Poly(acrylic\nacid)-Derived Zwitterionic Hydrogel Unlocking\nUnderwater Adhesion and Swelling Resistance for Applications as a\nTissue Patch

Adhesive hydrogels, capable of autonomously adhering\nto tissues,\noffer substantial promise for biomedical applications. However, their\npractical utility is often constrained by challenges and potential\nfailures in underwater adhesion, owing to the weakened interfacial\ninteractions caused by the surface hydration layer and structural\nswelling-induced degradation of adhesive performance. To tackle this,\nwe developed herein a polyzwitterionic hydrogel with underwater adhesion\nto several substrates, particularly biological tissues. This hydrogel,\ntermed PAA@QAC(20/1), represents a hybrid poly(acrylic acid (AA))\n(PAA)-based polymer incorporating interspersed quaternary ammonium\ncation (QAC) units, which retains and further surpasses the performance\nof traditional PAA hydrogels. QAC units can mimic the cationic amino\nacid residues in mussel foot proteins (Mfps) by replacing water molecules\nand hydrated cations in the hydration layer, allowing hydrogels to\nadhere firmly to the surface through electrostatic and hydrogen-bond\ninteractions. Additionally, internal electrostatic cross-linking between\nAA and QAC enhances the phase separation-induced hydrophobicity, enabling\nhydrogel to maintain its adhesive properties without swelling. These\nunique characteristics endow PAA@QAC(20/1) with direct and durable\nadhesion to a series of biological tissues in the presence of blood\nor fluids, making it a promising material for a wide range of adhesive-involved\nbiomedical applications.