Deterministic microfluidic ratchet based on the deformation of individual cells.

We present a microfluidic ratchet that exploits the deformation of individual cells through microscale funnel constrictions. The threshold pressure required to transport single cells through such constrictions is greater against the direction of taper than along the direction of taper. This physical asymmetry combined with an oscillatory excitation can enable selective and irreversible transport of individual cells in low Reynolds number flow. We devised a microfluidic device to measure the pressure asymmetry across various geometries of funnel constrictions. Using a chain of funnel constrictions, we showed that oscillatory pressure enables ratcheting transport when the pressure amplitude and oscillation period exceeds the threshold required to transport single cells. These experiments demonstrate the potential of using this mechanism to selectively transport biological cells based on their internal mechanics, and the potential to separate cells based on cell morphology or disease state.