(224i) Vector Separation of Suspended Particles Using an Array of Slanted Open Cavities

We present a microfluidic device that takes advantage of the flow characteristics in a channel in which the bottom surface is patterned with slanted ridges that create open cavities, to passively and continuously fractionate suspended particles based on their size and settling velocity. We exploit the flow that is created along the cavities to induce the vector separation of suspended particles with dimensions comparable to the height of the ridges and that move in the vicinity of the patterned surface. The width and height of the ridges are much smaller than those of the main channel to reduce the effect of recirculation in the bulk. We shall show that two regimes can be distinguished depending on the settling velocity of the particles  compared to their average velocity across the cavities imposed by the fluid flow. When these velocities are similar, heavier particles settle deeper into the open cavities and exhibit larger displacements along these cavities. On the other hand, if sedimentation is negligible, smaller particles are advected by the flow deeper into the cavities and therefore deflect more than larger particles. First, we illustrate the flow characteristics by numerically solving the particle-free flow. We then present experiments separating silica and polystyrene beads of the same and different size. We also show the potential of this method to separate cells showing that  different blood components can be deflected to a different extent. Finally, we discuss the potential versatility of this platform using  force fields other than gravity, e.g., electric, dielectrophoretic, and magnetic, to manipulate the settling velocity of the particles. In particular, we show the enrichment of rare blood cells by depleting magnetically labeled leukocytes.