Scleroglucan/borax/drug hydrogels: structure characterisation by means of rheological and diffusion experiments

This paper is aimed to the macro- and microscopic characterisation of a scleroglucan–borax gel system eventually hosting model drugs. A rheological study was carried out, also as a function of temperature, on samples at different polymer concentrations in the presence and without guest model drug. Applying the generalised Maxwell model the mechanical spectra, showing the gel-like characteristics dependent on polymer concentration, were obtained. Flory’s theory and the equivalent network approach were applied to the rheological data in order to describe the molecular arrangement of the scleroglucan chains in the presence of borate ions with an estimation of the network mesh size, n. Diffusion experiments of three model drugs, with different van der Waals radius, allowed the determination of the diffusion coefficients. An evaluation of the network mesh size was also obtained by means of a modified free volume theory and a good agreement between the two sets of n values was found.