Studies have demonstrated the role mechanical stress plays in regulating osteoblastic functions, such as cellular proliferation, osteogenic differentiation, signal transduction and apoptosis (14-16,26). Energy metabolism is essential to maintaining the biological activities of osteoblasts (17). In the present study, we revealed a novel mechanism in osteoblastic mechanobiology, through which cyclic stretch promotes osteoblastic energy metabolism by increasing the expression of enzymes associated with energy metabolism, partially through the Akt/mTOR/p70s6k signaling pathway. Firstly, cyclic mechanical stretch promoted energy metabolism in the MG-63 cells, which was evidenced by the increased glucose consumption, and the increased levels of lactate, intracellular ATP, and energy metabolism-related genes (ATP5B, ATP5F1, ATP5J, F1-ATPase α, LDHA and enolase 1), and ATP5B and ATP5J proteins. Secondly, cyclic mechanical stretch stimulated the activation of the Akt/mTOR/p70s6k pathway by prompting the ...
TY - JOUR. T1 - Acoustically detectable cellular-level lung injury induced by fluid mechanical stresses in microfluidic airway systems. AU - Huh, Dongeun. AU - Fujioka, Hideki. AU - Tung, Yi Chung. AU - Futai, Nobuyuki. AU - Paine, Robert. AU - Grotberg, James B.. AU - Takayama, Shuichi. PY - 2007/11/27. Y1 - 2007/11/27. N2 - We describe a microfabricated airway system integrated with computerized air-liquid two-phase microfluidics that enables on-chip engineering of human airway epithelia and precise reproduction of physiologic or pathologic liquid plug flows found in the respiratory system. Using this device, we demonstrate cellular-level lung injury under flow conditions that cause symptoms characteristic of a wide range of pulmonary diseases. Specifically, propagation and rupture of liquid plugs that simulate surfactant-deficient reopening of closed airways lead to significant injury of small airway epithelial cells by generating deleterious fluid mechanical stresses. We also show that the ...
As modern helmets have become quite capable of defeating the penetration capabilities of ballistic threats, Soldiers may experience head injuries due to blunt trauma caused by helmet back face deformation (BFD). Possible resulting injuries include skull fracture, hematoma, concussion, contusion, diffuse axonal injury, etc. Some of these injuries have been associated with traumatic brain injury. In order to assess potential injury mechanisms prior to fielding new helmets, we have developed a means to experimentally replicate and measure helmet BFD that can be correlated to injury criteria. In this study, helmet performance test methodology is developed using a digital image correlation (DIC) technique. DIC provides the capability to measure dynamic displacements, thereby providing the ability to calculate deformation, velocity, and acceleration rates. We have shown that digital image correlation is an experimentation technique that accurately captures BFD area and rate of deformation for impacts ...
TY - JOUR. T1 - Endothelial cell cytoskeletal alignment independent of fluid shear stress on micropatterned surfaces. AU - Vartanian, Keri B.. AU - Kirkpatrick, Sean J.. AU - Hanson, Stephen R.. AU - Hinds, Monica. PY - 2008/7/11. Y1 - 2008/7/11. N2 - Endothelial cells (ECs) in athero-protective regions are elongated with actin and microtubule fibers aligned parallel to the direction of blood flow. Fluid shear stress (FSS) affects EC shape and functions, but little is known about shape-dependent EC properties that are independent of FSS. To evaluate these properties, ECs were elongated on micropatterned (MP) 25 μm wide collagen-coated lanes (MPECs) and characterized by cell shape index, actin and microtubule alignment, and polarization of the microtubule-organizing center (MTOC). ECs on non-patterned surfaces were also exposed to FSS. MPEC elongation was microtubule-dependent (and actin-independent); shape indices and cytoskeletal alignment were comparable to FSS-elongated ECs. Cytoskeletal ...
We showed that arterial remodeling evolutes overtime with an enlargement and a thinning of the carotid artery, leading to an increased carotid circumferential wall stress. This kind of arterial remodeling evolution is unusual in this high cardiovascular risk population. The pathophysiology of increased carotid circumferential wall stress is not obvious. In response to increased BP, in particular, the pulsatile component, degenerative changes, and fractures of the extracellular matrix component occur in the arterial wall, leading to arterial enlargement.14 The response to dilation is a thickening of the arterial wall, generally considered as adaptive, aiming at normalizing circumferential wall stress. We have previously shown in hypertensive patients that local pulse pressure was associated with increased diameter and intima-media thickness; however, circumferential wall stress was not fully normalized.15 In this study, we showed that this response does not occur in CKD patients and instead we ...
The local mechanical environment is a crucial factor in determining cell and tissue differentiation during vertebrate skeletal development and repair. Unlike the basic response of bone to mechanical load, as described in Wolffs law, the mechanobiological relationship between the local mechanical environment and tissue differentiation influences everything from tissue type and molecular architecture to the formation of complex joints. This study tests the hypothesis that precisely controlled mechanical loading can regulate gene expression, tissue differentiation and tissue architecture in the adult skeleton and that precise manipulation of the defects local mechanical environment can initiate a limited recapitulation of joint tissue development. We generated tissue type predictions using finite element models (FEMs) interpreted by published mechanobiological fate maps of tissue differentiation. The experiment included a custom-designed external fixator capable of introducing daily bending, ...
The acute and chronic adaptation to changes in blood flow occur as a result of endothelium-dependent responses that regulate vascular tone and the organization of the blood vessel wall. Among the most rapid responses of vascular endothelial cells to changes in fluid shear stress are K+ channel activation,2 generation of inositol trisphosphate,3 an increase in [Ca2+]i,23 24 and changes in pHi.4 5 The present study shows that an abrupt decrease in fluid shear stress produces cytosolic alkalinization of vascular endothelial cells by affecting membrane ion transporters that contribute to pHi regulation. After a period of exposure to continuous fluid shear stress at 2.7 dyne/cm2, the abrupt reduction of fluid shear stress from 2.7 to 0.3 dyne/cm2 produced a bicarbonate-dependent increase in pHi of 0.27 pH unit, which was not affected by prior inhibition of the Na+-H+ exchanger alone. Recovery from an NH4Cl prepulse-induced acid load occurred more rapidly when fluid shear stress was abruptly reduced ...
Vascular smooth muscle cells (SMCs) populate in the media of the blood vessel, and play an important role in the control of vasoactivity and the remodeling of the vessel wall. Blood vessels are constantly subjected to hemodynamic stresses, and the pulsatile nature of the blood flow results in a cyclic mechanical strain in the vessel walls. Accumulating evidence in the past two decades indicates that mechanical strain regulates vascular SMC phenotype, function and matrix remodeling. Bone marrow mesenchymal stem cell (MSC) is a potential cell source for vascular regeneration therapy, and may be used to generate SMCs to construct tissue-engineered vascular grafts for blood vessel replacements. In this review, we will focus on the effects of mechanical strain on SMCs and MSCs, e.g., cell phenotype, cell morphology, cytoskeleton organization, gene expression, signal transduction and receptor activation. We will compare the responses of SMCs and MSCs to equiaxial strain, uniaxial strain and mechanical strain
TY - JOUR. T1 - Shear stress activation of SREBP1 in endothelial cells is mediated by integrins. AU - Liu, Yi. AU - Chen, Benjamin P C. AU - Lu, Min. AU - Zhu, Yi. AU - Stemerman, Michael B.. AU - Chien, Shu. AU - Shyy, John Y J. PY - 2002/1/29. Y1 - 2002/1/29. N2 - We investigated the effect of shear stress on the sterol regulatory element-binding protein 1 (SREBP1) in vascular endothelial cells (ECs) and the mechanotransduction mechanism involved. Application of a shear stress (12 dyn/cm2) caused the proteolytic cleavage of SREBP1 and the ensuing translocation of its transcription factor domain into the nucleus. As a result, shear stress increased the mRNAs encoding the low density lipoprotein receptor (LDLR), as well as the binding of 125I-LDL. Using a step flow channel, we showed that SREBP1 activation in ECs under laminar flow is transient, but disturbed flow causes sustained activation. In studying the shear stress-elicited molecular signaling that activates SREBP1, we found that blocking ...
