http://www.mdpi.com/journal/micromachines/special_issues/micromixers/ Dear Colleagues, Micromixer is a key component in a number of microsystems, especially lab-on-a-chip. Micromixers are miniaturized mixing devices for at least two different phases that can be liquids, solids or gases. The structures of a micromixer are fabricated partially or in whole using microtechnology or precision engineering. The characteristic channel size of micromixers is in the sub-millimeter range. Common channel widths are on the order of 100 to 500 μm, while channel length could be a few millimeters or more. The channel height is on the order of the channel width or smaller. The overall volume defined by a micromixer is from microliters to milliliters. Compared with molecular size scale, the length scale and volume scale of micromixers are still very large. This fact leads to two key characteristics of micromixers. First, designing micromixers still relies on manipulating the flow using channel geometry or external disturbances. Secondly, while micromixers bring advantages and new features into chemical engineering, molecular level processes such as reaction kinetics remain almost unchanged. The laminar flow regime poses a challenge to designers of micromixers. New mixing concepts and the optimization of known concepts are the hot research topics in recent years. This special issue aims at attracting and publishing the latest works on micromixers. Nam-Trung Nguyen, Ph.D. Guest Editor {snippet name="submission_info"} http://www.mdpi.com/2072-666X/2/2/179/ This review presents an extensive overview of a large number of microvalve and micropump designs with great variability in performance and operation. The performance of a given design varies greatly depending on the particular assembly procedure and there is no standardized performance test against which all microvalves and micropumps can be compared. We present the designs with a historical perspective and provide insight into their advantages and limitations for biomedical uses. http://www.mdpi.com/2072-666X/2/2/179/ Tue, 24 May 2011 00:00:00 CEST Micromachines 2011-05-24 2 2 Review 179 220 2072-666X Microvalves and Micropumps for BioMEMS 2011-05-24 doi: 10.3390/mi2020179 Anthony K. Au Hoyin Lai Ben R. Utela Albert Folch http://www.mdpi.com/2072-666X/1/2/36/ The performance of micro-mixers is evaluated in terms of deviations from perfectly mixed state and mixing length (i.e., device length required to achieve perfect mixing). Different variations of T-mixer are reported for improved mixing performance, including geometric constrictions/obstacles embedded in the channel wall, heterogeneously charged walls, grooves on channel base, etc. Most of the reported designs provide improved mixing at the expense of reduced flow rate; there exists therefore a tradeoff between mixing and transport. The reduced flow rate, which affects species residence time, is unfortunately not taken into account in most micro-mixing performance analyses. This issue is addressed by the comparative mixing index (CMI), which evaluates mixing performance more appropriately by normalizing the effect of residence time among different designs. In this study, the performance of several mixing strategies are evaluated based on the CMI; these are mixer designs that incorporate (a) physical constrictions, (b) induced charge electro-osmotic (ICEO) effects, and (c) heterogeneously charged walls. The present analysis clearly identifies conditions under which a given mixer design is superior to a T-mixer. http://www.mdpi.com/2072-666X/1/2/36/ Mon, 12 Jul 2010 00:00:00 CEST Micromachines 2010-07-12 1 2 Article 36 47 2072-666X Analysis of Electrokinetic Mixing Techniques Using Comparative Mixing Index 2010-07-12 doi: 10.3390/mi1020036 Jain Yeung Nandakumar http://www.mdpi.com/2072-666X/1/1/19/ We evaluated the dynamic micromixing performances in slanted groove micromixers (SGM) and staggered herringbone micromixers (SHM) and quantitatively compared their differences using concentration vs. channel length profiles obtained from numerical stimulations. It is found that faster and finer mixing took place in the SHM and the chaotic mixing was more effective at locations closer to the grooves; in comparison, slower and coarser mixing occurred throughout the whole channel of the SGM. Subsequently, the concentration profile-based characterization method was demonstrated in hybrid floor-grooved micromixers to study the interaction of SGM and SHM. http://www.mdpi.com/2072-666X/1/1/19/ Mon, 17 May 2010 00:00:00 CEST Micromachines 2010-05-17 1 1 Article 19 33 2072-666X Evaluation of Floor-grooved Micromixers using Concentration-channel Length Profiles 2010-05-17 doi: 10.3390/mi1010019 Du Zhang Yim Lin Cao