SOLUTE DIFFUSION WITHIN HYDROGELS - MECHANISMS AND MODELS

Solute diffusion in hydrogels is important in many biotechnology field s. Solute behavior in hydrogels has been explained in terms of reducti on in hydrogel free volume, enhanced hydrodynamic drag on the solute, increased path length due to obstruction, and a combination of hydrody namic drag and obstruction effects. In this article the various mathem atical models derived to explain and predict solute diffusion in hydro gels are reviewed and tested against literature data. These models can be divided into those applicable to hydrogels composed of flexible po lymer chains (i.e., homogeneous hydrogels) and those composed of rigid polymer chains (i.e., heterogeneous hydrogels). For homogeneous hydro gels it was determined that a scaling hydrodynamic model provided the best explanation for solute diffusion, while for heterogeneous hydroge ls obstruction models were more consistent with the experimental data. Both the scaling hydrodynamic model and the most appropriate obstruct ion model contain undefined parameters which must be clarified in orde r for these models to gain widespread acceptance.