Production of giant unilamellar vesicles by the water-in-oil emulsion-transfer method without high internal concentrations of sugars

Giant unilamellar vesicles (GUVs) are large vesicles bounded by a single lipid bilayer, which have been used in various applications as artificial, cell-like compartments. The water-in-oil (w/o) emulsion-transfer method has been attracting attention as a method to prepare GUVs that can efficiently encapsulate macromolecules. For efficient GUV production by this method, non-physiological, high concentrations of sugars are usually required in the inner solution of the GUVs. These sugars limit the utility of the GUVs for a wide range of applications. In this study, we investigated various compositions of the inner and outer solutions to achieve efficient production without high concentrations of sugars through the w/o emulsion-transfer method. Firstly, we adjusted the osmotic pressure and density of the outer solution with NaCl and succeeded in increasing the proportion of GUVs and the absolute number in the prepared liposome population. Secondly, we increased the density of the inner solution with cytochrome c, but the proportion of GUVs and absolute number of vesicles did not increase. Thirdly, we increased the density of the inner and outer solutions with glycerol, which is membrane permeable and can be removed from GUVs, and succeeded in increasing the GUV proportion. These results provide useful information for the efficient preparation of GUVs that enclose a physiologically-relevant environment by the w/o emulsion-transfer method.