Injectable Hydrogels for Cartilage and Bone Regeneration: Material Properties, Delivery Strategies, and Clinical Applications

The regeneration of cartilage and bone remains a significant clinical challenge because of their limited self-healing ability. Injectable hydrogels have been identified as potential tissue engineering materials for use in minimally invasive procedures. This review provides a comprehensive overview of injectable hydrogels for cartilage and bone regeneration, encompassing material properties, delivery strategies, and clinical applications. First, we discuss the classification of natural hydrogels (e.g., polysaccharides such as alginate and hyaluronic acid, proteins such as collagen and gelatin) and synthetic (e.g., poly(ethylene glycol) (PEG), poly(vinyl alcohol) (PVA)) polymers, hybrid hydrogels, and the characteristics that make them ideal in tissue engineering, such as mechanical strength, biocompatibility, degradation profiles and injectability. The review then delves into delivery strategies for enhanced tissue regeneration, focusing on cell encapsulation, controlled release of growth factors (e.g., TGF-β, BMPs), incorporation of mineralizing agents, and drug delivery for infection control. We then explored the use of these injectable hydrogels for cartilage repair, osteoarthritis and focal cartilage defects, and bone regeneration, including fracture healing and periodontal reconstruction, on the basis of the clinical results and selected clinical products. Finally, we address the current limitations and future directions, focusing on advanced materials, improved delivery strategies, personalized medicine approaches, combination therapies, and translational opportunities. This review underscores the potential of injectable hydrogels as versatile platforms for cartilage and bone regeneration and highlights the need for further research to optimize their therapeutic efficacy and clinical translation.