Bone adhesive with temporally-synchronized degradation for enhanced osteointegration.

Bone adhesives have emerged as promising alternatives for complex fracture fixation. However, discrepancies between material degradation rates and the physiological timeline of bone healing remain a critical limitation. Here, a polyurethane-based adhesive (TNC) was developed, synthesized from trimeric hexamethylene diisocyanate, nano-hydroxyapatite, and type I collagen. The TNC demonstrates strong initial adhesion to both wet and blood-contaminated bone surfaces and exhibits excellent biocompatibility. A distinguishing feature of TNC is its capacity to synchronize degradation with the stages of bone healing. During degradation, TNC forms a mineralized surface layer that releases calcium ions. The calcium ions activate cathepsin K, an enzyme integral to bone remodeling. This calcium-mediated mechanism accelerates TNC degradation by 1.9-fold during the remodeling phase compared to the initial phase. In a rat skull fracture model, TNC supported effective fracture stabilization and achieved favorable bone regeneration at 8 weeks after implantation. These findings demonstrate that TNC combines early mechanical stability with phase-specific degradability to facilitate bone regeneration in a temporally-controlled manner. The present work provides a framework for the development of bio-responsive bone adhesives that synchronize degradation behavior with healing phases for orthopedic applications.