Tannic Acid-Based Multifunctional Hydrogels with Facile Adjustable Adhesion and Cohesion Contributed by Polyphenol...

Adhesiveness of hydrogels depends on the balance and synergy of their cohesion and adhesion. However, it is a challenge to fabricate catechol-based hydrogels with high adhesiveness because the required condition for cohesion and adhesion of these hydrogels is in conflict with each other: strong cohesion (gelation) requires a weak basic condition, whereas strong adhesion requires an acidic condition. Here, we demonstrated that by utilizing polyphenol supramolecular chemistry, the coexistence of strong cohesion and adhesion can be achieved in a hydrogel via the one-pot method. Poly(dimethyl diallyl ammonium chloride)/tannic acid (PDDA/TA) hydrogel has been studied as a proof of concept. Compared with catechol moieties that covalently grafted on polymer chains, TA can bring high density of pyrogallol/catechol functional groups for polymers via a noncovalent pathway, as well as high acidity in the system. As a result, the cohesion of the hydrogel is enhanced significantly, the highest storage moduli can reach up to ca. 0.15 MPa; besides, the high acidity of the hydrogel prevents pyrogallol/catechol groups from oxidation and guarantees strong adhesion; thus, the hydrogel can adhere to diverse substrates steadily, including tissues, glass, metals, and plastic. Moreover, because of the adjustable adhesiveness via changing the pH, the PDDA/TA hydrogel becomes a unique system with patternable adhesiveness. In addition, the hydrogel has rapid self-healing and high ionic conductivity (∼4.3 S m^-1). This study demonstrates that utilizing polyphenol chemistry in the construction of hydrogels opens a new path toward multifunctional hydrogels with improved properties.