Constructing Self-Covalent Locking and Mechanically Tunable Hydrogel Coatings with Antibacterial and Oil–Water Separation Properties

To enhance the mechanical robustness and structural stability of hydrogel coatings, this study proposes a reinforcement strategy to fabricate mechanically tunable composite hydrogel coatings made of tannic acid (TA) and poly(vinyl alcohol) (PVA). Ethanol-mediated dynamic modulation of hydrogen-bond cross-linking between TA and PVA enables rapid and uniform hydrogel coating formation. Besides, silica (SiO2) nanoparticles are incorporated into the PVA@TA hydrogel coating, which is immersed in a glutaraldehyde (GA) solution to induce covalent cross-linking of hydroxyl groups, thereby constructing PVA@TA-SiO2-GA hydrogel coating with a stable multiscale network structure. This strategy optimizes the mechanical properties of the hydrogel coating, achieving a 62.5% enhancement in the fracture stress. Moreover, the fabricated hydrogel coating maintains structural integrity after ultrasonication (400 W, 48 h) and demonstrates efficient oil/water separation performance (flux >4000 L·m–2·h–1, separation efficiency >90%) and robust antibacterial properties against Escherichia coli and Staphylococcus aureus (inhibition rate >99.9%). This study provides a strategy for designing functional hydrogel coatings tailored to environmental demands.