Understanding the Yields of Giant Unilamellar Vesicles Composed of Charged Membranes

Abstract

Double-layer electrostatic interactions play an important role in colloid and surface phenomena including for biological membranes. While important for recapitulating biophysical phenomena such as virus fusion, protein binding, and for tuning interactions with biomedically important surfaces, the role of membrane electrostatic interactions in the surface-assisted assembly of cell-like giant unilamellar vesicles, GUVs, is still poorly understood. Here, we show that both the molar yield and the sizes of GUVs falls systematically with increasing mol fraction of the anionic charged lipids DOPG and DOPS. We use the budding and merging (BNM) model for the assembly of GUVs to understand the effect of electrostatic interactions. In the BNM model, GUVs assemble through the budding of nanoscale buds which then merge to form micrometer scale buds. Our calculations show that although membranes with higher mol fraction of charged lipids experience decreased interbilayer adhesive interactions thus reducing the energy cost for budding, the increased electrostatic potential between the nanoscale buds raises the energy cost for merging. The higher barrier to merging explains our result that increasing the fraction of charged lipids in the membrane decreases GUV yields and sizes. It also explains previous observations in the literature that it is difficult to obtain GUVs with membranes composed of anionic lipids. We show that the higher barrier to merging can be overcome by crowding the surface with nanoscale buds. We can obtain high yields of GUVs with charged membranes by increasing the surface concentration of lipids. These results enable us to optimize the yield of lipid mixtures that reflect physiological compositions of cell membranes and open up avenues into larger-scale production for applications that require cell mimics.