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

Abstract

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.

Long‐term stability of self‐assembled monolayers on electropolished L605 cobalt chromium alloy for stent applications

“…26,27 Although the specific electropolishing protocols for commercially available stents remains proprietary, phosphoric acid based electrolytes are commonly used to polish coronary stents and were thus employed on L605 CoCr in this study. Among previous literature reports, small amounts of phosphorous and fluorine have been detected on 316L SS after electropolishing, acid dipping, and cleaning.…”

“…Among previous literature reports, small amounts of phosphorous and fluorine have been detected on 316L SS after electropolishing, acid dipping, and cleaning. 27 In addition, phosphoric acid esters have been reported to bind to the tantalum-oxide surface as phosphates. 36 Therefore, it is likely that phosphoric acid binds to the metal-oxide surface similar to SAMs with phosphonic acid head groups but without the alkyl chain intermolecular stabilizing interactions.…”

“…26 This reveals the intrinsic crystal structure and produces a microscopically smooth surface free of defects, damaged layers, embedded debris, and carbon contaminants. 26,27 Importantly, microscopically smoother surfaces have been shown to form SAMs of higher integrity and with fewer defects. 28 Thus, surface preparation by electropolishing may lead to more uniform monolayer formation, potentially increasing the stability of SAMs under physiological conditions.…”

The Development of Carotid Stent Material

“…316L stainless steel has been one of the first materials to be used in carotid stenting. It is composed of chromium, nickel, molybdenum, manganese, silicon, carbon, phosphorus, sulfur and iron [10]. Stainless steel can be used in both balloon-expandable and self-expanding stents.…”

O bombardeamento da superfície de titânio com íons de argônio influencia a resposta biológica de pré-osteoblastos

“…Atualmente, os stents são produzidos a partir do TiCP sem tratamento ou de aço inoxidável. O uso de stents com superfície bombardeada por argônio poderia aumentar os índices de sucesso destes implantes, pelo fato da superfície favorecer a adesão celular, o que estaria de acordo com Haïdopoulos et al (2006) que observou redução na corrosão e no processo de oxidação do Ti tratado com plasma spray usado na confecção de stents.…”