A two layer model for the effects of blood contact on membrane transport in artificial organs.

The performance of many artificial organs can be strongly affected by the transport characteristics of the semi-permeable membranes used in these devices, but there is little data on the effects of blood contact on membrane transport properties. Experimental data were obtained for the solute flux through cellulosic, polyacrylonitrile, and polyethersulfone membranes using polydispersed dextrans. Blood contact had a very large effect on diffusive solute transport through the asymmetric polyethersulfone membranes, but only a small effect on diffusion through the symmetric AN69 and Cuprophan membranes. In contrast, blood contact caused a similar reduction in convective solute transport (sieving) through both the polyethersulfone and AN69 membranes. Convective transport through the blood contacted membranes was also dependent on the flow direction, with greater transport obtained when the membrane was oriented with the blood contacted surface downstream. These data were analyzed using a two layer membrane model consisting of an upper layer of blood cells and proteins adsorbed to the surface of the native membrane. This model accurately accounted for the different effects of blood contact on convection and diffusion, as well as the observed asymmetry in convective solute transport. These results have important implications for the analysis of solute transport in artificial organs.