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Definition from Google: Study of motion of fluids at a micro-scale.  Microfluidic systems comprising nozzles, pumps, reservoirs, mixers, valves, etc., can be used for a variety of applications including drug dispensing, ink-jet printing and general transport of liquid, gases and their mixtures.  Advantages of microfluidics compare to conventional fluidic systems are low fabrication cost, enhancement of analytical performance, low power budget and low consumption of chemicals.

Welcome to Dr. Velev's Microfluidics Page.  On this page you will find helpful information about microfluidics - current/previous research topics, links to other microfluidic information on the web, and published papers dealing with microfluidics (NCSU WRAP access only).

Microfluidics Resources
Developed by Undergraduate Students in Dr. Velev's Group

Microfluidic Cooling Devices for Microprocessors
  Dmitry Fomin
  Bryan James
  Elizabeth Morrell
  Andrea Naranjo
  Jebina Rajbhandari
Abstract:  Please see the website for more details.
Design Project

Fabrication and Study of Simple and Robust Microfluidic Devices
  Ryan Hill
  Jeffrey Millman
Abstract:   This microfluidics research project had the following three main objectives:  (1) to develop simple and robust hands-on technology for laboratory fabrication of microfluidic devices, (2) to observe and characterize fluid flow within microfluidic channels, and (3) to introduce the results in undergraduate student education and help prepare specialists in this emerging technology.  In order to advance the research and development of lab-on-a-chip technologies, colleges and universities must strive to develop innovative ways to prepare upcoming specialists in microfluidics.  The most widely used technology for industrial fabrication of microfluidic devices is photolithography.  This is a complex and costly process that can not be easily implemented in a student laboratory. This project focuses on producing microfluidic devices simply and inexpensively.
Research Paper

Dr. Velev's Microfluidics Class Notes
Lecture Notes 1     • Lecture Notes 2


Useful Internet Resources
Washington University's Microfluidic's Page
An excellent beginner's look at the different aspects of microfluidics.  Contains a simple tutorial of the basics of microfluidics.
Stanford University's Microfluidic's Homepage
Another great university-sponsored webpage.  Contains links to current research projects as well as a brief introduction to microfluidics.
Epigem - Chemical Manufacturing Co.
Epigem is a pace-setter in the field of polymer-based microengineering, providing product development and manufacturing services based on an expanding range of proprietry processes.
Duke's Microfluidics Page
Duke's corresponding website.
Google Search
A quick link to a Google-powered search for the term "microfluidics"
Local Resources
(login required)

Adiabatic Gas-liquid Flow in Microchannels
Abstract:   This article presents a review of adiabatic two-phase flow in minichannels and microchannels. Differences between them are identified and explained based on this review and our own research. Several channels of decreasing diameter were used in our experiments to determine the effect of the channel size on the two-phase flow of nitrogen gas and water. The effect of channel geometry was examined by characterizing the two-phase flow in a circular and square microchannel of similar size. Only slug flow was observed in the microchannels. Four new sub-classes of slug flow were subsequently defined. A new correlation was developed for the time-averaged void fraction data in the microchannels. The two-phase pressure drop in microchannels was predicted by treating the two phases as being separate with a large velocity difference. Regarding the effect of microchannel geometry, the transition boundaries on the two-phase flow regime maps were shifted for the slug flow subcategories.

A Review of Micropumps
Abstract:   We survey progress over the past 25 years in the development of microscale devices for pumping fluids. We attempt to provide both a reference for micropump researchers and a resource for those outside the field who wish to identify the best micropump for a particular application. Reciprocating displacement micropumps have been the subject of extensive research in both academia and the private sector and have been produced with a wide range of actuators, valve configurations and materials. Aperiodic displacement micropumps based on mechanisms such as localized phase change have been shown to be suitable for specialized applications. Electroosmotic micropumps exhibit favorable scaling and are promising for a variety of applications requiring high flow rates and pressures. Dynamic micropumps based on electrohydrodynamic and magnetohydrodynamic effects have also been developed. Much progress has been made, but with micropumps suitable for important applications still not available, this remains a fertile area for future research.

Chip Electrochromatography
Abstract:   Electrochromatography (EC) in microfluidic chips is emerging as an attractive alternative to capillary electrophoresis (CE) for on-chip separations. This review summarizes recent developments in the rapidly growing area of chip electrochromatography with a focus on "column" technologies. Relevant achievements are summarized according to the types of stationary phase used for the separations including open channels, microfabricated structures, and channels packed with beads or containing a porous monolith. The advantages and disadvantages of each, as well as practical aspects of their application, are discussed. The analytical performance of these devices is demonstrated with separations involving various families of compounds mostly in the reversed-phase chromatographic mode.

Fluid Mechanics of Electroosmotic Flow
Abstract:   Electroosmotic flow (EOF) usually accompanies electrophoretic migration of charged species in capillary electrophoresis unless special precautions are taken to supress it. The presence of the EOF provides certain advantages in separations. It is an alternative to mechanical pumps, which are inefficient and difficult to build at small scales, for transporting reagents and analytes on microfluidic chips. The downside is that any imperfection that distorts the EOF profile reduces the separation efficiency. In this paper, the basic facts about EOF are reviewed from the perspective of fluid mechanics and its effect on separations in free solution capillary zone electrophoresis is discussed in the light of recent advances.

