Home About us Contact
|
Home About us Contact | ||
|
|
||
Mechanical Load (mechanical + load)
Selected AbstractsMechanical load induced by glass microspheres releases angiogenic factors from neonatal rat ventricular myocytes cultures and causes arrhythmiasJOURNAL OF CELLULAR AND MOLECULAR MEDICINE, Issue 5b 2008D. Y. Barac Abstract In the present study, we tested the hypothesis that similar to other mechanical loads, notably cyclic stretch (simulating pre-load), glass microspheres simulating afterload will stimulate the secretion of angiogenic factors. Hence, we employed glass microspheres (average diameter 15.7 ,m, average mass 5.2 ng) as a new method for imposing mechanical load on neonatal rat ventricular myocytes (NRVM) in culture. The collagen-coated microspheres were spread over the cultures at an estimated density of 3000 microspheres/mm2, they adhered strongly to the myocytes, and acted as small weights carried by the cells during their contraction. NRVM were exposed to either glass microspheres or to cyclic stretch, and several key angiogenic factors were measured by RT-PCR. The major findings were: (1) In contrast to other mechanical loads, such as cyclic stretch, microspheres (at 24 hrs) did not cause hypertrophy. (2) Further, in contrast to cyclic stretch, glass microspheres did not affect Cx43 expression, or the conduction velocity measured by means of the Micro-Electrode-Array system. (3) At 24 hrs, glass microspheres caused arrhythmias, probably resulting from early afterdepolarizations. (4) Glass microspheres caused the release of angiogenic factors as indicated by an increase in mRNA levels of vascular endothelial growth factor (80%), angiopoietin-2 (60%), transforming growth factor-, (40%) and basic fibroblast growth factor (15%); these effects were comparable to those of cyclic stretch. (5) As compared with control cultures, conditioned media from cultures exposed to microspheres increased endothelial cell migration by 15% (P<0.05) and endothelial cell tube formation by 120% (P<0.05), both common assays for angiogenesis. In conclusion, based on these findings we propose that loading cardiomyocytes with glass microspheres may serve as a new in vitro model for investigating the role of mechanical forces in angiogenesis and arrhythmias. [source] Mechanical loading stimulates ecto-ATPase activity in human tendon cellsJOURNAL OF CELLULAR BIOCHEMISTRY, Issue 1 2005M. Tsuzaki Abstract Response to external stimuli such as mechanical signals is critical for normal function of cells, especially when subjected to repetitive motion. Tenocytes receive mechanical stimuli from the load-bearing matrix as tension, compression, and shear stress during tendon gliding. Overloading a tendon by high strain, shear, or repetitive motion can cause matrix damage. Injury may induce cytokine expression, matrix metalloproteinase (MMP) expression and activation resulting in loss of biomechanical properties. These changes may result in tendinosis or tendinopathy. Alternatively, an immediate effector molecule may exist that acts in a signal-dampening pathway. Adenosine 5,-triphosphate (ATP) is a candidate signal blocker of mechanical stimuli. ATP suppresses load-inducible inflammatory genes in human tendon cells in vitro. ATP and other extracellular nucleotide signaling are regulated efficiently by two distinct mechanisms: purinoceptors via specific receptor,ligand binding and ecto-nucleotidases via the hydrolysis of specific nucleotide substrates. ATP is released from tendon cells by mechanical loading or by uridine 5,-triphosphate (UTP) stimulation. We hypothesized that mechanical loading might stimulate ecto-ATPase activity. Human tendon cells of surface epitenon (TSC) and internal compartment (TIF) were cyclically stretched (1 Hz, 0.035 strain, 2 h) with or without ATP. Aliquots of the supernatant fluids were collected at various time points, and ATP concentration (ATP) was determined by a luciferin-luciferase bioluminescence assay. Total RNA was isolated from TSC and TIF (three patients) and mRNA expression for ecto-nucleotidase was analyzed by RT-PCR. Human tendon cells secreted ATP in vitro (0.5,1 nM). Exogenous ATP was hydrolyzed within minutes. Mechanical load stimulated ATPase activity. ATP was hydrolyzed in mechanically loaded cultures at a significantly greater rate compared to no load controls. Tenocytes (TSC and TIF) expressed ecto-nucleotidase mRNA (ENTPD3 and ENPP1, ENPP2). These data suggest that motion may release ATP from tendon cells in vivo, where ecto-ATPase may also be activated to hydrolyze ATP quickly. Ecto-ATPase may act as a co-modulator in ATP load-signal modulation by regulating the half-life of extracellular purine nucleotides. The extracellular ATP/ATPase system