Hemodialysis membranes are exposed to bleach during standard reprocessing methods, but there is little quantitative understanding of the effects of bleach on the mass transfer characteristics or surface properties of these membranes. A battery of experiments was used to evaluate the effects of bleach on the properties of Fresenius F80A, F80B, and Optiflux 180A dialyzers. Bleach caused a significant increase in the membrane hydraulic permeability. The clearance of urea (MW=60 Da) increased by only 3% after a 1-hour exposure to bleach at 50 °C compared to more than a 10-fold increase in the clearance of a 15 kD MW dextran. The solute clearance data were used to determine the effective membrane pore size using available hydrodynamic models. Bleach caused a significant increase in the effective pore size, which was attributed to the leaching of the polyvinylpyrrolidone (PVP) out of the polysulfone membrane. Bleach also caused a significant increase in the magnitude of the negative charge on the membrane surface; the zeta potential varied from −4.1 mV for the new membrane to −13.0 mV after a 14-hour exposure to bleach. These changes in pore size and surface properties provide important insights into the effects of bleach on hemodialysis membranes.
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