TY - JOUR. T1 - Mechanical regulation of macrophage function - Cyclic tensile force inhibits NLRP3 inflammasome-dependent IL-1β secretion in murine macrophages. AU - Maruyama, Kentaro. AU - Nemoto, Eiji. AU - Yamada, Satoru. PY - 2019/2/7. Y1 - 2019/2/7. N2 - Mechanical stress maintains tissue homeostasis by regulating many cellular functions including cell proliferation, differentiation, and inflammation and immune responses. In inflammatory microenvironments, macrophages in mechanosensitive tissues receive mechanical signals that regulate various cellular functions and inflammatory responses. Macrophage function is affected by several types of mechanical stress, but the mechanisms by which mechanical signals influence macrophage function in inflammation, such as the regulation of interleukin-1β by inflammasomes, remain unclear. In this review, we describe the role of mechanical stress in macrophage and monocyte cell function.. AB - Mechanical stress maintains tissue homeostasis by regulating ...
Previous studies have demonstrated that endothelial cells exposed to laminar shear stress are protected from apoptotic stimuli such as tumor necrosis factor (TNF)-alpha. The authors investigated the role of phosphatidylserine (PS) in this phenomenon. Western blot analysis of cleaved caspase 3 was used as an indicator of apoptosis and revealed that in the absence of serine, endothelial cells exposed to laminar shear stress were unable to protect against TNF-alpha-induced apoptosis, in contrast to sheared cells grown in regular medium. It was also found that shear-induced activation of the Akt pathway was significantly decreased in cells grown without serine. In addition, quantitation of PS using a novel isotopic labeling technique involving the use of formalin revealed that stearoyl-oleic PS (18:0/18:1) did not increase during shear treatment. These findings suggest that basal levels of PS are required to activate survival pathways in endothelial cells and thereby contribute to the overall ...
Introduction: Recent studies indicated that plaque rupture may be associated with: a) extreme mechanical stress/strain conditions; b) large lipid-rich necrotic core; c) thin and weakening fibrous cap; d) cap inflammation; e) intraplaque hemorrhage. Fayad et al and others have been developing multi-modality imaging technology using PET/CT (Positron Emission Tomography/ Computed Tomography) and MRI (magnetic resonance imaging) to identify inflammation in arteries. The goal of this paper is to investigate possible impact of cap inflammation on plaque stress/strain and flow shear stress conditions.. Method: An MRI-PET/CT-based modeling approach is proposed to develop fluid-structure interaction (FSI) models for human carotid plaque assessment and quantify the effect of inflammation on plaque stress/strain conditions. The combined PET/CT and MRI data was acquired from a 74 year old male patient (with informed consent) to assess arterial inflammation. The patient was imaged with dark blood ...
With gene expression profiling it was aimed to identify the differentially expressed genes associated with the regulation of the cytoskeleton to investigate the stretch-induced cell alignment mechanism. A whole genome microarray based analysis of the stretch-induced gene expression changes was done. Gene expression was measured at the beginning of the alignment process showing first reoriented cells after 5 h stretching and at the end after 24 h, where nearly all cells are aligned. Cyclic mechanical stretching of cells results in cellular alignment perpendicular to the stretch direction regulating cellular response. This stress response is assumed to be an adaptation mechanism to reduce extensive stretching but also acts as architectural restructuring changing performance and biomechanics of the tissue. Gene expression profiling of control vs. stretched primary human dermal fibroblasts after 5 h and 24 h demonstrated the regulation of differentially expressed genes associated with metabolism,
Ukropec, Jon A., Fluid shear stress-induced reorganization of adherens junctions in human endothelial cells (1999). Theses. 24 ...
Pattie Mathieu, Paul Cahill, Joseph Mackle, James King, Caitriona Lally, Phenotypic Changes in Rat Smooth Muscle Cells Exposed to Varying Amplitudes of Cyclic Equibiaxial Tensile Strain, UK Society of Biomaterials, Belfast, Ireland, 25th-26th June 2015 ...
Mechanical strain on the artery wall is increased up to 30% in hypertension and is postulated to play a role in vascular injury.2-5 Thrombin is concentrated in vivo at sites of vascular injury, and its effects are mediated chiefly through PAR-1.21 PAR-1 is expressed at very low levels in normal arteries but increases after vascular injury12,18,22 and is increased in the arteries of hypertensive rats.11 Thus, we hypothesized that cyclic strain administered to VSMCs in vitro would increase PAR-1 expression.. Cyclic strain increased PAR-1 mRNA and protein levels (Figures 1 and 2⇑), and after 48 hours of cyclic strain, thrombin also produced a 50% increase in cell number (Figure 3). The significance of these findings is based on the opposite responses of PAR-1 expression to cyclic strain and shear stress. PAR-1 expression increases 2-fold under 20% cyclic strain for 24 hours, whereas it decreases by ≈4-fold under shear stress (25 dyne/cm2) for 24 hours.14 Thus, mechanical forces regulate the ...
The angiotensin II (AngII) type 1 (AT1) receptor is a G protein-coupled receptor that plays a crucial role in the development of load-induced cardiac hypertrophy. We previously reported that mechanical stress, the most important stimulus for cardiac hypertrophy, activates the AT1 receptor through an AngII-independent mechanism, and that this activation is inhibited by an inverse agonist candesartan. However, it remains unclear how mechanical stress activates AT1 receptor and how candesartan exerts inverse agonism. By serial studies using substituted cysteine accessibility mapping, we demonstrated that mechanical stress directly activates AT1 receptor by changing the conformation of AT1 receptor. Transmembrane (TM) VII of AT1 receptor showed a counterclockwise rotation and shift into the ligand-binding pocket in response to mechanical stretch, and candesartan suppressed this helical movement induced by stretch. Comparison of the inverse agonist activities of several AT1 receptor blockers (ARBs) ...
TY - JOUR. T1 - Chapter 7 Monitoring Oxidative Stress in Vascular Endothelial Cells in Response to Fluid Shear Stress. T2 - From Biochemical Analyses to Micro- and Nanotechnologies. AU - Rouhanizadeh, Mahsa. AU - Takabe, Wakako. AU - Ai, Lisong. AU - Yu, Hongyu. AU - Hsiai, Tzung. PY - 2008. Y1 - 2008. N2 - Hemodynamics, specifically, fluid shear stress, modulates the focal nature of atherosclerosis. Shear stress induces vascular oxidative stress via the activation of membrane-bound NADPH oxidases present in vascular smooth muscle cells, fibroblasts, and phagocytic mononuclear cells. Shear stress acting on the endothelial cells at arterial bifurcations or branching points regulates both NADPH oxidase and nitric oxide (NO) synthase activities. The former is considered a major source of oxygen-centered radicals (i.e., superoxide anion [O2· -]) that give rise to oxidative stress; the latter is a source of nitrogen-centered radicals (i.e., nitric oxide [NO]) that give rise to nitrative/nitrosative ...
Many phenomena depend on the features of the fine-scale structure of turbulence, including its intermittency. This article discusses the problem of the turbulent shear in biotechnology including the effect of the shear stress on particles (cells, flocs, cells immobilized on microcarriers). Traditionally, the effect of intermittency has not been taken into account in the shear problem and the theory of isotropic turbulence introduced by Kolmogorov (1941) based on average values of the rate of kinetic energy dissipation, velocity fluctuactions, rates of strain, turbulent stresses etc. has been applied. In this paper a multifractal formalism is employed to describe intermittency; the results of multifractal approach are then compared with predictions of other models of intermittent and non-intermittent turbulence. The multifractal model of intermittent turbulence has been used to derive equations describing flow-particle interactions, including: equations describing turbulent stresses acting upon ...
Fingerprint Dive into the research topics of Microtubule dynamics regulate cyclic stretch-induced cell alignment in human airway smooth muscle cells. Together they form a unique fingerprint. ...
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Soft tissue manual therapies are commonly utilized by osteopathic physicians, chiropractors, physical therapists and massage therapists. These techniques are predicated on subjecting tissues to biophysical mechanical stimulation but the cellular and molecular mechanism(s) mediating these effects are poorly understood. Previous studies established an in vitro model system for examining mechanical stimulation of dermal fibroblasts and established that cyclical strain, intended to mimic overuse injury, induces secretion of numerous pro-inflammatory cytokines. Moreover, mechanical strain intended to mimic soft tissue manual therapy reduces strain-induced secretion of pro-inflammatory cytokines. Here, we sought to partially confirm and extend these reports and provide independent corroboration of prior results. Using cultures of primary human dermal fibroblasts, we confirm cyclical mechanical strain increases levels of IL-6 and adding long-duration stretch, intended to mimic therapeutic soft tissue
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Although molecular dynamics (MD) simulation has been widely used to study of physical properties of nanomaterials, it suffers from a well-known time scale limitation where it cannot simulate processes that take longer than about hundreds of nanoseconds. However, many important processes in physics and materials science take place on time scales that cannot be reached by MD, and thus a key limitation of atomistic simulations is the ability to study the mechanical deformation of nanostructures at experimentally-relevant time scales. In this thesis, a new computational technique is proposed to overcome this issue. Specifically, a generic history-penalized self-learning metabasin escape (SLME) algorithm is developed which demonstrated high computational efficiency in potential energy surface exploration. The SLME method is then coupled, via transition state theory, to mechanical deformation, which enables a direct link between the externally applied strain rate and the energy barriers crossed on the ...
