Bioinspired Green Underwater Adhesive Gelatin‐Tannic Acid Hydrogel With Wide Range Adjustable Adhesion Strength and Multiple Environmental Adaptability

Abstract Underwater adhesion of hydrogels is essential for their applications in liquid environment. However, green raw materials, facile preparation process and multiple environmental adaptability are still issues that need to be improved. Inspired by the protein‐based underwater bio‐adhesion phenomena in nature, an effective stepwise immersion method is developed without any polymerization to prepare a green underwater adhesive hydrogel by combining gelatin and tannic acid (TA), two common materials from nature yet difficult to obtain their homogenous compound. By facile treatments in urea solution or heating, the hydrogels can realize stable immediate adhesion on various substrates and in different liquids in addition to water with a wide range of adjustable adhesion strength of 10 0 –10 3 kPa. The evolution of the hydrogel network structure and the adhesion mechanism are systematically studied. Furthermore, several typical portable products based on the adhesive hydrogels are demonstrated to show the commercialization possibility. This work presented a novel, facile, and distinctive strategy for designing environmentally friendly, multiple adaptive adhesives.