Tuning ultrasound-assisted MAO coatings on Ti-13Nb-13Zr via Ca/P-based electrolyte concentration: Morphology, topography, tribology and bioactivity

Implant failures remain a major challenge due to the insufficient properties of current biomaterials. Surface modifications, particularly micro-arc oxidation (MAO)-based coatings, offer a promising route to improve both mechanical and biological properties. This study systematically investigates the influence of calcium- and phosphorus-based electrolyte concentrations on the formation and properties of coatings produced via ultrasound-assisted micro-arc oxidation (UMAO) on Ti-13Nb-13Zr alloy. Coatings were analyzed in terms of morphology, composition, thickness, and surface topography. Selected samples were further examined for adhesion, mechanical response, tribological behavior, and in vitro bioactivity. An electrolyte with 22 g/L calcium acetate hydrate and 3 g/L β-glycerophosphate disodium salt pentahydrate yielded coatings with high isotropy (>80 %), optimal skewness (0.663 μm), and an elastic modulus (∼65 GPa) resembling bone. This coating exhibited good adhesion to the substrate (>20 N), low wear rate (0.79 × 10−3 mm3 N−1 m−1), and the highest Ca/P ratio (1.71) after bioactivity incubation. Immersion tests revealed a significant increase in calcium and phosphorus content, at 191 % and 163 %, respectively, compared to their pre-immersion levels. Overall, this work highlights the role of electrolyte composition in tailoring UMAO coatings, providing insights into their potential for durable, bone-mimetic implant surface modifications.