Electropolishing and Throughmask Electroetching of Nitinol Stents In An Aqueous Electrolyte

This paper will discuss the results of a Phase I NIH SBIR grant, aimed at demonstrating the feasibility of the FARADAYIC ElectroPolishing and Throughmask ElectroEtching processes for the fabrication of nitinol stents. The Throughmask ElectroEtching technology is being developed to enable rapid stent fabrication while maintaining pattern fidelity in a low-concentration, aqueous electrolyte. This process does not impart thermal damage to the stent, eliminating the need for descaling of undesired oxides. The objective of the work was to demonstrate the feasibility of this process with etch rates of >25 mm/min for patterns with strut widths of 50 to 100 mm and slot widths of 38 to 400 mm. A critical process step in conventional stent manufacturing is electropolishing, which is typically done in an electrolyte such as sulfuric/phosphoric acid. Faraday has considerable experience in electropolishing materials in simple, low concentration aqueous electrolytes using pulsed electrolytic fields tuned to the material of interest to achieve the desired surface finish. This process has been applied to a number of advanced engineered materials including stainless steel semiconductor valves and nickel and titanium based aerospace turbine components. This ElectroPolishing process could be equally applied as the final finishing step for any stent fabrication method, and will likely utilize the same electrolyte that will be used for the FARADAYIC ElectroEtching process. The results presented will discuss: 1) dimensional tolerance, 2) etch rate, and 3) surface finish. This effort is designed to transition into a Phase II program, in which a range of stent designs would be manufactured, in pilot-scale equipment.