedic procedure used for the treatment of diseased or damaged joints. The majority of these replacement systems incorporate a stemmed portion which is inserted into the bone canal, either with or without bone cement, to achieve fixation to the host bone. Although this procedure has proven effective, relative displacement at the bone-cement and/or cement-stem interfaces (i.e., implant loosening) is a common complication, leading to pain and the need for revision surgery.
Modeling of Lymphatic Contractility
Authors: Rahbar Elaheh , Placette Beth A. , Moore James E.
Published: July 2013

The lymphatic system is responsible for maintaining fluid and protein homeostasis, collecting approximately 4 liters of interstitial fluid per day and returning it to the venous system. Transporting this fluid, however, is no trivial task. Given that the point of return is located in the upper torso, most of the body’s lymph is pumped “uphill”. Furthermore, tissue pressures are very low, no higher than 15 mmHg, suggesting that lymph flow is not solely pressure driven. In fact, lymphatic vessels rely on intrinsic and extrinsic pumping mechanisms to propel lymph.
Three-Dimensional High Resolution Scaffold Fiber Architecture and Morphology in Tissue Engineered Heart Valve Tissue
Authors: Eckert Chad E. , Mikulis Brandon T. , Gerneke Dane , Gottlieb Danielle , Smaill Bruce , Mayer John E. , Sacks Michael S.
Published: July 2013

Engineered heart valve tissue (EHVT) has received much attention as a potential pediatric valve replacement therapy, offering prospective long-term functional improvements over current options. A significant gap in the literature exists, however, regarding estimating tissue mechanical properties from tissue-scaffold composites. Detailed three-dimensional structural information prior to implantation (in vitro) and after implantation in (in vivo) is needed for improved modeling of tissue properties. As such, a novel high-resolution imaging technique will be employed to obtain three-dimensional microstructural information. Analysis techniques will be used to fully quantify constituents of interest including scaffold, collagen, and cellular information and to develop appropriate two-dimensional sectioning sampling protocols. It is the intent of this work to guide modeling efforts to better elucidate EHVT tissue-specific mechanical properties.
A Novel Biomimetic Model for Studying Mechanics of Embryonic Morphogenesis and Differentiation
Authors: Henkels Julia A. , Zamir Evan A.
Published: July 2013

Before the explosion of genetics research in the last century, embryonic development was largely studied from a mechanical perspective. Paired with genetic advances in understanding developmental signaling pathways and induction mechanisms, an important goal for understanding morphogenesis is to discover how the genome codes for changes in the mechanical movements of the embryonic cells. After formation of the zygote, a phase of rapid mitotic cell division is followed by epithelialization resulting in a cohesive sheet of cells termed the epiblast. During the next major phase of triploblastic development called gastrulation, a group of undifferentiated cells in the epiblast moves collectively to the embryonic midline and eventually gives rise to the three primary germ layers: endoderm, mesoderm, and ectoderm. At the primitive streak—the “organizing center” in amniotes (reptiles, birds, and mammals) which delineates anterior-posterior polarity—prospective endodermal and mesodermal precursors undergo epithelial-to-mesenchymal transition (EMT), internalization, and eventually organogenesis. “It is not birth, marriage, or death, but gastrulation which is truly the most important time in your life” (Lewis Wolpert, 1986).
Simulated Osteotomy of the Trapezium Reduces Radial Subluxation and Improves Contact Pressure Distribution Across the Thumb Carpometacarpal Joint in Lateral Pinch
Authors: Mercer Deana , Salas Christina , Love James , Lansing Letitia , Medoro Amanda , Reda Taha Mahmoud M. , Cheema Tahseen
Published: July 2013

Joint laxity and radial subluxation of the metacarpal on the trapezium have been associated with arthritis of the carpometacarpal (CMC) joint of the thumb. In normal flexion and extension of the thumb, the ligaments and the joint are minimally stressed. However, in opposition and lateral pinch (key pinch), the two surfaces rotate on each other, generating an unequal surface stress. Over time, the unequal stresses lead to an asymmetrical wear pattern. This leads to increased strain on the ligaments and may lead to subluxation over time.1 Surgical treatment of early arthritis of the CMC joint includes ligament reconstruction or first metacarpal extension osteotomy to decrease joint laxity. Once laxity exists, joint degeneration is accelerated.2 The long-term impact of painful CMC arthritis on activities of daily living can be debilitating.
Objective Measures Relating Cervical Dysfunction to Clinical Diagnosis and Treatment Effects
Authors: Rutledge B. , Vorro J. , DeStefano L. , Francisco T. , Gorbis S. , Bush T. R.
Published: July 2013

