Ulrich Baurmeister

Membranes and polymer structures—Biocompatibility aspects with respect to production limits☆

Plasmapheresis can be performed by centrifugation and by use of membrane technology. With the latter technique we receive a plasma which is absolutely free from platelets. This is why membranes are gaining market shares in this particular field of medical application. Today plasmapheresis membranes are mostly fabricated from synthetic polymers, such as polypropylene (e.g. PLASMAPHAN), polysulfone, polyacrylonitrile, polymethylmethacrylate, polyvinylalcohol and others, the only exception being cellulose acetate. Parameters determining the biocompatibility of plasmapheresis membranes are generation of complement C3a or C5a, 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 the polymer surface and the different chemical structures and conformation of the polymer. In addition, membrane properties like pore distribution and geometry or the flow characteristics of a particular device-design may trigger cell activation or influence biocompatibility through the adsorption of various plasmacomponents. Most of the polymers which are used today for manufacturing plasmapheresis membranes have not 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 reason for this decision may be that the market volume of plasmapheresis technology is too small in order to justify specific and high-cost developments of polymers for this purpose. Polymer selection to achieve excellent biocompatibility profiles is determined by polymer-availability, costs, membrane-forming processes and environmental aspects related to possible pollution during the manufacturing process. The production of PLASMAPHAN by the unique Accurel-process combines several of these parameters. The main membrane production processes and especially the Accurel-process are described here. The influence of polymer-surface properties, membrane structure and module-design on the biocompatibility of plasmapheresis treatments are discussed and explained by appropriate examples.

Preparation of and optimal module housings for hollow fibre membrane ion exchangers

Macroporous polyamide 6 hollow fibres can be polymer coated by a three‐step procedure: first, reaction of the amino end groups with a bifunctional, double‐bond‐containing reagent; second, block polymerization with different monomers; and third, polymer analogue reactions with amines or sulphite salts to produce ion exchanger groups. The densities of double bonds are dependent on the amino densities and are in the range of 20–30 µmol/g polyamide 6. The ion exchanger fibres were packed in different types of module housings to get an optimal separation unit. The best housing seems to be a so‐called single‐dead‐end arrangement of fibres. Three types of ion exchanger hollow fibres have been produced: a weak and a strong anion exchanger and a strong cation exchanger. The dynamic protein‐binding capacities are in the range of 40 mg/ml membrane. Using these membrane modules, it is possible to separate proteins in the same way as with particle‐based ion exchangers. Fast protein separations with low pressure drop are possible. Copyright