Titania (TiO2) and TiO2/hydroxylapatite composite coatings (TiO2/HA) were formed
on porous NiTi shape memory alloy using a H2O2-oxidation for TiO2 coating and H2O2-
oxidation+ KOH treatment technique and the subsequent accelerated biomimetic process for
composite TiO2/HA coatings. Porous NiTi shape memory alloys prepared by powder
metallurgy method. The powders were compacted at four different compacting pressures (
200-800) MPa , then samples were sintered and heat treated. The XRD patterns for bare
samples showed that the austenitic phase B2 and martensitic phase B19 and small amount of
Ni3Ti phase, where the B2 and B19 are responsible of the shape memory effect for NiTi
shape memory alloys. The XRD patterns for samples treated with H2O2 showed the formation
of crystalline TiO2 in both forms (rutile and anatase). The XRD patterns of samples
immersed in higher strength simulated body fluid 5SBF after treated with H2O2 and KOH
solutions, showed the formation of hydroxylapatite in addition to anatase and rutile. In the
current investigation, Ni ion release testing in 0.9% NaCl solution at 37?C was employed to
assess biocompatibility properties of TiO2/HA composite coatings formed on porous
equiatomic NiTi SMA. The results showed that the Ni ion release increased with increasing
the impression time and porosity. It has been also showed that single coat of TiO2 is
insufficient to reduce the Ni ion release below the safety line, while the composite coatings of
TiO2/HA curves intersected the safety line and some of the points are lower than the safety
line.