Simulation Study On Behavior For Flow-induced Vesicles Through A Nanopore

Vesicles are very ‘‘soft'',consisting of a liquid internal medium enclosed by a very thin deformable membrane,which can be deformed easily by external flow field.Therefore,the study of the dynamic behavior of vesicles through restricted pores in microchannels is significant for their applications in the fields of drug transport,cell screening and film characterization.However,flow-induced dynamics of vesicles through a narrow pore was not clearly elaborated due to interactions between vesicles and fluid.In this work,the fluidsolid interaction method based on finite element is employed to systematically elucidate the movement of the flow-driven translocation of spherical vesicles through a narrow pore with the deformation and corresponding strain energy of the vesicles at different positions.The main findings are as follows: 1.The vesicle shows similar shape change from bullet-like to dumbbell-like,dumbbell-like to bulb-like,and bulb-like to parachute-like if it is pushed by flow field to pass through a narrow pore smaller than its size.We further find that the strain energy exhibits a higher peak and a lower peak in the whole translocation process,where the higher peak corresponds to the dumbbell-like shape and the lower peak corresponds to the parachute-like shape due to more stretching of the membrane for the dumbbell-like shape than that of the parachute-like shape.The translocation time of the vesicle from one side to the other side of the narrow pore increases with the decrease of inlet velocity,and the strain energy exhibits a decrease,but the requirement for the mechanical properties of the membrane is lower.However,vesicles could not complete migration with the further decrease of inlet velocity,which indicates that there is a minimum inlet velocity when vesicles pass through the pore,and the minimum inlet velocity is related to the size of vesicles.2.The vesicles show different deformations in migration process,in turn an oblique ellipseshape,slipper-shape,oval-shape.We find that the rotation angle of non-axially positioned vesicles mainly shows the trend of increase,besides the small fluctuation induced by deformation relaxation.Moreover,when the vesicles move towards the axis of the channel,the rotation angle exhibits a decrease because of the decrease of the shear force.However,rotation of axially positioned vesicles hardly occur due to symmetrical shear force.Our results further indicate that the rotation is faster nearby the pore for non-axially positioned vesicles.From the dynamic point of the vesicles passing through the pore driven by the flow field,we systematically describe the movement,deformation,stress distribution and strain energy of the vesicles passing through the confined pore in the micro channel,which enriches and develops the overall understanding of the non-equilibrium behavior of the vesicles passing through the confined pore.It provides calculation support for their applications in the fields of drug transport,cell screening,and related physiological processes.