Transport through polymeric membranes

Abstract

Publication costs assisted by the University of ColoradoMass transport through three polymeric membranes (Cuprophan, poly(acrylonitrile), and a poly(acry1onitrile) membrane with an adsorbed protein layer) is studied. A series of eight compounds ranging in molecular weight from 60 (urea) to 1355 (vitamin BIZ) were investigated. A complete set of transport properties are reported including the permeability coefficient, sieving coefficient, pressure-filtration coefficient, and frictional coefficients representing the interactions of solute-membrane, solute-solvent, and solvent-membrane. Solute permeability for diffusive transport correlates well for all membranes studied with solute molal volume except for sulfobromophthalein (BSP). Because of strong membrane-solute frictional interactions, BSP has a reduced permeability. The sieving coefficient, which characterizes convective transport, also correlated with solute molal volume except for BSP and the lipophilic compound thiopental, The reduced convective transport of BSP is again due to its high frictional interactions with the membranes. The sieving coefficient for thiopental is markedly reduced although its permeability was normal. The membrane tortuosity factors for thiopental were also reduced. These facts indicate the existence of multiple diffusive pathways for thiopental and its exclusion from some solvent pathways in the membranes studied. IntroductionThe purpose of this study is to evaluate the mechanisms of mass transport through polymeric membranes. Membranes are important separation devices extensively used in application such as renal dialysis and reverse osmosis. Although the theory of membrane transport is well established, there are few experimental studies of membrane transport mechanisms. The work of Kauffman and Leonard7y8 and Ginzberg and Katchalsky6 are notable exceptions. In order to test theoretical concepts a wide range of solutes and two membranes often used in renal dialysis were chosen for study.Membranes are usually characterized by the following three parameters of the solute: permeability coefficient, w , the pressure filtration coefficient, L,, and the reflection coefficient, u. Often the sieving coefficient, S = 1 -u, is used instead of the reflection coefficient. The flux equations written in terms of these coefficients are (Keedem and K a t~h a l s k y )~

Fouling of Ultrafiltration and Hemodialysis Membranes by Plasma Proteins

“…Contact with blood did not alter the transport properties of the Cu prophan membrane, but significantly de creased both water permeability and dextran sieving coefficients for the AN69 membrane. These experimental observations are similar to those previously reported [8,9]; however, Langsdorf and Zydney also determined dex tran sieving coefficients for the AN69 mem brane in the reverse orientation. It was ob served that solute transport across the AN69 membrane after blood contact was asymmet ric, and, therefore, equation 1 cannot be em ployed for describing the dependence of dex tran sieving coefficients on the ultrafiltration rate.…”

“…These observations provided additional evi dence that the mechanism resulting in de creased sieving coefficients was the adsorp tion of protein to the membrane. Additional studies using other membranes with a similar protocol were confirmatory [8], Since others had previously demonstrated that protein ad 286 Leypoldt Fouling of Membranes by Plasma Proteins sorption to hemodialysis membranes can alter their transport properties [9] and that solute sieving coefficients across laboratory ultrafil tration membranes were largely uninfluenced by concentration polarization of albumin [10], the major contribution of our studies was to demonstrate that the adsorption of plasma protein to the membrane played an important role in determining solute sieving coefficients of hemofiltration membranes un der operating conditions similar to those in the clinic. Thus, the physical model of an ultrafiltration membrane had to be altered.…”

Effect of Blood Contact on the Transport Properties of Hemodialysis Membranes: A Two-Layer Membrane Model

“…Blood contact had essentially no effect on the transport char acteristics of the Cuprophan membrane, in agreement with previous results [8, 12, 14], In contrast, blood contact caused a significant reduction in the transport parameters for the AN69 membrane; the asymptotic sieving coefficient decreased by a factor of approxi mately 2 for the 8,000 MW dextran and by more than a factor of 9 for the 20,000 MW dextran, while the overall diffusive perme ability decreased by 30 and 65% for these same dextrans. Collins and Ramirez [8] found much smaller percent reductions in the siev ing coefficients upon exposure of an AN69 membrane to an albumin solution which was due to their use of relatively small solutes (MW < 1,400). However, these authors actual ly found somewhat larger percent reductions in both the solute diffusive permeabilities (e.g., 43% for vitamin B|i) and the hydraulic permeability of the AN69 membrane than were obtained in this study.…”

“…The sieving coefficients through the AN69 membranes also decreased after albumin ad sorption, although these changes were rather small (e.g., 12% for vitamin B 12). Fabiani et al [9] found a 42% reduction in the water per meability of an AN69 membrane after filtra tion of a 50-g/l albumin solution at 24 kPa, with this reduction in permeability somewhat smaller than that seen by Collins and Ramirez [8] after simple protein adsorption. Sakai et al [10] examined the effect of blood filtration on water hydraulic permeability and urea dif fusive permeability for regenerated cellulose, polymethylmethacrylate, and ethylenevinyl alcohol hollow-fiber membranes.…”

“…All major plasma proteins Collins and Ramirez [8] measured water per meability, diffusive permeabilities, and siev ing coefficients for several small solutes (MW <1,400) before and after adsorption of albu min to Cuprophan and AN69 flat-sheet mem branes. Albumin adsorption had no effect on the transport characteristics of the Cupro phan membranes.…”