Enhancing mechanical and tribological performance of poly(ether-ether-ketone)/hydroxyapatite nanocomposites with flower-like zinc oxide for bone replacement

Driven by population aging, rising obesity rates, sports injuries, and road traffic accidents, the global orthopedic implant market is projected to reach US$79.5 billion by the end of this decade, highlighting the growing demand for durable and high-performance implant materials. Poly(ether-ether-ketone) (PEEK) has emerged as a promising alternative to traditional metallic implants due to its biocompatibility, excellent tribological properties, and mechanical characteristics similar to human bone. However, its bioinert nature limits osseointegration, affecting long-term implant stability. This study presents the development of PEEK-based nanocomposites reinforced with hydroxyapatite (HA) to promote osseointegration and zinc oxide (ZnO) nanoparticles in spherical (cZnO) and flower-like (fZnO) morphologies to enhance tribological performance. The nanocomposites were evaluated through scratch testing, providing quantitative insights into their mechanical and wear resistance properties. The results demonstrated that fZnO significantly improved scratch resistance, reducing residual scratch depth by 34 % compared to cZnO-reinforced composites. Moreover, while the addition of HA did not compromise the reinforcing effect of fZnO, the cZnO-HA hybrid nanocomposite exhibited a 20 % lower coefficient of friction (COF), which could be problematic for implant stability due to potential loosening. In contrast, the fZnO-HA hybrid nanocomposite demonstrated superior scratch resistance, lower pile-up formation, and improved fixation, making it a particularly promising candidate for load-bearing orthopedic applications such as hip prosthesis stems. These findings confirm that nanoparticle morphology plays a critical role in optimizing mechanical and tribological performance in PEEK-based nanocomposites, paving the way for advanced biomaterials with enhanced wear resistance and durability.