To understand the role of the endothelial glycocalyx in the filtration of plasma across the renal glomerular capillary wall, we synthesized glycosaminoglycan-agarose hydrogel membranes that mimic the composition of the glycocalyx. The permeability of the membranes to water and macromolecular solutes was measured, with emphasis on the role of charge. Extensive characterization of the hydraulic permeability of agarose-GAG membranes was performed on 3v% agarose gels with up to 0.4 v% GAG (129 mg GAG/g agarose) with solution ionic strengths ranging from 0.011 M to 1.0 M. Covalent attachment of GAG to agarose caused a two- to four-fold reduction in the hydraulic permeability, depending on the GAG concentration and ionic strength. There was a 50% reduction in permeability due to the presence of 0.4 v% GAG at 1 M salt concentration, and an additional 50% reduction in the permeability of 0.4 v% GAG at 0.01 M versus 1 M. Macroscopic and structural (double layer) electrokinetic models of flow through random fiber arrays were applied to the system, which required also an evaluation of available methods of modeling multi-fiber arrays. The decreases in hydraulic permeability from the addition of GAG fibers or decrease in ionic strength were captured by the models.

The permeability of the membranes to macromolecules (e.g., proteins and Ficolls) also was shown to depend on molecular charge. For 4 v% agarose gels with 0.2v% GAG (53 mg GAG/g agarose), the sieving coefficient for bovine serum albumin was reduced by half at a salt concentration of 0.01 M versus 1 M. However, 4 v% agarose without GAG had no change in sieving coefficient over the range of ionic strengths, illustrating the influence that a small amount of charged fibers can have on the sieving of charged solutes.