Differentiation of the microstructures of agarose hydrogels using terahertz time domain spectroscopy (THz-TDS)

Agarose hydrogels are widely used analytical separation media in chemistry and tissue scaffolds in biomedical engineering because of their highly tunable mechanical and rheological properties. The functional properties of these gels are attributed to their fibrillar mesh microstructure. However, a foil microstructure of the agarose hydrogel was recently observed and described. It is important to differentiate these two microstructure as they have different properties. In this work, the use of terahertz time domain spectroscopy (THz-TDS) to differentiate the two microstructure of agarose hydrogels was demonstrated. Using the global hydration number calculated from the THz permittivity, it was found that the two microstructures have different hydration environments, with the foil microstructure having a greater hydration number than the mesh microstructure. To validate the presence of the two distinct microstructures, cryo-scanning electron microcopy (cryo-SEM) was used to visualize the microstructures and rheometry was employed to demonstrate the difference in their chain flexibility.