Biomimetic Gradient Hydrogels Regulate Osteochondral Regeneration Microenvironment Remodeling via Spatiotemporal Programming Engineering

Osteochondral repair remains a critical challenge owing to conventional scaffolds' inadequate dynamic mechanical adaptability, poor interfacial integration, inefficient cell recruitment, and lack of spatiotemporal regulation of bioactive cues. Inspired by native tissue hierarchical gradients and endogenous healing mechanisms, we developed an electric field-driven continuous gradient hydrogel (GHZF4) via spatiotemporal programming. Integrating nanofiber-reinforced self-adaptive matrix, electric field-induced nanofiber alignment, and ZIF-8 nanocarrier-mediated bioactive release, GHZF4 constructs compositional/structural/mechanical gradients. Its bone-mimetic zone achieves burst release of PDGF-BB and sustained release of BMP-2 for vascularized osteogenesis, while the cartilage-mimetic zone sustains TGF-β3 release for chondrogenesis. In vitro, GHZF4 enhances macrophage M2 polarization, autologous stem cell recruitment, angiogenesis, and osteochondral differentiation. In rat/rabbit defect models, it enables seamless integration and functional repair, validated by micro-CT, nanoindentation and histology. Transcriptomic analysis reveals the potential upregulation of signaling pathways associated with immunomodulation, angiogenesis, and osteochondral differentiation, which shows strong consistency with our in vitro functional outcomes and in vivo regenerative phenotypes. This nanofunctionalized gradient scaffold spatiotemporally couples key repair processes, providing a promising proof-of-concept strategy for cell-free functional osteochondral repair.