Tannic acid–histidine hydrogel networks enable superamphiphilic, anti-fogging, and self-cleaning BOPET films

Transparent polymer films are widely used in packaging, displays, and functional coatings; however, their optical performance is readily compromised by fogging and surface contamination. Although superhydrophilic hydrogel coatings can effectively mitigate fogging, their weak interfacial adhesion to polymer substrates limits practical application. Herein, an amphiphilic tannic acid–histidine (TA–His) hydrogel coating was fabricated on biaxially oriented polyethylene terephthalate (BOPET) films through a facile drop-casting method. By integrating sodium alginate–Ca 2+ ionic coordination with TA–His covalent crosslinking, the coating forms a stable multifunctional network with balanced hydrophilicity, structural integrity, and interfacial adhesion. After optimization of TA:His ratio, the modified BOPET film exhibited excellent amphiphilicity, with the water contact angle decreasing from 67.4° to 0° and the oil contact angle decreasing from 37.2° to 0°. The optimized coating also showed effective anti-fogging performance, outstanding self-cleaning capability, and good chemical stability. Benefiting from its simple fabrication process, environmentally benign components, and balanced surface properties, this hydrogel-modified BOPET film shows promising potential for anti-fogging materials, anti-fouling films, and related transparent functional coatings.