Effect of the degree of sulfation on the hydration state of agarose gels investigated using terahertz time domain spectroscopy (THz-TDS)

Agarose is a biopolymer widely used as a separation medium in chemistry, as gelling agent in foods, and as scaffold in tissue-mimicking materials. The gel strength and the electroendoosmosis (EEO) value are important quality parameters of agarose which have direct impact on its functionality. These two attributes are correlated to the sulfate contents of agarose. In this work, the relationship between these parameters were investigated from the point of view of water dynamics. Terahertz time-domain spectroscopy (THz-TDS) was employed to study the hydration state of the hydrogels through an analysis of the THz dielectric parameters obtained from the Double-Debye model. It was found that an increase in the sulfate content of the agarose does not significantly change the relaxation time of water bound to the matrix, but it decreases the strength of the fast relaxation of water. This decrease in relaxation strength, attributed to a decrease in the amount of bound water, can affect the gel strength as bound water is thought to be responsible for stabilizing the junction zones of the gel network. The thinning of the hydration layer with increasing sulfate concentration can affect the EEO as more water becomes available for internal convection within the gel.