Impact of Coatings and Coverings on Corrosion Resistance of Nitinol Devices

The ASTM F2129 potentiodynamic polarization standard states that medical devices should be tested in their final finished form, which can lead to challenges when a device is coated or covered in a non-conductive material. Therefore, the current FDA nitinol guidance document recommends that nitinol medical devices with a non-conductive material should be tested as an uncoated version. However, it is not always feasible to produce a bare metal version that is fully representative of the finished device without introducing potential artifacts from sample preparation. Therefore, the goal of this study is to assess the impact of coatings and coverings on nitinol corrosion resistance.

Laser-cut nitinol stent rings with two different surface finishes (a thermally oxidized surface and an electropolished surface) will be used in this study. To address a variety of materials and processes, experimental groups will include devices with sewn-on pericardial tissue coverings, electrospun polyurethane coatings, thermally applied polymeric coatings (silicone), and thermally applied polymeric coverings (PTFE). Testing will be conducted on devices with full coatings/coverings, with coverings/coatings removed (manually or chemically), and with simulated applications of coverings/coatings (e.g., needle strikes or thermal processing). Testing of the bare rings will serve as the control. Pitting corrosion testing, Auger Electron Spectroscopy, Electrochemical Impedance Spectroscopy, light optical, and scanning electron microscopy will be performed to understand the impact of coatings and coverings on corrosion resistance and alterations in the surface. The findings of this study will allow for more efficient testing and review of coated and covered nitinol devices.