Surfaces engineering of polymeric films for biomedical applications P. Rossini a,b, * , P. Colpo a , G. Ceccone a , K.D. Jandt b,c , F. Rossi a a European Commission, Joint Research Centre, TP 203 21020 Ispra (VA), Italy b University of Bristol, Faculty of Medicine, Department of Oral and Dental Science, Lower Maudlin Street, Bristol, UK c Institute of Materials Science & Technology (IMT), Friedrich-Schiller-University Jena, Lo ¨bdergraben 32 D-07743 Jena, Germany Abstract The present study deals with the deposition of acrylic acid thin films by RF plasma assisted chemical vapour deposition. In situ diagnostics (Mass Spectrometry and Optical Emission Spectroscopy) have been used in order to control the deposition processes and analyse the fragmentation steps. The films have been characterised with X-ray Photoemission Spectroscopy (XPS) and Fourier Transformed Infrared Spectroscopy (FTIR). Surface energy of the coatings has been determined by contact angle measurements. The protein adsorption kinetics has been evaluated with the Quartz Crystal Microbalance (QCM) with Human Serum Albumin. The results demonstrate a strong link between monomer fragmentation in the plasma and functional groups retention in the films. By increasing the RF power, the COOH concentration in the films (XPS and FTIR) as well as hydrophylicity, hydrogen bondings and acid-base character decrease while the CO concentration in the plasma phase (MS and OES) increases. At the same time, the dispersive and the polar components of the surface-free energy increase. These surface properties have a strong influence on the protein attachment kinetics, as determined by QCM measurements. D 2002 Published by Elsevier Science B.V. 1. Introduction During the last decades, one of the major trends in the biomaterial research has been the functionalisation of the material surfaces to control the biological response of the host (human body) to improve the biocompatibility [1]. For this purpose, low-pressure plasma process has been widely recognized as a technology of choice for surface modifi- cation of biomedical devices. Plasma process presents the advantages to modify the very first layers of the surface, keeping the bulk material properties [2]. Furthermore, the plasma treatment or deposited films are easily controllable by choosing a suitable monomer and the appropriate conditions in the plasma. The selectivity (or density) and the mobility of the functional groups on the surface can be varied to some extent by changing the degree of cross- linking. Thus, vascular grafts, heart valves, stents, cathe- ters, blood bags and other biomedical devices can be engineered with different surface properties in order to improve their compatibility with the biological fluids. Among the wide treatment spectra, plasma polymerisation of acrylic acid has proven to provide highly functionalised surfaces, with the highest retention of the monomer struc- ture and the highest density of –COOH groups. This kind of surface modification is suitable for biomedical applica- tion to control protein adsorption [3] and to surface immobilization of bioactive molecules [4]. The present study deals with the deposition of acrylic acid thin films by RF plasma-assisted chemical vapour deposition. Plasma diagnostics, surface analysis and physical – chemical char- acterisation have been performed in order to relate the deposition processes to film properties. The protein attach- ment kinetics determined by the Quartz Crystal Micro- balance (QCM) measurements are presented. 2. Experimental The plasma source used for the deposition is a classical capacitively coupled plasma source. The plasma chamber is made of a cylindrical stainless steel jacket (U = 210 mm, h = 350 mm) in which the part to be processed is placed and the process gases introduced at reduced pressure (10 À 3 to 1 Torr). A vapour delivery system is connected to the 0928-4931/02/$ - see front matter D 2002 Published by Elsevier Science B.V. PII:S0928-4931(02)00286-2 * Corresponding author. European Commission, Joint Research Centre, TP 203 21020 Ispra (VA), Italy. E-mail address: nella.rossini@jrc.it (P. Rossini). www.elsevier.com/locate/msec Materials Science and Engineering C 23 (2003) 353 – 358