Multidimensional Classification of Dialysis Membranes.

Hemodialysis is a process of mass separation by a semipermeable membrane, utilized to cleanse blood from waste products retained in case of kidney failure. Traditionally, dialysis membranes have been classified based on composition and hydraulic conductance, creating the net differentiation between cellulosic versus non-cellulosic on one hand and low-flux versus high-flux on the other. With the evolution of biomaterials and improved spinning technology, new membranes have been introduced in the market with specific characteristics and refined individual properties. Therefore, we should consider new parameters to classify dialysis membranes including polymer blending, surface functionalization, molecular weight cut-off (MWCO), hydrophilic/hydrophobic properties, thickness and architecture, adsorption capacity, and electric potential. All these parameters may be utilized to characterize a membrane alone or in combination. Recently, a new parameter has been identified as an important element to characterize a new class of membranes. Beyond the classic MWCO describing the molecular weight at which the sieving value in pure convection = 0.1, the molecular weight retention onset (MWRO) is a new parameter that defines membrane sieving properties. The retention onset value is the molecular weight at which the sieving value = 0.9. The relationship between MWCO and MWRO describes the steepness of the sieving curve and the membrane pore size distribution with important consequences on the final mass separation process and solute removal.