Polymer-enabled micro flow control devices for lab-on-a-chip applications

Advances in microelectromechanical systems (MEMS) technology have matured to a point where integration and miniaturization of multiple laboratory processes into a single palm-sized device are possible. The advantages of these lab-on-a-chip type systems, compared with conventional bench-scale systems are wide ranging and include less reagent consumption, faster analysis, high sample throughput, and possibilities for integration and automation. In order to create successful lab-on-a-chip and other microfluidic systems, it is necessary to have the capability of precise control and delivery of fluid flow along the fluid circuit. For practical miniaturized point-of-care biological and chemical systems, it is also highly desirable to develop micro flow control devices with minimal energy consumption.; The focus of this thesis is to develop discrete micro flow control devices that can be potentially integrated into lab-on-a-chip systems to achieve effective flow gating, as well as supply of steady flow by exploiting microstructures either using the large, passive compliance, or realizing with latchability of phase-change polymer materials. A passive microfluidic variable resistor featuring a compliant vertical flap microstructure has been developed and simulated using FEM with fully-coupled fluid-structure interaction (FSI) capability. The variable resistor can function either as a check valve for a unidirectional flow or as a flow regulator to generate a constant flow under a large range of varying inlet pressure from 100-200 kPa. Using similar compliant flap-stopper microstructures, two types of planar check valves have been developed which can shut off reverse flow completely, thus with much higher valving diodicity. A special fabrication technique has been used to fabricate the valve with zero flap-stopper gap. A passive flow stabilization device has also been developed and simulated by a lumped-parameter model. The micro flow stabilizer exploits passive vibrations of compliant polymer membranes, and is able to rectify an upstream fluctuating flow and generate a steady flow with flow stabilization ratio up to 20. In addition, a latchable phase-change actuator using a low-melting-point paraffin wax has been demonstrated that can be used for microvalves in chip-on-a-chip systems with minimal energy consumption. Actuators with and without integrated micro heaters have been fabricated and measured. Experiments show that actuators with integrated heaters have faster flow switching time response.; Individual micro flow control devices has been designed, fabricated and characterized. These flow control devices utilize the large compliance of polymer, and can potentially be used in various lab-on-a-chip applications where supply of steady flow and power-efficient operation is required. These individual microfluidic devices can be readily scaled down to achieve integrated fluid control.