Fabrication of Hierarchically Structured Free‐Standing Supramolecular Hydrogels through Flow‐Driven Reaction‐Diffusion

Supramolecular hydrogels self-assembled by small molecular gelators have been recognized as a class of important soft materials. To realize their full potential, the structuring of supramolecular hydrogels at different length scales is required, yet remains a grand challenge. Here, we describe a simple flow-driven reaction-diffusion approach for the fabrication of hierarchically structured free-standing supramolecular hydrogels. The fabrication system comprises a flow channel made by agarose matrix that allows proton solutions to flow inside. Over time, the flowing protons diffuse across the channel wall, thereby triggering the self-assembly of acid-sensitive gelators at the channel surface. More interestingly, by adjusting the proton concentration, the self-assembled hydrogel fibers can be directed to grow along the diffusion direction. As a result, free-standing hydrogel tubes with aligned hydrogel fibers and different cross-section shapes are produced. Furthermore, upon a sequential growth of different supramolecular hydrogels at the channel surface, multilayered supramolecular hydrogel tubes can be created. Such a simple flow-driven reaction-diffusion approach for the structuring of supramolecular hydrogels at the levels of both fibers and macroscopic hydrogels may further unlock more functions and applications of supramolecular hydrogels.