Formation of a bioactive graded surface structure on Ti-15Mo-5Zr-3Al alloy by chemical treatment.

Simple NaOH and heat treatments provided a Ti-15Mo-5Zr-3Al alloy with a bioactive graded surface structure of an amorphous sodium titanate, where the sodium titanate on the top surface gradually changed into the alloy substrate through titanium oxide. The sodium titanate was free of alloying species of Mo, Zr and Al, since almost all of them were released from the surface of alloy during the first NaOH treatment. The sodium titanate transformed into a hydrated titania via Na+ ion release to induce a bone-like apatite formation on the alloy substrate in a simulated body fluid (SBF). The alloying species neither were released into the SBF nor affected the apatite formation. In the process of apatite formation, the graded surface structure developed into one where the apatite on the top surface gradually changed into the alloy composition through hydrated titania and titanium oxide. It is expected that this graded structure will lead to a strong interfacial bonding strength between the apatite layer and the alloy substrate, thereby providing a tight integration of the alloy with living bone through the apatite layer.