Membrane-tension-dominated growth mechanism and size modulation of giant unilamellar vesicles in electroformation

Giant unilamellar vesicles (GUVs) are excellent membrane model systems and nano-carriers for biophysical studies and biomedical applications. Electroformation is one of the most prevalent methods for GUV production, during which defect-free vesicles with high unilamellarity grow from lipid films under an electric field between electrodes. To overcome the weak controllability of electroformation and meet the requirement of grown GUVs with specific size, constructing electrode microstructures has been recently introduced in synthesis of size-controllable GUVs. However, the introduction of electrode microstructures is limited, as the strong adhesion at edges or corners of microstructures leads to difficult detachments of transferable GUVs from the electrodes. Moreover, the mechanism of GUV growth is ambiguous, and the size modulation of detachable GUVs is still a key challenge. Herein, we first performed theoretical modeling to reveal the growth mechanism of GUVs in electroformation, and we found that the membrane tension inhibits the growth of GUVs and leads to the coupling between vesicles that causes the growth instability as GUVs exceed certain critical sizes. Introducing the free boundaries on lipid films that can reduce the membrane tension and the coupling between vesicles, we experimentally obtained amounts of detachable GUVs of remarkable size uniformity. Eventually, we achieved the size modulation of detachable GUVs by constructing the island-like lipid patches on electrodes. Our work offers nanomechanical understandings of the GUV growth and paves the way for the preparation of detachable GUVs with controllable sizes.