Advances in Intra-Articular Injection Hydrogel Drug Delivery Systems in the Treatment of Rheumatoid Arthritis.

Rheumatoid arthritis (RA) is a systemic autoimmune disorder characterized by chronic inflammation of the synovial membrane, leading to synovial hyperplasia, infiltration of immune cells, and subsequent cartilage and bone erosion. This progressive joint pathology results in persistent pain and functional impairment. Currently, convenient oral traditional disease-modifying anti-rheumatic drugs (DMARDs) are available, and increasingly precise biologic agents and targeted synthetic DMARDs (tsDMARDs) have been developed, offering promising therapeutic options. However, systemic administration generally fails to achieve therapeutic drug concentrations in the joints owing to poor biodistribution and dose-limiting systemic toxicity. Intra-articular (IA) administration has demonstrated promising potential in addressing these challenges. Among the various strategies employed for IA administration, hydrogels have gained significant attention due to their tunable mechanical properties, biocompatibility, and controlled release capabilities. These unique properties enable hydrogel-based IA delivery systems to simultaneously modulate the inflammatory microenvironment and protect cartilage tissue. This review comprehensively summarizes the histopathological changes and associated cellular and molecular events in RA, while also highlighting the design principles of hydrogels and advanced strategies for hydrogel-based IA administration. By addressing the limitations of conventional treatments, hydrogel-based IA injection holds significant promise for improving RA treatment.