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.

Osteoarthritis (OA) is a common chronic joint disease characterized by articular cartilage degeneration, subchondral sclerosis, synovitis, and osteophyte formation. OA is associated with disability and impaired quality of life, particularly among the elderly. Leptin, a 16-kD non-glycosylated protein encoded by the obese gene, is produced on a systemic and local basis in adipose tissue and the infrapatellar fat pad located in the knee. The metabolic mechanisms employed by leptin in OA development have been widely studied, with attention being paid to aging as a corroborative risk factor for OA. Hence, in this review, we have attempted to establish a potential link between leptin and OA, by focusing on aging-associated mechanisms and proposing leptin as a potential diagnostic and therapeutic target in aging-related mechanisms of OA that may provide fruitful guidance and emphasis for future research.