Osteoinductive sandwich-structured HA/PEEK implant for rapid critical-size skull repair

Critical-size bone defects afflict millions annually, driving a cascade of inflammation and incomplete tissue regeneration. Polyetheretherketone (PEEK) remains the material of choice for load-bearing implants because its modulus mirrors that of cortical bone; yet its notorious bioinertness curtails both anti-inflammatory signaling and osseointegration, stalling the healing process. To break this stalemate, we designed a sandwich-structured, osteoinductive hydroxyapatite (HA)/PEEK implant tailored for skull repair. A porous PEEK core was engineered via the salting out technique and its surface was homogeneously functionalized with HA through simple physical blending, preserving the implant's open porosity while imparting potent osteoinductive activity. In a rabbit critical calvarial defect (10 mm diameter), new bone advanced from the periphery to the center, achieving full osseous continuity within only 4 months and markedly surpassing unmodified PEEK. The robust bone-implant integration demonstrated by this sandwich HA/PEEK construct not only converts a bioinert polymer into an osteoinductive implant but also may expand treatment options for growing children, offering a clinically translatable solution for skull repair after trauma, hemorrhage, tumor resection, or congenital dysplasia.