Research And Application On Planar PDMS Microvalve And Micropump For Microfluidic System

Microfluidic systems are such miniature systems that are able to precisely manipulate fluid in the microscale (1μm～1 mm) and automatibly perform the whole biological and chemical analysis process in only one miniature chip. They have broad applications in various fields, representing the development direction of the analytical equipments toward miniaturization, integration, portability. Among microfulidic systems, microvalves and micropumps are of the flow control components capable of precise and safe transportation of minute volumes of reagents, which are essentially important for the microfluidic manipulaiton, having found extensive application in micro-fuel cells, micro-drug dispense and delivery system, micro-computer CPU cooling system, micro-satellite propulsion system, and other biological and chemical analysis fields.Currently, mechinal microvalves and micropumps have gained considerable attention, and various kinds of such microvlaves and micropumps have been reported. However, current mechanical microvalves and micropumps are limited due to the following reasons:(1) they are commonly fabricated from silicon, having complicated fabrication process and high fabrication cost. (2) The structures of current microvalves and micropumps usually include non-planar multilayer check-valve congfiguration, complicating the design and fabrication process. More importantly, the non-planar structures of these devices have proven difficult to integrate with other microfluidic components. To address these issues, this paper, with use of polymer poly(dimethylsiloxane) (PDMS) as main material, develops novel planar PDMS microvalve and micropump devices to simplify the structure and fabrication, which not only allow for simple design and easy system integration, but also have advantages of low cost and improved performance.The main results and achivements of the paper are shown as following:1. Develop and fabricate a novel planar PDMS microvalve with use of zero-gap in-contact flap-stopper configuration, which not only allows for simple structure and fabrication process, but also results in reduced valve leakage, enhanced ratio of floward and reverse flow, and efficient fluid regulation. For the fabrication of the planar microvalve. the involved SU-8 molding technique and PDMS demolding fabrication process were investigated and optimized. Morever, a special clamping sandwich molding technique was exploited to obtain the in-contact flap-stoppoer based valve configuration. The performance of the microvalve has been characterized by study of its forward and reverse flow operation. The test results demonstrate the valve has virtually no reverse flow with a minute reverse flow down only to 0.9 nL/min. and a large diodity (i.e. the ratio of floward and reverse flow) up to 2.0×105, indicating its minimized reduced leakage and high reliability.2. Incorporating the zero-gap in-contact planar microvalve into the micropump, we further develop in-plane PDMS micropump, realizing the integration of the microvalve, pump chamber, and microchannel into one single PDMS layer, which not only allows for simple micropump design and fabrication process, but also efficiently prevents the leakage flow during the pump operation, and thus achieve continuous and one-way pumping flow. To investigate the dynamic operation of the planar micrdpump, a theoretic dynamic model for the planar micropump is developed by considering the coupled ineteraction between the pump membrane and fluid flow of the planar micropump, and verified its utility by experimental investigation, providing scientific insight on the dynamic behavior of the micropump.3. To satisfy the fluidic requirements of the micrfluidic injection anlysis systems (flow rate>1μL/min and backpressure>10 kPa) and micro-nano biological-chemical anlysis systems (flow rate<1μL/min, flow resolution 1～10 nL), this paper further developes pneumatic and electromagnetic planar PDMS micropumps. The principle, design and fabrication of the micropumps are investigated and optimized. Systematic experimental characterization of the micropumps has been performed in terms of the frequency response of the pumping flow rate with respect to varied factors including device geometry (e.g.chamber height) and operating parameters (e.g. pneumatic driving pressure, electromagnetic driving current, and backpressure). The experimental results demonstrate that the pneumatic micropump is able to produce a maximaml flow rate of 41μL/min, and a large backpressure up to 25 kPa, achieving the international advanced research level (the current reported maximal backpressure of similar micropumps is 20 kPa), and satisfying the requirement of the micrfluidic injection anlysis system. For the electromagnetic micropump chacterization, it demonstrates it could achieve an excellent flow rate accuracy of 0.15μL/min and a refined flow resolution down to 1 nL per stroke, promising its potential application in the micro-nano biological-chemical anlysis system.4. Based on the efficient flow regulation of the zero-gap in-contact planar microvalve, a novel microfluidic brain drug delivery prototype system consisting of the planar microvlave, dispense channel and delivery channel has been further developed for neurobiological studies. The performace of its prototype system has been systemically characterized in terms of its dispensed and delivered drug volume under varying pneumatic pressures and pulse duration. The test results demonstrate that the microfluidic device is capable of develivering a well-defined 10-30 nL volumes of drug solution within time pulses 50 ms in duration. Furthermore, in-vitro pulsatile delivery into mouse brain tissue using this device has also been performed at controlled drug volumes, demonstrating the potentially wide application of this microfluidic device in various neurobiological studies.