Particle Manipulation using Microfluidics

Abstract

The progress made by microfabrication technologies has escalated the interest in particle manipulation on micron scale. Particles are not only limited to solid particles but also include cells, droplets and bubbles. Activities involved in manipulation are trapping, sorting, separation and so on. The devices designed to execute such activities are aimed for a particular application. However, there lies a gap in literature to design an all-in-one device. Microfluidics research carried out at the Laboratory for Aero and Hydrodynamics is currently working on designing such devices which can carry out different manipulation tasks.
This thesis is aimed at designing and fabricating such a device where two particles can be manipulated simultaneously. The application of designing such a device would be to study cell-cell interaction, droplet coalescence and so on. To achieve this, a microfluidic device is designed as a Hele-Shaw flow cell. Since the height-averaged velocity in a Hele-Shaw flow cell is irrotational, analytical solution is possible for such a design. Although a Hele-Shaw flow is viscous flow between two closely spaced plates, it produces same streamline patterns as a 2D ideal flow. This enables the use of basic building blocks of an ideal flow field such as sources, sinks, uniform flow and so on. In this case, sources and sinks are superimposed to get the flow field inside the microfluidic device. The microfluidic device is fabricated using Polydimethylsiloxane (PDMS), a commonly used polymer to fabricate microfluidic devices. The design of the device is validated by comparing experimental flow fields, streamlines and stagnation points to the corresponding analytical solution. Single particle manipulation activities are carried out in the device. This is executed by manually controlling the flow rates or the strength of sources and sinks. Firstly, the particle is trapped at the stagnation point for a certain timespan. Finally, some manipulation activities are carried out using a single particle with the aid of streamlines produced by the sources and sinks.