From filament to print: Structural evolution and its impact on the mechanical properties of PEEK–HA–Mg₂SiO₄ composites

Polyether ether ketone (PEEK) is widely recognized for its biocompatibility, mechanical robustness, and radiolucency, making it a strong candidate for orthopedic and spinal implants. However, its intrinsic hydrophobicity and limited osteoconductivity restrict broader clinical applications. In this study, a 3D printable PEEK-based composite reinforced with hydroxyapatite (HA) and magnesium orthosilicate (Mg₂SiO₄) was developed to address these limitations. A composite consisting of 70 wt% PEEK, 25 wt% HA, and 5 wt% Mg₂SiO₄ was processed into filaments via twin-screw extrusion and subsequently printed using Fused Deposition Modeling (FDM). Structural and compositional differences between the filaments and printed parts were investigated using various characterization techniques. Mechanical testing based on ASTM standards demonstrated significantly enhanced flexural strength and modulus in the 3D printed composite, with a moderate improvement in tensile properties compared to unfilled PEEK. In addition, SAOS-2 cells seeded on the surfaces of both the filament and 3D-printed composite exhibited high viability, confirming the cytocompatibility of the materials. These results highlight the role of interfacial bonding and filler dispersion in tailoring mechanical behavior and support the use of this composite in customized, load-sharing orthopedic implants.