bluuebunny/crossref_metadata_2025 huggingface dataset:
Comparison of the Tissue Response to 3 Distinct Polypropylene Prolapse Meshes in a Primate vs Rodent Model
Authors: Feola Andrew , Moalli Pamela , Stein Suzan , Abramowitch Steven
Published: July 2013

Each year, an estimated 225,000–280,000 women undergo surgery for repair of pelvic floor disorders in the United States, with many involving placement of a synthetic polypropylene (PP) mesh designed to restore direct support to the vagina and hence indirect support to the pelvic organs (1). In spite of high anatomical success rates, the use of synthetic meshes has been hampered by mesh related complications causing significant patient morbidity (2) and prompting two recent FDA warnings against the use of mesh (3). Thus, as the concern about the use of mesh increases, there is an urgent need to define the impact of mesh on host tissue and to understand how different material properties of the mesh may direct the host response.
Stent Overlapping and Geometric Curvature Influence the Structural Integrity and Surface Characteristics of Coronary Stents
Authors: Kapnisis Konstantinos , Halwani Dina , Brott Brigitta , Lemons Jack , Anderson Peter , Anayiotos Andreas
Published: July 2013

A common clinical practice in interventional procedures, is the deployment of two or more overlapping stents, especially in areas of branches and bifurcations where the stenotic area is diffuse and cannot be covered by a single stent or in the cases of treating long or recurrent lesions. However, complex in vivo conditions such as vessel tortuousity, high curvature, vascular wall stresses as well as blood flow wall shear stresses and diffuse calcification, may cause additional interactions within overlapping stents resulting in enhanced surface damage and fracture of stents. Preliminary studies have revealed that some stents undergo corrosion and fatigue-induced fracture in vivo, with significant release of metallic ions into surrounding tissues. A direct link between corrosion and in-stent restenosis has not been clearly established; nonetheless in vitro studies have shown that relatively high concentrations of heavy metal ions can stimulate both inflammatory and fibrotic reactions, which are the main steps in the process of restenosis. This study presents the outcome of in vitro accelerated biomechanical testing of Nitinol stents placed in mock arteries in single and overlapping configurations with various degrees of curvature. The effect of overlapping dissimilar materials was also investigated by testing multiple alloy stent combinations combining NiTi with CoCr or SS stents.
Analysis of Ciliary Motion and the Axonemal Structure in the Mouse Respiratory Cilia
Authors: Ueno Hironori , Ishikawa Takuji , Bui Khanh Huy , Gonda Kohsuke , Ishikawa Takashi , Yamaguchi Takami
Published: July 2013

Mucociliary clearance on the surface of the tracheal lumen is an important component of lung defense against dust mites and viruses. However, the axonemal structure that achieves effective ciliary motion and the mechanisms by which discretely distributed ciliary cells generate directional flow are unknown. In this study, we examined individual ciliary motion with 7–9-nm spatial precision by labeling the ciliary tip with quantum dots, and detected an asymmetric beating pattern. Cryo-electron tomography revealed that the densities of two inner dynein arms were missing from at least two doublet microtubules in the axonemal structure. Although the flow directions generated by individual ciliated cells were unsteady and diverse, the time- and space-averaged velocity field was found to be directional. These results indicate that the asymmetric ciliary motion is driven by the asymmetric axonemal structure, and it generates overall directional flow from the lungs to the oropharynx on sparsely distributed ciliated cells.
Hemodynamic Impact of Stenting in the Total Cavopulmonary Connection With Lateral Tunnel Stenosis
Authors: Tang Elaine , McElhinney Doff B. , Yoganathan Ajit P.
Published: July 2013

2 per 1000 children in the US are born with functionally single ventricle (SV) heart defects. To restore the separate systemic and pulmonary circulations, a Total Cavopulmonary Connection (TCPC) is carried out through a series of surgical steps, which result in the direct connection of the superior vena cava (SVC) and inferior vena cava (IVC) to the pulmonary arteries without an intervening pulmonary ventricle. One way to complete the TCPC is by placing a synthetic patch in the right atrium, forming an intracardiac lateral tunnel (LT) as the final step. As patients grow, some LT pathways become stenosed. The stenosis can impose extra resistance to flow in addition to the TCPC in the SV circulation. One method of treating LT stenosis is by placement of an intravascular stent.
Probing Red Blood Cell Dynamics
Authors: van der Burgt René C. H. , Anderson Patrick D. , van de Vosse Frans N.
Published: July 2013

Because of the high volume contents of red blood cells (RBCs) in blood, mechanics of a single RBC plays a large role in the rheological description of blood. Moreover, RBC dynamics drive plasma mixing and lateral transport of its components, which are both involved in blood coagulation. Therefore, a characterization of the dynamical parameters of RBCs under different flow conditions is needed. Experimental methods, like pipette aspiration or optical trapping, seem to be unable to accurately capture RBC dynamics, due to contact of a solid with the cell membrane. Especially at larger deformations, a proper analysis is more complex due to this cell-solid interaction and the introduction of extra friction forces. In addition, not local but whole cell quantities are measured.
Investigation of an Early Intervention Tibial Component for Medial Osteoarthritis
Authors: Chaudhary Miriam E. , Walker Peter S.
Published: July 2013

