(76e) Connecting Network Structure to Flow Properties of Dynamic Hydrogels

Dynamic hydrogels are of interest for many applications that require flow, including injectable therapeutics and 3D bioprinting. However, the relationship between network structure and flow profiles is complex, with many hydrogels exhibiting non-monotonic relationships with shear. Here, we designed dynamic hydrogels using multi-arm poly(ethylene glycol) (PEG) macromers functionalized with dynamic covalent end groups. These gels exhibited shear thickening behavior, where the onset and magnitude of shear thickening depends on the bond exchange kinetics and polymer concentration of the gel. We probed the mechanism of shear thickening behavior using transient steady shear measurements, which indicated reversible shear thickening, as well as absorbance under shear measurements. These results point to chain stretching as a primary driver of shear thickening behavior. Interestingly, the hydrogel moduli demonstrate unique scaling behavior at low concentrations, indicating heterogeneous networks. Ongoing work will investigate the role of network defects on the nonlinear rheology. Altogether, these results provide insight to the molecular and structural characteristics that govern dynamic covalent PEG gelation, mechanics, and flow.