Additive manufacturing of silicon nitride fiber-reinforced polyetheretherketone composites with enhanced mechanical strength and multifunctional bioactivity for load-bearing bone defect repair

Polyether ether ketone (PEEK) is increasingly applied in bone defect repair due to its excellent biocompatibility and absence of artifact formation. However, the bio-inertness and inadequate mechanical properties of untreated PEEK remain significant challenges for PEEK-based implants. Hence, this study prepares a series of silicon nitride (Si3N4) fiber-reinforced PEEK composite porous scaffolds using twin-screw melt mixing-extrusion and material extrusion 3D printing. Comprehensive evaluations assess the mechanical properties, biocompatibility, osteogenic differentiation, angiogenesis activities, and antibacterial performances of various composites. Characterization results show that Si3N4 fiber-reinforced PEEK composites exhibit excellent printability, with well-oriented Si3N4 fibers uniformly distributed throughout the matrix. Furthermore, compared to non-reinforced PEEK, the addition of 8% Si3N4 fibers enhanced Young's modulus by 52.2% (6.36 GPa). Additionally, both in vitro and in vivo results indicate that all composite scaffolds exhibit excellent biocompatibility. Notably, the 8% Si3N4 fiber-reinforced PEEK composite demonstrated optimal multifunctional performance in osteogenic induction, angiogenic capacity, and antibacterial efficacy, significantly outperforming other experimental groups. In conclusion, this study offers a solution for enhancing the mechanical, anti-infective, and osseointegrative properties of PEEK, demonstrating its great potential for expanding the application of non-metallic orthopedic implants in bone defect repair.