Total knee arthroplasty (TKA) is usually the treatment of choice for severe osteoarthritis (OA) of the knee. Numerous clinical studies of TKA have shown high rates of long-term joint survival with good function [1]. Nevertheless, alternatives to this established procedure are being increasingly considered for several reasons. Postoperatively, patients frequently experience a slow rehabilitation and do not fully recover normal function [2]. On the other hand, there is a growing pressure to reduce operating time while increasing the use of less invasive surgical techniques.
MALCOLM: Improving Pediatric Cerebral Palsy Rehabilitation Through Diagnostics
Authors: Desmarais Jennifer , Joyce Jessica , Kienast Kurt , Lin Lawrence , Miller Leslie , Post Allison , Oden Z. M. , O’Malley M. K.
Published: July 2013

Rice Helping Hands (RHH) is tasked with designing and developing a wrist rehabilitation device for pediatric patients with spastic cerebral palsy (CP).
Evaluation of Intracranial Pressure Response in Rats Exposed to Complex Shock Waves
Authors: Dal Cengio Leonardi Alessandra , Keane Nickolas , Bir Cynthia , VandeVord Pamela
Published: July 2013

Studies on blast neurotrauma have focused on investigating the effects of exposure to free-field blast representing the simplest form of blast threat scenario without considering any reflecting surfaces. However, in reality personnel are often located within enclosures or nearby reflecting walls causing a complex blast environment, that is, involving shock reflections and/or compound waves from different directions. In fact, when a blast wave interacts with nearby structures, reflected shock waves are generated and complex three-dimensional shock waves are formed. Complex shock wave overpressure-time traces are significantly different from free-field profiles because reflections can cause super-positioning of shock waves resulting in increased pressure magnitudes and multiple pressure peaks. Very importantly, the shocks arrive from different directions which would invoke a different biomechanical response than a one-dimensional exposure. It has been reported that in complex wave environments, the extent of the injuries becomes a function of the location related to the surrounding structures rather than a function of the distance from the center of the explosion, as it is for free-field conditions (Yelverton et al. 1993; Mayorga 1997; Stuhmiller 1997). Furthermore, the resulting injuries when the individual is in confined spaces are noted to be more severe (Yelverton et al. 1993; Leibovici et al. 1996). The purpose of this study was to design a complex wave testing system and perform a preliminary investigation of the intracranial pressure (ICP) response of rats exposed to a complex blast wave environment. Furthermore, we explored the effects of head orientation in the same environment.
A Novel Phenomenological Ligament Modeling Approach Utilizing Robotic Calibration
Authors: Bandi Marc , Siggelkow Eik , Sauerberg Iris
Published: July 2013

While total knee arthroplasty (TKA) is a successful procedure to mitigate joint pain, there remain improvement opportunities with respect to restoring natural joint feeling and function [1]. It has been shown that prosthesis geometry and the retention of ligaments can have an influence on patient perception of how normal a TKA feels [2]. Numerical knee modeling offers the possibility to improve outcomes of feel and function by comparing the predicted behavior of TKAs using various designs and surgical variables with the behavior of intact knees. The TKA development process also benefits as these analyses and resulting optimizations can be performed in an early design stage.
Mechanics of Electrospun Polycaprolactone Nanofibers
Authors: Fee Timothy J. , Berry Joel L.
Published: July 2013

Electrospun biomaterials are gaining popularity as scaffolding for engineered tissues. This fibrous scaffolding of natural or synthetic polymers can mimic properties of the natural extra-cellular matrix. Moreover, undifferentiated cells seeded onto and within an electrospun matrix may be directed to differentiate into a desired tissue type through the application of the appropriate biochemical and mechanical conditions. It is becoming clear that the mechanical deformation of any electrospun matrix plays an important role in cell signaling. However, electrospun biomaterials have inherently complex geometries due to the random deposition of fibers during the electrospinning process. Even “aligned” electrospun matrices generate off-axis forces under load. This complex fiber geometry complicates any attempt at quantifying forces exerted on adherent cells during electrospun matrix deformation.
A Method for Predicting Collagen Fiber Alignment in the Glenohumeral Capsule During Clinically Relevant Deformations
Authors: Rainis Carrie A. , Amini Rouzbeh , Debski Richard E.
Published: July 2013

Injury to the anteroinferior (anterior band of the inferior glenohumeral ligament (AB-IGHL) and axillary pouch) glenohumeral capsule is a common result of anterior dislocation [1]. Validated finite element models of the capsule can be used to address research questions regarding diagnostic and repair techniques targeted to this region of the capsule. However, these models require adequate constitutive models to describe capsule behavior. Structural models have improved predictions of capsule behavior compared to phenomenological models [2] but current experimental techniques used to measure fiber distributions in biologic soft tissues require that the sample be planar and cannot be performed on three-dimensional structures. Although recent work has demonstrated that the fiber kinematics in the capsule do not precisely follow the global tissue deformation [3], the affine assumption is presently the best approximation to provide initial insight into changes in collagen fiber alignment under moderate deformations. The collagen fibers in localized areas of planar samples from the anteroinferior capsule align with the direction of loading [4,5]; however, their behavior may be quite different during the complex loading conditions experienced by the intact capsule. Therefore, the objective of this work was to computationally project planar fiber distribution information to the three-dimensional glenohumeral capsule and use the affine assumption to quantify the change in fiber alignment of the anteroinferior glenohumeral capsule from an inflated reference state to three clinically relevant joint positions.
Stiffness as an Effector of Lung Branching Morphogenesis
Authors: Clause Kelly C. , Segura Tatiana , Barker Thomas H.
Published: July 2013

