Injectable Bioactive Polyurethane Adhesive for Critical-Size Cranial Defect Restoration

Critical-size bone defects are difficult to autonomously regenerate. Bioactive tissue adhesives are promising materials for bone defect restoration, but the imbalance between the adhesion and cohesion of traditional adhesives leads to structural instability, ultimately resulting in suboptimal long-term repair outcomes. This work developed a dual-component injectable biodegradable polyurethane adhesive (PUA-H) with osteoinductive repair capability. Regardless of concentration, the structural design balances the adhesion and cohesion of PUA-H, with the bone adhesion strength achieved at 668.9 ± 80.6 kPa. Notably, this design mitigates the impact of wet environments and significantly enhances the adhesive durability. Nanohydroxyapatite (nHAP) was incorporated into the adhesive to further enhance the osteogenic activity. Inspired by mussels, catechol groups were grafted onto the chain extender and cross-linker to establish strong metal–ligand coordination, enabling sustained Ca2 + release over 60 days. In in vitro experiments and in critical-size cranial defect models, the PUA-H group exhibited exceptional osteoinductive activity and repair efficacy. This work provides a strategy for adhesion regulation in tissue adhesives, particularly suitable for the precision repair of large irregular bone defects.