Plasma polypyrrole micro-coatings on metallic stents

Abstract

Stainless steel stents were coated with biocompatible polypyrrole doped with iodine and synthesized by plasma to add a polymeric layer on the metallic surfaces that may reduce some implant rejection reactions in the human circulatory system due to the implantation of metallic surfaces. Trying to increase the adhesion in the polymer–metal interface, this study used erosion, oxidation and sensitization of the metallic stents with an in situ posterior polymerization of the monomer. All processes were carried out by plasma which increased the reactivity of the metallic surfaces producing chemical bonds between polymers and stents with a high possibility to resist the blood conditions without peeling or detachment that may expose the metallic surface to the blood. The results showed that the coatings contain pyrrole rings joined among them in different configurations which originated crosslinked polymers. The erosion did not change, substantially, the density of protrusions, but changed only their width and height, and the coatings acquired the morphology of the metallic surface with a 3.7 nm roughness and protrusion separation of 35.6 nm. The coated stents were immersed in phosphate-buffered saline (PBS) solutions with pH ~7.4 at 37 °C to partially simulate the chemical conditions in arteries and veins, in which the coating remained adhered on the stent up to 2 months without significant degradation. The immersion in PBS static fluids caused a roughness decrease from 3.7 to 2.4 nm with a protrusion separation of 35.4 nm, however, in PBS dynamic fluids, the erosion increased the roughness and protrusion separation up to 9.3 and 43.9 nm, respectively.