Growing evidence suggests that physical microenvironments and mechanical stresses direct cell fate in developing tissues. However, how these physical properties affect morphogenesis remains unknown. We show here that ECM mechanical properties, i.e. stiffness, reproduced by using hydrogel, guide tissue morphogenesis in the developing lung bud. In particular, decreasing substrate stiffness in cultured lung buds resulted in an inhibition of appropriate cleft formation and a resulting enlargement of epithelial buds. These findings suggest that the magnitude of mechanical stiffness across the lung bud alters the branching pattern. Additionally, physically designed hydrogel material is a valuable tool for producing the specific microenvironment to explore how physical cues affect and alter tissue morphogenesis for in vitro study.
Investigating the Sieving and Structural Property of the Osteocyte Pericellular Matrix: Experiments and Modeling
Authors: Zhou Xiaozhou , Wang Bin , Price Christopher , Li Wen , Pan Jun , Wang Liyun
Published: July 2013

Growing evidence shows that osteocytes, the most abundant bone cells, serve as the primary sensory cells that detect external mechanical forces [1], enabling the bone to adapt its mass and structure to meet its environmental requirements and to fulfill its weight bearing functions [2]. Although the cellular and molecular mechanisms of such adaptation phenomena are not fully understood, recent experiments and theoretical models suggest that the pericellular matrix (PCM) filling the tiny gap between the cell membrane and the canalicular matrix wall plays a critical role in the osteocytes’ outside-in signaling process [1]. Weinbaum first hypothesized that a proteoglycan-like fiber matrix, similar to the endothelial glycocalyx, must exist within the PCM to account for the surprisingly long relaxation times of the strain-generated potentials measured in bone [3]. Such a filling matrix was predicted to impose hydraulic resistance, impede fluid pressure relaxation and reduce fluid flow in the tiny lacunar-canalicular pore system in bone, thus protecting the cell membranes from being ruptured under shear. Later electronic microscopic studies confirmed the existence and the proteoglycan nature of the PCM [4]. Previous models using idealized PCM ultrastructure suggested that the hydrodynamic interactions between the PCM and fluid could determine the magnitude of drag forces that deform cytoskeleton via tethered transmembrane components or the focal contacts containing integrins [5,6]. In both scenarios, the PCM is the key to force transmission and strain signal amplification, and responsible for downstream mechanotransduction. In addition, once the mechanically excited osteocytes affect the release of molecular signals such as ATP, NO, PGE2, OPG, RANKL, and sclerostin [2], the PCM, as a molecular sieve and temporary storage, may influence the transport and availability of these bioactive molecules [7]. Therefore, the structural and sieving properties of PCM are important in regulating bone’s mechanotransduction and adaptation. However, due to the small dimensions of the PCM (∼100nm thick) and the difficulty in preserving the PCM in situ, its detailed structure and properties have remained elusive [4]. The objective of this study was to elucidate the sieving property of the PCM in mechanically loaded bone with an innovative imaging approach and to further deduce plausible PCM structures using mathematical modeling.
Chronic Mitral Valve Leaflet Growth Following Myocardial Infarction
Authors: Rausch Manuel K. , Tibayan Frederick A. , Miller D. Craig , Kuhl Ellen
Published: July 2013

One of the primary failure modes of the mitral valve is mitral regurgitation (MR). MR often follows myocardial infarction, in which case it is referred to as ischemic mitral regurgitation (IMR). IMR is a result of alterations to the annular and subvalvular apparatus secondary to left ventricular remodeling [1]. Recent studies showed that the mitral valve can adapt to IMR by increasing leaflet size to reduce the degree of regurgitation. Understanding the exact biomechanical and biochemical mechanisms behind mitral valve adaptation may open new treatment strategies for patients with mitral regurgitation [2]. In this study [3], we investigated the phenomenon of mitral valve leaflet “growth” in an ovine model to define the mechanisms that drive the “growth” process. We further quantified regional and directional variations in “growth” across the anterior mitral valve leaflet (AMVL).
Age-Related Differences in Haemodynamics of the Rabbit Aorta and Comparison With Average Maps of Atherosclerotic Lesion Prevalence
Authors: Peiffer Véronique , Rowland Ethan M. , Cremers Stephanie G. , Weinberg Peter D. , Sherwin Spencer J.
Published: July 2013

