Browsing by Author "Sudarsan, Arjun Penubolu"
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Item Fabrication of masters for microfluidic devices using conventional printed circuit technology(Texas A&M University, 2004-09-30) Sudarsan, Arjun PenuboluThe capability to easily and inexpensively fabricate microfluidic devices with negligible dependence on specialized laboratory equipment continues to be one of the primary forces driving the widespread use of plastic-based devices. These devices are typically produced as replicas of a rigid mold or master incorporating a negative image of the desired structures. The negative image is typically constructed from either thick photoresists or etched silicon substrates using conventional photolithographic fabrication processes. While these micromachining techniques are effective in constructing masters with micron-sized features, the need to produce masters rapidly in order to design, fabricate, and test microfluidic devices, is a major challenge in microfluidic technology. In this research, we use inexpensive photosensitized copper clad circuit board substrates to produce master molds using conventional printed circuit technology. The techniques provide the benefits of parallel fabrication associated with photolithography without the need for cleanroom facilities, thereby offering a degree of speed and simplicity that allows microfluidic master molds to be constructed in approximately 30 minutes in any laboratory. These techniques are used to produce a variety of microfluidic channel networks using PDMS (polydimethylsiloxane) and melt-processable plastic materials.Item Multivortex micromixing: novel techniques using Dean flows for passive microfluidic mixing(Texas A&M University, 2007-04-25) Sudarsan, Arjun PenuboluMixing of fluids at the microscale poses a variety of challenges, many of which arise from the fact that molecular diffusion is the dominant transport mechanism in the laminar flow regime. The unfavorable combination of low Reynolds numbers and high P????clet numbers implies that cumbersomely long microchannels are required to achieve efficient levels of micromixing. Although considerable progress has been made toward overcoming these limitations (e.g., exploiting chaotic effects), many techniques employ intricate 3-D flow networks whose complexity can make them difficult to build and operate. In this research, we show that enhanced micromixing can be achieved using topologically simple and easily fabricated planar 2-D microchannels by simply introducing curvature and changes in width in a prescribed manner. This is accomplished by harnessing a synergistic combination of (i) Dean vortices that arise in the vertical plane of curved channels as a consequence of an interplay between inertial, centrifugal, and viscous effects, and (ii) expansion vortices that arise in the horizontal plane due to an abrupt increase in a conduit??????s cross-sectional area. We characterize these effects using top-view imaging of aqueous streams labeled with tracer dyes and confocal microscopy of aqueous fluorescent dye streams, and by observing binding interactions between an intercalating dye and double-stranded DNA. These mixing approaches are versatile, scalable, and can be straightforwardly integrated as generic components in a variety of lab-on-a-chip systems.