Effect Of Cyclic Strain Research Articles

Effect of Cyclic Strain on the Mechanical Behavior of a Thermoplastic Polyurethane

Thermoplastic polyurethanes (TPUs) are polymeric materials employed in a wide array of applications in the industrial field. Knowledge of their mechanical behavior is essential in order to obtain an accurate prediction of stresses and deformations resulting from loading. Mechanical and physical properties of these materials have been studied in the past, but their stress-strain behavior in the presence of cyclic loading has comparatively received much less attention. In this paper, experimental and constitutive modeling aspects concerning cyclic mechanical response of a TPU are investigated. The effect of imposing a cyclic strain on a TPU is studied by means of an experimental procedure based on alternate-symmetric tests in strain control at different strain levels and frequencies. During the tests, the increase in temperature due to the hysteretic heating can also be controlled by means of a compressed air cooling apparatus specifically devised. By taking advantage of the possibility of controlling and stabilizing temperature, the cyclic mechanical response can then be investigated at different temperatures and strain levels. A transient thermal analysis using finite element method (FEM) was also carried out to investigate temperature distribution on the specimen. TPU exhibited cyclic softening, and by comparing stabilized material response at different temperatures, cyclic softening was shown to be composed of a mechanical contribution and a thermal component. The TPU’s stress-strain curve changed considerably under cyclic loading conditions. In particular, cyclic softening was observed to increase with temperature and imposed cyclic strain, with a progressive shrinking of hysteresis loop passing from virgin condition to stabilized cyclic condition. Based on the experimental data, the cyclic curve could be determined as a function of temperature and could be fitted with a hyperelastic law in which material parameters are temperature dependent. The TPU exhibited significant sensitivity to cyclic loading, and this study demonstrated the importance of considering mechanical response in cyclic condition for design purposes. In particular, the identification of mechanical and thermal contributions to cyclic softening can be useful when studying fatigue failure mechanisms of these materials. Knowledge of cyclic curve can help when developing constitutive model for polymers to better predict a long-term behavior when cyclic loading is expected. The introduction of a dependence of cyclic curve on temperature allows considering simultaneously the new “material state” of the cycled polymer and, with some limitations, the thermal influence on mechanical response.

Effects of cyclic strain on rat tail tenocytes

Cyclical mechanical strain is considered an important component in flexor tendon cell activation to prevent adhesions and enhance the healing process after tissue injury or surgery, but the biochemical events associated with this remain unclear. To address this, we examined the effects of cyclic tension on the expression of hyaluronic acid, an important lubricant and signal transducer in tendon, on its receptor (CD44), and on total glycosaminoglycan content in rat tail derived tendon fibroblasts in vitro. Tenocytes were plated on fibronectin coated silastic membranes and the cultures were held static or subjected to vacuum induced deformation for a period of 5 min once every 8 h as a model of cyclic mechanical stress. After 24 h medium and cell layers were collected for analyses by product specific ELISA, Western blot, and colorimetric dye-binding assays. Strained tenocytes produced a nearly two-fold increase in hyaluronic acid and a greater than 60% increase in CD44, but had an insignificant effect on total glycosaminoglycan content. Our results predict that high levels of strain may therefore rapidly enhance the expression of hyaluronic acid and cause, albeit still unresolved, downstream effects on CD44 activation, to influence tendon cell activity and enhance the process of tendon repair.

Effects of Cyclic Strain and Growth Factors on Vascular Smooth Muscle Cell Responses

Under physiological and pathological conditions, vascular smooth muscle cells (SMC) are exposed to different biochemical factors and biomechanical forces. Previous studies pertaining to SMC responses have not investigated the effects of both factors on SMCs. Thus, in our research we investigated the combined effects of growth factors like Bfgf (basic fibroblast growth factor), TGF-β (transforming growth factor β) and PDGF (platelet-derived growth factor) along with physiological cyclic strain on SMC responses. Physiological cyclic strain (10% strain) significantly reduced SMC proliferation compared to static controls while addition of growth factors bFGF, TGF-β or PDGF-AB had a positive influence on SMC growth compared to strain alone. Microarray analysis of SMCs exposed to these growth factors and cyclic strain showed that several bioactive genes (vascular endothelial growth factor, epidermal growth factor receptor, etc.) were altered upon exposure. Further work involving biochemical and pathological cyclic strain stimulation will help us better understand the role of cyclic strain and growth factors in vascular functions and development of vascular disorders.

