Membrane-Enabled Dialysate Regeneration for Wearable and Miniaturized Artificial Kidney Systems: Transport...

Low-volume dialysate recirculation couples the primary dialysis membrane to the regeneration circuit in wearable and miniaturized artificial kidneys. This narrative review examines membranes as blood-dialysate barriers, fractionation devices, adsorptive supports, and catalyst-containment interfaces. Nanofiltration, forward osmosis (FO), mixed-matrix adsorption, and membrane-supported catalysis are compared using transport, capacity, safety, and operating duration. Among the seven representative regeneration studies tabulated here, five tested only model or synthetic feeds, one operated at 70 °C, and three projected clinical-scale throughput or module requirements from bench data; and one demonstrated 24 h of coupled FO-oxidation bench operation. These overlapping counts describe the selected studies, not the entire literature. Commercial nanofiltration can separate urea from glucose and selected ions, while forward-osmosis and mixed-matrix systems enable urea transfer or capture. Sustained regeneration, nevertheless, requires a destination for the transferred urea: capture in a replaceable sorbent, chemical conversion with product control, or discharge. Membrane selection must, therefore, be evaluated together with electrolyte balance, fouling, return-stream safety, and cartridge capacity. Future studies should combine comparable reporting conditions with complete mass balances, patient-derived spent dialysate, prolonged closed-loop operation, and measured module mass and energy demand.