A mixed-charged monomer approach to robust protein-resistant polyurethane coatings

Durable protein-resistant materials that perform reliably under physiological conditions are essential for medical and marine applications, where surface interactions with the fouling environment determine functionality. While zwitterionic polymers have shown excellent antifouling properties, their widespread application is limited by high cost, poor mechanical durability, and complex synthesis. In this study, we present a new class of polyurethane (PU) coatings incorporating a mixture of commercially available ionic chain extenders—2,2-bis(hydroxymethyl)propionic acid (DMPA) and N-methyldiethanolamine (MDEA)—as a durable and cost-effective alternative. By introducing equal amounts of positively and negatively charged monomers as separate functional groups, rather than covalently linked zwitterionic units, we demonstrate a simple and effective strategy for designing biocompatible and antifouling coatings. Mixing independent ionic monomers as separate groups (rather than covalently linked zwitterionic units) represents a new design concept that has not been systematically explored for either thermoplastic or thermoset PUs. The resulting uniform distribution of charged groups enables hydration-driven surface rearrangement that minimizes protein adsorption while preserving mechanical integrity. Polyurethanes with 10% charged-group content, optimized in both thermoplastic and thermoset architectures, exhibit excellent biocompatibility, enhanced mechanical performance, and reduced material cost compared to zwitterionic systems. Spectroscopic (ATR-FTIR, NMR) and morphological (AFM) analyses confirm the uniform integration of charged groups, promoting hydration-driven surface rearrangement. Thermoset PUs, in particular, combine high tensile strength (>12 MPa), remarkable flexibility (>900% elongation), and low water uptake (12 MPa tensile strength and >900% elongation • Mixed-charge design offers low-cost, robust alternative to zwitterionic systems