Message from the Scientific Organizers

This volume of Tribology Letters contains articles that were presented at the 428th Wilhelm and Else Heraeus Seminar ‘‘Physics of Tribology—Understanding Friction and Wear in technical systems’’. The seminar took place at the ‘‘Physikzentrum’’ in Bad Honnef, Germany from 23rd to 25th of March, 2009 with 60 participants from 14 countries. The purpose of the seminar was to present and discuss the physics of friction and wear in a multi-scale approach from the atomic level up to the size of an engine component. Within this topical setting, several contributions dealt with plastic deformations and third-body formation caused by sliding friction and by manufacturing (grinding). Insights into how nanocrystalline microstructures in bcc and fcc metals are generated as an effect of cyclic straining is steadily being gained. In addition, the importance of on-line wear measurement and ultra-low wear rates was discussed in several talks. Another important topic for macroscopic systems was the use of novel water based lubricants and of polyols. On the simulation side, several presentations dealt with elastic contact mechanics. A new theory now allows the exact calculation of the contact area even between millimeter-sized technical (e.g., aluminum–silicon alloys) surfaces. A novel reactive potential allows more realistic MD simulations of diamond-like carbon (DLC). On the atomic scale the experimental focus was on friction force microscopy. New experimental results showed a link between atomic friction measured on graphene and electron–phonon coupling for the first time. Another talk showed that the widely used Prandtl–Tomlinson model is over-simplifying the fast motion of the AFM tip apex. The poster session also allowed younger researchers to present their work. The poster prize was awarded to a contribution from Julich which dealt with experiments on rubber sealing and was an impressive example of intelligent research on a small budget. Overall the seminar showed how atomic-scale experiments and simulations are able to stimulate engineering tribology and vice versa. It therefore seems that future workshops of this kind may help to fertilize all disciplines of tribology. At this point we would again like to thank the Wilhelm and Else Heraeus foundation for funding, as well as their perfect organization of the seminar.

The effect of cyclic strain on embryonic stem cell-derived cardiomyocytes

Cardiomyocytes in the body are subjected to cyclic mechanical strain induced by the rhythmic heart beating. In this study, we tested the hypothesis that cyclic strain promotes cardiomyogenesis of embryonic stem cell-derived cardiomyocytes (ESCs). ESCs cultured on elastic polymer [poly(lactide- co-caprolactone), PLCL] scaffolds subjected to cyclic strain in vitro displayed elevated cardiac gene expression compared to unstrained controls. Six weeks after implantation into infarcted rat myocardium, the elastic cardiac patches (ESC-seeded PLCL scaffolds) showed reduced fibrotic tissue formation, likely due to a combination of lower apoptotic activity, higher vascular endothelial growth factor (VEGF) expression, and more extensive angiogenesis in the strained versus unstrained control [ESC-seeded, non-elastic poly(lactide- co-glycolide) scaffolds] patches. Importantly, cardiac gene expression was upregulated in the elastic patches compared to control, with evidence for cardiomyocyte-specific microstructures including myofibrillar bundles and Z-lines. This study shows that the use of an elastic polymer scaffold designed to permit mechanical strain transduction as a cell transplantation vehicle significantly increases cardiomyogenesis of the implanted ESCs.

Ratchetting behaviour of nitrile butadiene rubber material

A series of uniaxial and multiaxial ratchetting experiments were conducted on nitrile butadiene rubber material (NBR). The effects of cyclic strain, stress and their histories on strain cyclic characteristics and ratchetting behaviour were studied respectively. Test results show that cyclic stabilisation of the stress–strain behaviour takes place under lower loading, but changed as the load increased under uniaxial ratchetting experiment. The ratchetting strain rate depends on loading conditions. Ratchetting strain and its rate rise with the increase of the axial stress and shear strain amplitude. In addition, loading history and loading sequence are found to have significant influence on ratchetting behaviour. The prior stress cycling with higher loading can restrain the ratchetting of subsequent stress cycling with lower loading. But the prior stress cycling with lower loading has little effect on the ratchetting of subsequent stress cycling with higher loading. Ratchetting behaviour is sensitive to the strain rate under multiaxial loading, and both ratchetting strain and its rate increase with decreasing shear strain rates. Creep behaviour plays an important role in the ratchetting strain and its influence on ratchetting behaviour can not be neglected.