may be important for tendon homeostasis by protecting tendon cells from responding to excessive load signals and activating injurious pathways. © 2005 Wiley-Liss, Inc. [source] Screening of the Interactions Between Mg-PSZ and TRIP-Steel and Its Alloys During Sintering,ADVANCED ENGINEERING MATERIALS, Issue 6 2010Christian Weigelt Ceramic,steel compound materials are used in a wide range of applications up to date. Major advantages are the mechanical properties due to the combination of brittle ceramic with tough steel. This study deals with effects of the sintering process on austenitic TRIP-steel/Mg-PSZ composite materials for mechanical load applications. Both, the FeCrNisteel and partially stabilized zirconia offer their special mechanical behavior only in a metastable state. The ability of phase transformation depends mainly on the chemical composition. Mutual interactions of the alloying metals (Cr, Ni, Mn, and Fe) and the ceramic stabilizer (MgO) during sintering may prevent the martensitic phase transformation. This may cause disadvantageous mechanical behavior on mechanical load in use. [source] Delivery of Two-Part Self-Healing Chemistry via Microvascular NetworksADVANCED FUNCTIONAL MATERIALS, Issue 9 2009Kathleen S. Toohey Abstract Multiple healing cycles of a single crack in a brittle polymer coating are achieved by microvascular delivery of a two-part, epoxy-based self-healing chemistry. Epoxy resin and amine-based curing agents are transported to the crack plane through two sets of independent vascular networks embedded within a ductile polymer substrate beneath the coating. The two reactive components remain isolated and stable in the vascular networks until crack formation occurs in the coating under a mechanical load. Both healing components are wicked by capillary forces into the crack plane, where they react and effectively bond the crack faces closed. Healing efficiencies of over 60% are achieved for up to 16 intermittent healing cycles of a single crack, which represents a significant improvement over systems in which a single monomeric healing agent is delivered. [source] Experimental and numerical investigations of the behaviour of a heat exchanger pileINTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 8 2006Lyesse Laloui Abstract The geothermal use of concrete geostructures (piles, walls and slabs) is an environmentally friendly way of cooling and heating buildings. With such geothermal structures, it is possible to transfer energy from the ground to fluid-filled pipes cast in concrete and then to building environments. To improve the knowledge in the field of geothermal structures, the behaviour of a pile subjected to thermo-mechanical loads is studied in situ. The aim is to study the increased loads on pile due to thermal effects. The maximum thermal increment applied to the pile is on the order of 21°C and the mechanical load reached 1300 kN. Coupled multi-physical finite element modelling is carried out to simulate the observed experimental results. It is shown that the numerical model is able to reproduce the most significant thermo-mechanical effects. Copyright © 2006 John Wiley & Sons, Ltd. [source] Involvement of the cytoskeletal elements in articular cartilage homeostasis and pathologyINTERNATIONAL JOURNAL OF EXPERIMENTAL PATHOLOGY, Issue 1 2009Emma J. Blain Summary The cytoskeleton of all cells is a three-dimensional network comprising actin microfilaments, tubulin microtubules and intermediate filaments. Studies in many cell types have indicated roles for these cytoskeletal proteins in many diverse cellular processes including alteration of cell shape, movement of organelles, migration, endocytosis, secretion, cell division and extracellular matrix assembly. The cytoskeletal networks are highly organized in structure enabling them to fulfil their biological functions. This review will primarily focus on the organization and function of the three major cytoskeletal networks in articular cartilage chondrocytes. Articular cartilage is a major load-bearing tissue of the synovial joint; it is well known that the cytoskeleton acts as a physical interface between the chondrocytes and the extracellular matrix in ,sensing' mechanical stimuli. The effect of mechanical load on cytoskeletal element expression and organization will also be reviewed. Abnormal mechanical load is widely believed to be a risk factor for the development of osteoarthritis. Several studies have intimated that the major cytoskeletal networks are disorganized or often absent in osteoarthritic cartilage chondrocytes. The implications and possible reasoning for this are more widely discussed and placed into context with their potential relevance to disease and therapeutic