Chaotic Mixer for Microchannels
25 Jan 2002-Science (American Association for the Advancement of Science)-Vol. 295, Iss: 5555, pp 647-651
TL;DR: This work presents a passive method for mixing streams of steady pressure-driven flows in microchannels at low Reynolds number, and uses bas-relief structures on the floor of the channel that are easily fabricated with commonly used methods of planar lithography.
Abstract: It is difficult to mix solutions in microchannels. Under typical operating conditions, flows in these channels are laminar—the spontaneous fluctuations of velocity that tend to homogenize fluids in turbulent flows are absent, and molecular diffusion across the channels is slow. We present a passive method for mixing streams of steady pressure-driven flows in microchannels at low Reynolds number. Using this method, the length of the channel required for mixing grows only logarithmically with the Pe «clet number, and hydrodynamic dispersion along the channel is reduced relative to that in a simple, smooth channel. This method uses bas-relief structures on the floor of the channel that are easily fabricated with commonly used methods of planar lithography.
Citations
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TL;DR: A review of the physics of small volumes (nanoliters) of fluids is presented, as parametrized by a series of dimensionless numbers expressing the relative importance of various physical phenomena as mentioned in this paper.
Abstract: Microfabricated integrated circuits revolutionized computation by vastly reducing the space, labor, and time required for calculations. Microfluidic systems hold similar promise for the large-scale automation of chemistry and biology, suggesting the possibility of numerous experiments performed rapidly and in parallel, while consuming little reagent. While it is too early to tell whether such a vision will be realized, significant progress has been achieved, and various applications of significant scientific and practical interest have been developed. Here a review of the physics of small volumes (nanoliters) of fluids is presented, as parametrized by a series of dimensionless numbers expressing the relative importance of various physical phenomena. Specifically, this review explores the Reynolds number Re, addressing inertial effects; the Peclet number Pe, which concerns convective and diffusive transport; the capillary number Ca expressing the importance of interfacial tension; the Deborah, Weissenberg, and elasticity numbers De, Wi, and El, describing elastic effects due to deformable microstructural elements like polymers; the Grashof and Rayleigh numbers Gr and Ra, describing density-driven flows; and the Knudsen number, describing the importance of noncontinuum molecular effects. Furthermore, the long-range nature of viscous flows and the small device dimensions inherent in microfluidics mean that the influence of boundaries is typically significant. A variety of strategies have been developed to manipulate fluids by exploiting boundary effects; among these are electrokinetic effects, acoustic streaming, and fluid-structure interactions. The goal is to describe the physics behind the rich variety of fluid phenomena occurring on the nanoliter scale using simple scaling arguments, with the hopes of developing an intuitive sense for this occasionally counterintuitive world.
4,044 citations
TL;DR: An overview of flows in microdevices with focus on electrokinetics, mixing and dispersion, and multiphase flows is provided, highlighting topics important for the description of the fluid dynamics: driving forces, geometry, and the chemical characteristics of surfaces.
Abstract: Microfluidic devices for manipulating fluids are widespread and finding uses in many scientific and industrial contexts. Their design often requires unusual geometries and the interplay of multiple physical effects such as pressure gradients, electrokinetics, and capillarity. These circumstances lead to interesting variants of well-studied fluid dynamical problems and some new fluid responses. We provide an overview of flows in microdevices with focus on electrokinetics, mixing and dispersion, and multiphase flows. We highlight topics important for the description of the fluid dynamics: driving forces, geometry, and the chemical characteristics of surfaces.
3,307 citations
Cites background from "Chaotic Mixer for Microchannels"
...For example, for straight ridges, the off-diagonal terms ofΛ are (K‖−K⊥) sinφ cosφ, where the termsα2K‖ andα2K⊥ are corrections to the hydrodynamic conductances parallel and perpendicular to the grooves (Stroock et al. 2002b)....
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...Properly designed three-dimensional flows can achieve this reduction; reduced dispersion was demonstrated with the herringbone mixer (Section 3.3) relative to an unmixed flow (Stroock et al. 2002a)....
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...We focus primarily on EOFs, and the electric generation and control of flows in microsystems....
