Micro-pillar barriers for guiding, mixing and sorting droplets

Discrete micro-droplet has the huge advantage in microfluidic applications. More flexible manners to manipulate droplet are desired. In this paper, a platform is constructed for droplet manipulation by directing the motion of water-in-oil droplets passively with micro-pillar array. These pillars are embedded inside a microchannel with very low aspect ratio. The pillars are arranged to set up a barrier positioned at an angle to the fluid flow. Main behaviors, such as the velocity along the pillars, the vortex pattern inside the droplet and the offset distance from the last pillar are studied experimentally. The result reveals that the current design is a robust integrated environment for guiding, mixing and sorting droplets compared to previous methods.