bluuebunny/crossref_metadata_2025 huggingface dataset:
Integrating vibrational signals, mitochondrial DNA and morphology for species determination in the genus Aphrodes (Hemiptera: Cicadellidae)
Authors: BLUEMEL JOANNA K. , DERLINK MAJA , PAVLOVČIČ PETRA , RUSSO ISA‐RITA M. , ANDREW KING ROBERT , CORBETT EMMA , SHERRARD‐SMITH ELEANOR , BLEJEC ANDREJ , WILSON MICHAEL R. , STEWART ALAN J. A. , SYMONDSON WILLIAM O. C. , VIRANT‐DOBERLET META
Published: March 2014

Reliable delimitation and identification of species is central not only to systematics, but also to studies of biodiversity, ecology and pest management. In the era of Internet‐based biodiversity databases misidentifications are rapidly disseminated and may have far‐reaching consequences. Leafhoppers from the genus Aphrodes (Hemiptera, Cicadellidae) are common and abundant, but, nevertheless, they are still a taxonomically challenging group whose members are often assessed in ecological studies and are also potential vectors of plant diseases. Previous study has shown that the syntype series for A. aestuarina (Edwards) includes also specimens of A. makarovi Zachvatkin and has suggested that misidentifications may be widespread in museum collections. We studied Aphrodes individuals collected from the U.K. and Slovenia in order to provide a more comprehensive analysis of this genus using multiple criteria. Combined work using male and female vibrational signals emitted during courtship, and a 600‐bp fragment within the barcoding region of the COI mtDNA gene, provided validated specimens that we also used for morphometric study. Analyses confirmed A. aestuarina, A. bicincta, A. diminuta and A. makarovi as behaviourally, genetically and morphologically distinct species. Although any of these approaches could be used alone to distinguish between species, combining morphological and molecular approaches will help to improve reliability, especially when identifying females. Morphological investigation of validated individuals from the U.K. and Slovenia also revealed geographic differences within species. By combining several body and aedeagus morphological characters males can be reliably identified, however, morphological differences between species are, nevertheless, relatively small. By contrast, observed genetic distances between Aphrodes species are relatively large (4.2–7.0%). At about half of our collecting sites more than one Aphrodes species was found and A. makarovi was collected together with every other species, including A. aestuarina on tidal saltmarshes. Due to low morphological variation between syntopic congeners it is likely that many museum specimens of Aphrodes have been assigned to the wrong species and species identification in ecological and vector studies may also be questionable.
High‐resolution conceptual hydrogeological model of complex basaltic volcanic islands: a Mayotte, Comoros, case study
Authors: Lachassagne Patrick , Aunay Bertrand , Frissant Nicolas , Guilbert Maud , Malard Arnauld
Published: March 2014

We present a high‐resolution conceptual hydrogeological model for complex basaltic volcanic islands based on Mayotte Island in the Comoros. Its geological structure and hydrogeological functioning are deduced from a large dataset: geological mapping, geophysics, some forty new boreholes, piezometric data, hydraulic conductivity, hydrochemical data, etc. We describe previously unknown deep cut‐and‐fill palaeovalleys. The resulting conceptual geological and hydrogeological model of the island is very different from the Hawaiian model, in that it lacks a low‐elevation basal aquifer and dyke‐impounded high‐level aquifers. It is closer to the Canary Islands model, which has, however, not yet been described at a high‐resolution scale. It does not have a continuous aquifer, but rather a discontinuous succession of perched aquifers separated by aquicludes and aquitards. This results more from the complex geological structure of the island, which has experienced several phases of volcanism, erosion and weathering, than from its age, but is also a result of the high‐resolution scale of the model. High‐resolution conceptual modelling is now necessary to solve problems of applied geology and hydrogeology.
French Documentary Perspectives on the Collective Politics of the Atlantic Shipyards, a Global Workplace
Authors: Evrard Audrey
Published: March 2014

Focusing on three French documentaries filmed at French shipyards—Le dernier navire (Jean‐Marc Moutout, 2000), Les prolos (Marcel Trillat, 2002) and Un monde moderne (Sabrina Malek and Arnaud Soulier, 2005)—this article addresses the impact of subcontracting, particularly the growing presence of temporary migrant workers, on labor collective organization and on the aesthetic of socially and politically committed documentary. Drawing from recent research conducted by French sociologists of labor and film analysis, it approaches these three films as a coherent corpus that manifests the erosion of twentieth‐century working‐class struggles, discourses, bodies, and sites but, most importantly, as a corpus that empowers early twenty‐first‐century migrant subcontracted labor, a category of workers typically lacking political representation and legal protections. Michel De Certeau's concepts of strategy and tactics provide a useful model to assess the changing nature of collective politics in the globalized workplace, from the power struggles of clearly identified classes during the twentieth century to the tactical reassemblage of contiguous but dispersed labor trajectories in the context of intensified economic globalization.
Cinematic Tropes of Migration: Cruise and Train Ride in Contemporary China
Authors: Beus Yifen T.
Published: March 2014

