Convenient hydrogel adhesion with crystalline zones

Adhering soft hydrogels to hard substrates is challenging. Existing adhesion approaches mainly rely on interfacial chemical bonds or physical interactions, which typically require complex fabrication processes or specific surface properties. Herein, we report a convenient approach to achieving effective hydrogel adhesion onto various hard substrates with in-situ formed crystalline zones by heating. Semi-crystallizable poly(vinyl alcohol) hydrogels were directly cast on various subtracts by a drying-swelling process, which demonstrates strong adhesion with adhesion energy as high as 890 J/m2. The adhesion performance demonstrates an obvious positive correlation with the crystalline property. Therefore, the factors determining the crystalline degree, including the polymer type and preparation temperature, demonstrate remarkable influences on the adhesion performance. Moreover, this adhesion performance manifests high durability in harsh environments. Benefitting from the strong and durable adhesion performance, the crystalline gels can serve as a tie coating layer to joint various hydrogels, which demonstrate satisfactory antifouling ability. Therefore, this strategy may endow the materials with great potential for various practical applications in the future.