Effect of membrane grain orientation on in vitro performance of a Kiil dialyzer

Abstract

The membranes used almost exclusively in artificial kidneys are cellophane and Cuprophan. In both, the polymer chains are arranged preferentially, though not completely, in the direction of extrusion. The physical properties of these microporous membranes have been extensively investigated [1, 2], and it has been shown [3] that the pores of these membranes are rather irregular but preferentially elliptical, with the greater diameter in the direction of extrusion. The effect, however, of grain orientation on their behavior during hemodialysis has not been reported. The problem is particularly important in the case of the Kiil dialyzer (Fig. 1), the most popular type in use, in which the membrane support consists of a number of V-shaped grooves lying parallel to the direction of flow of blood and dialysis fluid. The dialyzer is assembled in hospital or home using sheets of Cuprophan, or cellophane, which are available with the grain parallel to the grooves (long grain) or at right angles to them (cross grain); the choice at the moment depends on the whim of the physician. On behalf of the U.K. Department of Health and Social Security we have therefore investigated the effect of grain orientation on the performance characteristics of a Kiil dialyzer. A full report on this work is available on request [4].