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. [ABSTRACT FROM AUTHOR]