Low-temperature biomimetic formation of apatite/TiO2 composite coatings on Ti and NiTi shape memory alloy and their characterization

Through a low temperature process, a bilayer composite coating was formed on Ti and NiTi shape memory alloy (SMA). The composite coating consisted of a layer of titania, which was formed using a H2O2-oxidation and hot water aging technique, and a layer of apatite, which was formed through an accelerated biomimetic process by immersing as-oxidized metals in a high-strength simulated body fluid (5SBF). Various techniques including X-ray diffraction, scanning electron microscopy and energy dispersive X-ray spectroscopy were used to characterize the surfaces of samples at different stages of coating formation and the coatings formed. Bioactive apatite/TiO2 coatings could be formed on NiTi SMA and firmly bonded to the metal substrate. But there were differences for the formation of the composite coating on Ti and NiTi SMA substrates. The composite coatings formed will render both metals bioactive and hence bone-bonding.