An experimental study of electrochemical polishing for micro-electro-discharge-machined stainless-steel stents Derry Lappin • Abdolreza Rashidi Mohammadi • Kenichi Takahata Received: 30 August 2011 / Accepted: 1 December 2011 / Published online: 20 December 2011 Ó Springer Science+Business Media, LLC 2011 Abstract This paper reports electrochemical polishing (EP) of 316L stainless-steel structures patterned using micro-electro-discharge machining (lEDM) for application to stents including intelligent stents based on micro-electro- mechanical-systems technologies. For the process optimi- zation, 10 lm deep cavities lEDMed on the planar material were polished in a phosphoric acid-based electrolyte with varying current densities and polishing times. The EP con- dition with a current density of 1.5 A/cm 2 for an EP time of 180 s exhibited the highest surface quality with an average roughness of 28 nm improved from*400 nm produced with high-energy lEDM. The EP of lEDMed surfaces was observed to produce almost constant smoothness regardless of the initial roughness determined by varying discharge energies. Energy-dispersive X-ray spectroscopy was per- formed on the lEDMed surfaces before and after EP. A custom rotational apparatus was used to polish tubular test samples including stent-like structures created using lEDM, demonstrating uniform removal of surface roughness and sharp edges from the structures. 1 Introduction Vascular stents have served as a key device for minimally invasive treatment of cardiovascular disease, the leading cause of death in North America [1]. Stents have a tubular shape with mesh-like walls and are designed to be expanded, using an angioplasty balloon, in the radial direction to scaf- fold diseased sites of arteries narrowed by plaque deposition on the vessel walls [2]. Stents are most commonly implanted in the coronary artery, but they are also used for other applications [3–7]. Balloon-expanding stents are commonly made from 316L stainless steel [8]. Commercially available stents are typically manufactured using laser machining of tubes of the material [9–11]. Micro-electro-discharge machining (lEDM) is another potential approach to machining stents. lEDM is a non-contact micromachining technique that utilizes high-frequency pulses of thermome- chanical impact induced by a miniaturized electrical dis- charge generated between a microscopic electrode and a sample while both are immersed in dielectric liquid [12, 13]. The technique is versatile as it is applicable to any type of electrical conductor, including all kinds of metals and alloys. This technique can produce features of a few microns with submicron tolerances. In addition, complex three-dimen- sional (3D) shapes can be achieved through high-precision numerical control systems. A planar approach to stent fab- rication based on lEDM of stainless-steel sheets was reported [14]. The technique allows one to accurately control not only the lateral dimensions of machined structures but also the depth of the structures in both planar and cylindrical samples made of alloys typically used as stent materials. This high-precision 3D micromachining capability provides a unique opportunity in developing intelligent stents, a novel class of stents that incorporate micro-electro-mechanical systems (MEMS) and integrated circuits for monitoring of intravascular parameters through micro-scale sensors inte- grated with stents [15, 16]. In these ‘‘smart’’ stents, the stents themselves are designed and fabricated to work as radio frequency (RF) antennas so as to enable wireless D. Lappin Department of Mechanical Engineering, University of British Columbia, Vancouver, BC V6T 1Z4, Canada A. R. Mohammadi  K. Takahata (&) Department of Electrical and Computer Engineering Engineering, University of British Columbia, Vancouver, BC V6T 1Z4, Canada e-mail: takahata@ece.ubc.ca 123 J Mater Sci: Mater Med (2012) 23:349–356 DOI 10.1007/s10856-011-4513-2