This article examines in Up the Yangtze and Last Train Home how Chinese Canadian filmmakers Yung Chang and Lixin Fan positioned themselves, framed the migrant issues and their subjects, and utilized two visual motifs in documenting China's migrant workers' labor and (im)mobility—the cruise ship and the train that transport both tourists and migrant workers. Chang and Fan blend participatory or interactive filmmaking with cinéma vérité cinematography and embed these two imposing motifs in the mise‐en‐scène to foreground the human subjects as marginalized, forgotten, and ignored masses against a highly territorialized economic landscape in contemporary China, an irony resulting from the so‐called “socialist market economy” that replaced the used‐to‐be egalitarian communist model. The author, while not intending to provide a full close reading of both films, bases the analysis of them on Bill Nichols' discussion on the modes of documentary and argues that the filmmakers' cinematography projects the train and the ship as means to mobilize human resources horizontally between the rural and the urban areas, but they failed thus far, within China's current economic structure and social hierarchy, to provide the migrant workers mobility to move upward and escape their stigmatized caste.
Relationship Between Lumbar Disc Injury and Manual Lifting: A Finite Element Model Study
Authors: Natarajan Raghu N. , Williams Jamie R. , Lavender Steven A. , Andersson Gunnar B. J.
Published: March 2014

Back pain has been described as one of the most common and significant musculoskeletal problems in the United States leading to substantial amounts of morbidity, disability and economic loss. Among people under 45 years of age, low back disorders (LBDs) are the leading cause of activity limitation and affects up to 47% of workers with physically demanding jobs. Low back disorders are associated with occupational lifting. Retrospective studies of industrial injuries have identified manual material handling (MMH) as the most common cause of LBD. Disc degeneration has also been associated with physical work. Thus, loading due to lifting and manual material handling is believed to be a significant factor in the development of occupationally related LBDs.
Characterizing the Influence of Preconditioning on Initial Tension for Hamstring Tendon and Patella Tendon Grafts
Authors: Elias John J. , Rai Surya P. , Weinstein David M. , Ciccone William J.
Published: March 2014

The primary goal of ACL reconstruction is to limit post-operative anterior knee laxity without over-constraining the knee. For both hamstring tendon and patella tendon grafts used for ACL reconstruction, initial graft tension is applied to limit post-operative knee laxity. Both types of graft stress relax following implantation, decreasing the graft tension. Previous studies have shown that preconditioning reduces the tension decrease due to stress relaxation for both hamstring tendons [1] and patella tendons [2]. While hamstring tendon grafts are typically preconditioned in tension on a graft board prior to implantation to limit stress relaxation, patella tendon grafts are typically implanted without preconditioning. The current study focused on characterizing the influence of preconditioning on stress relaxation for both types of graft. The authors hypothesized that the tension loss due to stress relaxation would be larger for preconditioned hamstring tendon grafts than for preconditioned patella tendon grafts.
Mechanical Loading Uniquely Up-Regulates MMP-13 in Rat Supraspinatus Tendon But Not Achilles Tendon
Authors: Thornton Gail M. , Shao Xinxin , Chung May , Sciore Paul , Boorman Richard S. , Hart David A. , Lo Ian K. Y.
Published: March 2014

Tendon injuries and chronic pain, known as tendinopathy, are extremely common in supraspinatus and Achilles tendons. Despite their prevalence, the pathogenesis of these conditions is poorly understood. One of most common cited factors for injuries to the rotator cuff tendons is “impingement”, namely, mechanical compression of the supraspinatus tendon by the overlying coracoacromial arch [1]. To date, few studies have investigated the molecular processes underlying this condition.
Accuracy of Cartilage Geometry Reconstruction From Volumetric CT Data: A Phantom Study
Authors: Anderson Andrew E. , Ellis Benjamin J. , Peters Christopher L. , Weiss Jeffrey A.
Published: March 2014

Segmentation of medical image data is often used for the construction of computational models to study the mechanics of diarthrodial joints such as the hip and knee. The analyst must demonstrate that the reconstructed geometry is an accurate representation of the true continuum to ensure model validity. This becomes especially important for computational modeling of joint contact, which requires accurate reconstruction of articular cartilage. Although volumetric computed tomography (CT) is often used to image diarthrodial joints, the lower bounds for detecting articular cartilage thickness and the influence of imaging parameters on the ability to image cartilage have not been reported. The use of contrast agent (CT arthrography) is necessary to visualize the surface of articular cartilage in live patients. Thus, it is of primary interest to quantify the accuracy of CT arthrography to demonstrate the feasibility of patient-specific modeling. The objectives of this study were to assess the accuracy and detection limits of CT for measuring simulated cartilage thickness using a phantom and to quantify changes in accuracy due to alterations in contrast agent concentration, imaging plane direction, spatial resolution and joint spacing.
Systematic Error in the Measure of Microdamage by Modulus Degradation During Four-Point Bending Fatigue
Authors: Landrigan Matthew D. , Roeder Ryan K.
Published: March 2014

The accumulation of fatigue damage in bovine and human cortical bone is conventionally measured by modulus or stiffness degradation. The initial modulus or stiffness of each specimen is typically measured in order to normalize tissue heterogeneity to a prescribed strain [1,2]. Cyclic preloading at 100 N for 20 cycles has been used for this purpose in both uniaxial tension and four-point bending tests [1–3]. In four-point bending, the specimen modulus is often calculated using linear elastic beam theory as, (1)E=3Fl4bh2ε where F is the applied load, l is the outer support span, b is the specimen width, h is the specimen height, and ε is the maximum strain based on the beam deflection [2]. The maximum load and displacement data from preloading is used to determine the initial specimen modulus. The initial modulus and a prescribed maximum initial strain are then used to determine an appropriate load for fatigue testing under load control.
Freezing Induced Microstructural Change of Collagen Matrix
Authors: Han Bumsoo , Miller Jeffrey D. , Jung Jun K.
Published: March 2014

