Guar gum/borax hydrogel: rheological, low field NMR and release characterizations

Guar gum (GG) and Guar gum borax (GGb) hydrogels are studied by means of rheology, Low Field NMR and model drug release tests. These three approaches are used to estimate the mesh size (ξ) of the polymeric network. A comparison with similar Scleroglucan systems is carried out. In the case of GGb, the rheological and Low Field NMR estimations of ξ lead to comparable results, while the drug release approach seems to underestimate ξ. Such discrepancy is attributed to the viscous effect of some polymeric chains that, although bound to the network to one end, can freely fluctuate among meshes. The viscous drag exerted by these chains slows down drug diffusion through the polymeric network. A proof for this hypothesis is given by the case of Scleroglucan gel, where the viscous contribution is not so significant and a good agreement between the rheological and release test approaches was found.