Biocompatible nanostructured heterogeneous oxide coatings on Ti-15Nb-Ta alloys prepared via micro-arc oxidation for orthopedic applications

In this study, Ti-15Nb-Ta alloys (Ta = 0, 10, 20, and 30 wt%) were functionalized by micro-arc oxidation (MAO) to produce porous, micrometric ceramic coatings enriched with Ca and P for orthopedic applications. Comprehensive chemical, structural, and microstructural characterizations were performed using EDS and XPS, along with SEM, TEM, ASTAR-TEM, EBSD, XRD, and AFM, including both surface and cross-sectional analyses. The results demonstrated that the MAO process effectively generated porous coatings predominantly composed of TiO 2 , Nb 2 O 5 , and Ta 2 O 5 , with successful incorporation of bioactive Ca- and P-containing species. Structural analysis revealed that TiO 2 was the only crystalline phase identified, present as anatase and rutile. The coating exhibited a heterogeneous nanostructure, in which crystalline grains are mainly located in the inner region of the MAO layer, while an amorphous TiO 2 phase is distributed throughout the entire coating. Increasing Ta content promoted rutile suppression and reduced overall coating crystallinity. This structural evolution directly influenced the mechanical properties, as hardness measurements showed a decrease with increasing Ta content, consistent with the reduction of the rutile phase. AFM analysis revealed surface topography at the nanoscale and confirmed variations in roughness parameters, supporting the heterogeneous nature of the coatings. Wettability tests indicated that all surfaces were hydrophilic (contact angle < 90°), with higher Ta contents leading to increased surface energy and, consequently, a greater potential for osseointegration. Biological assays (MTT and cell adhesion), performed using pre-osteoblastic cells after 24 h, confirmed the absence of cytotoxicity for all compositions and demonstrated good cell adhesion. Among the alloys investigated, Ti-15Nb-20Ta and Ti-15Nb-30Ta exhibited good overall performance, combining higher surface energy, improved wettability, and enhanced biological response. These results highlight their potential as promising biomaterials for orthopedic implant applications.