Plasma polymerized allylamine films deposited on 316L stainless steel for cardiovascular stent coatings

Abstract

Coronary stents are metallic (316L stainless steel) medical devices used during balloon angioplasty to scaffold diseased arteries and prevent their reblockage. To reduce the restenosis rate, bare metal stent coating is a promising solution. The coating can protect the metallic surface of the stent from corrosion attack caused by the biological environment. In addition, according to Food and Drug Administration (FDA) the coating properties must be guaranteed even after stent expansion. The aim of this study was to develop a dry process to coat the metallic surface from the biological environment by depositing an ultra-thin, stable, cohesive and adhesive plasma polymerized allylamine (CH2=CH―CH2―NH2) coating with high selectivity towards primary amine groups. Plasma polymerized allylamine (PPAA) coatings were deposited on electropolished 316L stainless steel (316L SS) samples using a low pressure plasma reactor (70kHz). XPS (X-Ray Photoemission Spectroscopy) and FTIR-ATR (Fourier Transform Infrared-Attenuated Total Reflectance) spectroscopy measurements were used to investigate the chemical composition of the coatings. A chemical derivatization technique was employed in order to quantify the amine retention rate of the deposited films. Morphology of the films was evaluated by FE-SEM (Field Effect-Scanning Electron Microscopy) imaging. Furthermore, special attention was devoted to study the stability of the coating and its adhesion properties after plastic deformation up to 25%. The effect of the power discharge and treatment time on these properties was also investigated. Our results showed that coatings present the required adhesion and cohesion properties to be stable upon deionised (D.I.) water immersion and to resist to a stent expansion.