strategies. [source] Fibrocartilage at the entheses of the suprascapular (superior transverse scapular) ligament of man,a ligament spanning two regions of a single boneJOURNAL OF ANATOMY, Issue 5 2001B. MORIGGL The suprascapular ligament converts the suprascapular notch into a foramen separating the vessels and nerve of the same name. It connects 2 regions of the same bone and does not cross any joint, and no mechanical function has yet been attributed to it. Nevertheless, variations in its thickness and length, and its tendency to ossify, suggest that the ligament responds to changes in mechanical load. This should be reflected in the composition of the extracellular matrix. The primary purpose of the present study is to demonstrate that the suprascapular ligament has fibrocartilaginous entheses (i.e. insertion sites), even though there is no obvious change in insertional angle that directly results from joint movement. Such a change is more typical of tendons or ligaments that cross highly mobile joints. The complete ligament (including both entheses) was removed from 7 cadavers shortly after death and fixed in 90% methanol. Cryosections were immunolabelled with a panel of monoclonal antibodies against collagens (types I, II, III, VI), glycosaminoglycans (chondroitin 4 sulphate, chondroitin 6 sulphate, dermatan sulphate and keratan sulphates), proteoglycans (aggrecan and versican) and link protein. Both entheses were strongly fibrocartilaginous, and a moderately fibrocartilaginous matrix was also detected throughout the remainder of the ligament. The extracellular matrix of both entheses labelled strongly for type II collagen, aggrecan and link protein. The fibrocartilaginous character of the entheses suggests that the insertion sites of the ligament are subject to both compressive and tensile loading and are regions of stress concentration. This in turn probably reflects the complex shape of the scapula and the presence of a conspicuous indentation (the suprascapular notch) near the ligament. The loading patterns may reflect either the attachment of muscles and/or the forces transmitted to the suprascapular ligament from the neighbouring coracoclavicular ligament. [source] Mechanical load induced by glass microspheres releases angiogenic factors from neonatal rat ventricular myocytes cultures and causes arrhythmiasJOURNAL OF CELLULAR AND MOLECULAR MEDICINE, Issue 5b 2008D. Y. Barac Abstract In the present study, we tested the hypothesis that similar to other mechanical loads, notably cyclic stretch (simulating pre-load), glass microspheres simulating afterload will stimulate the secretion of angiogenic factors. Hence, we employed glass microspheres (average diameter 15.7 ,m, average mass 5.2 ng) as a new method for imposing mechanical load on neonatal rat ventricular myocytes (NRVM) in culture. The collagen-coated microspheres were spread over the cultures at an estimated density of 3000 microspheres/mm2, they adhered strongly to the myocytes, and acted as small weights carried by the cells during their contraction. NRVM were exposed to either glass microspheres or to cyclic stretch, and several key angiogenic factors were measured by RT-PCR. The major findings were: (1) In contrast to other mechanical loads, such as cyclic stretch, microspheres (at 24 hrs) did not cause hypertrophy. (2) Further, in contrast to cyclic stretch, glass microspheres did not affect Cx43 expression, or the conduction velocity measured by means of the Micro-Electrode-Array system. (3) At 24 hrs, glass microspheres caused arrhythmias, probably resulting from early afterdepolarizations. (4) Glass microspheres caused the release of angiogenic factors as indicated by an increase in mRNA levels of vascular endothelial growth factor (80%), angiopoietin-2 (60%), transforming growth factor-, (40%) and basic fibroblast growth factor (15%); these effects were comparable to those of cyclic stretch. (5) As compared with control cultures, conditioned media from cultures exposed to microspheres increased endothelial cell migration by 15% (P<0.05) and endothelial cell tube formation by 120% (P<0.05), both common assays for angiogenesis. In conclusion, based on these findings we propose that loading cardiomyocytes with glass microspheres may serve as a new in vitro model for investigating the role of mechanical forces in angiogenesis and arrhythmias. [source] Modulation of Na+ -H+ exchange isoforms NHE1 and NHE3 by insulin-like growth factor-1 in isolated bovine articular chondrocytesJOURNAL OF ORTHOPAEDIC RESEARCH, Issue 11 2008Amanda L. Tattersall Abstract Incubation with serum modulates the transporters that regulate intracellular pH (pHi) in articular chondrocytes, upregulating acid extrusion by Na+ -H+ exchange (NHE). There is stimulation of NHE1, together with induction of NHE3 activity. These isoforms exhibit differential responses to components of mechanical load experienced by chondrocytes during joint loading. The identity of the component(s) of serum responsible is unknown. A possibility, however, is insulin-like growth factor-1 (IGF-1), present in normal cartilage and found at enhanced levels in osteoarthritic tissue. In the present study, the effects of IGF-1 on pHi regulation have been characterized using fluorescence measurements of bovine articular chondrocytes, and the sensitivity of pHi regulation to hyperosmotic shock and raised hydrostatic pressure determined. For cells isolated in the absence of IGF-1, pHi recovery following acidification was predominantly mediated by NHE1. Recovery was enhanced when cells were incubated for 18 h with 20 ng mL,1 IGF; this effect represented increased acid extrusion by NHE1, supplemented by NHE3 activity. NHE3 activity was not detected in IGF-1-treated cells that had been incubated with the protein synthesis inhibitor cycloheximide, although NHE1 activity was unaffected. In the absence of IGF-1, suspension in hyperosmotic solutions or raised hydrostatic pressure enhanced pHi recovery of acidified cells. This response was missing in cells incubated with IGF-1. Unresponsiveness to hyperosmotic shock represented inhibition of NHE3 activity, and was prevented using the protein kinase A inhibitor KT5720. For raised hydrostatic pressure, a decrease in NHE1 activity was responsible, and was prevented by the protein kinase C inhibitor chelerythrine. © 2008 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 26:1428,1433, 2008 [source] Comparison of the Temperature-Dependent Ferroelastic Behavior of Hard and Soft Lead Zirconate Titanate CeramicsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 9 2010Mie Marsilius The ferroelastic properties of a hard acceptor-doped lead zirconate titanate (PZT) ceramic are investigated between room temperature and 300°C. Comparison with a soft PZT shows that acceptor doping has a stronger influence on mechanically induced domain switching than on switching caused by electric fields. A quantitative analysis of spontaneous and remanent strain and polarization indicates that poling in the soft material is dominated by 180° domain processes, while non-180° processes dominate the strain behavior. If the mechanical load exceeds a threshold level, the "hardening" effect of the acceptor doping vanishes, and hard and soft materials behave identically. The results are discussed based on the defect dipole model and the charge drift model for hardening and aging in acceptor-doped ferroelectric ceramics. [source] AB-polymer Networks with Cooligoester and Poly(n -butyl acrylate) Segments as a Multifunctional Matrix for Controlled Drug ReleaseMACROMOLECULAR BIOSCIENCE, Issue 9 2010Christian Wischke Abstract Semi-crystalline AB-copolymer networks from oligo[(, -caprolactone)- co -glycolide]dimethacrylates and n -butylacrylate have recently been shown to exhibit a shape-memory functionality, which may be used for self-deploying and anchoring of implants. In this study, a family of such materials differing in their molar glycolide contents ,G was investigated to determine structure,property functional relationships of unloaded and drug loaded specimens. Drug loading and release were evaluated, as well as their degradation behavior in vitro and in vivo. Higher ,G resulted in higher loading levels by swelling and a faster release of ethacridine lactate, lower melting temperature of polymer crystallites, and a decrease in shape fixity ratio of the programmed temporary shape. For unloaded networks, the material behavior in vivo was independent of the mechanical load associated with different implantation sites and agreed well with data from in vitro degradation studies. Thus, AB networks could be used as novel matrices for biofunctional implants, e.g., for urogenital applications, which can self-anchor in vivo and provide mechanical support, release drugs, and finally degrade in the body to excretable fragments. [source] Collagen dynamics in articular cartilage under osmotic pressureNMR IN BIOMEDICINE, Issue 8 2006Göran Zernia Abstract Cartilage is a complex biological tissue consisting of collagen, proteoglycans and water. The structure and molecular mobility of the collagen component of cartilage were studied by 13C solid-state NMR spectroscopy as a function of hydration. The hydration level of cartilage was adjusted between fully hydrated (,80 wt% H2O) and highly dehydrated (,30 wt% H2O) using the osmotic stress technique. Thus, the conditions of mechanical load could be simulated and the response of the tissue macromolecules to