Freezing of biological tissue occurs in many modern biomedical applications. These include cryosurgery for cancer, cryoablation for cardiac arrhythmia, cryoplasty for restenosis, and cryopreservation of native and engineered biomaterials. While the short-term success of these applications depends on the cellular viability — low viability for the therapeutic applications, and high viability for the preservation applications, the long-term success is determined by whether the functional properties of tissue are controlled as well as the viability. This becomes more important as the freezing-based technologies begin to be applied to larger and more complex biomaterials. However, the effects of freezing on these functional properties are rarely understood. Although several studies have been done on the freezing-induced change of the mechanical properties, the results are highly tissue-type dependent and the underlying biophysical mechanisms are poorly understood. Since the functional properties are associated with or often determined by the microstructural characteristics of the extracellular matrix (ECM), it is hypothesized that freezing-induced changes on the ECM microstructure affect the post-thaw functional properties. Thus, in this study, microstructural changes of collagen matrix were investigated using scanning electron microscopy and image analysis.
Reduction of the Wnt Inhibitor Dkk1 Correlates With Improved Bone Mechanical and Morphological Properties in Mice
Authors: Joiner Danese M. , MacDonald Bryan T. , He Xi , Hauschka Peter V. , Goldstein Steven A.
Published: March 2014

The Wnt/β-Catenin signaling pathway is a key regulator in bone development and bone homeostasis. Inactivating mutations in the Wnt co-receptor Low density lipoprotein Receptor related Protein 5 (LRP5) results in osteoporosis while “activating” mutations in LRP5 results in high bone mass. Dickkopf-1 (Dkk1) is a secreted Wnt inhibitor that binds to LRP5 and LRP6 reducing their availability to form a complex with Wnt and Frizzled and resulting in unrestrained Wnt signaling. It is expected that a decrease in Dkk1 will result in an increase in Wnt activity and ultimately a high bone mass phenotype. An allelic series of Dkk1 mutant mice were generated to examine the affects of reduced Dkk1 levels on bone density, morphology, and mechanical properties.
A New Hypothesis for Human Atherosclerotic Plaque Progression Based on Serial In Vivo MRI and Computational Modeling Method
Authors: Mondal Sayan , Yang Chun , Petruccelli Joseph D. , Yuan Chun , Liu Fei , Hatsukami Thomas , Tang Dalin
Published: March 2014

It has been well-accepted that atherosclerosis initiation and progression correlate positively with low and oscillating flow wall shear stresses. However, this shear stress mechanism cannot fully explain why advanced plaques continue to grow under elevated flow shear stress conditions. Our previous investigations using 3D computational models with fluid-structure interactions (FSI) based on in vivo/ex vivo magnetic resonance images (MRI) of human carotid atherosclerotic plaques indicated that there is a negative correlation between advanced plaque wall thickness and structural maximum principal stress (Stress-P1) in the plaque and a positive correlation between plaque wall thickness and flow shear stress [3].
Engineering Vein Grafts Using an External Electrospun Biodegradable Polymer Wrap to Gradually Impose Arterial Circumferential Wall Stress Over Time
Authors: El-Kurdi Mohammed S. , Hong Yi , Stankus John J. , Soletti Lorenzo , Wagner William R. , Vorp David A.
Published: March 2014

Failure of vein grafts via intimal hyperplasia (IH) remains a critical problem, with the 5-year reoperation rate at 60% of all cases[1]. Vein segments transposed to the arterial circulation for use as bypass grafts are exposed to increased bloodflow and intraluminal pressure[2]. Indeed, Liu and Fung showed that the average circumferential wall stress (CWS) in an arterial vein graft (AVG) immediately upon reestablishing flow could be 140 fold that in a vein under normal circumstances[2]. The tissue often responds to this perceived injury by thickening, which is thought to be an attempt to return the stress to venous levels. However, this response is uncontrolled and can over-compensate, leading to stenosis instead of the desired thickening or “arterialization” of the AVG. It has been suggested that this hyperplastic response by AVGs is a direct result of a “cellular shock” related to their abrupt exposure to the harsh new biomechanical environment[3]. We hypothesize that the adverse hyperplastic response by AVGs may be reduced or eliminated by more gradually exposing them to the arterial biomechanical environment. We believe that an adventitially-placed electrospun polymer wrap will allow an AVG ample opportunity to adapt and remodel to the stresses of its new environment in situ, thereby reducing cellular injury and limiting the initiating mechanisms of IH. Previous work has shown that preventing acute distension of AVGs by adding an external support or sheath can improve various pathologic responses[4, 5], but clinical utility of such a wrap is unproven. Liu et al. used a polytetrafluoroethylene external support to reduce IH in AVGs[2]. However, the immunological response to a permanent wrap is unfavorable and led Vijayan et al. to develop a biodegradable polyglactin sheath. These polyglactin sheaths were loose-fitting and allowed the AVG to expand to their maximum diameters under arterial pressure and thus did not offer mechanical support or prevent increased levels of CWS.
Gender Specific Material Properties in the Thoracic Spine
Authors: Stemper Brian D. , Board Derek , Yoganandan Narayan , Pintar Frank A. , Maiman Dennis J.
Published: March 2014

