Bio-adhesive from grape seed protein, tannic acid and chitosan with robust dry/wet adhesion, high switching ratio and full degradability.

Bio-adhesives are widely applied in bonding, product assembly, and packaging. However, they usually have low adhesion strength and poor water resistance. Herein, an eco-friendly adhesive was fabricated from grape seed protein (GSP), chitosan (CS), and partially oxidized tannic acid (OTA). Electrostatic interactions between GSP and CS, hydrogen bonds among GSP, CS, and OTA, as well as Schiff base reactions between ortho-quinone groups of OTA and amino groups synergistically increased the cohesive energy of the adhesive. Meanwhile, catechol groups of OTA formed diverse noncovalent interactions with substrate surfaces to enhance surface energy. Benefiting from the balance between cohesive and surface energies, the obtained adhesive realized robust adhesion to solid substrates (wood, glass, aluminum, iron, copper, and PET) with an adhesion strength of 6.78 ± 0.35 MPa on wood. Impressively, the dense covalent imine bond framework hindered penetration of water molecules, leading to an adhesion strength of 6.64 ± 0.48 MPa after immersing in water for 28 days. By leveraging the protonation of amino groups, dynamic adhesion switching was realized between weakly adhesive coacervates (at pH 4.5) and strongly adhesive gums (at pH 7.5) with an ultrahigh switching ratio of ≈7062 ± 127. Since all components were biodegradable, the adhesive underwent complete degradation within 8 days. Having several merits, it was suitable for daily bonding, detachable assemblies, and sealing materials.