Hydroxyapatite-chitosan biocomposites: Fabrication strategies and biological performance in bone regeneration

Bone defects caused by trauma, degenerative diseases, infections, or tumor resection require biomaterials that not only provide temporary mechanical support but are also capable of inducing stable osteogenesis and osteointegration. Hydroxyapatite (HA) has good osteoconductive properties due to its similarity to bone minerals, but it is fragile and lacks resorptive properties when used alone. Alternatively, chitosan (CS) is a biodegradable, bioadhesive, and antibacterial polysaccharide, but it has limited mechanical strength. The combination of HA and CS is a complementary strategy for engineering bioactive scaffolds for bone regeneration. This review summarizes the development of HA-CS composites, emphasizing fabrication strategies, interface mechanisms, structural and biological performance, functional modification, and challenges in clinical translation. The literature from the past 15 years was analyzed for synthesis methods, molecular interactions, physicochemical and mechanical properties, degradation behavior, and in vitro and in vivo osteogenic results. HA-CS systems created through co-precipitation, sol-gel, freeze-drying, 3D printing, and electrophoretic deposition utilize hydrogen bonds, electrostatic forces, and Ca²⁺ coordination to enhance stability, interconnected porosity, and surface bioactivity, thereby supporting cell adhesion, proliferation, and osteogenic differentiation. Further modifications via crosslinking, ion doping, polymer blending, and nanomaterials enable control of degradation, antibacterial activity, and local drug delivery. Despite showing potential for bone formation, challenges remain in achieving load-bearing strength, controlling degradation, and translating to clinical application. Future development should focus on biomimetic design and standardized manufacturing to enable effective bone repair applications.