MEMBRANES AND POLYMER STRUCTURES - BIOCOMPATIBILITY ASPECTS WITH RESPECT TO PRODUCTION LIMITS

Plasmapheresis can be performed by centrifugation and by use of membra ne technology. With the latter technique we receive a plasma which is absolutely free from platelets. This is why membranes are gaining mark et shares in this particular field of medical application. Today plasm apheresis membranes are mostly fabricated from synthetic polymers, suc h as polypropylene (e.g. PLASMAPHAN(R)), polysulfone, polyacrylonitril e, polymethylmethacrylate, polyvinylalcohol and others, the only excep tion being cellulose acetate. Parameters determining the biocompatibil ity of plasmapheresis membranes are generation of complement C3a or C5 a, hemolysis and possible thrombus formation. These parameters depend on various properties of the membrane polymer: e.g. the nature of the molecular end/side-groups, the distribution of electrical charges on t he polymer surface and the different chemical structures and conformat ion of the polymer. In addition, membrane properties like pore distrib ution and geometry or the flow characteristics of a particular device- design may trigger cell activation or influence biocompatibility throu gh the adsorption of various plasma-components. Most of the polymers w hich are used today for manufacturing plasmapheresis membranes have no t been developed for this purpose. They were originally selected to be used as textile fibers. Further, no present membrane polymer has been specifically developed to achieve high biocompatibility. The membrane profile was designed in such a way that pheresis properties were met rather than optimizing biochemical blood/polymer interactions. One rea son for this decision may be that the market volume of plasmapheresis technology is too small in order to justify specific and high-cost dev elopments of polymers for this purpose. Polymer selection to achieve e xcellent biocompatibility profiles is determined by polymer-availabili ty, costs, membrane-forming processes and environmental aspects relate d to possible pollution during the manufacturing process. The producti on of PLASMAPHAN(R) by the unique Accurel-process combines several of these parameters. The main membrane production processes and especiall y the Accurel-process are described here. The influence of polymer-sur face properties, membrane structure and module-design on the biocompat ibility of plasmapheresis treatments are discussed and explained by ap propriate examples.