Surface Characterization of Electro-polished Nitinol Devices by Auger Analysis

Implanted medical devices such as stents, orthopedic prostheses, and heart valves need to be resistant to corrosion to avoid adverse effects after deployment in the human body. For nickel-containing alloys such as nitinol, this resistance is dependent on the surface condition of the device as well as the alloy composition and microstructure. Optimization of the surface condition is critical and can be characterized by several complementary methods such as electrochemical corrosion testing and surface analysis. Auger Electron Spectroscopy (AES) enables both measurement of the surface oxide layer thickness and investigation of the oxide layer uniformity and elemental composition of electro-polished medical devices. It can be used to provide characteristic information of the surface condition from a device, or localized to highlight differences between various areas of interest or process variations. This paper investigates the use of AES Analysis to characterize resultant surfaces from different electrochemical and chemical processing conditions, environmental exposure, and design features.