Particle Migration and Focusing in Inertial Microfluidic Flows

The behavior of confined particles in microchannels at moderate Reynolds number has received much attention in recent years and has developed into a new area of research named “inertial microfluidics". This interest has been motivated by the development of high-throughput tools for the manipulation of bioparticles as a precursor for bio-analytic assays. However, a crucial first step towards developing these tools is understanding how particles are transported and localized in confined channels. Here I discuss how the interplay between axial and lateral flow in both a porous and curved microchannel results in non-trivial lateral migration and focusing of finite sized particles. To understand this behavior, I numerically explore this interplay by computing the lateral forces on a neutrally buoyant spherical particle that is subject to both inertial and secondary forces over a range of experimentally relevant particle sizes and channel Reynolds numbers. Interestingly, the lateral forces on the particles in both cases are well represented across a wide range of flow configurations using a simple perturbation based model. The representation of forces in this manner significantly reduces the complexity and time required to predict the migration of inertial particles in microfluidic channels. Finally, I experimentally validate this model and demonstrate how these moderate Reynolds number flows can be used to selectively enrich rare cells in a heterogeneous suspension