Particle Focusing in a Sprial Microchannel Using Viscoelastic Fluids

Particle focusing behavior is important for the development of microfluidic devices used in biomedical diagnostics for cell focusing, sorting, separation, etc. ​Biomedical fluids like blood and DNA solution exhibit non-Newtonian properties. We study viscoelastic PEO (Polyethylene Oxide) to understand particle behavior in these fluids. ​Our objective was to study the focusing behavior of particles in a spiral microchannel under the effects of a non-Newtonian fluid. ​The particles in the microchannel were induced by electrokinetic and pressure-driven flow. Electrokinetic flow increased the electric field from 80V/cm to 140V/cm. Pressure increased the flow from 0.1mL/hr - ​15mL/hr. We tested each Newtonian case, 0 PPM PEO, and a non-Newtonian case (50 PPM PEO). We found that the particles focused better when we increased the electric field or the flow rate. When we added the PEO for the electric field case, we found that it improved focusing in the same direction, causing it to be closer to the outer wall, and that it focused at a lower electric field. When we added PEO for the pressure-driven flow, it also focused on a lower flow rate, but it started focusing on the other side. The 0 PPM case focused on the inner wall, while the 50 PPM PEO case had the particle focusing toward the outer wall; however, as the forces began to balance out, particles started focusing toward the middle of the loop. The addition of PEO causes particles to focus sooner, while still maintaining similar focusing patterns as the Newtonian case.