Optimizing the Surface Treatment Processes to Enhance the Bioactivity of Ti–6Al–7Nb Alloy

Abstract

The current research is devoted to assessing the bioactivity of different surface-treated Ti–6Al–7Nb samples by assessing the formation of calcium phosphate compounds. Three surface modification processes were performed, followed by dynamic immersion in Hanks’ solution for 32 days at the body temperature. The first set of samples was treated by oxidation at 400, 500 and 600 °C for 1 and 2 h to study the optimum oxidation condition. The second group was alkaline-treated using different concentrations of NaOH and aged at 400 and 600 °C. The third group was treated by a strong acidic solution (H₂SO₄ and HCl) for 0.5–1.5 h and then aged at 400 and 600 °C. Growth of calcium phosphate compounds (CPC) was generally enhanced with the formation of NaCl dendritic network, as it worked as an adhesive layer. Formation of the oxide layer enhanced the affinity to precipitate CPC, and the optimum oxidation condition was 500 °C for 1 h; higher temperatures and/or longer periods tended to dissolve back the built-up regions. Alkaline treatment prior to aging resulted in the formation of uneven build-up of CPC. Increasing the aging temperature at constant concentration encouraged the formation of dendritic structure (NaCl) and increased the width of the branches resulting in increased precipitation of CPC. Alkaline treatment and aging for 1 h using 2 M solution at 400 °C was the best condition to grow dense flower-shaped precipitates of CPC. However, increasing the aging temperature to 600 °C using the same solution resulted in the formation of TiO₂ which created more sites for CPC growth, and hence more homogenously distributed particles with less concentration were obtained. In case of the acidic treatment, increasing the immersion time in the acidic solution beyond 1 h dissolved back NaCl built-up regions and thus decreased the surface ability to grow CPC. A palette of colors was obtained on the samples’ surfaces after the different treatments, which was beneficial in improving the esthetics of implant components and implant prosthesis substructures.