Modulating stiffness with photo-switchable supramolecular hydrogels

Stimuli-responsive hydrogels are attractive materials with many applications towards biomedicine, biology, construction, and manufacturing. Materials that can be cured or annealed rapidly at room temperature are of particular interest. In this work we develop a class of supramolecular coumarin-functionalised hydrogels formed via host-guest mediated self-assembly with cucurbit[8]uril that can photo-switch to covalent gels and reversibly toggle between the two states. A principle advantage of such materials is their ability to maintain a homogeneous chemical composition and crosslink density while selectively modulating stiffness with light. An investigation of the photo-reversibility of these functional materials elucidated that hydroxyethyl cellulose-coumarin based gels were soft and could only switch from a physical state to a covalent one, while hyaluronic acid-coumarin based gels were softer and could be photo-reversed back into a physical state after covalent curing. Supramolecular hyaluronic acid hydrogels formed via 2 : 1 homoternary complexes of coumarin and cucurbit[8]uril can reversibly toggle between physical and covalent states.