Multivalency Enables Dynamic Supramolecular Host-Guest Hydrogel Formation.

Supramolecular and dynamic biomaterials hold promise to recapitulate the time-dependent properties and stimuli-responsiveness of the native extracellular matrix (ECM). Host-guest chemistry is one of the most widely studied supramolecular bonds, yet the binding characteristics of host-guest complexes (β-CD/adamantane) in relevant biomaterials have mostly focused on singular host-guest interactions or nondiscrete multivalent pendent polymers. The stepwise synergistic effect of multivalent host-guest interactions for the formation of dynamic biomaterials remains relatively unreported. In this work, we study how a series of multivalent adamantane (guest) cross-linkers affect the overall binding affinity and ability to form supramolecular networks with alginate-CD (Alg-CD). These binding constants of the multivalent cross-linkers were determined via NMR titrations and showed increases in binding constants occurring with multivalent constructs. The higher multivalent cross-linkers enabled hydrogel formation; furthermore, an increase in binding and gelation was observed with the inclusion of a phenyl spacer to the cross-linker. A preliminary screen shows that only cross-linking Alg-CD with an 8-arm-multivalent guest results in robust gel formation. These cytocompatible hydrogels highlight the importance of multivalent design for dynamically cross-linked hydrogels. These materials hold promise for development toward cell- and small molecule-delivery platforms and allow discrete and fine-tuning of network properties.