Dynamic hydrogels with self-adaptable adhesion property induced by chain movement of amphiphilic macromolecules

Dynamically crosslinked multi-component hydrogels based on polyvinylalcohol (PVA) are prepared, where crosslinking mainly arises from boronic ester bonds and which contain cholic acid (CA) groups as hydrophobic modification (PVACA). These hydrogels show remarkable adhesive properties to a large range of hydrophobic and hydrophilic substrates in dry state and underwater, once a certain amount of CA is contained in the hydrogels. The adhesive strength correlates directly with the viscoelastic properties of the hydrogels, increasing largely with content of boronic ester and CA groups. Fluorescence and neutron reflectivity experiments show formation of hydrophobic domains by PVACA hydrogels on hydrophobic substrates, which becomes more pronounced when pressing the hydrogels onto the substrates. Correspondingly, the remarkable and versatile adhesive properties of this hydrogel can be explained by its tailored molecular architecture, where dynamic crosslinking (arising from the boronic ester bonds) allows for mobility of the CA groups to form hydrophobic domains at the interface of hydrophobic substrates, thereby enabling effective underwater adhesion through hydrophobic interaction. In summary, this is an easy to form hydrogel, whose adhesive properties to basically any type of material are easily tailored by its molecular composition, where the main parameters to be varied are the concentration of boronic ester (at least 1.2 wt%) and of CA groups (at least 0.24 wt%).