Highly Effective Polishing Process For Braided NiTi Stents

In braided stents, individual wires are often overlapping at numerous crossing points. Standard electropolishing processes have shown, so far, insufficient polishing results in these critical areas. Attempts to improve the surface quality by increasing polishing mass removal leads to unstable braids because the individual wires are not touching each other at the crossing points. As well technically very complex processes have so far yielded no satisfactory results.

The aim of this study was to develop an electropolishing process for braids, which is able to achieve excellent results with little technical effort. In order to achieve a very good surface quality even at the crossing points of the braids, the composition of the electrolyte was adjusted selectively. In addition, the process parameters are optimized so that a very uniform mass removal over the entire surface of the component can be obtained.

To evaluate different processed Nitinol braids (standard electropolishing, optimized electropolishing and natural oxide braids) comparative studies were carried out. For this propose, the radial force, the hydrogen content and the Nickel release were determined. In addition the corrosion behavior was analyzed. The individual surface quality was evaluated with a light microscope and with SEM. To characterize the oxide layer, surface analysis methods (Auger) were used.

With the optimized electropolishing process, it is possible to produce braided stents to an excellent quality.