Atomic layer deposited Al₂O₃ films on NiTi shape memory alloys for biomedical applications

NiTi shape memory alloys (SMAs) have been widely applied in biomedical fields owing to their excellent shape memory effect, super-elasticity, biomedical properties and fatigue performance. These applications include the cardiovascular stent, guidewire, stone extractors used in the cystic duct, artificial heart valve and orthodontic wire, etc. However, NiTi alloys might release out the Ni atoms in the physiological environment, which will induce the serious problems of allergic reaction, poisoning and causing cancer. This study employs the atomic layer deposition (ALD) technique to deposit Al2O3 films on the surfaces of NiTi SMAs. Experimental results show that the chemical compositions of ALD-Al2O3 films are well homogeneous. The ALD-Al2O3 films exhibit a fair adhesion with the NiTi substrates and sustain a suitable deformation strain. The ALD-Al2O3 films can also effectively inhibit the release out of Ni atoms from the NiTi SMAs. Meanwhile, the corrosion resistance of NiTi SMAs can be improved by the ALD-Al2O3 films.