(542b) Transient and Dissipative Host–Guest Hydrogels Regulated By Consumption of a Reactive Chemical Fuel

The transient self-assembly of molecules under the direction of a consumable fuel source is fundamental to biological processes, with certain biomolecular assemblies and networks existing in an out-of-equilibrium state and requiring continuous consumption of high energy molecules to sustain their structure. For example, the dynamic assembly of microtubules arises from a well-regulated feedback loop that is dependent on consumption of high-energy GTP molecules, with this process underlying important biological functions like cell motility, cellular transport, and proliferation. Conversely, the creation of bioinspired supramolecular hydrogels has traditionally focused on associations occurring at their thermodynamic equilibrium state, with work to access dissipative states of non-equilibrium reserved primarily to low molecular weight gelators. Here, a dissipative non-equilibrium host–guest hydrogel is demonstrated to have formation and lifetime driven by the direct reaction of a consumable chemical fuel. PEG macromers were prepared to present a cucurbit[7]uril (CB[7]) host macrocycle with others prepread to present a bicyclo[2.2.2]octane (BO) guest. By positioning a carboxylate adjacent to a typically high-affinity BO, its interaction with CB[7] is abrogated at pH 11 due to the electrostatic repulsion between the guest and the carbonyl-lined CB[7] portal. Accordingly, pH offers one route to control hydrogel formation through CB[7]–BO physical crosslinking. Moving toward autonomous gelation control driven by a chemical fuel, the direct chemical modification of this terminal carboxylate via DMS-fueled formation of its methyl ester product restores the high-affinity nature of the CB[7]–BO interaction, enabling hydrogel formation. However, the methyl ester species that results from this chemical reaction is labile under basic aqueous conditions, resulting in these hydrogels existing only transiently and subsequently dissipating to their sol state over time. In this way, the lifetime of transient hydrogel formation and the dynamic modulus observed are governed by fuel consumption, rather than being directed by equilibrium complex formation. This approach therefore points to a bioinspired and biomimetic route to realize non-equilibrium supramolecular hydrogel networks.