Membranes for dialysis.

Today, more than 30 different polymers or polymer blends are used as materials for dialysis membranes. They can be categorized following the scheme of a family tree of haemodialysis membranes. The trunk represents membranes from regenerated cellulose, major branches show either synthetically modified cellulose membranes or membranes manufactured from synthetic polymers. As the latter are standardly hydrophobic, small branches elucidate the technique on how these materials have been rendered partially or completely hydrophilic. Complications may arise, when comparing membranes only following their polymer names, such as polysulfone, polyacrylonitrile or polyamide. Due to varying polymer compositions, membranes with the same polymer names may differ in their haemocompatibility, flux properties and adsorption characteristics. Adsorption of proteins like beta 2-microglobulin, fibrinogen and coagulation factors, complement proteins, or hormones like parathormon and erythropoietin are differently adsorbed by dialysis membranes and thus adsorption contributes to the removal characteristics. Of central interest for membrane development and application is the question of how these membranes can be sterilized, as a series of patient adverse reactions has been attributed to the dialyser sterilization procedures. Apart from the cellulosic membranes Cuprophan and Hemophan, the majority of membranes cannot be sterilized by steam, as these materials degrade when exposed to above their class-point temperature. Finally, future aspects of modern membrane development should not neglect the needs of patient populations with specific blood properties, such as diabetics.