MEMBRANELESS DIALYSIS: PERFORMANCE OF SECONDARY SEPARATORS

Abstract

Membraneless separation of blood components does not discriminate solutes or allow adequate volume transport without a secondary separator (SS). SS’s control primary membraneless separators (PS’s) by recycling molecules to be preserved. SS’s also control PS performance by removing water, thereby raising the osmotic pressure of the recycle stream high enough to transport water in the PS in the absence of transmembrane pressure. SS’s may work by reaction, absorption, or selective membrane transport, and must be small and able to sustain performance for many hours. The performances of small dialysis devices as SS’s with respect to ultrafiltration (UF) and solute transport over in vitro measurement times up to 48 hours, using bovine plasma are discussed. UF rates corresponding to removal of 10 kg/wk water and dialysis rates corresponding to 200 g/wk urea were examined in small hollow-fiber modules with 500 cm2 area. Modest increases in SS transmembrane pressure and elevations of sheath fluid blood urea nitrogen (BUN) were seen when fixed loads of urea were imposed over long times. Changes in performance may be implemented by elevated shear rates (made possible when low cell counts are achieved in the fluid sent to the SS) and by changes in module area. Reported test data are also of interest because very little information is currently available in any environment to estimate the long-term, uninterrupted performance of dialysis fibers, and the effect of fluid shear on performance decrement.