Hydrogel membranes with mesh size asymmetry based on the gradient crosslinking of poly(vinyl alcohol)

Poly(vinyl alcohol) (PVA) hydrogel membranes with mesh size asymmetry were prepared and their transport properties were studied. Homogeneous membranes with water contents of 82%, 76% and 72% were prepared by crosslinking PVA with glutaraldehyde. These membranes were then modified to create asymmetry by establishing a glutaraldehyde concentration gradient across the hydrogel thickness. The reaction time and magnitude of the glutaraldehyde concentration gradient were varied to determine the optimum values of permeability and selectivity. Permeation experiments with creatinine, Fab and IgG were performed in a stirred diffusion cell through homogeneous and asymmetric PVA hydrogels. A modified version of the multiple-membrane technique was used to determine boundary layer resistance in order to determine the intrinsic membrane permeability. As expected, the selectivity of creatinine over IgG increased as the modification time increased. However, the selectivity of Fab over IgG initially increased as the modification time increased, but then decreased at longer times, indicating that the increased crosslinking at the surface effectively blocks both proteins. At a given value of IgG rejection, the asymmetric membranes had higher creatinine and Fab permeabilities than the corresponding homogeneous membranes. This indicates that creating mesh size asymmetry in a hydrogel can result in a high-flux, high-selectivity membrane for cell encapsulation or bioseparations.