Properties investigation on 3D-printed polyetherketoneketone (PEKK) - a proper candidate for bone replacement

Polyetherketoneketone (PEKK) has emerged as a highly promising material for bone substitutes due to its superior mechanical properties, biocompatibility, and patient-specific design capabilities. This study systematically investigated the mechanical properties of fused filament fabrication (FFF) 3D-printed PEKK in various printing orientations and found that PEKK specimens exhibited three times the tensile strength and flexural strength in the Z-axis compared to polyetheretherketone (PEEK). Surface assessments revealed that PEKK surfaces had greater roughness and wettability than those of PEEK under the same 3D printing conditions. In vitro biological evaluations of cell morphology and proliferation on PEKK surfaces demonstrated superior cell adhesion and cell proliferation compared to those of PEEK. Moreover, animal tests were conducted to assess their osseointegration performance followed by CT scanning, histological studies, and push-out tests. The CT scanning and histological results agree well with each other on the better bone quality and quantity surrounding the PEKK implants than those of the PEEK implants, which was consistent with the higher pushing-out force achieved in PEKK implant than those of the PEEK implant. In conclusion, the FFF 3D-printed PEKK is an ideal bone substitute material with outstanding mechanical and biological properties.