FIG. 3.

Gradient of electric field squared $\nabla {\left|E\right|}^2$ (dark blue arrows) and velocity of fluid flow u_f (light red arrows) in a device with ((a) and (c)) 100 μm pillars and ((b) and (d)) 20 μm pillars, when no cells are present ((a) and (b)) and when one cell is already trapped ((c) and (d)). Insulating pillars are shaded with yellow and cells with light blue. Log values of both vectors are plotted however they are scaled arbitrarily (not to compare size of $\nabla {\left|E\right|}^2$ and u_f) while the same scale is used in all panels. If a cell is already trapped in front of a pillar the next cells will be exposed to different forces. In front of a large 100 μm pillar there is enough space that cells can form a chain, while in front of a small 20 μm pillar the balance of DEP and drag force is different and cells are unlikely to form a chain.