We report the synthesis of a new cysteine-based methacrylic monomer (CysMA) by selective thia-Michael addition of a commercially-available methacrylate-acrylate precursor in aqueous solution with recourse to protecting group chemistry. Poly(cysteine methacrylate) (PCysMA) brushes were from the surface of planar silicon wafers by surface initiated atom-transfer radical polymerisation. The kinetics of brush growth were investigated. Brush thicknesses of ca. 27 nm were achieved within 270 min. at 20oC. Each CysMA residue comprises a primary amine and a carboxylic acid, hence the resulting PCysMA brushes exhibit either cationic, zwitterionic or anionic character depending on the solution pH. The pH-responsive behavior of photopatterned brushes was studied by atomic force microscopy. Surface zeta potential studies confirm that PCysMA brushes are highly extended either below pH 2 or above pH 9.5, since they possess either cationic or anionic character, respectively. However, at intermediate pH, PCysMA brushes acquire zwitterionic character and exhibit excellent anti-biofouling properties at around physiological pH, with essentially no cytotoxicity being observed. On exposure to UV radiation,  PCysMA brushes undergo photodegradation: AFM topographical imaging indicates significant mass loss from the brush layer, while XPS studies confirm that exposure to UV radiation produces surface aldehyde sites that can be derivatized subsequently with amines. UV exposure through a photomask yielded sharp, well-defined micro-patterned PCysMA brushes. Nano-patterned PCysMA brushes were fabricated using interference lithography (IL). Selective adsorption of green fluorescent protein (GFP) onto patterned PCysMA brushes was examined using confocal fluorescence microscopy and AFM. Unexposed PCysMA brushes proved to be highly protein-resistant, whereas protein conjugation to surface aldehyde groups occurred in the exposed regions.  Finally, PCysMA undergoes complex base-catalyzed degradation in alkaline solution, leading to the elimination of several small molecules. However, good chemical stability was observed when PCysMA brushes were immersed in aqueous solution at physiological pH.

Synthesis and nanometer-scale patterning of stimulus-responsive, biofouling-resistant zwitterionic poly(amino acid methacrylate) brushes

248th National Meeting (2014)

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