Evolving functional hydrogel strategies for cartilage engineering: from fundamentals to functional regeneration

Articular cartilage injury is a significant concern in osteoarthritis (OA), and while traditional pharmacological treatments and surgical interventions have provided some pain relief and promoted cartilage regeneration to a certain extent, long-term therapeutic outcomes remain suboptimal. The advancement of cartilage tissue engineering has introduced novel perspectives for cartilage regeneration. Hydrogel scaffolds, as crucial components in tissue functionality, have evolved from their initial role of physical coverage or single functionality to current combinations of diverse functionalities. This review thoroughly examines recent applications of functional hydrogels in cartilage regeneration. This article begins by discussing essential background information, including treatment strategies for cartilage defects and the fundamental characteristics of hydrogels. Next, within the framework of cartilage tissue engineering, we analyse five categories of functional hydrogels, emphasizing their distinctive physicochemical properties, drug delivery capabilities, and stimulus-responsive features for cartilage repair. The discussion extends to their mechanisms of action, classification, and limitations. Clinical products related to hydrogels in this field are also summarized. Finally, recommendations are offered to address current challenges and future directions in the development of functional hydrogels for cartilage regeneration.