bluuebunny/crossref_metadata_2025 huggingface dataset:
An Improved Cryosurgical Probe Testbed Based on Convective Exchange Boundary Conditions
Authors: Etheridge Michael L. , Choi Jeunghwan , Zastrow Stephanie , Ramadhyani Satish , Bischof John C.
Published: July 2013

Cryosurgery has demonstrated significant capabilities as a minimally invasive technique for treating cancer and other conditions [1], but has been limited by the ability to accurately predict treatment outcome and damage to surrounding tissues. Contributing to this problem has been the accuracy of predictive modeling and translating this to effective pretreatment planning. The two key factors in accurately modeling cryosurgical freezing are the temperature-dependent thermal properties of the freezing medium and cryoprobe boundary conditions. Both of these issues are considered in this study.
Reproducibility of Bone Microstructure and Stiffness Measurements in Rats by In Vivo Micro Computed Tomography and Finite Element Analysis
Authors: Lan Shenghui , Chandra Abhishek , Qin Ling , Liu X. Sherry
Published: July 2013

Micro computed tomography (μCT) has been widely used to study 3-dimensional (3D) microstructure of bone specimens. In the recent decade, in vivo μCT scanners have become available to monitor longitudinal bone changes in rodents (1,2). The current in vivo μCT scan can obtain images with an isotropic voxel size up to 10.5 μm, which is high enough for direct 3D bone microstructural analyses. Moreover, based on these high-resolution images, micro finite element (μFE) models can be generated to estimate mechanical properties of bone. Therefore, by using in vivo μCT imaging and μFE analysis techniques, changes in geometry, microstructure, and mechanical properties of rodent bone, in response to either diseases or treatments, can be visualized and quantified over time.
Hemodynamic Shear Regulates Intercellular Forces and Permeability of Endothelial Cell Monolayers
Authors: Ting Lucas H. , Sniadecki Nathan J.
Published: July 2013

In the cardiovascular system, the flow of blood within the complex vascular network creates hemodynamic shear forces experienced by cells. Situated between the circulating blood and the bulk vascular tissue, the endothelium is a cell monolayer acting as a barrier that protects the underlying arterial tissue. Shear forces have been seen to interact with and regulate endothelial cells through mechanotransduction induced cytoskeletal changes within the cell [1]. Shear forces can be beneficial in cases of laminar flow, which are thought to be atheroprotective by aligning and organizing endothelial cells [2]. However, disturbances to a smooth flow field, caused by vessel bifurcations or obstructions like an implanted stent or a bulging atherosclerotic lesion, can cause recirculation zones to form downstream. In these flow regions, detrimental monolayer remodeling occurs which breaks down the endothelial barrier function [3]. Biochemically, it has been seen that shear forces drive signaling cascades in the Rho/Rac pathways that cascade into morphological changes in the cytoskeleton [4].
Lower Transient Stresses in an Aortic Valve Leaflet With Oblique Reinforcement Fibers: A Finite Element Study
Authors: Hammer Peter E. , Howe Robert D. , del Nido Pedro J.
Published: July 2013

Native aortic valve leaflets contain a network of strong collagen fibers within a matrix of relatively distensible tissue. This composite structure leads to anisotropic mechanical properties and is believed to play an important role in the ability of the structure to withstand the stresses of cyclic loading over billions of heart beats. Replacement valves that consist of animal tissues also contain such fibers, but all designs in clinical use are chemically cross-linked, which increases the in-plane stiffness of the tissue and decreases anisotropy. Tissue replacement valves suffer from poor durability due to calcification and tissue degeneration in regions of high stress, including at the base of the coaptation region and at the leaflet commissures [1]. A better understanding of leaflet stresses in these regions and how to mitigate them is important in order to improve the design of replacement heart valves to improve durability.
Diameter Constriction Reduces Intramural Circumferential Stress Gradient in the Vein Under Arterial Pressures
Authors: Wang Roy , Gleason Rudolph L. , Brewster Luke
Published: July 2013

Coronary and peripheral artery diseases are a leading cause of morbidity and mortality in developed countries. For severe cases, surgical intervention to bypass the disease using autologous vessels continues to be the preferred choice of treatment. These bypass vessels are typically obtained from the venous vasculature. Despite the superior long-term patency of veins over synthetic grafts, one-year failure rates approach 30–40% in both the coronary and peripheral systems [1–2]. Still, bypass surgery remains the recommended therapy for most persons with severe arterial blockages [3]. As the number of bypass procedures increase and patients receiving bypasses live longer, improving the lifetime of bypass grafts is increasingly important.
Longitudinal Effect of Wall Shear Stress on the Amount of Intimal-Medial Thickening of Venous Wall in Arteriovenous Fistula
Authors: Rajabi-Jaghargh Ehsan , Roy-Chaudhury Prabir , Krishnamoorthy Mahesh K. , Wang Yang , Banerjee Rupak K.
Published: July 2013