Design of a New Stretching Apparatus and the Effects of Cyclic Strain and Substratum on Mouse Lung Epithelial-12 Cells

The pulmonary epithelium is exposed to mechanical strains during normal breathing or mechanical ventilation. While important for the regulation of cellular processes, excessive strains damage epithelial cells. To investigate the effects of strain on the epithelium, we developed a stretching device to apply equi-biaxial strains to cells cultured on elastic membranes. Following device validation, we exposed a murine epithelial cell line (MLE-12) to 30 min of cyclic stretch with 0, 25, 50, 75 and 100% change in surface area on pronectin or type I collagen coated membranes. Following stretch, we assessed cell viability using fluorescent immunocytochemisty and surfactant secretion using [(3)H] labeled phosphatidylcholine (PC). Cell injury increased with increasing strain with cells on pronectin showing more injury than on type I collagen. Stretching had no effect on surfactant secretion on either substratum suggesting MLE-12 cells are a poor model for stretch-induced surfactant secretion. The cells grown on pronectin, however, demonstrated a 3-fold increase in surfactant secretion compared to those grown on type I collagen at all strains. This suggests that, while this cell line does not demonstrate stretch-induced surfactant secretion, the underlying extracellular matrix plays a crucial factor in both cell death and signal transduction in response to strain.

Cyclic Straining of Cell-Seeded Synthetic Ligament Scaffolds: Development of Apparatus and Methodology

Cyclic tensile strains acting along a ligament implant are known to stimulate cells that colonize it to proliferate and to synthesize an extracellular matrix (ECM), which will then remodel and form a new ligament structure. However, this process of tissue induction is poorly understood. As a first step toward elucidating this process, we aimed to investigate the effect of cyclic tensile strain on the proliferation of, and possible ECM synthesis by, cells colonizing ligament scaffolds. Because there was no commercially available apparatus to undertake such investigation the objectives of this study were to develop an apparatus for the application of cyclic tensile strains on cell-seeded synthetic ligament scaffolds and to develop and validate (through preliminary data obtained using the apparatus) methodology for studying the effect of cyclic strain on cell proliferation. We designed a multi-station test apparatus that operated inside an incubator. It allowed the application of tensile cyclic strains of between 0.5% and 5% at a frequency of 1 Hz on cell-seeded polyester ligament scaffolds immersed in culture medium. Test stations with windows in their bases could be easily de-coupled from the apparatus. This allowed monitoring of cell proliferation and morphology, with inverted light microscopy, through the transparent glass bases of the culture wells. Preliminary experiments lasting for 1 day or 9 weeks examined the effect of selected aspects of the cyclic strain on proliferation of cells seeded onto ligament scaffolds. Tests lasting for 1 day showed that the application of cyclic tensile strain of 5% for 4 h increased cell proliferation 24% above that observed in unstrained controls (p < .05). Scanning electron microscopy data from tests lasting for 9 weeks demonstrated further the dependency of cell proliferation and possible ECM synthesis on the magnitude of the strain. The larger the amplitude, the greater was the coverage of the scaffold with cells and ECM. Transmission electron microscopy of the ECM observed at 9 weeks showed evidence of collagen fibrils aligned in the direction of load in strained scaffolds, whereas the tissue on the control scaffolds was random.

The Effects of Cyclic Strains on the Hybrid Aligned Nanofibrous Scaffold Seeded with Smooth Muscle Cells

The Effects of Cyclic Strains on the Hybrid Aligned Nanofibrous Scaffold Seeded with Smooth Muscle Cells

Effect of Cyclic Strain on the Orientation of Cultured Macrophages

When macrophages are cultured under cyclic strain, they align parallel to the direction of strain, in contrast to the perpendicular alignment reported for other types of cells. However, the time at which their orientation starts and the influence of fluid shear stress acting on cells during cyclic stretching have not been identified. In the present study, murine peritoneal macrophages were attached to silicone membranes and cultured up to 8 hours under cyclic uniaxial stretch of 10% amplitude and 1 Hz frequency. Cell morphology was observed and the angle of orientation of spindle-shaped cells (spindle cells) was determined. Distributions of actins in macrophages were also examined after the application of cyclic strain. Percentage of spindle cells increased with culture period, and the cells were getting longer with time. After around 2 hours, spindle cells started to align parallel to the direction of strain. At 8 hours, 53% of spindle cells were aligned within the angle of 20 degrees to the direction of strain. Prior to the orientation of cell bodies, accumulation of actin filaments was observed in the peripheral area of cells in the direction parallel to the strain direction. When the silicone membranes were moved back-and-forth in culture medium without stretching for 8 hours, macrophages did not show preferential orientation. These results suggest that macrophages actively align parallel to the direction of strain and start to orient around 2 hours after the initiation of cyclic strain.

