Biopolymer-based hydrogels for cartilage tissue engineering

Hydrogels hold a macromolecular structure comparable to that of native tissues and thus are very attractive materials for tissue engineering. The authors prepared three-dimensional bioartificial matrices based on methacrylated gelatin and chondroitin sulfate that can be tuned to closely mimic the natural environment of specific cell types - for example, chondrocytes. The authors investigated the hydrogel's gel yield, swellability, mechanical strength, cytocompatibility, degradation and effect on chondrocyte redifferentiation. Furthermore, porcine chondrocytes were photoencapsulated into hydrogels and cultivated for 21 d. It was found that the methacrylation of chondroitin sulfate is crucial for the generation of stable hydrogels with methacrylated gelatin. Compared to pure gelatin, hybrid hydrogels possessed significantly higher swellability, while the mechanical strength remained constant. The hydrogel properties could be controlled by the mass fraction and the cross-linking density. The hydrogels as well as the cross-linking conditions were proven to render cytocompatible. Furthermore, it was found that the addition of chondroitin sulfate promoted a spherical morphology and thus chondrocyte phenotype retention. Thus, it is suggested that chondroitin sulfate is a potential redifferentiating agent of articular chondrocytes. In summary, hydrogels based on both chondroitin sulfate and gelatin hold tunable physical and biological properties and are preferable matrices for cartilage tissue engineering.