Superelastic Ti-Zr-Nb-Sn Thin Films Fabricated by Magnetron Sputtering: Biocompatibility and Bacterial Biofilm...

Nickel-titanium (NiTi) alloys are widely used in orthopedics because of their excellent mechanical properties; however, hypersensitivity remains a concern because of Ni ion release during long-term implantation. To address this issue, we manufactured Ti-Zr-xNb-Sn thin films (x = 10, 15, 17, 20 at.%) using magnetron-sputtering, intended as coatings for NiTi devices. Given the superelasticity of Ti-Zr-Nb-Sn alloys, these coatings are expected to not only suppress the Ni ion release from the NiTi substrate but also reduce the formation of cracks in the coating by accommodating the substrate's deformation. The biocompatibility of the coatings was evaluated both in vitro and in vivo, as well as the potential risk of forming bacterial biofilms. Ti-Zr-xNb-Sn coatings (x = 15, 17 at.%) promoted pre-osteoblast differentiation compared to uncoated NiTi, without increasing the risk of biofilm formation by Staphylococcus epidermidis. The coated NiTi wires were implanted subcutaneously in mice for 28 days, and no strong rejection reaction was observed compared to uncoated NiTi. Additionally, the coatings showed superior corrosion resistance, indicating improved long-term stability. The deposition angle during sputtering influenced cell differentiation, suggesting that both chemical composition and surface morphology contribute to osteogenic responses. Overall, Ti-Zr-Nb-Sn coatings are a promising surface modification strategy for NiTi orthopedic implants.