Applied mechanics and bio-microfluidic applications for open microfluidic systems

Microfluidics is attractive in many aspects and advancement of technology on these micron-scales have led to the development of devices often used in industries such as clinical and forensic analysis; micro-reaction engineering; surface patterning; and optical engineering. Despite its popularity, traditional microfluidic applications however, are known to have large dead volume; awkward chip-to-world interfaces; difficulty in exchanging solutions; and limited parallelization. Recent progresses in open microfluidic systems have shown great potential in addressing the aforementioned limitations. The aim of this thesis is to expand our understanding regarding fluid behaviour and interaction in the micro-domain scale of an open environment. Knowledge obtained through these studies could then be implemented in developing systems involving microfluidic components and bio-microfluidic applications. As a prelude to the main body of work, a basic theoretical framework on the background of microfluidics and the physics of the micro-scale is presented. The research can be divided into two major components, Part I: Open Microchannels and Part II: Microdroplets. These components were then further sub-categorized according to their applications including microfluidic pumping; mixing; liquid transfer; cell lysis; and concentration gradient generation. In all these, an open environment allowing for external interaction and manipulation was implemented. In Part I, flows on open channels and films was investigated. The open structures include a straight open channel defined by a narrow strip of solid surface and a wider structure allowing for multiple inputs and outputs. Computational models were also developed for fluid flow and the findings used to describe the factors affecting the stability of the system in both structures. The system can be seen as either a self-contained open fluidic device, or an open section in an otherwise enclosed system. Following on, the mixing mechanism of a Y-junction open raised channel was examined. The open nature of the channel employed allowed introduction of external shear stresses on the interfacial surface to aid in the mixing process, while maintaining the simplicity of the system as a whole. This mode of mixing provides a versatile platform where alterations can be made to the open system to accommodate mixing without the added complexities. In Part II, investigation was first carried out on two different mechanisms of vertical liquid transfer. The first is through the formation and detachment of a liquid bridge and the second is through the liquid jet formed upon rupture of an encapsulated bubble within a microdroplet. Both mechanisms demonstrated selective transfer of discrete volumes of fluid, a process that will prove useful in many droplet-based microfluidic applications. From the results gathered, the role of the bubble in inducing cell lysis in a controlled and repeatable environment was explored. The fluid jet was then presented as a method capable of causing effective 100% cell lysis of a droplet of suspended cells. Apart from that, a method using microdroplets administered on a planar surface to produce a gradient of droplet concentrations over an array of open wells is presented. The system was tailored to generate concentration gradients in a close quantitative agreement to a two-fold dilution system akin to routine pipetting operations. The findings presented in this thesis are unique in their nature as the methods and applications demonstrated were able to extract the advantages of open microfluidics. Benefits include and are not limited to minimal fabrication and consequently lower production costs involved; small sample volume requirements; selectivity; rapid operation time; and greater control. It is hoped that these results would promote the use of open microfluidics and encourage further exploration of this topic in the future.