Arteriovenous fistula (AVF) maturation failure is mainly due to venous stenosis characterized by significant amount of intima-media thickening (IMT). Although hemodynamic endpoints are believed to play a crucial role in pathogenesis of venous stenosis, the exact mechanism behind this is unclear. Our hypothesis is that longitudinal (temporal) changes of hemodynamic parameters, specifically wall shear stress (WSS), influences amount of IMT in maturation process of AVF. AVFs were created in curved (C-AVF) and straight (S-AVF) configurations between femoral artery and vein of 3 pigs. CT-scans and ultrasound were utilized to calculate WSS at 2D (D: days), 7D, and 28D post-surgery. IMT was measured at 4 histological blocks along the vein of AVFs. It was found that C-AVF underwent outward remodeling characterized by consistent increase in venous diameter and larger IMT. This remodeling process was governed by negative temporal gradient of WSS (τ′) [−0.99 ± 0.60 dyn/cm2/day]. In contrast, S-AVF underwent inward remodeling characterized by temporal decrease in venous diameter and relatively smaller IMT. This remodeling process was governed by positive τ′ (0.42 ± 0.6 dyn/cm2/day). In summary, temporal gradient of WSS influences IMT. Temporal decrease of WSS in C-AVF resulted in vasodilation and outward growth of wall (favorable to maturation). However, temporal increase in WSS in S-AVF leaded to vasoconstriction and inward growth of wall (detrimental to maturation). Thus, clinically it can be of great importance to surgeons to create AVF in a configuration that can result in favorable hemodynamic parameters and histological end-points.
Surgeon Perception of Cancellous Screw Fixation
Authors: Stoesz Michael J. , Jastifer James R. , Chess Joseph L. , Patel Bipin , Gustafson Peter A.
Published: July 2013

The ability of surgeons to optimize screw insertion torque in nonlocking fixation constructs is important for stability, particularly in osteoporotic and cancellous bone. This study evaluated screw torque applied by surgeons during simulated cancellous fixation. It evaluated the frequency that synthetic cancellous bone were stripped by the surgeon, factors associated with bone stripping, and the ability of surgeons to recognize it.
Effect of Hydrogen Bonding Ability, Dipole-Dipole Interactions and Viscosity of Extracellular Matrix Fluid on the Bone Mechanical Behavior
Authors: Samuel Jitin , Zhao Cong-Gui , Giri Bijay , Sinha Debarshi , Wang Xiaodu
Published: July 2013

Fragility fracture as a mode of pathologic failure in bone is a major healthcare concern and has adverse consequences with respect to morbidity, cost and to a lesser extent mortality. Understanding the structure/composition and functional relationships among the bone constituents is an important step towards prevention/treatment of fragility fractures.
Fluorescently Labeled Carbon Nanohorns as Intracellular Drug Delivery Vehicles
Authors: Zimmermann Kristen A. , Inglefield David , Long Timothy E. , Rylander Christopher G. , Rylander M. Nichole
Published: July 2013

Nanomaterials have been investigated for biomedical applications due to their unique properties. Their shape, size, surface, and material can be altered specifically for the type of application. Carbon nanomaterials (CNMs) have been effectively utilized as photoabsorbers to enhance laser-based therapies [1] and can be easily loaded with drugs or targeting moieties [2, 3]. The strong carbon bonds in this material provide a chemical and mechanical inertness that can serve as a barrier to protect chemotherapeutic agents from degrading quickly as they are transported to the site of interest [2].
Detecting Presence of Bubbles Within Simulated Blood Vessels Using a Piezoelectric Ring Set to Oscillate at Matching Resonant Conditions
Authors: Valentin Francisco I. , Cancelos Silvina
Published: July 2013

A variety of methods have been used to detect and measure the presence and size of bubbles that occur naturally in tubes or blood vessels. These traits have recently produced interest in biomedical fields including drug delivery systems and decompression sickness, among others. To detect and measure bubbles, optical, acoustic, and equivalent bulk properties methods have primarily been used; each exploiting unique characteristics of bubbles [1]. Among these, Doppler techniques based on the backscattering of ultrasound waves, have been used to detect and measure bubbles within fluid media [2,3].
Phase Change Electrodes for Reducing Joule Heating During Irreversible Electroporation
Authors: Arena Christopher B. , Mahajan Roop L. , Rylander Marissa Nichole , Davalos Rafael V.
Published: July 2013

Irreversible electroporation (IRE) is a non-thermal tissue ablation modality that is gaining momentum as a viable treatment option for tumors and other non-cancerous pathologies [1]. The protocol consists of delivering a series of short (∼ 100 μs) and intense (∼ 1000 V/cm) pulsed electric fields through electrodes inserted directly into or around a targeted tissue. The pulses induce a rapid buildup of charge across the plasma membrane of cells comprising the tissue that results in the creation of permanent membrane defects, ultimately leading to cell death. Because the extent of cell death relies predominately on the extent of charge buildup and not thermal processes, extracellular matrix components are spared, including major nerve and blood vessel architecture. Additionally, the ablation volume is predictable based on the electric field distribution and visible in real-time via MRI, CT, and ultrasound.
Changes in Medial Knee Contact Force Through Gait Modification
Authors: Hall Allison L. , Besier Thor F. , Silder Amy , Delp Scott L. , D’Lima Darryl D. , Fregly Benjamin J.
Published: July 2013

