Development of microfluidic systems for biological applications and their transport issues
Microfluidic systems have been an exciting research area with a wide variety of promising biomedical applications. However, many challenging issues are still facing the research community with regard to mechanical as well as biological issues. The goal of this dissertation is to develop novel microfluidic systems targeting biomedical and life sciences applications with detailed investigation of thermal/fluid transport, materials and mechanics, and micromanufacturing processes. For a valveless micropump used for fluid delivery, a theoretical model is derived to analyze a lead zirconate titanate (PZT) microactuator and a system level analytical analysis is carried out for the PZT-actuated micropump. The effects of several important parameters and nondimensional variable groups on the actuator performances are also investigated. For rapid DNA analysis, a continuous-flow polymerase chain reaction (PCR) microchip with regional velocity control is developed. Finite element analysis is conducted to study the temperature uniformity of each reaction zone. A semi-analytical heat transfer model is developed to study heat transfer inside the PCR chip. Fluid velocity in the microchannel is measured using micro-particle image velocimetry (µ-PIV). The PCR chip is successfully amplified 90 base pair DNA sample. To connect a microfluidic device with other devices, novel polydimethysiloxane (PDMS) based interconnects have been fabricated. Microfabrication processes for through-hole type and “┌” type PDMS interconnects of glass and plastic capillary tubing have been developed. Leakage pressure, leakage flow rate, and pull-out force are characterized for these PDMS interconnects bonded to a variety of substrates. Two disposable analysis microchips in PDMS have been developed for protein/DNA detection. An established bead-based fluorescent assays for C-reactive protein (CRP) is used to characterize these chips. The detection limit of a single chamber chip is found to be as low as 0.1ng/ml. To increase detection capacity, a multiplechamber PDMS chip has also been developed. Fluid flow through the multiple-chamber microchip is improved by a back pressure compensation method. This has significantly improved the performances of the microchip.