Importance of Molecular and Bulk Dynamics in Supramolecular Hydrogels in Dictating Cellular Spreading

Cellular spreading is affected not only by the stiffness of the matrix but also by its dynamics. Synthetic hydrogels, formed by the assembly of supramolecular monomers, are intrinsically dynamic and tunable in their stiffness. However, the importance of molecular dynamics resulting in differences in bulk dynamics and stiffness remains elusive. Here, we present two different hydrogel systems employing slow-exchanging ureidopyrimidinone monomers and fast-exchanging benzene-1,3,5-tricarboxamide monomers to decipher design rules for supramolecular hydrogel-cell interactions. To achieve cell spreading, both robust incorporation of cell-binding ligands, reflected in slow molecular dynamics (monomer exchange), and sufficient material resistance, reflected in slow bulk dynamics (stress relaxation), are crucial. Epithelial cells respond to gel dynamics as cells remain round on fast-relaxing gels, independent of gel stiffness. Fibroblasts respond to gel dynamics on soft gels (∼100-200 Pa), but gel stiffness overrules gel dynamics on stiffer gels (∼1 kPa). Together, our results disclose that (1) molecular dynamics at the supramolecular fiber level is translated to bulk dynamics on the hydrogel level, (2) gel dynamics is the dominant factor in dictating cellular spreading in soft gels, and (3) design rules for supramolecular hydrogel-cell interaction are cell-type-dependent.