Preparation And Characterization Of Gelatin-chitosan IPN Biohydrogels By Bienzymatic Crosslinking Approach

Biohydrogels have attracted much attention in the field of biomedical materials in recent years. Preparation of tough biohydrogels, and maintain the advantages of natural polymer material in biocompatibility and biodegradation is a challenge. In order to improve their mechanical properties and degradation resistance, bienzymatic crosslinking approach has been developed to prepare biohydrogels of gelatin and chitosan with an interpenetrating polymer network (IPN) structure in this report. Moreover, the mechanical performances, swelling ratio, degradation behavior, and cytocompatibility of the IPN hydrogels were investigated in detail.First of all, chitosan-PA hydrogel precursor was synthesized by a general carbodiimide/active ester-mediated coupling reaction. And the effects of the molar ratio of carboxylic groups of PA to chitosan amino groups on the degree of substitution (DS) of phloretic acid in the chitosan have been studied further. The effects of gelatin concentration, HRP concentration, H2O2 concentration, and DS of phloretic acid in the chitosan on gel time were investigated to pave the way for the subsequent preparation of IPN hydrogels.Furthermore, dual networks hydrogel was designed:one chitosan-PA network crosslinked by HRP in the presence of a low concentration of H2O2 and another gelatin network crosslinked by transglutaminase (TG). The gelation process of gelatin/chitosan-PA IPN hydrogels was monitored by a rheometer to confirm the formation of the IPN structure. In addition, the mechanical performances of the hydrogels were measured by a universal testing machine. It was found that the mechanical properties of the IPN gels were significantly improved compared with gelatin hydrogel crosslinked by TG. Moreover, the swelling ratio, degradation behavior, and cytocompatibility of the IPN hydrogels were investigated in detail. The results indicated that the gelatin/chitosan IPN hydrogels prepared by bienzymatic crosslinking approach have excellent biocompatibility and mechanical properties.Finally, gelatin/chitosan IPN hydrogel firbers with IPN structure were prepared by bienzymatic crosslinking approach using wet spinning technology. Meanwhile, pure gelatin and pure chitosan-PA had no spinnability. The mechanical strength of the IPN hydrogel fibers was measured by an electronic single fiber strength tester. The results showed that gelatin/chitosan-PA IPN hydrogel fibers had a significant improvement of mechanical strength as the gelatin concentration and chitosan-PA concentration increased. The IPN fiber has the highest tension of 38.56 cN and elongation of 387.2%. The swelling ratio and biodegradability behavior of fibers were studied by the gravimetric method. Moreover, the cytocompatibility of the IPN hydrogels fiber were investigated in detail. It was found that the IPN fibers prepared by bienzymatic crosslinking approach have good hygroscopicity, biodegradability and biocompatibility. Fibers can be designed to have an extremely high porosity for cellular infiltration, and exhibit good mechanical properties and suitable compliance for handling and conformability to varying tissue and organ shapes.In this thesis, we developed a new method-bienzymatic crosslinking to prepare biopolymer based IPN hydrogels with improved mechanical strength and favourable biocompatibility. Biohydrogels composed of gelatin and chitosan-PA with IPN structure prepared by bienzymatic crosslinking approach is expected to be novel candidate biomaterials in the biomedical material field. Moreover, the bienzymatic crosslinking technique should be applicable to other natural polymers, such as, fibrinogen, hyaluronic acid, heparin and alginate, to extend the library of hydrogel biomaterials.