Solute permeation through the polyurethane-NIPAAm hydrogel membranes with various cross-linking densities

A series of thermo-sensitive polyurethane-NIPAAm hydrogel membranes with various cross-linking densities have been obtained by the UV-curable method. Sucrose, beta-cyclodextrin and dextran were used as the model compounds to evaluate the solute permeability through the hydrogel membranes. The solute permeability depends on the solute size, the hydration and the cross-link density of the hydrogel. Sucrose permeability has been found following the free-volume theory but with different permeating behaviors between the high- and low-hydration hydrogels. The water structure in the hydrogel has been analyzed by the DSC method. It has been found that the high-hydration hydrogels contain relatively more freezing water, while the low-hydration hydrogels are occupied mainly by the nonfreezing bound water. The different water structures between the high- and low-hydration hydrogels are considered to be responsible for their discrepancy in the permeability.