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...…Description of Three-Dimensional Flow in Patterned Channels We next consider in more detail the role of patterned surface topography for pressure-driven flow in a channel of average heighth and widthw >> h (Stroock et al. 2002b, Ajdari 2002) and focus on the main physical and scaling ideas....
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...In a channel with sidewalls, the transverse slip flow establishes a transverse pressure gradient similar to a lid-driven cavity (Stroock et al. 2002b) (see the inset of Figure 6)....
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TL;DR: This Account summarizes techniques for fabrication and applications in biomedicine of microfluidic devices fabricated in poly(dimethylsiloxane) (PDMS).
Abstract: This Account summarizes techniques for fabrication and applications in biomedicine of microfluidic devices fabricated in poly(dimethylsiloxane) (PDMS). The methods and applications described focus on the exploitation of the physical and chemical properties of PDMS in the fabrication or actuation of the devices. Fabrication of channels in PDMS is simple, and it can be used to incorporate other materials and structures through encapsulation or sealing (both reversible and irreversible).
2,490 citations
TL;DR: This paper describes the compatibility of poly(dimethylsiloxane) (PDMS) with organic solvents; this compatibility is important in considering the potential of PDMS-based microfluidic devices in a number of applications, including that of microreactors for organic reactions.
Abstract: This paper describes the compatibility of poly(dimethylsiloxane) (PDMS) with organic solvents; this compatibility is important in considering the potential of PDMS-based microfluidic devices in a number of applications, including that of microreactors for organic reactions. We considered three aspects of compatibility: the swelling of PDMS in a solvent, the partitioning of solutes between a solvent and PDMS, and the dissolution of PDMS oligomers in a solvent. Of these three parameters that determine the compatibility of PDMS with a solvent, the swelling of PDMS had the greatest influence. Experimental measurements of swelling were correlated with the solubility parameter, δ (cal1/2 cm-3/2), which is based on the cohesive energy densities, c (cal/cm3), of the materials. Solvents that swelled PDMS the least included water, nitromethane, dimethyl sulfoxide, ethylene glycol, perfluorotributylamine, perfluorodecalin, acetonitrile, and propylene carbonate; solvents that swelled PDMS the most were diisopropylam...
2,370 citations
TL;DR: The developing world does not have access to many of the best medical diagnostic technologies; they were designed for air-conditioned laboratories, refrigerated storage of chemicals, constant supply of calibrators and reagents, stable electrical power, highly trained personnel and rapid transportation of samples.
Abstract: The developing world does not have access to many of the best medical diagnostic technologies; they were designed for air-conditioned laboratories, refrigerated storage of chemicals, a constant supply of calibrators and reagents, stable electrical power, highly trained personnel and rapid transportation of samples. Microfluidic systems allow miniaturization and integration of complex functions, which could move sophisticated diagnostic tools out of the developed-world laboratory. These systems must be inexpensive, but also accurate, reliable, rugged and well suited to the medical and social contexts of the developing world.
1,920 citations
References
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TL;DR: Fabrication of microfluidic devices in poly(dimethylsiloxane) (PDMS) by soft lithography provides faster, less expensive routes to devices that handle aqueous solutions.
Abstract: Microfluidic devices are finding increasing application as analytical systems, biomedical devices, tools for chemistry and biochemistry, and systems for fundamental research. Conventional methods of fabricating microfluidic devices have centered on etching in glass and silicon. Fabrication of microfluidic devices in poly(dimethylsiloxane) (PDMS) by soft lithography provides faster, less expensive routes than these conventional methods to devices that handle aqueous solutions. These soft-lithographic methods are based on rapid prototyping and replica molding and are more accessible to chemists and biologists working under benchtop conditions than are the microelectronics-derived methods because, in soft lithography, devices do not need to be fabricated in a cleanroom. This paper describes devices fabricated in PDMS for separations, patterning of biological and nonbiological material, and components for integrated systems.
3,344 citations
Book•
01 May 1989
TL;DR: In this article, the authors present a list of frequently used symbols for chaotic flows and their application in different types of chaotic flows, such as mixing and chaos in two-dimensional time-periodic flows, three-dimensional and open flows, and Hamiltonian systems.
