Polymers employed as biomaterials in nephrology serve for different applications: they form membranes for dialysis and plasmapheresis, are used as materials for dialyser housings and as a potting mass for capillary membranes, they make up tubing-systems for extracorporeal circuits and – in the form of beads – act as parts of adsorber columns for hemoperfusion or immunoadsorption. However, generally speaking, many polymers have not yet been designed for their final application. To date, many polymers are still taken from the chemist's shelf according to their alleged performance properties or to their sterilisability. When used in medical application, polymers must show a high purity. Uncontrolled leaching of oligomers from the polymer backbone or of additives from or during the manufacturing process must be avoided. Blood and other body fluids are extremely effective in extracting any loosely bound polymers. During long-term application, e.g. in patients suffering from chronic diseases, these effects may lead to an accumulation of these compounds in circulating blood, tissue, or joints. Consequently, polymers should show an excellent biostability and not degrade during their ageing process. The amount of extractable material should be kept low in order to avoid inflammatory reactions. Polymers must have high blood compatibility in terms of minimized cell-and complement activation. Polymers for medical application should at best be able to stand high temperatures in order to survive steam sterilisation. If this is impossible, their release kinetics for residual quantities of sterilizing agents should be fast. Finally, protein adsorption should appear under controlled conditions, otherwise a reduced performance through protein adsorption will take place. Further, the uncontrolled activation of biochemical cascades, such as the coagulation, complement or contact phase cascade, following blood/material contact must be minimized. A final aspect has been recently made responsible for adverse patients reactions, the interaction between polymers and medicinal drugs. This drug/material interaction must be low, at best zero, apart form those situations, where a controlled drug-release is wanted. The chemical variety of polymers for medical application is large. However, all typical requirements cannot be met by one single polymer. Compromises have to be found between properties and application. Polymer selection for application in nephrology has always to be made under the premise of final application.
The blood compatibility challenge. Part 2: Protein adsorption phenomena governing blood reactivity