The focal occurrence of atherosclerotic lesions around branching points and in curved vessels has led to the hypothesis that haemodynamics plays an important role in the development of the disease. The spatial distribution of atherosclerosis is also age-dependent in humans and rabbits [1]; detailed maps of disease prevalence in aortas of immature and mature rabbits were presented recently [2]. Vincent et al. [3] applied computational fluid dynamics to study blood flow in the aorta of a mature rabbit, but they did not investigate age-dependent effects. The purpose of the present study was to quantify differences in aortic haemodynamics between immature and mature rabbits, and to compare averaged distributions of the flow-related wall shear stress with maps of disease prevalence. As blood flow is heavily dependent on vessel geometry, the shapes of the aorta in the two age groups were also compared.
Exogenous Temporal Assessment of Lysyl Oxidase on Engineered Articular Cartilage as a Method for Promoting Collagen Crosslinking
Authors: Makris Eleftherios A. , Responte Donald J. , Hu Jerry , Athanasiou Kyriacos A.
Published: July 2013

The poor ability of articular cartilage (AC) to repair following disease and/or injury makes the tissue a key target for cell-based regenerative strategies. Progress made in the development of tissue engineered AC, using a 3-dimensional, scaffoldless, self-assembly method, has yielded neotissues with compressive properties on par with native tissue [1]. However, the tensile properties of these engineered tissues remain to be improved. This is particularly important because, while the tissue functions mainly in compression, the tensile strains within the joint nonetheless present a mechanically challenging environment.
Investigation of Vessel Growth and its Impact on Hemodynamics in Patients With Lateral Tunnel Total Cavopulmonary Connection
Authors: Restrepo Maria , Mirabella Lucia , Tang Elaine , Haggerty Chris , Fogel Mark A. , Valente Anne Marie , McElhinney Doff B. , Yoganathan Ajit P.
Published: July 2013

Single ventricle heart defects affect 2 per 1000 live births in the US and are lethal if left untreated. The Fontan procedure used to treat these defects consists of a series of palliative surgeries to create the total cavopulmonary connection (TCPC), which bypasses the right heart. In the last stage of this procedure, the inferior vena cava (IVC) is connected to the pulmonary arteries (PA) using one of the two approaches: the extra-cardiac (EC), where a synthetic graft is used as the conduit; and the lateral tunnel (LT) where part of the atrial wall is used along with a synthetic patch to create the conduit. The LT conduit is thought to grow in size in the long term because it is formed partially with biological tissue, as opposed to the EC conduit that retains its original size because it contains only synthetic material. The growth of the LT has not been yet quantified, especially in respect to the growth of other vessels forming the TCPC. Furthermore, the effect of this growth on the hemodynamics has not been elucidated. The objective of this study is to quantify the TCPC vessels growth in LT patients from serial magnetic resonance (MR) images, and to understand its effect on the connection hemodynamics using computational fluid dynamics (CFD).
Thresholds for Embryonic CNS Axon Integrity, Degeneration, and Regrowth Using a Focal Compression Platform
Authors: Fournier Adam , Hosmane Suneil , Ramesh K. T.
Published: July 2013

Traumatic axonal injuries (TAI) are broadly defined as the focal or multi-focal damage of axons within white matter tracts of the central nervous system (CNS), and can occur in the setting of spinal cord injury (SCI) and traumatic brain injury (TBI). TAI can result from mechanical forces associated with the rapid deformation of white matter regions during trauma. Through combinations of compression, stretch, and shear, axon injury often results in an irreversible loss of functional neural connectivity, since the scope for axonal regeneration in the CNS is extremely limited.
Comparative Muscle Activation Patterns of Healthy Control Limbs and Contralateral Limbs in ACL Reconstruction
Authors: Marsh Chelsea , Tashman Scott
Published: July 2013

ACL reconstruction (ACLr) has been found to restore the functionality and mobility of those afflicted with ACL tears. In the process of this restoration, previous work has shown alterations in the activity of the musculature surrounding the reconstructed knee [1]. Specifically, at 5 months post-op, the gastrocnemius, vastus lateralis, and rectus femoris demonstrate significantly different activation patterns. These differences raise the question if the reconstructed leg is the only limb affected by ACLr.
Characterizing the Phenotypic Response of Endothelial Cells Cultured on Pro-Angiogenic In Vitro Tumor Mimics
Authors: Szot Christopher S. , Buchanan Cara F. , Freeman Joseph W. , Rylander Marissa Nichole
Published: July 2013

Despite the 200 billion dollars invested in cancer therapy research and development since 1971, only 5% of new drugs entering clinical trials successfully obtain FDA approval [1, 2]. There is a growing concern in the cancer research community that this slow movement in progress stems from the need for improved preclinical models for testing new therapeutic agents [1]. A burgeoning interface between cancer research and tissue engineering is transforming how tumor development is being studied in vitro. As a result, complex 3D cancer cell culture models are beginning to be developed with phenotypes representative of in vivo cancer progression [3].
Methods for Comparison of Liver and Spleen Location in the Supine and Upright Positions of the 50th Percentile Male
Authors: Rhyne Ashley C. , Gayzik F. Scott , Moreno Daniel P. , Stitzel Joel D.
Published: July 2013

The location and shape variation of the liver and spleen due to postural changes has implications in the prediction of blunt abdominal trauma via computational models or other human surrogates. Although abdominal injuries occur in only 3–5% of injuries in car crashes, they are often seen in serious crashes with AIS≥4 injuries. The location and shape variation of the liver and spleen due to postural changes are likely to play a role in the severity of injury, as a result of rib coverage and location. One means of studying this variation is through computational modeling for impact biomechanics studies. This study reviews the methods used to quantify variation in the location of the liver and the spleen relative to surrounding bony structures for two different postures, supine and seated. Through the use of various imaging modalities three-dimensional datasets depicting the affect of posture change on the size and shape of the liver and spleen can be investigated through three-dimensional renderings and center of gravity measurements.
The Role of Scleraxis in Supraspinatus Enthesis Development
Authors: Killian Megan L. , Thomopoulos Stavros
Published: July 2013