mechanical stress is reported. From the NMR measurements, the following results were obtained. (i) Measurements of motionally averaged dipolar 1H,13C couplings were carried out to study the segmental mobility in cartilage collagen at full hydration. Backbone segments undergo fast motions with amplitudes of ,35° whereas the collagen side-chains are somewhat more mobile with amplitudes between 40 and 50°. In spite of the high water content of cartilage, collagen remains essentially rigid. (ii) No chemical shift changes were observed in 13C cross-polarization magic angle spinning spectra of cartilage tissue at varying hydration indicating that the collagen structure was not altered by application of high osmotic stress. (iii) The 1H,13C dipolar coupling values detected for collagen signals respond to dehydration. The dipolar coupling values gradually increase upon cartilage dehydration, reaching rigid limit values at ,30 wt% H2O. This indicates that collagen is essentially dehydrated in cartilage tissue under very high mechanical load, which provides insights into the elastic properties of cartilage collagen, although the mechanical pressures applied here exceed the physiological limit. Copyright © 2006 John Wiley & Sons, Ltd. [source] Frequency of the sit-to-stand task: a pilot study of free-living adultsPHYSIOTHERAPY RESEARCH INTERNATIONAL, Issue 3 2008Andy Kerr Purpose.,To report contemporary data on the daily frequency of the sit-to-stand (STS) movement in a healthy, independently living, adult population.,Relevance.,As a key determinant of functional independence, which has a high mechanical load, the STS movement is a common feature of rehabilitation. Knowledge of STS frequency during daily activities could inform rehabilitation goals and content, but has rarely been examined. To date, only McLeod et al. (1975) have investigated this, reporting an average of 92 daily STS transitions in healthy young participants.,Methods.,Fifteen healthy, free-living, ambulant adults (three males; mean age 40 years) were recruited from the general population. An activity monitor (activPALTM, PALtechnologies, Glasgow, UK) reported free-living activity for each subject for seven consecutive days.,Analysis.,The average number of STS transitions per day was calculated from the whole period. Data were separated into working and non-working days, and compared using a paired t-test.,Results.,On average, participants performed 64 (±19) STS movements each day, with large individual differences [range 35,105]. Participants performed significantly (p = 0.047) more STS movements on a working day [68 (±24)] than on a non-working day [55 (±17)].,Discussion.,Fewer STS movements were recorded than previously reported (McLeod et al., 1975). This may reflect general changes in lifestyle; however, comparisons should consider the small samples involved and methodological differences.,Conclusion.,This study provides contemporary data for STS frequency and demonstrates a significant difference between working and non-working days. This information could guide rehabilitation and future research. Copyright © 2008 John Wiley & Sons, Ltd. [source] Ocular rigidity in living human eyes in health and diseaseACTA OPHTHALMOLOGICA, Issue 2009IG PALLIKARIS Purpose It is known that the balance between aqueous humor secretion and outflow rate controls the steady - state average intraocular pressure (IOP). It has been also early identified that blood circulation results to IOP fluctuations practically synchronous to cardiac function. IOP is the primary mechanical load to several ocular structures including the optical nerve head. Methods In-vivo intraoperative measurement of these quantities as well as secretion/outflow coefficients in humans allowed us to quantify ocular rigidity, IOP and its fluctuations (and pulsatile blood flow) in a series of physiological and pathological eyes. Ocular rigidity, outflow facility and pulsatile ocular blood flow were measured intraoperatively in a cohort of 63 patients undergoing cataract surgery. Measurements were also performed in a series of age related macular degeneration (AMD) patients. Results The eye, is a living structure under a continuously varying mechanical load that is strongly related to ocular haemodynamics. Ocular rigidity ranged from 0.0122 to 0.0343 (mean 0.0208),l-1. Outflow facility coefficient (derived from pressure decay curves) was 0.33 (sd 0.15),l/min/mmHg. Pulsatile ocular blood flow exhibited a strong negative correlation to IOP in all subjects. The ocular rigidity coefficient was higher in wet AMD patients compared to patients with dry AMD and healthy controls. Conclusion There are indications that this mechanical load, associated also to ocular rigidity, can not only inter-modulate blood flow but also have a long-term effect on other structures in the eye. Understanding the role of these parameters may contribute to the understanding of ocular disease. [source] GENETIC INFLUENCES ON THE ARTERIAL WALLCLINICAL AND EXPERIMENTAL PHARMACOLOGY AND PHYSIOLOGY, Issue 7 2007Bronwyn Kingwell SUMMARY 1Arterial stiffness, which has independent predictive value for cardiovascular events, seems to have a genetic component, largely independent of the influence of blood pressure and other cardiovascular risk factors. 