Adsorptive membranes for sustainable and accessible hemodialysis

The increasing number of patients with chronic kidney disease who require haemodialysis results in an increased consumption of water needed for the process. This is the main motivation for the study of new systems to regenerate spent dialysate especially from uremic toxins. Mixed matrix membrane adsorbents (MMMAs), consisting of a membrane of cellulose acetate and zeolite as a filler, have been studied and characterised to be used as an adsorbent material for waste metabolites, such as uremic toxins and especially urea, present in spent dialysate. The membranes have been shown to have satisfactory properties and characteristics; the mechanical resistance is sufficient to prevent membrane crushing and rupture up to a maximum pressure of 0.05 bar, and the permeability reaches values of 4200 L/(m2 h bar). The adsorbent is homogeneously dispersed in the membrane, and its skin layer is porous and less than 2 µm thick. In contrast, the morphology of the section is characterised by finger-like pores. Finally, MMMAs with 10 wt% zeolite show an equilibrium binding capacity of 17 mg/cm3. Particular interest was devoted to the study of the parameters that most influence membrane morphology in order to obtain membranes with the desired microstructure. The factors that influence membrane structure are many; among those analysed are the concentration of porogen and polymer, and the temperature of the coagulation bath. The bath temperature is definitely the factor that has the greatest impact on morphology.