The controlled manipulation of particles from very large volumes of fluid at high throughput is critical for many biomedical, environmental and industrial applications. One promising approach is to use microfluidic technologies in which particles migrate laterally to stable equilibrium positions within a confined channel geometry. Previous studies have been limited to microfluidic flows that are either inertia-dominant or elasticity-dominant. When simultaneously important, inertia and elasticity have been shown to act constructively to stabilize a given flow, but it is unknown whether particle focusing in microchannels can exist when both effects are present in a non-dominant manner. Here we show that upon the addition of micromolar concentrations of hyaluronic acid (HA), the resulting fluid viscoelasticity can be used to control the focal position of bioparticles at Reynolds numbers up to Re ≈ 10,000 (and at Weissenberg numbers up to Wi ≈ 2,000) with corresponding flow rates and particle velocities up to 50 ml.min-1 and 130 m.s-1. We found that it is not secondary flows or shear-thinning in the fluid rheology but rather the presence of viscoelastic normal stresses that drive the deterministic particle migration in the HA solution. Furthermore, the rheological properties of the viscoelastic fluid can be tuned to generate an optimal balance between particle focusing and particle stretching in mammalian cells over a wide range of Reynolds numbers. Our results demonstrate that particle focusing can occur in a previously unexplored flow regime in which both inertia (Re >> 1) and elasticity (Wi >> 1) are present. We anticipate this study to motivate the development of microfluidic technologies capable of high-throughput particle sorting from very large fluid volumes. For example, inertio-elastic focusing may ultimately be used for isolation of tumor cells from bronchoalveolar lavages or removal of floc aggregates within water treatment systems. Moreover, the tunable nature of particle focusing and stretching in mammalian cells offers potential applications in deformability cytometry and intracellular delivery of macromolecules.
Committee: Joel Voldman, Martin Schmidt, Mehmet Toner