Effect of cyclic strain and plating matrix on cell proliferation and integrin expression by ligament fibroblasts

The role of cell surface integrins in cell migration, proliferation, and attachment to matrix molecules is well known. Integrin-matrix interactions have been implicated in mechanotransduction and load transmission from the outside to the inside of the cell. In this study, the effect of cyclic strain on the cell proliferation, attachment, and expression of integrin subunits beta1, beta3, and alpha5 was determined in anterior cruciate ligament (ACL) and medial collateral ligament (MCL) fibroblasts grown on polystyrene, Type I collagen, laminin, elastin, and fibronectin. ACL fibroblast proliferation was not affected by growth substrate whereas MCL cells reached confluence more rapidly on fibronectin compared with collagen or polystyrene. Exposure to 5% cyclic strain resulted in a significant decrease in ACL and MCL fibroblast proliferation on fibronectin and Type I collagen. MCL cells showed a greater strain-dependent inhibition of cells grown on a fibronectin substrate than those grown on collagen. This matrix-dependent effect of strain on cell proliferation was not seen with ACL cells. Attachment of ACL and MCL fibroblasts was stronger to fibronectin compared with Type I collagen, laminin, and polystyrene. In the absence of applied load, the expression of beta1, beta3, and alpha5 subunits was not substrate dependent and the expression of beta1 and alpha5 integrin subunits was higher in MCL cells than ACL cells on all substrates. In contrast, the expression of beta3 integrin subunit was higher in ACL cells than MCL cells. In response to 5% strain, beta1, and alpha5 expression increased in all fibroblasts with MCL cells having a higher magnitude of expression. beta3 expression showed a 90% increase in response to load when grown on laminin for both MCL and ACL fibroblasts and demonstrated no change in expression on Type I collagen or fibronectin. The duration of applied strain from 2 versus 22 h had no effect on cell proliferation or integrin expression.

The effect of cyclic straining on the drawing stress of low carbon steel bars

The investigations covering the work hardening behavior of metals under strain path changes have pointed out the possibility of employing the strain softening phenomenon in sequential forming operations, specially in the case of cyclic straining. In this paper, the effects of cyclic torsion on the drawing stress of low carbon steel bars have been investigated. The material was drawn up to five passes. Cyclic straining was carried out between the last two stages of drawing and between every drawing pass. The substructural aspects of the bars were also analyzed. Cyclic torsion led to a decrease in the drawing stress values, whose magnitude depended on the number of forming passes considered in the experiment. The results also showed the occurrence of non-cumulative strain softening effects. Dislocation restructuring was found to be the softening mechanism related to the results.

A three-dimensional collagen matrix as a suitable culture system for the comparison of cyclic strain and hydrostatic pressure effects on intervertebral disc cells

To study intervertebral disc cell mechanobiology, the authors developed experimental systems that allow the application of cyclic strain and intermittent hydrostatic pressure (IHP) on isolated disc cells under equal three-dimensional (3D) culture conditions. The purpose of the study was to characterize disc cell proliferation, viability, morphology, and gene expression in 3D collagen matrices. The effects of cyclic strain (1, 2, 4, and 8% strain; 1 Hz) and IHP (0.25 MPa, 0.1 Hz) on gene expression (real-time polymerase chain reaction) of anabolic and catabolic matrix proteins were investigated and compared with those derived from mechanically unstimulated controls. Intervertebral disc cells proliferated in the collagen gels (mean viability 91.6%) and expressed messenger RNA for collagen I, collagen II, aggrecan, matrix metalloproteinase (MMP)-2, and MMP-3. Morphologically, both spindle-shaped cells with longer processes and rounded cells were detected in the collagen scaffolds. Cyclic strain increased collagen II and aggrecan expression and decreased MMP-3 expression of anulus fibrosus cells. No significant difference between the four strain magnitudes was found. Intermittent hydrostatic pressure tended to increase collagen I and aggrecan expression of nucleus cells and significantly decreased MMP-2 and -3 expression of nucleus cells, whereas aggrecan expression of anulus cells tended to decrease. Based on these results, the collagen matrix appeared to be a suitable substrate to apply both cyclic strain and IHP to intervertebral disc cells under 3D culture conditions. Individual variations may be influenced by the extent of degeneration of the disc specimens from which the cells were isolated. This experimental setup may be suitable for studying the influence of degeneration on the disc cell response to mechanical stimuli.

