A new device is used for each flow test, which typically runs for ∼25 minutes. Before a suspension flow test, pure water is first flowed through the microfluidic device at different ∆P while measuring Q. This procedure allows us to determine the hydraulic resistance (R H ) of the devices, and ensure they are in proper working condition. The plot of Q vs. ∆P is linear, and the hydraulic resistance R H is the reciprocal of the slope. The linearity of Q vs.