Degradation et reparation du cartilage articulaire: Etudes des composantes mecaniques dans la degradation de la matrice et des mecanismes de migration des cellules souches mesenchymateuses dans le contexte du genie tissulaire

In this work a brief summary of the membrane production processes with a particular focus on the stretching process is described in the literature review section. In the process of the membrane production by stretching two main steps are studied: (1) Preparation of the precursor films with appropriate lamellar morphology (row nucleated lamellar structure). (2) Stretching of the prepared precursor films with such lamellar structure to create pores and establishing a porous structure.; For the first part five homo polypropylenes different in molecular weight and molecular weight distribution were selected and the effect of molecular structure and extrusion process were studied.; Among the resin factors, the relaxation time of polymer chains was the most important factor which is a function of polymer chain structure. For the process, a smooth extrusion aids to obtain the uniform and stable precursor films. The cooling of the extrudate right after the die prevents the quick relaxation of the elongated chains. Draw ratio controls the number and degree of the chain extension at the die. The orientation of the crystalline structure was revealed to be a key parameter in obtaining an appropriate lamellar structure. It was found that a minimum orientation of 0.3 for crystal lamellae along machine direction (Herman's orientation) for the precursor film is necessary for obtaining a microporous membrane. Annealing improves the orientation for both crystalline and amorphous phases and significantly changes the response of the sample to tensile tests with the formation of two lamellae distributions. In cold stretching (room temperature) lamellae get separated and pores are created. Interconnection between the pores determines the effective pore diameter (passing through the thickness of the membrane). Further mercury porosimetery tests showed that the effective pore diameter and porosity were smaller for the membranes based on the low molecular weight resin. For the resin with low molecular weight, the lower amount of pores is attributed to poor orientation of the lamellae, where most of the stress in the stretching process will be spent on the motion and rotation of crystal blocks rather than separating them.; The situation for high molecular weight polypropylene is different since it renders a large number of fibrils where they bond the lamellae strongly together and limits lamellae separation. Generally, high molecular weight chains have advantages as: (1) They improve the process ability with an in increase in melt draw ability, (2) They also generate long fibrils for nuclei in melt stretching at the die to improve the lamellar crystallization. However, a large number of the fibrils create strong connections between the lamellae, which make the lamella separation difficult.; In hot stretching some parts of the lamellae (thin surface layers) are locally broken and reoriented to form some more connected bridges. We believe that the sources for the formation of the interconnected bridges are: (1) Stretched tie chains, which will be crystallized afterward and (2) The separated crystal parts of the lamellae, which will be reoriented with stretching and join the very thin bridges to reinforce them. (Abstract shortened by UMI.)...