Interpenetrating polymer network hydrogels composed of chitosan and photocrosslinkable gelatin with enhanced mechanical properties for tissue engineering.

Gelatin and chitosan (CS) are widely used natural biomaterials for tissue engineering scaffolds, but the poor mechanical properties of pure gelatin or CS hydrogels become a big obstacle that limits their use as scaffolds, especially in load-bearing tissues. This study provided a novel mechanism of forming interpenetrating network (IPN) of gelatin methacryloyl (GelMA) and CS hydrogels by covalent bonds and hydrophobic interactions through photocrosslinking and basification, respectively. By characterization of the compressive and tensile moduli, ultimate tensile stress and strain, it was found that semi-IPN and IPN structure can greatly enhance the mechanical properties of GelMA-CS hydrogels compared to the single network CS or GelMA. Moreover, the increase of either GelMA or CS concentration can strengthen the hydrogel network. Then, the swelling, enzymatic degradation, and morphology of GelMA-CS hydrogels were also systematically investigated. The excellent biocompatibility of GelMA-CS hydrogels was demonstrated by large spreading area of bone mesenchymal stem cells on hydrogel surfaces when CS concentration was <2% (w/v). According to this study, the multiple requirements of properties can be fulfilled by carefully selecting the GelMA and CS compositions for IPN hydrogels.