Mechanical strain plays a significant role in the regulation of bone matrix turnover, which is mediated in part by matrix metalloproteinase (MMP)-13 and tissue inhibitors of matrix metalloproteinase (TIMP)-1. However, little is known about the correlation between mechanical strain and osteoblastic cell activities, including extracellular matrix (ECM) metabolism. Herein, we determined the effect of different magnitudes of cyclic tensile strain (0%, 6%, 12%, and 18%) on MMP-13 and TIMP-1 mRNA and protein expression in MC3T3-E1 osteoblasts. Furthermore, we employed specific inhibitors to examine the role of distinct signal transduction pathways known to mediate cellular responses to mechanical strain. We identified a magnitude-dependent increase in MMP-13 and TIMP-1 mRNA and protein levels in response to mechanical strains corresponding to 6%, 12%, and 18% elongation. The strain-induced increases in MMP-13 and TIMP-1 mRNA expression were inhibited by PD098059 and cycloheximide, respectively. Our results
1. Elasticity: The tendency of a material to regain its original dimensions (size and shape) upon the removal of load or force. Eg. Steel is more elastic than rubber. The ratio between tensile stress and tensile strain or Compressive stress and compressive strain is called youngs modulus of Elasticity.. Youngs Modulus of elasticity = E = Stress/Strain = σ / ε. Modulus of rigidity or shear modulus is the ratio of shear stress to the shear strain.. Modulus of Rigidity or Shear Modulus = Shear stress/shear strain Bulk or Volume modulus of elasticity is the ratio of normal stress to the volumetric strain.. Bulk Modulus = Normal stress/Volumetric strain 2. Plasticity: The tendency of a material to permanently deform when subjected to external load beyond the elastic limit. 3. Toughness: The ability of a material to absorb energy in plastic deformation till the point of fracture is known as toughness. Toughness is indicated by the total area under the stress strain curve up to the fracture point. ...
In 1975, we started a research project for the development of microexplosion lith-otripsy. In this project, we investigated the mechanical properties of the urinary tract organs to clarify factors to prevent complications from the method. Tension and expansion tests were performed on the middle portion of the normal ureter taken from fresh cadavers in 1983.. A tension test was performed on eleven ureters in the longitudinal direction and seven in the transverse direction using a universal tensile tester. Tensile strength and maximum tensile stress in the transverse direction of the ureter were weaker than those in the longitudinal direction. Accordingly, it was presumed that ureteral injury first occurred in the transverse direction. The maximum tensile stress of the ureter was higher than that of the bladder, which was previously reported in another paper.. Expansive tests were performed on ten ureters. At the leakage point, the tensile strength and elongation ratio of the external diameter ...
This study is the first to analyze the relationship between in vivo measured shear rate and SS and structural and functional properties of a peripheral conduit artery in patients with ESRD. Patients with ESRD were characterized by outward remodeling of BA, with larger inner diameter and increased stiffness. The outward remodeling was not associated with higher blood flow but with an acceleration of age-associated changes. Whereas BA circumferential wall stress did not differ from that in control subjects, SS was reduced significantly in patients with ESRD as a result of lower shear rate and decreased WBV. Hand warming-induced SS augmentation was associated with FMD and enhanced BAC, which were significantly less pronounced in patients with ESRD, but dilation in response to GTN did not differ in control subjects and patients with ESRD. In patients with ESRD, the partial anemia correction increased SS as a result of enhanced WBV and was associated with an increased FMD and improved BAC.. Arterial ...
We investigated the mechanisms that are responsible for the basal release of endothelium-derived relaxing factor (EDRF), which is likely to be identical with nitric oxide, in the intact coronary circulation. The increase in cGMP content of platelets passing through the coronary bed of the isolated rabbit heart was used as an index of EDRF release. Platelet cGMP content after passage through the heart under control conditions (flow rate of 20 ml/min) amounted to 0.50 +/- 0.10 pmol/mg protein. Inhibition of endothelial nitric oxide synthesis by 30 microM NG-nitro-L-arginine (L-NNA) reduced this amount by more than 60%. Increasing flow rate from 20 ml/min to 40 and 60 ml/min led to flow-dependent dilation as reflected by the subsequent drop in perfusion pressure after an initial rise. The flow-dependent dilation was associated with a significant increase in the normalized platelet cGMP content. L-NNA abolished completely both the flow-dependent dilation and the increase in platelet cGMP content. ...
CiteSeerX - Scientific documents that cite the following paper: Focal contacts as mechanosensors: externally applied local mechanical force induces growth of focal contacts by an mDia1-dependent and ROCK-independent mechanism.
TY - JOUR. T1 - Remodeling of blood vessels. T2 - Responses of diameter and wall thickness to hemodynamic and metabolic stimuli. AU - Pries, Axel R.. AU - Reglin, Bettina. AU - Secomb, Timothy W.. PY - 2005/10. Y1 - 2005/10. N2 - Vascular functions, including tissue perfusion and peripheral resistance, reflect continuous structural adaptation (remodeling) of blood vessels in response to several stimuli. Here, a theoretical model is presented that relates the structural and functional properties of microvascular networks to the adaptive responses of individual segments to hemodynamic and metabolic stimuli. All vessels are assumed to respond, according to a common set of adaptation rules, to changes in wall shear stress, circumferential wall stress, and tissue metabolic status (indicated by partial pressure of oxygen). An increase in vessel diameter with increasing wall shear stress and an increase in wall mass with increased circumferential stress are needed to ensure stable vascular adaptation. ...
The importance of fibre reinforced plastics continually increases due to the excellent mechanical properties, low material and manufacturing costs combined with significant weight reduction. Today, components are usually designed and calculated numerically by using finite element methods (FEM) to avoid expensive laboratory tests. These programs are based on material models including material specific deformation characteristics. In this research project, material models for short glass fibre reinforced plastics are presented to simulate the visco-elasto-plastic deformation behaviour. Prior to modelling specimens of the material EMS Grivory HTV-5H1, consisting of a Polyphthalamide matrix reinforced by 50wt.-% of short glass fibres, are characterized experimentally in terms of the highly time dependent deformation behaviour of the matrix material. To minimize the experimental effort, the cyclic deformation behaviour under tensile and compressive loading (R = −1) is characterized by isothermal ...
An expandable stent having end rings with enhanced strength and radiopacity for implantation in a body lumen, such as an artery, is disclosed. The stent consists of a plurality of radially expandable cylindrical elements generally aligned on a common longitudinal stent axis and interconnected by one or more interconnecting members placed so that the stent is flexible in the longitudinal direction. The expandable cylindrical elements have regions which are subject to high stresses and regions subject to low stresses when the cylindrical elements are radially expanded. In order to increase the radiopacity of the stent, the width of the strut in the low stress region of the stent is designed to be wider than the width of the strut in the high stress regions. If a high radiopaque material is utilized and reduced radiopacity is desired, the width of the strut in the low stress region of the stent can be designed to be narrower than the strut width in the high stress regions. The end rings of the stent are
Growing experimental evidence suggests that mechanical tension plays a significant role in determining the growth, guidance, and function of neurons. Mechanical tension in axons contributes to neurotr
TY - JOUR. T1 - Effects of disturbed flow on endothelial cells. AU - Chiu, J. J.. AU - Wang, D. L.. AU - Usami, S.. AU - Chien, S.. AU - Skalak, R.. PY - 1998/2. Y1 - 1998/2. N2 - Atherosclerotic lesions tend to localize at curvatures and branches of the arterial system, where the local flow is often disturbed and irregular (e.g., flow separation, recirculation, complex flow patterns, and nonuniform shear stress distributions). The effects of such flow conditions on cultured human umbilical vein endothelial cells (HUVECs) were studied in vitro by using a vertical-step flow channel (VSF). Detailed shear stress distributions and flow structures have been computed by using the finite volume method in a general curvilinear coordinate system. HUVECs in the reattachment areas with low shear stresses were generally rounded in shape. In contrast, the cells under higher shear stresses were significantly elongated and aligned with the flow direction, even for those in the area with reversed flow. When ...
