Mechanical reinforcement and growth factor delivery strategies for in situ cartilage repair

In situ cartilage engineering aims to repair damaged cartilage within the body by using biomaterials such as hydrogels, often loaded with regenerative cells to support tissue formation at the injury site. Hydrogels are promising candidates for in situ cartilage repair due to their biocompatibility and tunable properties. Two major strategies have been explored to enhance their performance: mechanical reinforcement, through the incorporation of secondary structures to improve mechanical behavior and structural integrity; and growth factor delivery, to stimulate cell proliferation, differentiation, and extracellular matrix synthesis. This review first analyzes mechanical reinforcement and growth factor delivery separate, discussing their advantages, limitations, and gaps in the context of in situ applications. It then highlights the emerging opportunity to combine these strategies within composite, cell-laden hydrogels, and critically examines the current studies, alongside the additional challenges in clinical translation that arises. Finally, future directions are proposed to guide the design and testing of composite hydrogels for more effective and translatable in situ cartilage repair therapies.