Instability in the formation of lipid vesicles from microfluidic double emulsions

Lipid vesicles are capsules with lipid bilayer membranes, similar to the cells in our bodies. Their structure and biocompatiability allow them to serve as model systems for cells and as carriers for drug delivery. Among the various methods to create vesicles, researchers have recently focused on microfluidics, which can produce monodisperse vesicles with much higher throughput. In the microfluidic method, water-in-oil-in-water (W/O/W) double emulsions are first generated, and the solvent in the oil layer should be removed to form vesicles. However, achieving complete and fast solvent removal from the W/O/W double emulsions poses a challenge due to rupture. To address this issue, we observed the removal process of the oil phase from the double emulsions using confocal and optical microscopes. Our finding revealed that some solvents remain after the oil phase dewetting, and the emulsion rupture stems from the low adhesion energy of lipids in the residual thin oil layer. Additionally, we discovered that controlling the evaporation rate of solvents can increase the adhesion energy of the lipid bilayer, suppressing the breakdown of the emulsions.