Optically accessible microchannels formed in a single-crystal silicon substrate for studies of blood rheology

An attempt to use microgrooves as blood flow channels in single-crystal silicon is described. Grooves were formed in the (100) crystalline surface by means of photolithography and orientation-dependent etching. This substrate surface was tightly covered with an optically flat glass plate to prevent leakage. This structure was used to microscopically observe flow behavior of blood cells. As a first design of such a cell-flow apparatus, many parallel same-size channels of relatively short length (equivalent diameter 6 microns, length 14.4 microns, number 2600) have been produced to simultaneously measure the total volume flow rate of blood under constant suction. Despite differences in cross-sectional shape and length, the ratio of blood flow velocity to pressure gradient in the channels was comparable with estimates for capillary vessels in vivo. Activated white blood cells blocked the channels, while aggregations of red blood cells showed unexpectedly small resistance to channel transit.