The development of medial knee osteoarthritis (OA) has been attributed to overloading of the medial compartment articular cartilage [1]. Therefore, treatment strategies are often focused on reducing medial compartment loads. Gait modification represents a non-invasive method for achieving this goal. Previous studies have shown that a variety of gait modifications (e.g., toeing out, increased medial-lateral trunk sway, walking with medialized knees (i.e., medial thrust gait)) are effective in reducing the external knee adduction moment [e.g., 2–4]. Although the external knee adduction moment is often used as a surrogate measure of medial compartment force, a recent study showed that reductions in the external knee adduction moment do not guarantee reductions in medial compartment force [5]. Therefore, direct measurements of changes in medial contact force are important for determining the effectiveness of gait modifications.
Regulation of Adhesion Strength by Focal Adhesion Position and Cell Shape
Authors: Gallant Nathan D. , Elineni Kranthi Kumar
Published: July 2013

Cell adhesion to extracellular matrices is critical to numerous cellular functions and is primarily mediated by integrin receptors. Binding and aggregation of integrins leads to the formation of focal adhesions (FA) which connect the cytoskeleton to the extracellular matrix in order to reinforce adhesion and transmit signals [1]. Preliminary observations indicated preferential recruitment of FAs to the periphery of the cell spreading area on both uniformly coated and micropatterned fibronectin surfaces (Fig. 1). The current study investigates the biophysical regulation of cell adhesion strength based on the size and position of FA with the central hypothesis that peripheral FAs stabilize adhesion strength. The hypothesis was tested by delineating the cell spreading area from the total cell adhesive area by employing microcontact printing to pattern substrates with a series of circular and annular adhesive islands which control cell shape (Fig. 2). A well characterized hydrodynamic shear assay known as the spinning disk device was used to quantify the adhesion strength of cells adhered to the micropatterns [2].
Experimental Evaluation of Computationally Predicted Changes in Knee Loads Resulting From Medial Thrust Gait
Authors: Hall Allison L. , Walter Jonathan P. , Besier Thor F. , Silder Amy , Delp Scott L. , D’Lima Darryl D. , Fregly Benjamin J.
Published: July 2013

Abnormal loading of the medial compartment of the knee is believed to be a contributing factor to the development of medial compartment knee osteoarthritis (OA) [1]. Treatment strategies for patients with medial knee OA include both invasive (i.e., surgery) and non-invasive (e.g., gait modification) options. A variety of modified gait patterns have been proposed as non-invasive treatments for patients with medial knee OA.
Parametric Evaluation of Hindfoot and Forefoot Properties and Their Effect on the Angular Stiffness of Prosthetic Feet
Authors: Adamczyk Peter G. , Roland Michelle , Hahn Michael E.
Published: July 2013

Prosthetic foot stiffness has been recognized as an important factor in optimizing the walking performance of amputees [1–3]. Commercial feet are available in a range of stiffness categories and geometries. The stiffness of linear displacements of the hindfoot and forefoot for several commercially available feet have been reported to be within a range of 27–68 N/mm [4] and 28–76 N/mm [5], respectively, but these values are most relevant only to the earliest and latest portions of stance phase, when linear compression or rebound naturally occur. In contrast, mid-stance kinetics are more related to the angular stiffness of the foot, which describes the ankle torque produced by angular progression of the lower limb over the foot during this phase. Little data is available regarding the angular stiffness of any commercially available feet. The variety of geometries between manufacturers and models of prosthetic feet makes a direct calculation of effective angular stiffness challenging due to changes in moment arms based on loading condition, intricacies of deformation mechanics of the structural components, and mechanical interaction between hindfoot and forefoot components. Thus, modeling the interaction between hindfoot stiffness, forefoot stiffness, and keel geometries and their combined effect on the angular stiffness of the foot may be a useful tool for correlating functional outcomes with stiffness characteristics of various feet. To understand how each of these factors affects angular stiffness, we developed a foot that can parametrically adjust each of these factors independently. The objective of this study was to mathematically model, design, and experimentally validate a prosthetic foot that has independent hindfoot and forefoot components, allowing for parametric adjustment of stiffness characteristics and keel geometry in future studies of amputee gait.
Parameter Sensitivity Analysis of a Lumped-Parameter Model of Lymphangions in Series
Authors: Jamalian Samira , Moore James E. , Bertram Christopher D. , Richardson Will
Published: July 2013

The lymphatic system is responsible for vital functions in the human body. In particular, it plays an important role in the immune system mechanism whereby undesirable elements are destroyed in the lymph nodes. But cancer cells also spread via the lymphatic system. The system maintains fluid and protein balance by gathering approximately 4 L/day of interstitial fluid and returning it to the venous system. Lymphedema, an ailment of the system for which there is no known cure, primarily affects cancer patients who have undergone lymph node dissection [1]. To understand how to treat such pathologies of the lymphatic system, it is first necessary to examine its fluid flow and pumping mechanisms quantitatively.
Effect of Common Carotid Artery Inlet Length on Helical Flow at the Carotid Bifurcation: Influence on Exposure to Disturbed Shear
Authors: Gallo Diego , Steinman David A. , Morbiducci Umberto
Published: July 2013

There is evidence that helical blood flow elicits atheroprotective fluid-wall interaction processes and regulates the transport of atherogenic particles at the luminal surface [1]. In particular, with reference to the carotid bifurcation it was also suggested that helical flow might play a key role in determining wall shear stress patterns [2]. Those findings suggest that a relationship could exist in the carotid bifurcation between exposure to disturbed shear and helical bulk flow patterns, an hypothesis that has been tested only in simplified models [3]. For this reason, in the present study we aim to gain further knowledge on the existence of a link between local risk factors in atherosclerosis and the amount of helicity in the bulk flow of carotid bifurcations. In particular, here we want to confirm if a high amount of helical flow is instrumental in suppressing flow disturbances.
Quantitative Analysis of Glabrous Skin Blood Flow and its Role in Human Thermoregulation
Authors: Hensley Daniel W. , Mark Andrew E. , Wissler Eugene H. , Diller Kenneth R.
Published: July 2013

