Uses of parallel fluid flows inside microfluidic channels. (a) Parts of the microfluidic channel can be treated differently by pumping two types of media into the two inlets. In this case, a fluorescent label was added to one of the parallel fluid streams. Flow is from bottom to top; scale bar is 50 . (b) When flow rates are sufficiently low, media reside in the channel long enough for diffusion to take place. This phenomenon can be used to generate and maintain steady gradients in a channel. In this case, three parallel inlet streams were used, containing 0 g/mL, 5 g/mL, and 10 g/mL dextran-rhodamine, respectively. When quantifying the fluorescence over the width of the channel, an almost linear gradient can be observed (white square box in the image, plotted in the inset). (c) By using parallel flows, the middle part of the channel was treated with trypsin. As a result, endothelial cells in the middle of the channel are selectively removed, creating an artificial wound. The closing of this wound can be followed over time to quantify cell migration rates.