Gender differences have been identified in a variety of spine-related disorders including rates of thoracic sagittal plane scoliosis and rates of whiplash associated disorder following automotive rear impacts. For example, female gender was identified as a main risk factor for thoracic curve progression in adolescent idiopathic scoliosis [1]. Clinical and epidemiological studies have identified females to be more susceptible to whiplash injury [2]. However, biomechanical evidence for these discrepancies has been limited. Experimental investigations using human volunteers and post mortem human head-neck specimens have identified dynamic gender differences in overall head kinematics relative to T1 [3] and segmental and localized spinal kinematics [4, 5] following simulated automotive rear impacts. However, it remains unclear whether dynamic gender differences resulted from anthropometry, or geometrical or structural differences in the head-neck complex and/or cervical spine. Structural gender differences identified in anterior cruciate ligaments of the knee [6] and histological differences identified in the ligamentum flavum of the lumbar spine may indicate possible structural or material gender differences in spinal ligaments [7]. Therefore, the present investigation was conducted to experimentally identify soft tissue structural differences in spinal biomechanics.
Effect of Deformation Rate on the Mechanical Properties of Rectangular and Cruciform Arterial Samples: Uniaxial and Biaxial Testing
Authors: Virues Delgadillo Jorge O. , Delorme Sebastien , DiRaddo Robert , Hatzikiriakos Savvas G.
Published: March 2014

The elastic behavior of arteries is nonlinear when subjected to large deformations. In order to measure their anisotropic behavior, planar biaxial tests are often used. Uniaxial tests are also commonly used due to simplicity of data analysis, but their capability to fully describe the in vivo behavior of a tissue remains to be proven. Mechanical behaviour of arteries submitted to uniaxial or biaxial testing has been done previously [1–4]. Each one of these works was performed only at one deformation rate: 1 %/s [1, 3], 10 %/s [2], 1 Hz [4]; but those works do not show the behaviour of the arterial wall when it is submitted to different deformation rates. Thus, in this study we present the effect of deformation rate in the material properties (i.e. loading forces) of uniaxial and biaxial tests.
Mechanism of Force Generation in Kinesin Motility
Authors: Hwang Wonmuk , Lang Matthew J.
Published: March 2014

Conventional kinesin is a dimeric motor protein that uses adenosine triphosphate (ATP) to walk processively along the microtubule. Although its nucleotide dependent conformational switching and binding of the neck linker (NL) on the motor head are known to be key events in kinesin motility, the basic mechanism by which it amplifies a small conformational change upon ATP binding to generate the force of the walking stroke has not been known. We combined structural analysis with a set of molecular dynamics simulations to identify the 9-residue long N-terminal region, which we named the ‘cover strand’ (CS), as an additional element essential for kinesin’s power stroke. It operates by differentially forming a β-sheet with NL when ATP binds, whereby the ‘cover-neck bundle’ (CNB) has an inherent conformational bias that drives NL into its binding pocket on the motor head. After the initial stroke, the later half of NL, starting with the ‘asparagine latch’ in the middle, forms specific bonds with the motor head to ensure tight binding. We constructed the force map generated by CNB, which showed a forward bias in agreement with single molecule motility measurements. Our result is consistent with other experimental observations, including the estimated stall force and the transverse anisotropy. The novel mechanism of force generation by the dynamic folding of CNB appears to hold in various kinesin families, and elucidates the economy in the design principle of the smallest known processive motor.
Experimental In-Vitro Method to Measure the Migration of Cementless Prosthesis
Authors: Zivkovic Ivan , Amirouche Farid , Gonzalez Mark
Published: March 2014

In total hip arthroplasty, adequate initial fixation of prosthesis to host bone represents great challenge to its success and satisfactory performance.
Numerical and Experimental Analysis of Articular Chondrocyte Deformation: Calibration of a Multiscale Finite Element Model
Authors: Bevill Scott L. , Briant Paul L. , Andriacchi Thomas P.
Published: March 2014

Mechanical loading of chondrocytes in isolation [1] and of articular cartilage in culture [2] has been reported to be a potent regulator of chondrocyte metabolism. Experimental studies have related tissue-level and cell-level strains in mechanically loaded cartilage explants [3], but cannot be readily extended to address more physiologic loading cases. Numerical models, which might address this need, have primarily been axisymmetric [4, 5] or two-dimensional [6] and have idealized chondrocyte geometry. Given the complexity of the mechanism of the load transfer between the tissue and cell, however, there remains a lack of information regarding the in vivo level of cell stresses and strains. Thus, the purpose of this study was to develop a multiscale experimental/numerical approach to calibrate a three-dimensional finite element (FE) model of a chondrocyte based on experimentally derived chondrocyte morphology and deformation data. The method was than applied to determine the modulus of a chondrocyte located in the superficial zone.
Deformation of the Human Brain Induced by Mild Angular Acceleration
Authors: Sabet Arash A. , Christoforou Eftyxios , Zatlin Benjamin , Genin Guy M. , Bayly Philip V.
Published: March 2014

