Ultrafiltration properties of hydrogel analogues of basement membrane: a comparison of the pore theory and the fibre-matrix hypothesis

Abstract

The filtration behaviour of highly hydrated thin films of poly (glyceryl methacrylate) hydrogel has been studied and compared with the behaviour of renal basement membrane. Solvent flux increased with hydrostatic pressure in a non-linear manner so that the hydraulic permeability coefficient declined with pressure; solute flux tended to remain constant, with the rejection of myoglobin increasing consequently with pressure. In these respects the hydrogel films paralleled the behaviour of basement membrane as compressible ultrafilters. Studies of hydrogel compression under hydraulic pressure showed that the relationship between film thickness and pressure was non-linear though the film behaved elastically. The pore theory and the fibre-matrix hypothesis were compared as theoretical bases for modelling permeation. The pore theory predicted declining pore radii with increasing pressure, r p = 3.5 nm at 10 kPa; however, the theory tended to underestimate the void volume of the hydrogel. The fibre-matrix hypothesis predicted consistently that the hydrogel was a random matrix of fibres of 0.80 nm radius occupying 15% of the space of the material; this compared well with a measured void volume of 0.85. Thus, the fibre-matrix hypothesis provided closer predictions than the pore theory and yielded insights regarding the structure of the ultrafiltration barrier.