Abstract
A microfluidic system, which integrates sample pretreatment, transportation, reaction, separation and detection on a small chip, can be realized by combining several microfluidic subsystems with specific functions. For the microfluidic systems, the precise handling of small volumes of test reagents is essential. Practical microfluidic applications require an efficient way for both microscale pumping and flow control. Thus, continuous liquid handling is critical to the microfluidic system. For the handling of continuous liquid, this research focuses on the development of microfluidic system chip which is capable of pumping and guiding continuous liquid inside multi-ported microchannels. This thesis is therefore aimed at investigating two microfluidic subsystems — the 1*N micro fluidic switch and the low-power consumption micropump. In the micro fluidic switch design, we introduce a robust approach by utilizing the hydrophobic/hydrophilic properties that generate the capillary force and the barrier pressure to achieve the switching function. The distributed hydrophobic-patch design and the programmable time-sequence bubble actuation are taken advantage for the function of microfluidic switch. The design and implementation of a novel thermal-bubble-actuated 1×N micro flow switch without the need of external macro pumps is presented. The switch mechanism among different microchannels is dominated by controlling the format and the timing of power input that generates the actuation thermal-bubbles. The experimental results successfully demonstrate the switch function in a chip to guide the sample liquid into desired outlet ports via programmable time-sequence control pulses. In the micropump design, a novel actuation mechanism utilizing the roughness gradient surface to achieve the net pumping flow is investigated. This micropump is implemented by taking advantage of the electrolysis actuation, the surface tension effect and the periodic generation of electrolysis-bubble. This proposed micropump design not only achieves a net pumping flow but also resolves the main problem that exists in most electrolytic bubble actuators on the issue of degassing the insoluble gases out of microchannels. This micropump driven by a simple circuit control without mechanical moving parts is suitable for the development of low power-consumption and compact micropumps. Experimental results demonstrate the pumping function of our micropump to continuously push liquid forward based on our roughness gradient design and the periodic electrolytic-bubble generation in the microchannel. Furthermore, experimental results also show that the liquid displacement and the pumping rate could be easily and accurately controlled by adjusting the amplitude and the frequency of the applied voltage. In this study, our 1*N micro fluidic switches and the low-power consumption micropumps have been successfully demonstrated. The theoretical analysis, design, micromachining process, operating principles, and characterization are all described in this thesis. The long-term goal of this work is to integrate the micro fluidic switches and the micropumps into a closed-loop microfluidic system for specific flow guiding, specific flow injection, and precise liquid volume control.