R. Steegmüller, M. Quellmalz, A. Schüßler, Admedes Schuessler GmbH, Pforzheim, Germany
X-ray visibility of Nitinol stents is often improved by attaching radiopaque rivets to the stent structure. Riveting materials used today differ with regard to their radiopacity, deformability and corrosion potentials. For example: Gold (Au) has the highest deformability, while the radiopacity of Platinum-Iridium (PtIr) is the best and Tantalum (Ta) is reported to provide the lowest electrochemical potential if coupled to Nitinol. This investigation studied rivets of materials Au, PtIr and Ta attached to electropolished Nitinol stents. Additionally, the influence of riveting quality was investigated by analyzing riveting tooling and foreign material residuals e.g. wear from riveting tooling.
Riveted Nitinol stents of Au, PtIr and Ta underwent potentiodynamic corrosion tests. SEM analysis of the rivet areas was conducted before and after the respective corrosion testing. The open circuit and breakdown potentials for each material combination were compared to the results with test data obtained for Nitinol stents without rivets. Standard immersion tests in HBSS (Hanks balanced salt solution) were performed to determine the Nickel release of the different material combinations. Furthermore, explanted Nitinol stents with Gold rivets from an animal study were analyzed in the SEM. Results of this analysis are discussed with respect to literature data as well as benchmark riveted stents.
Summary: X-ray visibility of Nitinol stents is often improved by attaching radiopaque rivets to the stent structure. In this study rivets of Gold, Platinum Iridium and Tantalum attached to electropolished Nitinol stents were inspected. Additionally, the influence of riveting quality was investigated by analyzing riveting tooling and foreign material residuals e.g. wear from riveting tooling. The riveted stents underwent potentiodynamic corrosion tests, SEM analysis and immersion tests to determine the Nickel release. Furthermore, explanted stents with Gold rivets from an animal study were analyzed in the SEM. Results of this analysis are discussed with respect to literature data as well as benchmark riveted stents.