2In animal models of essential hypertension (stroke-prone spontaneously hypertensive rats and spontaneously hypertensive rats), structural modifications of the arterial wall include an increase in the number of elastin,smooth muscle cell connections and smaller fenestrations of the internal elastic lamina, possibility leading to redistribution of the mechanical load towards elastic materials. These modifications may give rise to mechanisms explaining why changes in arterial wall material accompanying wall hypertrophy in these animals are not associated with an increase in arterial stiffness. 3In monogenic connective tissue diseases (Marfan, Williams and Ehlers,Danlos syndromes) and the corresponding animal models, precise characterization of the arterial phenotype makes it possible to determine the influence of abnormal, genetically determined, wall components on arterial stiffness. 4Such studies have highlighted the role of extracellular matrix signalling in the vascular wall and have shown that elastin and collagen not only display elasticity or rigidity, but are also involved in the control of smooth muscle cell function. 5These data provide strong evidence that arterial stiffness is affected by the amount and density of stiff wall material and the spatial organization of that material. [source] EVOLUTION OF SCAPULA SIZE AND SHAPE IN DIDELPHID MARSUPIALS (DIDELPHIMORPHIA: DIDELPHIDAE)EVOLUTION, Issue 9 2009Diego Astúa The New World family Didelphidae, the basal lineage within marsupials, is commonly viewed as morphologically conservative, yet includes aquatic, terrestrial, scansorial, and arboreal species. Here, I quantitatively estimated the existing variability in size and shape of the Didelphidae scapula (1076 specimens from 56 species) using geometric morphometrics, and compared size and shape differences to evolutionary and ecologic distances. I found considerable variation in the scapula morphology, most of it related to size differences between species. This results in morphologic divergence between different locomotor habits in larger species (resulting from increased mechanical loads), but most smaller species present similarly shaped scapulae. The only exceptions are the water opossum and the short-tailed opossums, and the functional explanations for these differences remain unclear. Scapula size and shape were mapped onto a molecular phylogeny for 32 selected taxa and ancestral size and shapes were reconstructed using squared-changed parsimony. Results indicate that the Didelphidae evolved from a medium- to small-sized ancestor with a generalized scapula, slightly more similar to arboreal ones, but strikingly different from big-bodied present arboreal species, suggesting that the ancestral Didelphidae was a small scansorial animal with no particular adaptations for arboreal or terrestrial habits, and these specializations evolved only in larger-bodied clades. [source] Meshfree simulation of failure modes in thin cylinders subjected to combined loads of internal pressure and localized heatINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 8 2008Dong Qian Abstract This paper focuses on the non-linear responses in thin cylindrical structures subjected to combined mechanical and thermal loads. The coupling effects of mechanical deformation and temperature in the material are considered through the development of a thermo-elasto-viscoplastic constitutive model at finite strain. A meshfree Galerkin approach is used to discretize the weak forms of the energy and momentum equations. Due to the different time scales involved in thermal conduction and failure development, an explicit,implicit time integration scheme is developed to link the time scale differences between the two key mechanisms. We apply the developed approach to the analysis of the failure of cylindrical shell subjected to both heat sources and internal pressure. The numerical results show four different failure modes: dynamic fragmentation, single crack with branch, thermally induced cracks and cracks due to the combined effects of pressure and temperature. These results illustrate the important roles of thermal and mechanical loads with different time scales. Copyright © 2008 John Wiley & Sons, Ltd. [source] The cells of the rabbit meniscus: their arrangement, interrelationship, morphological variations and cytoarchitectureJOURNAL OF ANATOMY, Issue 5 2000MARIE-PIERRE HELLIO LE GRAVERAND Four major morphologically distinct classes of cells were identified within the adult rabbit meniscus using antibodies to cytoskeletal proteins. Two classes of cell were present in the fibrocartilage region of the meniscus. These meniscal cells exhibited long cellular processes that extended from the cell body. A third cell type found in the inner hyaline-like region of the meniscus had a rounded form and lacked projections. A fourth cell type with a fusiform shape and no cytoplasmic projections was found along the superficial regions of the meniscus. Using a monoclonal antibody to connexin 43, numerous gap junctions were observed in the fibrocartilage region, whereas none were seen in cells either from the hyaline-like or the superficial zones of the meniscus. The majority of the cells within the meniscus exhibited other specific features such as primary cilia and 2 centrosomes. The placement of the meniscal cell subtypes as well as their morphology and architecture support the supposition that their specific characteristics underlie the ability of the meniscus to respond to different types of environmental mechanical loads. [source] Mechanical load induced by glass microspheres releases angiogenic factors from neonatal rat ventricular myocytes cultures and causes arrhythmiasJOURNAL OF CELLULAR AND MOLECULAR MEDICINE, Issue 5b 2008D. Y. Barac Abstract In the present study, we tested the hypothesis that similar to other mechanical loads, notably cyclic stretch (simulating pre-load), glass microspheres simulating afterload will stimulate the secretion of angiogenic factors. Hence, we employed glass microspheres (average diameter 15.7 ,m, average mass 5.2 ng) as a new method for imposing mechanical load on neonatal rat ventricular myocytes (NRVM) in culture. The collagen-coated microspheres were spread over the cultures at an estimated density of 3000 microspheres/mm2, they adhered strongly to the myocytes, and acted as small weights carried by the cells during their contraction. NRVM were exposed to either glass microspheres or to cyclic stretch, and several key angiogenic factors were measured by RT-PCR. The major findings were: (1) In contrast to other mechanical loads, such as cyclic stretch, microspheres (at 24 hrs) did not cause hypertrophy. (2) Further, in contrast to cyclic stretch, glass microspheres did not affect Cx43 expression, or the conduction velocity measured by means of the Micro-Electrode-Array system. (3) At 24 hrs, glass microspheres caused arrhythmias, probably resulting from early afterdepolarizations. (4) Glass microspheres caused the release of angiogenic factors as indicated by an increase in mRNA levels of vascular endothelial growth factor (80%), angiopoietin-2 (60%), transforming growth factor-, (40%) and basic fibroblast growth factor (15%); these effects were comparable to those of cyclic stretch. (5) As compared with control cultures, conditioned media from cultures exposed to microspheres increased endothelial cell migration by 15% (P<0.05) and endothelial cell tube formation by 120% (P<0.05), both common assays for angiogenesis. In conclusion, based on these findings we propose that loading cardiomyocytes with glass microspheres may serve as a new in vitro model for investigating the role of mechanical forces in angiogenesis and arrhythmias. [source] Pressure,pain threshold of oral mucosa and its region-specific modulation by pre-loadingJOURNAL OF ORAL REHABILITATION, Issue 11 2003T. Ogawa summary Once subjected to denture wearing, oral mucosa has to withstand mechanical loads of various levels and durations. However, how this load affects oral mucosal sensitivity is unknown. This study investigated the pressure,pain threshold (PPT) of oral mucosa with or without pre-loading. An electric pressure algometer was developed specifically for measuring the PPT of oral mucosa. Measurements of 10 dentulous maxillae showed that the baseline PPT (BPPT) of the palatal site was 4·9- and 3·7-fold greater than that of the labial or buccal sites, respectively. The PPT of the labial site decreased significantly compared with its BPPT after 2 s,100% BPPT and 5 s,100% BPPT pre-loading. The PPT of the palatal site increased after 5 s,50% BPPT and 5 s,80% BPPT and 0·2 s,100% BPPT and 2 s,100% BPPT pre-loading. The PPT of the buccal site did not change after all levels and durations of pre-loadings tested. These results indicated the disproportionate modulation of oral mucosal PPT following various loads, suggesting that oral mucosa possesses