Lattice Boltzmann-immersed boundary approach for vesicle navigation in microfluidic channel networks

We investigate the path selection (navigation) of a single moving vesicle in a microfluidic channel network using a lattice Boltzmann-immersed boundary method (IBM). The lattice Boltzmann method is used to determine incompressible fluid flow with a regular Eulerian grid. The IBM is used to study a vesicle with a Lagrangian grid. Previous studies of microchannels suggest that the path selection of a bubble at a T-shaped junction depends on the flow rates in downstream channels. We perform simulations to observe the path selection of a vesicle with three different capillary numbers at a tertiary junction. The hypothesis that higher flow rate determines path selection is not validated by our data on low capillary number ( Ca ≤ 0.025) of a vesicle in tertiary downstream channels. We use the resultant velocity hypothesis to explain the path selection of a vesicle in microfluidic systems. Our results suggest that, for a low capillary number, instead of being affected by the viscous force from a high flow rate, a vesicle in a tertiary junction tends to follow the resultant velocity hypothesis. We analyze the change in hydrodynamic resistance caused by the movement of a vesicle to support the resultant velocity hypothesis. We also study the residence time of a vesicle at a junction for different cases and analyze the relationship between the residence time and the resultant velocity. The resultant velocity (rather than the flow rate in individual channels) can be used to predict the path selection of a vesicle in low capillary number. In addition, the residence time of vesicle is decided by average velocity of each channel.