Giant liposomes as microcapsules with large trapping volumes: Downsizing through various membrane filters and analysis with a calcein quenching method

Giant unilamellar vesicles (GUVs), or giant liposomes, are very similar to actual cells about the size (∼1 – 100 µm); therefore, GUVs have much larger trapping volumes than conventional liposomes (large unilamellar vesicles, LUVs; ∼100 nm). Albeit having such large trapping volumes, GUVs are rarely employed as microcapsules for biomedical purposes because of their difficulties of the preparation in physiological buffer solutions in large quantities with the narrow size distributions. Here, we comparatively downsized giant liposomes by making them filtrated through various membrane filters including polycarbonate, polytetrafluoroethylene and nitrocellulose/cellurose acetate membranes, and measured their trapping volumes using a calcein quenching method. Any filters with around 1–5 µm pore sizes were useful to reduce the size from more than 10 µm to less than 5 µm, and their trapping volumes were estimated to be around ten times higher than those of 100-nm LUVs, which are reasonable values; however, somewhat large fractions of vesicles that were much smaller than the pore sizes remained in the sample.