Investigation of Electroosmotic Flow in Various Microfluidic Structures
Enclosed microfluidic devices provide excellent systems for the study of biological processes such as cell-cell, paracrine, and autocrine signaling systems. By minimizing the fluid volume within the chambers, microfluidic devices diminish the dilution of secreted products which makes the detection of the secreted products a more straightforward task. A major design problem associated with the construction of microfluidic devices for biological research is the need to provide well-controlled fluidic transportation for cells, the nutrients that the cells need, and waste removal. Most precision syringe pumps which can accurately provide low flow rates are expensive and constitute a barrier to experiment design. Electroosmotic pumps could potentially provide a valuable alternative as a low volume flow rate pumping system for many types of microfluidic devices. We have developed a poly(dimethylsiloxane) (PDMS) microfluidic device that incorporates both electroosmotic flow and pressure driven flow. The device is designed to increase the relative strength of the electroosmotic flow (EOF) component of the total flow through the use of an array of small volume parallel pumping channels which provide higher passive resistance to pressure driven flow than a larger volume single-channel EOF pump. Using a novel microfluidic instrumentation device which we call the "Micro Programmable Object Navigation Gadget" (µ-PONG), we investigate how different properties and geometries of the device affect the EOF rate.Â In addition, we demonstrate that fluid flow driven by a small hydraulic pressure head can be completely canceled by an user initiated EOF in the pumping channels which are incorporated into a microfluidic device. The ability to modulate the flow and to create "stop flow" conditions in microfluidic devices is also important for biological research.