The role of STAT-3 in the mediation of smooth muscle cell response to cyclic strain

Hemodynamic forces, including shear stress and cyclic strain, have been recognised as important modulators of vascular cell morphology and function. However, the mechanism by which vascular cells sense and transduce the extracellular mechanical signals into the cell nucleus has not yet been clarified. The purpose of our study was to assess the involvement of the signal transducer and activator of transcription-3 (STAT-3) in the signaling pathway mediating the response of vascular smooth muscle cells (SMC) to cyclic strain. Embryonic A7r5 SMC derived from thoracic aortas of DB1X rats were seeded on flexible collagen I-coated plates. Cells were subjected to 10% average strain at 60 cycles/min for various time periods. Activation of STAT-3, p38, extracellular signal-regulated kinase (ERK) 1/2 and Src was assessed by immunoblotting using phosphospecific antibodies. The interactions between STAT-3 phosphorylation and p38, ERK1/2, phosphatidylinositol-3 (PI3K), mammalian target of rapamycin (mTOR), Janus kinase (JAK) 2 and Src were evaluated by pretreating the cells with specific inhibitors including SB202190, PD98059, LY294002, wortmannin, rapamycin, AG490 and PP1. Serine phosphorylation of STAT-3 was increased by 2-fold after 15 min of cyclic strain, while tyrosine phosphorylation was increased by 2.3-fold after 60 min. Inhibition of ERK1/2 by PD98059 prevented serine phosphorylation of STAT-3, whereas inhibition of Src by PP1 prevented STAT-3 tyrosine phosphorylation. Pretreating the cells with SB202190, a specific inhibitor of p38, resulted in an increase in basal phosphorylation of ERK1/2 and a subsequent increase in basal serine phosphorylation of STAT-3. In conclusion, both serine and tyrosine phosphorylation of STAT-3 are involved in the signaling pathway mediating the effects of cyclic strain on vascular SMC. Serine phosphorylation of STAT-3 is mediated by ERK1/2, while tyrosine phosphorylation is mediated by Src. A negative feedback loop was also found between p38 and ERK1/2.

Cyclic strain modulates FGF-b expression and secretion in vitro, implications in cerebral aneurysm formation

Abstract Introduction: Saccular aneurysms develop in cerebral vessels during aging at sites of increased mechanical stress. We investigated the effects of cyclic strain on rat aortic smooth muscle cells and A7r5 smooth muscle cell line. Since FGF-b regulates proliferation and survival of smooth muscle and endothelial cells, our primary end points were transcriptional levels of FGF-b, release of FGF-b into the medium, and the effects of the stretch-conditioned medium on FGF-b expression in static cells. Methods: Cells were grown on silicon membranes coated with 0.5% collagen and exposed to 7%, 1Hz cyclic stretch. Relative gene expression was measured by real time PCR after stretching for 2, 6, and 24 hrs. FGF-b in the medium was measured by ELIZA. Experiments and transcripts were run in triplicates. Results are expressed as mean ± SEM. Results: Mild strain decreased the expression of FGF-b in a time dependant manner (6.8 ± 1.2 fold @ 2hrs and 700 ± 140 @ 6hrs). Stretch-conditioned medium decreased FGF-b expression in static A7r5 cells (60 ± 14 fold by 2hr medium, and 490 ± 64 fold by 6hr medium). Surprisingly, stretching increased FGF-b release in the medium ( Conclusions: Cyclic strain released FGF-b from smooth muscle cells. It also released another factor that decreased the expression of FGF-b gene in spite of the autoinductive properties of FGF-b. This may partly explain the observation that early aneurysms exhibit thickening of the endothelium and progressive regression of the media.

Molecular and biological effects of hemodynamics on vascular cells.

