Mechanically stable tantalum coating on a nano-roughened NiTi stent for enhanced radiopacity and biocompatibility

Abstract

Mechanically stable tantalum (Ta) coatings were deposited onto nano-roughened and Ta-incorporated nickel-titanium (NiTi) alloy substrates to enhance their radiopacity and biocompatibility. A target-ion induced plasma sputtering process was used to induce highly uniform nanoscale roughness on the NiTi alloys, with Ta implantation. Characterization by field-emission scanning electron microscopy, X-ray diffraction, and transmission electron microscopy revealed that a dense alpha-phase Ta coating layer was tightly anchored to the NiTi substrate via the nano-roughened interface structures. The mechanical stability and stretchability of the Ta coating was examined using scratch and tensile tests, respectively. The adhesion strength and mechanical stability of the Ta coating on the nano-roughened NiTi surface showed remarkable improvement compared with the Ta coating on a flat NiTi surface. X-ray microscopic images showed that the radiopacity of a NiTi stent was enhanced by the Ta coating layer because of its high X-ray absorption coefficient and large thickness. In vitro cell adhesion and MTS assay revealed that the Ta coating was beneficial for endothelial cell attachment and proliferation. These results demonstrate that the Ta coating deposited onto nano-roughened NiTi substantially improved the mechanical stability, radiopacity, and biocompatibility of the NiTi stent.