Soak n' Boost: A universal strategy to manufacture hybrid double-network hydrogels with eminent mechanical properties is developed by postformation of the chitosan microcrystalline and chain-entanglement physical networks via simple treatment of the chitosan composite hydrogels using alkaline and saline solutions. The strategy may open an avenue to fabricate multifarious double-network hydrogels for promising applications in antifouling materials, drug delivery, and tissue engineering.

The development of facile and versatile strategies with low-cost for hydrogel construction is of tremendous scientific interest. Herein, we demonstrate that naturally derived, cost-effective tannic acid (TA) can be an efficient gelation binder for the hydrogel formation with a series of commercially available water-soluble polymers. With a five-polyphenol-arm structure, TA molecules are able to grasp polymer chains through either hydrogen or ionic bonds and cross-link them together by coordinate bonds in the presence of Fe(III) ions. These two interactions can be elegantly balanced by tuning the weight ratios of polymer/TA and TA/ Fe 3+ , which is the key point for the construction of supramolecular hydrogels. The supramolecular hydrogels exhibit multiple functionalities including mechanical tenability, rapid self-healing, pH-stimuli responsiveness, and free radical scavenging abilities. TA as a dynamic and versatile catechol group modifier provides a simple path to the construction of multifunctional hydrogels, which shows obvious advantages such as easy and green processing, low cost, and large-scale preparation.