Design and characterization of hydrogel films and hydrogel-ceramic composites for biomedical applications

Abstract : The replacement of soft osteoarticular tissues by synthetic hydrogel implants is often limited by a weak anchorage to bone tissues. One approach to strengthen the bone-implant interface consists in functionalizing the surface of the implant by a coating of bioceramics. In this thesis, we investigate two approaches to coat hydrogels of poly(vinyl alcohol) (PVA) with ceramic particles of hydroxyapatite (HA). In a first “soft” process, based on dip-coating, hydrogel substrates were coated with hydroxyapatite particles embedded in a non-degradable PVA hydrogel matrix. In this process, the control of the soaking solution composition allows to finely tune the thickness, the cohesion and the adhesion of the coating, as well as the HA exposure at the coating surface. The biocompatibility with surgical handling and the osteointegration of these systems were assessed by an in vivo study in a rabbit model of bone tunnel healing. This first approach led to the discovery of a new approach to grow physical hydrogel films by a self-sustained process, consisting in using the solvent depletion created at the surface of a swelling polymer substrate immersed in a PVA solution to induce the gelation of hydrogel films without external action. In this process, the growth of these hydrogel films depends on the solution concentration, the soaking time and the swelling kinetics of the substrate. We verified the gentle character of this process by encapsulating fibroblasts, which remain viable for 48h. In a second more “energetic” process, dense coatings of submicronic HA particles were produced on PVA hydrogel by cold spray. Spraying parameters (temperature, pressure and stand-off distance) were varied systematically to determine efficient spraying condition. Based on microscopic observations, a picture explaining the formation of the coating is proposed. Both processes and their combination open new routes for the design of ceramic-hydrogel systems having controlled microstructural, mechanical and biological properties.
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David Moreau. Design and characterization of hydrogel films and hydrogel-ceramic composites for biomedical applications. Materials. PSL Research University, 2016. English. ⟨NNT : 2016PSLEM015⟩. ⟨tel-01450519⟩

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