Glabrous (hairless) skin found on the hands, feet, face, and ears is a unique component of the thermoregulatory system. Its anatomy and control physiology differ markedly from those of the rest of the skin. Glabrous regions contain vascular networks capable of supporting large blood flows due to the presence of highly tortuous and densely packed arteriovenous anastomoses (AVAs) and associated venous collecting networks [1]. When dilated, these vessels bring large volumes of blood close to the body surface where they function as highly efficient heat exchangers. Furthermore, the manner in which this blood flow is controlled is very unique, exhibiting, for example, rapid and high-magnitude responses, as well as a greater sensitivity to central core signals [1]. In this light, glabrous skin is an important but often overlooked tool the body uses to rapidly and finely adjust energy balance to maintain thermal equilibrium.
Influence of Chondrocyte Zone on Co-Cultures With Mesenchymal Stem Cells in HA Hydrogels for Cartilage Tissue Engineering
Authors: Kim Minwook , Burdick Jason A. , Mauck Robert L.
Published: July 2013

Mesenchymal stem cells (MSCs) are an attractive cell type for cartilage tissue engineering in that they can undergo chondrogenesis in a variety of 3D contexts [1]. Focused efforts in MSC-based cartilage tissue engineering have recently culminated in the formation of biologic materials possessing biochemical and functional mechanical properties that match that of the native tissue [2]. These approaches generally involve the continuous or intermittent application of pro-chondrogenic growth factors during in vitro culture. For example, in one recent study, we showed robust construct maturation in MSC-seeded hyaluronic acid (HA) hydrogels transiently exposed to high levels of TGF-β3 [3]. Despite the promise of this approach, MSCs are a multipotent cell type and retain a predilection towards hypertrophic phenotypic conversion (i.e., bone formation) when removed from a pro-chondrogenic environment (e.g., in vivo implantation). Indeed, even in a chondrogenic environment, many MSC-based cultures express pre-hypertrophic markers, including type X collagen, MMP13, and alkaline phosphatase [4]. To address this issue, recent studies have investigated co-culture of human articular chondrocytes and MSCs in both pellet and hydrogel environments. Chondrocytes appear to enhance the initial efficiency of MSC chondrogenic conversion, as well as limit hypertrophic changes in some instances (potentially via secretion of PTHrP and/or other factors) [5–7]. While these findings are intriguing, articular cartilage has a unique depth-dependent morphology including zonal differences in chondrocyte identity. Ng et al. showed that zonal chondrocytes seeded in a bi-layered agarose hydrogel construct can recreate depth-dependent cellular and mechanical heterogeneity, suggesting that these identities are retained with transfer to 3D culture systems [8]. Further, Cheng et al. showed that differences in matrix accumulation and hypertrophy in zonal chondrocytes was controlled by bone morphogenic protein [9]. To determine whether differences in zonal chondrocyte identity influences MSC fate decisions, we evaluated functional properties and phenotypic stability in photocrosslinked hyaluronic acid (HA) hydrogels using distinct, zonal chondrocyte cell fractions co-cultured with bone marrow derived MSCs.
Using Modeling Software to Visualize Biomechanics in an Introductory Undergraduate Bioengineering Course
Authors: Kusano Stephanie M.
Published: July 2013

The modeling software MADYMO was used as a visual teaching tool for teaching human body modeling during an introductory undergraduate bioengineering course. The human body modeling lecture was covered during the six-week biomechanics section of a 15-week course. The students in this introductory bioengineering course were primarily second year, second semester students, from a wide range of engineering disciplines. Biomechanics is a challenging topic to teach to undergraduate students because of the students’ limited understanding of general mechanics and physiology. Education research has shown the effectiveness of using visual teaching tools (Felder, 1988). MADYMO is an industry-standard modeling tool for human crash response. Considering the challenges of introducing human body modeling in a single lecture to undergraduate students, we believe using MADYMO as a visual tool helps the students realize a basic understanding and appreciation for human body modeling.
Longitudinal Variation in the Mechanical Properties of the Posterior Side of Thoracic Aorta is Larger Than Those of the Anterior Side During the Inflation Test
Authors: Kim Jungsil , Dupay Alexander , Baek Seungik
Published: July 2013

The mechanical properties of arterial wall have been assumed isotropic and homogeneous, but advances in biomedical imaging and computational biomechanics bring a need for understanding regional difference in the biomechanical properties of arties. Particularly, vascular diseases such as aortic aneurysm and dissection are likely to be developed in the elderly and they are still life-threatening. Thus understanding of the regional variation in the mechanical behavior of arteries is critical for the clinical treatments and biomedical engineering applications.
Characterization of Multilayer Material Properties of Descending Aorta
Authors: Hemmasizadeh Ali , Darvish Kurosh , Autieri Michael
Published: July 2013

