CONSIDERATIONS ON DEVELOPMENTAL ASPECTS OF BIOCOMPATIBLE DIALYSIS MEMBRANES

Modern strategies in developing new polymers for dialysis membranes ai m to improve their blood compatibility. To achieve such a goal, two ap proaches have been successfully applied: existing cellulosic polymers were modified, either by introducing functional groups through ester o r ether bonds, by mixing synthetic polymers with bulk additives, or by using copolymerization techniques. As a detailed example, the first s ynthetically modified cellulose membrane, Hemophan, was prepared by su bstituting some hydrogen atoms in the cellulosic glucose unit by dieth yl-amino-ethyl groups with the modification having a considerable impa ct on the membrane's hemocompatibility. It is further known that the h emocompatibility of hydrophobic synthetic membranes is improved by ren dering these materials partially hydrophilic. We tested the hypothesis , whether the hemocompatibility of a material, which is hydrophilic pe r se, such as unmodified cellulose, is changed after the introduction of hydrophobic substituents. For this purpose, the number and nature o f substituents have been systematically varied in order to alter surfa ce properties, and these variations have been subsequently related to blood compatibility parameters. As expected, thrombin generation as we ll as complement- and cell-activation depend on the number and nature of the substituents whereby some of the substituents show a very narro w optimum if their hemocompatibility is related to the degree of subst itution. Changes in hemocompatibility can be followed by physical meth ods, such as surface angle analyses and zeta potential determinations. Data show that alterations in the lipophilic/hydrophilic balance on t he polymer surface may explain substituent-related changes in polymer hemocompatibility. Molecular modeling of membrane surface and protein structures may be of further help in understanding possible interactio ns. The recent conclusion is that polymer modification and techniques in membrane surface characterization help us to optimize membrane fabr ication for specific applications.