Biomimetic bone cartilage scaffolds based on trilayer methacrylated hydroxyapatite/GelMA composites for full-thickness osteochondral regeneration.

Since cartilage injury is often accompanied by subchondral bone damage, conventional single-phase materials cannot accurately simulate the osteochondral structure or repair osteochondral injury. In this work, a gradient gelatin-methacryloyl (GelMA) hydrogel scaffold was constructed by a layer-by-layer stacking method to realize full-thickness regeneration of cartilage, calcified cartilage and subchondral bone. Of note, to surmount the inadequate mechanical property of GelMA hydrogel, nanohydroxyapatite (nHA) was incorporated and further functionalized with hydroxyethyl methacrylate (nHA-hydroxyethyl methacrylate, nHAMA) to enhance the interfacial adhesion with the hydrogel, resulting in better mechanical strength akin to human bone. Specifically, the biomimetic nHAMA/GelMA (B-nHAMA) scaffold involved a pure GelMA top layer for cartilage, a 30/70% (w/w) nHAMA/GelMA intermediate layer for calcified cartilage, and a 70/30% (w/w) nHAMA/GelMA bottom layer for subchondral bone. This B-nHAMA scaffold exhibited optimal porosity (continuous-gradient pore size), mechanical performance (Young's modulus, 181.48 ± 29.94 kPa), biodegradability (degradation rate in 25 day, 66.04 ± 7.19%) and swelling properties (swelling ratio in 25 h, 424.8 ± 9.9%) that cater to osteochondral tissue environment. It also showed excellent biocompatibility, cell adaptability, chondrogenic and osteogenic properties, leading to effective osteochondral regeneration. Collectively, the developed B-nHAMA scaffold with similar osteochondral microenvironment of trilayered structure could facilitate simultaneous osteochondral regeneration, providing a promising strategy to improve the full-thickness cartilage injury regeneration. STATEMENT OF SIGNIFICANCE: This research presents a significant advancement in osteochondral repair with the development of a biomimetic B-nHAMA scaffold. The scaffold's design overcomes the inadequate stiffness of gelatin-methacryloyl (GelMA) by incorporating hydroxyethyl methacrylate-functionalized nanohydroxyapatite (nHAMA), enhancing interfacial adhesion and achieving mechanical strength equivalent to human bone. Through a layer-by-layer stacking approach, the B-nHAMA scaffold features a gradient composition that replicates the anisotropic nature of osteochondral tissue, with distinct layers tailored for cartilage, calcified cartilage and subchondral bone. Its biomimetic structure, closely resembling native cartilage in physicochemical and osteogenic properties, positions the B-nHAMA scaffold as a potent therapeutic candidate for the full-thickness repair of osteochondral defects, offering a clinically viable solution.