In a wide range of biomechanical modeling of aorta from traumatic injury to stent grafts, the arterial wall has been considered as a single homogeneous layer vessel, ignoring the fact that arteries are composed of distinct anatomical layers with different mechanical characteristics. In this study, using a custom-made nanoindentation technique, changes in the mechanical properties of porcine thoracic aorta wall in the radial direction were characterized using a quasi-linear viscoelastic model. Two layers of equal thickness were mechanically distinguishable based on the radial variations in the instantaneous Young’s modulus E and reduced relaxation function G(t). The overall results showed that the outer half was stiffer and showed less relaxation than the inner half. These layers may correspond to media and adventitia in the specimens.
Precision of a Novel Vertebral Motion Analysis System: Preliminary Results
Authors: Yeager Matthew S. , Cook Daniel J. , Cheng Boyle C.
Published: July 2013

Imaging modalities such as X-Ray, computerized tomography (CT), magnetic resonance imaging (MRI), and bone scan have all become essential to the evaluation of bone and soft tissue in patients with back pain. All techniques provide valuable static images of the spine, yet lack the capability of providing detailed information about spinal motion. Dynamic end-range x-rays, the standard in assessment of range of motion and vertebral translation, are taken at the patient’s maximum voluntary bending angle in flexion and extension (FE) and/or lateral bending (LB). The current standard of practice is to measure, with ruler and protractor, the relative change between adjacent vertebrae at each bending extreme. The resulting rotational or translational values are then expressed as the intervertebral angle (IVA) or as a percentage of vertebral body depth, respectively. This method, however, is subject to a high level of patient, imaging site, and observer related variability, in the form of uncontrolled bending angles, disparities in equipment and practices, and manual image analysis. An additional limitation of static imagery is the inability to assess motion in the spine as it traverses between end ranges. This information may expose motion abnormalities that occur mid-range that might otherwise be missed by clinicians. Lastly, motion of the spine may present differently in weighted and un-weighted positions. Effects of muscle activation and gravitational forces are not accounted for by current standards.
The Mechanics of Brain Motion During Free-Field Blast Loading
Authors: Merkle A. C. , Wing I. D. , Carneal K. C.
Published: July 2013

Overpressure is the primary metric considered when investigating head injuries due to primary blast loading. However, capturing the mechanics of brain motion is necessary to understand the risk of additional injury mechanisms. The Human Surrogate Head Model (HSHM) is used to measure relative brain motion due to live-fire blast loading. Although the initial blast loading resulted in almost no brain motion, the subsequent head rotation generated up to 3 mm of relative brain displacement.
Influence of Variable Native Arterial Diameter on Fractional Flow Reserve: An In-Vitro Study
Authors: Goswami Ishan , Peelukhana Srikara V. , Al-Rjoub Marwan , Back Lloyd H. , Banerjee Rupak K.
Published: July 2013

Fractional flow reserve (FFR), the ratio of the pressures distal (Pd) and proximal (Pa) to a stenosis, and coronary flow reserve (CFR), the ratio of flows at maximal vasodilation to the resting condition, are widely used for determining the functional severity of a coronary artery stenosis. However, the diameter of the native artery might influence the FFR values. Therefore, using an in-vitro experimental study, we tested the variation of FFR for two arterial diameters, 2.5 mm (N1) and 3 mm (N2). We hypothesize that FFR is not influenced by native arterial diameter. For both N1 and N2, vasodilation-distal perfusion pressure (CFR-Prh) curves were obtained using a 0.35 mm guidewire by simulating physiologic flows under different blockage conditions: mild (64% area stenosis (AS)), intermediate (80% AS) and severe (90% AS). The FFR values for the two arterial models differed insignificantly, within 3%, for mild and intermediate stenoses but differed appreciably for severe stenosis (∼25%). This significant difference in FFR values for severe stenosis can be attributed to relatively larger difference in guidewire obstruction effect at the stenotic throat region of the two native arterial models. These findings confirm that FFR will not differ for the clinically relevant cases of mild and intermediate stenosis for different arterial diameters.
Biomechanical Characterization of Sheep Vaginal Wall Tissue: A Potential Application in Human Pelvic Floor Disorders
Authors: Patnaik Sourav S. , Weed Benjamin , Borazjani Ali , Bertucci Robbin , Begonia Mark , Wang Bo , Williams Lakiesha , Liao Jun
Published: July 2013

Pelvic Organ Prolapse (POP) is a leading women’s health issue affecting a significant portion of the population and has been recently coined as a “silent epidemic”. POP leads to a considerable reduction in women’s quality of life and can cause chronic pelvic pain, sexual dysfunction, and social/psychological issues. The lifetime risk for having surgery for POP is approximately 11% with 200,000 POP procedures performed each year in USA, with an annual direct cost of over $1000 million. Exact etiology of POP is unclear, but it is understood that POP is multi-factorial in nature. Risk factors for POP include increasing age, obesity, multiple vaginal births, gravidity, history of hysterectomy, smoking, chronic cough conditions, frequent heavy lifting, and some genetic factors. POP results due to loss or damage of structural supports that support the pelvic organs (i.e. rectum, bowel, bladder, etc). Vaginal wall prolapse (anterior and posterior) is the most common presentation. This can result from weakening of the levator ani muscle and other connective tissue structures which not only control the mechanical function, but also help support neurological and anatomical function[1].
Investigation on a Relationship Between Hemodynamics and Wall-Thinning in an Unruptured Human Cerebral Aneurysm
Authors: Tobe Yasutaka , Yagi Takanobu , Takahashi Sara , Iwabuchi Yuki , Yamanashi Momoko , Iwasaki Kiyotaka , Umezu Mitsuo , Hayashi Yoshifumi , Yoshida Hirotaka , Nishitani Kazutoshi , Okada Yoshifumi , Sugawara Michihito , Hiraguchi Shin , Kubo Toshiro , Kitahara Shigemi
Published: July 2013

