A transient experiment to measure the diffusive permeability of hollow fiber membranes

Abstract

A precise and rapid transient diffusion experiment has been developed to measure the diffusive permeability of hollow fibers. In this experiment a sealed hollow fiber containing a radioactive solute is exposed sequentially to several well-stirred solute-free reservoirs. This method was used to measure the diffusive permeability of collagen and Cuprophan hollow fibers in an isotonic saline solution for a spectrum of 14C labelled solutes: urea, sucrose and polyethylene glycol (PEG). To study the effect of environment on membrane permeability, collagen membranes were investigated with urea, sucrose and tritiated water in the following solutions with varying ionic strength and hydrogen ion concentration: pH2 HCl, distilled water and pH2 HCl with 0.8 M NaCl. In each environment, the membranes showed the expected decreases in diffusive permeaability with increasing molecular weight. Collagen membranes ranged from 4 (urea) to 40 (PEG) times the permeability of Cuprophan membranes. The Cuprophan data are consistent with results obtained elsewhere using scaled-down dialyzers. In response to environmental changes, the diffusive permeability of collagen membranes changed overall by a factor of 3 with the following rank: pH 2 HCl > distilled water > pH2 HCl and 0.8 M NaCl. The hydraulic permeability of these membranes changed by a factor of 2 but in a different order pH2 HCl > pH2 HCl and 0.8 M NaCl > distilled water. These permeability changes can be explained in terms of the known environmental dependence for the structure of collagen membranes and have been shown to be consistent with trends predicted by simple transport models.