Rheological aspects of plasmaseparation by membrane

Abstract

In order to investigate the parameters governing plasma separation by a microporous membrane, plasma filtration rates were measured in two single-channel filter press devices of 170 and 600 cm² membrane area with adjustable blood film thickness. The filtration rate reaches a maximum at a mean transmembrane pressure of 70 to 100 mm Hg. The maximum filtration rate is very well correlated with the inlet wall shear rate γ_w as γ_w^0.76. The maximum filtration rate is also found to decrease with increasing platelet concentration c_p as ℓn (1/c_p). These observations are consistant with the assumption that the plasma filtration rate is limited by platelet concentration polarization taking into account enhancement of platelet diffusivity by red blood cell motion. At low platelet concentrations the filtration rate decreases linearly with increasing hematocrit. The resulting model is used to predict the maximum filtration rates as a function of geometrical parameters of the filters.