High localized stresses can develop at the interface between dissimilar materials; their attachment is therefore a major engineering challenge. During the development of the tendon-to-bone attachment (the “enthesis”), tendon transitions into fibrocartilage and then into mineralized fibrocartilage as it inserts into bone [1,2]. While natural development leads to a strong and tough enthesis, surgical reattachment and healing of tendon to bone often fails [3]. Thus, a better understanding of the developmental cues necessary for enthesis formation may help to navigate future repair and tissue engineering approaches for tendon-to-bone repair.
Collapsible Load Bearing Assistive Standing Device for Paraplegics
Authors: Book Jennifer , Giraldo Isabel , Peterson Sean D.
Published: July 2013

There are several health benefits to persons with spinal cord injuries and other mobility related disabilities achieved by standing and load bearing for a period of time, such as enhancing psychological well-being, maintaining vital organ capacity, and reducing abnormal muscle tone and spasticity [1]. Assistive standing devices for paraplegics are normally used while individuals are attending rehabilitation centers, as these devices are often impractical or undesirable for home use. Designs of standing structures for paraplegics that are currently available on the market often take up too much floor space in the home and are expensive, costing up to $2500. Therefore, in order to extend the health benefits of standing to paraplegics with limited floor space, budget, and/or a dislike of bulky medical devices in their home, it would be beneficial to have an inexpensive, aesthetically appealing, small-footprint option available for personal use.
Enhancing the Biomechanical Properties of Self-Assembled, Costochondral Cell Neocartilage Through Modulation of Seeding Density and Expansion Media
Authors: Murphy Meghan , Reimer Andrew , Huey Daniel , Hu Jerry , Athanasiou Kyriacos
Published: July 2013

Disorders of the soft tissues of the temporomandibular joint (TMJ), including the TMJ disc and cartilages, have elicited work in engineering tissue replacements; these must be able to function within the joint’s mechanically demanding environment. Such efforts are met with the challenges of 1) identifying a suitable source of donor cells and 2) expanding these cells while maintaining a phenotype that generates mechanically robust tissue.
Effect of Inflammation on the Osmotic Response of Nucleus Pulposus Cells
Authors: Maidhof Robert , Rajan Neena , Chahine Nadeen O.
Published: July 2013

Intervertebral disc (IVD) degeneration is accompanied by elevated levels of pro-inflammatory cytokines, particularly IL-1β and TNF-α [1]. Disc cells from the nucleus pulposus (NPs) respond to cytokine stimulation with increased catabolic breakdown of the tissue, resulting in a positive feedback of disc integrity loss and further inflammation [2]. Previous studies by our group have examined the response of NP cells to Toll-Like Receptor-4 (TLR-4) activation through stimulation with lipopolysaccharide (LPS). TLR-4 is a pattern recognition receptor that is activated in innate immunity and by polysaccharide fragments from degenerated proteoglycans. TLR-4 activation by LPS results in stimulation of multiple cytokines by NP cells [3]. Moreover, we have shown that in vivo LPS injection results in catabolic changes in the IVD, including matrix breakdown, decrease in biomechanical properties and loss of disc height [4]. However, the specific cellular mechanisms for these catabolic changes remain to be elucidated.
Characterization of the Elasticity of Valve Interstitial Cells on Soft Substrates Using Atomic Force Microscopy
Authors: Liu Haijiao , Simmons Craig A. , Sun Yu
Published: July 2013

Mechanical stimuli, including the elasticity of the extracellular matrix (ECM), can have profound effects on the function of cells and their responsiveness to other microenvironmental cues, thereby regulating homeostasis and disease development. For example, the response of aortic valve interstitial cells (VICs) to growth factors [1] and VIC differentiation to pathological phenotypes [2] depend on ECM elasticity. The ability of cells to sense and respond to mechanical stimuli depends on several factors, including their inherent cellular-level mechanical properties. The mechanical properties of suspended VICs [3, 4] and VICs grown on stiff glass/polystyrene [5] have been reported. However, neither of these test conditions is physiological, as VICs adhere to ECM that is orders of magnitude more compliant than glass. Some other cell types adapt their stiffness to that of their substrate [6]; we hypothesized that adherent VICs would similarly change their elasticity in response to the elastic properties of their ECM.
Mechanics of Optic Cup Invagination in the Embryonic Chick Eye
Authors: Oltean Alina , Beebe David C. , Taber Larry A.
Published: July 2013

Invagination of epithelia is an essential morphogenetic process that occurs in early eye development. The mechanics of the tissue forces necessary for eye invagination are not yet understood [1]. The eyes begin as two optic vesicles that grow outwards from the forebrain and adhere to the surface ectoderm. At this point of contact, both the surface ectoderm and optic vesicle thicken, forming the lens placode and retinal placode, respectively. The two placodes then bend inward to create the lens vesicle and bilayered optic cup (OC) [1, 2].
Covalent Cross-Linking Accelerates Collagen Enzyme Mechano-Kinetic Cleavage: Nanomechanics Predicts Microscale Behavior
Authors: Bourne Jonathan W. , Lippell Jared M. , Torzilli Peter A.
Published: July 2013

