Sulfonated Surfaces by Sulfur Dioxide Plasma Surface Treatment of Plasma Polymer Films Kim S. Siow,* Leanne Britcher, Sunil Kumar, Hans J. Griesser Introduction It is well established that the surface composition of biomaterials dictates, upon contact between a material or device and a biological environment, ensuing biological processes such as competitive protein adsorption from complex media. Thus there has been a large body of literature on the fabrication of materials surfaces with various chemical compositions and the study of their bio- interfacial interactions. Early interest in sulfur containing compounds arose from the role played by the sulfate groups of heparin in anti-thrombogenicity. [1–3] Sulfate groups are also found in other glycosaminoglycans present in extra- cellular matrices, such as chondroitin sulfate, and as a charged ionic group it is likely to be an essential part in defining biological intermolecular interactions, and, hence, also some interactions between biological molecules and materials surfaces. Sulfated materials surfaces may there- fore be useful biomaterials interfaces, enabling the study of the role played by these groups in protein/surface interactions and extracellular signalling. It may, however, be easier to fabricate sulfonated surfaces, and the surface forces and effects may be very similar due to the very similar properties, such as pK, of sulfonate (CSO 3 ) and sulfate (COSO 3 ) groups on polymer surfaces. Besides biomaterials applications, sulfonate containing surfaces have been investigated as potential proton exchange membranes in fuel cell application. [4–6] SO x containing organic surfaces have been produced by bulk polymerisa- tion, [7–13] gas [14–20] or acid sulfonation, [21,22] self assembled monolayers, [23–25] and photochemical grafting. [26] These methods, however, often lead to deterioration of mechan- ical properties, [12,13] or are limited to a small number of suitable substrates. [24,25] Plasma approaches may overcome these problems, as well as providing reduced process effluent discharge. [27] Unfortunately, however, while various other biomaterials Full Paper K. S. Siow, L. Britcher, S. Kumar, H. J. Griesser Ian Wark Research Institute, University of South Australia, Mawson Lakes, SA 5095, Australia Fax: 65-68737192.; E-mail: kimshyong@gmail.com The preparation of thin film coatings with sulfonate and sulfate groups by plasma techniques is not straightforward due to limited volatility of suitable process vapours. We report a combination of plasma polymerisation and plasma treatment, treating heptylamine (HA-SO 2 ) and 1,7-octadiene (OD-SO 2 ) plasma polymers with sulfur dioxide plasma. HA-SO 2 and OD-SO 2 plasma polymer surfaces exhibited different com- positions with the latter showing almost twice the amount of sulfur, as well as polysulfonate. Ageing of HA-SO 2 plasma polymer surfaces in air or saline solution led to the disappearance of oligomers containing sulfonate and sulfate. Angle-dependent XPS analysis of HA-SO 2 plasma polymers suggested that sulfur containing groups reptated into the plasma polymer upon storage after preparation. Plasma Process. Polym. 2009, 6, 583–592 ß 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim DOI: 10.1002/ppap.200950004 583