Synergy of Host–Guest and Cation−π Interactions for an Ultrastretchable, pH-Tunable, Surface-Adaptive, and Salt-Resistant Hydrogel Adhesive

The adhesion to wet, acidic, and saline biointerfaces with large deformation is important in the fields of wound dressing and motion monitoring but has proven to be extremely challenging. There is a need for a facile method to improve the stretchability and salt resistance simultaneously. Here, an ultrastretchable, pH-tunable, surface-adaptive, and salt-resistant hydrogel adhesive is reported. The hydrogel adhesive is prepared through cross-linking acrylamide with a supramolecular complex of poly(β-cyclodextrin) (PCD) and benzimidazole (BI). The dynamic association between PCD and BI causes an extra energy dissipation and improves the breaking strain to be larger than 4000%. The hydrogel exhibits stable adhesiveness to varieties of surfaces due to the multiple types of hydrogel–surface interactions, including ionic bond, π–π stacking, and hydrogen bond. Notably, the adhesive strength of the hydrogel gets significantly enhanced in an acidic environment and shows no attenuation in a saline environment. This is due to the unique adjacent cation−π structure of BI: the imidazole can be protonized upon acidification, and the phenyl group can repel water and enhance the ionic attraction with the substrates. The ultrastretchability, the stable adhesion on biointerfaces, and the salt resistance render the hydrogel a promising candidate for the surgical patch and motion sensors that serve in wet, acidic, and dynamic environments.