Calcium phosphate coating of Ti–Nb–Zr–Sn titanium alloy

This study focuses on rapid formation of calcium phosphate coating on a β type Ti–Nb–Zr–Sn biomedical titanium alloy by alkali treatment. The results show that a bioconductive surface layer forms on specimens immersed in 1–5 M KOH solution but only treatment in 1 M KOH avoids formation of crevices, producing a potassium titanate layer with porous network structure. Heat treatment at 600 °C after the alkali treatment promotes titanate growth. Following the above treatments, a continuous apatite layer forms within 4 h of soaking in a calcium phosphate solution with high ionic concentration. Such rapid apatite formation is due to high concentration of calcium ions in the solution used in this study and the buffering function of NaHCO₃. Results of dissolution experiment show that Ca and P ions release gradually from the coating during soaking in a 0.9% NaCl solution, which may be helpful to the formation of natural bone if implanted in human body. Cell culture experiment shows that the apatite layer favours adhesion and proliferation of rat osteoblast as compared with coating-free Ti–Nb–Zr–Sn alloy and commercially pure titanium (CP Ti).