Improvement of Cu and Zr doped Diamond-like carbon coatings on comprehensive performance of Ni-Ti alloy potentially used in braided vascular stent

Abstract

Wear and corrosion between braided wires will not only release toxic nickel ions, but also cause fatigue fracture of Ni-Ti alloy-based braided stents. In this study, Cu and Zr doped Diamond-like carbon (DLC) film containing Cr intermediate layer and Cr:C gradient layer were prepared with the total thickness of about 2.17 μm and 2.05 μm, respectively. In order to study the improvement of DLC coating on the comprehensive properties of Ni-Ti based stent, the nano-mechanical, tribological, electrochemical corrosion, nickel ion release and cytotoxicity properties were all evaluated. The results showed that the nano hardness and elastic modulus for Zr-DLC film were 12.32 GPa and 138.49 GPa, respectively increased by 192% and 102% compared with bare NiTi. Cu-DLC and Zr-DLC coatings can not only significantly reduce the friction coefficient, but also greatly reduce the wear rate such as by three orders of magnitude in dry sliding condition compared with bare NiTi. Zr-DLC film reduced the icorr value with a reduction amount of 96.1%, with the values of 8.41 × 10−8 and 3.26 × 10−9 A/cm2 for NiTi and Zr-DLC, respectively. After 28 days of soak experiment in phosphate buffer solution, the total nickel ion release amount was only 5.6 ng/L for Cu-DLC and 6.9 ng/L for Zr-DLC, which was reduced by 96.1% and 95.2%, respectively. The relative cell proliferation rate results showed that NiTi and Zr-DLC were both Grade 0, which indicated good cytotoxicity result. However, the cytotoxicity of Cu-DLC reached grade 2 (the relative cell proliferation rate was 71.73%). Based on the above results, Zr-DLC showed good comprehensive performances and was expected to be used as a protective layer on the surface.