MedWorm.com provides a medical RSS filtering service. Over 6000 RSS medical sources are combined and output via different filters. This feed contains the latest items from the 'Biomechanics and Modeling in Mechanobiology' source. Thu, 09 Feb 2012 14:07:49 +0100 http://www.medworm.com/index.php?rid=5671444&cid=s_37325_61_f&fid=37325&url=http%3A%2F%2Fwww.ncbi.nlm.nih.gov%2Fentrez%2Fquery.fcgi%3Ftmpl%3DNoSidebarfile%26db%3DPubMed%26cmd%3DRetrieve%26list_uids%3D22307681%26dopt%3DAbstract Authors: Kowalski WJ, Teslovich NC, Dur O, Keller BB, Pekkan K Abstract In the early embryo, a series of symmetric, paired vessels, the aortic arches, surround the foregut and distribute cardiac output to the growing embryo and fetus. During embryonic development, the arch vessels undergo large-scale asymmetric morphogenesis to form species-specific adult great vessel patterns. These transformations occur within a dynamic biomechanical environment, which can play an important role in the development of normal arch configurations or the aberrant arch morphologies associated with congenital cardiac defects. Arrested migration and rotation of the embryonic outflow tract during late stages of cardiac looping has been shown to produce both outflow tract and several arch abnormalities. H... Biomechanics and Modeling in Mechanobiology journals http://www.medworm.com/rss/comments.php?id=5671444 Sat, 04 Feb 2012 05:00:00 +0100 5671444 http://www.medworm.com/index.php?rid=5671443&cid=s_37325_61_f&fid=37325&url=http%3A%2F%2Fwww.ncbi.nlm.nih.gov%2Fentrez%2Fquery.fcgi%3Ftmpl%3DNoSidebarfile%26db%3DPubMed%26cmd%3DRetrieve%26list_uids%3D22307682%26dopt%3DAbstract Authors: Zhou EH, Xu F, Quek ST, Lim CT Abstract Physical forces can elicit complex time- and space-dependent deformations in living cells. These deformations at the subcellular level are difficult to measure but can be estimated using computational approaches such as finite element (FE) simulation. Existing FE models predominantly treat cells as spring-dashpot viscoelastic materials, while broad experimental data are now lending support to the power-law rheology (PLR) model. Here, we developed a large deformation FE model that incorporated PLR and experimentally verified this model by performing micropipette aspiration on fibroblasts under various mechanical loadings. With a single set of rheological properties, this model recapitulated the diverse micropipette aspiration data obt... Biomechanics and Modeling in Mechanobiology journals http://www.medworm.com/rss/comments.php?id=5671443 Sat, 04 Feb 2012 05:00:00 +0100 5671443 http://www.medworm.com/index.php?rid=5671442&cid=s_37325_61_f&fid=37325&url=http%3A%2F%2Fwww.ncbi.nlm.nih.gov%2Fentrez%2Fquery.fcgi%3Ftmpl%3DNoSidebarfile%26db%3DPubMed%26cmd%3DRetrieve%26list_uids%3D22307683%26dopt%3DAbstract Authors: Fisher CI, Chen J, Merryman WD Abstract Calcific aortic valve disease (CAVD) results in impaired function through the inability of valves to fully open and close, but the causes of this pathology are unknown. Stiffening of the aorta is associated with CAVD and results in exposing the aortic valves to greater mechanical strain. Transforming growth factor β1 (TGF-β1) is enriched in diseased valves and has been shown to combine with strain to synergistically alter aortic valve interstitial cell (AVIC) phenotypes. Therefore, we investigated the role of strain and TGF-β1 on the calcification of AVICs. Following TGF-β1 pretreatment, strain induced intact monolayers to aggregate and calcify. Using a wound assay, we confirmed that TGF-β1 increases tension in the monolayer in ... Biomechanics and Modeling in Mechanobiology journals http://www.medworm.com/rss/comments.php?id=5671442 Sat, 04 Feb 2012 05:00:00 +0100 5671442 http://www.medworm.com/index.php?rid=5671445&cid=s_37325_61_f&fid=37325&url=http%3A%2F%2Fwww.ncbi.nlm.nih.gov%2Fentrez%2Fquery.fcgi%3Ftmpl%3DNoSidebarfile%26db%3DPubMed%26cmd%3DRetrieve%26list_uids%3D22294208%26dopt%3DAbstract This study reveals the existence of major differences in wall-shear stress pulsatility and magnitude on TAV and BAV leaflets. Given the ability of abnormal fluid shear stress to trigger valvular inflammation, the results support the existence of a mechano-etiology of CAVD in the BAV. PMID: 22294208 [PubMed - as supplied by publisher] (Source: Biomechanics and Modeling in Mechanobiology) Biomechanics and Modeling in Mechanobiology journals http://www.medworm.com/rss/comments.php?id=5671445 Wed, 01 Feb 2012 05:00:00 +0100 5671445 http://www.medworm.com/index.php?rid=5618465&cid=s_37325_61_f&fid=37325&url=http%3A%2F%2Fwww.ncbi.nlm.nih.gov%2Fentrez%2Fquery.fcgi%3Ftmpl%3DNoSidebarfile%26db%3DPubMed%26cmd%3DRetrieve%26list_uids%3D22246054%26dopt%3DAbstract Authors: van Vlimmeren MA, Driessen-Mol A, Oomens CW, Baaijens FP Abstract In tissue engineered heart valves, cell-mediated stress development during culture results in leaflet retraction at time of implantation. This tissue retraction is partly active due to traction forces exerted by the cells and partly passive due to release of residual stress in the extracellular matrix and the cells. Within this study, we unraveled the passive and active contributions of cells and matrix to generated force and retraction in engineered heart valve tissues. Tissue engineered rectangular strips, fabricated from PGA/P4HB scaffolds and seeded with human myofibroblasts, were cultured for 4 weeks, after which the cellular contribution was changed at different levels. Elimination of the active cellu... Biomechanics and Modeling in Mechanobiology journals http://www.medworm.com/rss/comments.php?id=5618465 Sat, 14 Jan 2012 05:00:00 +0100 5618465 http://www.medworm.com/index.php?rid=5618467&cid=s_37325_61_f&fid=37325&url=http%3A%2F%2Fwww.ncbi.nlm.nih.gov%2Fentrez%2Fquery.fcgi%3Ftmpl%3DNoSidebarfile%26db%3DPubMed%26cmd%3DRetrieve%26list_uids%3D22234779%26dopt%3DAbstract This study was aimed at identifying possible causes for cell death in impact loading by quantifying chondrocyte mechanics when cartilage was subjected to a 5% nominal tissue strain at different strain rates. Multi-scale modelling techniques were used to simulate cartilage tissue and the corresponding chondrocytes residing in the tissue. Chondrocytes were modelled by accounting for the cell membrane, pericellular matrix and pericellular capsule. The results suggest that cell deformations, cell fluid pressures and fluid flow velocity through cells are highest at the highest (impact) strain rate, but they do not reach damaging levels. Tangential strain rates of the cell membrane were highest at the highest strain rate and were observed primarily in superficial tissue cells. Since cell death f... Biomechanics and Modeling in Mechanobiology journals http://www.medworm.com/rss/comments.php?id=5618467 Wed, 11 Jan 2012 05:00:00 +0100 5618467 http://www.medworm.com/index.php?rid=5618466&cid=s_37325_61_f&fid=37325&url=http%3A%2F%2Fwww.ncbi.nlm.nih.gov%2Fentrez%2Fquery.fcgi%3Ftmpl%3DNoSidebarfile%26db%3DPubMed%26cmd%3DRetrieve%26list_uids%3D22234780%26dopt%3DAbstract In this study, we employ stochastic modeling fitted to experiments for characterizing the influence of mechanical stretching delivered to adipocyte monolayers on the probabilities of commitment to the adipocyte lineage, mitosis, and growth after mitosis in 3T3-L1 adipocytes. We found that the probability of a cell to become committed to the adipocyte lineage in a single division when cultured on an elastic substrate was 0.025, which was indistinguishable between cultures that were radially stretched (to 12% strain) and control cultures. The probability of undergoing mitosis however was different between the groups, being 0.4 in the stretched cultures and 0.6 in the controls. The probability of growing after mitosis was affected by the stretching as well and was 0.9 and 0.8 in the stretched... Biomechanics and Modeling in Mechanobiology journals http://www.medworm.com/rss/comments.php?id=5618466 Wed, 11 Jan 2012 05:00:00 +0100 5618466 http://www.medworm.com/index.php?rid=5618468&cid=s_37325_61_f&fid=37325&url=http%3A%2F%2Fwww.ncbi.nlm.nih.gov%2Fentrez%2Fquery.fcgi%3Ftmpl%3DNoSidebarfile%26db%3DPubMed%26cmd%3DRetrieve%26list_uids%3D22231673%26dopt%3DAbstract This study investigated the regional variation in meniscus cell mechanics in comparison with articular chondrocytes and ligament cells. It was found that the meniscus contains two biomechanically distinct cell populations, with outer meniscus cells being stiffer (1.59 ± 0.19 kPa) than inner meniscus cells (1.07 ± 0.14 kPa). Additionally, it was found that both outer and inner meniscus cell stiffnesses were similar to ligament cells (1.32 ± 0.20 kPa), and articular chondrocytes showed the highest stiffness overall (2.51 ± 0.20 kPa). Comparison of compressibility characteristics of the cells showed similarities between articular chondrocytes and inner meniscus cells, as well as between outer meniscus cells and ligament cells. These results show that cellular biomechanics vary regiona... Biomechanics and Modeling in Mechanobiology journals http://www.medworm.com/rss/comments.php?id=5618468 Tue, 10 Jan 2012 05:00:00 +0100 5618468 http://www.medworm.com/index.php?rid=5618469&cid=s_37325_61_f&fid=37325&url=http%3A%2F%2Fwww.ncbi.nlm.nih.gov%2Fentrez%2Fquery.fcgi%3Ftmpl%3DNoSidebarfile%26db%3DPubMed%26cmd%3DRetrieve%26list_uids%3D22227796%26dopt%3DAbstract Authors: Cilla M, Peña E, Martínez MA Abstract Plaque rupture plays a role in the majority of acute coronary syndromes. Rupture has usually been associated with stress concentrations, which are mainly affected by the plaque geometry and the tissue properties. The aim of this study is to evaluate the influence of morphology on the risk of plaque rupture, including the main geometrical factors, and to assess the role of circumferential and axial residual stresses by means of a parametric 3D finite element model. For this purpose, a 3D parametric finite element model of the coronary artery with eccentric atheroma plaque was developed. Healthy (adventitia and media in areas without atheroma plaque) and diseased (fibrotic and lipidic) tissues were considered in the model. The geometri... Biomechanics and Modeling in Mechanobiology journals http://www.medworm.com/rss/comments.php?id=5618469 Sat, 07 Jan 2012 05:00:00 +0100 5618469 http://www.medworm.com/index.php?rid=5575981&cid=s_37325_61_f&fid=37325&url=http%3A%2F%2Fwww.ncbi.nlm.nih.gov%2Fentrez%2Fquery.fcgi%3Ftmpl%3DNoSidebarfile%26db%3DPubMed%26cmd%3DRetrieve%26list_uids%3D22218996%26dopt%3DAbstract Authors: Ji B, Genever PG, Patton RJ, Putra D, Fagan MJ Abstract After an initial phase of growth and development, bone undergoes a continuous cycle of repair, renewal and optimisation by a process called remodelling. This paper describes a novel mathematical model of the trabecular bone remodelling cycle. It is essentially formulated to simulate a remodelling event at a fixed position in the bone, integrating bone removal by osteoclasts and formation by osteoblasts. The model is developed to construct the variation in bone thickness at a particular point during the remodelling event, derived from standard bone histomorphometric analyses. The novelties of the approach are the adoption of a predator-prey model to describe the dynamic interaction between osteoclasts and osteoblasts, ... Biomechanics and Modeling in Mechanobiology journals http://www.medworm.com/rss/comments.php?id=5575981 Thu, 05 Jan 2012 05:00:00 +0100 5575981 http://www.medworm.com/index.php?rid=5557778&cid=s_37325_61_f&fid=37325&url=http%3A%2F%2Fwww.ncbi.nlm.nih.gov%2Fentrez%2Fquery.fcgi%3Ftmpl%3DNoSidebarfile%26db%3DPubMed%26cmd%3DRetrieve%26list_uids%3D22200886%26dopt%3DAbstract Authors: Punal VM, Roth BJ Abstract This research focuses on finding analytical solutions to the mechanical bidomain model for cardiac tissue. In particular, a perturbation expansion is used to analyze the equations, with the perturbation parameter being inversely proportional to the spring constant coupling the intracellular and extracellular spaces. The results indicate that the intracellular and extracellular pressures are not equal and that the two spaces can move relative to each other. This calculation is complicated enough to illustrate the implications of the mechanical bidomain model but is nevertheless simple enough to solve analytically. One application of the calculation is to the mechanical behavior of active cardiac tissue surrounding an ischemic region. PMID: 222... Biomechanics and Modeling in Mechanobiology journals http://www.medworm.com/rss/comments.php?id=5557778 Tue, 27 Dec 2011 05:00:00 +0100 5557778 http://www.medworm.com/index.php?rid=5544348&cid=s_37325_61_f&fid=37325&url=http%3A%2F%2Fwww.ncbi.nlm.nih.gov%2Fentrez%2Fquery.fcgi%3Ftmpl%3DNoSidebarfile%26db%3DPubMed%26cmd%3DRetrieve%26list_uids%3D22198036%26dopt%3DAbstract Authors: Lemaire T, Lemonnier S, Naili S Abstract The lacuno-canalicular permeability has been shown to play a key role in the behavior of bone tissue. The aim of this study is, by giving an overview of the determinations of this parameter, to question the paradoxical values provided by theoretical predictions and recent experimental measurements. We propose therefore a Kozeny-like law obtained by a numerical method which relates the permeability to the textural parameters of cortical bone microstructure. Moreover, we suggest possible explanations for this paradox considering the empirical difficulties and possible multiphysical effects. PMID: 22198036 [PubMed - as supplied by publisher] (Source: Biomechanics and Modeling in Mechanobiology) Biomechanics and Modeling in Mechanobiology journals http://www.medworm.com/rss/comments.php?id=5544348 Sat, 24 Dec 2011 05:00:00 +0100 5544348 http://www.medworm.com/index.php?rid=5544349&cid=s_37325_61_f&fid=37325&url=http%3A%2F%2Fwww.ncbi.nlm.nih.gov%2Fentrez%2Fquery.fcgi%3Ftmpl%3DNoSidebarfile%26db%3DPubMed%26cmd%3DRetrieve%26list_uids%3D22190268%26dopt%3DAbstract Authors: Fois G, Wittekindt O, Zheng X, Felder ET, Miklavc P, Frick M, Dietl P, Felder E Abstract A commonly used technique to investigate strain-induced responses of adherent cells is culturing them on an elastic membrane and globally stretching the membrane. However, it is virtually impossible to acquire microscopic images immediately after the stretch with this method. Using a newly developed technique, we recorded the strain-induced increase of the cytoplasmic Ca(2+) concentration ([Ca(2+)](c)) in rat primary alveolar type II (ATII) cells at an acquisition rate of 30ms and without any temporal delay. We can show that the onset of the mechanically induced rise in [Ca(2+)](c) was very fast (<30 ms), and Ca(2+) entry was immediately abrogated when the stimulus was withdrawn. T... Biomechanics and Modeling in Mechanobiology journals http://www.medworm.com/rss/comments.php?id=5544349 Thu, 22 Dec 2011 05:00:00 +0100 5544349 http://www.medworm.com/index.php?rid=5506003&cid=s_37325_61_f&fid=37325&url=http%3A%2F%2Fwww.ncbi.nlm.nih.gov%2Fentrez%2Fquery.fcgi%3Ftmpl%3DNoSidebarfile%26db%3DPubMed%26cmd%3DRetrieve%26list_uids%3D22161021%26dopt%3DAbstract Authors: Lui C, Lee K, Nelson CM Abstract The regenerative capacity of the mammary gland following post-lactational involution depends on the presence of multipotent stem or progenitor cells. Mammary progenitor cells exist as a quiescent and self-renewing population capable of differentiating into luminal epithelial and myoepithelial cells and generating ductal and alveolar structures. The fate choices of these cells are regulated by several soluble signals as well as their surrounding extracellular matrix. Whereas matrix stiffness has been implicated in organ-specific differentiation of embryonic and mesenchymal stem cells, the effects of substratum compliance on the more limited fate switches typical of tissue-specific progenitor cells are unknown. Here, we examined how the mecha... Biomechanics and Modeling in Mechanobiology journals http://www.medworm.com/rss/comments.php?id=5506003 Sat, 10 Dec 2011 05:00:00 +0100 5506003 http://www.medworm.com/index.php?rid=5506004&cid=s_37325_61_f&fid=37325&url=http%3A%2F%2Fwww.ncbi.nlm.nih.gov%2Fentrez%2Fquery.fcgi%3Ftmpl%3DNoSidebarfile%26db%3DPubMed%26cmd%3DRetrieve%26list_uids%3D22120599%26dopt%3DAbstract Authors: Sengupta D, Kahn AM, Burns JC, Sankaran S, Shadden SC, Marsden AL Abstract Kawasaki Disease (KD) is the leading cause of acquired pediatric heart disease. A subset of KD patients develops aneurysms in the coronary arteries, leading to increased risk of thrombosis and myocardial infarction. Currently, there are limited clinical data to guide the management of these patients, and the hemodynamic effects of these aneurysms are unknown. We applied patient-specific modeling to systematically quantify hemodynamics and wall shear stress in coronary arteries with aneurysms caused by KD. We modeled the hemodynamics in the aneurysms using anatomic data obtained by multi-detector computed tomography (CT) in a 10-year-old male subject who suffered KD at age 3 years. The altered hemod... Biomechanics and Modeling in Mechanobiology journals http://www.medworm.com/rss/comments.php?id=5506004 Sun, 27 Nov 2011 05:00:00 +0100 5506004 http://www.medworm.com/index.php?rid=5506006&cid=s_37325_61_f&fid=37325&url=http%3A%2F%2Fwww.ncbi.nlm.nih.gov%2Fentrez%2Fquery.fcgi%3Ftmpl%3DNoSidebarfile%26db%3DPubMed%26cmd%3DRetrieve%26list_uids%3D22109098%26dopt%3DAbstract Authors: Parnell WJ, Vu MB, Grimal Q, Naili S Abstract We compare theoretical predictions of the effective elastic moduli of cortical bone at both the meso- and macroscales. We consider the efficacy of three alternative approaches: the method of asymptotic homogenization, the Mori-Tanaka scheme and the Hashin-Rosen bounds. The methods concur for specific engineering moduli such as the axial Young's modulus but can vary for others. In a past study, the effect of porosity alone on mesoscopic properties of cortical bone was considered, taking the matrix to be isotropic. Here, we consider the additional influence of the transverse isotropy of the matrix. We make the point that micromechanical approaches can be used in two alternative ways to predict either the macroscopic (size of cort... Biomechanics and Modeling in Mechanobiology journals http://www.medworm.com/rss/comments.php?id=5506006 Wed, 23 Nov 2011 05:00:00 +0100 5506006 http://www.medworm.com/index.php?rid=5506005&cid=s_37325_61_f&fid=37325&url=http%3A%2F%2Fwww.ncbi.nlm.nih.gov%2Fentrez%2Fquery.fcgi%3Ftmpl%3DNoSidebarfile%26db%3DPubMed%26cmd%3DRetrieve%26list_uids%3D22109099%26dopt%3DAbstract Authors: Suárez DR, Weinans H, van Keulen F Abstract Post-operative change in the mechanical loading of bone may trigger its (mechanically induced) adaptation and hamper the mechanical stability of prostheses. This is especially important in cementless components, where the final fixation is achieved by the bone itself. The aim of this study is, first, to gain insight into the bone remodelling process around a cementless glenoid component, and second, to compare the possible bone adaptation when the implant is assumed to be fully bonded (best case scenario) or completely loose (worst case scenario). 3D finite element models of a scapula with and without a cementless glenoid component were created. 