Poly(acrylic acid)-Derived Zwitterionic Hydrogel Unlocking Underwater Adhesion and Swelling Resistance for Applications as a Tissue Patch

Adhesive hydrogels, capable of autonomously adhering to tissues, offer substantial promise for biomedical applications. However, their practical utility is often constrained by challenges and potential failures in underwater adhesion, owing to the weakened interfacial interactions caused by the surface hydration layer and structural swelling-induced degradation of adhesive performance. To tackle this, we developed herein a polyzwitterionic hydrogel with underwater adhesion to several substrates, particularly biological tissues. This hydrogel, termed PAA@QAC(20/1), represents a hybrid poly(acrylic acid (AA)) (PAA)-based polymer incorporating interspersed quaternary ammonium cation (QAC) units, which retains and further surpasses the performance of traditional PAA hydrogels. QAC units can mimic the cationic amino acid residues in mussel foot proteins (Mfps) by replacing water molecules and hydrated cations in the hydration layer, allowing hydrogels to adhere firmly to the surface through electrostatic and hydrogen-bond interactions. Additionally, internal electrostatic cross-linking between AA and QAC enhances the phase separation-induced hydrophobicity, enabling hydrogel to maintain its adhesive properties without swelling. These unique characteristics endow PAA@QAC(20/1) with direct and durable adhesion to a series of biological tissues in the presence of blood or fluids, making it a promising material for a wide range of adhesive-involved biomedical applications.