Architecturally Refined Cerium‐Integrated Hydroxyapatite/CNT Nanocomposite Coatings: Enhanced Mechanics and Biofunction for Orthopaedic Implantation

Hydroxyapatite (HAP) composite coatings have emerged as promising candidates in orthopaedic implantology because they promote osteoconduction and facilitate biological integration. This study investigates the effect of cerium (Ce) incorporation at graded concentrations (0.3-0.8 wt.%) on the microstructural, interfacial, and functional properties of hydroxyapatite/carbon nanotube (HAP/CNT) hybrid nanocomposite coatings fabricated via electrochemical deposition mode. Among the developed systems, the HAP-CNT-0.8Ce formulation demonstrated outstanding performance, exhibiting a Ca/P atomic ratio of 1.56, a water contact angle of 40.8° with surface roughness of 0.66 µm, a maximum hardness of 354 HV, an adhesion strength of 52 MPa, and pronounced antibacterial activity, reducing the viability of E. coli and S. aureus to ∼67.5%, and ∼45.6%, respectively. The bioactivity analysis revealed that HAP-CNT-Ce coatings exhibited sustained ion release-mediated apatite nucleation in simulated body fluid, leading to enhanced HAP crystallisation and superior biomineralization potential. The HAP-CNT-0.8Ce variant, characterized by a nanoscale crystallite size of 20 ± 2.1 nm and a crystallinity degree of 44.45%, exhibited a refined grain architecture that markedly enhanced its mechanical and biological performance, thereby affirming its structural robustness and interfacial integrity. Altogether, the integration of multifunctional attributes, including mechanical robustness, cellular compatibility, and enhanced osseointegration, positions this advanced coating as a highly viable solution for next-generation orthopaedic implants and bone regeneration platforms in the context of translational biomedical engineering.