Enhanced bacteriostatic activity, osteogenesis and osseointegration of silicon nitride/polyetherketoneketone composites with femtosecond laser induced micro/nano structural surface

Abstract Poor cell adhesion and osteogenic activity impede the bone regeneration and osseointegration effects of polyetherketoneketone (PEKK) implants. Surface modification and incorporation of bioactive fillers are effective strategies to promote the cellular responses of PEKK implants and their integration with bone tissues. In this study, silicon nitride (SN) microparticles were blended with PEKK to develop bioactive composite implants (SPC). Femtosecond laser was then used to modify SPC surfaces inducing favorable micro/nano structural surface (FSPC). After the laser ablation, irregularly shaped SN microparticles were converted to “petal-like” clusters composed of “pin-like” SN nanoparticles, while the entire surface was covered by SN particles due to the removal of PEKK. The roughness, hydrophilicity, content of surface chemical groups (e.g., -NH2), and protein adsorption capability of FSPC were significantly enhanced compared to SPC and PEKK. Also, the release of biologically active Si ions was increased after the femtosecond laser treatment, inducing a positive microenvironment favorable for cellular activities. Moreover, FSPC exhibited a greater bacteriostatic activity against Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) than SPC. The presence of micro/nano structure also remarkably promoted adhesion, proliferation, and osteogenic differentiation of rat bone mesenchymal stem cells (rBMSCs). In vivo evaluation of the composites in a rabbit femur defect model verified that FSPC could enhance osteogenesis and osseointegration to a greater extent than SPC, evidenced with greater bone-implant contacts and push-out force. These results indicate that the femtosecond laser induced micro/nano structural surface on SN/PEKK implants can significantly promote osseointegration and bone repair. The femtosecond laser exhibits great potential in surface modifying bioceramic/polymer composites. The fabricated FSPC have shown great potential as bone implants in orthopedic applications considering their excellent biocompatibility, bacteriostatic property, osteogenic activity, and osseointegration.