3D geometry of the scapula, material properties, and several physiological loading c... Biomechanics and Modeling in Mechanobiology journals http://www.medworm.com/rss/comments.php?id=5506005 Wed, 23 Nov 2011 05:00:00 +0100 5506005 http://www.medworm.com/index.php?rid=5436312&cid=s_37325_61_f&fid=37325&url=http%3A%2F%2Fwww.ncbi.nlm.nih.gov%2Fentrez%2Fquery.fcgi%3Ftmpl%3DNoSidebarfile%26db%3DPubMed%26cmd%3DRetrieve%26list_uids%3D22086167%26dopt%3DAbstract Authors: Creane A, Maher E, Sultan S, Hynes N, Kelly DJ, Lally C Abstract Many soft biological tissues contain collagen fibres, which act as major load bearing constituents. The orientation and the dispersion of these fibres influence the macroscopic mechanical properties of the tissue and are therefore of importance in several areas of research including constitutive model development, tissue engineering and mechanobiology. Qualitative comparisons between these fibre architectures can be made using vector plots of mean orientations and contour plots of fibre dispersion but quantitative comparison cannot be achieved using these methods. We propose a 'remodelling metric' between two angular fibre distributions, which represents the mean rotational effort required to transform one in... Biomechanics and Modeling in Mechanobiology journals http://www.medworm.com/rss/comments.php?id=5436312 Wed, 16 Nov 2011 05:00:00 +0100 5436312 http://www.medworm.com/index.php?rid=5411241&cid=s_37325_61_f&fid=37325&url=http%3A%2F%2Fwww.ncbi.nlm.nih.gov%2Fentrez%2Fquery.fcgi%3Ftmpl%3DNoSidebarfile%26db%3DPubMed%26cmd%3DRetrieve%26list_uids%3D22052000%26dopt%3DAbstract Authors: Zöllner AM, Buganza Tepole A, Gosain AK, Kuhl E Abstract Tissue expansion is a common surgical procedure to grow extra skin through controlled mechanical over-stretch. It creates skin that matches the color, texture, and thickness of the surrounding tissue, while minimizing scars and risk of rejection. Despite intense research in tissue expansion and skin growth, there is a clear knowledge gap between heuristic observation and mechanistic understanding of the key phenomena that drive the growth process. Here, we show that a continuum mechanics approach, embedded in a custom-designed finite element model, informed by medical imaging, provides valuable insight into the biomechanics of skin growth. In particular, we model skin growth using the concept of an incompatible grow... Biomechanics and Modeling in Mechanobiology journals http://www.medworm.com/rss/comments.php?id=5411241 Fri, 04 Nov 2011 04:00:00 +0100 5411241 http://www.medworm.com/index.php?rid=5375944&cid=s_37325_61_f&fid=37325&url=http%3A%2F%2Fwww.ncbi.nlm.nih.gov%2Fentrez%2Fquery.fcgi%3Ftmpl%3DNoSidebarfile%26db%3DPubMed%26cmd%3DRetrieve%26list_uids%3D22048330%26dopt%3DAbstract Authors: Kim JH, Avril S, Duprey A, Favre JP Abstract The present study aims at investigating biomechanical failure behaviour of human aneurismal aortic tissues so as to diagnose the rupture risk of aneurysms more accurately. An inflation test is performed on aneurismal aortic tissues up to failure and full-field measurements are achieved using stereo digital image correlation. Then, an appropriate constitutive model derived from histological structure of arteries is adopted to retrieve the Cauchy stress. The virtual fields method is used as an inverse procedure to identify material parameters. Next, the Cauchy stress components are calculated from the identified parameters and the measured Lagrange strain fields. Finally, an important stress parameter which can quantify the streng... Biomechanics and Modeling in Mechanobiology journals http://www.medworm.com/rss/comments.php?id=5375944 Thu, 03 Nov 2011 04:00:00 +0100 5375944 http://www.medworm.com/index.php?rid=5375946&cid=s_37325_61_f&fid=37325&url=http%3A%2F%2Fwww.ncbi.nlm.nih.gov%2Fentrez%2Fquery.fcgi%3Ftmpl%3DNoSidebarfile%26db%3DPubMed%26cmd%3DRetrieve%26list_uids%3D22038402%26dopt%3DAbstract Authors: Aernouts J, Dirckx JJ Abstract An accurate estimation of tympanic membrane stiffness is important for realistic modelling of middle ear mechanics. Tympanic membrane stiffness has been investigated extensively under either quasi-static or dynamic loading conditions. It is known that biological tissues are sensitive to strain rate. Therefore, in this work, the mechanical behaviour of the tympanic membrane was studied under both quasi-static and dynamic loading conditions. Experiments were performed on the pars tensa of four gerbil tympanic membranes. A custom-built indentation apparatus was used to perform in situ tissue indentations and testing was done applying both quasi-static and dynamic sinusoidal indentations up to 8.2 Hz. The unloaded shape of the tympanic membrane ... Biomechanics and Modeling in Mechanobiology journals http://www.medworm.com/rss/comments.php?id=5375946 Sat, 29 Oct 2011 04:00:00 +0100 5375946 http://www.medworm.com/index.php?rid=5375945&cid=s_37325_61_f&fid=37325&url=http%3A%2F%2Fwww.ncbi.nlm.nih.gov%2Fentrez%2Fquery.fcgi%3Ftmpl%3DNoSidebarfile%26db%3DPubMed%26cmd%3DRetrieve%26list_uids%3D22042381%26dopt%3DAbstract Authors: Luo XY, Griffith BE, Ma XS, Yin M, Wang TJ, Liang CL, Watton PN, Bernacca GM Abstract We investigate the behaviour of a dynamic fluid-structure interaction model of a chorded polyurethane mitral valve prosthesis, focusing on the effects on valve dynamics of including descriptions of the bending stiffnesses of the valve leaflets and artificial chordae tendineae. Each of the chordae is attached at one end to the valve annulus and at the other to one of two chordal attachment points. These attachment points correspond to the positions where the chords of the real prosthesis would attach to the left-ventricular wall, although in the present study, these attachment points are kept fixed in space to facilitate comparison between our simulations and earlier results obtained from ... Biomechanics and Modeling in Mechanobiology journals http://www.medworm.com/rss/comments.php?id=5375945 Wed, 26 Oct 2011 04:00:00 +0100 5375945 http://www.medworm.com/index.php?rid=5308712&cid=s_37325_61_f&fid=37325&url=http%3A%2F%2Fwww.ncbi.nlm.nih.gov%2Fentrez%2Fquery.fcgi%3Ftmpl%3DNoSidebarfile%26db%3DPubMed%26cmd%3DRetrieve%26list_uids%3D21986796%26dopt%3DAbstract Authors: Väänänen SP, Jurvelin JS, Isaksson H Abstract Measurement of bone mineral density (BMD) by dual-energy X-ray absorptiometry (DXA) alone is only a moderate predictor of fracture risk. Finite element analysis (FEA) of bone mechanics, based on DXA images, may improve the prediction of fracture risk. We developed a method to estimate the 3D shape and density distribution of the proximal femur, using a 2D BMD image and a femur shape template. Proximal femurs of eighteen human cadavers were imaged using computed tomography and divided into two sets (N = 9 + 9). The template was created from the samples in first set by using 3D generalized Procrustes analysis and thin-plate splines. Subsequently, the template and 2D BMD image were utilized to estimate the shape and internal de... Biomechanics and Modeling in Mechanobiology journals http://www.medworm.com/rss/comments.php?id=5308712 Tue, 11 Oct 2011 04:00:00 +0100 5308712 http://www.medworm.com/index.php?rid=5308711&cid=s_37325_61_f&fid=37325&url=http%3A%2F%2Fwww.ncbi.nlm.nih.gov%2Fentrez%2Fquery.fcgi%3Ftmpl%3DNoSidebarfile%26db%3DPubMed%26cmd%3DRetrieve%26list_uids%3D21986797%26dopt%3DAbstract Authors: Ohayon J, Mesnier N, Broisat A, Toczek J, Riou L, Tracqui P Abstract The structure of mouse atherosclerotic lesions may differ from that of humans, and mouse atherosclerotic plaques do not rupture except in some specific locations such as the brachiocephalic artery. Recently, our group was the first to observe that the amplitudes of in vivo stresses in ApoE(-/-) mouse aortic atherosclerotic lesions were much lower and differed from those found in a previous work performed on human lesions. In this previous preliminary work, we hypothesized that the plaque mechanical properties (MP) may in turn be responsible for such species differences. However, the limited number of human samples used in our previous comparative study was relevant but not sufficient to broadly validate s... Biomechanics and Modeling in Mechanobiology journals http://www.medworm.com/rss/comments.php?id=5308711 Tue, 11 Oct 2011 04:00:00 +0100 5308711 http://www.medworm.com/index.php?rid=5293597&cid=s_37325_61_f&fid=37325&url=http%3A%2F%2Fwww.ncbi.nlm.nih.gov%2Fentrez%2Fquery.fcgi%3Ftmpl%3DNoSidebarfile%26db%3DPubMed%26cmd%3DRetrieve%26list_uids%3D21964839%26dopt%3DAbstract The objective of this study was to measure AF nonlinear mechanics of the EFM in tension and compression. To accomplish this, a combination of osmotic swelling and confined compression in disk radial direction, perpendicular to the lamella, was used. For this type of analysis, it was necessary to define a stress-free reference configuration. Thus, a brief analysis on residual stress in the disk and a procedure to estimate the reference configuration are presented. The proposed method was able to predict similar swelling deformations when using different loading protocols and models for the EFM, demonstrating its robustness. The stress-stretch curve of the EFM was linear in the range 0.9 < λ(3) < 1.3 with an aggregate modulus of 10.18±3.32 kPa; however, a significant nonlinearity wa... Biomechanics and Modeling in Mechanobiology journals http://www.medworm.com/rss/comments.php?id=5293597 Sun, 02 Oct 2011 04:00:00 +0100 5293597 http://www.medworm.com/index.php?rid=5272649&cid=s_37325_61_f&fid=37325&url=http%3A%2F%2Fwww.ncbi.nlm.nih.gov%2Fentrez%2Fquery.fcgi%3Ftmpl%3DNoSidebarfile%26db%3DPubMed%26cmd%3DRetrieve%26list_uids%3D21959747%26dopt%3DAbstract The objective of the analysis presented is to relate the lacunar-canalicular permeability to a particular phase angle that is measurable when the bone is subjected to infinitesimal cyclic strain. The phase angle of interest is the lag angle between the applied strain and the resultant stress. Cyclic strain causes the interstitial fluid to move. This movement is essential for the viability of osteocytes and is believed to play a major role in the bone mechanotransduction mechanism. However, certain bone fluid flow properties, notably the permeability of the lacunar-canalicular porosity, are still not accurately determined. In this paper, formulas for the phase angle as a function of permeability for infinitesimal cyclic strain are presented and mathematical expressions for the storage modul... Biomechanics and Modeling in Mechanobiology journals http://www.medworm.com/rss/comments.php?id=5272649 Fri, 30 Sep 2011 04:00:00 +0100 5272649 http://www.medworm.com/index.php?rid=5240177&cid=s_37325_61_f&fid=37325&url=http%3A%2F%2Fwww.ncbi.nlm.nih.gov%2Fentrez%2Fquery.fcgi%3Ftmpl%3DNoSidebarfile%26db%3DPubMed%26cmd%3DRetrieve%26list_uids%3D21927824%26dopt%3DAbstract We examined samples of bovine, ovine and murine bone ex vivo and observed processes passing across crack faces: some were still intact whilst others had ruptured. The number of intact processes per unit crack length decreased significantly with increasing crack length and also decreased in samples, which had been tested in vitro at higher stress levels. A theoretical model that we had developed previously was able to predict the overall magnitude and general trends in the experimental data. This work has provided further support for our "scissors" model, which proposes that microcracks can be detected because they disturb the osteocyte network, specifically by rupturing cellular processes where they pass across the crack faces. PMID: 21927824 [PubMed - as supplied by publisher] (Source... Biomechanics and Modeling in Mechanobiology journals http://www.medworm.com/rss/comments.php?id=5240177 Sat, 17 Sep 2011 04:00:00 +0100 5240177 http://www.medworm.com/index.php?rid=5240176&cid=s_37325_61_f&fid=37325&url=http%3A%2F%2Fwww.ncbi.nlm.nih.gov%2Fentrez%2Fquery.fcgi%3Ftmpl%3DNoSidebarfile%26db%3DPubMed%26cmd%3DRetrieve%26list_uids%3D21927825%26dopt%3DAbstract Authors: Nazzal CM, Mulligan LJ, Criscione JC Abstract Cardiac dyssynchrony often accompanies patients with heart failure (HF) and can lead to an increase in mortality rate. Cardiac resynchronization therapy (CRT) has been shown to provide substantial benefits to the HF population with ventricular dyssynchrony; however, there still exists a group of patients who do not respond to this treatment. In order to better understand patient response to CRT, it is necessary to quantitatively characterize both electrical and mechanical dyssynchrony. The quantification of mechanical dyssynchrony via characterization of contraction strain field inhomogeneity is the focus of this modeling investigation. Raw data from a 3D finite element (FE) model were received from Roy Kerckhoffs et al. and an... Biomechanics and Modeling in Mechanobiology journals http://www.medworm.com/rss/comments.php?id=5240176 Sat, 17 Sep 2011 04:00:00 +0100 5240176 http://www.medworm.com/index.php?rid=5225467&cid=s_37325_61_f&fid=37325&url=http%3A%2F%2Fwww.ncbi.nlm.nih.gov%2Fentrez%2Fquery.fcgi%3Ftmpl%3DNoSidebarfile%26db%3DPubMed%26cmd%3DRetrieve%26list_uids%3D21918835%26dopt%3DAbstract Authors: Tanasic I, Milic-Lemic A, Tihacek-Sojic L, Stancic I, Mitrovic N Abstract It was the purpose of this study to determine and analyse strains in the bone of posterior mandible below the removable and fixed partial dentures using Digital Image Correlation Method. Dried mandible with shortened dental arch (Kennedy Class 1) was used in the experiment. The mandible model was prepared for accepting two types of restorations for bilaterally missing molars conventional therapy, and removable and fixed partial dentures were manufactured following standard prosthetic protocol. The models with prosthetic restorations placed in situ were subjected to loading of 50-300 N, and photographed using two digital cameras as part of the digital image correlation method equipment. Afterwards, th... Biomechanics and Modeling in Mechanobiology journals http://www.medworm.com/rss/comments.php?id=5225467 Thu, 15 Sep 2011 04:00:00 +0100 5225467 http://www.medworm.com/index.php?rid=5215377&cid=s_37325_61_f&fid=37325&url=http%3A%2F%2Fwww.ncbi.nlm.nih.gov%2Fentrez%2Fquery.fcgi%3Ftmpl%3DNoSidebarfile%26db%3DPubMed%26cmd%3DRetrieve%26list_uids%3D21901546%26dopt%3DAbstract In this study, compliant latex thin-walled aneurysm models are fabricated to investigate the effects of expansion of shape memory polymer foam. A simplified cylindrical model is selected for the in-vitro aneurysm, which is a simplification of a real, saccular aneurysm. The studies are performed by crimping shape memory polymer foams, originally 6 and 8 mm in diameter, and monitoring the resulting deformation when deployed into 4-mm-diameter thin-walled latex tubes. The deformations of the latex tubes are used as inputs to physical, analytical, and computational models to estimate the circumferential stresses. Using the results of the stress analysis in the latex aneurysm model, a computational model of the human aneurysm is developed by changing the geometry and material properties. The m... Biomechanics and Modeling in Mechanobiology journals http://www.medworm.com/rss/comments.php?id=5215377 Thu, 08 Sep 2011 04:00:00 +0100 5215377 http://www.medworm.com/index.php?rid=5215379&cid=s_37325_61_f&fid=37325&url=http%3A%2F%2Fwww.ncbi.nlm.nih.gov%2Fentrez%2Fquery.fcgi%3Ftmpl%3DNoSidebarfile%26db%3DPubMed%26cmd%3DRetrieve%26list_uids%3D21898099%26dopt%3DAbstract In conclusion, we demonstrated that specimen-specific FE analyses provide accurate estimates of peri-implant bone strains in the rat tibia loading model. Further investigations of the bone-implant interface are needed to quantify implant osseointegration. PMID: 21898099 [PubMed - as supplied by publisher] (Source: Biomechanics and Modeling in Mechanobiology) Biomechanics and Modeling in Mechanobiology journals http://www.medworm.com/rss/comments.php?id=5215379 Tue, 06 Sep 2011 04:00:00 +0100 5215379 http://www.medworm.com/index.php?rid=5215378&cid=s_37325_61_f&fid=37325&url=http%3A%2F%2Fwww.ncbi.nlm.nih.gov%2Fentrez%2Fquery.fcgi%3Ftmpl%3DNoSidebarfile%26db%3DPubMed%26cmd%3DRetrieve%26list_uids%3D21898100%26dopt%3DAbstract Authors: Manda K, Eriksson A Abstract Recently, physiological and biomechanical studies on animal models with metal implants filling full-thickness cartilage defects have resulted in good clinical outcomes. The knowledge of the time-dependent macroscopic behavior of cartilage surrounding the metal implant is essential for understanding the joint function after treating such defects. We developed a model to investigate the in vivo time-dependent behavior of the tibiofemoral cartilages surrounding the metal implant, when the joint is subjected to an axial load for various defect sizes. Results show that time-dependent effects on cartilage behavior are significant, and can be simulated. These effects should be considered when evaluating the results from an implant. In particular, the ... Biomechanics and Modeling in Mechanobiology journals http://www.medworm.com/rss/comments.php?id=5215378 Sun, 04 Sep 2011 04:00:00 +0100 5215378 http://www.medworm.com/index.php?rid=5186549&cid=s_37325_61_f&fid=37325&url=http%3A%2F%2Fwww.ncbi.nlm.nih.gov%2Fentrez%2Fquery.fcgi%3Ftmpl%3DNoSidebarfile%26db%3DPubMed%26cmd%3DRetrieve%26list_uids%3D21877192%26dopt%3DAbstract The objective of this study was to evaluate the effect of sample preparation on the biomechanical behaviour of chondrocytes. We compared the volumetric and dimensional changes of chondrocytes in the superficial zone (SZ) of intact articular cartilage and cartilage explant before and after a hypotonic challenge. Calcein-AM labelled SZ chondrocytes were imaged with confocal laser scanning microscopy through intact cartilage surfaces and through cut surfaces of cartilage explants. In order to clarify the effect of tissue composition on cell volume changes, Fourier Transform Infrared microspectroscopy was used for estimating the proteoglycan and collagen contents of the samples. In the isotonic medium (300 mOsm), there was a significant difference (p < 0.05) in the SZ cell volumes and aspe... Biomechanics and Modeling in Mechanobiology journals http://www.medworm.com/rss/comments.php?id=5186549 Mon, 29 Aug 2011 23:00:00 +0100 5186549 http://www.medworm.com/index.php?rid=5170815&cid=s_37325_61_f&fid=37325&url=http%3A%2F%2Fwww.ncbi.nlm.nih.gov%2Fentrez%2Fquery.fcgi%3Ftmpl%3DNoSidebarfile%26db%3DPubMed%26cmd%3DRetrieve%26list_uids%3D21858691%26dopt%3DAbstract Authors: Ma G, Petersen E, Leong KW, Liao K Abstract As a prelude to the understanding of mechanotransduction in human embryonic stem cell (hESC) differentiation, the mechanical behavior of hESCs in the form of cell pellet is studied. The pellets were tested after 3 or 5 weeks of cell culture in order to demonstrate the effect of the duration of cell culture on the mechanical properties of the pellets. A micromechanical tester was used to conduct unconfined compression on hESC pellet, and experimental, numerical, and analytical methods were combined to determine the mechanical properties of hESC pellet. It is assumed that the mechanical behavior of hESC pellets can be described by an isotropic, linear viscoelastic model consisting of a spring and two Maxwell units in parallel, and... Biomechanics and Modeling in Mechanobiology journals http://www.medworm.com/rss/comments.php?id=5170815 Sat, 20 Aug 2011 23:00:00 +0100 5170815 http://www.medworm.com/index.php?rid=5170816&cid=s_37325_61_f&fid=37325&url=http%3A%2F%2Fwww.ncbi.nlm.nih.gov%2Fentrez%2Fquery.fcgi%3Ftmpl%3DNoSidebarfile%26db%3DPubMed%26cmd%3DRetrieve%26list_uids%3D21853351%26dopt%3DAbstract In this study, we investigated the effects of introducing gradients of interstitial flow on the evolution of compositional heterogeneity in engineered cartilage. Using a parallel-plate bioreactor, we observed that Poiseuille flow stimulation of chondrocyte-seeded agarose hydrogels led to an increase in glycosaminoglycan and type II collagen deposition in the surface region of the hydrogel exposed to flow. Experimental measurements of the interstitial flow fields based on the fluorescence recovery after photobleaching technique suggested that the observed heterogeneity in composition is associated with gradients in interstitial flow in a boundary layer at the hydrogel surface. Interestingly, the interstitial flow velocity profiles were nonlinearly influenced by flow rate, which upon closer ... Biomechanics and Modeling in Mechanobiology journals http://www.medworm.com/rss/comments.php?id=5170816 Thu, 18 Aug 2011 23:00:00 +0100 5170816 http://www.medworm.com/index.php?rid=5170817&cid=s_37325_61_f&fid=37325&url=http%3A%2F%2Fwww.ncbi.nlm.nih.gov%2Fentrez%2Fquery.fcgi%3Ftmpl%3DNoSidebarfile%26db%3DPubMed%26cmd%3DRetrieve%26list_uids%3D21847614%26dopt%3DAbstract Authors: van Donkelaar CC, Wilson W Abstract Chondrocyte hypertrophy is a characteristic of osteoarthritis and dominates bone growth. Intra- and extracellular changes that are known to be induced by metabolically active hypertrophic chondrocytes are known to contribute to hypertrophy. However, it is unknown to which extent these mechanical conditions together can be held responsible for the total magnitude of hypertrophy. The present paper aims to provide a quantitative, mechanically sound answer to that question. To address this aim requires a quantitative tool that captures the mechanical effects of collagen and proteoglycans, allows temporal changes in tissue composition, and can compute cell and tissue deformations. These requirements are met in our numerical model that is vali... Biomechanics and Modeling in Mechanobiology journals http://www.medworm.com/rss/comments.php?id=5170817 Tue, 16 Aug 2011 23:00:00 +0100 5170817 http://www.medworm.com/index.php?rid=5138600&cid=s_37325_61_f&fid=37325&url=http%3A%2F%2Fwww.ncbi.nlm.nih.gov%2Fentrez%2Fquery.fcgi%3Ftmpl%3DNoSidebarfile%26db%3DPubMed%26cmd%3DRetrieve%26list_uids%3D21830072%26dopt%3DAbstract Authors: Jeong D, Yun A, Kim J A scaffold is a three-dimensional matrix that provides a structural base to fill tissue lesion and provides cells with a suitable environment for proliferation and differentiation. Cell-seeded scaffolds can be implanted immediately or be cultured in vitro for a period of time before implantation. To obtain uniform cell growth throughout the entire volume of the scaffolds, an optimal strategy on cell seeding into scaffolds is important. We propose an efficient and accurate numerical scheme for a mathematical model to predict the growth and distribution of cells in scaffolds. The proposed numerical algorithm is a hybrid method which uses both finite difference approximations and analytic