Microchannels have been used in the biomedical sciences to produce a well-defined shear field in the vicinity of a reactive planar boundary. In our laboratory, we have used such systems (h∼200 microns) to probe the affinity of circulating white blood cells, human blood platelets, and stem cells for various immobilized adhesion proteins. Computer simulations are used in conjunction with in vitro flow experiments to study the behavior of cells in the context of inflammatory and cardiovascular diseases. These simulations have been instrumental in demonstrating the collective physical phenomena that occur through cell-cell hydrodynamic interactions in dense suspensions of circulating cells. Recently, we have shown that microchannels with molecular micropatterned walls are much more effective at capturing flowing cells from the free stream than equivalent uniform surfaces. These systems have great potential for biotechnology applications such as high-throughput purification of bone marrow-derived stem cells. Finally, I discuss recent results characterizing the spatial patterns of leukocyte adhesion around branched microvessels (D<40 microns) in the live mouse microcirculation, which highlight the need for engineered microchannel systems for better understanding of the transport in these geometries.

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