Healthy kidneys regulate acid–base balance and electrolytes, produce hormones, and clear excess fluids and uremic toxins. Progressive kidney function loss in chronic kidney disease leads to end-stage kidney disease (ESRD), where fluid and toxin accumulation causes severe complications and can be fatal. ESRD requires renal replacement therapy; kidney transplantation is preferred; however, limited availability of donor organs makes hemodialysis (HD) the most used treatment option. Current HD membranes can efficiently remove small water-soluble uremic toxins but can inadequately remove middle sized molecules and protein-bound uremic toxins. In the last years, many studies had focused on development of new membranes with improved toxin removal, however, these studies implement various experimental conditions making direct comparison between membranes challenging. This work aims to address this by developing an in vitro system for evaluating various membranes under HD conditions. We develop the system by using a commercially available membrane (FX1000, Fresenius) as well as a newly developed mixed matrix membrane (MMM), both membranes are assembled in a mini dialyzer. We used creatinine (Cr), hippuric acid (HA) and indoxyl sulfate (IS) as model uremic toxins and assessed their removal by the membranes in human plasma and full human blood under a range of conditions. For obtaining better insights concerning toxin removal, membrane fouling and concentration polarization, we mainly implemented dialysate recirculation which allowed accurate estimation of the toxin mass balance. Moreover, we used dialysance (DL) normalized by membrane effective area (mL min−1 m−2) as key parameter for assessing the various transport phenomena affecting membrane performance. Our results are in good agreement to various literature studies using small and larger scale dialyzers indicating that our in vitro system can be used for evaluation of commercial as well as developmental hollow fiber membranes for HD.