closed-form solutions. The effects of each parameter in the mathematic... Biomechanics and Modeling in Mechanobiology journals http://www.medworm.com/rss/comments.php?id=5138600 Tue, 09 Aug 2011 23:00:00 +0100 5138600 http://www.medworm.com/index.php?rid=5138611&cid=s_37325_61_f&fid=37325&url=http%3A%2F%2Fwww.ncbi.nlm.nih.gov%2Fentrez%2Fquery.fcgi%3Ftmpl%3DNoSidebarfile%26db%3DPubMed%26cmd%3DRetrieve%26list_uids%3D21818636%26dopt%3DAbstract Authors: Yan WW, Cai B, Liu Y, Fu BM Tumor cell adhesion to vessel walls in the microcirculation is one critical step in cancer metastasis. In this paper, the hypothesis that tumor cells prefer to adhere at the microvessels with localized shear stresses and their gradients, such as in the curved microvessels, was examined both experimentally and computationally. Our in vivo experiments were performed on the microvessels (post-capillary venules, 30-50 μm diameter) of rat mesentery. A straight or curved microvessel was cannulated and perfused with tumor cells by a glass micropipette at a velocity of ~1mm/s. At less than 10 min after perfusion, there was a significant difference in cell adhesion to the straight and curved vessel walls. In 60 min, the averaged adhesion rate in the curv... Biomechanics and Modeling in Mechanobiology journals http://www.medworm.com/rss/comments.php?id=5138611 Thu, 04 Aug 2011 23:00:00 +0100 5138611 http://www.medworm.com/index.php?rid=5087866&cid=s_37325_61_f&fid=37325&url=http%3A%2F%2Fwww.ncbi.nlm.nih.gov%2Fentrez%2Fquery.fcgi%3Ftmpl%3DNoSidebarfile%26db%3DPubMed%26cmd%3DRetrieve%26list_uids%3D21796413%26dopt%3DAbstract The objective of this paper is to propose and assess an estimation procedure-based on data assimilation principles-well suited to obtain some regional values of key biophysical parameters in a beating heart model, using actual Cine-MR images. The motivation is twofold: (1) to provide an automatic tool for personalizing the characteristics of a cardiac model in order to achieve predictivity in patient-specific modeling and (2) to obtain some useful information for diagnosis purposes in the estimated quantities themselves. In order to assess the global methodology, we specifically devised an animal experiment in which a controlled infarct was produced and data acquired before and after infarction, with an estimation of regional tissue contractility-a key parameter directly affected by the pa... Biomechanics and Modeling in Mechanobiology journals http://www.medworm.com/rss/comments.php?id=5087866 Wed, 27 Jul 2011 23:00:00 +0100 5087866 http://www.medworm.com/index.php?rid=5087870&cid=s_37325_61_f&fid=37325&url=http%3A%2F%2Fwww.ncbi.nlm.nih.gov%2Fentrez%2Fquery.fcgi%3Ftmpl%3DNoSidebarfile%26db%3DPubMed%26cmd%3DRetrieve%26list_uids%3D21769620%26dopt%3DAbstract Authors: Ronken S, Arnold MP, Ardura García H, Jeger A, Daniels AU, Wirz D Articular cartilage is a multicomponent, poroviscoelastic tissue with nonlinear mechanical properties vital to its function. A consequent goal of repair or replacement of injured cartilage is to achieve mechanical properties in the repair tissue similar to healthy native cartilage. Since fresh healthy human articular cartilage (HC) is not readily available, we tested whether swine cartilage (SC) could serve as a suitable substitute for mechanical comparisons. To a first approximation, cartilage tissue and surgical substitutes can be evaluated mechanically as viscoelastic materials. Stiffness measurements (dynamic modulus, loss angle) are vital to function and are also a non-destructive means of evaluation. Sinc... Biomechanics and Modeling in Mechanobiology journals http://www.medworm.com/rss/comments.php?id=5087870 Mon, 18 Jul 2011 23:00:00 +0100 5087870 http://www.medworm.com/index.php?rid=5087868&cid=s_37325_61_f&fid=37325&url=http%3A%2F%2Fwww.ncbi.nlm.nih.gov%2Fentrez%2Fquery.fcgi%3Ftmpl%3DNoSidebarfile%26db%3DPubMed%26cmd%3DRetrieve%26list_uids%3D21769621%26dopt%3DAbstract Authors: Sáez P, Alastrué V, Peña E, Doblaré M, Martínez MA An anisotropic damage model for soft fibered tissue is presented in this paper, using a multi-scale scheme and focusing on the directionally dependent behavior of these materials. For this purpose, a micro-structural or, more precisely, a microsphere-based approach is used to model the contribution of the fibers. The link between micro-structural contribution and macroscopic response is achieved by means of computational homogenization, involving numerical integration over the surface of the unit sphere. In order to deal with the distribution of the fibrils within the fiber, a von Mises probability function is incorporated, and the mechanical (phenomenological) behavior of the fibrils is defined by an exponential-type mod... Biomechanics and Modeling in Mechanobiology journals http://www.medworm.com/rss/comments.php?id=5087868 Sat, 16 Jul 2011 23:00:00 +0100 5087868 http://www.medworm.com/index.php?rid=5038726&cid=s_37325_61_f&fid=37325&url=http%3A%2F%2Fwww.ncbi.nlm.nih.gov%2Fentrez%2Fquery.fcgi%3Ftmpl%3DNoSidebarfile%26db%3DPubMed%26cmd%3DRetrieve%26list_uids%3D21750906%26dopt%3DAbstract In this study, we propose a new modeling constraint concerning the in-situ fiber orientation (β (phys)). β (phys), which is a major contributor to the arterial stress-strain behavior, was determined for porcine and human coronary arteries using a mixed numerical-experimental method. The in-situ situation was mimicked using in-vitro experiments at a physiological axial pre-stretch, in which pressure-radius and pressure-axial force were measured. A single-layered, hyperelastic, thick-walled, two-fiber material model was accurately fitted to the experimental data, enabling the computation of stress, strain, and fiber orientation. β (phys) was found to be almost equal for all vessels measured (36.4 ± 0.3)°, which theoretically can be explained using netting analysis. In further research, ... Biomechanics and Modeling in Mechanobiology journals http://www.medworm.com/rss/comments.php?id=5038726 Tue, 12 Jul 2011 23:00:00 +0100 5038726 http://www.medworm.com/index.php?rid=5038728&cid=s_37325_61_f&fid=37325&url=http%3A%2F%2Fwww.ncbi.nlm.nih.gov%2Fentrez%2Fquery.fcgi%3Ftmpl%3DNoSidebarfile%26db%3DPubMed%26cmd%3DRetrieve%26list_uids%3D21748425%26dopt%3DAbstract Authors: Maas R, Siebert T, Leyendecker S In this work, we implement a typical nonlinear Hill-type muscle model in a structure-preserving simulation framework and investigate the differences to standard simulations of muscle-actuated movements with MATLAB/Simulink. The latter is a common tool to solve dynamical problems, in particular, in biomechanic investigations. Despite the simplicity of the examples used for comparison, it becomes obvious that the MATLAB/Simulink integrators artificially loose or gain energy and angular momentum during dynamic simulations. The relative energy error of the MATLAB/Simulink integrators related to a very low actual muscle work can naturally reach large values, even higher than 100%. But also during periods with large muscle work, the relative energy e... Biomechanics and Modeling in Mechanobiology journals http://www.medworm.com/rss/comments.php?id=5038728 Mon, 11 Jul 2011 23:00:00 +0100 5038728 http://www.medworm.com/index.php?rid=5038727&cid=s_37325_61_f&fid=37325&url=http%3A%2F%2Fwww.ncbi.nlm.nih.gov%2Fentrez%2Fquery.fcgi%3Ftmpl%3DNoSidebarfile%26db%3DPubMed%26cmd%3DRetrieve%26list_uids%3D21748426%26dopt%3DAbstract The objectives of this study were to measure human AF biaxial tensile mechanics and to apply and validate a constitutive model to determine material properties. Biaxial tensile tests were performed on samples oriented along the circumferential-axial and the radial-axial directions. Data were fit to a structurally motivated anisotropic hyperelastic model composed of isotropic extra-fibrillar matrix, nonlinear fibers, and fiber-matrix interactions (FMI) normal to the fibers. The validated model was used to simulate shear and uniaxial tensile behavior, to investigate AF structure-function, and to quantify the effect of degeneration. The biaxial stress-strain response was described well by the model (R (2) > 0.9). The model showed that the parameters for fiber nonlinearity and the normal ... Biomechanics and Modeling in Mechanobiology journals http://www.medworm.com/rss/comments.php?id=5038727 Mon, 11 Jul 2011 23:00:00 +0100 5038727 http://www.medworm.com/index.php?rid=5038729&cid=s_37325_61_f&fid=37325&url=http%3A%2F%2Fwww.ncbi.nlm.nih.gov%2Fentrez%2Fquery.fcgi%3Ftmpl%3DNoSidebarfile%26db%3DPubMed%26cmd%3DRetrieve%26list_uids%3D21744269%26dopt%3DAbstract Authors: Rezakhaniha R, Agianniotis A, Schrauwen JT, Griffa A, Sage D, Bouten CV, van de Vosse FN, Unser M, Stergiopulos N Mechanical properties of the adventitia are largely determined by the organization of collagen fibers. Measurements on the waviness and orientation of collagen, particularly at the zero-stress state, are necessary to relate the structural organization of collagen to the mechanical response of the adventitia. Using the fluorescence collagen marker CNA38-OG488 and confocal laser scanning microscopy, we imaged collagen fibers in the adventitia of rabbit common carotid arteries ex vivo. The arteries were cut open along their longitudinal axes to get the zero-stress state. We used semi-manual and automatic techniques to measure parameters related to the waviness and ori... Biomechanics and Modeling in Mechanobiology journals http://www.medworm.com/rss/comments.php?id=5038729 Sat, 09 Jul 2011 23:00:00 +0100 5038729 http://www.medworm.com/index.php?rid=5038731&cid=s_37325_61_f&fid=37325&url=http%3A%2F%2Fwww.ncbi.nlm.nih.gov%2Fentrez%2Fquery.fcgi%3Ftmpl%3DNoSidebarfile%26db%3DPubMed%26cmd%3DRetrieve%26list_uids%3D21744014%26dopt%3DAbstract Authors: Xiong W, Zhang J Red blood cell (RBC) motion and trajectories in bifurcated microvessels are simulated using a two-dimensional immersed boundary-lattice Boltzmann method (IB-LBM). A RBC is modeled as a capsule with viscous interior fluid enclosed by a flexible membrane. For the symmetric bifurcation model employed, the critical offset position in the mother branch, which separates the RBC flux toward the two branches, has been calculated. The RBC flux and the hematocrit partitioning between the two daughter branches have also been studied. Effects of the flow-rate ratio, cell deformability and suspending viscosity have been examined. Simulation results indicate that increased cell rigidity and suspending viscosity have counter effects on cell trajectory through a bifurcation: ... Biomechanics and Modeling in Mechanobiology journals http://www.medworm.com/rss/comments.php?id=5038731 Fri, 08 Jul 2011 23:00:00 +0100 5038731 http://www.medworm.com/index.php?rid=5038730&cid=s_37325_61_f&fid=37325&url=http%3A%2F%2Fwww.ncbi.nlm.nih.gov%2Fentrez%2Fquery.fcgi%3Ftmpl%3DNoSidebarfile%26db%3DPubMed%26cmd%3DRetrieve%26list_uids%3D21744015%26dopt%3DAbstract Authors: Freed AD, Einstein DR A simple, isotropic, elastic constitutive model for the spongy tissue in lung is formulated from the theory of hypo-elasticity. The model is shown to exhibit a pressure dependent behavior that has been interpreted in the literature as indicating extensional anisotropy. In contrast, we show that this behavior arises naturally from an analysis of isotropic hypo-elastic invariants and is a result of non-linearity, not anisotropy. The response of the model is determined analytically for several boundary value problems used for material characterization. These responses give insight into both the material behavior as well as admissible bounds on parameters. The model predictions are compared with published experimental data for dog lung. PMID: 21744015 [Pu... Biomechanics and Modeling in Mechanobiology journals http://www.medworm.com/rss/comments.php?id=5038730 Fri, 08 Jul 2011 23:00:00 +0100 5038730 http://www.medworm.com/index.php?rid=5038734&cid=s_37325_61_f&fid=37325&url=http%3A%2F%2Fwww.ncbi.nlm.nih.gov%2Fentrez%2Fquery.fcgi%3Ftmpl%3DNoSidebarfile%26db%3DPubMed%26cmd%3DRetrieve%26list_uids%3D21739086%26dopt%3DAbstract Authors: Wilson E, Rustighi E, Newland PL, Mace BR Muscle models are an important tool in the development of new rehabilitation and diagnostic techniques. Many models have been proposed in the past, but little work has been done on comparing the performance of models. In this paper, seven models that describe the isometric force response to pulse train inputs are investigated. Five of the models are from the literature while two new models are also presented. Models are compared in terms of their ability to fit to isometric force data, using Akaike's and Bayesian information criteria and by examining the ability of each model to describe the underlying behaviour in response to individual pulses. Experimental data were collected by stimulating the locust extensor tibia muscle and measur... Biomechanics and Modeling in Mechanobiology journals http://www.medworm.com/rss/comments.php?id=5038734 Thu, 07 Jul 2011 23:00:00 +0100 5038734 http://www.medworm.com/index.php?rid=5038733&cid=s_37325_61_f&fid=37325&url=http%3A%2F%2Fwww.ncbi.nlm.nih.gov%2Fentrez%2Fquery.fcgi%3Ftmpl%3DNoSidebarfile%26db%3DPubMed%26cmd%3DRetrieve%26list_uids%3D21739087%26dopt%3DAbstract Authors: Maceri F, Marino M, Vairo G This paper aims to highlight the need for a refined tendon model to reproduce the main mechanical features of the integrated muscle-tendon unit (MTU). Elastic nonlinearities of the tendon, both at the nano and microscale, are modeled by a multiscale approach, accounting for the hierarchical arrangement (from molecules up to the fibers) of the collagen structures within the tissue. This model accounts also for the variation of tendon stiffness due to physical activity. Since the proposed tendon model is based on tissue-structured histology, the training-driven adaptation laws are directly formulated starting from histological evidences. Such a tendon description is integrated into a viscoelastic Hill-type model of the whole MTU. A fixed-end contracti... Biomechanics and Modeling in Mechanobiology journals http://www.medworm.com/rss/comments.php?id=5038733 Thu, 07 Jul 2011 23:00:00 +0100 5038733 http://www.medworm.com/index.php?rid=5038732&cid=s_37325_61_f&fid=37325&url=http%3A%2F%2Fwww.ncbi.nlm.nih.gov%2Fentrez%2Fquery.fcgi%3Ftmpl%3DNoSidebarfile%26db%3DPubMed%26cmd%3DRetrieve%26list_uids%3D21739088%26dopt%3DAbstract We present a modified distribution, formed as a weighted mixture of the semi-circular uniform distribution and the semi-circular von Mises distribution. It is described by three parameters: β, which weights the contribution from each mixture component; k, the fiber concentration factor; and θ ( p ), the preferred fiber orientation. This distribution was used to fit data obtained by small-angle light scattering experiments from various thin soft tissues. Initial use showed that satisfactory fits of fiber distributions could be obtained (error generally < 1%), but at the cost of non-physically meaningful values of k and β. To address this issue, an empirical constraint between the parameters k and β was introduced, resulting in a constrained 2-parameter fiber distribution. Compared to... Biomechanics and Modeling in Mechanobiology journals http://www.medworm.com/rss/comments.php?id=5038732 Thu, 07 Jul 2011 23:00:00 +0100 5038732 http://www.medworm.com/index.php?rid=5038736&cid=s_37325_61_f&fid=37325&url=http%3A%2F%2Fwww.ncbi.nlm.nih.gov%2Fentrez%2Fquery.fcgi%3Ftmpl%3DNoSidebarfile%26db%3DPubMed%26cmd%3DRetrieve%26list_uids%3D21735242%26dopt%3DAbstract Authors: Christen P, van Rietbergen B, Lambers FM, Müller R, Ito K Bone adapts its morphology (density/micro- architecture) in response to the local loading conditions in such a way that a uniform tissue loading is achieved ('Wolff's law'). This paradigm has been used as a basis for bone remodeling simulations to predict the formation and adaptation of trabecular bone. However, in order to predict bone architectural changes in patients, the physiological external loading conditions, to which the bone was adapted, need to be determined. In the present study, we developed a novel bone loading estimation method to predict such external loading conditions by calculating the loading history that produces the most uniform bone tissue loading. We applied this method to murine caudal vertebra... Biomechanics and Modeling in Mechanobiology journals http://www.medworm.com/rss/comments.php?id=5038736 Wed, 06 Jul 2011 23:00:00 +0100 5038736 http://www.medworm.com/index.php?rid=5038735&cid=s_37325_61_f&fid=37325&url=http%3A%2F%2Fwww.ncbi.nlm.nih.gov%2Fentrez%2Fquery.fcgi%3Ftmpl%3DNoSidebarfile%26db%3DPubMed%26cmd%3DRetrieve%26list_uids%3D21735243%26dopt%3DAbstract Authors: Herchenhan A, Kalson NS, Holmes DF, Hill P, Kadler KE, Margetts L Tendons are composed of longitudinally aligned collagen fibrils arranged in bundles with an undulating pattern, called crimp. The crimp structure is established during embryonic development and plays a vital role in the mechanical behaviour of tendon, acting as a shock-absorber during loading. However, the mechanism of crimp formation is unknown, partly because of the difficulties of studying tendon development in vivo. Here, we used a 3D cell culture system in which embryonic tendon fibroblasts synthesise a tendon-like construct comprised of collagen fibrils arranged in parallel bundles. Investigations using polarised light microscopy, scanning electron microscopy and fluorescence microscopy showed that tendon ... Biomechanics and Modeling in Mechanobiology journals http://www.medworm.com/rss/comments.php?id=5038735 Wed, 06 Jul 2011 23:00:00 +0100 5038735 http://www.medworm.com/index.php?rid=4994412&cid=s_37325_61_f&fid=37325&url=http%3A%2F%2Fwww.ncbi.nlm.nih.gov%2Fentrez%2Fquery.fcgi%3Ftmpl%3DNoSidebarfile%26db%3DPubMed%26cmd%3DRetrieve%26list_uids%3D21706231%26dopt%3DAbstract Authors: Maeda E, Ye S, Wang W, Bader DL, Knight MM, Lee DA Gap junction communication is an essential component in the mechanosensitive response of tenocytes. However, little is known about direct mechanoregulation of gap junction turnover and permeability. The present study tests the hypothesis that mechanical loading alters gap junction communication between tenocyte within tendon fascicles. Viable tenocytes within rat tail tendon fasicles were labelled with calcein-AM and subjected to a fluorescent loss induced by photobleaching (FLIP) protocol. A designated target cell within a row of tenocytes was continuously photobleached at 100% laser power whilst recording the fluorescent intensity of neighbouring cells. A mathematical compartment model was developed to estimate the intercell... Biomechanics and Modeling in Mechanobiology journals http://www.medworm.com/rss/comments.php?id=4994412 Fri, 24 Jun 2011 23:00:00 +0100 4994412 http://www.medworm.com/index.php?rid=4994413&cid=s_37325_61_f&fid=37325&url=http%3A%2F%2Fwww.ncbi.nlm.nih.gov%2Fentrez%2Fquery.fcgi%3Ftmpl%3DNoSidebarfile%26db%3DPubMed%26cmd%3DRetrieve%26list_uids%3D21695444%26dopt%3DAbstract Authors: Ruess M, Tal D, Trabelsi N, Yosibash Z, Rank E Standard methods for predicting bone's mechanical response from quantitative computer tomography (qCT) scans are mainly based on classical h-version finite element methods (FEMs). Due to the low-order polynomial approximation, the need for segmentation and the simplified approach to assign a constant material property to each element in h-FE models, these often compromise the accuracy and efficiency of h-FE solutions. Herein, a non-standard method, the finite cell method (FCM), is proposed for predicting the mechanical response of the human femur. The FCM is free of the above limitations associated with h-FEMs and is orders of magnitude more efficient, allowing its use in the setting of computational steering. This non-standard me... Biomechanics and Modeling in Mechanobiology journals http://www.medworm.com/rss/comments.php?id=4994413 Tue, 21 Jun 2011 23:00:00 +0100 4994413 http://www.medworm.com/index.php?rid=4994414&cid=s_37325_61_f&fid=37325&url=http%3A%2F%2Fwww.ncbi.nlm.nih.gov%2Fentrez%2Fquery.fcgi%3Ftmpl%3DNoSidebarfile%26db%3DPubMed%26cmd%3DRetrieve%26list_uids%3D21691849%26dopt%3DAbstract Authors: Hwang M, Berceli SA, Garbey M, Kim NH, Tran-Son-Tay R Although vein bypass grafting is one of the primary options for the treatment of arterial occlusive disease and provides satisfactory results at an early stage of the treatment, the patency is limited to a few months in many patients. When the vein is implanted in the arterial system, it adapts to the high flow rate and high pressure of the arterial environment by changing the sizes of its layers, and this remodeling is believed to be a precursor of future graft failure. Hemodynamic forces, such as wall shear stress (WSS) and wall tension, have been recognized as major factors impacting vein graft remodeling. Although a wide range of experimental evidence relating hemodynamic forces to vein graft remodeling has been reporte... Biomechanics and Modeling in Mechanobiology