Homogeneous "Hard-Soft" Biphasic Bone Adhesives Promote Comminuted Fracture Healing through Interfacial Adaptation and Mechanical Property Maintenance.

Bone adhesives provide remarkable clinical solutions in treating highly comminuted fractures that are difficult to perform surgery with metal fixation. However, no commercial bone adhesives exhibit high adhesion, strength, and osteogenic activity for instant and sustainable fixation in dynamic, wet humoral environments at weight-bearing sites. Here, phase engineering is employed to construct a homogeneous hard-soft biphasic bone adhesive (HB-PTN) with a sea urchin-inspired structure of phosphorylated polyglutamic acid (P-PGA) encapsulating tetracalcium phosphate (TTCP) (hard phase) and a viscoelastic hydrogel composed of amino-functionalized PEGylated poly (glycerol sebacate) (PEGS-NH2) and P-PGA (soft phases) for immediate, stable fixation. The adhesion and strength of the HB-PTN hydrogel can be tuned by modulating the soft phase/hard phase ratio. The PTN-2 hydrogel exhibited an adhesive strength of ≈280 kPa, a compressive modulus of ≈1.02 MPa, and high fatigue resistance (92%). Moreover, the PTN-2 hydrogel showed limited swelling (130%) and maintained mechanical properties (102%) after immersion in simulated human body fluid. Furthermore, this strategy avoids the agglomeration of inorganic particles and the formation of cracks due to stress concentration observed with traditional mixing methods. In vivo, the PTN adhesives reveal durable and stable adhesion and accelerate fracture healing, demonstrating great clinical potential in comminuted fracture repair.