Deformation of the human brain was measured in tagged magnetic resonance images (MRI) obtained dynamically during angular acceleration of the skull. This study was undertaken to provide much needed experimental data for the quantitative study of traumatic brain injury (TBI). A custom device was made to impart mild angular acceleration to the skull of a human volunteer inside an MR scanner. Images with a superimposed grid of “tag” lines were obtained using spatial modulation of magnetization (SPAMM) in a fast gradient-echo imaging sequence. Images of the moving brain were obtained dynamically by synchronizing the imaging process with the motion of the head. The deformation of the brain was characterized quantitatively with Lagrangian strain. Strain fields showed reduced strain along the central fissure and to a lesser degree, the central sulcus, suggesting that divisions between regions of the brain may serve to mechanically isolate these regions. Results emphasize the critical role of the brain’s suspension, including the dura mater, falx cerebri, and tentorium membranes, in modulating its deformation.
Constitutive Modeling of Skeletal Muscle Tissue
Authors: Odegard G. M. , Haut Donahue T. L. , Morrow D. A. , Kaufman K. R.
Published: March 2014

The main functions of the human musculoskeletal system are to sustain loads and provide mobility. Bones and joints themselves cannot produce movement; skeletal muscles provide the ability to move. Knowledge of muscle forces during given activities can provide insight into muscle mechanics, muscle physiology, musculoskeletal mechanics, neurophysiology, and motor control. However, clinical examinations or instrumented strength testing only provides information regarding muscle groups. Musculoskeletal models are typically needed to calculate individual muscle forces.
Peak Gluteal Muscle Strain and Stress Values During Sitting Are Greater in Paraplegics Than in Normals
Authors: Linder-Ganz Eran , Shabshin Noga , Itzchak Yacov , Siev-Ner Itzhak , Gefen Amit
Published: March 2014

Deep tissue injury (DTI) is a severe type of pressure ulcers affecting the viability of muscle tissue under bony prominences first [1]. Most researchers agree that prolonged elevated muscle tissue strains and stresses cause the onset of DTI. We recently showed that internal strain and stress distributions in muscle tissue of individuals can be evaluated by integrating Open-MRI examinations with subject-specific finite element (FE) analyses [2]. However, sub-dermal soft tissue strain and stress data from paraplegic wheelchair users are missing in the literature. Our present goals were therefore (i) to determine the strain and stress distributions in the gluteus muscles and enveloping fat under the ischial tuberosities (IT) of paraplegic wheelchair users during sitting and lying in an Open-MRI, (ii) to compare the paraplegic data to those obtained previously from normal subjects [2], and (iii) to compare between results obtained from paraplegics in the sitting and lying postures, in order to quantify the effect of posture on sub-dermal tissue mechanical conditions, particularly intramuscular shear stress.
A Structural, Kinetic Model of Soft Tissue Thermomechanics
Authors: Stylianopoulos Triantafyllos , Aksan Alptekin , Barocas Victor H.
Published: March 2014

Sub-ablative heating of collagenous soft tissues is central to thermal therapies such as thermal capsulorrhaphy, thermokeratoplasty and skin resurfacing [1]. These therapies target the heat-induced denaturation of the collagen molecule, which starts in a temperature range of 55–75 °C. There are relatively few theoretical studies describing the heat-induced alterations in soft tissues, which are mainly phenomenological [2]. In this work, a methodology for studying the kinetics of soft tissue thermomechanics is presented and used to predict the thermal response of New Zealand white patellar tendons [3]. The modeling approach accounts for the microstructure of the tissue and utilizes information at the single-molecule level to obtain the macroscopic response.
Decorin Deficient Cells Demonstrate Increased Proliferation and Altered Phenotypic Properties
Authors: Peterson Sherket B. , Ferdous Zannatul , Höök Magnus , Grande-Allen K. Jane
Published: March 2014

Decorin (DCN), a class I member of the small leucine-rich proteoglycan (SLRP) family, is composed of a protein core of approximately 40kDa [1, 2] substituted with a single glycosaminoglycan (GAG) chain of chondroiton/dermatan sulfate on the N-terminal site [3]. DCN has been reported to interact with collagen [4,5] via its core protein, influence collagen fibrillogenesis [6], and inhibit the growth rates of various cell types when added exogenously to cell cultures [5,6]. There has recently been growing interest and studies in DCN related research using the knockout (KO) mice model which provides an excellent example of inherited disorders that stem from deficiencies in decorin expression [7]. Skin and tendon tissues from DCN KO mice have been characterized as being extremely fragile with significantly reduced strength and stiffness [8, 9]. The DCN KO tissues also show potential functional biglycan compensation [9] and at the microscopic level collagen fibrils with highly irregular diameters, abnormal lateral fusion, and loose packing [6] in contrast to wild type (WT) mice. Despite the intensive investigation of the DCN KO mice, the complexity of the animal model makes it difficult to assess the actual influence of decorin. In an attempt to take a more simplistic approach 2D cell phenotypic characterization studies were performed in addition to studying cell growth, contraction, and matrix organization in 3-D models to show the very distinct biochemical responses to type I collagen when compared to WT control cells.
Computational Analysis of Atherosclerotic Plaque Vulnerability Due to Hemodynamic Effects
Authors: Galaz Ramses , Mongrain Rosaire , Pazos Valerie , Leask Richard , Tardif Jean Claude
Published: March 2014

