Dynamic 3D velocity control with microfluidic device

Many innovative techniques for microscopic manipulation have been developed due to the growing need for precise experimental probes into the world of microorganisms. Here we present a technique rooted deeply in the symmetry granted by the low Reynolds number regime, coupled with a well-chosen device geometry which exploits that symmetry. We show that the use of this pairing allows for the finely-controlled application of pressure to generate microscale 3D flows with symmetry-induced qualities that are purely directional and strain-free, or stationary and purely strainful. Further, we demonstrate that this set of flow modes can be dynamically used to control the velocity for any prescribed motion of microobjects through a fluid. Thus, our apparatus fills a unique need to control microobjects that are sensitive to the mechanical properties of the medium in which they are swimming, and to stimulate them only as experimentally desired.