Membranes for dialysis: can we do without them?

Over the past five decades, membranes used for the treatment of chronic kidney disease have continuously evolved. In the course of this evolution, the use of classical non-modified cellulose membranes has declined in favor of cellulose-based membranes in which the basic structure has been modified to improve the biocompatibility profile of the material as well as membranes based on synthetic polymers. In addition to providing improved biocompatibility, manufacturing methods have been innovatively adapted to produce membranes with optimized pore size and pore size distribution. This has led to the more effective removal of molecules involved in the development of complications associated with dialysis treatment. More recently, the approach has been move membranes beyond being just selective barriers with a high performance and to incorporate biological function. Despite these advances, membranes in current clinical use represent a compromise: while efficient in their removal of water soluble compounds, they are non selective, retain some bioreactivity and differ in their ability to adsorb endotoxins or bacterial fragments that may be present in the dialysis fluid. In this paper, an overview of the membranes used in current clinical practice and their limitations are discussed, together with approaches to solute transport in which no membranes are used.