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Effect of membrane composition and structure on solute removal and biocompatibility in hemodialysis. Significant changes in extracorporeal membranes have occurred over the past five decades in which hemodialysis (HD) has been available as a therapy for both acute renal failure (ARF) and end-stage renal disease (ESRD). For cellulosic membranes, these changes have included a reduction in thickness, hydroxyl group substitution, and an increase in pore size. These modifications have resulted in enhanced efficiency of small solute removal, a broader spectrum of overall solute removal, and an attenuation of complement activation in comparison to the thick, unsubstituted cellulosic membranes of low permeability used in the early days of HD therapy. Synthetic membranes, originally developed specifically for use in high-flux HD and hemofiltration, have also evolved during this same time period. In fact, the initially clear distinction between low-flux regenerated cellulosic and high-flux synthetic membranes has become blurred, as membrane formulators have developed products designed to appeal to enthusiasts for both membrane formats. The purpose of this review is to characterize both the solute removal and biocompatibility characteristics of dialysis membranes according to their composition (that is, polymeric makeup) and structure. In this regard, the manner in which membrane biocompatibility interacts with flux is highlighted.

Near-infrared (n.i.r.) spectroscopy in both the short wavelength region (700–1100 nm) and the long wavelength region (1100–1500 nm) is evaluated as a rapid method for the simultaneous estimation of the freezing point and volume percentages of aromatics and saturates of aviation fuels. Thirty-three JP-4 samples were independently analysed by six industrial and government laboratories for freezing point and for volume per cent aromatics and volume per cent saturates by fluorescent indicator adsorption. These results were then used to calibrate the sample's n.i.r. spectra. Both multiple linear regression and partial least squares calibration methods were evaluated and gave comparable performance. The n.i.r. spectral analysis predictions for these properties were within the standard deviations of the round-robin values. Specifically, the per cent aromatics and per cent saturates were within 1% and the freezing point within 2.5 °C of the laboratory-determined values. N.i.r. spectroscopy appears to have considerable promise as a rapid non-destructive method for jet fuel analysis.

Membrane technology is being increasingly applied to the collection of plasma by plasmapheresis, a procedure in which plasma is separated from whole blood, and the cellular components reinfused to the donor. Although still somewhat controversial, there is a general understanding of the physics and fluid mechanics involved in the transport phenomena associated with the microporous filtration of whole blood. The filtration process is governed by concentration polarization, with the red blood cell being the polarizing species. Shear-enhanced cellular diffusion has been proposed to explain how such a large cell can depolarize to allow the observed separation rates. The filtration rate per unit area is proportional to the first power of the shear rate and therefore, can remain approximately constant if the shear rate is increased to accommodate a decrease in surface area. Three automated membrane-based plasmapheresis systems are currently in use, primarily at fixed-site locations. They all collect 500-600 cc of plasma within 30-50 min. Two use hollow fiber membrane filter modules, while the third uses a rotating cylinder which relies on Couette rather than Poiseuille flow to generate the required shear rates at the membrane surface. Two portable systems have been developed; one centrifuge-based system requires house current, the other membrane system uses gravity, augmented by a battery power source. Both of the latter systems, due to their size and low weight are well suited for use in an environment where the equipment is moved on a frequent basis.