Carboxybetaine, sulfobetaine, and cationic block copolymer coatings: A comparison of the surface properties and antibiofouling behavior

Two different zwitterionic block copolymers (BCs) and a cationic BC were synthesized from the same BC precursor, which consisted of a polystyrene (PS) block and a poly[N-(3-dimethylamino-1-propyl)acrylamide] block. The zwitterionic BCs contained the dimethylammonioacetate (carboxybetaine) and dimethylammoniopropyl sulfonate (sulfobetaine) groups. Thin films cast from these polymers were investigated for surface wettability, surface charge, and protein adsorption. Surface-energy parameters calculated with advancing contact angle (theta a) and receding contact angle (theta(r)) of different probe liquids showed that it was theta r and not theta a that was representative of the polar/ionic groups in the near-surface regions of the coatings. Electrophoretic mobility was used to characterize the influence of pH on the net surface charge. In aqueous dispersions, the carboxybetaine polymer showed an ampholyte behavior with an isoelectric point of 6, whereas the sulfobetaine polymer was found to be anionic at all pH values between 2 and 10. Protein adsorption on the carboxybetaine BC was relatively independent of the net charges on the protein or the polymer, but the negatively charged sulfobetaine polymer showed a higher adsorption of positively charged protein molecules. Regardless of the net protein charge, both zwitterionic coatings adsorbed less protein compared to the PS and poly(2,3,4,5,6-pentafluorostyrene) controls. The sulfobetaine and cationic BCs adsorbed higher amounts of oppositely charged protein molecules than like-charged protein molecules. However, the adsorption of oppositely charged protein was much higher on the cationic surface than on the sulfobetaine surface. The zwitterionic BCs, particularly the carboxybetaine polymer, from this article are expected to function as stable, low-fouling surface modifiers in different biological environments. (C) 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012