Extrusion of small vesicles through nanochannels: a model for experiments and molecular dynamics simulations

We propose a model that predicts the final sizes of lipid bilayer vesicles produced by pressure extrusion through nanochannels and we conduct large-scale coarse-grained molecular dynamics simulations of the phenomenon. We show that, to a first approximation independent of pressure, vesicle size can be predicted by a simple geometrical argument that considers an invariable inner vesicle volume enclosed by a finitely extensible lipid bilayer. The pressure dependence is then incorporated in our model by arguing that the effective channel radius decreases with increasing pressure due to a thickening of the lubrication layer between the vesicles and the channel wall. We fit our model to the experimental data of Patty and Frisken [Biophys. J. 85, 996 (2003)]. We predict that at high pressure, vesicle size significantly depends on channel length and, therefore, flow rate. The CGMD simulations reproduce the physical principles of the model. They also show the build-up of the stress in the vesicle, and typical rupture scenarios as the pressure gradient is increased.