A Microfluidic Dialysis Chip for Continuous Purification of Lipid Nanoparticles

Synthesis of lipid nanoparticles (LNPs) for mRNA delivery is now standardized and automated. In contrast, post-synthesis purification-ethanol removal, clearance of unencapsulated components, and buffer exchange-remains less controlled. Conventional bulk dialysis is time-consuming, whereas centrifugal ultrafiltration, although rapid, can result in reduced particle recovery and mRNA preservation; both of these laboratory-scale approaches present limitations for reproducible high-throughput processing. Here we report a 3D-printed microfluidic dialysis chip for continuous LNP purification. Mirrored serpentine sample and wash-buffer channels run counter-current across a clamped, interchangeable membrane in a three-layer printed chip. A mass-transfer model relating ethanol removal to the number of transfer units (NTU) identified channel height as the principal geometric design parameter under the fixed-flow-rate conditions tested. At a 100 kDa cut-off and 25 µL/min, the chip removed >99% ethanol and adjusted pH from 4.0 to 7.4, processing 1 mL in 40 min at steady state. Membrane choice set a trade-off: Polyethersulfone removed ethanol faster, whereas regenerated cellulose gave the highest particle recovery (83%). Förster resonance energy transfer (FRET) confirmed preserved LNP integrity, and on-chip purified mRNA-LNPs matched bulk dialysis in transfection efficiency. Serial or parallel configurations offer a gentle, scalable route to LNP purification.