In biomecanics the influence of mechanical conditions on healing of biological tissues as bones or soft tissues are analysed. In the frame of this work the mechanical behavior of intact and fractured bones with different bone qualities (osteoporotic versus normal) has been examined in a proximal humerus. Therefore a finite element model of the bone was constructed. It was found that the bone quality has a stronger impact on healing than the actual physiological loading condition does. Hence, for a future therapy of osteoporosis the precise density distribution of each individual bone must be considered. In a second step a biphasic, linear-elastic model for tissue differentiation was developed, where osteochondral healing was simulated by iterative calculation of the elastic modulus of Young within the joint region. By using this model it was possible to predict in which order in all regions of the joint the osteochondral healing took place. The stiffnesses of the newly differentiated tissues ...
In biomecanics the influence of mechanical conditions on healing of biological tissues as bones or soft tissues are analysed. In the frame of this work the mechanical behavior of intact and fractured bones with different bone qualities (osteoporotic versus normal) has been examined in a proximal humerus. Therefore a finite element model of the bone was constructed. It was found that the bone quality has a stronger impact on healing than the actual physiological loading condition does. Hence, for a future therapy of osteoporosis the precise density distribution of each individual bone must be considered. In a second step a biphasic, linear-elastic model for tissue differentiation was developed, where osteochondral healing was simulated by iterative calculation of the elastic modulus of Young within the joint region. By using this model it was possible to predict in which order in all regions of the joint the osteochondral healing took place. The stiffnesses of the newly differentiated tissues ...
TY - CONF. T1 - The Detection of Compression-Induced Recrystallisation of Amorphous Indomethacin. AU - Craig, D.Q.M.. AU - Murphy, J.. AU - Kett, Victoria. AU - Reading, M.. PY - 2003/11. Y1 - 2003/11. M3 - Paper. SP - 1199. EP - 1199. T2 - AAPS Annual Meeting. Y2 - 1 November 2004 through 1 November 2004. ER - ...
Using a free-energy approach introduced by Born and Huang in studying crystalline elasticity, molecular constitutive equations isothermal or adiabatic conditions were developed for elastic polymeric solids. The molecular model consists of non-spherical molecules which are dispersed throughout a random network of crosslinked chain molecules. The non-spherical molecules are assumed to possess an intramolecular separation potential involving the mean-square end-to-end chain distance and a torsional oscillation potential. These non-spherical molecules interact with each other and the network chains via physical physical entanglements and orientational-dependent secondary interactions. Explicit relationships for the number of such subchains were developed and depend upon the distribution, number functionality and chemical efficiency of the crosslink sites, and the functionality of the chain ends. The isothermal constitutive equations depend upon the statistical averages involving the various potentials and a
The present study shows that SMC exposure to laminar flow, at arterial levels of shear stress, reduced PDGF-BB-directed cell migration and invasion. A major mechanism for this effect was the decrease in PDGF-Rβ mRNA expression and protein levels, because shear-dependent inhibition of SMC migration was abolished in cells forced to overexpress PDGF-Rβ. It is of interest that diminished PDGF binding10 and mitogenic response to PDGF10 13 have also been observed in SMCs derived from the intima of injured carotid arteries, suggesting the possibility that SMC exposure to hemodynamic shear stress in vivo may be a mechanism for these effects.. A second mechanism that may contribute to the effect of shear stress to diminish SMC invasiveness across Matrigel is the decrease in MMP-2. MMPs are required for SMCs to invade a barrier constituted by ECM components,3 24 and lower MMP-2 levels without a change in TIMP-2, the main MMP-2 inhibitor,29 may account, at least in part, for the results shown in Figure ...
High compressive stresses will be developed in the coatings while substrates will be subjected to very low tensile stresses (Table 2). In principle, compressive stresses would not lead to cracking of the coatings and the expected tensile stresses are not sufficient to originate cracking of the YTZP substrates. The observed delamination in the specimens with the thickest coatings (Fig. 1) can be attributed to the presence of high shear stresses at the interfaces. The non flat faces of the additional transverse and parallel cracks with large openings reveal that they were probably formed during sintering by a combination of stresses due to thermal expansion and sintering rate mismatches.. Cracks were not observed in the specimens with thinnest coatings (Fig. 2). Even though the necessary condition for delamination should be fulfilled due to the high shear stresses expected at the interfaces, the critical relationship to produce cracking between thickness and residual stresses proposed by Evans ...
We calculate low-density lipoprotein (LDL) transport from blood into arterial walls in a three-dimensional, patient-specific model of a human left coronary artery. The in vivo anatomy data are obtained from computed tomography images of a patient with coronary artery disease. Models of the artery anatomy in its healthy and diseased states are derived after segmentation of the vessel lumen, with and without the detected plaque, respectively. Spatial shear stress distribution at the endothelium is determined through the reconstruction of the arterial blood flow field using computational fluid dynamics. The arterial endothelium is represented by a shear stress-dependent, three-pore model, taking into account blood plasma and LDL passage through normal junctions, leaky junctions, and the vesicular pathway. Intraluminal pressures of 70 and 120 mmHg are employed as the normal and hypertensive operating pressures, respectively. By applying our model to both the healthy and diseased states, we show that ...
Hyaluronan (HA), a highly negatively charged unsulfated glycosaminoglycan (GAG), with an extended length of up to 25 μm seems to be a constitutive component of the endothelial surface layer (ESL). It has been shown that the inner blood vessel surface is lined with a gel-like surface structure, measuring at least 0.5 μm thick. This layer is a protection against coagulation and inflammation, and defends the vessel wall from the development of arteriosclerotic plaques. Interestingly, the size of this surface layer is significantly reduced at vessel sites with disturbed blood flow and low shear stress. Removal of hyaluronan by treatment with hyaluronidase results in a reduction of the ESL to less than 0.1 μm thick and impaired vessel dilatation properties. Recently, studies showed that distinct shear stress conditions can increase the incorporation of hyaluronan into the ESL. Therefore, the present study was undertaken to prove the hypothesis that shear stress can increase the amount of ...
was observed. Intercellular adhesion molecule 1, vascular cell adhesion molecule 1, and E-selectin exhibited a sustained increase in protein expression with time. The mRNA levels of these molecules were transiently upregulated and this was followed by a decrease in expression to levels lower than static controls. Regionally, increased inflammatory marker expression was observed in regions of WSS gradients both proximal and distal to the stenosis when compared with the uniform flow regions, whereas the atheroprotective markers were expressed to a greater extent in regions of elevated WSS magnitudes. The results from the straight/tubular model cannot explain the regional variation seen in the stenosis models. This may help explain the localization of inflammatory cells at the shoulders of plaques in vivo.. ...
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When I was a kid, my father proved himself a powerful wizard when he magically stuck a balloon to the wall just by rubbing it on his head. Of course, I would later find out not only was it not magic, but the static electricity that was my childhood fascination can be a nightmarish problem for converters. The decision to purchase static control equipment and which equipment to purchase are choices
Superimposition of length fluctuations on contracted ASM have shown to reduce active force and stiffness. This effect is usually attributed to disruption of the actomyosin crossbridge cycle; however no direct experimental data is available to support this hypothesis. This in vitro study investigated the effect of the mechanical strains on 1) the ASM reactivity and 2) on the actin-myosin crossbridges. Experiments were carried out on maximally contracted bovine ASM subjected to length strains at various frequency in the range from 10 to 100Hz, superimposed on normal tidal stretches (frequency 0.33Hz, amplitude 4%). An organ bath system was used to apply strains and measure the force; immunofluorescence technique was performed to assess the crossbridges. The results show that superimposed length strains increase breathing relaxation effect with an optimal effect obtained at 50Hz. The cholinergic stimulation promotes actin-myosin connection, and length stretches promote the detachment of those ...
Ive talked at length on my site about DAVIS LAW of TISSUE DEFORMATION (HERE as well). H.G. Davis was a renowned Civil War-era surgeon who rightly realized, like Dr. Wolf did with bones before him (see links on Davis for info on Wolf), that soft tissues would remodel themselves in response to mechanical stresses put upon them. The problem is, if there arent enough of these mechanical stresses running around (or if the stresses never really change), then the tissues will inevitably shorten --- a common phenomenon that I refer to in my clinic as TETHERING. What else do we know? If you are putting the kinds of mechanical stresses on MUSCLES and other connective tissues that Donnie and his crew are on a regular basis (LIGAMENTS, FASCIA, TENDONS, etc), said tissues are forced to adapt --- they have no choice. These adaptations are not anything novel and arent much different than the physical adaptations that occur from lifting weights or engaging in other forms of training (its known as getting ...
