FIG. 2.
DEP alters cell trajectories within the microfluidic device, leading to changes in the mean collision frequency for cells within a given device geometry. Advection dominates DEP at the obstacles' shoulder, but the reverse is true at the obstacles' leading and trailing edges, where the fluid flow stagnates; as such, a cell's response in the high electric field magnitude region at the leading and trailing edges has the most effect on its trajectory through the array. For medium and large cells (e.g., diameters B and C in this figure), pDEP attracts the cells to the high field magnitude regions near the leading and trailing edges, increasing the mean collision frequency and the time in contact (which supports capture), whereas nDEP (fCM < 0) repels cells from these regions. Likewise, pDEP forces small diameter cells (e.g., diameter A) toward the region of high field magnitude, increasing collision frequency compared to without DEP, but the overall collision frequency remains low. Although nDEP does indeed repel these small cells from the high field magnitude regions, nDEP displaces particle diameter A enough to cause a brief “grazing” cell-obstacle collision, increasing the collision frequency; these grazing events are brief and occur where the shear stress is highest, so capture of these cells is unlikely. (Shown here for an illustrative Δ = 4 μm array).