The majority of musculoskeletal (MSD) impairments in the cervical (neck) region cannot be determined through MRIs or radiographs but are instead diagnosed through a clinical assessment technique using palpation. Palpatory diagnostic techniques are based on range of motion (ROM), tissue textures, quality of motion (smooth, elastic or bone on bone) and symmetry [1]. However, because scientifically accepted objective measures are not yet available to complement a clinical diagnosis, the documentation of the impairment as well as effects of treatment can be challenging. Thus, the purpose of this research was to explore the use of three-dimensional kinematics as a potential tool for relating movement patterns of the head/neck to clinical diagnosis and documenting treatment effects.
Toward a Functional Tolerance Criterion for the Hippocampus Developed From Organotypic Slice Cultures
Authors: Yu Zhe , Kang Woo Hyeun , Morrison Barclay
Published: July 2013

Approximately 1.5 million traumatic brain injuries (TBI) occur each year which result in 50,000 deaths, and about 80,000 people are left with a permanent disability. The annual cost associated with these injures is estimated to be $60 billion. Because there is no pharmacological treatment for TBI, engineering strategies to prevent these injuries enabled through an improved understanding of injury biomechanics is crucial. To this end, finite element models play a central role for predicting brain deformation induced by various loading scenarios such as falls or motor vehicle accidents. Novel protection strategies can then be tested in silico before the start of physical testing. However, in their current form, finite element models predict only mechanical responses and cannot predict the biological response of the brain tissue to the imposed deformation.
Measuring Strain Distributions in the Anterior Cruciate Ligament Using Ultrasound
Authors: Cochran Amy , Gao Yingxin , Krotscheck Ursula , Thompson Margret , Stouffer James , Nafis Robert
Published: July 2013

Optimal prevention and treatment strategies of anterior cruciate ligament (ACL) injury can be realized with a detailed understanding of how physiological factors impact the ACL. A noninvasive, in vivo method that assesses the ACL’s mechanical integrity is needed to help clarify this multi-factorial pathophysiology. We investigated the use of the noninvasive, in vivo technique, ultrasound strain elastography (USE) (1), to distinguish between normal and injured ACLs. USE is used as a diagnostic tool in oncological (2), hepatic (3), and cardiovascular (4) applications. This technique uses ultrasonic RF data to track tissue motion in order to estimate strain within the tissue.
Experimental and Numerical Analysis of Thermal Ablation in Biological Tissues Using Short Pulse Lasers
Authors: Sajjadi Amir , Onyejekwe Ogugua , Mitra Kunal , Grace Michael S.
Published: July 2013

For the past few years various photothermal methods such as Laser-induced Hyperthermia [1] and Laser Interstitial Thermal Therapy [2] has been developed for tumor ablation. In all of these existing techniques, either continuous wave (CW) or long pulse laser sources have been used, which often produces heat affected zones that are larger than the boundaries of the tumor, which leads to collateral damage of surrounding healthy tissue. Moreover for these applications, either collimated or diffused laser beams are used, resulting in much of the energy being absorbed by tissues at the skin surface and very little remaining energy penetrating the skin. Such drawbacks can be eliminated if a beam from a short pulse laser source is focused directly at the targeted subsurface location. Tight focusing ensures that sufficient intensity to drive nonlinear optical absorption can be achieved with low pulse energy. This technique has been effectively used in applications such as non-ablative dermal remodeling [3] and treatment of striated muscles [4]. However, the use of focused beam from an ultra-short pulse laser source has never been applied to tumor ablation and is investigated in this paper.
Lumbar Degenerative Disc Disease Increases Deformations at Cephalad Adjacent Levels In Vivo
Authors: Wang Shaobai , Kozanek Michal , Wood Kirkham B. , Li Guoan
Published: July 2013

Low back pain, one of the most common causes of disability in working population is in the vast majority of cases attributed to degeneration of the lumbar intervertebral disc (IVD). It has been reported that in patients with degenerative disc diseases (DDD) at one level, the discs adjacent to the diseased level have a greater tendency to degenerate. Studies have also suggested altered biomechanics as causative factors [1, 2]. However, to date no data has been reported on the deformation of the disc in vivo in DDD patients. The purpose of this study was to evaluate the effect of lumbar IVD degeneration on the deformation of the discs at the adjacent levels during functional weightbearing postures.
Biomechanical Properties of Human Coronary Sinus for Minimally Invasive Mitral Valve Repair
Authors: Pham Thuy , Sun Wei
Published: July 2013

