Antibacterial effect of nickel-titanium alloy owing to nickel ion release

This paper demonstrates that a NiTi shape memory alloy demonstrates antibacterial effect owing to the release of Ni ions from the alloy itself. Moreover, non-cytotoxic NiTi alloy with antibacterial properties can be prepared by simple post-heat treatment. We demonstrated that applying Escherichia coli to a NiTi surface resulted in 40% reduction in the number of cells following a 4 h incubation in an ambient atmosphere. When the alloy was heated at 450 °C in air, the antibacterial effect was slightly reduced but the cytotoxicity was drastically reduced. This result indicates that the production of an antibacterial NiTi alloy (without cytotoxic effects) is feasible with an appropriate surface modification. We further revealed that the appropriate Ni ion concentration for both antibacterial effect and biosafety was in the range from 0.05 mg L−1 to 3 mg L−1. Our novel finding represents a new and unique strategy for improving the antibacterial performance of NiTi alloy.