Recent studies of cerebral aneurysms are held using the blood flow simulation with patient-specific luminal geometries. In the study of development of cerebral aneurysms, wall shear stress (WSS) is focused as one of the key factors1–2. But the answer to the relationship between the extension of aneurysm and the theory of low WSS and high WSS still remains a question. One reason this question remains unsolved is because the current research about the cerebral aneurysms are held only using the vascular geometry developed from the medical images. From the intra-operative observation of cerebral aneurysms, the appearance of the cerebral aneurysm is not unified. Certain parts of the cerebral aneurysm have thin-walled structures where the blood flow of the aneurysm can be observed through the aneurysm wall. These differences in the wall structures cannot be predicted from the medical images. The purpose of this study is to see the relationship between hemodynamic patterns and thin-walled structure in human cerebral aneurysms.
Biomechanical Response of Human Liver and Spleen Parenchyma in Uniaxial Unconfined Compression
Authors: Kemper Andrew R. , Santago Anthony C. , Stitzel Joel D. , Sparks Jessica L. , Duma Stefan M.
Published: July 2013

Motor vehicle collisions (MVCs) commonly result in serious blunt abdominal injuries [1]. Although abdominal injuries account for only 3–5% of all injuries observed in MVCs, they comprise 8% of AIS 3+ injuries, 16.5% of AIS 4+ injuries and 20.5% of AIS 5+ injuries [24]. Currently, no crash test dummies used to assess injury risk in MVCs are equipped to represent individual solid abdominal organs located asymmetrically in the human abdomen. Consequently, researchers and safety engineers rely on finite element models (FEMs) to assess the risk of automotive related abdominal injuries. However, the response of these models must be locally and globally validated based on appropriate biomechanical data in order to accurately assess injury risk. There have only been a few studies which have investigated the compressive material properties of liver or spleen by performing compression tests on isolated samples [5–8]. Although these studies have provided considerable insight into the factors that affect the material response of the liver and spleen parenchyma, these studies have been limited to testing of animal tissue, sub-failure loading, or a single loading rate. Therefore, the purpose of this study was to quantify the compressive material properties of human liver and spleen parenchyma at various loading rates in order to characterize the viscoelastic and failure response.
Influence of Ionic Concentration on Swelling Behavior and Shear Properties of the Bovine Cornea
Authors: Hatami-Marbini Hamed , Etebu Ebitimi
Published: July 2013

The mechanical properties and structure of connective tissues such as the cornea and the cartilage are derived from the functions and properties of their extracellular matrix, a polyelectrolyte gel composed of collagenous fibers embedded in an aqueous matrix. The collagen fibers in the extracellular matrix of the corneal stroma are arranged in regular lattice structures, which is necessary for corneal transparency and transmitting the incident light to the back of the eye. This regular pseudo hexagonal arrangement is attributed to the interaction of collagen fibers with the proteoglycans as these regularities are lost in knock-out mice [i]. Proteoglycans (PGs) are heavily glycosylated glycoproteins. They consist of a core protein to which is glycosaminoglycan chains are covalently attached. The main PG in the corneal stroma is the proteoglycan decorin. Decorin is the simplest small leucine-rich PG and only has a single glycosaminoglycan side chain. It has a horse shape core protein and binds collagen fibrils at regular sites. Chondroitin sulfate (CS), dermatan sulfate (DS), keratan sulfate (KS) are among the prevalent glycosaminoglycans found in the cornea. Under physiological conditions, these linear carbohydrate polymers are ionized and carry negative charges due to the presence of negatively charged carboxylate and sulfate groups. Therefore, a hydrated gel is formed in the empty space between collagen fibrils by attracting water. The interaction of negatively charged glycosaminoglycans with themselves and their interaction with the free ions contribute to the corneal swelling pressure and subsequently to its compressive stiffness. From structural view point, the corneal stroma is a composite polyelectrolyte system in which the observed regular spacings of the collagens are suggested to exist because of the structural interaction of collagens, negatively charged glycosaminoglycans, and the free ions in the interfibrillar space.
Cell Velocity Gradients Underlie Early Morphogenesis of the Avian Gut Tube
Authors: Nerurkar Nandan L. , Tabin Clifford J.
Published: July 2013

At the end of gastrulation, the endoderm forms the ventral surface of the developing embryo. Subsequently, through a series of poorly understood morphogenetic events, the initially flat endoderm is transformed into the gut tube, a cylindrical structure that gives rise to the epithelial lining of the entire respiratory and gastrointestinal tracts. At present there is no mechanistic understanding of how the endoderm is transformed from a planar sheet to a simple tube. In avian and mammalian species, formation of the gut tube begins with two invaginations at the anterior and posterior poles of the embryo, termed the anterior (AIP) and caudal intestinal portals (CIP). The AIP, which forms the foregut, and CIP which forms the hindgut, begin moving toward one another, “zipping” the gut tube closed along the embryonic midline (Fig. 1A). The AIP and CIP meet at the umbilicus (mammals) or yolk stalk (avian), where the midgut is formed.
Effect of Body Geometry on the Motile Behavior of Bacteriabots
Authors: Sahari Ali , Canter Meghan , Behkam Bahareh
Published: July 2013