Background and Objective: Cell adhesion plays important roles in maintaining the structural integrity of connective tissues and sensing changes in the biomechanical environment of cells. The objective of the present investigation was to extend our understanding of the effect of cyclic mechanical strain on the expression of adhesion-related genes by human periodontal ligament cells. Material and Methods: Cultured periodontal ligament cells were subjected to a cyclic in-plane tensile deformation of 12% for 5s (0.2Hz) every 90s for 6-24h in a Flexercell FX-4000 Strain Unit. The following parameters were measured: (i)cell viability by the MTT assay; (ii)caspase-3 and -7 activity; and (iii)the expression of 84 genes encoding adhesion-related molecules using real-time RT-PCR microarrays. Results: Mechanical stress reduced the metabolic activity of deformed cells at 6h, and caspase-3 and -7 activity at 6 and 12h. Seventy-three genes were detected at critical threshold values <35. Fifteen showed a ...
Many previous biomechanical studies of bone and bone substitutes have estimated strains in these materials using strain gages. The purpose of this study was to compare digital image correlation (DIC) strain measurements to those obtained from strain gages in order to assess the applicability of DIC technology to common biomechanical testing scenarios. Compression and bending tests were conducted on aluminum alloy, polyurethane foam, and laminated polyurethane foam specimens. Results showed no significant differences in the principal strain values (or the variances) between strain gage and DIC measurements on the aluminum alloy and laminated polyurethane foam specimens. There were significance differences between the principal strain measurements of the non-laminated polyurethane foam specimens, but the deviation from the theoretical results was similar for both measurement techniques. In summary, DIC techniques provide similar results to those obtained from strain gages and also provide full ...
To obtain a more detailed description of the stress-free state of the intestinal wall, longitudinal residual strain measurements are needed. Furthermore, data on longitudinal stress-strain relations in visceral organs are scarce. The present study aims to investigate the longitudinal residual strain and the longitudinal stress-strain relationship in the rat small intestine. The longitudinal zero-stress state was obtained by cutting tissue strips parallel to the longitudinal axis of the intestine. The longitudinal residual stress was characterized by a bending angle (unit: degrees per unit length and positive when bending outwards). Residual strain was computed from the change in dimensions between the zero-stress state and the no-load state. Longitudinal stresses and strains were computed from stretch experiments in the distal ileum at luminal pressures ranging from 0-4 cmH2O. Large morphometric variations were found between the duodenum and ileum with the largest wall thickness and wall area in the
TY - JOUR. T1 - Mechanical stress-induced apoptosis of nucleus pulposus cells. T2 - An in vitro and in vivo rat model. AU - Kuo, Yi Jie. AU - Wu, Lien Chen. AU - Sun, Jui Sheng. AU - Chen, Ming Hong. AU - Sun, Man Ger. AU - Tsuang, Yang Hwei. PY - 2014. Y1 - 2014. N2 - Background: Un-physiological loads play an important role in the degenerative process of inter-vertebral discs (IVD). In this study, we used an in vitro and in vivo rat model to investigate the mechanism of nucleus pulposus (NP) cells apoptosis induced by mechanical stress. Methods: Static compressive load to IVDs of rat tails was used as the in vivo model. For the in vitro model, NP cells were tested under the physiological and un-physiological loading. For histological examination, apoptotic index study, and apoptotic gene expression, we also selected cytokines [bone morphogenetic protein (BMP)-2/7, insulin-like growth factor (IGF)-1, platelet-derived growth factor (PDGF)] to be analyzed. Results: Under mechanical loading, ...
Lu, Yiling and Li, Wei-Qi and Oraifige, I. and Wang, Wen (2014) Converging parallel plate flow chambers for studies on the effect of the spatial gradient of wall shear stress on endothelial cells. Journal of Biosciences and Medicines, 2. pp. 50-56. ISSN 2327-5081 ...
Purpose: : In the presence of ocular pulse (2.7 mmHg/sec), outflow facility of perfused anterior segments decreases. The exact mechanism by which conventional outflow tissues respond to cyclic pressure oscillations is unknown. The aim of the present study was to test the hypothesis that trabecular meshwork (TM) cell contractility mediates outflow facility responses to cyclic mechanical stress. Methods: : We modified an Ussing chamber perfusion system to deliver cyclic pressure oscillations while monitoring intrachamber pressure in real time (an inverse indicator of contraction-mediated changes in hydraulic conductivity). Mature human TM cell monolayers on polycarbonate filters were perfused at a constant flow rate of 2.5 µl/min until reaching a stable baseline pressure (5-20 mmHg). Chamber contents were exchanged using DMEM (control) or compounds known to affect cell contractility (isoproterenol, Y27632, pilocarpine and nifedipine). After reaching a new baseline, monolayers were subjected to ...
The objective of this work was to further our understanding of the influence hemodynamic forces have on the cardiovascular system. Specifically, the effect of shear stress on platelet aggregability under two pathophysiological conditions was studied. Elevated shear stress levels in stenosed vessels induce platelet aggregation. Increased plasma catecholamine concentrations have also been implicated in the onset of acute coronary ischemic syndromes. This first study was designed to examine the synergistic platelet activation by the interaction of shear stress and epinephrine. Platelets suspensions sheared at subthreshold levels in a cone and plate viscometer showed little or no aggregation unless pretreated with subthreshold concentrations of epinephrine. Monoclonal antibody blockade of glycoproteins (Gp) Ib and IIb/IIIa showed that the synergistic platelet aggregation required functional Gp IIb/IIIa but could partially bypass Gp Ib-von Willebrand factor (vWF) interaction. Binding studies ...
TY - JOUR. T1 - Fluid mechanical shear induces structural transitions in assembly of a peptide-lipid conjugate. AU - Shimada, Tomoko. AU - Megley, Katie. AU - Tirrell, Matthew. AU - Hotta, Atsushi. PY - 2011/10/7. Y1 - 2011/10/7. N2 - Peptide amphiphiles (PA) can self-assemble into both spherical micelles and worm-like micelles. The control of worm-like micelle formation of PA is an area of active research, most often accomplished by modulating the temperature, salt content, or pH of the environment. In this work, we demonstrate the shear-induced formation of worm-like micelles in our designed peptide amphiphile C 16-W3K. Before adding shear, the peptide amphiphiles form spherical micelles in solution and exhibit little to no viscoelasticity. As the solution is subjected to simple shear flow, with increasing shear rate, spherical micelles form rapidly into elongated worm-like micelles up to microns in length. Though it has been reported that some dilute surfactant solutions exhibit shear-induced ...
TY - JOUR. T1 - Association of remodeling with endothelial shear stress, plaque elasticity, and volume in coronary arteries. T2 - A pilot coronary computed tomography angiography study. AU - Katranas, Sotirios A.. AU - Kelekis, Anastasios L.. AU - Antoniadis, Antonios P.. AU - Chatzizisis, Yiannis S.. AU - Giannoglou, George D.. PY - 2014/5. Y1 - 2014/5. N2 - We sought to noninvasively assess the relationship between arterial remodeling, endothelial shear stress (ESS), and wall stiffness in coronary arteries. We studied 28 coronary arteries from 22 patients undergoing coronary computed tomography angiography (CCTA). The ESS was calculated in 2-mm long segments using computational fluid dynamics. Local remodeling, plaque dimensions, and local wall stiffness were assessed in each segment. The ESS was lower in the regions of excessive expansive remodeling versus compensatory expansive versus inadequate expansive versus constrictive remodeling. Areas of decreased wall stiffness more frequently ...
Fluid shear stress is an important factor to consider when studying the behavior of endothelial cells in vascular system. The main focus of this study is to relate the spatial and temporal variations in shear stress with the extent of oxidative stress, specifically in arterial branching points in comparison with straight regions in the vessels. For this purpose, a micro shear stress sensor has been designed and fabricated with the backside wire binding feature. The sensors were flush mounted in a 3-D scaled up model of carotid arterial bifurcation to measure the spatial variations in shear stress. These measurements were validated by computational fluid dynamics simulations. Arteries with complex geometries develop a low profile and bidirectional type of shear stress, namely oscillatory however unidirectional and high profile of shear stress, namely pulsatile shear stress develops at straight regions of the vessels. We compared the extent of oxidative stress for the endothelial cells which were ...
