Macromolecule adsorption to hemodialysis membranes depends on molecular size

Adsorption to hemodialysis membranes was studied by determining the binding kinetics of model macromolecules, polydisperse DEAE dextran (molecular radii 10-70 A), to an acrylonitrile-methallyl sulfonate copolymer membrane. Hemodialyzers were studied in a postdilution hemofiltration circuit where both blood path output and ultrafiltrate streams were returned to the reservoir. Changes in the reservoir concentration of and sieving coefficients for DEAE dextran were monitored over 24 h. Decreases (or increases) in reservoir concentration were assumed to result from adsorption to (or desorption from) the membrane. Small macromolecules adsorbed rapidly to the membrane but later desorbed. This rapid adsorption resulted in low initial sieving coefficients. Large macromolecules adsorbed slowly over the entire 24-hour study period. Additional experiments suggested that desorption of small macromolecules was due to displacement by large macromolecules. Adsorption and desorption of macromolecules to hemodialysis membranes are dynamic processes and depend on molecular size.