journals http://www.medworm.com/rss/comments.php?id=4994414 Mon, 20 Jun 2011 23:00:00 +0100 4994414 http://www.medworm.com/index.php?rid=4994415&cid=s_37325_61_f&fid=37325&url=http%3A%2F%2Fwww.ncbi.nlm.nih.gov%2Fentrez%2Fquery.fcgi%3Ftmpl%3DNoSidebarfile%26db%3DPubMed%26cmd%3DRetrieve%26list_uids%3D21688057%26dopt%3DAbstract In conclusion, we showed that strain gauge measurements are very sensitive to the exact strain gauge location on the bone; hence, the use of strain gauge data only is not recommended for studies that address at identifying reliable relationships between tissue response and local strains. Instead, specimen-specific micro FE models of rat tibiae provide accurate estimates of tissue-level strains. PMID: 21688057 [PubMed - as supplied by publisher] (Source: Biomechanics and Modeling in Mechanobiology) Biomechanics and Modeling in Mechanobiology journals http://www.medworm.com/rss/comments.php?id=4994415 Fri, 17 Jun 2011 23:00:00 +0100 4994415 http://www.medworm.com/index.php?rid=4896882&cid=s_37325_61_f&fid=37325&url=http%3A%2F%2Fwww.ncbi.nlm.nih.gov%2Fentrez%2Fquery.fcgi%3Ftmpl%3DNoSidebarfile%26db%3DPubMed%26cmd%3DRetrieve%26list_uids%3D21633819%26dopt%3DAbstract In this study, we examined the effects of intermittent FSS and continuous FSS on the osteogenic differentiation of hMSCs. The phosphorylation level of ERK1/2 and FAK is measured to investigate the effects of different FSS application manners on the activation of signaling molecules. The results showed that intermittent FSS could promote the osteogenic differentiation of hMSCs. The expression level of osteogenic genes and the alkaline phosphatase (ALP) activity in cells under intermittent FSS application were significantly higher than those in cells under continuous FSS application. Moreover, intermittent FSS up-regulated the activity of ERK1/2 and FAK. Our study demonstrated that intermittent FSS is more effective to induce the osteogenic differentiation of hMSCs than continuous FSS. P... Biomechanics and Modeling in Mechanobiology journals http://www.medworm.com/rss/comments.php?id=4896882 Wed, 01 Jun 2011 23:00:00 +0100 4896882 http://www.medworm.com/index.php?rid=4896883&cid=s_37325_61_f&fid=37325&url=http%3A%2F%2Fwww.ncbi.nlm.nih.gov%2Fentrez%2Fquery.fcgi%3Ftmpl%3DNoSidebarfile%26db%3DPubMed%26cmd%3DRetrieve%26list_uids%3D21626394%26dopt%3DAbstract In this study, a novel multiscale mechanobiological modelling framework is presented, which takes advantage of lattice-free agent-based models coupled with the finite element method to investigate the dynamics of VSMC growth in vascular tissue engineering scaffolds. The results illustrate the ability of the mechanobiological modelling approach to capture complex multiscale mechanobiological phenomena. Specifically, the framework enabled the study of the influence of scaffold compliance and loading regime in regulating the growth of VSMCs in vascular scaffolds and their role in development of intimal hyperplasia (IH). The model demonstrates that low scaffold compliance compared to host arteries leads to increased luminal ingrowth and IH development. In addition, culture of a tissue-engineer... Biomechanics and Modeling in Mechanobiology journals http://www.medworm.com/rss/comments.php?id=4896883 Mon, 30 May 2011 23:00:00 +0100 4896883 http://www.medworm.com/index.php?rid=4896884&cid=s_37325_61_f&fid=37325&url=http%3A%2F%2Fwww.ncbi.nlm.nih.gov%2Fentrez%2Fquery.fcgi%3Ftmpl%3DNoSidebarfile%26db%3DPubMed%26cmd%3DRetrieve%26list_uids%3D21614531%26dopt%3DAbstract Authors: Yamaoka H, Matsushita S, Shimada Y, Adachi T The adaptive structure and functional changes of the actin cytoskeleton are induced by its mechanical behavior at various temporal and spatial scales. In particular, the mechanical behaviors at different scales play important roles in the mechanical functions of various cells, and these multiscale phenomena require clarification. To establish a milestone toward achieving multiscale modeling and simulation, this paper reviews mathematical analyses and simulation methods applied to the mechanics of the filamentous actin cytoskeleton. The actin cytoskeleton demonstrates characteristic behaviors at every temporal and spatial scale, and mathematical models and simulation methods can be applied to each level of actin cytoskeletal structur... Biomechanics and Modeling in Mechanobiology journals http://www.medworm.com/rss/comments.php?id=4896884 Wed, 25 May 2011 23:00:00 +0100 4896884 http://www.medworm.com/index.php?rid=4896885&cid=s_37325_61_f&fid=37325&url=http%3A%2F%2Fwww.ncbi.nlm.nih.gov%2Fentrez%2Fquery.fcgi%3Ftmpl%3DNoSidebarfile%26db%3DPubMed%26cmd%3DRetrieve%26list_uids%3D21611762%26dopt%3DAbstract In this study, a phenomenological model for collagen remodelling is introduced that incorporates angular remodelling (fibre reorientation) and the adaptation of the so-called transition stretch. This is achieved by introducing a local stress-free configuration for the collagen network by a multiplicative decomposition of the deformation gradient and the appropriate definition of the anisotropic free Helmholtz energy potentials and structure tensors. The collagen network is either treated using discrete fibre directions or a continuous angular distribution. The first part of the study illustrates the influence of force- and displacement-controlled loading on either stress- or deformation-driven remodelling processes in tissues with various degrees of fibre reinforcement. The model is then a... Biomechanics and Modeling in Mechanobiology journals http://www.medworm.com/rss/comments.php?id=4896885 Tue, 24 May 2011 23:00:00 +0100 4896885 http://www.medworm.com/index.php?rid=4896887&cid=s_37325_61_f&fid=37325&url=http%3A%2F%2Fwww.ncbi.nlm.nih.gov%2Fentrez%2Fquery.fcgi%3Ftmpl%3DNoSidebarfile%26db%3DPubMed%26cmd%3DRetrieve%26list_uids%3D21604146%26dopt%3DAbstract Authors: Pang H, Shiwalkar AP, Madormo CM, Taylor RE, Andriacchi TP, Kuhl E The goal of this study is to explore the potential of computational growth models to predict bone density profiles in the proximal tibia in response to gait-induced loading. From a modeling point of view, we design a finite element-based computational algorithm using the theory of open system thermodynamics. In this algorithm, the biological problem, the balance of mass, is solved locally on the integration point level, while the mechanical problem, the balance of linear momentum, is solved globally on the node point level. Specifically, the local bone mineral density is treated as an internal variable, which is allowed to change in response to mechanical loading. From an experimental point of view, we perform ... Biomechanics and Modeling in Mechanobiology journals http://www.medworm.com/rss/comments.php?id=4896887 Sat, 21 May 2011 23:00:00 +0100 4896887 http://www.medworm.com/index.php?rid=4896886&cid=s_37325_61_f&fid=37325&url=http%3A%2F%2Fwww.ncbi.nlm.nih.gov%2Fentrez%2Fquery.fcgi%3Ftmpl%3DNoSidebarfile%26db%3DPubMed%26cmd%3DRetrieve%26list_uids%3D21604147%26dopt%3DAbstract Authors: Metzler SA, Digesu CS, Howard JI, Filip To SD, Warnock JN Soft tissues, such as tendons, skin, arteries, or lung, are constantly subject to mechanical stresses in vivo. None more so than the aortic heart valve that experiences an array of forces including shear stress, cyclic pressure, strain, and flexion. Anisotropic biaxial cyclic stretch maintains valve homeostasis; however, abnormal forces are implicated in disease progression. The response of the valve endothelium to deviations from physiological levels has not been fully characterized. Here, we show the design and validation of a novel stretch apparatus capable of applying biaxial stretch to viable heart valve tissue, while simultaneously allowing for live en face endothelial cell imaging via confocal laser scanning micr... Biomechanics and Modeling in Mechanobiology journals http://www.medworm.com/rss/comments.php?id=4896886 Sat, 21 May 2011 23:00:00 +0100 4896886 http://www.medworm.com/index.php?rid=4850977&cid=s_37325_61_f&fid=37325&url=http%3A%2F%2Fwww.ncbi.nlm.nih.gov%2Fentrez%2Fquery.fcgi%3Ftmpl%3DNoSidebarfile%26db%3DPubMed%26cmd%3DRetrieve%26list_uids%3D21590345%26dopt%3DAbstract Authors: Zhu F, Wagner C, Dal Cengio Leonardi A, Jin X, Vandevord P, Chou C, Yang KH, King AI A combined experimental and numerical study was conducted to determine a method to elucidate the biomechanical response of a head surrogate physical model under air shock loading. In the physical experiments, a gel-filled egg-shaped skull/brain surrogate was exposed to blast overpressure in a shock tube environment, and static pressures within the shock tube and the surrogate were recorded throughout the event. A numerical model of the shock tube was developed using the Eulerian approach and validated against experimental data. An arbitrary Lagrangian-Eulerian (ALE) fluid-structure coupling algorithm was then utilized to simulate the interaction of the shock wave and the head surrogate. After ... Biomechanics and Modeling in Mechanobiology journals http://www.medworm.com/rss/comments.php?id=4850977 Tue, 17 May 2011 23:00:00 +0100 4850977 http://www.medworm.com/index.php?rid=4850978&cid=s_37325_61_f&fid=37325&url=http%3A%2F%2Fwww.ncbi.nlm.nih.gov%2Fentrez%2Fquery.fcgi%3Ftmpl%3DNoSidebarfile%26db%3DPubMed%26cmd%3DRetrieve%26list_uids%3D21562831%26dopt%3DAbstract Authors: Ruffoni D, Müller R, van Lenthe GH The determining factors for the fixation of uncemented screws in bone are the bone-implant interface and the peri-implant bone. The goal of this work was to explore the role of the peri-implant bone architecture on the mechanics of the bone-implant system. In particular, the specific aims of the study were to investigate: (i) the impact of the different architectural parameters, (ii) the effects of disorder, and (iii) the deformations in the peri-implant region. A three-dimensional beam lattice model to describe trabecular bone was developed. Various microstructural features of the lattice were varied in a systematic way. Implant pull-out tests were simulated, and the stiffness and strength of the bone-implant system were computed. The resul... Biomechanics and Modeling in Mechanobiology journals http://www.medworm.com/rss/comments.php?id=4850978 Wed, 11 May 2011 23:00:00 +0100 4850978 http://www.medworm.com/index.php?rid=4850979&cid=s_37325_61_f&fid=37325&url=http%3A%2F%2Fwww.ncbi.nlm.nih.gov%2Fentrez%2Fquery.fcgi%3Ftmpl%3DNoSidebarfile%26db%3DPubMed%26cmd%3DRetrieve%26list_uids%3D21559968%26dopt%3DAbstract This study characterizes, for the first time, the variation in growth plate mechanical properties for the same animal (porcine) and bone (ulna) model with developmental stage and provides new insight into the progression of musculoskeletal diseases during growth spurts in response to mechanical loading. PMID: 21559968 [PubMed - as supplied by publisher] (Source: Biomechanics and Modeling in Mechanobiology) Biomechanics and Modeling in Mechanobiology journals http://www.medworm.com/rss/comments.php?id=4850979 Tue, 10 May 2011 23:00:00 +0100 4850979 http://www.medworm.com/index.php?rid=4797632&cid=s_37325_61_f&fid=37325&url=http%3A%2F%2Fwww.ncbi.nlm.nih.gov%2Fentrez%2Fquery.fcgi%3Ftmpl%3DNoSidebarfile%26db%3DPubMed%26cmd%3DRetrieve%26list_uids%3D21538011%26dopt%3DAbstract Authors: Humphrey JD PMID: 21538011 [PubMed - as supplied by publisher] (Source: Biomechanics and Modeling in Mechanobiology) Biomechanics and Modeling in Mechanobiology journals http://www.medworm.com/rss/comments.php?id=4797632 Mon, 02 May 2011 23:00:00 +0100 4797632 http://www.medworm.com/index.php?rid=4797631&cid=s_37325_61_f&fid=37325&url=http%3A%2F%2Fwww.ncbi.nlm.nih.gov%2Fentrez%2Fquery.fcgi%3Ftmpl%3DNoSidebarfile%26db%3DPubMed%26cmd%3DRetrieve%26list_uids%3D21538012%26dopt%3DAbstract Authors: Wang Z, Chesler NC Chronic hypoxic pulmonary hypertension (HPH) is associated with large pulmonary artery (PA) stiffening, which is correlated with collagen accumulation. However, the mechanisms by which collagen contributes to PA stiffening remain largely unexplored. Moreover, HPH may alter mechanical properties other than stiffness, such as pulse damping capacity, which also affects ventricular workload but is rarely quantified. We hypothesized that collagen content and cross-linking differentially regulate the stiffness and damping capacity of large PAs during HPH progression. The hypothesis was tested with transgenic mice that synthesize collagen type I resistant to collagenase degradation (Col1a1(R/R)). These mice and littermate controls (Col1a1(+/+)) were exposed to hypo... Biomechanics and Modeling in Mechanobiology journals http://www.medworm.com/rss/comments.php?id=4797631 Mon, 02 May 2011 23:00:00 +0100 4797631 http://www.medworm.com/index.php?rid=4797633&cid=s_37325_61_f&fid=37325&url=http%3A%2F%2Fwww.ncbi.nlm.nih.gov%2Fentrez%2Fquery.fcgi%3Ftmpl%3DNoSidebarfile%26db%3DPubMed%26cmd%3DRetrieve%26list_uids%3D21516431%26dopt%3DAbstract In conclusion, we demonstrated the feasibility of using CFD-based tools, as a reliable and cost-effective strategy to assist the design of a 3D cardiogenic bioprocess. PMID: 21516431 [PubMed - as supplied by publisher] (Source: Biomechanics and Modeling in Mechanobiology) Biomechanics and Modeling in Mechanobiology journals http://www.medworm.com/rss/comments.php?id=4797633 Fri, 22 Apr 2011 23:00:00 +0100 4797633 http://www.medworm.com/index.php?rid=4797634&cid=s_37325_61_f&fid=37325&url=http%3A%2F%2Fwww.ncbi.nlm.nih.gov%2Fentrez%2Fquery.fcgi%3Ftmpl%3DNoSidebarfile%26db%3DPubMed%26cmd%3DRetrieve%26list_uids%3D21505895%26dopt%3DAbstract Authors: Nowlan NC, Dumas G, Tajbakhsh S, Prendergast PJ, Murphy P In genetically modified mice with abnormal skeletal muscle development, bones and joints are differentially affected by the lack of skeletal muscle. We hypothesise that unequal levels of biophysical stimuli in the developing humerus and femur can explain the differential effects on these rudiments when muscle is absent. We find that the expression patterns of four mechanosensitive genes important for endochondral ossification are differentially affected in muscleless limb mutants, with more extreme changes in the expression in the humerus than in the femur. Using finite element analysis, we show that the biophysical stimuli induced by muscle forces are similar in the humerus and femur, implying that the removal of muscl... Biomechanics and Modeling in Mechanobiology journals http://www.medworm.com/rss/comments.php?id=4797634 Tue, 19 Apr 2011 23:00:00 +0100 4797634 http://www.medworm.com/index.php?rid=4797635&cid=s_37325_61_f&fid=37325&url=http%3A%2F%2Fwww.ncbi.nlm.nih.gov%2Fentrez%2Fquery.fcgi%3Ftmpl%3DNoSidebarfile%26db%3DPubMed%26cmd%3DRetrieve%26list_uids%3D21476072%26dopt%3DAbstract In this study, an axonal strain injury criterion is used to estimate the probability of diffuse axonal injury (DAI), which accounts for a large percentage of deaths due to brain trauma and is characterized by damage to neural axons in the deep white matter regions of the brain. We present an analytical and computational model that treats the white matter as an anisotropic, hyperelastic material. Diffusion tensor imaging is used to incorporate the structural orientation of the neural axons into the model. It is shown that the degree of injury that is predicted in a computational model of DAI is highly dependent on the incorporation of the axonal orientation information and the inclusion of anisotropy into the constitutive model for white matter. PMID: 21476072 [PubMed - as supplied by p... Biomechanics and Modeling in Mechanobiology journals http://www.medworm.com/rss/comments.php?id=4797635 Thu, 07 Apr 2011 23:00:00 +0100 4797635 http://www.medworm.com/index.php?rid=4689127&cid=s_37325_61_f&fid=37325&url=http%3A%2F%2Fwww.ncbi.nlm.nih.gov%2Fentrez%2Fquery.fcgi%3Ftmpl%3DNoSidebarfile%26db%3DPubMed%26cmd%3DRetrieve%26list_uids%3D21472383%26dopt%3DAbstract In this study, we attempt to predict cortical and trabecular bone adaptation in the mouse caudal vertebrae loading model using knowledge of bone's local mechanical environment at the onset of loading. In a previous study, we demonstrated appreciable 25.9 and 11% increases in both trabecular and cortical bone volume density, respectively, when subjecting the fifth caudal vertebrae (C5) of C57BL/6 (B6) mice to an acute loading regime (amplitude of 8N, 3000 cycles, 10 Hz, 3 times a week for 4 weeks). We have also established a validated finite element (FE) model of the C5 vertebra using micro-computed tomography (micro-CT), which characterizes, in 3D, the micro-mechanical strains present in both cortical and trabecular compartments due to the applied loads. To investigate the relationship bet... Biomechanics and Modeling in Mechanobiology journals http://www.medworm.com/rss/comments.php?id=4689127 Wed, 06 Apr 2011 23:00:00 +0100 4689127 http://www.medworm.com/index.php?rid=4689128&cid=s_37325_61_f&fid=37325&url=http%3A%2F%2Fwww.ncbi.nlm.nih.gov%2Fentrez%2Fquery.fcgi%3Ftmpl%3DNoSidebarfile%26db%3DPubMed%26cmd%3DRetrieve%26list_uids%3D21465260%26dopt%3DAbstract Authors: Yap CH, Saikrishnan N, Yoganathan AP Aortic valve (AV) calcification is a highly prevalent disease with serious impact on mortality and morbidity. The exact causes and mechanisms of AV calcification are unclear, although previous studies suggest that mechanical forces play a role. It has been clinically demonstrated that calcification preferentially occurs on the aortic surface of the AV. This is hypothesized to be due to differences in the mechanical environments on the two sides of the valve. It is thus necessary to characterize fluid shear forces acting on both sides of the leaflet to test this hypothesis. The current study is one of two studies characterizing dynamic shear stress on both sides of the AV leaflets. In the current study, shear stresses on the ventricular surf... Biomechanics and Modeling in Mechanobiology journals http://www.medworm.com/rss/comments.php?id=4689128 Mon, 04 Apr 2011 23:00:00 +0100 4689128 http://www.medworm.com/index.php?rid=4689129&cid=s_37325_61_f&fid=37325&url=http%3A%2F%2Fwww.ncbi.nlm.nih.gov%2Fentrez%2Fquery.fcgi%3Ftmpl%3DNoSidebarfile%26db%3DPubMed%26cmd%3DRetrieve%26list_uids%3D21461899%26dopt%3DAbstract Authors: Lake SP, Cortes DH, Kadlowec JA, Soslowsky LJ, Elliott DM Structural constitutive modeling approaches are often based on the assumption of affine fiber kinematics, even though this assumption has rarely been evaluated experimentally. We are interested in applying mathematical models to understand the mechanisms responsible for the inhomogeneous, anisotropic, and non-linear properties of human supraspinatus tendon (SST); however, the relationship between macroscopic and fiber-level deformation in this tendon remains unknown and current methods for making this assessment are inadequate. Therefore, the purpose of this study was to develop an improved method for quantitatively assessing agreement between two distributions and to examine the affine assumption in SST by comparing ex... Biomechanics and Modeling in Mechanobiology journals http://www.medworm.com/rss/comments.php?id=4689129 Sat, 02 Apr 2011 23:00:00 +0100 4689129 http://www.medworm.com/index.php?rid=4689130&cid=s_37325_61_f&fid=37325&url=http%3A%2F%2Fwww.ncbi.nlm.nih.gov%2Fentrez%2Fquery.fcgi%3Ftmpl%3DNoSidebarfile%26db%3DPubMed%26cmd%3DRetrieve%26list_uids%3D21451947%26dopt%3DAbstract Authors: Huyghe JM, Jongeneelen CJ Understanding of the mechanics of disc tissue calls for measurement of strains in physiological conditions. Because the intervertebral disc is gripped between two vertebrae, the swelling is constrained in vivo, resulting in a intradiscal pressure of 0.1-0.2 MPa in supine position. The excision of isolated disc tissue samples results often in non-physiological swelling. The purpose of the present study is to measure 3D finite strains in isolated bovine disc tissue specimens under physiological osmolarity and pressure, particularly around discontinuities of the collagen network. The collagen is stained by means of CNA35 probe, and the (dead) cells are stained by means of propidium iodide. The tissue is observed under confocal microscopy, under an exter... Biomechanics and Modeling in Mechanobiology journals http://www.medworm.com/rss/comments.php?id=4689130 Wed, 30 Mar 2011 23:00:00 +0100 4689130 http://www.medworm.com/index.php?rid=4689131&cid=s_37325_61_f&fid=37325&url=http%3A%2F%2Fwww.ncbi.nlm.nih.gov%2Fentrez%2Fquery.fcgi%3Ftmpl%3DNoSidebarfile%26db%3DPubMed%26cmd%3DRetrieve%26list_uids%3D21442297%26dopt%3DAbstract Authors: Vermolen FJ, Gefen A We consider the movement and viability of individual cells in cell colonies. Cell movement is assumed to take place as a result of sensing the strain energy density as a mechanical stimulus. The model is based on tracking the displacement and viability of each individual cell in a cell colony. Several applications are shown, such as the dynamics of filling a gap within a fibroblast colony and the invasion of a cell colony. Though based on simple