Drug-eluting stents (DESs) have been associated with adverse clinical effects. Moreover, recent publications have shown that the coating of DESs suffers from defects. The purpose of this contribution is to examine a three-step process for surface modification as a means of improving the durability of DESs. In the first step, 4-(2-bromoethyl)benzenediazonium tetrafluoroborate was electrografted onto a stainless steel (SS) stent. X-ray photoelectron spectroscopy (XPS) of the modified stent confirmed the formation of the organic layer. In the second step, methyl methacrylate was polymerized onto the grafted surface by atom-transfer radical polymerization. XPS, electrochemical impedance spectroscopy, and contact-angle measurements were used to characterize the polymer brushes. The last step involved spray-coating of the stent with a drug-in-polymer matrix [poly(n-butyl methacrylate)/poly(ethylene-co-vinyl acetate) + paclitaxel]. Scanning electron microscopy confirmed the considerably improved durability of the drug-in-polymer matrix. Bare controls showed greater cracking and delamination of the coating than did the two-step modified stents after incubation under physiological (37 degrees C) and accelerated (60 degrees C) conditions. Finally, paclitaxel controlled release from the modified SS DESs was moderate compared with that of nontreated samples. In conclusion, the proposed method significantly improves the durability of drug-in-polymer matrixes on a SS DESs.

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Organic coatings based on N-(2-carboxyethyl)pyrrole (PPA) and a butyl ester of PPA (BuOPy) were deposited via electrochemical oxidation. The homo- and copolymers were electropolymerized on glassy carbon and stainless steel in acetonitrile using tetrabutylammonium tetrafluoraborate (Bu4NF4B) as the electrolyte. The mechanism of deposition on stainless steel was studied by chronoamperometry and by the tapping and phase angle imaging modes of atomic force microscopy. The electrochemical properties and growth of the films were investigated by cyclic voltammetry. The composition of the copolymers was determined by reflection-absorption Fourier transform infrared spectroscopy. We found that while the hydrophilic monomer PPA undergoes progressive nucleation followed by instantaneous growth the hydrophobic BuOPy nucleates instantaneously. The rate of BuOPy electropolymerization was higher than that of PPA, and the resulting film was thicker yet fluffier. Copolymer films were enriched by BuOPy as compared with the electropolymerization solution, which is attributed to the faster rate of electropolymerization of BuOPy than PPA.

The coating of medical implants by polymeric films aims at increasing their biocompatibility as well as providing a durable matrix for the controlled release of a drug. In many cases, the coating is divided into a primer layer, which bridges between the medical implant and the drug-eluting matrix. The primer coating must be very carefully designed in order to provide optimal interactions with the surface of the medical implant and the outer layer. Here we present a simple and versatile approach for designing the primer layer based on electropolymerization of a carefully chosen blend of three different pyrrole derivatives: N-methylpyrrole (N-me), N-(2-carboxyethyl)pyrrole (PPA), and the butyl ester of N-(2-carboxyethyl)pyrrole (BuOPy). The composition and physical properties of the primer layer were studied in detail by atomic force microscopy (AFM) and a nano scratch tester. The latter provides the in-depth analysis of the adhesion and viscoelasticity of the coating. AFM phase imaging reveals a uniform distribution of the three monomers forming rough morphology. This primer layer significantly improved the morphology, stability, and paclitaxel release profile of a paclitaxel-eluting matrix based on methyl and lauryl methacrylates.

Nonbiodegradable polymer coating based on N-(2-carboxyethyl)pyrrole (PPA) and butyl ester of PPA (BuOPy) were successfully electrodeposited on a stainless steel stent surface using cyclic voltammetry. Chemical composition of the coating was examined by X-ray photoelectron spectroscopy. Polymer stability was examined by immersing the coated stent into 1:1 solution of fetal calf serum:seline solution up to 1 year and implantation subcutaneously in mouse for 1 week. Morphology changes were then recorded by scanning electron microscopy. Paclitaxel loading was carried out by immersion into drug solution and its release was detected by HPLC. The results show that thin (single micrometers), uniform coating with various morphology and hydrophobicity can be created by electrochemical deposition. The polymer did not show significant histopathological or morphological changes in vitro and in vivo. The surface properties allow loading appropriate amounts of paclitaxel and release it slowly up to a month.