Potassium Ion Transport through Hydrogel Membranes in the Presence of Blood Components: Plasma Proteins

Abstract

A mathematical model and conceptualization of membrane ion transport by diffusion and phase transfer as coupled to adsorbed protein associated ion specific adsorption has been developed. The model is verified by monitoring K⁺ transport through poly-(2-hydroxyethyl methacrylate) membranes in the presence of plasma in concentrations of 20, 50, 80 and 100% by volume. The transport data can be adequately described by the model where the surface oriented K⁺ is assumed to be constant and related to bulk protein content. Control studies provide a baseline value for an effective diffusion coefficient for K⁺, D_eff, of 2.82 x 10⁻⁸ cm²/sec. The addition of plasma to the transport study solutions shows an increase in the transport of K⁺ such that the rate is exponentially related to plasma percent. Since the dimension of the albumin molecule is appropriate to reside in the surface convection layer (100 Å) and albumin itself is the majority protein in plasma, values of known albumin bulk concentrations and published surface concentrations are useful for extended analysis. The surface concentration of K⁺ at 100% plasma is 12.9 nEq/cm² and the ratio of ion to protein is 4.3 Eq K⁺/mM albumin. These results provide insight into the role of protein adsorption to biomaterials as they relate to ion transport. The transport chamber approach is ideally suited to modification of the biomaterial interfacial microenvironment where, as in this study, the effects of plasma protein interactions are separated from cellular interactions. In medical devices, this phenomenon is important in the design of electrochemical blood chemistry sensors and artificial kidney membranes.