Silanisation de polysaccharides en milieu liquide ionique et réactivité d’un organoalkoxysilane vis-à-vis de nucléophiles simples : vers des hydrogels injectables pour l’ingénierie tissulaire du cartilage

Tissue engineering is a real challenge for the treatment of cartilage pathologies. In this field, biomimetic hydrogels based on natural polymers are among the most commonly used matrices. A hydrogel made of silanized hydroxypropylmethylcellulose (HPMC-Si) is especially promising because it can be injected in cartilaginous lesions by minimally invasive surgery. However, the current synthesis of HPMC-Si is limited by the insolubility of hydroxypropylmethylcellulose (HPMC). This thesis work was focused on finding new synthesis conditions for the design of HPMC-Si hydrogel. In order to obtain a complete solubilization of HPMC and to improve its functionalization by the (3-glycidyloxypropyl) trimethoxysilane (GPTMS), the use of ionic liquids (IL), which are excellent solvents for polysaccharides, was undertaken. The beginning of this study was first devoted to the selection of an IL and then to the development of new reaction conditions. With these new conditions, higher silicon rates were obtained for HPMC modified in ionic liquid medium, however no hydrogel could be formed. The second part was therefore devoted to the synthesis of GPTMS 13C. Indeed, thanks to this radiolabeling, a structural characterization by 13C NMR of the HPMC-Si could be achieved. Finally, the reactivity in organic solvents of three organosilanes, including the GPTMS, was investigated toward nucleophiles representing the common functions found in natural polymers (e.g. -NH2, -OH, -SH). The results of this thesis have provided insights into the GPTMS reactivity in organic medium and thus paves the way to new conditions for the silanization of polysaccharides.

Ionic composition of endolymph in teleosts: Origin and importance of endolymph alkalinity

Ionic (Na+, K+, Cl-, PO43-, pH), total CO2, total calcium and protein concentrations in the plasma and endolymph of the inner ear were compared in trout Oncorhynchus mykiss and turbot Scophthalmus maximus. In both species, saccular endolymph was characterized by high levels of K+ and total CO2 and in trout by an alkaline pH, The kinetic characteristics of proton secretion across the saccular epithelium of trout were investigated using a titration technique in which isolated saccules were mounted as closed sacs. The rate of proton secretion depends strongly on the pH of the Ringer's solution and secretion stops at a pH below 7.2, Proton secretion is driven by an energy-dependent mechanism involving basolateral ouabain-sensitive Na+/K+ exchangers. Proton secretion was partially inhibited by acetazolamide and completely inhibited in Na+-free Ringer or in the presence of 1 mmol l(-1) amiloride. A cellular model stressing the importance of proton exchange through the saccular epithelium is proposed to explain the regulation of endolymph pH, a crucial factor for the deposition of otolith calcium.