Mitral valve regurgitation, the leakage of blood back to the left atrium during systole, is a significant cause of morbidity and mortality. The current treatment options for symptomatic mitral regurgitation are mitral valve repair and replacement. However, the operative mortality for both of these treatments remains substantial (1). Furthermore, these treatments are often not referred for elderly patients with comorbidities. Thus, there is a pressing need for less invasive, non-surgical treatments of mitral regurgitation.
Finite Element Analysis of Cytoskeletal Remodeling During Micropipette Aspiration
Authors: Ronan William , Deshpande Vikram S. , McMeeking Robert M. , McGarry Patrick
Published: July 2013

Numerous in-vitro studies have established that cells react to their physical environment and to applied mechanical loading [1, 2]. However, the mechanisms underlying such phenomena are poorly understood. Previous computational cell models of micropipette aspiration have not examined the salient mechanisms governing the material response; instead, they fit experimental data to linear elastic, viscoelastic or simplified biphasic models [3–5]. In order to gain an in-depth understanding of mechanotransduction, modeling based on the active sub-cellular biomechanical behavior and biochemical processes must be combined with experimental investigation. Such modeling will produce novel and realistic insights into sub-cellular mechanics and provide a powerful predictive tool for tissue engineering. Consistent with this concept, an active constitutive formulation for the remodeling and contractile behavior of the actin cytoskeleton is used in this study to simulate micropipette aspiration of suspended and adhered cells.
Extended Long-Term Culture of MSC-Laden Agarose Constructs Does Not Produce Functional Tissue Comparable to Primary Chondrocytes
Authors: Huang Alice H. , Mauck Robert L.
Published: July 2013

Articular cartilage lines the surfaces of joints and transmits the forces arising from locomotion. The poor ability of cartilage to self-repair has motivated efforts to engineer replacements that recapitulate this load-bearing function. While chondrocyte-laden constructs have been generated with near-native mechanical properties, limitations in chondrocyte availability may preclude their clinical use. Therefore, mesenchymal stem cells (MSCs), which can undergo chondrogenesis in 3D culture, have emerged as a promising alternative [1]. However, although MSCs deposit a cartilaginous matrix, mechanical and biochemical properties are lower than those achieved with chondrocytes [1, 2]. Using microarray analysis, we recently showed that limitations in functional MSC chondrogenesis may stem from incomplete or incorrect molecular induction; molecular differences were observed between donor-matched differentiated chondrocytes and newly differentiated MSCs over 8 weeks of culture [2]. While some genes remained consistently low in MSCs compared to chondrocytes, others gradually increased with time, approaching chondrocyte levels by 8 weeks. As these molecules may underlie the functional disparity between chondrocytes and MSCs, we hypothesized that longer culture durations may improve MSC-seeded construct properties and chondrogenesis. To test this hypothesis, we characterized the evolution of functional properties of MSC- and chondrocyte-seeded constructs over 4 months of in vitro culture in pro-chondrogenic medium.
Variation of Whole-Body Angular and Linear Momentum During Human Locomotion
Authors: Jackson Jennifer N. , Hass Chris J. , De Witt John K. , Walter Jonathan P. , Fregly Benjamin J.
Published: July 2013

Bipedal walking is a typical activity of daily living, but the overarching control strategy used by the central nervous system (CNS) to make this motion efficient, or even possible, remains unknown. Researchers in robotics have developed control strategies for bipedal gait through the regulation of central (i.e., about the mass center) angular momentum resolved along three orthogonal directions during the walking cycle. Although recent research has focused on conservation of whole-body central angular momentum as a possible control law for walking [1–3], there is little data to support this theory for other motions such as running or marching. Even less data exist for how whole-body linear momentum varies during human locomotion.
Musculoskeletal Modeling of Acetabular Dysplasia-Kinematics, Muscle and Joint Reaction Forces
Authors: Harris Michael D. , Davis Ryan S. , MacWilliams Bruce A. , Peters Christopher L. , Anderson Andrew E.
Published: July 2013

Anatomical pathologies of the hip, such as developmental dysplasia are a common cause of hip pain in the young adult. While it is generally accepted that cartilaginous lesions and tears to the acetabular labrum initiate pain, muscle compensation/weakness may also contribute, especially for patients who do not have evidence of soft-tissue damage. Musculoskeletal models provide estimates of muscle forces as well as the equivalent force that acts upon the joint. Force data can then be compared to any observed differences in joint kinematics, thereby improving the interpretability of data from traditional gait studies. While a few studies have reported alterations in hip joint kinematics due to acetabular dysplasia, to our knowledge, muscle force differences have not been estimated [1, 2]. The purpose of this study was to couple traditional gait analysis with musculoskeletal modeling to compare hip joint kinematics, muscle forces, and joint reaction forces between subjects with acetabular dysplasia and normal controls.
Deformation Mechanisms in Nanoindentation of Bone
Authors: Paietta Rachel C. , Olesiak Sara E. , Ferguson Virginia L.
Published: July 2013

