Prediction of rheological properties via structure elucidation of solvated hydrogels

Hydrogels are prevalent materials with applications ranging from drug delivery systems, contact lenses and tissue engineering scaffolds. However, they require considerable perturbation to observe their nanoscale, solution-phase structures necessary for predicting bulk properties. Although studies suggest that methylcellulose, a quintessential hydrogel material, can be described by a semiflexible biopolymer network model, there remain demonstrable inconsistencies in the predicted concentration dependence of rheological properties and in the observation of higher-order features. Here we image solvated hydrogels with high spatiotemporal resolution via liquid-phase transmission electron microscopy to avoid desolvation and shear artefacts. Corroborated by scattering and scanning electron microscopy, we observe that methylcellulose hydrogels form a network with high persistence length and micrometre-scale fibril bundles arranged in hierarchical assemblies, providing a more accurate prediction of bulk rheology. In addition, network structures are observed for hydroxypropyl methylcellulose and hydroxypropyl cellulose. These observations across multiple-length scales lead to a clearer understanding of how nanoscale structure impacts microscale structure and macroscopic behaviour, aiding the development of more accurate structure-property relationships for hydrogel materials.