A novel thermoresponsive hydrogel based on chitosan.

Injectable thermosetting chitosan hydrogels are attractive systems for drug delivery and tissue engineering that combine biodegradability, biocompatibility and the ability to form in situ gel-like implants. Thermally-induced gelation relies advantageously on biopolymer secondary interactions, avoiding potentially toxic polymerization reactions that may occur with in situ polymerizing formulations. In view of a biomedical use, such formulations have to be sterilizable and storable on extended periods without losing their thermosetting properties. These two key features have been studied in the present paper. Chitosans from two different sources were added with several phosphate-free polyols or polyoses as gelling agents. Despite a reduction in chitosan molecular weight following autoclaving, the hydrogels prepared with autoclaved chitosan showed the desired thermosetting properties. Hence, chitosan steam sterilization combined with aseptic preparation of the hydrogel allows a sterile formulation to be obtained. Whereas thermosetting hydrogels were shown to be unstable when refrigerated, freezing was shown to be conceivable as a storage method. When trehalose or mannitol was used as stabilizing agent, the formulation reconstituted from a lyophilizate displayed thermosetting properties and was still injectable, paving the way to the development of a clinically utilizable, novel chitosan thermosetting hydrogel.