Micro-structures with complex geometries are being increasingly utilized in many fields from micro-robotics to targeted drug delivery [1,2]. Motility of spherical microstructures actuated by an ensemble of attached bacteria has been thoroughly characterized in previous literature [2–5] but a systematic study of the effect of micro structure geometry on propulsive behavior is currently missing. Mobile microrobots along with optimal body geometries are envisioned to impact minimally invasive diagnosis, localized treatment of diseases and environmental monitoring. Limited particle diffusion and directional coefficient of drag are some of the attributes that are enhanced through such bio-hybrid systems. In this work, we have utilized a low-cost and high throughput technique to obtain non-spherical mico-particles and investigate the effect of particle shape on the motile behavior of the BacteriaBots, which are bio-hybrid microrobots consisting of living propellers (bacteria) and a synthetic body.
The Role of Collagen Synthesis in Ventricular and Vascular Adaptation to Hypoxic Pulmonary Hypertension
Authors: Schreier David , Hacker Timothy , Song Guoqing , Chesler Naomi
Published: July 2013

Pulmonary hypertension (PH) is a debilitating disease that affects millions of Americans. Most research to date has focused on the deleterious effects of PH within the small vessels of the lungs that determine resistance. A relatively recent focus of PH is on the large pulmonary arteries (PAs) that provide compliance. Loss of compliance in these arteries, or arterial stiffening, is an excellent predictor of mortality in PH [1], which is most often caused by right ventricular (RV) hypertrophy and failure [2].
Magnetic Alignment of Type I Collagen as a Method for Altering Tensile Mechanical Properties
Authors: Novak Tyler , Canter Jamie , Chen Dafang , Hungate Joel , Voytik-Harbin Sherry , Neu Corey
Published: July 2013

To date, ligament and tendon replacements largely utilize autograft/allograft transplantation, although the use of tissue engineered materials remain a promising solution [10]. The development of an engineered solution may depend on the choice of scaffold materials with optimal fiber alignment. Type I collagen is an abundant extracellular matrix component in musculoskeletal tissues. The controlled alignment of type I collagen for tissue engineering and regenerative medicine applications enables the fabrication of unique scaffolds that emulate the ultrastructure of their native counterparts. Moreover, the alignment of type I collagen has become a common technique to manipulate mechanical properties of tissue constructs and the biological response of embedded cells [1,2]. It is additionally important to develop noninvasive methods to align collagen structures while maintaining inherent structural integrity and biological activity.
Genipin-Crosslinked Fibrin Hydrogels Modified With Collagen or Fibronectin as an Annulus Fibrosus Sealant
Authors: Guterl Clare Canal , Kim Tyler , Nicoll Steven B. , Iatridis James C.
Published: July 2013

Low back pain (LBP) affects 80% of all adults at some point in their lives [1], and is often associated with intervertebral disc (IVD) degeneration, therefore, restorative solutions are of high importance. The IVD is composed of an outer ring of annulus fibrosus (AF) containing the pressurized nucleus pulposus (NP) center. NP replacement approaches and IVD procedures such as discectomy or discography involve rupture of the AF tissue for diagnosis or repair purposes. Even small defects to the outer AF can accelerate IVD degeneration [2]. Current closure techniques are limited to sutures and offer little in the way of tissue replacement or mechanical restoration of the AF [3]. A genipin crosslinked fibrin hydrogel offers some promise as an adhesive AF sealant [4]. Fibrin is FDA approved and genipin is a plant based chemical crosslinker with low cytotoxicity used with a variety of materials including fibrin for articular cartilage engineering [5]. Genipin crosslinked fibrin is a tunable material with comparable mechanical properties to native AF tissue and although cells remained viable on the gel, the relatively slow proliferation and presence of abnormal cells with rounded morphology motivated further optimization. To improve cytomorphology, key extracellular matrix proteins, collagen and fibronectin, were added to the formulation. It was hypothesized that the addition of these proteins would maintain the mechanical properties of this gel while improving cell morphology and viability. Several additional analyses were included to further characterize this gel including push-out strength, degradation and contraction tests.
Evaluation of a Novel Statistical Method for EMG-to-Moment Estimation During Gait
Authors: Meyer Andrew J. , Patten Carolynn , Fregly Benjamin J.
Published: July 2013

Neuromusculoskeletal models have the potential to improve the design of clinical interventions for disorders such as stroke and osteoarthritis that affect walking function. Application of such models to clinical problems will likely require model customization to the unique anatomical and neurological conditions of each patient. Unfortunately, current modeling methods make model customization to patient data difficult, especially for model parameter values related to muscle-tendon models and musculoskeletal geometry [1]. Improved methods are needed so that patient-specific neural control capabilities and limitations can be easily incorporated into predictive gait optimizations to be used for intervention planning purposes.
Buckling of Porcine Aorta Under Static and Dynamic Loading
Authors: Rastgar Agah Mobin , Laksari Kaveh , Darvish Kurosh , Rachev Alexander
Published: July 2013