A variety of systemic risk factors, including smoking, hypertension, hyperlipidemia and diabetes have been found to promote atherosclerosis. Although these elements affect blood vessels equally, clinically significant lesions develop at predictable locations, i.e., major branch points and bifurcations. This suggests that the development of clinically significant atherosclerotic plaques involves a complex interplay between vascular anatomy, vascular biology and hemodynamic forces. Cyclic strain, circumferential pulsatile pressure exerted upon a vessel wall, has been found to cause changes in endothelial cells that tend to disfavor atherosclerosis formation. Cultured endothelial cells have been shown to migrate, proliferate and alter cytoskeletal alignment in response to cyclic strain. Levels of macromolecules such as prostacyclin, endothelin, nitric oxide and tissue plasminogen activator have been found to be altered by cyclic strain. Additionally, cyclic strain has been shown to stimulate expression of cellular adhesion molecules such as ICAM-1 and intracellular second messenger systems such as the adenylate cyclase-cAMP, diacylglycerol-IP3, and protein kinase C pathways. This article reviews the most current pertinent literature and summarizes the presently known effects of cyclic strain on endothelial cells.

Effects of cyclic strain on vascular cells.

Hemodynamic forces, including shear stress and cyclic strain, have been recognized as important modulators of vascular cell morphology and function. The mechanism by which vascular cells sense and transduce the extracellular mechanical signals into the cell nucleus has only recently begun to come to light. Integrins, ion channels, platelet-derived growth factor receptors, and G proteins have been recognized as mechanosensors, converting the mechanical stimuli into chemical signals. Activation of second messengers, including mitogen-activated protein kinases, protein kinase C, and Akt, follows, leading to an increase in the activity of transcription factors such as activator protein (AP)-1, AP-2, cAMP-responsive element (CRE), early growth response (Egr)-1, and nuclear factor (NF)-kappa B. Binding of these factors to the DNA leads to activation of numerous genes that regulate cell proliferation, apoptosis, differentiation, morphology, migration, and secretory function. Understanding of these responses has provided new insights in the pathogenesis and treatment of vascular diseases, such as atherosclerosis and intimal hyperplasia.

Uniaxial and non-proportionally multiaxial ratcheting of U71Mn rail steel: experiments and simulations

The ratcheting and strain cyclic characteristics of U71Mn rail steel were experimentally researched under uniaxial and non-proportionally multiaxial cyclic loading at room temperature. The effects of cyclic strain, stress and their histories on strain cyclic characteristics and ratcheting were studied, respectively. It is shown that: U71Mn rail steel exhibits a cyclic stabilization and non-memorization for previous loading history under strain cycling; however, the ratcheting of the material depends greatly not only on the current values of mean stress and stress amplitude, but also on their histories; the non-proportionality of multiaxial loading path only causes a negligible additional hardening for the material. Based on the Ohno–Wang non-linear kinematic hardening model [Int. J. Plast. 9 (1993) 375, 391], the uniaxial and multiaxial ratcheting behaviours of the material were simulated by a visco-plastic constitutive model. The simulated results are in good consistence with the experimental ones.

Effect of cyclical stretch on matrix synthesis of human patellar tendon cells

The significance of mobilization and loading for healing ligaments and tendons is generally accepted today. Local deformation of cells thereby represents the key stimulus for the cellular response. Less is known, however, about the effects of cyclic strain on the cellular and molecular level. The aim of the in vitro investigation was to determine the effect of cyclic mechanical strain on collagen type I and III and on fibronectin formation in human patellar tendon derived fibroblasts. Human patellar tendon derived fibroblasts from 5 donors (mean age 29.2 years) were cultured under standard conditions. Monolayers of subconfluently grown 3rd passage cells were stretched in rectangular silicone dishes with cyclic movement along their longitudinal axes. Cyclic strain (5%, 1 Hz) was applied for 30 min and 60 min, respectively. Carboxyterminal procollagen type I propeptide (P-I-CP) and aminoterminal procollagen type III propeptide (P-III-NP) release was measured by a radio-immunoassay 6 h and 12 h after stretching. The release of fibronectin was measured by nephelometry following immunoreaction with a specific antiserum. Cells from each donor without any cyclic stretching served as controls. Compared with the controls, only cyclic stretching for 60 min resulted in a significantly increased release of P-I-CP and fibronectin after 6 h. The release of P-III-NP was significantly increased 12 h after 30 min of cyclic stretching as well as 6 h and 12 h after 60 min of cyclic stretching, respectively. We conclude that cyclic stretching causes a time-dependent, differential regulation of formation of fibronectin and collagen type I and III. This may effect the quality and thus the mechanical properties of healing tendon and ligament tissues. In order to improve current treatment protocols and to enlarge our knowledge of tissue healing, it is necessary to understand the cellular response to cyclic strain.

1411 繰り返しひずみがマクロファージの泡沫化に及ぼす影響

1411 繰り返しひずみがマクロファージの泡沫化に及ぼす影響