A super-hydrophilic coating with a macro/micro/nano triple hierarchical structure on titanium by two-step micro-arc oxidation treatment for biomedical applications

Abstract

A super-hydrophilic coating with a macro/micro/nano triple hierarchical structure was prepared on titanium surface by a two-step micro-arc oxidation (MAO) treatment consisting of macropores (100–300μm), microslots (3–10μm) and submicro/nanopores (80–200nm). The first hierarchical structures (macropores) were formed by MAO treatment in a NaNO3 and NaOH electrolyte, and the latter two hierarchies, forming a “cortex-like” structure, were generated through a second MAO treatment in a Na2B4O7 electrolyte. The influence of the concentration of NaOH in the electrolyte and MAO electrical parameters on the macroporous structure was explored. The morphology, composition, hydrophilicity and the formation of hydroxyapatite in simulated body fluid of the two types of structure, together with the combined structure, were studied. The results suggest that NaOH enhances the corrosion ability of NaNO3, and has a major effect on the size and uniformity of macropores. The coating hydrophilicity and the formation of hydroxyapatite of the coating were determined by the second step treatment, i.e. the “cortex-like” structure. This novel triple hierarchical structure may be promising to improve the adhesion of osteoblasts to implants as well as the fixation of implants.