Osteoinductive and Biocompatibility Assessment of a 3D-Printed Polymeric–Hydroxyapatite Composite Interference Screw

Anterior cruciate ligament reconstruction relies on interference screw fixation, yet insufficient graft osseointegration remains a critical clinical challenge. This study aimed to develop and characterize a 3D-printed polymeric–hydroxyapatite composite interference screw with an osteoinductive surface to enhance localized osteogenic responses. Screws were designed, modeled, and fabricated using fused deposition modeling 3D printing with a polycaprolactone-poly(lactic-co-glycolic acid)-hydroxyapatite composite. Physico-chemical characterization was performed using scanning electron microscopy. Biocompatibility was assessed through mesenchymal stem cell metabolic activity assays and morphological analysis. Osteogenic gene expression was quantified by RT-qPCR following culture in osteogenic differentiation medium. In vivo osseointegration was evaluated histologically at five and nine weeks following implantation in the proximal tibial epiphysis of a rat model. 3D printing successfully produced screws with consistent geometry and surface characteristics. The composite material supported robust mesenchymal stem cell proliferation without cytotoxicity or morphological abnormalities. Histological examination revealed progressive bone formation with no adverse tissue reactions, including the absence of cyst formation, osteolysis, or excessive fibrosis. RT-qPCR revealed upregulation of osteogenic markers in those enhanced screws. These results indicate that the 3D-printed polymeric–hydroxyapatite composite screws are biocompatible and capable of stimulating localized osteogenic activity, supporting their potential as a biological foundation for future evaluation in anterior cruciate ligament reconstruction applications.