Fundamentals and applications of particle focusing within non-Newtonian fluids using inertial microfluidic systems

Over the last decades, inertial microfluidics has gained substantial attention due to its capability to control and manipulate particles accurately. However, these inertial forces in Newtonian fluids are not sufficient to efficiently focus small microparticles which limits their applications to larger bioparticles including stem cells, circulating tumor cells and blood cells. To address this inadequacy, recently elasto-inertial microfluidic systems have been introduced as a powerful method to sort smaller microparticles more effectively. These systems can break the restrictions of low-throughput, additional external components, and complex channel designs in Newtonian systems for submicron particle sorting. So far, there have been several studies on the applications and fundamentals of particle migration in non-Newtonian fluids. However, most of them are limited to simple rectangular straight channels, due to the difficulty of fabrication and modeling of particle migration in non-Newtonian fluids within channels with nonlinear cross-sections. Therefore, the main purpose of this research is to study the fundamentals of particle migration in elasto-inertial microfluidic systems as well as introducing new workflows for the fabrication of non-conventional microchannels to not only explore new physics in elasto-inertial systems but to increase the efficiency and effectiveness of the current elasto-inertial devices. To this end, in chapter two, basics and applications of particle migration in non-Newtonian fluids are reviewed and categorized based on the channel structure and design. In chapter four, the physics of elasto-inertial focusing in straight channels of different cross-sections are numerically and experimentally investigated. Then, in chapter five and six, two different Wax and DLP 3D printers for the first time are used to create novel non-conventional straight and curved microchannels suitable for inertial microfluidic applications. We propose new fabrication workflows to easily construct complex channels that are almost impossible or extremely difficult to fabricate with previous microfabrication methods. Finally, in chapter seven, a new design for blood-plasma separation is proposed based on the non-Newtonian property of the blood, Zweifach-Fung effect, and plasma skimming phenomenon. We numerically model several microchannels with different daughter branches and bifurcations to obtain the best combination of flow rate and geometry for plasma extraction. We believe that our proposed fabrication methods and presented fundamentals can pave the way for further research on elasto-inertial systems in more complex channels.