2.2 Planar (XY) Mixing Evaluation
To demonstrate the mixing produced by active posts at the macroscale, we have developed planar and axial mixing assays wherein a colored liquid is added to a chamber/well containing a clear liquid and the time required to mix the two is calculated. Each well within the microwell plate was filled with a clear 1% solution of Triton X-100 (Thermo Scientific™ 85111). Afterward, a diluted blue food dye solution was prepared (McCormick) and a volume of 4 µL was delivered via pipet to the well. The 4-well chip was then placed over a 1-inch drive magnet (120 mT). At this time, the drive system was engaged at the pre-determined rpm (3000, 6000, 9000), or left off in the case of diffusion. Videos of the four independent mixing wells driven simultaneously with identical drive conditions were captured using LCD digital microscope. The data collected via mixing video analysis was analyzed using the relative mixing index (RMI) as outlined in Hashmi, 2014 [14]. A computer program was written to pull in each frame of a video, select the appropriate ROI, and perform the analysis for each well in the frame. For this study, the threshold for a mixed state was set at an RMI of 0.85. The resulting graphs show the average RMI for each independent drive speed evaluation (n=4).