Nickel release behavior and surface characteristics of porous NiTi shape memory alloy modified by different chemical processes

As a non-line-of-sight surface modification technique, chemical treatment is an effective method to treat porous NiTi with complex surface morphologies and large exposed areas due to its liquidity and low temperature. In the work described here, three different chemical processes are used to treat porous NiTi alloys. Our results show that H₂O₂ treatment, NaOH treatment, and H₂O₂ pre-treatment plus subsequent NaOH treatment can mitigate leaching of nickel from the alloy. The porous NiTi samples modified by the two latter processes favor deposition of a layer composed of Ca and P due to the formation of bioactive Na₂TiO ₃ on the surface. Among the three processes, H₂O ₂ pre-treatment plus subsequent NaOH modification is the most effective in suppressing nickel release. Small area X-ray photoelectron spectroscopy reveals that the surfaces treated by different chemical processes have different structures and compositions. The sample modified by the H ₂O₂ treatment is composed of rough TiO₂ on the outer surface and an oxide transition layer underneath whereas the sample treated by NaOH comprises a surface layer of titanium oxide and Na ₂TiO₃ together with a transition layer. The sample processed by the H₂O₂ and NaOH treatment has a pure Na₂TiO₃ layer on the surface and a transition layer underneath. These results help to elucidate the different nickel release behavior and bioactivity of porous NiTi alloys processed by different methods. © 2008 Wiley Periodicals, Inc.