We introduce the use of microfabrication techniques to construct on a silicon wafer a synthetic capillary bed with 2.5- to 4-micron (mu)-wide channels. Establishment of a fluid pressure gradient allowed us to observe simultaneously using optical microscopy hundreds of cells flowing through the bed at physiological speeds. We find a large distribution of mobilities among red cells flowing through the structure; smaller channels provide a greater impedance to flow than larger ones, indicating that kinetic drag variations provide the origin of the distribution. The mobility of a particular cell is not correlated with the cell diameter but appears to be inversely correlated with intracellular calcium concentration of the cell, as determined by fluorescence of the calcium-binding dye fluo-3 AM. Also, we are able to use the parallel processing nature of our arrays to observe isolated events where the rigidity of the red cell seems to change suddenly over several orders of magnitude as it blocks a channel in the array.
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