Ultrahigh yields of giant vesicles obtained through mesophase evolution and breakup

Self-assembly of dry amphiphilic lipid films on surfaces upon hydration is a crucial step in the formation of cell-like giant unilamellar vesicles (GUVs). GUVs are useful as biophysical models, as soft materials, as chassis for bottom-up synthetic biology, and in biomedical applications. Here via combined quantitative measurements of the molar yield and distributions of sizes and high-resolution imaging of the evolution of thin lipid films on surfaces, we report the discovery of a previously unknown pathway of lipid self-assembly which can lead to ultrahigh yields of GUVs of >50%. This yield is about 60% higher than any GUV yield reported to date. The "shear-induced fragmentation" pathway occurs in membranes containing 3 mol% of the poly(ethylene glycol) modified lipid PEG2000-DSPE (1,2-distearoyl-sn-glycero-3-phosphoethanolamine-N-[methoxy(polyethylene glycol)-2000]), when a lipid-dense foam-like mesophase forms upon hydration. The membranes in the mesophase fragment and close to form GUVs upon application of fluid shear. Experiments with varying mol% of PEG2000-DSPE and with lipids with partial molecular similarity to PEG2000-DSPE show that ultrahigh yields are only achievable under conditions where the lipid-dense mesophase forms. The increased yield of GUVs compared to mixtures without PEG2000-DSPE was general to flat supporting surfaces such as stainless steel sheets and to various lipid mixtures. In addition to increasing their accessibility as soft materials, these results demonstrate a route to obtaining ultrahigh yields of cell-sized liposomes using longstanding clinically-approved lipid formulations that could be useful for biomedical applications.