Ammonia RF-Plasma on PTFE Surfaces: Quantification of the Species Created on the Surface by Vapor - Phase Chemical Deriv
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Ammonia RF-Plasma on PTFE surfaces : Quantification of the Species Created on the Surface by Vapor - Phase Chemical Derivatization Chevallier P.1, Castonguay M. 1, Mantovani D. 1,2, and Laroche G. 1,3 1. Quebec Biomaterials Institute, 10 rue de l’Espinay, Quebec City, (Qc) G1L 3L5, Canada 2. Department of Materials Engineering, Laval University, Quebec City, (Qc) G1K 7P4, Canada 3. Department of Surgery, Laval University, Quebec City, (Qc) G1K 7P4, Canada. Abstract A cylindrically-configured plasma treatment system in Radio Frequency Glow Discharges fed with ammonia was used with the aim of modifying the internal surface of ePTFE arterial prostheses to improve their biocompatibility. In order to understand the effects of this treatment on the PTFE polymer surface, we have first realized RF-plasma treatment experiments on PTFE films. Preliminary XPS analyses have shown that about 15% of the surface atoms were substituted by nitrogen (N/C ratio of 0.3) whereas the F/C ratio decreased from 2 to 0.6, therefore leading to the conclusion that several chemical species are created onto the surface upon an ammonia plasma treatment. As X-Ray Photoelectron Spectroscopy (XPS) analysis does not allow the direct determination of the nature of the N-species grafted on the surface (chemical shifts are not different enough), vapor phase chemical derivatization was carried out on PTFE films to quantify the concentration of these new surface moities grafted on the polymer surface. Introduction Low pressure plasma surface treatments are an advantageous technique for the development of new biocompatible materials because surface modifications can be achieved without altering the material bulk properties. In this context, the use of NH3 plasmas allows to introduce amine groups on the surface, known to react fairly easily with other chemical species, thus allowing covalent attachment of molecules with appropriate biocompatibility properties. The formation of a covalent bond could prevent the removal of the attached molecules by the blood flow. However, the first step of surface modification experiments is to identify and quantify the species created upon plasma treatment. This information is of paramount importance in the understanding and control of the subsequent molecule grafting to the surface. As far as RFGD ammonia plasma treatment on PTFE is concerned, XPS measurements clearly indicate that amine groups are not the sole moities grafted on the surface as, on one hand defluorination is higher and, on the other hand N incorporation is lower than expected [1, 2]. Unfortunately, positive identification of N-containing species by High Resolution XPS is often difficult owing to the small chemical shift variations in the N1s region for the various N-containing species. Chemical derivatization has thus been used to overcome this problem. Basically, the treated surfaces are exposed to a reagent with a specific functional group, with the reagent chosen to bear a unique element which is not previously present on the surface. The common markers
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