Metallic endovascular stents are used as medical devices to scaffold biological lumen, most often diseased arteries, after balloon angioplasty. They are commonly made of 316L stainless steel or Nitinol, two alloys containing nickel, an element classified as potentially toxic and carcinogenic by the International Agency for Research on Cancer. Although they are largely implanted, the long-term safety of such metallic elements is still controversial, since the corrosion processes may lead to the release of several metallic ions, including nickel ions in diverse oxidation states. To avoid metallic ion release in the body, the strategy behind this work was to develop a process aiming the complete isolation of the stainless steel device from the body fluids by a thin, cohesive and strongly adherent coating of RF-plasma-polymerized fluoropolymer. Nevertheless, prior to the polymer film deposition, an essential aspect was the development of a pre-treatment for the metallic substrate, based on the electrochemical polishing process, aiming the removal of any fragile interlayer, including the native oxide layer and the carbon contaminated layer, in order to obtain a smooth, defect-free surface to optimize the adhesion of the plasma-deposited thin film. In this work, the optimized parameters for electropolishing, such as the duration and the temperature of the electrolysis, and the complementary acid dipping were presented and accurately discussed. Their effects on roughness as well as on the evolution of surface topography were investigated by Atomic Force Microscopy, stylus profilometry and Scanning Electron Microscopy. The modifications induced on the surface atomic concentrations were studied by X-ray Photoelectron Spectroscopy. The improvements in terms of the surface morphology after the pre-treatment were also emphasized, as well as the influence of the original stainless steel surface finish.

Plasma oxidation of plasma deposited polystyrene (pPS) films was performed in an inductively coupled plasma reactor. Reconstruction of the oxygen concentration depth profiles based on angle‐resolved XPS data showed that two competitive mechanisms (functionalization and etching) happened during the oxygen plasma treatment. Static water contact angle measurements confirmed this result. Oxidized pPS films were also not stable with time; a loss of hydrophilicity was observed and reorganization of the topmost functionalized surface occurred involving diffusion of oxygen groups from the surface towards the bulk and re‐contamination by reaction of trapped radicals with hydrocarbon molecules present in ambient air.

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Summary: Metallic intravascular stents are medical devices used to scaffold a biological lumen, most often diseased arteries, after balloon angioplasty. They are commonly made of 316L stainless steel or Nitinol, two alloys containing nickel and chromium, which are classified as potentially toxic and carcinogenic by the International Agency for Research on Cancer. Their long‐term safety is therefore controversial, since the corrosion processes may lead to the release of several metallic compounds potentially toxic. Therefore, the strategy behind this work was to develop a process aiming the complete isolation of the devices from the body fluids by a thin, cohesive and strongly adherent coating of a plasma‐polymerized fluoropolymer. Ultra thin fluorocarbon films were deposited on pre‐treated stainless steel surfaces by radio frequency glow discharge plasma. Chemical composition, structure, hydrophobicity and morphology of the plasma‐polymer films were investigated by X‐ray photoelectron spectroscopy, Fourier‐transform infrared spectroscopy, water contact angle measurements and atomic force microscopy. Results show that the films were partially hydrogenated, amorphous, highly hydrophobic, smooth and pinhole‐free. Deposition on as‐received substrates however leads to partially hydrogenated, porous fluorocarbon coatings that consisted of heterogeneously distributed nanospherical particles. Thus, careful pre‐treatment prior to deposition proved essential, as demonstrated by its strong influence on the chemical composition of the interface, as well as the chemical structure and the morphology of the plasma‐polymer films. Finally, plasma‐polymer films were validated with respect to impermeability in a medium reproducing the physiological conditions that prevail in coronary arteries. magnified image