High-speed three-dimensional characterization of fluid flows induced by micro-objects in deep microchannels

Bio-inspired studies of micro-objects in microfluidics demand quantitative microflow visualization tools to evaluate their three-dimensional (3D) fluid dynamic performance. Experimental fluid dynamic measurements of bio-hybrid systems are employed when non-traditional small-scales, magnetohydrodynamic coupling and nonlinear material properties are involved. In this study a stereoscopic micro- Particle Image Velocimetry(μPIV) system was developed to characterize instantaneous flow fields induced by (1) a micro-robot (280×200×150 μm3) and (2) self-assembled magnetically actuated artificial cilia (∼50 μm in diameter and 500 μm in depth). A custom built micro jet flow microchannel was tested to provide the quantitative evidence of measurement accuracy with 14% error compared to theoretical solutions in the out-of-plane velocity component. Followed by these verification experiments, instantaneous in-plane spinning motion was analyzed in conjunction with translational movement and out-of-plane rotational movements of the micro-robot to obtain the induced 2D-3C (two-dimension, three-component) fluid velocity data. The second test case investigated the microscale vortical flow structures that were generated by self-assembled magnetically driven artificial cilia. The strength of this 3D micro vortex structure was computed based on the 3D flow measurements. In combination with the asymmetric cyclic motion of the magnetically actuated artificial cilia, it is expected that these structures can generate transverse flow efficiently in 3D, and thus provide a potential alternative for mixing in low Reynolds number flows, analogous to a micromixer. The acquired 3D microflow field, along with the validation tests, further extends the capability of using stereoscopic μPIV technique to evaluate the performance of noninvasive microflow manipulators.