Cortical bone is a hierarchical, composite material composed of mineralized collagen fibrils organized into lamellae and osteons as classically described by Lakes [1]. The inherent heterogeneity and hierarchy of bone tissue makes it an interesting material to study at various size scales using a range of spherical tip sizes in nanoindentation. Further, the prevalence of pointed, Berkovich nanoindenter tips enable researchers to readily generate nanoindentation data. However, other tip geometries and sizes may provide an advantage over the Berkovich tip by enabling a more elastic contact and testing over a range of contact areas and structures.
Effects of the Initial Alignment and Passive Reorientation of Actin Fibers on the Tensile Stiffness of Whole Cells
Authors: Ujihara Yoshihiro , Nakamura Masanori , Miyazaki Hiroshi , Wada Shigeo
Published: July 2013

Actin filaments are known to be concerned with cell stiffness and shape stability of cells. Structurally, actin filaments are classified into two. One is a cortical actin network beneath cell membrane and the other is actin fibers (AFs) which run transversely within a cell. Reportedly, skewed alignment of AFs induces anisotropic deformation of a cell [1]. Therefore, it is important to understand how the alignments of AFs are reflected in the mechanical properties of a cell.
Combined Rigid-Deformable Modeling of Lumbar Spine Mechanics
Authors: Deacy James S. , Rao Milind , Smith Sean , Petrella Anthony J. , Laz Peter J. , Rullkoetter Paul J.
Published: July 2013

Finite element (FE) models of the spine have been used to assess natural and pathological spine mechanics and evaluate performance of various fusion and posterior stabilization devices [1–3]; however, analysis times may be prohibitive for clinical and design phase assessments. Muscle-actuated, rigid body models have also been developed and used to estimate spinal loading conditions during simulated activities [4]. Although rigid body dynamics platforms typically require less computational time, they are unable to evaluate internal stresses and strains in deformable structures. This study proposes to develop a combined rigid – deformable surrogate spine model where the behavior of the intervertebral disc, facet cartilage and ligaments are replicated by simulated mechanical constraint at desired levels. The explicit FE platform is able to accommodate the spectrum of representations, including fully deformable, fully rigid body, implanted, or any combination. Accordingly, the objective of the current study was to assess the ability of a combined rigid-deformable spine model to accurately reproduce the behavior of the fully deformable representation in the natural state with improved computational efficiency. Specifically, this study compared results for a lumbar (L1-L5) spine under follower load and moment conditions for representations ranging from fully deformable to fully rigid. The combined rigid-deformable model includes the deformable disc, facet cartilage contact, ligament representations at L4-L5, while the other levels are modeled using a simplified mechanical constraint.
Novel Method of Laser Direct Writing for Precise Patterning of Human Dermal Fibroblasts
Authors: Schiele Nathan R. , Chrisey Douglas B. , Corr David T.
Published: July 2013

The ability to control a cell’s location, pattern geometry, and proximity to neighboring cells, in vitro, is highly desired to gain insight into cell-cell interactions, such as the modes of cellular signaling (direct cell contact, paracrine, or endocrine). A laser-based cell patterning technique, laser direct write, enables the precise spatial placement of living cells, with all the advantages of CAD/CAM control [1]. However, this technique is limited in usefulness due to the dependence on Matrigel® (BD Biosciences, Bedford, MA). The growth factor constituents of Matrigel® may interfere with many cellular processes under investigation and may preclude or greatly limit the utility of laser direct writing for precise cell cultures [2]. Therefore, to address this limitation, the objective of this study was to develop a Matrigel®-free laser direct writing method. Through the use of customized gelatin coatings on both the ribbon and receiving substrate, we effectively adapted the direct write technique to precisely pattern cells without the use of Matrigel®, as demonstrated with human dermal fibroblasts. The gelatin partially encapsulates the trypsinized cells on the ribbon, providing a volitization zone to protect the cells, and on the receiving substrate cushions the impact of transfer while maintaining moisture. Gelatin liquefies at 37°C, which allows it to be removed from the growth surface ensuring cellular proliferation, uninhibited by growth surface treatments. This represents a fundamental change from the original direct write technique in which cells must first form initial attachments to the ribbon via Matrigel® and then are written to a Matrigel® coated receiving substrate for their sustained growth. Additionally, we have developed a method to monitor the location of the patterned cells post-transfer to show that a gelatin coated-receiving substrate is effective as a patterning surface and ensures the registry of the pattern until cell attachment, even after the gelatin has been removed with the first growth medium application. This precise patterning technique can now be used in many biomedical applications, including those that involve cell types highly sensitive to growth factors, such as stem cells and cancer cells.