Compatibilité et co-structuration dans des systèmes contenant des scléroprotéines et des polysaccharides

L obtention de substrats cyto-favorables , aptes à soutenir la régénération tissulaire, impose l utilisation de biomatériaux qui portent des domaines de reconnaissance cellulaire, comme par exemple les scléroprotéines et certains polysaccharides. La membrane des cellules spécifiques aux tissus conjonctifs dispose de mécanismes qui facilitent l ancrage aux substrats solides ou à l état de gel où se retrouvent des macromolécules ou des fibrilles de (atelo) collagène, associées ou non à l acide hyaluronique. On peut générer de tels substrats par des techniques de rassemblement moléculaire spontané ordonné (tout comme dans le cas de la restructuration du collagène quasi-natif pour former des fibrilles), ou induite physico-chimiquement ensuite stabilisé morphologiquement (tout comme dans le cas de la préparation des hydrogels mixtes, atelocollagène hyaluronate de sodium, diversement réticulés ensuite transformés en cryo- ou vitri-gels). Dans le cadre de la thèse, nous étudions les moyens d obtention et de purification des précurseurs bio-macromoléculaires nécessaires, par la suite, à l obtention de substrats cyto-favorables , ainsi que leurs modalités de génération et de caractérisation. Les méthodes de restructuration auxquelles on en appelle sont de nature physico-chimique (la co-précipitation contrôlée dans des mélanges binaires et ternaires d atelocollagène et d hyaluronate de sodium), ou chimique (la réticulation par des ponts moléculaires à longueur minimale). On a étudié les possibilités de mélanger de l atelocollagène (aK) avec deux types de polysaccharides, le hyaluronate de sodium (NaHyal) et le gellane. On a établi des formulations et les procédures optimales pour obtenir des hydrogels avec des caractéristiques rhéologiques contrôlables, et avec la réactivité et la morphologie capables de permettre la fixation et la prolifération des fibroblastes. On constate que les hydrogels et cryogels obtenus à partir des mélanges 5:1 aK:NaHyal réticulés avec du 1,4-butanediol diglycidyl éther ont des propriétés rhéologiques qui permettent leurs manipulation dans les conditions des techniques de culture cellulaire. Ils ne présentent pas de cytotoxicité et ils assurent la viabilité cellulaire dans les milieux de culture standards. La morphologie des cryogels obtenus montre une macro-porosité qui dépend de la formulation des mélanges et peu la technique d'obtention. La présence de gellane dans les mélanges conduit à une séparation de phases, même à faible concentration, soulignant la diversité des caractéristiques de substrats.Obtaining "cyto-favourable" substrates able to support tissue regeneration leads to use biomaterials holding cellular recognition domains, as scleroproteins and some polysaccharides as examples. Cellules membranes specific to conjunctive tissues have mechanisms making easier the anchoring to solid or gel substrates where macromolecules or fibrils of (aceto)collagen, associated or not to hyaluronic acid, are found. Such substrates may be generated using spontaneous molecular gathering (as in native collagen restructuration to fibrils), or physico-chemically induced (as the preparation of mixed hydrogels then transformed in cryo- or vitri-gels). In this thesis, were studied the obtaining and purification of bio-macromolecular presursors necessary to obtaining "cyto-favourable" substrates, and the procedures to generate and characterize them. Used restructuration methods are of physico-chemical nature (controlled co-precipitation in binary and ternary mixtures of acetocollagen and sodium hyaluronate) or chemical one (crosslinking).The mixture of acetocolagen (aK) with two polysaccharides, sodium hyaluronate (NaHyal) and gellan were investigated. Formulations and optimal conditions were established to obtain hydrogels with controlled rheological characteristics, and reactivity and morphology able to allow fibroplast fixation and proliferation. Hydrogels and cryogels prepared from 5:1 aK:NaHyal crosslinked with 1,4-butanediol diglycidyl ether were defined as the best materials we have prepared. They do not show any cytotoxicity and they ensure the cellular viability within standard cellule culture media. The cryogel morphology shows macro-porosity depending on the formulation but a few on the obtaining process. The presence of gellan in the mixtures leads to a phase separation, even at low concentration.PAU-BU Sciences (644452103) / SudocSudocFranceF

Chitine et chitosane

International audienc

Cement cake properties in static filtration. On the role of fluid loss control additives on the cake porosity

cited By 24International audienceThe mechanism of the action of fluid loss control additives in cementing oilwell operations is principally the reduction of permeability of the cement filter cake. From filtration equations physical characteristics as porosity of the cement filter cake were investigated and compared with experimental data. A good correlation is observed when no adsorption is involved. The smallest pore diameter for obtaining an efficient control of fluid loss is shown to be of the same order of magnitude as the gyration radius of used macromolecular chains. © 1993

Autoassociative natural polymer derivatives: the alkylchitosans. Rheological behaviour and temperature stability

International audienc

Cement cake properties in static filtration. Influence of polymeric additives on cement filter cake permeability

cited By 36International audienceDuring cementing operations on oil wells, fluid loss control additives are generally used to prevent water loss and to maintain a constant water-to-solid ratio in cement slurries. But their mechanism of action is not yet completely understood. An experimental procedure is described to discriminate between the two predominant phenomena which are the increase of interstitial water viscosity and the decrease of cement cake permeability. The influence of polymeric additives is studied and more particularly the efficiency of fluid loss control additives is related with a threshold concentration corresponding to the overlapping concentration of macromolecular chains in solution. © 1993

Contribution of chitin derivatives to the modification of physicochemical properties of formulations

International audienc

Chitin and chitosan [Chitine et chitosane]

cited By 1International audienceChitin is the second natural polymer available at the earth surface. The chemical structure is composed of N-acetylglucosamine units and the physical structure shows three different forms due to the arrangement of the macromolecular chains. The major problem encountered in the chitin chemistry is its preparation and its extraction to obtain a chitin with characteristics similar to the original polymer (molar mass and acetylation degree). The different treatments used for its extraction are discussed. Chitin is poorly valorised due to difficulties to be processed related to a bad solubilisation. Many derivatives are prepared, particularly chitosan obtained from the deacetylation of chitin. This derivative has the particularity to have amino groups and hence to be a cationic polyelectrolyte, in acidic medium, due to protonation of these groups. The degree of acetylation, the molar mass but also the repartition of N-acetylated units along the macromolecular chain are characteristics of the macromolecular chain. These characteristics allow this polymer to have original properties compared with other polysaccharides which are generally anionic. These properties and applications are discussed, demonstrating the large range of domains in which this polymer may be used