Tortuosity and buckling of blood vessels are defined as the deviation from original configuration and has been observed throughout the vascular system. The blood flow in the regions down-stream of tortuous section decreases, which may cause a deficiency in blood supply to the organs and ischemia. Although tortuosity of blood vessels has been associated with aging, atherosclerosis, hypertension, genetic and other cardiovascular disease, the mechanism behind its initiation and development is not yet understood. In a series of theoretical and experimental studies, biomechanical aspects of buckling of arteries has been investigated under quasi-static loading (Han, 2007; Liu and Han, 2011); however, it has been shown theoretically that the buckling behavior of arteries under dynamic loading are different and arteries may become mechanically unstable at pressures other than the static critical loading (Rachev, 2009). This work addresses buckling of porcine aorta and experimental verification of dynamic buckling in this case. We hypothesize that dynamic buckling can partly contribute to the traumatic rupture of aorta that is a leading cause of fatality in motor vehicle crashes.
Mechanical Communication Between Cardiac Cell Leads to Synchrony in Beating
Authors: Tang Xin , Bajaj Piyush , Bashir Rashid , Saif Taher
Published: July 2013

It is generally understood that cardiac cells synchronize their beating through electro-chemical signalling. Here we show, theoretically and experimentally, that isolated cardiac cells can communicate with each other through an intervening deformable media. Such communication leads to coupled dynamics and emergence of synchronous beating. The interaction between the cells depends inversely with the elastic modulus of the media, and the distance between them. This finding may explain asynchronous beating of the atrium in patients with atrial fibrillation where the stiffness of the atrial wall becomes significantly harder due to fibrosis [1].
A Device to Subject Cells to Longitudinal Stretch Gradients on a Tube In Vitro
Authors: Richardson William J. , van der Voort Dennis D. , Moore James E.
Published: July 2013

In the US, cardiovascular disease accounts for more than 800,000 deaths and an economic burden of nearly $300 billion per year. A major pathology afflicting the cardiovascular system is atherosclerosis, characterized by intraluminal plaque formation, producing a stenosis and obstructing flow. Balloon angioplasty, often coupled with the implantation of either a bare-metal or drug-eluting stent, has become a standard treatment of atherosclerosis. However, the host tissue’s response to stenting is frequently maladaptive, leading to intimal hyperplasia via smooth muscle cell (SMC) division and migration to the intima, and increased matrix protein synthesis, all contributing to restenosis of the vessel.
Micromechanical Model of a Collagen Based Tendon Surrogate: Development and Validation
Authors: Reese Shawn P. , Weiss Jeffrey A.
Published: July 2013

In tendons and ligaments, collagen is organized hierarchically into nanoscale fibrils, microscale fibers and mesoscale fascicles. Force transfer across scales is complex and poorly understood, and macroscale strains are not representative of the microscale strains [1]. Since innervation, the vasculature, damage mechanisms and mechanotransduction occur at the microscale, understanding such multiscale interactions is of high importance. In this study, a physical model was used in combination with a computational model to isolate and study the mechanisms of force transfer between scales. The objectives of this study were to develop a collagen based tendon surrogate for use as a physical model and subject it to tensile loading, and to create and validate a 3D micromechanical finite element (FE) model of the surrogate.
Time-reversal invariance and time asymmetry in classical electrodynamics
Authors: Boozer A. D.
Published: July 2013

We clarify several issues involving the concepts of time-reversal invariance and time asymmetry in classical electrodynamics. Specifically, we consider three questions: (I) If electrodynamics is time-reversal invariant, why are the radiative processes that occur in nature time asymmetric? (II) Why doesn't the time-reversal invariance of electrodynamics contradict the fact that a charged particle in motion feels a radiation damping force? (III) Why don't the advanced solutions to Maxwell's equations occur in nature—is there some principle that forbids them? We argue that these questions are not specific to electrodynamics, but also arise in many other systems in which waves are radiated, and answer them in the context of a simple model describing a coupled particle-field system in (1+1) dimensions.
Imaging of the CO Snow Line in a Solar Nebula Analog
Authors: Qi Chunhua , Öberg Karin I. , Wilner David J. , D’Alessio Paola , Bergin Edwin , Andrews Sean M. , Blake Geoffrey A. , Hogerheijde Michiel R. , van Dishoeck Ewine F.
Published: July 2013

Solar Snow Lines

Models of the formation of our solar system have suggested that condensation lines, or snow lines—the distance from a star beyond which a gas or a liquid can condense into the solid phase—are favorable locations for planet formation. Taking advantage of the increase of N
2
H
+
abundance in cold regions where CO condenses out of the gas phase,

Qi
et al.

(p.
630
, published online 18 July) used the Atacama Large Millimeter/Submillimeter Array to image the CO snow line in the disk around TW Hya, an analog of the solar nebula from which the solar system formed. This disk's snow line corresponds to Neptune's orbit in our solar system.
The Hologenomic Basis of Speciation: Gut Bacteria Cause Hybrid Lethality in the Genus
Nasonia
Authors: Brucker Robert M. , Bordenstein Seth R.
Published: July 2013

Microbes → Host Speciation?

No living organism is an individual—an individual's microbiota can outnumber the host's somatic cells. Working in parasitoid wasps,
Brucker and Bordenstein
(p.
667
, published online 18 July) now suggest that the gut microbiota can play a crucial role in speciation and hybrid lethality. In a clade of parasitoid wasps, interspecies hybrids survived when reared on antibiotic-treated sterile food (thus eliminating gut microbiota), but experienced high mortality when reared on conventional diet or host material.