High precision electrolytic polishing of Ni-Ti shape memory alloy for biomedical vascular stents

There is a continuous demand for multi-disciplinary design approaches for the development of new implant materials. A potential biomaterial that is suitable for vascular stents and catheters is Ni-Ti alloy (Nitinol), which exhibits excellent biocompatibility, superelasticity, and shape memory effects. Corrosion resistance of Ni-Ti vascular stents in body fluids is significantly dependent on its surface finishing characteristics. In the study, as-drawn Ni-Ti wires were electropolished from a methanolic sulfuric acid electrolyte. The effect of various electropolishing (EP) parameters, i.e., current density, electropolishing time, and electrode gap, on the surface properties of Ni-Ti wires were examined. The surface morphology and topography of the Ni-Ti wires were characterized via scanning electron microscopy (SEM) and atomic force microscopy (AFM). The root mean square (R-a) surface roughness of electropolished Ni-Ti wires was also measured using AFM. The results indicated that the surface finishing of Ni-Ti alloy exhibited maximum sensitivity to electropolishing current density. An optimum combination of surface morphology and roughness was obtained at a parameter set with current density of approximately 0.5 A/cm(2), polishing time of 10 s, and electrode gap of 1.0 cm.