RATIONALE: Mutations in the LMNA gene, which encodes the nuclear lamina proteins lamin A and lamin C, are the most common cause of familial dilated cardiomyopathy (DCM). Mechanical stress-induced apoptosis has been proposed as the mechanism underpinning DCM in lamin A/C-deficient hearts, but supporting in vivo evidence has been lacking. OBJECTIVE: Our aim was to study interventions to modify mechanical stress in heterozygous Lmna knockout (Lmna(+/-)) mice. METHODS AND RESULTS: Cardiac structure and function were evaluated before and after exercise training, thoracic aortic constriction, and carvedilol treatment. Lmna(+/-) mice develop adult-onset DCM with relatively more severe disease in males. Lmna(+/-) cardiomyocytes show altered nuclear morphology and perinuclear desmin organization, with enhanced responses to hypo-osmotic stress indicative of cytoskeletal instability. Despite these structural defects that provide a template for mechanical stress-induced damage, young Lmna(+/-) mice ...
Purpose: To investigate the involvement of miR-146a in the regulation of responses induced by cyclic mechanical stress (CMS) in human trabecular meshwork (HTM) cells and its effects on intraocular pressure in vivo.. Methods: Effects of miR-146a on the responses to CMS were evaluated in cells transfected with miR-146a mimic or controls transfected with scrambled microRNA. Two primary HTM cell culture lines were incubated in triplicate on flexible bottom plates and subjected to cyclic mechanical stress (20% stretching, 1 cycle per second, during 3 hours). Non-stress parallel control cultures were incubated in similar plates under identical conditions. The effects of miR-146 inhibitor were tested in one primary HTM culture. Changes in expression for miR-146a, IL6, IL8, IL1beta, BMP2, MMP3, HSP70, IRAK1, Serpin, COX1 and COX2 were analyzed by quantitative real time PCR. Three Sprague-dawley rats were injected into the anterior chamber with influenza virus (IAV) expressing miR-146a and the ...
Accurate imaging and measurement of hemodynamic forces is vital for investigating how physical forces acting on the embryonic heart are transduced and influence developmental pathways. Of particular importance is blood flow-induced shear stress, which influences gene expression by endothelial cells and potentially leads to congenital heart defects through abnormal heart looping, septation, and valvulogenesis. However no imaging tool has been available to measure shear stress on the endocardium volumetrically and dynamically. Using 4D structural and Doppler OCT imaging, we are able to accurately measure the blood flow in the heart tube in vivo and to map endocardial shear stress throughout the heart cycle under physiological conditions for the first time. These measurements of the shear stress patterns will enable precise titration of experimental perturbations and accurate correlation of shear with the expression of molecules critical to heart development.. ©2012 Optical Society of ...
The mechanical induction of specific cell phenotypes can only be properly controlled if the local stimuli applied to the cells are known as a function of the external applied loads. Finite element analysis of the cell carriers would be one method to calculate these local conditions. Furthermore, the constitutive model of the construct material should be able to describe mechanical events known to be responsible for cell stimulation, such as interstitial fluid flow. The aim of this study was to define a biphasic constitutive model for fibrin, a natural hydrogel often used for tissue engineering but not yet thoroughly characterized. Large strain poroelastic and poroviscoelastic constitutive equations were implemented into a finite element model of a fibrin gel. The parameter values for both formulations were found by either analytically solving equivalent low strain equations, or by optimizing directly the large strain equations based on experimental stress relaxation data. No poroelastic ...
article{181863, author = {Leybaert, Luc and DEHEMPTINNE, A}, issn = {0014-4819}, journal = {EXPERIMENTAL BRAIN RESEARCH}, language = {eng}, number = {3}, pages = {392--402}, title = {Changes of intracellular free calcium following mechanical injury in a spinal cord slice preparation.}, volume = {112}, year = {1996 ...
TY - JOUR. T1 - Transduction of compressive stress by bronchial epithelium. AU - Tschumperlin, D. J.. AU - Drazen, J. M.. PY - 2002/12/1. Y1 - 2002/12/1. N2 - The epithelial lining of the asthmatic airway is exposed to compressive stress as a consequence of smooth muscle constriction. We have shown previously that in vitro compression of bronchial epithelial cells stimulates extracellular signal-regulated kinase (ERK) phosphorylation and downstream gene expression. Here we show that inhibition of signaling through the epidermal growth factor receptor (EGFR) with a tyrosine kinase inhibitor (AG1478) or a neutralizing antibody to the ligand-binding domain of the EGFR blocks compression-induced ERK phosphorylation. A metalloprotease inhibitor (Galardin) and a neutralizing antibody to heparin binding epidermal growth factor (HB-EGF), but not EGF, also attenuates the compression-induced ERK activation. Our results demonstrate that compressive activation of the ERK signaling pathway requires signaling ...
The relationship of Na+K+ATPase and hypertension has been a topic of concentrated study for the past twenty years. During the onset of hypertension, an increase in Na+K+ATPase in the cellular membranes of the aortic smooth muscle cells has been found to occur. The reason for this increased manifestation of Na+K+ATPase during the beginning stages of hypertension and how the cells regulate this mechanism are still unclear. An initial stage of hypertension is the increase in blood pressure, which contracts the aortic smooth muscle cell lining. Previous in vitro studies have shown the contraction of the aortic smooth muscle cells does demonstrate this increased expression of Na+K+ATPase. The objective of this study was to begin to understand the regulation of the increased expression by beginning with mRNAs control and regulation. Using a Flexercell Strain Unit which cyclically stretches cells, the mRNA expression during 20%, 10%, and non-stretch controls were measured by analysis of Northern ...
TY - JOUR. T1 - Mechanical compression induces VEGFA overexpression in breast cancer via DNMT3A-dependent miR-9 downregulation. AU - Kim, Baek Gil. AU - Gao, Ming Qing. AU - Kang, Suki. AU - Choi, Yoon Pyo. AU - Lee, Joo Hyun. AU - Kim, Ji Eun. AU - Han, Hyun Ho. AU - Mun, Seong Gyeong. AU - Cho, Nam Hoon. N1 - Publisher Copyright: © 2017 The Author(s).. PY - 2017/3/2. Y1 - 2017/3/2. N2 - Tumor growth generates mechanical compression, which may trigger mechanotransduction in cancer and stromal cells and promote tumor progression. However, very little is known about how compression stimulates signal transduction and contributes to tumor progression. In the present study, we demonstrated that compression enhances a tumor progression phenotype using an in vitro compression model, and validated the results from the in vitro model with high-and low-compressed breast cancer tissues. Mechanical compression induced miR-9 downregulation by DNMT3A-dependent promoter methylation in the MDA-MB-231 and ...
In this study, we provide a set of model examples for which we compare the values of the shear modulus under increasing compression or tension with experimental data for brain and fat tissues. The viscoelasticity of brain and adipose tissues was measured following the protocol described in [4]. The dynamic shear storage modulus G′ was measured as a function of time for increasing tensile or compressive strain (from 0% to 40%). Details are given in appendix A.. A hyperelastic constitutive material has a unique stress-strain relationship, independent of strain rate. However, the stress-strain response for viscoelastic materials changes with strain rate, and a strain-energy density function does not exist for these materials. Nonetheless, for many soft tissues, the shape of the nonlinear stress-strain curve is typically invariant with respect to strain rate. In this case, at fixed strain rate, the shear modulus may be captured by a nonlinear hyperelastic model (an example of this approach for fat ...
TY - JOUR. T1 - Influence of biomechanical factors on substructure of pointing movements. AU - Dounskaia, Natalia. AU - Wisleder, Deric. AU - Johnson, Travis. N1 - Funding Information: Acknowledgements The study was supported by NSF grant BCS 0213653 awarded to Dr. Natalia Dounskaia.. PY - 2005/7. Y1 - 2005/7. N2 - Irregularities in the velocity profile near the end of pointing movements have been interpreted as corrective submovements whose purpose is to provide accuracy of pointing to the target. The purpose of the present study was to investigate whether two additional factors related to biomechanical properties of the arm also cause submovements. First, motion termination and stabilization of the limb in the final position required by a discrete pointing task may contribute to submovements. Second, inaccurate regulation of interactive torque at the joints may also cause submovements. To investigate the contributions of these two biomechanical factors and the traditionally considered factor ...
TY - CONF. T1 - Investigation of fundamental powder flow properties of fine lactose particles following mechanical surface modification. AU - Zhou, Qi. AU - Roberts, Benjamin Armstrong. AU - Morton, David Alexander Vodden. AU - Stewart, Peter James. PY - 2008. Y1 - 2008. M3 - Other. SP - 49. EP - 51. ER - ...