Fibrillar collagens are an integral structural element of tissues throughout the body and help provide tensile strength. These collagens are highly resistant to degradation other than by a small number of collagenolytic enzymes. Examples of tensile mechanical forces in vivo include expansion and contraction of blood vessels, tension on tendons and ligaments, and compression and swelling of cartilage.
A Computational Analysis of Error in Locating the Rotational Axes of the Tibiofemoral Joint With an Instrumented Spatial Linkage
Authors: Bonny Daniel P. , Howell Stephen M. , Hull Maury L.
Published: July 2013

A method to measure the two kinematic axes of the tibiofemoral joint, the flexion-extension (F-E) axis and longitudinal rotation (LR) axis [1], was developed by Gatti [2]. This method used an instrumented spatial linkage (ISL), a series of six instrumented revolute joints that can measure motion between two rigid bodies. While Gatti’s method demonstrated success in locating the F-E and LR axes, defining the axes and their errors using anatomically relevant coordinate systems would improve clinical relevance. While errors due to revolute joint transducer resolution were computed, errors due to nonlinearity and hysteresis in the transducers were not examined, and errors due to different applied tibiofemoral motions were not examined. Thus the objective was to computationally determine, using anatomically relevant coordinate systems, the errors in locating the F-E and LR axes due to nonlinearity and hysteresis in the revolute joint transducers for three different simulations of applied tibiofemoral motion.
Assessment of the Effect of Coronary Occlusion on Aortic Valve Dynamics Using a Global 3D FSI Model
Authors: Nobari Soroush , Mongrain Rosaire , Leask Richard , Cartier Raymond
Published: July 2013

Coronary artery disease (CAD) is considered to be a major cause of mortality and morbidity in the developing world. It has recently been shown that aortic root pathologies such as aortic stiffening and calcific aortic stenosis can contribute to the initiation and progression of this disease by affecting coronary blood flow [1,2]. Such pathologies influence the distensibility of the aortic root and therefore the hemodynamics of the entire region. As a consequence the coronary blood flow and velocity profiles will be altered [3,4,5] which could accelerate the development of an existing coronary artery disease. However, it would be very interesting to see if an occluded coronary artery would have a mutual impact on valvular dynamics and aortic root pathologies. This bi-directionality could aggravate and contribute to the progression of both the coronary and aortic root pathology.
Adhesive Strength of Atherosclerotic Plaques Depends on Collagen Content
Authors: Wang Ying , Johnson John A. , Fulp Abigail , Sutton Michael A. , Lessner Susan M.
Published: July 2013

Atherosclerotic plaque rupture is a major cause of myocardial infarction, coronary thrombosis and stroke. In a previous study, we proposed a new plaque rupture mechanism, plaque separation at the shoulder, and developed a novel quantitative mechanical test to measure the adhesive strength between the atherosclerotic plaque and the underlying vascular wall in mouse models using the local energy release rate, G, as a quantifiable metric for direct comparison of plaque separation strengths (1). We have now investigated structure-function relationships between the local energy release rate and local plaque composition. We hypothesize that adhesive strength varies with plaque composition in mice of different genotypes, and that it correlates with collagen deposition and macrophage content in lesions. Mice which are genetically deficient in matrix metalloproteinase 12 (MMP12), have previously been shown to demonstrate altered lesion composition (2). Therefore, we used apoE knockout (KO) and apoE MMP-12 double knockout (DKO) mice for our experiments and expected to see a difference in local energy release rates between strains.
Isolated Lymphatic Vessel Perfusion System Design for Independently Controlling Hoop Stress and Shear Stress
Authors: Kornuta Jeffrey A. , Dixon J. Brandon
Published: July 2013

Most tissues in the body are supported by the lymphatic system for a variety of functions, including the regulation of fluid balance, the removal of particulate matter from the interstitium, as well as the transport of fat from the intestine to the blood, among others. Lymphedema, a chronic disease characterized by an inability of the lymphatics to maintain tissue homeostasis and estimated to affect over 130 million people worldwide, can result in serious clinical problems for which there are very few beneficial cures or therapies [1]. However, despite the importance of lymphatics and the prevalence of lymphatic disease, very little is known about the particular mechanisms through which the lymphatics fulfill its primary functions.
Comparison Between Actual Stenosis and Internal Balloon Obstruction for Equivalent Pressure in a Porcine Model
Authors: Kolli Kranthi K. , Paul Anup K. , Back Lloyd H. , Effat Mohamed , Banerjee Rupak K.
Published: July 2013

