Development of an optimized electrochemical process for subsequent coating of 316 stainless steel for stent applications

• Published in: Journal of materials science. Materials in medicine Vol. 17; no. 7; pp. 647 - 657
• Main Authors: Haïdopoulos, M, Turgeon, S, Sarra-Bournet, C, Laroche, G, Mantovani, D
• Format: Journal Article
• Language: English
• Published: United States Springer Nature B.V 01.07.2006
• Subjects: Alloying elements; Arteries; Atomic force microscopy; Austenitic stainless steels; Biomedical materials; Body fluids; Carcinogens; Cardiovascular system; Chemical polishing; Coated Materials, Biocompatible - chemistry; Electrochemistry; Electrochemistry - methods; Electrolysis; Electrolytes - chemistry; Electropolishing; Fluoropolymers; Free surfaces; Implants; Interlayers; Ions; Materials science; Materials Testing; Medical equipment; Microscopy, Atomic Force; Microscopy, Electron, Scanning; Nickel; Nickel titanides; Oxidation; Photoelectron spectroscopy; Photoelectrons; Polymer films; Polymers; Pretreatment; Prostheses and Implants; Scanning electron microscopy; Shape memory alloys; Stainless steel; Stainless Steel - chemistry; Stents; Styli; Substrates; Surface finish; Surface Properties; Surgical implants; Thin films; X-Ray Diffraction
• ISSN: 0957-4530; 1573-4838
• DOI: 10.1007/s10856-006-9228-4

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.