principles, the model is qualitatively validated by experiments on living fibroblasts on a flat substrate. PMID: 21442297 [PubMed - as supplied by publisher] (Source: Biomechanics and Modeling in Mechanobiology) Biomechanics and Modeling in Mechanobiology journals http://www.medworm.com/rss/comments.php?id=4689131 Sat, 26 Mar 2011 00:00:00 +0100 4689131 http://www.medworm.com/index.php?rid=4632703&cid=s_37325_61_f&fid=37325&url=http%3A%2F%2Fwww.ncbi.nlm.nih.gov%2Fentrez%2Fquery.fcgi%3Ftmpl%3DNoSidebarfile%26db%3DPubMed%26cmd%3DRetrieve%26list_uids%3D21431883%26dopt%3DAbstract Authors: Vetter A, Witt F, Sander O, Duda GN, Weinkamer R During secondary bone healing, different tissue types are formed within the fracture callus depending on the local mechanical and biological environment. Our aim was to understand the temporal succession of these tissue patterns for a normal bone healing progression by means of a basic mechanobiological model. The experimental data stemmed from an extensive, previously published animal experiment on sheep with a 3 mm tibial osteotomy. Using recent experimental data, the development of the hard callus was modelled as a porous material with increasing stiffness and decreasing porosity. A basic phenomenological model was employed with a small number of simulation parameters, which allowed comprehensive parameter studies. The model... Biomechanics and Modeling in Mechanobiology journals http://www.medworm.com/rss/comments.php?id=4632703 Thu, 24 Mar 2011 00:00:00 +0100 4632703 http://www.medworm.com/index.php?rid=4632704&cid=s_37325_61_f&fid=37325&url=http%3A%2F%2Fwww.ncbi.nlm.nih.gov%2Fentrez%2Fquery.fcgi%3Ftmpl%3DNoSidebarfile%26db%3DPubMed%26cmd%3DRetrieve%26list_uids%3D21416247%26dopt%3DAbstract Authors: Yap CH, Saikrishnan N, Tamilselvan G, Yoganathan AP Aortic valve (AV) calcification is a highly prevalent disease with serious impact on mortality and morbidity. Although exact causes and mechanisms of AV calcification are unclear, previous studies suggest that mechanical forces play a role. Since calcium deposits occur almost exclusively on the aortic surfaces of AV leaflets, it has been hypothesized that adverse patterns of fluid shear stress on the aortic surface of AV leaflets promote calcification. The current study characterizes AV leaflet aortic surface fluid shear stresses using Laser Doppler velocimetry and an in vitro pulsatile flow loop. The valve model used was a native porcine valve mounted on a suturing ring and preserved using 0.15% glutaraldehyde solution. This... Biomechanics and Modeling in Mechanobiology journals http://www.medworm.com/rss/comments.php?id=4632704 Fri, 18 Mar 2011 00:00:00 +0100 4632704 http://www.medworm.com/index.php?rid=4570896&cid=s_37325_61_f&fid=37325&url=http%3A%2F%2Fwww.ncbi.nlm.nih.gov%2Fentrez%2Fquery.fcgi%3Ftmpl%3DNoSidebarfile%26db%3DPubMed%26cmd%3DRetrieve%26list_uids%3D21384200%26dopt%3DAbstract Authors: Heise RL, Parekh A, Joyce EM, Chancellor MB, Sacks MS Mechanical cues that trigger pathological remodeling in smooth muscle tissues remain largely unknown and are thought to be pivotal triggers for strain-induced remodeling. Thus, an understanding of the effects mechanical stimulation is important to elucidate underlying mechanisms of disease states and in the development of methods for smooth muscle tissue regeneration. For example, the urinary bladder wall (UBW) adaptation to spinal cord injury (SCI) includes extensive hypertrophy as well as increased collagen and elastin, all of which profoundly alter its mechanical response. In addition, the pro-fibrotic growth factor TGF-β1 is upregulated in pathologies of other smooth muscle tissues and may contribute to pathological re... Biomechanics and Modeling in Mechanobiology journals http://www.medworm.com/rss/comments.php?id=4570896 Tue, 08 Mar 2011 00:00:00 +0100 4570896 http://www.medworm.com/index.php?rid=4570897&cid=s_37325_61_f&fid=37325&url=http%3A%2F%2Fwww.ncbi.nlm.nih.gov%2Fentrez%2Fquery.fcgi%3Ftmpl%3DNoSidebarfile%26db%3DPubMed%26cmd%3DRetrieve%26list_uids%3D21380846%26dopt%3DAbstract Authors: Hwang D, Gabai AS, Yu M, Yew AG, Hsieh AH Solid-fluid interactions play an important role in mediating viscoelastic behaviour of biological tissues. In the intervertebral disc, water content is governed by a number of factors, including age, disease and mechanical loads, leading to changes in stiffness characteristics. We hypothesized that zonal stress distributions depend on load history, or the prior stresses experienced by the disc. To investigate these effects, rat caudal motion segments were subjected to compressive creep biomechanical testing in vitro using a protocol that consisted of two phases: a Prestress Phase (varied to represent different histories of load) followed immediately by an Exertion Phase, identical across all Prestress groups. Three analytical models we... Biomechanics and Modeling in Mechanobiology journals http://www.medworm.com/rss/comments.php?id=4570897 Sun, 06 Mar 2011 00:00:00 +0100 4570897 http://www.medworm.com/index.php?rid=4570898&cid=s_37325_61_f&fid=37325&url=http%3A%2F%2Fwww.ncbi.nlm.nih.gov%2Fentrez%2Fquery.fcgi%3Ftmpl%3DNoSidebarfile%26db%3DPubMed%26cmd%3DRetrieve%26list_uids%3D21373889%26dopt%3DAbstract This study proposes a technique to parameterize stent geometry, by varying the shape of circumferential rings and the links, and assess performance by modelling the processes of balloon expansion and drug diffusion. Finite element analysis is used to expand each stent (through balloon inflation) into contact with a representative diseased coronary artery model, followed by a drug release simulation. Also, a separate model is constructed to measure stent flexibility. Since the computational simulation time for each design is very high (approximately 24 h), a Gaussian process modelling approach is used to analyse the design space corresponding to the proposed parameterization. Four objectives to assess recoil, stress distribution, drug distribution and flexibility are set up to perform opti... Biomechanics and Modeling in Mechanobiology journals http://www.medworm.com/rss/comments.php?id=4570898 Fri, 04 Mar 2011 00:00:00 +0100 4570898 http://www.medworm.com/index.php?rid=4570899&cid=s_37325_61_f&fid=37325&url=http%3A%2F%2Fwww.ncbi.nlm.nih.gov%2Fentrez%2Fquery.fcgi%3Ftmpl%3DNoSidebarfile%26db%3DPubMed%26cmd%3DRetrieve%26list_uids%3D21369918%26dopt%3DAbstract Authors: Feng R, Xenos M, Girdhar G, Kang W, Davenport JW, Deng Y, Bluestein D Flow and stresses induced by blood flow acting on the blood cellular constituents can be represented to a certain extent by a continuum mechanics approach down to the order of the μm level. However, the molecular effects of, e.g., adhesion/aggregation bonds of blood clotting can be on the order of nm. The coupling of the disparate length and timescales between such molecular levels and macroscopic transport represents a major computational challenge. To address this challenge, a multiscale numerical approach based on discrete particle dynamics (DPD) methodology derived from molecular dynamics (MD) principles is proposed. The feasibility of the approach was firstly tested for its ability to simulate viscous... Biomechanics and Modeling in Mechanobiology journals http://www.medworm.com/rss/comments.php?id=4570899 Thu, 03 Mar 2011 00:00:00 +0100 4570899 http://www.medworm.com/index.php?rid=4570900&cid=s_37325_61_f&fid=37325&url=http%3A%2F%2Fwww.ncbi.nlm.nih.gov%2Fentrez%2Fquery.fcgi%3Ftmpl%3DNoSidebarfile%26db%3DPubMed%26cmd%3DRetrieve%26list_uids%3D21365198%26dopt%3DAbstract Authors: Nilsen N, Brownell WE, Sun SX, Spector AA Prestin was found in the membrane of outer hair cells (OHCs) located in the cochlea of the mammalian inner ear. These cells convert changes in the membrane potential into dimensional changes and (if constrained) to an active electromechanical force. The OHCs provide the ear with the mechanism of amplification and frequency selectivity that is effective up to tens of kHz. Prestin is a crucial part of the motor complex driving OHCs. Other cells transfected with prestin acquire electromechanical properties similar to those in the native cell. While the mechanism of prestin has yet to be fully understood, the charge transfer is its critical component. Here we investigate the effect of the mechanics of the surrounding membrane on electric c... Biomechanics and Modeling in Mechanobiology journals http://www.medworm.com/rss/comments.php?id=4570900 Wed, 02 Mar 2011 00:00:00 +0100 4570900 http://www.medworm.com/index.php?rid=4516896&cid=s_37325_61_f&fid=37325&url=http%3A%2F%2Fwww.ncbi.nlm.nih.gov%2Fentrez%2Fquery.fcgi%3Ftmpl%3DNoSidebarfile%26db%3DPubMed%26cmd%3DRetrieve%26list_uids%3D21336969%26dopt%3DAbstract Authors: Hambli R, Rieger R Developing mathematical models describing the bone transduction mechanisms, including mechanical and metabolic regulations, has a clear practical applications in bone tissue engineering. The current study attempts to develop a plausible physiologically based mathematical model to describe the mechanotransduction in bone by an osteocyte mediated by the calcium-parathyroid hormone regulation and incorporating the nitric oxide (NO) and prostaglandin E2 (PGE2) effects in early responses to mechanical stimulation. The inputs are mechanical stress and calcium concentration, and the output is a stimulus function corresponding to the stimulatory signal to osteoblasts. The focus will be on the development of the mechanotransduction model rather than investigating the... Biomechanics and Modeling in Mechanobiology journals http://www.medworm.com/rss/comments.php?id=4516896 Sun, 20 Feb 2011 00:00:00 +0100 4516896 http://www.medworm.com/index.php?rid=4516897&cid=s_37325_61_f&fid=37325&url=http%3A%2F%2Fwww.ncbi.nlm.nih.gov%2Fentrez%2Fquery.fcgi%3Ftmpl%3DNoSidebarfile%26db%3DPubMed%26cmd%3DRetrieve%26list_uids%3D21318374%26dopt%3DAbstract Authors: Christophy M, Faruk Senan NA, Lotz JC, O'Reilly OM A new musculoskeletal model for the lumbar spine is described in this paper. This model features a rigid pelvis and sacrum, the five lumbar vertebrae, and a rigid torso consisting of a lumped thoracic spine and ribcage. The motion of the individual lumbar vertebrae was defined as a fraction of the net lumbar movement about the three rotational degrees of freedom: flexion-extension lateral bending, and axial rotation. Additionally, the eight main muscle groups of the lumbar spine were incorporated using 238 muscle fascicles with prescriptions for the parameters in the Hill-type muscle models obtained with the help of an extensive literature survey. The features of the model include the abilities to predict joint reactions, musc... Biomechanics and Modeling in Mechanobiology journals http://www.medworm.com/rss/comments.php?id=4516897 Sat, 12 Feb 2011 00:00:00 +0100 4516897 http://www.medworm.com/index.php?rid=4516901&cid=s_37325_61_f&fid=37325&url=http%3A%2F%2Fwww.ncbi.nlm.nih.gov%2Fentrez%2Fquery.fcgi%3Ftmpl%3DNoSidebarfile%26db%3DPubMed%26cmd%3DRetrieve%26list_uids%3D21308391%26dopt%3DAbstract Authors: Zeng Y, Yip AK, Teo SK, Chiam KH We have developed a three-dimensional random network model of the intracellular actin cytoskeleton and have used it to study the role of the cytoskeleton in mechanotransduction and nucleus deformation. We use the model to predict the deformation of the nucleus when mechanical stresses applied on the plasma membrane are propagated through the random cytoskeletal network to the nucleus membrane. We found that our results agree with previous experiments utilizing micropipette pulling. Therefore, we propose that stress propagation through the random cytoskeletal network can be a mechanism to effect nucleus deformation, without invoking any biochemical signaling activity. Using our model, we also predict how nucleus strain and its relative displacem... Biomechanics and Modeling in Mechanobiology journals http://www.medworm.com/rss/comments.php?id=4516901 Thu, 10 Feb 2011 00:00:00 +0100 4516901 http://www.medworm.com/index.php?rid=4516900&cid=s_37325_61_f&fid=37325&url=http%3A%2F%2Fwww.ncbi.nlm.nih.gov%2Fentrez%2Fquery.fcgi%3Ftmpl%3DNoSidebarfile%26db%3DPubMed%26cmd%3DRetrieve%26list_uids%3D21308392%26dopt%3DAbstract Authors: Liu J, Shi J, Fitton LC, Phillips R, O'Higgins P, Fagan MJ Finite elements analysis (FEA) is now used routinely to interpret skeletal form in terms of function in both medical and biological applications. To produce accurate predictions from FEA models, it is essential that the loading due to muscle action is applied in a physiologically reasonable manner. However, it is common for muscle forces to be represented as simple force vectors applied at a few nodes on the model's surface. It is certainly rare for any wrapping of the muscles to be considered, and yet wrapping not only alters the directions of muscle forces but also applies an additional compressive load from the muscle belly directly to the underlying bone surface. This paper presents a method of applying muscle wrap... Biomechanics and Modeling in Mechanobiology journals http://www.medworm.com/rss/comments.php?id=4516900 Thu, 10 Feb 2011 00:00:00 +0100 4516900 http://www.medworm.com/index.php?rid=4516899&cid=s_37325_61_f&fid=37325&url=http%3A%2F%2Fwww.ncbi.nlm.nih.gov%2Fentrez%2Fquery.fcgi%3Ftmpl%3DNoSidebarfile%26db%3DPubMed%26cmd%3DRetrieve%26list_uids%3D21308393%26dopt%3DAbstract The objective of this work is to address the formulation of an adequate model of the external tissue environment when studying a portion of the arterial tree with fluid-structure interaction. Whereas much work has already been accomplished concerning flow and pressure boundary conditions associated with truncations in the fluid domain, very few studies take into account the tissues surrounding the region of interest to derive adequate boundary conditions for the solid domain. In this paper, we propose to model the effect of external tissues by introducing viscoelastic support conditions along the artery wall, with two-possibly distributed-parameters that can be adjusted to mimic the response of various physiological tissues. In order to illustrate the versatility and effectiveness of our a... Biomechanics and Modeling in Mechanobiology journals http://www.medworm.com/rss/comments.php?id=4516899 Thu, 10 Feb 2011 00:00:00 +0100 4516899 http://www.medworm.com/index.php?rid=4516898&cid=s_37325_61_f&fid=37325&url=http%3A%2F%2Fwww.ncbi.nlm.nih.gov%2Fentrez%2Fquery.fcgi%3Ftmpl%3DNoSidebarfile%26db%3DPubMed%26cmd%3DRetrieve%26list_uids%3D21308394%26dopt%3DAbstract Authors: Wagner H, Boström K, Rinke B Motivated by biochemical processes during muscular contraction, a model is constructed that predicts isometric force from surface electromyographic signals (sEMG). The model is experimentally validated and then it is used to predict contractions from sEMG data. The calculated simulations reveal a highly non-linear relationship between sEMG and isometric force. PMID: 21308394 [PubMed - as supplied by publisher] (Source: Biomechanics and Modeling in Mechanobiology) Biomechanics and Modeling in Mechanobiology journals http://www.medworm.com/rss/comments.php?id=4516898 Thu, 10 Feb 2011 00:00:00 +0100 4516898 http://www.medworm.com/index.php?rid=4458765&cid=s_37325_61_f&fid=37325&url=http%3A%2F%2Fwww.ncbi.nlm.nih.gov%2Fentrez%2Fquery.fcgi%3Ftmpl%3DNoSidebarfile%26db%3DPubMed%26cmd%3DRetrieve%26list_uids%3D21287395%26dopt%3DAbstract Authors: Nerurkar NL, Mauck RL, Elliott DM Mechanical function of the annulus fibrosus of the intervertebral disc is dictated by the composition and microstructure of its highly ordered extracellular matrix. Recent work on engineered angle-ply laminates formed from mesenchymal stem cell (MSC)-seeded nanofibrous scaffolds indicates that the organization of collagen fibers into planes of alternating alignment may play an important role in annulus fibrosus tissue function. Specifically, these engineered tissues can resist tensile deformation through shearing of the interlamellar matrix as layers of collagen differentially reorient under load. In the present work, a hyperelastic constitutive model was developed to describe the role of interlamellar shearing in reinforcing the tensile respo... Biomechanics and Modeling in Mechanobiology journals http://www.medworm.com/rss/comments.php?id=4458765 Thu, 03 Feb 2011 00:00:00 +0100 4458765 http://www.medworm.com/index.php?rid=4458766&cid=s_37325_61_f&fid=37325&url=http%3A%2F%2Fwww.ncbi.nlm.nih.gov%2Fentrez%2Fquery.fcgi%3Ftmpl%3DNoSidebarfile%26db%3DPubMed%26cmd%3DRetrieve%26list_uids%3D21267625%26dopt%3DAbstract The objective of this paper was to quantify the size and content of possible cortical bone mesoscale RVEs. RVE size was defined as the minimum size: (1) for which the apparent (homogenized) stiffness tensor becomes independent of the applied boundary conditions or (2) for which the variance of elastic properties for a set of microstructure realizations is sufficiently small. The field of elastic coefficients and microstructure in RVEs was derived from one acoustic microscopy image of a human femur cortical bone sample with an overall porosity of 8.5%. The homogenized properties of RVEs were computed with a finite element technique. It was found that the size of the RVE representative of the overall tissue is about 1.5 mm. Smaller RVEs (~0.5 mm) can also be considered to estimate local me... Biomechanics and Modeling in Mechanobiology journals http://www.medworm.com/rss/comments.php?id=4458766 Wed, 26 Jan 2011 00:00:00 +0100 4458766 http://www.medworm.com/index.php?rid=4391002&cid=s_37325_61_f&fid=37325&url=http%3A%2F%2Fwww.ncbi.nlm.nih.gov%2Fentrez%2Fquery.fcgi%3Ftmpl%3DNoSidebarfile%26db%3DPubMed%26cmd%3DRetrieve%26list_uids%3D21253808%26dopt%3DAbstract Authors: Nguyen VH, Lemaire T, Naili S It is well known that microcracks act as a stimulus for bone remodelling, initiating resorption by osteoclasts and new bone formation by osteoblasts. Moreover, microcracks are likely to alter the fluid flow and convective transport through the bone tissue. This paper proposes a quantitative evaluation of the strain-induced interstitial fluid velocities developing in osteons in presence of a microcrack in the interstitial bone tissue. Based on Biot theory in the low-frequency range, a poroelastic model is carried out to study the hydro-mechanical behaviour of cracked osteonal tissue. The finite element results show that the presence of a microcrack in the interstitial osteonal tissue may drastically reduce the fluid velocity inside the neighbouring... Biomechanics and Modeling in Mechanobiology journals http://www.medworm.com/rss/comments.php?id=4391002 Fri, 21 Jan 2011 00:00:00 +0100 4391002 http://www.medworm.com/index.php?rid=4391001&cid=s_37325_61_f&fid=37325&url=http%3A%2F%2Fwww.ncbi.nlm.nih.gov%2Fentrez%2Fquery.fcgi%3Ftmpl%3DNoSidebarfile%26db%3DPubMed%26cmd%3DRetrieve%26list_uids%3D21253809%26dopt%3DAbstract Authors: Maul TM, Chew DW, Nieponice A, Vorp DA Mesenchymal stem cell (MSC) therapy has demonstrated applications in vascular regenerative medicine. Although blood vessels exist in a mechanically dynamic environment, there has been no rigorous, systematic analysis of mechanical stimulation on stem cell differentiation. We hypothesize that mechanical stimuli, relevant to the vasculature, can differentiate MSCs toward smooth muscle (SMCs) and endothelial cells (ECs). This was tested using a unique experimental platform to differentially apply various mechanical stimuli in parallel. Three forces, cyclic stretch, cyclic pressure, and laminar shear stress, were applied independently to mimic several vascular physiologic conditions. Experiments were conducted using subconfluent MSCs for 5 d... Biomechanics and Modeling in Mechanobiology journals http://www.medworm.com/rss/comments.php?id=4391001 Fri, 21 Jan 2011 00:00:00 +0100 4391001 http://www.medworm.com/index.php?rid=4391003&cid=s_37325_61_f&fid=37325&url=http%3A%2F%2Fwww.ncbi.nlm.nih.gov%2Fentrez%2Fquery.fcgi%3Ftmpl%3DNoSidebarfile%26db%3DPubMed%26cmd%3DRetrieve%26list_uids%3D21221700%26dopt%3DAbstract Authors: Gurev V, Lee T, Constantino J, Arevalo H, Trayanova NA PMID: 21221700 [PubMed - as supplied by publisher] (Source: Biomechanics and Modeling in Mechanobiology) Biomechanics and Modeling in Mechanobiology journals http://www.medworm.com/rss/comments.php?id=4391003 Sun, 09 Jan 2011 00:00:00 +0100 4391003 http://www.medworm.com/index.php?rid=4391004&cid=s_37325_61_f&fid=37325&url=http%3A%2F%2Fwww.ncbi.nlm.nih.gov%2Fentrez%2Fquery.fcgi%3Ftmpl%3DNoSidebarfile%26db%3DPubMed%26cmd%3DRetrieve%26list_uids%3D21213013%26dopt%3DAbstract Authors: Haider MA, Olander JE, Arnold RF, Marous DR, McLamb AJ, Thompson KC, Woodruff WR, Haugh JM A phenomenological mixture model is presented for interactions between biosynthesis of extracellular matrix (ECM) constituents and ECM linking in a scaffold seeded with chondrocytes. A system of three ordinary differential equations for average apparent densities of unlinked ECM, linked ECM and scaffold is developed along with associated