STRATEGIES FOR THE DEVELOPMENT OF HEMOCOMPATIBLE DIALYSIS MEMBRANES

Haemocompatibility is the number one target of membrane development fo r haemodialysis, because chronic renal failure and the subsequent dial ysis-treatment is affecting more and more patients. Two strategies are currently in use to achieve the goal of new blood compatible polymers : Firstly, existing cellulosic membranes are modified by introducing f unctional groups through ether and ester bonds and secondly, synthetic polymers are mixed with bull additives or copolymerized with other po lymers. Biological responses as a consequence of blood/material intera ction are common observations. However, blood compatibility in general cannot be improved by a single membrane surface feature. The assessme nt of a series of surface properties shows that physiological defense systems, like complement and cell activation, or coagulation are diffe rently stimulated by means of the same surface structures of biomateri als. Thus, a compromise has to be found, already during membrane devel opment. We synthetized a series of modifications of cellulosic membran es with the aim to investigate whether the type of substituent and its degree of substitution has an influence on the blood compatibility of these dialysis membranes. Data indicate that alterations in the lipop hilic/hydrophilic balance (HLB) on the polymer surface may explain sub stituent-related changes in haemocompatibility. Optimal degrees of sub stitution are characteristic for a given type of substituent and enabl es the membrane manufacturer to tailor materials for improved blood co mpatibility.