Alternating Growth for InSitu Post‐Programing Hydrogels’ Sizes and Performance

Growing polymer materials emerge as a class of new intelligent systems, but they are all covalently cross-linked. Herein, an alternating growth strategy for enabling tough supramolecular hydrogels is described to integrate externally provided compounds to change their sizes, geometric shapes, mechanical properties, etc. The hydrogels have dynamic acid-base complex (ABC) structures made from acidic and basic monomers, in which the acid-base pairs equilibrate between ionic and nonionic states to show either strong electrostatic or weak acid-base interactions. The growth process includes swelling of acidic/basic monomers, polymerization of the absorbed monomers, and homogenization of the original and newborn polymers, in which the balance between electrostatic and acid-base interactions is reversibly shifted to enable the process. As a result of such repeatable growth cycles, the hydrogels can continuously expand without compromising material mechanical properties. The growing sub-processes and the monomer compositions can be used to post-modulate the structure and properties of the grown products. It is demonstrated that the hydrogels may be designed as artificial tissues capable of growth under force-bearing states.