Adsorption of low molecular weight proteins to hemodialysis membranes: experimental results and simulations.

Adsorption of alpha-lactalbumin and Cytochrome C on different hollow-fiber hemodialysis modules, whose main membrane constituent was polyacrylonitrile (PAN), polymethylmethacrylate (PMMA) or polysulfone (PS), were compared under different pH and flow rate conditions. These proteins were chosen as models of small scarce proteins like beta2-microglobulin from which the patient's blood should be epurated. Influence of pH suggests the importance of electrostatic interactions on a charged membrane since adsorption greatly decreases at pH 10.9 for Cytochrome C (pI = 10.6) and at pH 7.4 for alpha-lactalbumin (pI = 5). The difference in adsorbance between different membranes is most probably due to their different microstructures. However, the chemical nature of the support plays a non-negligible role since PMMA membranes have smaller initial adsorption rates than PAN membranes. This is correlated with the density of membrane surface charge showing the importance of electrostatic interactions. The influence of the wall shear rate on adsorption kinetics is analyzed through numerical simulations, in terms of transport limitation in the liquid phase and interfacial reaction.