Spatiotemporal Control of Viscoelasticity in Phototunable Hyaluronic Acid Hydrogels.

Viscoelasticity has emerged as a critical regulator of cell behavior. However, there is an unmet need to develop biomaterials where viscoelasticity can be spatiotemporally controlled to mimic the dynamic and heterogeneous nature of tissue microenvironments. Toward this objective, we developed a modular hyaluronic acid hydrogel combining light-mediated covalent and supramolecular cross-linking to afford spatiotemporal control of network viscoelastic properties. Covalently cross-linked elastic hydrogels or viscoelastic hydrogels combining covalent and supramolecular interactions were fabricated to match healthy and fibrotic liver mechanics. LX-2 human hepatic stellate cells cultured on viscoelastic hydrogels displayed reductions in spreading, actin stress fiber organization, and myocardin-related transcription factor A (MRTF-A) nuclear localization compared to cells on elastic hydrogels. We further demonstrated the dynamic capabilities of our hydrogel system through photo-mediated secondary incorporation of either covalent or supramolecular cross-links to modulate viscoelastic properties. We used photopatterning to create hydrogels with well-controlled patterned regions of stiff elastic mechanics representing fibrotic tissue nodules surrounded by regions of soft viscoelastic hydrogel mimicking healthy tissue. Cells responded to the local mechanics of the patterned substrates with increased spreading in fibrosis-mimicking regions. Together, this work represents an important step forward toward the creation of hydrogel models with spatiotemporal control of both stiffness and viscoelastic cell-instructive cues.