Bioinspired Hierarchical PEEK and Amorphous Silicon Nitride Composite Coatings on Titanium Alloy Biomedical Implants

Titanium alloys are studied for decades as bone and dental implants, showing great potential in biomedical applications. However, the relatively high stiffness and lack of resistance to bacterial corrosion in titanium-based implants are always a problem. Polyetheretherketone (PEEK) is emerging significantly as a new biomaterial for tissue engineering scaffolds, due to its excellent biocompatibility and stability, while the mechanical properties of PEEK cannot match those of natural bones and teeth. In biomineralized tissues, the incorporation of bioceramics into the organic matrix provides a strategy to enhance the mechanical properties of polymers. Inspired by this process, the current work successfully prepared a composite coating on Ti-6Al-4 V (TC4) titanium alloy that contains both organic (PEEK) and inorganic silicon nitride (SiN_x) phases. Combining spin coating with physical vapor deposition methods, PEEK/SiN_x composite coatings that resemble the hierarchical natural mineralized organic fibers are thus realized. The Young's modulus of the "mineralized" PEEK/SiN_x fibers in the composite coatings reaches 45-65 GPa, comparable to the cortical bone and tooth enamel. The novel coatings exhibit superior wear and corrosion resistance. Because of the hierarchical porous structure, the affinity to simulated body fluid (SBF) is notably increased in TC4 coated with PEEK/SiN_x. In vitro cell culture experiments (Alkaline phosphatase activity and qPCR tests, etc.) further verify the bioinspired composite coatings significantly improve cell adhesion, proliferation, and differentiation, potentially inspiring the development of new tissue-like orthopedic and dental implant materials.