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.