Improving the bioactivity of NiTi shape memory alloy by heat and alkali treatment

TiO2 films were formed on an NiTi alloy surface by heat treatment in air at 600 °C. Heat treated NiTi shape memory alloys were subsequently alkali treated with 1 M, 3 M and 5 M NaOH solutions respectively, to improve their bioactivity. Then treated NiTi samples were soaked in 1.5SBF to evaluate their in vitro performance. The results showed that the 3 M NaOH treatment is the most appropriate method. A large amount of apatite formed within 1 day's soaking in 1.5SBF, after 7 day's soaking TiO2/HA composite layer formed on the NiTi surface. SEM, XRD, FT-IR and TEM results showed that the morphology and microstructure are similar to the human bone apatite.