TY - CHAP. T1 - Role of the plasma membrane in endothelial cell mechanosensation of shear stress. AU - Butler, Peter J.. AU - Chien, Shu. PY - 2013/1/1. Y1 - 2013/1/1. N2 - Mechanotransduction, which is the process by which cells convert mechanical stimuli to biochemical signaling cascades, is involved in the homeostasis of numerous tissues (reviewed in [21] and [56]). The mechanotransduction of hemodynamic shear stress by endothelial cells (ECs) has garnered special attention because of its role in regulating vascular health and disease. In particular, there is intense interest in identifying the primary molecular mechanisms of the EC sensing of shear stress because its (or their) discovery may lead to clinical interventions in atherosclerosis and other diseases related to mechanobiology. In this chapter, we address the hypothesis that the plasma membrane lipid bilayer is one endothelial cell mechanosensor. Here we define mechanosensor as a cellular structure that responds to mechanical ...
Primary among the mechanical factors linked with abdominal aortic aneurysm (AAA) rupture is peak wall stress, frequently quantified as either the maximum principal or Von Mises stress exerted along the diseased arterial wall. Intraluminal pressure, as an impinging normal force on the wall, has been hypothesized as the dominant influence on this stress and thus the majority of numerical modeling studies of AAA mechanics have focused on static computational solid stress (CSS) predictions [1,2]. Unfortunately, retrospective studies comparing the magnitude of wall stress with the failure strength of the aneurysmal wall have yet to consistently predict the outcome for patient-specific AAAs [3,4]. Previous studies have shown that hemodynamics also plays a significant role in both the biological and mechanical factors that exist within AAAs. In the present investigation, partially and fully coupled fluid-structure interaction (p-FSI and f-FSI, respectively) computations of patient-specific AAA models ...
TY - JOUR. T1 - Tensile stress evolution during the early-stage constrained sintering of Gadolinium-doped ceria films. AU - Sheldon,Brian W.. AU - Nicholas,Jason D.. AU - Mandowara,Sunil. PY - 2011/1. Y1 - 2011/1. N2 - In situ measurements during the constrained sintering of Gd-doped ceria reveal tensile stresses up to ∼250 MPa. These large tensile stresses are likely to contribute to the reduced densification (compared with freely sintered material) typically observed during constrained sintering. While existing models postulate that the tensile stress in a densifying constrained film cannot exceed the sintering stress,sigma;S, the observed tensile stresses are significantly larger than the estimated sigma;S for these materials. To explain this observation, we propose that the formation and extension of interparticle grain boundaries induce substantial tensile stresses in constrained films. A model of this phenomenon shows that converting excess surface energy to elastic strain energy can ...
To mimic in vivo vibration of vocal fold cells, we studied the controllability and range of frequency, acceleration, duration, and shear stress in a new bioreactor attachment. The custom multiwell disc appliance fits into a commercially built rheometer, together termed a torsional rheometer bioreactor (TRB). Previous attachments to the TRB were capable of 50-100 Hz vibrations at relatively high strains but were limited to single-sample experiments. The TRB-multiwell disc system accommodates 20 samples in partially fluid-filled wells in an aseptic environment delivering three different acceleration conditions to different samples simultaneously. Frequency and amplitude used to calculate acceleration along with duration and shear stress were controllable and quantifiable using a combination of built-in rheometer sensors, manufacturer software, and smooth particle hydrodynamics (SPH) simulations. Computed shear stresses at the well bottom using SPH in two and three dimensions were verified with analytical
Plants respond to grazing by producing chemical defense compounds such as protease inhibitors and secondary metabolites such as flavonoids, making them less palatable for feeding and negatively affecting the physiology of insects. The purpose of this study was to assess the phytochemical response of soybean cultivars Glycine max resistant (IAC-17, IAC-24) and susceptible (IAC-P1) to insects after mechanical damage. These cultivars were mechanically injured, and after 24 HPLC was used to identify and quantify flavonoids in plant samples for several hours. The flavonoids daidzein, quercetin, and rutin were measured, with daidzin having the highest concentration. soybean cultivars after mechanical damage. Rutin was biosynthesized by IAC-24. The cultivars IACPL1, IAC-17, and IAC-24 did not show a flavonoid response to mechanical damage. Flavonoids are not produced by mechanical damage in soybean cultivars ...
TY - ABST. T1 - Response of mechanical properties of glasses to their chemical, thermal and mechanical histories. AU - Yue, Yuanzheng. N1 - An invited talk. PY - 2012. Y1 - 2012. N2 - Mechanical properties are a key factor to be considered when designing new glass compositions, optimizing glass processing parameters and defining the glass application fields. However, mechanical properties of glasses are complex values since they are influenced by many factors such as structure, surface, thermal history or excess entropy of the final glass state. Here I review recent progresses in understanding of the responses of mechanical properties of oxide glasses to the compositional variation, thermal history and mechanical deformation. The tensile strength, elastic modulus and hardness of glass fibers are dependent on the thermal history (measured as fictive temperature), tension, chemical composition and redox state. However, the fictive temperature affects the hardness of bulk glass in a complicated ...
TY - JOUR. T1 - Endothelial cell respiration is affected by the oxygen tension during shear exposure. T2 - Role of mitochondrial peroxynitrite. AU - Jones, Charles I.. AU - Han, Zhaosheng. AU - Presley, Tennille. AU - Varadharaj, Saradhadevi. AU - Zweier, Jay L.. AU - Ilangovan, Govindasamy. AU - Alevriadou, B. Rita. PY - 2008/7. Y1 - 2008/7. N2 - Cultured vascular endothelial cell (EC) exposure to steady laminar shear stress results in peroxynitrite (ONOO-) formation intramitochondrially and inactivation of the electron transport chain. We examined whether the hyperoxic state of 21% O2, compared with more physiological O2 tensions (PO2), increases the shear-induced nitric oxide (NO) synthesis and mitochondrial superoxide (O 2.-) generation leading to ONOO- formation and suppression of respiration. Electron paramagnetic resonance oximetry was used to measure O2 consumption rates of bovine aortic ECs sheared (10 dyn/cm2, 30 min) at 5%, 10%, or 21% O2 or left static at 5% or 21% O2. Respiration ...
Title:Flow Shear Induced Changes in Membrane Fluidity: Dependence on Cell- Substrate Adhesion Strength. VOLUME: 9 ISSUE: 1. Author(s): Tamal Das, Tapas K. Maiti and Suman Chakraborty. Affiliation:Department of Mechanical Engineering, Indian Institute of Technology Kharagpur, Kharagpur-721302, India.. Keywords:Cell adhesion, Fluidization, Fluorescence recovery after photobleaching, Lipid raft, Membrane fluidity, Traction force microscopy. Abstract:Besides the internal genetic content and the chemical exchanges with external tissue environment, the physical interactions of cancer cells with its microenvironment also provide the guidelines for successful oncogenesis. During its metastatic journey from primary tumor to distant locations of body, a cancer cell is exposed to stresses of diverse origin and kind, of which fluid shear stresses of interstitial and haematogenic nature have been least studied in relation to their impact in cancer progression. Here, we have designed a biomicrofluidic system ...
Background and Aims Because plants protect each other from wind, stand density affects both the light climate and the amount of mechanical stress experienced by plants. But the potential interactive effects of mechanical stress and canopy shading on plant growth have rarely been investigated and never in stoloniferous plants which, due to ... read more their creeping growth form, can be expected to respond differently to these factors than erect plants. † Methods Plants of ten genotypes of the stoloniferous species Potentilla reptans were subjected to two levels of mechanical stress (0 or 40 daily flexures) and two levels of spectral shading (15 % of daylight with a red : far red ratio of 0.3 vs. 50 % daylight and a red : far red ratio of 1.2). † Key Results Mechanically stressed plants produced more leaves with shorter more flexible petioles, more roots, and more but less massive stolons. Responses to spectral shading were mostly in the opposite direction to thigmomorphogenesis, including ...
Overview. Bacterial adhesion and subsequent colonization of surfaces are the first steps toward forming biofilms, which are a major concern for implanted medical devices and in many diseases. Biofilms are resistant to innate host defences, mechanical removal and antibiotic treatments. It is therefore important to understand the physiological environment and mechanisms that lead to the spread of bacteria. Experimental conditions of biofilm formation on cardiovascular stents, tubing, different surfaces and in the intestines can easily be studied using Cellixs microfluidic pumps and biochips. The dimensions of the biochips facilitate both high and low shear stress conditions. The microcapillary walls of Cellixs biochips may be pre-coated with proteins of interest to promote adhesion and culture of biofilms under different shear stress conditions. Once the biofilm is cultured, it is then possible to flow different substances (e.g. antibiotics) over the biofilm to investigate detachment. There are ...
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Morphological and electrophysiological studies have shown that neurons respond to specific mechanical environments. However, studies linking specific neuropeptide release based on changes in the mechanical environment are lacking. To further study the effect of mechanical stress on the cells of the nervous system, DRG cells isolated from Sprague-Dawley rats have been cultured on a mechanical stress platform which is then subjected to 20% tensile strain. To study the chemical peptide profile...