Atherosclerotic plaque rupture has been extensively associated with acute myocardial infarctions, the leading cause of death in developed countries. When a plaque ruptures in the coronary arteries, it often leads to a clot formation that restricts the flow of blood downstream of the coronaries causing damage to the myocardial tissue. Hemodynamic factors combined with certain plaque morphologies and material properties play an important role in the mechanical failure of the plaque [1]. It is essential for clinicians to understand the vulnerability of plaques and the particular physiological conditions that lead to their mechanical failure. Our study focused on understanding the physical interaction between blood flow, plaque morphology and tissue properties to assess the plaque’s degree of vulnerability.
A Structural-Based Constitutive Model for Valvular Tissues Under Generalized Deformation
Authors: Schmidt David E. , Sacks Michael S.
Published: March 2014

Passive in nature, heart valves react to the inertial forces exerted by blood flow. Pressure differences operate on the valve leaflets to initiate rapid opening and closure of the valve. In the closed position, the coapted leaflets are exposed to significant transvalvular pressure. In contrast, relatively small pressure gradients are required to initiate an opening or closure event. To facilitate efficient cycling, valve leaflets must demonstrate a high degree of compliance relative to the applied inertial loads while in transition. Functionally the leaflet is required to exhibit diverse properties under varied states and modes of deformation.
Viscoelastic Properties of Injured and Uninjured Rat Brain Tissue
Authors: Shafieian Mehdi , Darvish Kurosh
Published: March 2014

In this study, changes in the viscoelastic material properties of brain tissue due to traumatic diffuse axonal injury (DAI) were investigated. The impact acceleration model was used to generate DAI in rat brain stem. The viscoelastic material properties of brain tissue along the corticospinal (CSpT) tract in the brain stem were characterized using an indentation technique and a quasilinear theory. The results show significant reduction in the elastic response of brain tissue due to injury. In regions with significantly more DAI, larger changes in the elastic shear modulus and relaxation function were observed. These findings can improve the injury predictability of computational models of brain injury.
Fracture Mechanics of Architecture Dependent Fracture in Trabecular Bone Using the Cohesive Finite Element Method
Authors: Tomar Vikas
Published: March 2014

Trabecular bone fracture is closely related to the trabecular architecture and microdamage accumulation. Micro-finite element models have been used to investigate the elastic and yield properties of trabecular bone but have only seen limited application in modeling the microstructure dependent fracture of trabecular bone, [1, 2]. In the presented research a cohesive finite element method (CFEM) based approach that can be used to model microstructure and loading rate dependent fracture in trabecular bone is developed for the first time. The emphasis is on understanding the effect of the rate of loading and its correlation with the bone microstructure on the microdamage accumulation and fracture behavior in the trabecular bone. Analyses focus on understanding the effect of the rate of loading, change in bone tissue properties with aging, and their correlation with the bone microstructure on the microdamage accumulation and the fracture behavior in the trabecular bone.
MR Safety and In Vivo Thermal Characterization of an RF Coil at 9.4T
Authors: Shrivastava Devashish , Hanson Timothy , Schlentz Robert , Gallagher William , Snyder Carl , DelaBarre Lance , Prakash Surya , Iaizzo Paul , Vaughan J. Thomas
Published: March 2014

Correlating In vivo temperatures to the radio-frequency (RF) coil induced total RF power is necessary to ensure human safety in an ultra high field magnetic resonance (MR) application. Thus to ensure human safety in an ultra high field MR head imaging experiment, temperatures were measured as a function of time in the brain and surrounding cutaneous layer of twelve human sized, anesthetized swine (mean animal weight = 52kg, SD = ±6.7kg). In vivo temperatures were correlated to the RF power by developing coil and geometry specific normalized temperatures such that the RF coil induced cranial temperature change could be obtained during an MR exam by measuring only the whole head average specific absorption rate (ASAR) and the duration of the RF deposition. Thus, the feasibility of the thermal characterization of an RF volume head coil was shown. More specifically, a continuous wave (CW) RF was deposited in porcine cranium using a four loop RF head coil at 400 MHz (proton larmor frequency at 9.4T). Temperatures were recorded continuously using an inline probe placed at a predetermined location of 15mm inside the brain and a separate probe in the cutaneous layer. To differentiate the temperature response caused by the RF from that of anesthesia, the temperatures were recorded in four unheated, anesthetized swine for the complete duration of experiments (∼8hours). To study the effect of the spatial distribution of the RF as well as the tissue thermal/electrical properties and blood perfusion, the inline temperature probe was placed at two locations (N = 4 for each location). Results showed that the thermal characterization of an RF coil was possible such that the normalized temperature maps when multiplied by the ASAR and the RF heating time would predict In vivo temperature change during heating. Further, it was shown that at 9.4 T 1) the RF heating caused an inhomogeneous normalized temperature distribution in the brain; and 2) the skin temperature change was an unreliable parameter to assess In vivo temperature change.
Interactions Between Factors Influencing Optic Nerve Head Biomechanics
Authors: Sigal Ian A. , Flanagan John G. , Ethier C. Ross
Published: March 2014