initial conditions for scaffold material properties. Equations for unlinked ECM synthesis and ECM linking include an inhibitory mechanism where associated rates decrease as unlinked ECM concentration in the interstitial fluid increases. Linking rates are proposed to depend on average porosity in the evolving tissue construct. The resulting initial value ... Biomechanics and Modeling in Mechanobiology journals http://www.medworm.com/rss/comments.php?id=4391004 Fri, 07 Jan 2011 00:00:00 +0100 4391004 http://www.medworm.com/index.php?rid=4391010&cid=s_37325_61_f&fid=37325&url=http%3A%2F%2Fwww.ncbi.nlm.nih.gov%2Fentrez%2Fquery.fcgi%3Ftmpl%3DNoSidebarfile%26db%3DPubMed%26cmd%3DRetrieve%26list_uids%3D21207094%26dopt%3DAbstract Authors: Yoo L, Gupta V, Lee C, Kavehpore P, Demer JL Reported mechanical properties of orbital connective tissue and fat have been too sparse to model strain-stress relationships underlying biomechanical interactions in strabismus. We performed rheological tests to develop a multi-mode upper convected Maxwell (UCM) model of these tissues under shear loading. From 20 fresh bovine orbits, 30 samples of connective tissue were taken from rectus pulley regions and 30 samples of fatty tissues from the posterior orbit. Additional samples were defatted to determine connective tissue weight proportion, which was verified histologically. Mechanical testing in shear employed a triborheometer to perform: strain sweeps at 0.5-2.0 Hz; shear stress relaxation with 1% strain; viscometry at 0.01-0.5Â... Biomechanics and Modeling in Mechanobiology journals http://www.medworm.com/rss/comments.php?id=4391010 Wed, 05 Jan 2011 00:00:00 +0100 4391010 http://www.medworm.com/index.php?rid=4391005&cid=s_37325_61_f&fid=37325&url=http%3A%2F%2Fwww.ncbi.nlm.nih.gov%2Fentrez%2Fquery.fcgi%3Ftmpl%3DNoSidebarfile%26db%3DPubMed%26cmd%3DRetrieve%26list_uids%3D21207095%26dopt%3DAbstract Authors: Masson I, Beaussier H, Boutouyrie P, Laurent S, Humphrey JD, Zidi M The goal of this study was to model the in vivo non-linear mechanical behavior of human common carotid arteries (CCAs) and then to compare wall stresses and associated contributions of micro-constituents in normotensive (NT) and treated hypertensive (HT) subjects. We used an established theoretical model of 3D arterial mechanics that assumes a hyperelastic, anisotropic, active-passive, and residually stressed wall. In vivo data were obtained non-invasively from CCAs in 16 NT (21-64 years old) and 25 treated HT (44-69 years old) subjects. The associated quasi-static boundary value problem was solved semi-analytically over a cardiac cycle while accounting for surrounding perivascular tissue. Best-fit values of... Biomechanics and Modeling in Mechanobiology journals http://www.medworm.com/rss/comments.php?id=4391005 Wed, 05 Jan 2011 00:00:00 +0100 4391005 http://www.medworm.com/index.php?rid=4304594&cid=s_37325_61_f&fid=37325&url=http%3A%2F%2Fwww.ncbi.nlm.nih.gov%2Fentrez%2Fquery.fcgi%3Ftmpl%3DNoSidebarfile%26db%3DPubMed%26cmd%3DRetrieve%26list_uids%3D21191628%26dopt%3DAbstract We describe this system theoretically using a 'bilayer' model in which a growing cell layer adheres to a thin compressible elastic beam. We compare this with the 'supported-monolayer' model due to Edwards and Chapman (Bull Math Biol 69:1927-1942, 2007) for an incompressible expanding beam (representing crypt epithelium), which incorporates viscoelastic tethering to underlying stroma. We show that the bilayer model can exhibit buckling via parametric growth (in which the system passes through a sequence of equilibrium states, parameterised by the total beam length); in this case, non-uniformities in cell growth and variations in cell-substrate adhesion are predicted to have minimal effect on the shape of resulting buckled states. The supported-monolayer model reveals how competition between... Biomechanics and Modeling in Mechanobiology journals http://www.medworm.com/rss/comments.php?id=4304594 Thu, 30 Dec 2010 00:00:00 +0100 4304594 http://www.medworm.com/index.php?rid=4304595&cid=s_37325_61_f&fid=37325&url=http%3A%2F%2Fwww.ncbi.nlm.nih.gov%2Fentrez%2Fquery.fcgi%3Ftmpl%3DNoSidebarfile%26db%3DPubMed%26cmd%3DRetrieve%26list_uids%3D21188611%26dopt%3DAbstract We present the underlying constitutive equations and their algorithmic implementation within an implicit nonlinear finite element framework. To demonstrate the features of the proposed approach, we study two classical growth phenomena in the heart: left and right ventricular wall thickening in response to systemic and pulmonary hypertension. PMID: 21188611 [PubMed - as supplied by publisher] (Source: Biomechanics and Modeling in Mechanobiology) Biomechanics and Modeling in Mechanobiology journals http://www.medworm.com/rss/comments.php?id=4304595 Sat, 25 Dec 2010 00:00:00 +0100 4304595 http://www.medworm.com/index.php?rid=4304596&cid=s_37325_61_f&fid=37325&url=http%3A%2F%2Fwww.ncbi.nlm.nih.gov%2Fentrez%2Fquery.fcgi%3Ftmpl%3DNoSidebarfile%26db%3DPubMed%26cmd%3DRetrieve%26list_uids%3D21181227%26dopt%3DAbstract In this study, experimental results of single cell spreading between two parallel microplates are exploited through finite element modeling. Axisymmetric computations at finite strains are performed to extract the mechanical properties of the cell which can account for cell shape evolution and traction force generation. Our model includes two distinct components representing the cortex associated with the bilayer membrane on the one hand, and the rest of the cell on the other hand. The former is modeled as a homogeneous hyperelastic material described by a slightly compressible Gent strain energy function, while the latter is idealized either as a quasi-incompressible Newtonian fluid or as another homogeneous hyperelastic material. The kinetics of spreading is ensured by a stapling procedu... Biomechanics and Modeling in Mechanobiology journals http://www.medworm.com/rss/comments.php?id=4304596 Thu, 23 Dec 2010 00:00:00 +0100 4304596 http://www.medworm.com/index.php?rid=4269527&cid=s_37325_61_f&fid=37325&url=http%3A%2F%2Fwww.ncbi.nlm.nih.gov%2Fentrez%2Fquery.fcgi%3Ftmpl%3DNoSidebarfile%26db%3DPubMed%26cmd%3DRetrieve%26list_uids%3D21165757%26dopt%3DAbstract This study provides a method for verification and shows its performance. For this purpose, shear loading of a finite crack is addressed analytically and through a commercial finite element code. Impulsive shear loading by two-edge dislocation of a crack was considered in a 2D plane strain model for an ionized porous medium. To derive the analytical solution, the system of equation is decoupled by stress functions. The shear stress distribution at the plane of the crack is derived using Fourier and Laplace transformations. The analytical solution for the shear stress distribution is compared with computer simulations in ABAQUS version 6.4-5. Decoupling of the equations makes it possible to solve some boundary value problems in porous media taking chemical effects into account. The numerical... Biomechanics and Modeling in Mechanobiology journals http://www.medworm.com/rss/comments.php?id=4269527 Fri, 17 Dec 2010 00:00:00 +0100 4269527 http://www.medworm.com/index.php?rid=4269528&cid=s_37325_61_f&fid=37325&url=http%3A%2F%2Fwww.ncbi.nlm.nih.gov%2Fentrez%2Fquery.fcgi%3Ftmpl%3DNoSidebarfile%26db%3DPubMed%26cmd%3DRetrieve%26list_uids%3D21161562%26dopt%3DAbstract Authors: Creane A, Maher E, Sultan S, Hynes N, Kelly DJ, Lally C Many studies have used patient-specific finite element models to estimate the stress environment in atherosclerotic plaques, attempting to correlate the magnitude of stress to plaque vulnerability. In complex geometries, few studies have incorporated the anisotropic material response of arterial tissue. This paper presents a fibre remodelling algorithm to predict the fibre architecture, and thus anisotropic material response in four patient-specific models of the carotid bifurcation. The change in fibre architecture during disease progression and its affect on the stress environment in the plaque were predicted. The mean fibre directions were assumed to lie at an angle between the two positive principal strain directions.... Biomechanics and Modeling in Mechanobiology journals http://www.medworm.com/rss/comments.php?id=4269528 Thu, 16 Dec 2010 00:00:00 +0100 4269528 http://www.medworm.com/index.php?rid=4245890&cid=s_37325_61_f&fid=37325&url=http%3A%2F%2Fwww.ncbi.nlm.nih.gov%2Fentrez%2Fquery.fcgi%3Ftmpl%3DNoSidebarfile%26db%3DPubMed%26cmd%3DRetrieve%26list_uids%3D21136134%26dopt%3DAbstract Authors: Bonfoh N, Novinyo E, Lipinski P Bone remodeling occurs in an adult's skeleton to adapt its architecture to external loadings. This involves bone resorption by osteoclasts cells followed by formation of new bone by osteoblasts cells. During bone remodeling, osteoclasts and osteoblasts interact with each other by expressing autocrine and paracrine factors that regulate cells' population. Therefore, changes in bone density depend on the amount of each acting cell population. The aim of this paper is to propose a model for the bone remodeling process, which takes into account the opposite activity of both types of cells. For this purpose, a system of differential equations, proposed by Komarova et al. (Bone 33:206-215, 2003), is introduced to describe bone cell interactions using... Biomechanics and Modeling in Mechanobiology journals http://www.medworm.com/rss/comments.php?id=4245890 Tue, 07 Dec 2010 00:00:00 +0100 4245890 http://www.medworm.com/index.php?rid=4245891&cid=s_37325_61_f&fid=37325&url=http%3A%2F%2Fwww.ncbi.nlm.nih.gov%2Fentrez%2Fquery.fcgi%3Ftmpl%3DNoSidebarfile%26db%3DPubMed%26cmd%3DRetrieve%26list_uids%3D21127938%26dopt%3DAbstract Authors: Grasa J, Ramírez A, Osta R, Muñoz MJ, Soteras F, Calvo B This paper presents a three-dimensional finite element model of skeletal muscle and its validation incorporating inital tissue strains. A constitutive relation was determined by using a convex free strain energy function (SEF) where active and passive response contributions were obtained fitting experimental data from the rat tibialis anterior (TA) muscle. The passive and active finite strains response was modelled within the framework of continuum mechanics by a quasi-incompressible transversely isotropic material formulation. Magnetic resonance images (MRI) were obtained to reconstruct the external geometry of the TA. This geometry includes initial strains also taken into account in the numerical model. The numerical... Biomechanics and Modeling in Mechanobiology journals http://www.medworm.com/rss/comments.php?id=4245891 Fri, 03 Dec 2010 00:00:00 +0100 4245891 http://www.medworm.com/index.php?rid=4213759&cid=s_37325_61_f&fid=37325&url=http%3A%2F%2Fwww.ncbi.nlm.nih.gov%2Fentrez%2Fquery.fcgi%3Ftmpl%3DNoSidebarfile%26db%3DPubMed%26cmd%3DRetrieve%26list_uids%3D21107636%26dopt%3DAbstract Authors: Jor JW, Nash MP, Nielsen PM, Hunter PJ This paper presents a structurally based modeling framework to characterize the structure-function relation in skin tissues, based upon biaxial tensile experiments performed in vitro on porcine skin. Equi-axial deformations were imposed by stretching circular skin specimens uniformly along twelve directions, and the resultant loads at the membrane attachment points were measured. Displacement fields at each deformation step were tracked using an image 2D cross-correlation technique. A modeling framework was developed to simulate the experiments, whereby measured forces were applied to finite element models that were created to represent the geometry and structure of the tissue samples. Parameters of a structurally based constitutive relat... Biomechanics and Modeling in Mechanobiology journals http://www.medworm.com/rss/comments.php?id=4213759 Thu, 25 Nov 2010 00:00:00 +0100 4213759 http://www.medworm.com/index.php?rid=4213760&cid=s_37325_61_f&fid=37325&url=http%3A%2F%2Fwww.ncbi.nlm.nih.gov%2Fentrez%2Fquery.fcgi%3Ftmpl%3DNoSidebarfile%26db%3DPubMed%26cmd%3DRetrieve%26list_uids%3D21104422%26dopt%3DAbstract Authors: Leong FY, Li Q, Lim CT, Chiam KH Cell entry into a micro-channel has potential applications in cell sorting and cancer diagnostics. In this paper, we numerically model breast cancer cell entry into a constricted micro-channel. Our results indicate that the cell velocity decreases during entry and increases after entry, an observation in agreement with experiments. We found that the cell entry time depend strongly on the cortical stiffness and is minimum at some critical cortical elasticity. In addition, we found that for the same entry time, a stiff nucleus is displaced toward the cell front, whereas a viscous nucleus is displaced toward the rear. In comparison, the nucleus is less sensitive to the viscosity of the cytoplasm. These observations suggest that specific intra-cell... Biomechanics and Modeling in Mechanobiology journals http://www.medworm.com/rss/comments.php?id=4213760 Tue, 23 Nov 2010 00:00:00 +0100 4213760 http://www.medworm.com/index.php?rid=4164137&cid=s_37325_61_f&fid=37325&url=http%3A%2F%2Fwww.ncbi.nlm.nih.gov%2Fentrez%2Fquery.fcgi%3Ftmpl%3DNoSidebarfile%26db%3DPubMed%26cmd%3DRetrieve%26list_uids%3D21069414%26dopt%3DAbstract Authors: Qin KR, Xiang C, Cao LL In this paper, a dynamic model is proposed to quantify the relationship between fluid flow and Cl(-)-selective membrane current in vascular endothelial cells (VECs). It is assumed that the external shear stress would first induce channel deformation in VECs. This deformation could activate the Cl(-) channels on the membrane, thus allowing Cl(-) transport across the membrane. A modified Hodgkin-Huxley model is embedded into our dynamic system to describe the electrophysiological properties of the membrane, such as the Cl(-)-selective membrane current (I), voltage (V) and conductance. Three flow patterns, i. e., steady flow, oscillatory flow, and pulsatile flow, are applied in our simulation studies. When the extracellular Cl(-) concentration is constant,... Biomechanics and Modeling in Mechanobiology journals http://www.medworm.com/rss/comments.php?id=4164137 Thu, 11 Nov 2010 00:00:00 +0100 4164137 http://www.medworm.com/index.php?rid=4164136&cid=s_37325_61_f&fid=37325&url=http%3A%2F%2Fwww.ncbi.nlm.nih.gov%2Fentrez%2Fquery.fcgi%3Ftmpl%3DNoSidebarfile%26db%3DPubMed%26cmd%3DRetrieve%26list_uids%3D21069415%26dopt%3DAbstract In conclusion, this paper shows that a linear elastic material is not appropriate to describe pars flaccida's behaviour in the quasi-static pressure regime, that the currently used membrane stiffness estimates do not hold for large deformations and that incorporating an in situ strain in the models is necessary for a good description for small static pressures. PMID: 21069415 [PubMed - as supplied by publisher] (Source: Biomechanics and Modeling in Mechanobiology) Biomechanics and Modeling in Mechanobiology journals http://www.medworm.com/rss/comments.php?id=4164136 Thu, 11 Nov 2010 00:00:00 +0100 4164136 http://www.medworm.com/index.php?rid=4164135&cid=s_37325_61_f&fid=37325&url=http%3A%2F%2Fwww.ncbi.nlm.nih.gov%2Fentrez%2Fquery.fcgi%3Ftmpl%3DNoSidebarfile%26db%3DPubMed%26cmd%3DRetrieve%26list_uids%3D21069416%26dopt%3DAbstract Authors: van Oers RF, van Rietbergen B, Ito K, Hilbers PA, Huiskes R Bone formation responds to mechanical loading, which is believed to be mediated by osteocytes. Previous theories assumed that loading stimulates osteocytes to secrete signals that stimulate bone formation. In computer simulations this 'stimulatory' theory successfully produced load-aligned trabecular structures. In recent years, however, it was discovered that osteocytes inhibit bone formation via the protein sclerostin. To reconcile this with strain-induced bone formation, one must assume that sclerostin secretion decreases with mechanical loading. This leads to a new 'inhibitory' theory in which loading inhibits osteocytes from inhibiting bone formation. Here we used computer simulations to show that a sclerostin-ba... Biomechanics and Modeling in Mechanobiology journals http://www.medworm.com/rss/comments.php?id=4164135 Thu, 11 Nov 2010 00:00:00 +0100 4164135 http://www.medworm.com/index.php?rid=4164134&cid=s_37325_61_f&fid=37325&url=http%3A%2F%2Fwww.ncbi.nlm.nih.gov%2Fentrez%2Fquery.fcgi%3Ftmpl%3DNoSidebarfile%26db%3DPubMed%26cmd%3DRetrieve%26list_uids%3D21069417%26dopt%3DAbstract Authors: Hollenstein M, Ehret AE, Itskov M, Mazza E This paper communicates a novel and robust method for the mechanical testing of thin layers of soft biological tissues with particular application to porcine skin. The key features include the use of a surgical dermatome and the highly defined deformation kinematics achieved by pure shear testing. Thin specimens of accurate thickness were prepared using a dermatome and were subjected to different quasi-static and dynamic loading protocols. Although simple in its experimental realisation, pure shear testing provides a number of advantages over other classic uni- and biaxial testing procedures. The preparation of thin specimens of porcine dermis, the mechanical tests as well as first representative results are described and discussed in... Biomechanics and Modeling in Mechanobiology journals http://www.medworm.com/rss/comments.php?id=4164134 Thu, 11 Nov 2010 00:00:00 +0100 4164134 http://www.medworm.com/index.php?rid=4164138&cid=s_37325_61_f&fid=37325&url=http%3A%2F%2Fwww.ncbi.nlm.nih.gov%2Fentrez%2Fquery.fcgi%3Ftmpl%3DNoSidebarfile%26db%3DPubMed%26cmd%3DRetrieve%26list_uids%3D21061141%26dopt%3DAbstract Authors: Zhang X, Gan RZ The incudostapedial (IS) joint between the incus and stapes is a synovial joint consisting of joint capsule, cartilage, and synovial fluid. The mechanical properties of the IS joint directly affect the middle ear transfer function for sound transmission. However, due to the complexity and small size of the joint, the mechanical properties of the IS joint have not been reported in the literature. In this paper, we report our current study on mechanical properties of human IS joint using both experimental measurement and finite element (FE) modeling analysis. Eight IS joint samples with the incus and stapes attached were harvested from human cadaver temporal bones. Tension, compression, stress relaxation and failure tests were performed on those samples in a micr... Biomechanics and Modeling in Mechanobiology journals http://www.medworm.com/rss/comments.php?id=4164138 Tue, 09 Nov 2010 00:00:00 +0100 4164138 http://www.medworm.com/index.php?rid=4164140&cid=s_37325_61_f&fid=37325&url=http%3A%2F%2Fwww.ncbi.nlm.nih.gov%2Fentrez%2Fquery.fcgi%3Ftmpl%3DNoSidebarfile%26db%3DPubMed%26cmd%3DRetrieve%26list_uids%3D21053043%26dopt%3DAbstract Authors: Zeinali-Davarani S, Raguin LG, Vorp DA, Baek S Recent advances in computational modeling of vascular adaptations and the need for their extension to patient-specific modeling have introduced new challenges to the path toward abdominal aortic aneurysm modeling. First, the fundamental assumption in adaptation models, namely the existence of vascular homeostasis in normal vessels, is not easy to implement in a vessel model built from medical images. Second, subjecting the vessel wall model to the normal pressure often makes the configuration deviate from the original geometry obtained from medical images. To address those technical challenges, in this work, we propose a two-step optimization approach; first, we estimate constitutive parameters of a healthy human aorta intrinsic t... Biomechanics and Modeling in Mechanobiology journals http://www.medworm.com/rss/comments.php?id=4164140 Sat, 06 Nov 2010 00:00:00 +0100 4164140 http://www.medworm.com/index.php?rid=4164141&cid=s_37325_61_f&fid=37325&url=http%3A%2F%2Fwww.ncbi.nlm.nih.gov%2Fentrez%2Fquery.fcgi%3Ftmpl%3DNoSidebarfile%26db%3DPubMed%26cmd%3DRetrieve%26list_uids%3D21053042%26dopt%3DAbstract Authors: Cox LG, van Rietbergen B, van Donkelaar CC, Ito K Bone has an architecture which is optimized for its mechanical environment. In various conditions, this architecture is altered, and the underlying cause for this change is not always known. In the present paper, we investigated the sensitivity of the bone microarchitecture for four factors: changes in bone cellular activity, changes in mechanical loading, changes in mechanotransduction, and changes in mechanical tissue properties. The goal was to evaluate whether these factors can be the cause of typical bone structural changes seen in various pathologies. For this purpose, we used an established computational model for the simulation of bone adaptation. We performed two sensitivity analyses to evaluate the effect of the four ... Biomechanics and Modeling in Mechanobiology journals http://www.medworm.com/rss/comments.php?id=4164141 Fri, 05 Nov 2010 00:00:00 +0100 4164141 http://www.medworm.com/index.php?rid=4164139&cid=s_37325_61_f&fid=37325&url=http%3A%2F%2Fwww.ncbi.nlm.nih.gov%2Fentrez%2Fquery.fcgi%3Ftmpl%3DNoSidebarfile%26db%3DPubMed%26cmd%3DRetrieve%26list_uids%3D21053044%26dopt%3DAbstract Authors: Lutz A, Nackenhorst U, von Lewinski