High-Strength and Low-Swelling Poly(amic acid) Salt Hydrogels for Marine Antifouling

Abstract Hydrogels exhibit exceptional resistance against bacterial colonization and diatom adhesion, yet suffer from poor mechanical properties, with tensile strengths usually below 1 MPa in marine environments. Despite the significant progress, developing antifouling hydrogels with simultaneous antimicrobial performance, optimal mechanical robustness, and antifouling efficacy suitable for marine applications is still challenging. Herein, a series of polyelectrolyte hydrogels, featuring a fully aromatic backbone, were synthesized by polymerizing 3,3″,4,4″-biphenyltetracarboxylic dianhydride (BPDA) and p-phenylenediamine (PDA), using water as a solvent and different organic bases (namely 1,2-dimethylimidazole (DMZ), 1-(2-hydroxyethyl)imidazole (HIM), imidazole (IM), triethylamine (TEA), and N,N-dimethylethanolamine (DEMA)) to yield poly(amic acid) salt (PAAS) hydrogels with excellent mechanical properties, low swelling ratios in seawater, and favorable antifouling properties. The abundant carboxylate anions in the PAASs facilitated the in situ cross-linking with multivalent cations (e.g., Ca2+, Mg2+) in seawater, improving stability in marine environments. The optimized PAAS hydrogel (DMZ-PAAS-80, with 80 representing the content of PAAS in the hydrogel) achieves high tensile strength (>9.3 MPa), low swelling ratios (<40%), superior antifouling performance (bactericidal efficiency > 99.9%), and reduced adhesion of algae and proteins. Overall, the proposed new paradigm paves the way for designing high-performance hydrogels with exceptional mechanical, antiswelling, and antifouling properties, suitable for marine antifouling applications.