Finishing of laser-machined coronary stents by plasma electrolytic polishing

Cardiovascular stents are biomedical devices for the treatment of stenosis problem in the vascular system. Stenosis can be considered as the narrowing of the vessel in a way that creates a block or contraction to blood flow. In order to overcome such blockings, stents are placed and expanded in the narrowing location. Stent manufacturing is vastly done by laser beam machining and requires a good accuracy and control of the process to be successful. Recent studies have assessed nanosecond-pulsed lasers for efficient production in terms of productivity and quality. To achieve the required properties with regard to burr and dross removal, edge rounding and surface finishing, currently chemical etching followed by electrochemical polishing is applied after laser machining. Both from the perspective of process control, speed and repeatability as well as biocompatibility, these chemical finishing processes, using concentrated acids, are far from optimal. Plasma electrolytic polishing (PeP) can provide an alternative, using biocompatible, aqueous solutions and high DC voltages of u > 200 V to establish a vapour skin around the workpiece which leads to the generation of an atmospheric plasma. Here, electrochemical and electrothermal reactions take place which remove burr and dross and smoothen the workpieces' surface. Roughness values of Ra ≥ 0.02 μm have been achieved. This work presents the study of a novel stent manufacturing route for producing permanent stents in AISI 316L stainless steel. The stent mesh was microcut employing a ns-pulsed fiber laser. The stents were post-processed via traditional chemical etching and PeP. The results were compared in terms of geometrical integrity and surface roughness.