The Author(s) 2020. Published by Oxford University Press on behalf of Nucleic Acids Research. We used coarse-grained molecular dynamics simulations to characterize the global and local mechanical properties of a DNA origami triangle nanostructure. The structure presents two metastable conformations separated by a free energy barrier that is lowered upon omission of four specific DNA staples (defect). In contrast, only one stable conformation is present upon removing eight staples. The metastability is explained in terms of the intrinsic conformations of the three trapezoidal substructures. We computationally modeled the local accessibility to endonucleases, to predict the reactivity of twenty sites, and found good agreement with the experimental data. We showed that global fluctuations affect local reactivity: the removal of the DNA staples increased the computed accessibility to a restriction enzyme, at sites as distant as 40 nm, due to an increase in global fluctuation. These results raise the ...
The corrosion behavior of a 2024 T351 aluminum alloy exposed to a chloride solution was studied in the present paper. The work was focused on the effect of an environmental and thermal cyclic exposure to corrosive media and aimed to identify the main parameters explaining the changes observed between continuous and cyclic immersion tests. Optical and scanning electron microscope observations showed an increase of the intergranular corrosion damage with the extension of the corrosion from the grain boundaries to the subgrain boundaries for samples exposed to cyclic tests. An experimental set-up, including a laser beam, allowed mechanical stresses induced by the solidification of the electrolyte trapped in the corrosion damage during exposure to negative temperatures to be revealed and the chloride concentration of the electrolyte to be determined. Results were helpful in proposing corrosion mechanism during thermal and environmental cyclic exposure to chloride solutions. ...
TY - JOUR. T1 - Disentangling the multifactorial contributions of fibronectin, collagen and cyclic strain on MMP expression and extracellular matrix remodeling by fibroblasts. AU - Zhang, Y.. AU - Lin, Z.. AU - Foolen, J.. AU - Schoen, I.. AU - Santoro, A.. AU - Zenobi-Wong, M.. AU - Vogel, Viola. PY - 2014. Y1 - 2014. N2 - Early wound healing is associated with fibroblasts assembling a provisional fibronectin-rich extracellular matrix (ECM), which is subsequently remodeled and interlaced by type I collagen. This exposes fibroblasts to time-variant sets of matrices during different stages of wound healing. Our goal was thus to gain insight into the ECM-driven functional regulation of human foreskin fibroblasts (HFFs) being either anchored to a fibronectin (Fn) or to a collagen-decorated matrix, in the absence or presence of cyclic mechanical strain. While the cells reoriented in response to the onset of uniaxial cyclic strain, cells assembled exogenously added Fn with a preferential Fn-fiber ...
Mechanical Engineering Assignment Help, Determine equivalent maximum shear stress in spring, Determine equivalent maximum shear stress in spring: A close coiled helical spring contains a stiffness of 10 N/mm. Its length while fully compressed, with adjacent coils touching each other is 400 mm. G = 80 GPa. (a) Find out the wire diamet
The tensile behavior of Grade 2 α-titanium is characterized for static loading and at moderately high strain rates (200-1000 s-1). An experimental method is proposed to introduce sufficiently long tensile pulses to induce fracture in ductile specimens by incorporating a sacrificial fracture piece of adequately large diameter into a pendulum-driven tensile Kolsky bar. It is established that flow stress increases with strain rate. Necking in α-titanium occurs much earlier at high strain rates compared to static loading and results in significantly smaller necking and fracture strains. An equation describing the influence of strain rate and temperature softening on necking (tensile instability) is derived. The true stress-strain response between necking and fracture is estimated by measuring the final reduction in cross-sectional area. Fracture in specimens was observed using an optical microscope, which revealed typical ductile fracture characteristics. © 2001 Elsevier Science Ltd. All rights ...
Horn, R., Peth, S., & Baumgarten, W. 2012. Development of soil structure and functions: How can mechanical and hydraulic approaches contribute to quantify soil structure dynamics? Soil and Tillage Research 125, 1-2. Mordhorst, A., Zimmermann, I., Peth, S., & Horn, R. 2012. Effect of hydraulic and mechanical stresses on cyclic deformation processes of a structured and homogenized silty Luvic Chernozem. Soil and Tillage Research 125, 3-13. Baba, H.O., & Peth, S. 2012. Large scale soil box test to investigate soil deformation and creep movement on slopes by Particle Image Velocimetry (PIV). Soil and Tillage Research 125, 38-43. Holthusen, D., Haas, C., Peth, S., & Horn, R. 2012. Are standard values the best choice? A critical statement on rheological soil fluid properties viscosity and surface tension. Soil and Tillage Research 125, 61-71 Holthusen, D., Peth, S., Horn, R., & Kühn, T. 2012. Flow and deformation behavior at the microscale of soils from several long‐term potassium fertilization ...
We use a 2 dimensional finite element model with heterogeneous elastic strengths in continental areas to model the regional stress field orientation and relative magnitudes in and around India for 33 Ma, 20 Ma and the present day. The large-scale geological structure of India is embedded in our model by using published outlines of cratons, fold belts and basins, associated with estimates of their relative strengths, enabling the modelling of stress field deflections along interfaces between relatively strong and weak tectonic elements through time. … Read more…. ...
Mechanical stimuli initiate adaptive signal transduction pathways, yet exceeding the cellular capacity to withstand physical stress results in death. The molecular mechanisms underlying trauma-induced degeneration remain unclear. In the nematode C. elegans, we have developed a method to study cellular degeneration in response to mechanical stress caused by blunt force trauma. Herein, we report that physical injury activates the c-Jun kinase, KGB-1, which modulates response elements through the AP-1 transcriptional complex. Among these, we have identified a dual-specificity MAPK phosphatase, VHP-1, as a stress-inducible modulator of neurodegeneration. VHP-1 regulates the transcriptional response to mechanical stress and is itself attenuated by KGB-1-mediated inactivation of a deubiquitinase, MATH-33, and proteasomal degradation. Together, we describe an uncharacterized stress response pathway in C. elegans and identify transcriptional and post-translational components comprising a feedback loop on Jun
The results of this study confirm that an empirical relationship exists between the mechanical environment and gene expression, tissue formation and tissue architecture within a mechanically stimulated healing bone defect. The analyses of tissue types and their molecular architecture verify that mechanical intervention influences tissue repair and that some aspects of early development can be recapitulated within a healing adult defect. It also suggests that the repair process for virtually all skeletal tissues can be manipulated towards desirable outcomes based on precise mechanical intervention.. The FEMs accurately predicted the production and persistence of cartilage within the defects and went as far as to predict the presence of fibrous tissues in specific areas of both the bending and shear models. The mechanical stimulations created uniform cartilage bands across the entire defects that persisted well past the timeframe of bony bridging found in the controls. The bending model predicted ...
An automatic injection device includes a drug-filled vessel having a flexible membrane over a first opening thereof and a puncturable seal in a wall thereof, a hollow needle attached at a first end to the flexible membrane and having a sharp end positioned proximate the puncturable seal housing. A pressure source such as a combustible propellant provides a compressed gas above the flexible membrane to force the membrane into the drug-filled vessel, forcing the hollow needle through the puncturable seal and the drug contained in the vessel through the hollow needle. After the drug has been substantially evacuated from the vessel, the membrane is allowed to return to its pre-expanded state thus retracting the hollow needle into the vessel. Preferably, the flexible membrane is an elastomeric material having a plurality of concentrically configured corrugations to allow expansion of the membrane into the vessel. The inner surface of the vessel may have a dome-like shape such that expansion of the membrane
The Journal of the Mechanical Behavior of Biomedical Materials is concerned with the mechanical deformation, damage and failure under applied forces, of biolo…
The presence of growth-induced solid stresses in tumors has been suspected for some time, but these stresses were largely estimated using mathematical models. Solid stresses can deform the surrounding tissues and compress intratumoral lymphatic and blood vessels. Compression of lymphatic vessels elevates interstitial fluid pressure, whereas compression of blood vessels reduces blood flow. Reduced blood flow, in turn, leads to hypoxia, which promotes tumor progression, immunosuppression, inflammation, invasion, and metastasis and lowers the efficacy of chemo-, radio-, and immunotherapies. Thus, strategies designed to alleviate solid stress have the potential to improve cancer treatment. However, a lack of methods for measuring solid stress has hindered the development of solid stress-alleviating drugs. Here, we present a simple technique to estimate the growth-induced solid stress accumulated within animal and human tumors, and we show that this stress can be reduced by depleting cancer cells, ...