Branched sulfoisobutylbetaine acrylamide polymers with hydrolytically stable amide linkages for long-term durable anti-biofouling surfaces

Zwitterionic polymer coatings have been widely explored for the construction of bio-inactive surfaces. However, many conventional zwitterionic polymers exhibit reduced functionality under long-term use owing to the hydrolysis of ester linkages. Sulfobetaine-type polymers also display enhanced interchain interactions with increasing molecular weight, which can induce water insolubility and aggregation. In this study, we synthesized a new zwitterionic monomer, sulfoisobutylbetaine acrylamide (SBBAm), based on a molecular design that (i) connects the vinyl group and the zwitterionic side chain through a hydrolysis-stable amide linkage and (ii) introduces a branched isobutyl linker between the anionic and cationic moieties to suppress interchain association. Copolymers of SBBAm with a silane-coupling monomer were prepared and immobilized on glass substrates to fabricate zwitterionic coatings. Bio-inactivity was evaluated by protein adsorption and cell adhesion assays, and durability was examined by long-term incubation in phosphate-buffered saline (PBS) at 37 °C. SBBAm-based coatings maintained low protein adsorption and cell adhesion even after 1 year in PBS, whereas coatings from conventional zwitterionic monomers showed a decrease in bio-inactivity after 1 week. A comparison with a sulfopropylbetaine-type polymer confirmed the effectiveness of the isobutyl linker. These results provide molecular design guidelines for sulfobetaine-based zwitterionic materials with long-term durable bio-inactive surfaces.