Synthesis and Characterization of Poly(3-Sulfopropylmethacrylate) Brushes for Potential Antibacterial Applications Madeleine Ramstedt,* ,†,£ Nan Cheng, † Omar Azzaroni, † Dimitris Mossialos, ‡,§ Hans Jo ¨rg Mathieu, £ and Wilhelm T. S. Huck* ,† MelVille Laboratory for Polymer Synthesis, Department of Chemistry, UniVersity of Cambridge, Lensfield Road, Cambridge, CB2 1EW, UK, Department of Fundamental Microbiology, UniVersity of Lausanne (UNIL), CH-1015 Lausanne, Switzerland, Department of Biochemistry and Biotechnology, UniVersity of Thessaly, GR-41221 Larissa, Greece, and Material Science, Ecole Polytechnique Fe ´ de ´ rale de Lausanne (EPFL), Station 12, CH-1015, Lausanne, Switzerland ReceiVed September 12, 2006. In Final Form: December 20, 2006 This article describes the aqueous atom transfer radical polymerization synthesis of poly(3-sulfopropylmethacrylate) brushes onto gold and Si/SiO 2 surfaces in a controlled manner. The effect of Cu(I)/Cu(II) ratio was examined, and a quartz crystal microbalance was used to study the kinetics of the brush synthesis. The synthesized brushes displayed a thickness from a few nanometers to several hundred nanometers and were characterized using atomic force microscopy, ellipsometry, Fourier transform infrared spectroscopy (FTIR), contact angle measurements, and X-ray photoelectron spectroscopy (XPS). The as-synthesized sulfonate brushes had very good ion-exchange properties for the ions tested in this study, i.e., Na + ,K + , Cu 2+ , and Ag + . FTIR and XPS show that the metal ions are coordinating to sulfonate moieties inside the brushes. The brushes were easily loaded with silver ions, and the effect of silver ion concentration on silver loading of the brush was examined. The silver-loaded brushes were shown to be antibacterial toward both gram negative and gram positive bacteria. The silver leaching was studied through leaching experiments into water, NaNO 3 , and NaCl (physiological medium). The results from these leaching experiments are compared and discussed in the article. Introduction In many sectors of our society there exists a need for antibacterial surfaces. One of the most obvious areas is in the healthcare sector where bacterial infections of implants and medical devices cause increased suffering, prolonged hospital visits, rejections of transplants, recurrent operations, and sometimes even death. 1,2 The antibacterial properties of silver have been known for centuries, and silver (in a variety of forms) has emerged as a very efficient bactericide due to its efficiency and low toxicity to humans. 3 Silver is antibacterial through a combination of several processes. Silver ions forms bonds to, e.g., DNA and to the surface of bacterial membrane proteins, thereby influencing a multitude of different cell functions. This multi-action makes it difficult for bacteria to develop resistance toward silver and, furthermore, to transfer such resistance between bacterial strains. 4-5 Many examples of antibacterial surfaces containing silver have been described in the literature in the form of silver nanoparticles, 6,7 silver halide salts, 8,9 or silver ions 10,11 in different organic matrices. Polymer brushes consist of polymer chains that are tethered to a surface at sufficiently high grafting densities to force the polymer chains to exhibit a stretched confirmation that is rarely found in bulk polymers. 12 By growing brushes from the surface (“grafting from”), a higher density of polymer chains per surface area can be achieved compared to when polymers are grafted onto a surface (“grafting to”). 13 In combination with a ‘living’ polymerization, polymer brushes with well-defined lengths, grafting densities, and composition can be obtained. Polyelec- trolyte brushes are constructed from monomers carrying either positively or negatively charged functional groups. These films are very useful for ion exchange or to trap counter ions within the brush structure. The film properties depend on a large variety of factors such as fraction of dissociated ionic groups in the brush and salt concentration in the surrounding solution. 14 When a polyelectrolyte brush is collapsed in salt solution, excess electrolyte ions from solution get trapped inside the brush, and these can subsequently be leached out by repeated rinsing. 15 Brushes carrying functional groups such as phosphate, sulfonate, and carboxylate groups will display different properties depending on the pH of the surrounding fluid as a result of protonation of * To whom correspondence should be addressed. Phone: +447784716633 (M.R.); +441223334370 (W.T.S.H.). E-mail: kmr48@cam.ac.uk (M.R.); wtsh2@cam.ac.uk (W.T.S.H.). † University of Cambridge. ‡ University of Lausanne. § University of Thessaly. £ Ecole Polytechnique Fe ´de ´rale de Laussanne. (1) Rimondini, L.; Fini, M.; Giardino, R. J. Appl. Biomater. Biomech. 2005, 3,1-10. (2) Campoccia, D.; Montanaro, L.; Arciola, C. R. Biomaterials 2006, 27, 2331- 2339. (3) Melaiye, A.; Youngs, W. J. Expert Opin. Ther. Pat. 2005, 15, 125-130. (4) Percival, S. L.; Bowler, P. G.; Russel, D. J. Hosp. Infect. 2005, 60,1-7. (5) Modak, S. M.; Fox, C. L. Jr. Biochem. Pharmacol. 1973, 22, 2391-2404. (6) Davenas, J.; The ´venard, P.; Philippe, F.; Arnaud, M. N. Biomol. Eng. 2002, 19, 263-268. (7) Morones, J. R.; Elechiguerra, J. L.; Camacho, A.; Holt, K.; Kouri, J.B.; Ramirez, J. T.; Yacaman, M. J. Nanotechnology 2005, 16, 2346-2353. (8) Sambhy, V.; MacBride, M.; Peterson, B. R.; Sen, A. J. Am. Chem. Soc. 2006, 128, 9798-9808. (9) Adams, A. P.; Santschi, E. M.; Mellencamp, M. A. Vet. Surg. 1999, 28, 219-225. (10) Shi, Z.; Neoh, K. G.; Zhong, S. P.; Yung, L. Y. L.; Kang, E. T.; Wang, W. J. Biomed. Mater. Res. 2005, 76A, 826-834. (11) Ramstedt, M.; Houriet, R.; Mosialos, D.; Haas, D.; Mathieu, H. J. Wet chemical silver treatment of endotracheal tubes in order to produce antibacterial surfaces, manuscript submitted to J. Biomed. Mater. Res. B, in press, 2007. (12) Jones, A. L.; Richards, R. W. Polymers at Surfaces and Interfaces; Cambridge University Press: New York, 1999. (13) Zhao, B.; Brittain, W. J. Prog. Polym. Sci. 2000, 25, 677-710. (14) Dobrynin, A. V.; Rubinstein, M. Prog. Polym. Sci. 2005, 1049-1118. (15) Azzaroni, O.; Moya, S.; Farhan, T.; Brown, A. A.; Huck, W. T. S. Macromolecules 2005, 38, 10192-10199. 3314 Langmuir 2007, 23, 3314-3321 10.1021/la062670+ CCC: $37.00 © 2007 American Chemical Society Published on Web 02/10/2007