Development of Fabrication Platform for Microfluidic Devices and Experimental Study of Magnetic Mixing and Separation

Microfluidics is a new and emerging field that has applications in a myriad of microfluidic industrial applications such as biochemical engineering, analytical processing, biomedical engineering and separation of cells. Microfluidics operations are carried out in microfluidic chips, and the traditional method of fabrication is carried out in a cleanroom. However, this fabrication method is very costly and also requires professional trained personnel. In this thesis, a low-cost fabrication platform was developed based on soft-lithography technique developed to fabricate the microfluidic devices with resolution at microscale. This fabrication method is advantageous and novel because it is able to achieve the microscale fabrication capability with simple steps and lower-level laboratory configuration. In the developed fabrication platform, an array of ultraviolet light was illuminated onto a photoresist film that has a negative photomask with a microfluidic design on it. The photoresist film is then developed, and a silicon polymer of polydimethylsiloxane (PDMS) is chosen to be the material for the device. In this work, the performance and resolution of the fabrication system was evaluated using scanning electron microscopy (SEM), polymer resolution test and light intensity analysis. Based on the success of the development of microfluidics fabrication platform, various experiment of mixing and separation was conducted and studied because the utilization of the microfluidic device for mixing and separation is very valuable in biomedical and chemical engineering. Although there are a lot of applications reported, the precise separation and mixing at microscale still meet some difficulties. Mixing in micromixers is extremely time-consuming and requires very long microchannels due to laminar flow and low Reynolds number. Particle separation is also hard to be achieved because the size of micron bioparticles is very small and thus the force is not strong enough to manipulate their motion. The integration of magnetic field is an active method to strengthen both mixing and separation that has been widely applied in the biomedical industry overcome these difficulties because of its compatibility with organic particles. However, most magnetic mixing and separation use bulky permanent magnets that leave a large footprint or electromagnets that generate harmful Joule heat to organic and bio-particles. In this work, microscale magnet made of a mixture of neodymium powder and polydimethylsiloxane was developed and integrated into microfluidic system to achieve both rapid mixing of ferrofluids and separation of microparticles. Systematic experiments were conducted to discuss the effect of various parameters on the performance of magnetic mixing and separation of microparticles. It was found that channel geometry, flow filed, and magnetic properties will affect the transport phenomena of ferrofluid and microparticles, and thus mixing and separation efficiency. These findings are of great significance for the high throughput sorting of cancer cells and its mixing between drug for therapy treatment