G, Windhagen H, Floerkemeier T Numerical investigations with regard to the subtrochanteric fracture risk induced by three alternative methods for the treatment of femoral head necrosis are outlined in this presentation. The traditional core decompression technique will be compared with minimal invasive multiple low diameter drillings and the implantation of an innovative tantalum implant. With emphasis to the newly introduced computational strategies and modeling approaches, the modeling of critical loading conditions as well as mesh convergence is outlined in detail. In addition to the immediate postoperative fracture risk, the long-term stability of the different approaches for treating femoral head necrosis is predicted by performing well... Biomechanics and Modeling in Mechanobiology journals http://www.medworm.com/rss/comments.php?id=4164139 Thu, 04 Nov 2010 00:00:00 +0100 4164139 http://www.medworm.com/index.php?rid=4134833&cid=s_37325_61_f&fid=37325&url=http%3A%2F%2Fwww.ncbi.nlm.nih.gov%2Fentrez%2Fquery.fcgi%3Ftmpl%3DNoSidebarfile%26db%3DPubMed%26cmd%3DRetrieve%26list_uids%3D21046424%26dopt%3DAbstract This study presents a constrained mixture model for postnatal development of mouse aorta with multiple step increases in pressure, length and flow. The baseline model assumes that smooth muscle cells (SMCs) in the vessel wall immediately constrict or dilate the inner radius after a perturbation to maintain the shear stress and then remodel the wall thickness to maintain the circumferential stress. The elastin, collagen and SMCs have homeostatic stretch ratios and passive material constants that do not change with developmental age. The baseline model does not predict previously published experimental data. To approximate the experimental data, it must be assumed that the SMCs dilate a constant amount, regardless of the step change in mechanical forces. It must also be assumed that the home... Biomechanics and Modeling in Mechanobiology journals http://www.medworm.com/rss/comments.php?id=4134833 Wed, 03 Nov 2010 00:00:00 +0100 4134833 http://www.medworm.com/index.php?rid=4106933&cid=s_37325_61_f&fid=37325&url=http%3A%2F%2Fwww.ncbi.nlm.nih.gov%2Fentrez%2Fquery.fcgi%3Ftmpl%3DNoSidebarfile%26db%3DPubMed%26cmd%3DRetrieve%26list_uids%3D20967483%26dopt%3DAbstract In this study, it was hypothesized that Pluronic F-68 (PLF-68) increases matrix synthesis of osteoarthritis (OA) chondrocytes in addition to its well-documented cell survival effect. To test this hypothesis, rat articular chondrocytes were embedded in agarose discs and were exposed to 5-azacytidine (Aza-C) to induce OA-like alterations. Chondrocytes were then treated with PLF-68 (8 and 12 mg/ml) for 10 days. Aza-C-exposed and PLF-68-untreated chondrocytes and Aza-C-unexposed and PLF-68-untreated chondrocytes were used as negative and positive control groups, respectively. Dynamic hydrostatic pressure (max 0.2 MPa, 0.1 Hz) was applied to discs for 30 min/day (5 days/week). Cell viability, collagen and proteoglycan deposition in discs were determined. Unconfined compression stress rela... Biomechanics and Modeling in Mechanobiology journals http://www.medworm.com/rss/comments.php?id=4106933 Thu, 21 Oct 2010 23:00:00 +0100 4106933 http://www.medworm.com/index.php?rid=4087533&cid=s_37325_61_f&fid=37325&url=http%3A%2F%2Fwww.ncbi.nlm.nih.gov%2Fentrez%2Fquery.fcgi%3Ftmpl%3DNoSidebarfile%26db%3DPubMed%26cmd%3DRetrieve%26list_uids%3D20963623%26dopt%3DAbstract Authors: Zou Y, Zhang Y In this paper, we studied the viscoelastic behaviors of isolated aortic elastin using combined modeling and experimental approaches. Biaxial stress relaxation and creep experiments were performed to study the time-dependent behavior of elastin. Experimental results reveal that stress relaxation preconditioning is necessary in order to obtain repeatable stress relaxation responses. Elastin exhibits less stress relaxation than intact or decellularized aorta. The rate of stress relaxation of intact and decellularized aorta is linearly dependent on the initial stress levels. The rate of stress relaxation for elastin increases linearly at stress levels below about 60 kPa; however, the rate changes very slightly at higher initial stress levels. Experimental results a... Biomechanics and Modeling in Mechanobiology journals http://www.medworm.com/rss/comments.php?id=4087533 Wed, 20 Oct 2010 23:00:00 +0100 4087533 http://www.medworm.com/index.php?rid=4039783&cid=s_37325_61_f&fid=37325&url=http%3A%2F%2Fwww.ncbi.nlm.nih.gov%2Fentrez%2Fquery.fcgi%3Ftmpl%3DNoSidebarfile%26db%3DPubMed%26cmd%3DRetrieve%26list_uids%3D20922556%26dopt%3DAbstract Authors: Lemon G, Howard D, Yang H, Ratchev SM, Segal JI, Rose FR, Jensen OE, Waters SL, King JR This paper presents a mathematical model to describe the growth of tissue into a rapid-prototyped porous scaffold when it is implanted onto the chorioallantoic membrane (CAM). The scaffold was designed to study the effects of the size and shape of pores on tissue growth into conventional tissue engineering scaffolds, and consists of an array of pores each having a pre-specified shape. The experimental observations revealed that the CAM grows through each pore as an intact layer of tissue, provided the width of the pore exceeds a threshold value. Based on these results a mathematical model is described to simulate the growth of the membrane, assuming that the growth is a function of the loca... Biomechanics and Modeling in Mechanobiology journals http://www.medworm.com/rss/comments.php?id=4039783 Mon, 04 Oct 2010 23:00:00 +0100 4039783 http://www.medworm.com/index.php?rid=4025129&cid=s_37325_61_f&fid=37325&url=http%3A%2F%2Fwww.ncbi.nlm.nih.gov%2Fentrez%2Fquery.fcgi%3Ftmpl%3DNoSidebarfile%26db%3DPubMed%26cmd%3DRetrieve%26list_uids%3D20878440%26dopt%3DAbstract Authors: Branigan T, Bolster D, Vázquez BY, Intaglietta M, Tartakovsky DM The level of hematocrit (Hct) is known to affect mean arterial pressure (MAP) by influencing blood viscosity. In the healthy population, an increase in Hct (and corresponding increase in viscosity) tends to raise MAP. However, data from a clinical study of type 2 diabetic patients indicate that this relationship is not universal. Instead, individuals in the lower levels of Hct range display a decrease in MAP for a given rise in Hct. After reaching a minimum, this trend is reversed, so that further increases in Hct lead to increases in MAP. We hypothesize that this anomalous behavior occurs due to changes in the circulatory autoregulation mechanism. To substantiate this hypothesis, we develop a physically based... Biomechanics and Modeling in Mechanobiology journals http://www.medworm.com/rss/comments.php?id=4025129 Tue, 28 Sep 2010 23:00:00 +0100 4025129 http://www.medworm.com/index.php?rid=4025131&cid=s_37325_61_f&fid=37325&url=http%3A%2F%2Fwww.ncbi.nlm.nih.gov%2Fentrez%2Fquery.fcgi%3Ftmpl%3DNoSidebarfile%26db%3DPubMed%26cmd%3DRetrieve%26list_uids%3D20865436%26dopt%3DAbstract Authors: Sacco R, Causin P, Zunino P, Raimondi MT In vitro tissue engineering is investigated as a potential source of functional tissue constructs for cartilage repair, as well as a model system for controlled studies of cartilage development and function. Among the different kinds of devices for the cultivation of 3D cartilage cell colonies, we consider here polymeric scaffold-based perfusion bioreactors, where an interstitial fluid supplies nutrients and oxygen to the growing biomass. At the same time, the fluid-induced shear acts as a physiologically relevant stimulus for the metabolic activity of cells, provided that the shear stress level is appropriately tuned. In this complex environment, mathematical and computational modeling can help in the optimal design of the bioreactor c... Biomechanics and Modeling in Mechanobiology journals http://www.medworm.com/rss/comments.php?id=4025131 Thu, 23 Sep 2010 23:00:00 +0100 4025131 http://www.medworm.com/index.php?rid=4025130&cid=s_37325_61_f&fid=37325&url=http%3A%2F%2Fwww.ncbi.nlm.nih.gov%2Fentrez%2Fquery.fcgi%3Ftmpl%3DNoSidebarfile%26db%3DPubMed%26cmd%3DRetrieve%26list_uids%3D20865437%26dopt%3DAbstract This study predicted critical variations of fluid shear stress when cells differentiated. If these variations are not controlled in vitro, they can impede the formation of new matured tissue. PMID: 20865437 [PubMed - as supplied by publisher] (Source: Biomechanics and Modeling in Mechanobiology) Biomechanics and Modeling in Mechanobiology journals http://www.medworm.com/rss/comments.php?id=4025130 Thu, 23 Sep 2010 23:00:00 +0100 4025130 http://www.medworm.com/index.php?rid=3987708&cid=s_37325_61_f&fid=37325&url=http%3A%2F%2Fwww.ncbi.nlm.nih.gov%2Fentrez%2Fquery.fcgi%3Ftmpl%3DNoSidebarfile%26db%3DPubMed%26cmd%3DRetrieve%26list_uids%3D20853016%26dopt%3DAbstract Authors: Thompson MS, Abercrombie SR, Ott CE, Bieler FH, Duda GN, Ventikos Y A widely used commercially available system for the investigation of mechanosensitivity applies a biaxial strain field to cells cultured on a compliant silicone substrate membrane stretched over a central post. As well as intended substrate strain, this device also provides a fluid flow environment for the cultured cells. In order to interpret the relevance of experiments using this device to the in vivo and clinical situation, it is essential to characterise both substrate and fluid environments. While previous work has detailed the substrate strain, the fluid shear stresses, to which bone cells are known to be sensitive, are unknown. Therefore, a fluid structure interaction computational fluid dynamics model... Biomechanics and Modeling in Mechanobiology journals http://www.medworm.com/rss/comments.php?id=3987708 Fri, 17 Sep 2010 23:00:00 +0100 3987708 http://www.medworm.com/index.php?rid=3953300&cid=s_37325_61_f&fid=37325&url=http%3A%2F%2Fwww.ncbi.nlm.nih.gov%2Fentrez%2Fquery.fcgi%3Ftmpl%3DNoSidebarfile%26db%3DPubMed%26cmd%3DRetrieve%26list_uids%3D20827500%26dopt%3DAbstract Authors: Peiffer V, Gerisch A, Vandepitte D, Van Oosterwyck H, Geris L Bone fracture healing is a complex process in which angiogenesis or the development of a blood vessel network plays a crucial role. In this paper, a mathematical model is presented that simulates the biological aspects of fracture healing including the formation of individual blood vessels. The model consists of partial differential equations, several of which describe the evolution in density of the most important cell types, growth factors, tissues and nutrients. The other equations determine the growth of blood vessels as a result of the movement of leading endothelial (tip) cells. Branching and anastomoses are accounted for in the model. The model is applied to a normal fracture healing case and subjected to a s... Biomechanics and Modeling in Mechanobiology journals http://www.medworm.com/rss/comments.php?id=3953300 Wed, 08 Sep 2010 23:00:00 +0100 3953300 http://www.medworm.com/index.php?rid=3953301&cid=s_37325_61_f&fid=37325&url=http%3A%2F%2Fwww.ncbi.nlm.nih.gov%2Fentrez%2Fquery.fcgi%3Ftmpl%3DNoSidebarfile%26db%3DPubMed%26cmd%3DRetrieve%26list_uids%3D20821245%26dopt%3DAbstract Authors: Kindberg K, Oom C, Ingels NB, Karlsson M Left ventricular myofibers are connected by an extensive extracellular collagen matrix to form myolaminar sheets. Histological cardiac tissue studies have previously observed a pleated transmural distribution of sheets in the ovine heart, alternating sign of the sheet angle from epicardium to endocardium. The present study investigated temporal variations in myocardial fiber and sheet architecture during the cardiac cycle. End-diastolic histological measurements made at subepicardium, midwall, and subendocardium at an anterior-basal and a lateral-equatorial region of the ovine heart, combined with transmural myocardial Lagrangian strains, showed that the sheet angle but not the fiber angle varied temporally throughout the cardiac cycle.... Biomechanics and Modeling in Mechanobiology journals http://www.medworm.com/rss/comments.php?id=3953301 Mon, 06 Sep 2010 23:00:00 +0100 3953301 http://www.medworm.com/index.php?rid=3953302&cid=s_37325_61_f&fid=37325&url=http%3A%2F%2Fwww.ncbi.nlm.nih.gov%2Fentrez%2Fquery.fcgi%3Ftmpl%3DNoSidebarfile%26db%3DPubMed%26cmd%3DRetrieve%26list_uids%3D20809392%26dopt%3DAbstract In this study, we applied a method to estimate the 3D geometrical shape of bone based on a 2D BMD image and a femur shape template. Proximal femurs of eighteen human cadavers were imaged with computed tomography (CT) and divided into two groups. Image data from the first group (N = 9) were applied to create a shape template by using the general Procrustes analysis and thin plate splines. This template was then applied to estimate the shape of the femurs in the second group (N = 9), using the 2D BMD image projected from the CT image, and the geometrical errors of the shape estimation method were evaluated. Finally, finite element analysis with stance loading condition was conducted based on the original CT and the estimated geometrical shape to evaluate the effect of the geometrical errors ... Biomechanics and Modeling in Mechanobiology journals http://www.medworm.com/rss/comments.php?id=3953302 Tue, 31 Aug 2010 23:00:00 +0100 3953302 http://www.medworm.com/index.php?rid=3909911&cid=s_37325_61_f&fid=37325&url=http%3A%2F%2Fwww.ncbi.nlm.nih.gov%2Fentrez%2Fquery.fcgi%3Ftmpl%3DNoSidebarfile%26db%3DPubMed%26cmd%3DRetrieve%26list_uids%3D20737282%26dopt%3DAbstract This study explores the relationship between impact severity and resulting pulmonary contusion (PC) for four impact conditions using a rat model of the injury. The force-deflection response from a Finite Element (FE) model of the lung was simultaneously matched to experimental data from distinct impacts via a genetic algorithm optimization. Sprague-Dawley rats underwent right-side thoracotomy prior to impact. Insults were applied directly to the lung via an instrumented piston. Five cohorts were tested: a sham group and four groups experiencing lung insults of varying degrees of severity. The values for impact velocity (V) and penetration depth (D) of the cohorts were Group 1, (V = 6.0 m . s(-1), D = 5.0 mm), Group 2, (V = 1.5 m . s(-1),D = 5.0 mm), Group 3, (V = 6 m . s(-1), D = 2.0 mm), ... Biomechanics and Modeling in Mechanobiology journals http://www.medworm.com/rss/comments.php?id=3909911 Tue, 24 Aug 2010 23:00:00 +0100 3909911 http://www.medworm.com/index.php?rid=3909912&cid=s_37325_61_f&fid=37325&url=http%3A%2F%2Fwww.ncbi.nlm.nih.gov%2Fentrez%2Fquery.fcgi%3Ftmpl%3DNoSidebarfile%26db%3DPubMed%26cmd%3DRetrieve%26list_uids%3D20734100%26dopt%3DAbstract In this study, we investigated the effects of anisotropy by varying the relative stiffness between the fibre and the matrix components, whilst maintaining the same overall stress-strain response in the fibre direction. A foetal skull was passed through two pelvic floor models, which incorporated the LA muscle with different anisotropy ratios. Results showed a substantial decrease in the magnitude of the force required for delivery as the fibre anisotropy was increased. The anisotropy ratio markedly affected the mechanical response of the LA muscle during a simulated vaginal delivery. It is apparent that we need to obtain experimental data on muscle mechanics in order to better approximate the LA muscle mechanical properties for quantitative analysis. These models may advance our understand... Biomechanics and Modeling in Mechanobiology journals http://www.medworm.com/rss/comments.php?id=3909912 Mon, 23 Aug 2010 23:00:00 +0100 3909912 http://www.medworm.com/index.php?rid=3890656&cid=s_37325_61_f&fid=37325&url=http%3A%2F%2Fwww.ncbi.nlm.nih.gov%2Fentrez%2Fquery.fcgi%3Ftmpl%3DNoSidebarfile%26db%3DPubMed%26cmd%3DRetrieve%26list_uids%3D20725846%26dopt%3DAbstract Authors: Klöppel T, Wall WA A novel finite element approach is presented to simulate the mechanical behavior of human red blood cells (RBC, erythrocytes). As the RBC membrane comprises a phospholipid bilayer with an intervening protein network, we propose to model the membrane with two distinct layers. The fairly complex characteristics of the very thin lipid bilayer are represented by special incompressible solid shell elements and an anisotropic viscoelastic constitutive model. Properties of the protein network are modeled with an isotropic hyperelastic third-order material. The elastic behavior of the model is validated with existing optical tweezers studies with quasi-static deformations. Employing material parameters consistent with literature, simulation results are in excelle... Biomechanics and Modeling in Mechanobiology journals http://www.medworm.com/rss/comments.php?id=3890656 Thu, 19 Aug 2010 23:00:00 +0100 3890656 http://www.medworm.com/index.php?rid=3890657&cid=s_37325_61_f&fid=37325&url=http%3A%2F%2Fwww.ncbi.nlm.nih.gov%2Fentrez%2Fquery.fcgi%3Ftmpl%3DNoSidebarfile%26db%3DPubMed%26cmd%3DRetrieve%26list_uids%3D20721679%26dopt%3DAbstract Authors: Inoue Y, Adachi T Membrane protrusion is a mechanochemical process of active membrane deformation driven by actin polymerization. Previously, Brownian ratchet (BR) was modeled on the basis of the underlying molecular mechanism. However, because the BR requires a priori load that cannot be determined without information of the cell shape, it cannot be effective in studies in which resultant shapes are to be solved. Other cellular-scale models describing the protrusion have also been suggested for modeling a whole cell; however, these models were not developed on the basis of coarse-grained physics representing the underlying molecular mechanism. Therefore, to express the membrane protrusion on the cellular scale, we propose a novel mathematical model, the coarse-grained BR (CBR... Biomechanics and Modeling in Mechanobiology journals http://www.medworm.com/rss/comments.php?id=3890657 Wed, 18 Aug 2010 23:00:00 +0100 3890657 http://www.medworm.com/index.php?rid=3869280&cid=s_37325_61_f&fid=37325&url=http%3A%2F%2Fwww.ncbi.nlm.nih.gov%2Fentrez%2Fquery.fcgi%3Ftmpl%3DNoSidebarfile%26db%3DPubMed%26cmd%3DRetrieve%26list_uids%3D20706764%26dopt%3DAbstract Authors: McGrath B, Mealing G, Labrosse MR Understanding mechanotransduction pathways leading to thrombosis will require progressive steps, including determination of the mechanical behavior of the platelet membrane in response to applied loads. The platelet membrane deformation capacity, as quantified by membrane progression into a borosilicate glass micropipette of defined internal diameter, was probed in murine platelets using a controlled range of negative pressure (0-7 cm H(2)O). Based on our observations that the platelet portion outside the micropipette was mostly spherical and that the platelet volume did not change upon aspiration, a novel continuum mechanics-based model of the platelet micropipette aspiration experiment was created, and a new hyperelastic isotropic material m... Biomechanics and Modeling in Mechanobiology journals http://www.medworm.com/rss/comments.php?id=3869280 Thu, 12 Aug 2010 23:00:00 +0100 3869280 http://www.medworm.com/index.php?rid=3869281&cid=s_37325_61_f&fid=37325&url=http%3A%2F%2Fwww.ncbi.nlm.nih.gov%2Fentrez%2Fquery.fcgi%3Ftmpl%3DNoSidebarfile%26db%3DPubMed%26cmd%3DRetrieve%26list_uids%3D20700624%26dopt%3DAbstract Authors: Owen JR, Wayne JS The superficial tangential zone (STZ) plays a significant role in normal articular cartilage's ability to support loads and retain fluids. To date, tissue engineering efforts have not replicated normal STZ function in cartilage repairs. This finite element study examined the STZ's role in normal and repaired articular surfaces under different contact conditions. Contact area and pressure distributions were allowed to change with time, tension-compression nonlinearity modeled collagen behavior in the STZ, and nonlinear geometry was incorporated to accommodate finite deformation. Responses to loading via impermeable and permeable rigid surfaces were compared to loading via normal cartilage, a more physiologic condition, anticipating the two rigid loading surfac... Biomechanics and Modeling in Mechanobiology journals http://www.medworm.com/rss/comments.php?id=3869281 Tue, 10 Aug 2010 23:00:00 +0100 3869281 http://www.medworm.com/index.php?rid=3850017&cid=s_37325_61_f&fid=37325&url=http%3A%2F%2Fwww.ncbi.nlm.nih.gov%2Fentrez%2Fquery.fcgi%3Ftmpl%3DNoSidebarfile%26db%3DPubMed%26cmd%3DRetrieve%26list_uids%3D20686811%26dopt%3DAbstract Authors: Varga P, Dall'ara E, Pahr DH, Pretterklieber M, Zysset PK Osteoporotic (Colles' type) fractures of the distal radius occur relatively early in lifetime and could estimate risk of fracture of other, more endangered anatomical sites. High-resolution peripheral quantitative computed tomography (HR-pQCT) based micro finite element (muFE) analysis was shown to better predict fracture load of the distal radius than densitometry or histomorphometric measures. As an alternative to muFE, homogenization-based FE (hFE) approach may provide at least equivalent predictive power with reduced computational needs. The aim of this study was to