Integrated strategy of collagen fiber arrangement-inspired magnetic nanochain-doped ordered biphasic scaffold and gradient magnetic field stimulation for osteochondral regeneration

Background: Osteochondral defects pose significant clinical challenges owing to the complex anisotropic collagen alignment of osteochondral tissue and its limited self-healing capacity. Although mechanically biomimetic scaffolds have been widely applied in osteochondral repair, existing scaffolds exhibit limited structural and functional biomimicry, resulting in osteochondral repair efficacy that requires further improvement. Technology: Bioinspired by the unique collagen fiber alignment of natural osteochondral tissue, this study developed a technology of magnetically guided ordered biphasic scaffold combined with gradient magnetic field stimulation. Via alkaline dissolution and thermal crosslinking, Fe₃O₄ nanochains (NCs) were horizontally oriented in the agarose-based cartilage phase and vertically oriented in the poly(ethylene glycol) diacrylate/agarose-based subchondral bone phase. This scaffold system synergized with a 3–15 mT gradient magnetic field (MF) to enable the integrated repair of osteochondral defects. Results: We adjusted the scaffold's magnetism by modulating the content of Fe₃O₄ NCs, and further investigated the impacts of the magnetic ordered scaffolds and external MF on the differentiation of bone marrow mesenchymal stem cells. Results showed that the cartilage-phase scaffold (0.025 % w/v NCs, 0.27 emu/g) upregulated type II collagen (chondrogenesis), while the subchondral bone-phase scaffold (1.0 % w/v NCs, 1.20 emu/g) boosted osteogenic differentiation. Specifically, 3 mT static MF enhanced chondrogenesis via ECM-receptor signaling, while 15 mT static MF stimulated osteogenesis by activating PI3K/Akt pathway. Animal studies demonstrated that the magnetic biphasic hierarchical scaffold combined with 3–15 mT gradient MF significantly improved osteochondral repair, including nearly double the new subchondral bone volume fraction, a smoother cartilage surface, and collagen fiber alignment that more closely resembled natural osteochondral tissue. This work highlights the potential of the magnetic ordered scaffold-gradient MF technology in osteochondral repair, and is further poised for synergistic development with 3D bioprinting, intelligent manufacturing, and single-cell sequencing, injecting new impetus into the clinical translation of magnetic tissue engineering.