Formation and cytocompatibility of a hierarchical porous coating on Ti-20Zr-10Nb-4Ta alloy by micro-arc oxidation

Beta-Ti alloy has great potential for hard tissue replacement in the biomedical field. Here, a novel hierarchical porous coating was directly prepared on a beta-Ti alloy of Ti-20Zr-10Nb-4Ta by micro-arc oxidation (MAO) in a Na2B4O7 electrolyte for improving its bioactivity. The microstructure, phase composition, adhesion to the substrate, hydrophilicity, and cytocompatibility of the coatings were evaluated, and the effect of the interaction between alloying elements and the electrolyte on the coating formation was discussed. The hierarchical structure of the coating consisted of submicron pores and layered micron pores. It was mainly composed of rutile TiO2 and a small amount of oxides formed by alloying elements. The adhesion to the substrate was improved due to the lower internal stress. The coating exhibited excellent hydrophilicity (water contact angle: 10.6 +/- 1.6 degrees). The analysis of the coating morphology evolution showed that the oxide ejected from the discharge channel during MAO was partially dissolved by the Na2B4O7 electrolyte, which was the main reason for the formation of the hierarchical porous structure. The cell culture tests demonstrated that the novel coating had better cell adhesion and spreading ability, which indicates that this coating on the beta-Ti alloy may have significant potential in dental and orthopedic applications.