Unbalanced Zwitterionic Polyelectrolyte Coatings Enable Reversible Electrostatic Protein Adsorption for Superior Anti-fouling

Protein adsorption to surfaces in aqueous environments is driven by strong enthalpic and entropic interactions, widely regarded as thermodynamically inevitable and effectively irreversible, leading to persistent and chronic biofouling in real-world settings. Here, we demonstrate a serendipitous reversibility of electrostatic protein adsorption on unbalanced zwitterionic polyelectrolyte (UZIPE) coatings composed of poly(diallyldimethylammonium chloride) (PDDA) and poly(acrylic acid) (PAA) bilayers. When the surface-exposed anionic-to-cationic moiety ratio is tuned to a narrow range of 0.32-0.53, UZIPE coatings can effectively preserve electrostatically adsorbed proteins in their native conformation, and even strongly adhesive fibrinogen can be fully released by rinsing with physiological saline (0.9% NaCl). This reversibility allows UZIPE coatings to suppress microbial colonization and biofilm development for over 2 months in seawater and 1 month in freshwater, outperforming conventional hydration-based antifouling coatings. These findings establish reversible electrostatic protein adsorption as a distinct antifouling mechanism and offer a scalable route to environmentally benign, high-performance surface protection.