Abstract: Preface Acknowledgments 1. Introduction 2. Flow, trajectories and deformation 3. Conservation equations, change of frame, and vorticity 4. Computation of stretching and efficiency 5. Chaos in dynamical systems 6. Chaos in Hamiltonian systems 7. Mixing and chaos in two-dimensional time-periodic flows 8. Mixing and chaos in three-dimensional and open flows 9. Epilogue: diffusion and reaction in lamellar structures and microstructures in chaotic flows Appendix List of frequently used symbols References Author index Subject index.
2,107 citations
"Chaotic Mixer for Microchannels" refers background in this paper
...In a steady chaotic flow, the stretching and folding of volumes of the fluid proceed exponentially as a function of the axial distance traveled by the volume: Dr 5 l exp(2Dy/l), where the initial transverse distance is taken to be l, and l is a characteristic length determined by the geometry of trajectories in the chaotic flow (11, 12)....
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...1 cm) (12); mixing on microscales remains difficult....
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TL;DR: A device was developed that uses microfabricated fluidic channels, heaters, temperature sensors, and fluorescence detectors to analyze nanoliter-size DNA samples to facilitate the use of DNA analysis in applications such as rapid medical diagnostics and point-of-use agricultural testing.
Abstract: A device was developed that uses microfabricated fluidic channels, heaters, temperature sensors, and fluorescence detectors to analyze nanoliter-size DNA samples. The device is capable of measuring aqueous reagent and DNA-containing solutions, mixing the solutions together, amplifying or digesting the DNA to form discrete products, and separating and detecting those products. No external lenses, heaters, or mechanical pumps are necessary for complete sample processing and analysis. Because all of the components are made using conventional photolithographic production techniques, they operate as a single closed system. The components have the potential for assembly into complex, low-power, integrated analysis systems at low unit cost. The availability of portable, reliable instruments may facilitate the use of DNA analysis in applications such as rapid medical diagnostics and point-of-use agricultural testing.
1,486 citations
TL;DR: A three-dimensional serpentine microchannel design with a "C shaped" repeating unit is presented in this paper as a means of implementing chaotic advection to passively enhance fluid mixing.
Abstract: A three-dimensional serpentine microchannel design with a "C shaped" repeating unit is presented in this paper as a means of implementing chaotic advection to passively enhance fluid mixing. The device is fabricated in a silicon wafer using a double-sided KOH wet-etching technique to realize a three-dimensional channel geometry. Experiments using phenolphthalein and sodium hydroxide solutions demonstrate the ability of flow in this channel to mix faster and more uniformly than either pure molecular diffusion or flow in a "square-wave" channel for Reynolds numbers from 6 to 70. The mixing capability of the channel increases with increasing Reynolds number. At least 98% of the maximum intensity of reacted phenolphthalein is observed in the channel after five mixing segments for Reynolds numbers greater than 25. At a Reynolds number of 70, the serpentine channel produces 16 times more reacted phenolphthalein than a straight channel and 1.6 times more than the square-wave channel. Mixing rates in the serpentine channel at the higher Reynolds numbers are consistent with the occurrence of chaotic advection. Visualization of the interface formed in the channel between streams of water and ethyl alcohol indicates that the mixing is due to both diffusion and fluid stirring.
1,218 citations
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TL;DR: A wide range of new lead finding and lead optimization opportunities result from novel screening methods by NMR, which are the topic of this review article.
Abstract: In recent years, tools for the development of new drugs have been dramatically improved. These include genomic and proteomic research, numerous biophysical methods, combinatorial chemistry and screening technologies. In addition, early ADMET studies are employed in order to significantly reduce the failure rate in the development of drug candidates. As a consequence, the lead finding, lead optimization and development process has gained marked enhancement in speed and efficiency. In parallel to this development, major pharma companies are increasingly outsourcing many components of drug discovery research to biotech companies. All these measures are designed to address the need for a faster time to market. New screening methodologies have contributed significantly to the efficiency of the drug discovery process. The conventional screening of single compounds or compound libraries has been dramatically accelerated by high throughput screening methods. In addition, in silico screening methods allow the evaluation of virtual compounds. A wide range of new lead finding and lead optimization opportunities result from novel screening methods by NMR, which are the topic of this review article.
803 citations