Membrane-Enabled Dialysate Regeneration for Wearable and Miniaturized Artificial Kidney Systems: Transport Requirements, Hybrid Architectures, and Translational Constraints

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.