(576a) Supramolecular Networks Via Equilibrium & Non-Equilibrium Host–Guest Crosslinking

The recognition afforded by host macrocycles in binding a suite of different guests enables an approach to rationally design soft materials from the molecular scale, control the exchange rate of network crosslinking interactions, and afford specific and tunable functionality for various applications. Certain macrocyclic host–guest chemistries are able to achieve among the highest affinity interactions ever observed, offering a non-covalent approach to enable recognition and bond formation even in complex environments. One particular macrocycle, cucurbit[7]uril (CB[7]), offers a range of binding affinities (K_eq) to an array of guests extending over ~8-10 orders of magnitude. Using CB[7], we have thus probed the parameter of host–guest affinity in the design of assorted supramolecular hydrogels. The affinity of crosslinking interactions in this platform enables a molecular-scale approach to control the crosslink exchange dynamics of the material, translates to tunable diffusion and release of macromolecular payloads, and dictates the rate of cell infiltration and material clearance when used as injectable biomaterials in vivo. These properties and functions in application are directly dictated by network exchange dynamics. In breaking from traditional equilibrium-governed associative interactions in supramolecular materials, CB[7]–guest recognition can furthermore be governed by consumption of reactive chemical fuels. By this approach, hydrogel states are thus possible through transiently upgrading guest binding affinity to yield non-equilibrium gel products, enabling temporal control over material formation and crosslinking dynamics. The materials subsequently dissipate autonomously to resume their sol state at a rate directed by the dosage of fuel applied and the environmental conditions of the reaction cycle. Accordingly, through both equilibrium and non-equilibrium crosslinking interactions, dynamic host–guest supramolecular polymer networks can be achieved with bulk material properties originating at the molecular scale.