Enzyme-Cross-linked Gelatin Hydrogel Enriched with an Articular Cartilage Extracellular Matrix and Human Adipose-Derived Stem Cells for Hyaline Cartilage Regeneration of Rabbits

Hyaline cartilage regeneration remains clinically challenging. In this study, microbial transglutaminase was used to cross-link gelatin. The articular cartilage extracellular matrix (cECM), mainly comprising collagen type II and glycosaminoglycans (GAGs), which can support chondrogenesis, was enclosed in this enzyme-catalyzed hydrogel. After human adipose-derived stem cells (hASCs) were encapsulated in the hydrogel enriched with the cECM, the results demonstrated that the enzymatic cross-linking reaction is of low cytotoxicity. Moreover, the stem cells showed great proliferation and chondrogenic differentiation potential in the hydrogel. Most importantly, we assessed the therapeutic effects of applying a hydrogel enriched with the cECM and hASCs to repair a full-thickness osteochondral defect. At 8 weeks after surgery, the GCC group (hydrogel encapsulating cells and the cECM) exhibited a smooth articular surface with transparent new hyaline-like tissue macroscopically. According to histological analysis, inflammatory responses were hardly observed, and sound chondrocytes were aligned in the newly formed chondral layer. In addition, the GCC group exhibited significant improvement in the GAG content between weeks 4 and 8. In summary, the implantation of a gelatin hydrogel enriched with the cECM and hASCs could facilitate the hyaline cartilage regeneration significantly in rabbit knee joint models.