Glaucoma is the second most common cause of blindness worldwide, and elevated intraocular pressure (IOP) is the primary risk factor for developing this disease. It has been postulated that IOP-induced mechanical strain on optic nerve head (ONH) glial cells leads to retinal ganglion cell damage and the consequent loss of vision in glaucoma. To better evaluate this theory it is important to understand the biomechanical environment within the ONH. Unfortunately it is very difficult to make measurements in the ONH, and it is particularly difficult to access the region in the ONH where the ganglion cells are thought to be injured, namely the lamina cribrosa. We have therefore developed models of the ONH and used the finite element method (FEM) to predict ONH mechanical response to changes in IOP [1].
Fiber-Based Constitutive Model of Myocardial Scar Tissue
Authors: Coughlin Dezba G. , Fomovsky Gregory M. , Holmes Jeffrey W.
Published: March 2014

It has largely been accepted that collagen fibers play an important role in the mechanics of myocardial scar tissue; however, few studies have performed both mechanical and structural analysis on the same samples to confirm this. Therefore, the goal of this study was to combine both types of analysis with a structure-based constitutive model, which incorporates measured collagen fiber orientations, to gain a better understanding of the structural basis for the mechanics of two-week-old scar tissue.
Wall Shear Stress Change Due to Arterial Wall Stiffness; Fluid-Solid Interactions Study
Authors: Fukui Tomohiro , Parker Kim H. , Imai Yohsuke , Tsubota Ken-ichi , Ishikawa Takuji , Wada Shigeo , Yamaguchi Takami
Published: March 2014

Blood flow plays an important role in regulating blood vessel structure and developing vascular pathology such as atherosclerosis. Of particular importance is the role of the shear stress on a surface of the blood vessel, which is known as wall shear stress (WSS). It is recognized today that atherosclerosis develops in areas where the WSS is low, i.e., low-shear hypothesis by Caro et al., therefore, many researchers have been studying WSS distribution in time and space in order to predict the precise region where atherosclerosis occurs by CFD simulations. Practically, however, most of the studies involve an assumption that the arterial wall is rigid. Although this assumption is widely accepted, arterial wall movements during the pulse propagation should be considered for more detailed information. Recently, we have considered the effects of arterial wall motion on WSS by fluid-solid interactions analysis, and showed that the contribution of the wall motion to the WSS is up to 1.0 Pa. In this study, we assessed the influence of the arterial wall stiffness on WSS during the pulse wave propagation.
The Protective Role of Bacillus Anthracis Exosporium in Macrophage-Mediated Killing by Nitric Oxide
Authors: Weaver John , Kang Tae Jin , Raines Kimberly , Cao Guan-Liang , Hibbs Stephen , Tsai Pei , Baillie Les , Rosen Gerald , Cross Alan
Published: March 2014

The ability of the endospore-forming, gram-positive bacterium Bacillus anthracis to survive exposure to antibacterial killing mechanisms by activated macrophages is key to its germination and survival. These antibacterial killing mechanisms include, but are not limited to the generation of free radicals such as nitric oxide (•NO) and superoxide (O2•−) from the upregulation of inducible nitric oxide synthase (NOS 2) along with products derived from them, e.g., peroxynitrite (ONOO−), as part of microbicidal activity. However questions still remain as to how these species are involved in microbial killing, specifically with respect to B. anthracis. In a previous study, we demonstrated that exposure of primary murine macrophages to sonicated B. anthracis endospores up-regulated NOS 2 and demonstrated a •NO-dependent bactericidal response, but unanswered in that study was which of the NOS 2-derived reactive oxygen species was responsible for the observed bactericidal response. Since NOS 2 also generates O2•−, experiments were designed to determine whether NOS 2 formed ONOO− from the reaction of •NO with O2•− and if so, was ONOO− microbicidal toward B. anthracis.
Tissue Strain Transduction and Amplification at the Osteocyte as a Result of Microstructural Changes in the Bone Matrix
Authors: Bonivtch Amber Rath , Bonewald Lynda F. , Nicolella Daniel P.
Published: March 2014

It is well known that bone adapts to changes in its mechanical environment and that this adaptation is controlled at the cellular level through the coordinated actions of osteoblasts, osteocytes, and osteoclasts. Osteocytes make up over 90% of all bone cells [1], and are hypothesized to be the mechanosensors in bone [2] that mediate the effects of bone loading through their extensive communication network. The application of force to the skeletal system produces several potential stimuli for osteocyte function including hydrostatic pressure, fluid flow-induced shear stress, and bone tissue strain. Previously, the basis used for studying the stimulatory effects of mechanical strain on bone cell biological responses in vitro has been the direct measurement of bone strain in humans during various physical activities [3,4]. The limitation of applying this strain magnitude data to cells in vitro, however, is that the in vivo strain gage measurements represent continuum measures of bone deformation. Clearly, at the spatial level of bone cells, cortical bone is not a continuum and microstructural inhomogeneities will result in inhomogeneous microstructural strain fields; local tissue strains will be magnified in association with microstructural features [5,6]. It is unclear as to how much of these magnified strains will be directly transmitted to the osteocyte itself. Additionally, if the osteocyte has the ability to alter its perilacunar environment [7], it is unknown what effect do these changes have on the strain that is transmitted to the osteocyte and cell process.
Stented Artery Biomechanics in the Presence of Stenoses and Tapering
Authors: Timmins Lucas H. , Meyer Clark A. , Moreno Michael R. , Moore James E.
Published: March 2014

