Atomic layer deposited TiO2 films on an equiatomic NiTi shape memory alloy for biomedical applications.

• TiO 2 film was deposited on surface of Ni50Ti50 substrate using atomic layer deposition techniques. • TiO 2 film thickness, surface roughness, corrosion resistance and biocompatibility were investigated. • TiO 2 film thickness is directly proportional with number of ALD cycles. • The maximum corrosion resistance, excellent surface morphology and Cell proliferation was achieved after 200 ALD cycles. NiTi shape memory alloys (SMAs) have been widely applied in biomedical fields due to their excellent shape memory effect, super-elasticity, and biocompatibility. In this study, the plasma- enhanced atomic layer deposition was applied to deposit TiO 2 film on the surface of Ni50Ti50 substrate. The characterization and surface properties of TiO 2 film, bending strain test, corrosion resistance, nickel release and in vitro biocompatibility were studied to evaluate the performance of ALD-TiO 2 film. The results show that the ALD-TiO 2 film is uniform and exhibits an amorphous structure. The ALD-TiO 2 films are less hydrophilic than the Ni50Ti50 substrate. As the deposition cycle increases, the water contact angle of ALD-TiO 2 film only changes slightly. The ALD-TiO 2 film exhibits an adequate adhesion to the Ni50Ti50 substrate and can withstand proper bending strain. ALD-TiO 2 film can effectively inhibit the release of nickel ions. After being immersed in the simulated body fluid for 30 days, the amount of nickel ions released decreases from 60 ppb for Ni50Ti50 substrate to 20–20 ppb for Ni50Ti50 with 200-cycle ALD-TiO 2 film. Meanwhile, Ni50Ti50 with ALD-TiO 2 films have better corrosion resistance than the Ni50Ti50 substrate. In vitro biocompatibility reveals that the ALD-TiO 2 film can enhance cell adhesion, promote cell proliferation and reduce cytotoxicity. After 5 days of culture, the 200-cycle ALD-TiO 2 film can enhance the cell proliferation by 2.7 times and reduce the cytotoxicity from 48% for Ni50Ti50 substrate to 37% for Ni50Ti50 with 200-cycle ALD-TiO 2 film. These results indicate that the TiO 2 films deposited by PE-ALD technique can effectively improve the biocompatibility of NiTi SMAs. [ABSTRACT FROM AUTHOR]