region-specific psychophysical tolerance to mechanical stimuli. [source] In situ monitoring of residual strain development during composite curePOLYMER COMPOSITES, Issue 3 2002Allan S. Crasto Internal (residual) stresses build up in a thermosetting composite as the matrix shrinks during cure, and again as the composite is cooled to ambient from its elevated processing temperature. These stresses can be significant enough to distort the dimensions and shape of a cured part as well as initiate damage in off-axis plies, either during fabrication or under the application of relatively low mechanical loads. The magnitude of these stresses depends on a number of factors including constituent anisotropy, volume fraction and thermal expansion, ply orientation, process cycle, and matrix cure chemistry. In this study, embedded strain gauges were employed to follow, in situ, the buildup of residual strains in carbon fiber-reinforced laminates during cure. The data were compared to those from volumetric dilatometer studies to ascertain the fraction of resin shrinkage that contributed to residual stress buildup during cure. Based on earlier studies with single-fiber model composites, the process cycle in each case was then varied to determine if the cycles optimized to minimize residual stresses for isolated fibers in an infinite matrix were applicable to the reduction of residual stresses in conventional multifiber composites. The results of these studies are reported here. [source] The effects of total hip arthroplasty on the structural and biomechanical properties of adult boneAMERICAN JOURNAL OF PHYSICAL ANTHROPOLOGY, Issue 2 2009Joshua J. Peck Abstract The responsiveness of bone to mechanical stimuli changes throughout life, with adaptive potential generally declining after skeletal maturity is reached. This has led some to question the importance of bone functional adaptation in the determination of the structural and material properties of the adult skeleton. A better understanding of age-specific differences in bone response to mechanical loads is essential to interpretations of long bone adaptation. The purpose of this study is to examine how the altered mechanical loading environment and cortical bone loss associated with total hip arthroplasty affects the structural and biomechanical properties of adult bone at the mid-shaft femur. Femoral cross sections from seven individuals who had undergone unilateral total hip arthroplasty were analyzed, with intact, contralateral femora serving as an approximate internal control. A comparative sample of individuals without hip prostheses was also included in the analysis. Results showed a decrease in cortical area in femora with prostheses, primarily through bone loss at the endosteal envelope; however, an increase in total cross-sectional area and maintenance of the parameters of bone strength, Ix, Iy, and J, were observed. No detectable differences were found between femora of individuals without prostheses. We interpret these findings as an adaptive response to increased strains caused by loading a bone previously diminished in mass due to insertion of femoral prosthesis. These results suggest that bone accrued through periosteal apposition may serve as an important means by which adult bone can functional adapt to changes in mechanical loading despite limitations associated with senescence. Am J Phys Anthropol 2009. © 2008 Wiley-Liss, Inc. [source] Influence of forces on peri-implant boneCLINICAL ORAL IMPLANTS RESEARCH, Issue S2 2006Flemming Isidor Abstract: Occlusal forces affect an oral implant and the surrounding bone. According to bone physiology theories, bones carrying mechanical loads adapt their strength to the load applied on it by bone modeling/remodeling. This also applies to bone surrounding an oral implant. The response to an increased mechanical stress below a certain threshold will be a strengthening of the bone by increasing the bone density or apposition of bone. On the other hand, fatigue micro-damage resulting in bone resorption may be the result of mechanical stress beyond this threshold. In the present paper literature dealing with the relationship between forces on oral implants and the surrounding bone is reviewed. Randomized controlled as well as prospective cohorts studies were not found. Although the results are conflicting, animal experimental studies have shown that occlusal load might result in marginal bone loss around oral implants or complete loss of osseointegration. In clinical studies an association between the loading conditions and marginal bone loss around oral implants or complete loss of osseointegration has been stated, but a causative relationship has not been shown. [source] | |||||||||||||||||||