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1

Introduction to mecanobiology of cells

Stoltz J. F., Wang X., Muller S., Labrador V.

Applied Mechanics and Engineering

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1999

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Vol. 4, no spec.

177-183

EN

One fundamental property of living tissues is their ability of adaptation to environment because cells are always exposed to mechanical stresses related to environment or to movement (i.e. external pressure, blood flow pressure related to walking, ...). Today it's generally accepted that these mechanical forces can modify the biological behaviour of cells by affecting their metabolism, secretion of autocrin factors, phenotype, etc ... and that tissus can be remodelled by the mechanical environment. The modifications induced by mechanical factors are now considered as determinant to the comprehension of some patho-physiological processes (i.e.: atherosclerosis, thrombosis, arthrosis, inflammation, ...). In this work, we are going to demonstrate, through 3 examples of cells (cartilage chondrocyte, osteocyte and vascular endothelial cell), the importance of the mechanical factors in cell behaviour and the need of a better link between physics, mechanics and biology. Although numerous studies on this topics, the mechanisms of transduction from a mechanical signal to physiological responses or gene expression in cells remain unclear. In vitro studies on cultured cells allow us to have a good control of mechanical parameters and thus to understand better the induced modifications.

2

Influence of the non linear properties of the venous vascular wall on the deformation of vasa-vasorum

Maurice G., Wache P., Wang X., Canteri L., Blondel W., Stoltz J. F.

Applied Mechanics and Engineering

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1999

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Vol. 4, no spec.

145-150

EN

Known since a long time but relatively neglected, the venous vasa vasorum form a tiny network to irrigate and drainer the wall. Actually it is re-realized that, just like any tissues, the vein is a living tissue and the vasa vasorum play a key role in the maintenance of its homeostasis. Under the effects of intraluminal pressure, the Young's modulus (E) of the vein following an empirical relationship (Log E)2= - ('alpha' Log(p) + 'beta'), can vary in a very large range (a factor of 100) en even in physiological conditions. In this work, we simulated the deformation of venous vasa vasorum by finite element method. Thus it can be suggested that, at first, a permanent venous hypertension provoquer a local modification of the wallís mechanical properties (decrease of E) to favoriser a large deformation which will lead to a decrease of the irrigation, and secondly, with the decreased irrigation, the wall will loose its elasticity, become rigidified and keep its large deformation. A vicious cycle could be thus created.

3

Influence of laminar shear stress on cytoskeleton and ICAM-1 expression of endothelial cells

Muller S., Sun R., Legrand S., Labrador V., Wang X., Stoltz J. F.

Applied Mechanics and Engineering

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1999

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Vol. 4, no spec.

151-156

EN

The aim of this work was to study the morphological behavior and the surface adhesion molecules expression and localization of a human endothelial cell line subjected in vitro to a laminar flow in a parallel plate flow chamber, by a 3-D fluorescence microscopy and cytofluorimetry. At rest, endothelial cells showed an array of microfilament bundles of the actin fibers, and a peripheral distribution of ICAM-1 molecules. After shear stress (1 to 30 dyne/cm2, 1 to 24 hours), the stress fibers appeared and were oriented related to the flow direction but also to the shear. The ICAM-1 expression varied according to the shear stress characteristics and their distribution at the cell surface appeared also modified and related to the stress fibers formation.

4

Deformation of a model endothelial cell in flow: A two-dimensional numerical simulation

Wang X., Wache P., Maurice G., Lucius M., Stoltz J. F.

Applied Mechanics and Engineering

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1999

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Vol. 4, no spec.

185-190

EN

Mechanical forces induced by blood flow influence largely endothelial cells' behavior. Also they can modify the expression and distribution of biological receptors, orient cytoskeleton, modify vasoactive factors, etc.. The objective of this study was to determine the deformation of a model endothelial cell exposed to a laminar flow. The cell was supposed to be a two dimensional elastic material. The interaction between the flow and cell deformation was simulated numerically by finite element method. Thus the distributions of mechanical forces on cell surface were obtained. The numerical results showed that the cell deformation depended on imposed flow velocity and that the mechanical stresses on cell surface were not uniform and lower with deformation than without. These numerical results suggest that it'll be interesting to study eventual correlation between the distribution of cell's biological receptors and that of mechanical factors.