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Preparation of Composite Hydrogels for Medical Applications: Experimental Study and Modeling of Mass Transfers

The aim of this work is to prepare wound dressing hydrogels permitting (i) to cure chronicle pathologies; (ii) to remove unsuitable odors coming from healing. Thus, chitosan, a natural polymer with biological properties, and activated carbon (AC), a well-known adsorbent, are mixed within a composite hydrogel. To get a suitable porous structure for healing, the vapor induced phase separation process (VIPS) is used. It permits to slow down mass transfers kinetics compared to other elaboration processes such as the wet process. Hence, a better control of the final porous matrix is reached throughout the elaboration process.In this work, the mass transfers occurring through the elaboration of the composites were studied thanks to gravimetric measurements carried out during the VIPS process. Results showed there were two main steps in the gelation process. A weight intake, due to an ammonia flux allowing the gelation to happen, was followed by a weight loss, mainly controlled by a water outtake. This second part could be compared to a slow drying in smooth conditions. Gelation with a color indicator was also performed, which provided complementary experimental information on mass transfers barrier.A modeling of mass transfers mechanisms occurring during the gel elaboration is presented to get an overview of limiting phenomena leading to the final composite structures. It involves a coupling between chemical reactions, external mass transfers and internal diffusion within the polymeric matrix. Results show that internal diffusion is the main barrier to gelation.To qualify the gel structure, drying kinetics were compared on the elaborated gels. Whatever the gel, the drying kinetics were globally the same and could be divided into three steps. Considering the process used and this result, it was believed that the matrixes prepared were homogeneous and rather symmetric. They could constitute the first layer of wound dressings.