The study of hemodynamics in an animal model associated with coronary stenosis has been limited due to the lack of a safe, accurate, and reliable technique for creating an artificial stenosis. Creating artificial stenosis using occluders in an open-chest procedure has often caused myocardial infarction (MI) or severe injury to the vessel resulting in high failure rates. To minimize these issues, closed-chest procedures with internal balloon obstruction were often used to create artificial stenosis. However, it should be noted that the hemodynamics in a blood vessel with internal balloon obstruction as opposed to actual stenosis hasn’t been compared. Hence, the aim of this research is to computationally evaluate the pressure drop in balloon obstruction and compare with that in actual stenosis. It was observed that the flow characteristics in balloon obstruction are more viscous dominated, whereas it is momentum dominated in actual stenosis. Balloon radius was iteratively varied to get a pressure drop equivalent to that of actual stenosis at mean hyperemic flow rates. A linear relation was obtained to predict equivalent balloon obstruction for actual stenosis.
Sensing of Local, Highly Concentrated Magnetic Field Gradients in Magnetotactic Bacteria Induces Motility Reversal
Authors: González Lina M. , Ruder Warren C. , Messner William C. , LeDuc Philip R.
Published: July 2013

Many motile unicellular organisms have evolved specialized behaviors for detecting and responding to chemical gradients (chemotaxis) or oxygen (aerotaxis), while magnetotactic bacteria sense magnetic fields to align their direction of movement. Herein we show that Magnetospirillum magneticum (AMB-1) have the ability to sense and respond not only to the direction of magnetic fields of naturally occurring magnitude, but also to local, highly concentrated magnetic field gradients that do not occur in their natural environment. We imposed these gradients through our system integrating Helmholtz coils and permalloy (Ni80Fe20) microstructures. The AMB-1 exhibit three distinct behaviors as they approached gradients near the microstructures—unidirectional, single direction reversal, and double direction reversal. These results indicate previously unknown capabilities of the magnetic sensing systems of AMB-1.
Applied Osmotic Loading for Promoting Development of Engineered Cartilage
Authors: Sampat Sonal R. , Robinson Drew A. , Ackerman George P. , Dermksian Matthew V. , Ateshian Gerard A. , Hung Clark T.
Published: July 2013

The avascular nature of cartilage and the harsh joint loading environment lead to a poor intrinsic healing capacity after injury, motivating the development of cell-based therapies for repair. Synovium-derived stem cells (SDSCs) have the potential for differentiating down a chondrogenic lineage and are thought to aid in articular cartilage repair after damage in vivo1. In the present study, we adopt a two-pronged strategy for growing clinically relevant cartilage grafts. Firstly, we compare the potential of SDSCs versus chondrocytes for engineering functional constructs. Secondly, we investigate the effect of extracellular osmolarity on mechanical and biochemical properties of SDSCs and similarly passaged chondrocytes in 3D culture. This approach is motivated by the fact that the in situ osmotic environment of chondrocytes varies with proteoglycan content and tissue deformation, altering the regulation of chondrocyte activity through mechanotransduction pathways2. We test the hypothesis that application of a hypertonic, more physiologic osmotic environment (created by addition of NaCl and KCl) relative to hypotonic media (300 mOsm), during 3D culture of SDSCs or chondrocytes in agarose hydrogels, improves the biochemical composition and mechanical properties of engineered tissue constructs.
Incomplete Restoration of Homeostatic Shear Stress Within Arteriovenous Fistulae
Authors: McGah Patrick M. , Riley James J. , Aliseda Alberto , Leotta Daniel F. , Beach Kirk W.
Published: July 2013

Arteriovenous fistulae are created surgically to provide an adequate access for dialysis in patients with End-Stage Renal Disease (ESRD). Producing an autogenous shunt linking an artery and a vein in the peripheral circulation bypasses the high resistance capillary bed in order to provide the necessary flow rates at sites easily accessible for dialysis. In successful fistulae, venous flow rates can easily exceed 1000 mL/min. It has long been recognized that the hemodynamics constitute the primary external influence on the remodeling process [1]; The high flow rate, together with the exposure of the venous tissue to the high arterial pressure, leads to a rapid process of wall remodeling that may end in a mature access or in failure. Recent hemodynamic simulations [2,3] have computed very high viscous wall shear stresses within fistulae; Stresses > 15Pa have been reported which are much greater than what is typically considered normal (i.e. homeostatic, ≈ 1Pa). Both sustained high shear and sustained low shear have been hypothesized to cause pathological venous remodeling (i.e. intimal hyperplasia) which causes stenoses and threatens fistula patency. The role of high vs. low shear stress in effecting patency remains unclear. Given the high failure rate of dialysis access sites (up to 50% require surgical revision within one year [4]), understanding the dynamics of blood flow within the fistula is a necessary step in understanding the remodeling, and ultimately, in improving clinical outcomes.
Finite Element Modeling of Flap Design After Skin Expansion
Authors: Buganza Tepole Adrián , Zöllner Alexander M. , Kuhl Ellen
Published: July 2013

Tissue expansion is a common technique in reconstructive surgery used to resurface damaged areas such as burns, birth defects or after tumor removal. The procedure is characterized by the inflation of a balloon below the skin that leads to three-dimensional dome-like shapes of tissue. Skin then needs to be cut to create a flap, which is extended to cover the excised area. The latter procedure, called flap design, has been empirically studied and advantages and disadvantages of the use of one type of flap over another have been discussed [1]. However, to date, flap design has never been optimized from a mechanical point of view.
Increased Levels of Myo-Inositol are Associated With Impaired Working Memory and Active Avoidance in Blast Neurotrauma Animals
Authors: Sajja Sujith , Perrine Shane A. , Ghoddoussi Farhad , Galloway Matthew P. , VandeVord Pamela J.
Published: July 2013