The implantation of a balloon expandable stent induces chronic stent-induced stresses on the artery wall. These highly non-physiologic stresses can provoke inflammation and smooth muscle cell proliferation. Ultimately, this cascade of events leads to restenosis, or the development of a new blockage in the stented artery. Since the initial human implantation of balloon expandable stents, technological advances in stent design, material properties, and deliverability have expanded the application and success rate of the procedure. More recently, anti-restenotic strategies such as drug-eluting stents have aimed to counteract the restenosis process. While clinical trials have demonstrated the success of drug eluting stents in coronary arteries [1], risk of late thrombosis [2] and failure to prevent restenosis in peripheral arteries [3] has limited this technology. A further investigation into the artery wall stresses induced by stent implantation, and the pursuit of strategies to minimize them could reduce the restenosis rates for both bare metal and drug-eluting stents.
Neurite Elongation and Branching on DNA Crosslinked Polyacrylamide Hydrogels
Authors: Jiang Frank X. , Du Yangzhou , Chippada Uday , Li Lulu , Firestein Bonnie L. , Yurke Bernard , Shreiber David I. , Schloss Rene S. , Langrana Noshir A.
Published: March 2014

Mechanical cues have been found to play an important role in the cell decision making process, as manifested in survival, adhesion, growth, proliferation, differentiation and functioning. Due to their resemblance to the natural tissues, polyacrylamide hydrogels have been used in the studies of mechanobiology and particularly cell-substrate interactions for various cell types including fibroblasts, hepatocytes and neurons [1]. As the initial investigation, we have successfully cultured rat spinal cord neurons on bis-crosslinked gels with large range of stiffnesses [2].
Identification of a Mathematical Model for the Prediction of Platelet Damage Accumulation in Artificial Organs: A Preliminary Study
Authors: Nobili Matteo , Sheriff Jawaad , Morbiducci Umberto , Redaelli Alberto , Bluestein Danny
Published: March 2014

Platelets are the pre-eminent cell involved in hemostasis and thrombosis. In recent years it has been demonstrated that flow-induced platelet activation is a major cause for the relatively high incidence of thromboembolic complications in mechanical heart valves (MHVs) [1,2].The platelet activation state (PAS) assay has proved to be a reliable technique for the experimental measurement of procoagulant activity [3]. A Predictive numerical model for platelets damage accumulation could provide critical information for thrombogenicity optimization of implantable prosthetic devices. This would lead to improving the safety and efficacy of implantable devices. Reliable models able to predict this phenomenon are still lacking. The aim of this work is an attempt to bridge this gap. A model for describing the activation of formed elements in blood requires establishing a correlation between mechanical loading, exposure time and the phenomenological response of these elements to it. A physically consistent phenomenological model is used [4] and genetic algorithms (GAs) [5], have been successfully applied to the tuning of the model parameters by correlating its predictions to PAS measurements conducted in a Hemodynamic Shearing Device (HSD) by exposing platelets to prescribed shear stress loading waveforms.
Cytoskeletal Bundle Mechanics
Authors: Bathe Mark , Heussinger Claus , Claessens Mireille , Bausch Andreas , Frey Erwin
Published: March 2014

Filamentous actin (F-actin) is a stiff biopolymer that is tightly crosslinked in vivo by actin-binding proteins (ABPs) to form stiff bundles that form major constituents of a multitude of slender cytoskeletal processes including stereocilia, filopodia, microvilli, neurosensory bristles, cytoskeletal stress fibers, and the acrosomal process of sperm cells (Fig. 1). The mechanical properties of these cytoskeletal processes play key roles in a broad range of cellular functions — the bending stiffness of stereocilia mediates the mechanochemical transduction of mechanical stimuli such as acoustic waves to detect sound, the critical buckling load of filopodia and acrosomal processes determines their ability to withstand compressive mechanical forces generated during cellular locomotion and fertilization, and the entropic stretching stiffness of cytoskeletal bundles mediates cytoskeletal mechanical resistance to cellular deformation. Thus, a detailed understanding of F-actin bundle mechanics is fundamental to gaining a mechanistic understanding of cytoskeletal function.
Elevated Basement Membrane Fibroblast Growth Factor-2 Protects Endothelial Cells in High Glucose
Authors: Morss Alisa , Jonas Michael , Edelman Elazer R.
Published: March 2014

Vascular disease is the primary cause of morbidity and mortality in diabetics. Diabetic vascular disease is disseminated and includes renal capillary hypertrophy, reduced wound repair, impaired angiogenesis, and rapid and excessive hyperplasia after endovascular intervention [1, 2]. No single biochemical aberration unifies the diffuse nature of diabetic vascular disease. Hyperglycemia has been implicated, and yet glucose effects persist long after restoration of euglycemia. It is possible that acute fluctuations in glucose concentration have prolonged cell and tissue effects.
Impact of the Balloon Folding Pattern on the Transient Stent Expansion Behaviour: A Finite Element Study
Authors: Mortier Peter , De Beule Matthieu , Van Loo Denis , Van Impe Rudy , Verhegghe Benedict , Verdonck Pascal
Published: March 2014

Stenting is the most commonly used medical procedure to restore blood flow in stenotic arteries. During this endovascular intervention, a small tube-like structure is implanted in the narrowed section of the diseased artery. The vast majority of stents are crimped (i.e. plastically deformed) on a folded balloon (balloon expandable stents). After insertion through a small incision in the femoral or radial artery using a catheter, the balloon is inflated and the stent deploys. Following to the expansion, the balloon is deflated and retracted and from then on, the stent acts as a mechanical scaffold for the enlarged lumen.