validate the hFE approach with compression tests of 25 distal radius sections extracted at the location which is relevant in Colles' fractures. HR-pQCT-... Biomechanics and Modeling in Mechanobiology journals http://www.medworm.com/rss/comments.php?id=3850017 Wed, 04 Aug 2010 23:00:00 +0100 3850017 http://www.medworm.com/index.php?rid=3823352&cid=s_37325_61_f&fid=37325&url=http%3A%2F%2Fwww.ncbi.nlm.nih.gov%2Fentrez%2Fquery.fcgi%3Ftmpl%3DNoSidebarfile%26db%3DPubMed%26cmd%3DRetrieve%26list_uids%3D20683635%26dopt%3DAbstract Authors: Akhter MP, Alvarez GK, Cullen DM, Recker RR Sedentary life style may degrade bone mass and microstructure resulting in osteoporosis. We characterized trabecular bone structural properties to determine if the LRP5 G171V mutation will protect against disuse-related bone loss. Forty-eight adult male mice representing three genotypes (WT = wild type, KO = LRP5-knockout +/-, HBM = High bone with the LRP5 G171V mutation) were each randomly divided between control and disuse (4 week hindlimb suspension) groups. Trabecular bone volume fraction (BV/TV) declined in all the three genotypes. Trabecular thickness was lower in the HBM and LRP5 (+/-) KO disuse groups when compared to their respective controls. While the remaining measures of bone structure (Trabecular number, connectivity de... Biomechanics and Modeling in Mechanobiology journals http://www.medworm.com/rss/comments.php?id=3823352 Tue, 03 Aug 2010 23:00:00 +0100 3823352 http://www.medworm.com/index.php?rid=3803111&cid=s_37325_61_f&fid=37325&url=http%3A%2F%2Fwww.ncbi.nlm.nih.gov%2Fentrez%2Fquery.fcgi%3Ftmpl%3DNoSidebarfile%26db%3DPubMed%26cmd%3DRetrieve%26list_uids%3D20652615%26dopt%3DAbstract Authors: Morbiducci U, Ponzini R, Rizzo G, Cadioli M, Esposito A, Montevecchi FM, Redaelli A The hemodynamics within the aorta of five healthy humans were investigated to gain insight into the complex helical flow patterns that arise from the existence of asymmetries in the aortic region. The adopted approach is aimed at (1) overcoming the relative paucity of quantitative data regarding helical blood flow dynamics in the human aorta and (2) identifying common characteristics in physiological aortic flow topology, in terms of its helical content. Four-dimensional phase-contrast magnetic resonance imaging (4D PC MRI) was combined with algorithms for the calculation of advanced fluid dynamics in this study. These algorithms allowed us to obtain a 4D representation of intra-aortic flow fie... Biomechanics and Modeling in Mechanobiology journals http://www.medworm.com/rss/comments.php?id=3803111 Wed, 21 Jul 2010 23:00:00 +0100 3803111 http://www.medworm.com/index.php?rid=3776667&cid=s_37325_61_f&fid=37325&url=http%3A%2F%2Fwww.ncbi.nlm.nih.gov%2Fentrez%2Fquery.fcgi%3Ftmpl%3DNoSidebarfile%26db%3DPubMed%26cmd%3DRetrieve%26list_uids%3D20640475%26dopt%3DAbstract Authors: Fraldi M, Cutolo A, Esposito L, Guarracino F A mechanical analysis of the conductive keratoplasty on hyperopic eyes has been carried out, and the attention has been focused on incorporating the actual viscoelastic properties of the human corneal tissue and on the stress gradients induced by the intervention. By avoiding unnecessary complications which may obscure the essential behaviour of the model, the results are in very good agreement with the clinical and experimental findings and suggest that the major role in the commonly observed decrease of the initial degree of the refractive correction might be played by the stress gradients at the intervention spots, which are likely to influence the wound-healing. The study aims to contribute some firm mechanical roots to the pred... Biomechanics and Modeling in Mechanobiology journals http://www.medworm.com/rss/comments.php?id=3776667 Fri, 16 Jul 2010 23:00:00 +0100 3776667 http://www.medworm.com/index.php?rid=3764524&cid=s_37325_61_f&fid=37325&url=http%3A%2F%2Fwww.ncbi.nlm.nih.gov%2Fentrez%2Fquery.fcgi%3Ftmpl%3DNoSidebarfile%26db%3DPubMed%26cmd%3DRetrieve%26list_uids%3D20635116%26dopt%3DAbstract In this study, a relation between the mechanical state at the tissue level and the cellular level is established. A model has been developed that is based on pathological observations of local axonal injury. The model contains axons surrounding an obstacle (e.g., a blood vessel or a brain soma). The axons, which are described by an anisotropic fiber-reinforced material model, have several physically different orientations. The results of the simulations reveal axonal strains being higher than the applied maximum principal tissue strain. For anisotropic brain tissue with a relatively stiff inclusion, the relative logarithmic strain increase is above 60%. Furthermore, it is concluded that individual axons oriented away from the main axonal direction at a specific site can be subjected to eve... Biomechanics and Modeling in Mechanobiology journals http://www.medworm.com/rss/comments.php?id=3764524 Thu, 15 Jul 2010 23:00:00 +0100 3764524 http://www.medworm.com/index.php?rid=3758761&cid=s_37325_61_f&fid=37325&url=http%3A%2F%2Fwww.ncbi.nlm.nih.gov%2Fentrez%2Fquery.fcgi%3Ftmpl%3DNoSidebarfile%26db%3DPubMed%26cmd%3DRetrieve%26list_uids%3D20628781%26dopt%3DAbstract Authors: Grytz R, Meschke G, Jonas JB The biomechanics of the optic nerve head is assumed to play an important role in ganglion cell loss in glaucoma. Organized collagen fibrils form complex networks that introduce strong anisotropic and nonlinear attributes into the constitutive response of the peripapillary sclera (PPS) and lamina cribrosa (LC) dominating the biomechanics of the optic nerve head. The recently presented computational remodeling approach (Grytz and Meschke in Biomech Model Mechanobiol 9:225-235, 2010) was used to predict the micro-architecture in the LC and PPS, and to investigate its impact on intraocular pressure-related deformations. The mechanical properties of the LC and PPS were derived from a microstructure-oriented constitutive model that included the stretch-d... Biomechanics and Modeling in Mechanobiology journals http://www.medworm.com/rss/comments.php?id=3758761 Tue, 13 Jul 2010 23:00:00 +0100 3758761 http://www.medworm.com/index.php?rid=3758760&cid=s_37325_61_f&fid=37325&url=http%3A%2F%2Fwww.ncbi.nlm.nih.gov%2Fentrez%2Fquery.fcgi%3Ftmpl%3DNoSidebarfile%26db%3DPubMed%26cmd%3DRetrieve%26list_uids%3D20628782%26dopt%3DAbstract This study presents a step toward those goals. PMID: 20628782 [PubMed - as supplied by publisher] (Source: Biomechanics and Modeling in Mechanobiology) Biomechanics and Modeling in Mechanobiology journals http://www.medworm.com/rss/comments.php?id=3758760 Tue, 13 Jul 2010 23:00:00 +0100 3758760 http://www.medworm.com/index.php?rid=3733263&cid=s_37325_61_f&fid=37325&url=http%3A%2F%2Fwww.ncbi.nlm.nih.gov%2Fentrez%2Fquery.fcgi%3Ftmpl%3DNoSidebarfile%26db%3DPubMed%26cmd%3DRetrieve%26list_uids%3D20602142%26dopt%3DAbstract Authors: Nguyen TD, Boyce BL An inverse finite element method was developed to determine the anisotropic properties of bovine cornea from an in vitro inflation experiment. The experiment used digital image correlation (DIC) to measure the three-dimensional surface geometry and displacement field of the cornea at multiple pressures. A finite element model of a bovine cornea was developed using the DIC measured surface geometry of the undeformed specimen. The model was applied to determine five parameters of an anisotropic hyperelastic model that minimized the error between the measured and computed surface displacement field and to investigate the sensitivity of the measured bovine inflation response to variations in the anisotropic properties of the cornea. The results of the parameter... Biomechanics and Modeling in Mechanobiology journals http://www.medworm.com/rss/comments.php?id=3733263 Fri, 02 Jul 2010 23:00:00 +0100 3733263 http://www.medworm.com/index.php?rid=3733264&cid=s_37325_61_f&fid=37325&url=http%3A%2F%2Fwww.ncbi.nlm.nih.gov%2Fentrez%2Fquery.fcgi%3Ftmpl%3DNoSidebarfile%26db%3DPubMed%26cmd%3DRetrieve%26list_uids%3D20596743%26dopt%3DAbstract Authors: Martínez-Reina J, Domínguez J, García-Aznar JM A micromechanical multiscale model which estimates the elastic properties of cortical bone as a function of porosity and mineral content is presented. The steps of the model are divided into two main phases. In the first one, the elastic properties of the collagen fibril, collagen fiber and lamella are given. In the second phase, porosity is included in the lamella in the form of canaliculi, lacunae and Haversian canals, to provide the elastic properties of the osteonal tissue. Then, a symmetrization technique is used to estimate the transversely isotropic elasticity tensor of the osteon. Osteons are superimposed using a self-consistent scheme, and finally, the fluid filling the pores is included to estimate the elastic c... Biomechanics and Modeling in Mechanobiology journals http://www.medworm.com/rss/comments.php?id=3733264 Thu, 01 Jul 2010 23:00:00 +0100 3733264 http://www.medworm.com/index.php?rid=3719246&cid=s_37325_61_f&fid=37325&url=http%3A%2F%2Fwww.ncbi.nlm.nih.gov%2Fentrez%2Fquery.fcgi%3Ftmpl%3DNoSidebarfile%26db%3DPubMed%26cmd%3DRetrieve%26list_uids%3D20589408%26dopt%3DAbstract Authors: Gurev V, Lee T, Constantino J, Arevalo H, Trayanova NA Current multi-scale computational models of ventricular electromechanics describe the full process of cardiac contraction on both the micro- and macro- scales including: the depolarization of cardiac cells, the release of calcium from intracellular stores, tension generation by cardiac myofilaments, and mechanical contraction of the whole heart. Such models are used to reveal basic mechanisms of cardiac contraction as well as the mechanisms of cardiac dysfunction in disease conditions. In this paper, we present a methodology to construct finite element electromechanical models of ventricular contraction with anatomically accurate ventricular geometry based on magnetic resonance and diffusion tensor magnetic resonance imagi... Biomechanics and Modeling in Mechanobiology journals http://www.medworm.com/rss/comments.php?id=3719246 Tue, 29 Jun 2010 23:00:00 +0100 3719246 http://www.medworm.com/index.php?rid=3707533&cid=s_37325_61_f&fid=37325&url=http%3A%2F%2Fwww.ncbi.nlm.nih.gov%2Fentrez%2Fquery.fcgi%3Ftmpl%3DNoSidebarfile%26db%3DPubMed%26cmd%3DRetrieve%26list_uids%3D20582612%26dopt%3DAbstract Authors: Félix Quiñonez A, Summers JL, Fisher J, Jin ZM A simplified analytical solution has been obtained for the radial and tangential displacements on the surface of a thin, hemispherical layer of porous-elastic articular cartilage firmly bonded to a rigid foundation. A static pressure distributed according to a paraboloid of revolution is applied simulating cartilage compression by a porous indenter. The solution method is in the form of an asymptotic series and uses Laplace transforms. The analytical predictions are in qualitative agreement with the behaviour of biphasic articular cartilage reported in the literature. A direct comparison with numerical simulations using commercially available Finite Element Modelling (FEM) software was also carried out for conditions relevan... Biomechanics and Modeling in Mechanobiology journals http://www.medworm.com/rss/comments.php?id=3707533 Sat, 26 Jun 2010 23:00:00 +0100 3707533 http://www.medworm.com/index.php?rid=3672701&cid=s_37325_61_f&fid=37325&url=http%3A%2F%2Fwww.ncbi.nlm.nih.gov%2Fentrez%2Fquery.fcgi%3Ftmpl%3DNoSidebarfile%26db%3DPubMed%26cmd%3DRetrieve%26list_uids%3D20556629%26dopt%3DAbstract Authors: van den Broek CN, van der Horst A, Rutten MC, van de Vosse FN Constitutive models describing the arterial mechanical behavior are important in the development of catheterization products, to be used in arteries with a specific radius. To prove the possible existence of a constitutive model that, provided with a generic set of material and geometric parameters, is able to predict the radius-specific mechanical behavior of a coronary artery, the passive pressure-inner radius (P-r ( i )) and pressure-axial force change (P-DeltaF ( z )) relations of seven porcine left anterior descending coronary arteries were measured in an in-vitro set-up and fitted with the model of Driessen et al. in J Biomech Eng 127(3):494-503 (2005), Biomech Model Mechanobiol 7(2):93-103 (2008). Additionall... Biomechanics and Modeling in Mechanobiology journals http://www.medworm.com/rss/comments.php?id=3672701 Wed, 16 Jun 2010 23:00:00 +0100 3672701 http://www.medworm.com/index.php?rid=3672702&cid=s_37325_61_f&fid=37325&url=http%3A%2F%2Fwww.ncbi.nlm.nih.gov%2Fentrez%2Fquery.fcgi%3Ftmpl%3DNoSidebarfile%26db%3DPubMed%26cmd%3DRetrieve%26list_uids%3D20549292%26dopt%3DAbstract We present an integrated experimental-computational mechanobiology model of chondrogenesis. The response of human articular chondrocytes to culture medium perfusion, versus perfusion associated with cyclic pressurisation, versus non-perfused culture, was compared in a pellet culture model, and multiphysic computation was used to quantify oxygen transport and flow dynamics in the various culture conditions. At 2 weeks of culture, the measured cell metabolic activity and the matrix content in collagen type II and aggrecan were greatest in the perfused+pressurised pellets. The main effects of perfusion alone, relative to static controls, were to suppress collagen type I and GAG contents, which were greatest in the non-perfused pellets. All pellets showed a peripheral layer of proliferating ce... Biomechanics and Modeling in Mechanobiology journals http://www.medworm.com/rss/comments.php?id=3672702 Fri, 11 Jun 2010 23:00:00 +0100 3672702 http://www.medworm.com/index.php?rid=3653046&cid=s_37325_61_f&fid=37325&url=http%3A%2F%2Fwww.ncbi.nlm.nih.gov%2Fentrez%2Fquery.fcgi%3Ftmpl%3DNoSidebarfile%26db%3DPubMed%26cmd%3DRetrieve%26list_uids%3D20532944%26dopt%3DAbstract Conclusions of this study are particularly relevant to patient-specific models or artificial disc designs. PMID: 20532944 [PubMed - as supplied by publisher] (Source: Biomechanics and Modeling in Mechanobiology) Biomechanics and Modeling in Mechanobiology journals http://www.medworm.com/rss/comments.php?id=3653046 Tue, 08 Jun 2010 23:00:00 +0100 3653046 http://www.medworm.com/index.php?rid=3653047&cid=s_37325_61_f&fid=37325&url=http%3A%2F%2Fwww.ncbi.nlm.nih.gov%2Fentrez%2Fquery.fcgi%3Ftmpl%3DNoSidebarfile%26db%3DPubMed%26cmd%3DRetrieve%26list_uids%3D20532586%26dopt%3DAbstract Authors: Liu Q, Zeng M, Fu BM To investigate microvascular hyperpermeability and thrombosis induced by photodynamic therapy or light/dye treatment, we quantified the initiation time for thrombus formation, thrombus growth rate, and the time for the microvessel occlusion in post-capillary venules of rat mesenteries. Under similar light/dye treatments, we also measured the microvessel hydraulic conductivity (Lp) and solute permeability (P) to TRITC-BSA (bovine serum albumin), respectively, in the same type of microvessels as for thrombosis. Under an irradiation power of 0.37 mW/mm(2), thrombus was initiated in 3.8 +/- 0.4 min, its growth rate was 3.9 +/- 0.3% of the vessel mid-plane area/min, and the microvessels were completely occluded in 29.3 +/- 2.2 min (SE, n = 8). Under the same ir... Biomechanics and Modeling in Mechanobiology journals http://www.medworm.com/rss/comments.php?id=3653047 Mon, 07 Jun 2010 23:00:00 +0100 3653047 http://www.medworm.com/index.php?rid=3641838&cid=s_37325_61_f&fid=37325&url=http%3A%2F%2Fwww.ncbi.nlm.nih.gov%2Fentrez%2Fquery.fcgi%3Ftmpl%3DNoSidebarfile%26db%3DPubMed%26cmd%3DRetrieve%26list_uids%3D20526790%26dopt%3DAbstract Authors: van Turnhout MC, Kranenbarg S, van Leeuwen JL The collagen fibril network is an important factor for the depth-dependent mechanical behaviour of adult articular cartilage (AC). Recent studies show that collagen orientation is parallel to the articular surface throughout the tissue depth in perinatal animals, and that the collagen orientations transform to a depth-dependent arcade-like structure in adult animals. Current understanding on the mechanobiology of postnatal AC development is incomplete. In the current paper, we investigate the contribution of collagen fibril orientation changes to the depth-dependent mechanical properties of AC. We use a composition-based finite element model to simulate in a 1-D confined compression geometry the effects of ten different collagen or... Biomechanics and Modeling in Mechanobiology journals http://www.medworm.com/rss/comments.php?id=3641838 Sat, 05 Jun 2010 23:00:00 +0100 3641838 http://www.medworm.com/index.php?rid=3641840&cid=s_37325_61_f&fid=37325&url=http%3A%2F%2Fwww.ncbi.nlm.nih.gov%2Fentrez%2Fquery.fcgi%3Ftmpl%3DNoSidebarfile%26db%3DPubMed%26cmd%3DRetrieve%26list_uids%3D20526729%26dopt%3DAbstract Authors: Zhang NH, Shan JY Experiments show that deflections of microcantilever-DNA chip can be induced by many factors, such as grafting density, hybridization efficiency, concentration, length and sequence of DNA molecules, buffer salt concentration, time, and temperature variation. However, there are few theoretical works on microcantilever-DNA chips. The present paper is aimed to study the influence of counterion effects of single-stranded DNA (ssDNA) polyelectrolyte solution on the nanomechanical behaviors of microcantilever-based ssDNA chips during packing process. First, the effect of osmotic pressure induced by ingress of counterions into DNA brush structures is studied with Hagan's model for a cylindrical polyelectrolyte brush system on the basis of Poisson-Boltzmann distribut... Biomechanics and Modeling in Mechanobiology journals http://www.medworm.com/rss/comments.php?id=3641840 Fri, 04 Jun 2010 23:00:00 +0100 3641840 http://www.medworm.com/index.php?rid=3641839&cid=s_37325_61_f&fid=37325&url=http%3A%2F%2Fwww.ncbi.nlm.nih.gov%2Fentrez%2Fquery.fcgi%3Ftmpl%3DNoSidebarfile%26db%3DPubMed%26cmd%3DRetrieve%26list_uids%3D20526730%26dopt%3DAbstract Authors: Li Z, Yang W It was reported that a single-strand DNA (ssDNA) could be inbreathed spontaneously into a carbon nanotube (CNT). In this work, the complementary process, i.e. pulling a piece of ssDNA out of a single-walled (SW) CNT, is simulated using molecular dynamic methods. The pulling force is found to fluctuate around a plateau of 250 pN with the base types identifiable by the varying amplitudes. One may thus numerate the bases in DNA by counting the fluctuation repetition or detect the information of DNA sequence by considering the fluctuating amplitudes. PMID: 20526730 [PubMed - as supplied by publisher] (Source: Biomechanics and Modeling in Mechanobiology) Biomechanics and Modeling in Mechanobiology journals http://www.medworm.com/rss/comments.php?id=3641839 Fri, 04 Jun 2010 23:00:00 +0100 3641839 http://www.medworm.com/index.php?rid=3633096&cid=s_37325_61_f&fid=37325&url=http%3A%2F%2Fwww.ncbi.nlm.nih.gov%2Fentrez%2Fquery.fcgi%3Ftmpl%3DNoSidebarfile%26db%3DPubMed%26cmd%3DRetrieve%26list_uids%3D20521160%26dopt%3DAbstract Authors: Yuan F, Stock SR, Haeffner DR, Almer JD, Dunand DC, Brinson LC Bone, because of its hierarchical composite structure, exhibits an excellent combination of stiffness and toughness, which is due substantially to the structural order and deformation at the smaller length scales. Here, we focus on the mineralized collagen fibril, consisting of hydroxyapatite plates with nanometric dimensions aligned within a protein matrix, and emphasize the relationship between the structure and elastic properties of a mineralized collagen fibril. We create two- and three-dimensional representative volume elements to represent the structure of the fibril and evaluate the importance of the parameters defining its structure and properties of the constituent mineral and collagen phase. Elastic stiff... Biomechanics and Modeling in Mechanobiology journals http://www.medworm.com/rss/comments.php?id=3633096 Wed, 02 Jun 2010 23:00:00 +0100 3633096 http://www.medworm.com/index.php?rid=3625943&cid=s_37325_61_f&fid=37325&url=http%3A%2F%2Fwww.ncbi.nlm.nih.gov%2Fentrez%2Fquery.fcgi%3Ftmpl%3DNoSidebarfile%26db%3DPubMed%26cmd%3DRetrieve%26list_uids%3D20512608%26dopt%3DAbstract Authors: Repetto R, Tatone A, Testa A, Colangeli E Posterior vitreous detachment is a fairly common condition in elderly people. Tractions exerted by the detached vitreous on the retina may result in retinal tears and detachments. We studied how these tractions can arise from saccadic eye movements. Numerical simulations have been performed on a two-dimensional model of the vitreous chamber within a rigid spherical sclera, subjected to prescribed finite-amplitude rotations about a vertical axis. The vitreous chamber was assumed to be split into two regions: one occupied by the detached vitreous, modeled as an elastic viscous solid, and the other occupied by the separated liquefied vitreous, modeled as a Newtonian fluid. At the interface between the two phases, we also considered the pr... Biomechanics and Modeling in Mechanobiology journals http://www.medworm.com/rss/comments.php?id=3625943 Sat, 29 May 2010 23:00:00 +0100 3625943