Researchers in the microfluidics community have focused on using microfluidics for lab-on-a-chip applications including biomedical devices, environmental sensors, mixers, and fuel cells with very small footprints over the past few years . Furthermore, hydrodynamic focusing of one laminar stream by another has inspired new approaches for separations, biosensors, and cell analysis . For example, straight diagonal grooves on the top and bottom of the channel are used to wrap the sample fluid with sheath fluid. Passing through more grooves, the sheath fluid moves toward the far side of the sample stream and sample stream becomes focused more toward the center of the channel. The Mixing limitations at low Reynolds numbers have been another area of microfluidics that have received a great deal of attention. Microorganisms experience a very different environment dominated by viscous forces at low Reynolds number that make mixing difficult. They could have a significant contribution to local mixing at cellular scale but their impact on global mixing is not still well understood. The fluid flows generated by the movement of flagella of microorganisms play a central role in nutrient uptake (limited by diffusion) of solutes by single cells and multi-cellular organisms. Microfluidic devices can take advantage of these effects in order to increase mixing in microfluidic channels and to direct material transport using either cell cultures or device geometry.
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