Living organisms are capable of dynamically changing their structures for adaptive functions through sophisticated reaction-diffusion processes. Here we show how active supramolecular hydrogels with programmable lifetimes and macroscopic structures can be created by relying on a simple reaction-diffusion strategy. Two hydrogel precursors (poly(acrylic acid) PAA/CaCl₂ and Na₂CO₃) diffuse from different locations and generate amorphous calcium carbonate (ACC) nanoparticles at the diffusional fronts, leading to the formation of hydrogel structures driven by electrostatic interactions between PAA and ACC nanoparticles. Interestingly, the formed hydrogels are capable of autonomously disintegrating over time because of a delayed influx of electrostatic-interaction inhibitors (NaCl). The hydrogel growth process is well explained by a reaction-diffusion model which offers a theoretical means to program the dynamic growth of structured hydrogels. Furthermore, we demonstrate a conceptual access to dynamic information storage in soft materials using the developed reaction-diffusion strategy. This work may serve as a starting point for the development of life-like materials with adaptive structures and functionalities.

Transient materials that function out-of-equilibrium have been of great interest due to their unique properties that are rarely observed in thermodynamically stable occasions. However, the current advances are still limited to supramolecular objects, and the applications using this transient nature remain largely unexplored. Herein we report on chemical fuel powered transient polymer hydrogels for controlled formation and free release of pharmaceutical crystals. The transient polymer hydrogels with highly tunable stiffness and lifetime were created by chemical fuel powered crosslinking, which can be well regenerated without obvious deteriorations by simply refueling. On the basis of these properties, especially the transient nature, these hydrogels can serve as novel reusable platforms to control the pharmaceutical crystallization, more importantly, freely release the obtained crystals, which is inaccessible by conventional static gels. This work is expected to serve as an example to accelerate the development of more advanced out-of-equilibrium materials and exploitations of their high-tech applications.

The present work shows how transient supramolecular hydrogels can be formed by catalytically controlled molecular self-assembly. Catalysis formation of molecular gelators leads the self-assembly along a kinetically favored pathway, resulting in transient hydrogels. This work demonstrates an effective approach towards pathway-dependent supramolecular materials.