On the Interface between Plasma Fluorocarbon Films and 316L Stainless Steel Substrates for Advanced Coated Stents

Abstract

As intravascular biomedical devices, metallic stents are particularly susceptible to corrosion induced by the physiological environment, causing the degradation of mechanical properties and leading to the release of toxic and carcinogenic ions from the SS316L bulk. Therefore, several works have been focused on the development of an ultra-thin fluorocarbon coating that could act both as a drug-carrier for in-stent restenosis and as an anti-corrosion barrier. However, the increase of the corrosion performance was limited by the inevitable permeability of the coating, which exposed some of the sensitive interfacial region to the corrosive environment. Indeed, in previous works, adhesion and growth rate of the film were promoted by the removal of the native oxide layer of the stainless steel which is inhomogeneous, brittle and mechanically unstable. Further refinements of the interface are therefore required in order to enhance the overall corrosion performance without compromising the fluorocarbon film properties and adhesion. Hence, the aim of this work was to enhance the corrosion behaviour of coated SS316L by the creation of a controlled interfacial oxide layer. The native oxide layer was first removed under vacuum and the bare metal surface was subjected to a plasma-reoxidation treatment. Tafel measurements were used to assess the corrosion rates of the specimens. Coated and uncoated modified interfaces were also characterized by X-Ray Photoelectron Spectroscopy (XPS) and Atomic Force Microscopy (AFM).