Water Transportation through Nano/Microsized Lipid Protocells with a Significant Deviation from the van’t Hoff Osmotic Rule

Osmotic pressure is known to be an important driving force that induces water transport through membranes, which is crucial for many biophysical processes. Here, we observed that under a relatively low osmotic pressure induced by sugars’ protocells (vesicles) with a diameter of ∼110 nm barely shrank. However, NaCl and CaCl₂ at lower concentrations induced a rapid decrease in the vesicle size as evidence of water transportation through the membrane. An additional mechanical pressure resulting from the increase in interfacial tension of the lipid membrane was proposed to be the main driving force of this electrolyte-specific effect. These results indicate that osmotic pressure is not the only driving force of water transport in nano/microsized lipid protocells.