Impaired working memory and anxiety are major clinical symptoms commonly associated with subjects exposed to blast overpressure [1–4]. Despite this association, there remains a vital need for biomarkers to help effectively diagnosis blast-induced neurotrauma (BINT). Clinically, elevated myo-inositol has been associated with several neurodegenerative disorders including dementia and elevated levels may reflect activation of microglia. In the present study, we evaluated the cognitive and behavioral changes in blast exposed animals using the novel object recognition (working memory paradigm) and light/dark (anxiety test) assessments. In addition, we used high resolution magic angle spinning H-MRS to assess neurochemical changes in the prefrontal cortex and amygdala, brain regions associated with working memory and anxiety respectively. Results suggest that exposure to blast has a significant effect on the levels of myo-inositol which appear to be linked with impaired working memory.
Nucleotomy Alters Mechanical Function Following Cyclic Loading and Unloaded Recovery of Human Discs
Authors: Showalter Brent L. , MacLean Ian S. , Elliott Dawn M. , Malhotra Neil R.
Published: July 2013

The intervertebral disc plays a critical role in supporting loads, permitting spinal motion, and dissipating energy. Unfortunately, it is also commonly degenerated, resulting in altered spinal mechanics and low back pain. Nucleotomy is a common treatment for herniated discs and is also used experimentally to simulate degeneration.[1] The procedure, which involves a posterior annular incision and removal of a portion of the nucleus pulposus (NP), has also been shown to alter disc mechanics. These changes include acute changes of decreased NP pressure, decreased disc height, and increased neutral zones.[2, 3] Cyclic studies have shown that trans-endplate nucleotomy permanently alters creep mechanical properties of sheep discs.[4] However, the effects of annular nucleotomy on the cyclic properties of human discs have not yet been studied. This work studied the mechanical effect of annular nucleotomy on human discs subjected to physiological axial cyclic loading.
Bistable Structures Exhibiting Snap-Through Instability: From Slap Bracelets to the Venus Flytrap
Authors: Chen Zi , Guo Qiaohang , Majidi Carmel , Chen Wenzhe , Srolovitz David J. , Haataja Mikko
Published: July 2013

Bistable structures, exemplified by the Venus flytrap [1] and slap bracelets (see Fig. 1), can tranform quickly from one functional shape to the other upon mechanical actuation. Potential applications can be found in mechanical/electromechanical devices from bio-inspired robots to deployable aerocraft wings. Related challenges emerged include theoretically modeling the spontaneous curving and buckling of thin objects such as leaves, flowers, nanohelices, nanoscrolls and flexible electronics [2, 3]. Despite the significant modeling efforts about such large deformation of shell structures [4, 5], the nonlinear geometric effects remain poorly understood. Here we present a continuum elasticity theory that incorporates geometric nonlinearity for large deformation of shells, and investigates, through both theoretical analysis and table-top experiments, the geometric and mechanical conditions for bistability, and the role of edge effects. Our work classifies the conditions for bistability, defines the design space for bistable morphing structures, and extends the theory of plates and shells with large deformation. A mechanical framework is provided for analyzing morphogenesis associated with growth and instability, which will also facilitate the design of multistable structures, from bio-inspired robots to deployable structures in aerospace applications.
Micromechanical Analysis of Mouse Aortic Valve Leaflets With Atomic Force Microscopy
Authors: Sewell-Loftin M. K. , Brown Christopher B. , Baldwin H. Scott , Merryman W. David
Published: July 2013

A significant limitation in our ability to study congenital heart valve disease and defects is due to lack of appropriate animal models and also in part to our incomplete understanding of biomechanical properties of the leaflet tissues. Biomechanical changes in leaflets as they develop and throughout a person’s lifetime are not well understood. With improved understanding of such changes, more intuitive approaches could be used to develop tissue engineered heart valves. Each year in the United States, over 20,000 children are born with congenital heart defects; many requiring valve replacement surgery [1–2]. Additionally, over 300,000 people worldwide require heart valve replacement surgery each year [3–4]. The creation of better valve replacements would improve treatment and quality of patient life.
CFD Challenge: Solutions Using the In-House Finite-Element-Based Solver NEWTETR
Authors: Hoi Yiemeng , Steinman David A.
Published: July 2013

Briefly, this Challenge aims to test the sensitivity of steady and pulsatile pressure drops as predicted by different CFD solvers or groups, and ultimately against in vitro pressure measurements. The current study focuses on the Phase I of the Challenge. We simulated steady state and pulsatile pressure drops based on the nominal surface geometry and specific inlet flow rates on a giant cerebral aneurysm with proximal stenosis.
Theoretical Model of the Dynamic Stress on the Retina During Eye Rotations
Authors: Meskauskas Julia , Repetto Rodolfo , Siggers Jennifer H.
Published: July 2013

The vitreous humor is the transparent gel-like material that fills the vitreous chamber, the largest chamber of the eye, which has an approximately spherical shape. The viscoelastic properties of the vitreous humor have been studied by several authors [1–3].