BLOOD MATERIAL INTERACTIONS AT THE SURFACES OF MEMBRANES IN MEDICAL APPLICATIONS

Membrane based medical therapies have increased considerably in recent years. At the same time, awareness of the side-effects caused by bloo d material incompatibility has grown. The necessity of mass production at low cost has also contributed to the formation of demands placed o n any membrane used in medical applications today. These demands are a pplication specific transport characteristics, high clearance, blood c ompatibility and a design enabling cost efficient ways of production. A theoretical approach relating membrane structure to transport proper ties suggests that the deciding factors are pore radius, porosity, tor tuosity, diffusion coefficients, pore shape and protein adsorption pot ential. A hollow fiber structure, which fits these demands for hemodia lysis, hemodialfiltration and hemofiltration, is a three-layer structu re consisting of an inner blood facing skin layer, followed by a spong e structure and a macroporous finger structure. The influence of the m embrane surface on protein adsorption, leading to a change in permeabi lity, has also been investigated. Two concepts for limiting protein an d cell interaction with artificial surfaces are introduced. Copolymeri zation and blending of hydrophobic and hydrophilic polymers have been successful approaches. To limit blood-membrane interactions, an optimi zed microdomain surface structure formed by hydrophilic patches in a h ydrophobic matrix has evolved. In vitro test methods for measuring act ivation levels of coagulation, kallikrein-kinin pathways, cell stimula tion and complement activation were necessary for the development of h ighly optimized artificial membranes made for hemodialysis, hemodiafil tration and hemofiltration. The Polyflux S membranes, consisting of th e hydrophobic polymers polyamide and polyarylethersulfone as well as h ydrophilic poylvinylpyrrolidone, with their integral three-layer micro domain structures performed well in all of the mentioned in vitro test s. (C) 1998 Elsevier Science B.V. All rights reserved.