An Osteoconductive Janus Hydrogel with Full Barrier Protection and Adaptable Degradation Properties for Superior Bone Regeneration

Implant materials for bone regeneration necessitate a barrier function to block bacterial adhesion and fibroblast infiltration, while maintaining a delicate equilibrium between material degradation and osteogenesis. Here, a spatiotemporally and hierarchically-guided bone regeneration hydrogel with a Janus structure is engineered through a sequential photocuring protocol, which features full barrier protection by the outer dense phase and superior osteoconductivity within the inner loose phase. The Janus hydrogel exhibits stable spatiotemporal layering, adaptable degradation, asymmetrical combination of network structures, and mechanical strength. The dense phase, with space maintenance capacity, completely covers the defective area, continuously blocking fibroblast infiltration, and preventing bacterial adhesion. In addition, the loose phase is shape-adapted to the defective cavity, allowing osteoblast-associated cells to migrate and create a favorable osteogenic microenvironment. In situ implantation of this Janus hydrogel effectively promoted osteogenesis, angiogenesis, and neurogenesis in both mouse calvarial and rat periodontal bone defect models. Furthermore, the osteogenic efficiency achieved by the Janus hydrogel implanted in mouse calvarial defects and rat periodontal defects is increased by 42% and 13.7%, respectively, as compared with previous studies. These findings thus demonstrated the synergy of protective barrier function, osteoconductive properties, and adaptive degradation within a single scaffold, which is conducive to bone regeneration.