In situ forming chitosan hydrogels: Preliminary evaluation of the in vivo inflammatory response

- Physical and physico/chemical chitosan hydrogels show diverse structural properties.
- The behavior of these hydrogels was compared both in vitro and in vivo.
- Biodegradability and biocompatibility was performed by histological analysis.
- Degradation of both hydrogels are quite distinct in vitro but similar in vivo.
- Both hydrogels show good results for in vivo biodegradation and biocompatibility.

This study aims to provide important preliminary in vivo data on the general biocompatibility and degradation of in situ forming chitosan hydrogels which differ in the type of cross-linking: physical cross-linking (with glycerol phosphate disodium salt) and physico/chemical co-cross-linking (with glycerol phosphate disodium salt and genipin). Additionally, in vitro degradation studies, using lysozyme, were conducted for comparison. The subcutaneous implantation of the liquid formulations of both hydrogels in animal model (Wistar rats) was performed to assess tissue response at the end of two time periods (8 and 30 days).Although the properties of both hydrogels are different (namely, pore size and mechanical strength), leading to remarkably distinct in vitro degradation behaviors, the in vivo degradation is quite similar for both types. Regarding biocompatibility, the in vivo evaluation performed by histological analysis, showed a mild to moderate chronic inflammatory reaction with no foreign body reaction, demonstrating that both hydrogels show good results for in vivo biodegradation and biocompatibility, therefore are most adequate for biomedical applications.