Integrated Microfluidic Devices
Abstract:   "With the fundamentals of microscale flow and species transport well developed, the recent trend in microfluidics has been to work towards the development of integrated devices which incorporate multiple fluidic, electronic and mechanical components or chemical processes onto a single chip sized substrate. Along with this has been a major push towards portability and therefore a decreased reliance on external infrastructure (such as detection sensors, heaters or voltage sources)." In this review we provide an in-depth look at the "state-of-the-art" in integrated microfludic devices for a broad range of application areas from on-chip DNA analysis, immunoassays and cytometry to advances in integrated detection technologies for and miniaturized fuel processing devices. In each area a few representative devices are examined with the intent of introducing the operating procedure, construction materials and manufacturing technique, as well as any unique and interesting features.

Principles of droplet electrohydrodynamics for lab-on-a-chip
Abstract:   Electrically controlled droplet-based labs-on-a-chip operate under the principles of elctro-capillarity and dielectrophoreseis.  The microfluidic mechanics of manipulating electrified droplets are complex and not entirely understood.  In this article, we analyse these operating principles, especially electrowetting on dielectric (a form of electro-capillarity) and dielectrophoresis, under a unified framework of droplet electrohydrodynamics.  We differentiate them by their electric origins and their energy transduction mechanisms.  Our study shows that both electrowetting on dielectric and dielectrophoresis are effective for droplet generation and manipulation.  In addition, our study demonstrates: (1) the presence of a wetting contribution to dielectrophoresis; and (2) contact angle reduction is merely an observable consequence of, not a condition for, the occurrence of electrowetting on dielectric.  Simulations are used extensively in this article to illustrate device operation, to expose underlying physics, and to validate our conclusions.  Simulations of electrically driven droplet generation, droplet translocation, droplet fusion, and droplet fission are presented.

Microfluidique et applications biologiques : enjeux et tendances
Abstract:   Microfluidics and biological applications: the stakes and trends. Bioanalytical systems based on microfluidics, also called “lab-on-chips” or “micro Total Analysis Systems (microTAS), are still not very common, but they represent a very challenging and fast-developing area of research. They bear the promise of developing in the near future low cost, powerful and high throughput systems for biological and medical research, in strong synergy with the genomic revolution. They should also provide the basis for simple, low cost and user friendly ‘point of care’ devices, to help the application of the rapid progress of molecular biology and genomics in the fields of diagnosis and biotechnology. In the present review, we recall the biological and medical context in which this research takes place, and we provide a few examples of present challenges and trends, and of devices and technologies presently under development.  Note: entire paper is in French.

Lab-on-a-chip for drug development
Abstract:   Significant advances have been made in the development of micro-scale technologies for biomedical and drug discovery applications. The first generation of microfluidics-based analytical devices have been designed and are already functional. Microfluidic devices offer unique advantages in sample handling, reagent mixing, separation, and detection. We introduce and review microfluidic concepts, microconstruction techniques, and methods such as flow-injection analysis, electrokinesis, and cell manipulation. Advances in micro-device technology for proteomics, sample preconditioning, immunoassays, electrospray ionization mass spectrometry, and polymerase chain reaction are also reviewed.

Manipulating light by microfluidic motion in microstructured optical fibers
Abstract:   We review methods for manipulating light in a microstructured optical fiber by displacing and positioning microfluids along the air-holes of the fiber. To manipulate light propagating in the microstructured optical fiber, we describe two different systems where efficient interaction is obtained between the modal field and microfluids infused in the air-channels. One method involves writing a grating that couples the core to cladding modes whose field distribution is sensitive to the cladding/air-channels interface. The other method consists of tapering the fiber into smaller diameter where the mode field spreads out of the core and into the cladding and becomes sensitive to materials infused into the air-channels. To obtain tunability, microfluidic plugs incorporated into the air-channels of the microstructured optical fiber are displaced along the fiber to overlap with the mode field. In this context we review different applications such as tunable filters/attenuators, polarizers, and periodic gratings.

Microchip-based chemical and biochemical analysis systems
Abstract:   This review focuses on chemical and biochemical analysis systems using pressure-driven microfluidic devices or microchips. Liquid microspace in a microchip has several characteristic features, for example, short diffusion distances, high specific interfacial area and small heat capacity. These characteristics are the key to controlling micro unit operations and constructing new integrated chemical systems. By combining multiphase laminar flow and the micro unit operations, such as mixing, reaction, extraction and separation, continuous flow chemical processing systems are realized in the microchip format. By applying these concepts, several different analysis systems were successfully integrated on a microchip. In this paper, we introduce the microchip-based chemical systems for wet analysis of cobalt ion, multi-ion sensors, immunoassay, and cellular analysis.

Microfabricated devices in biotechnology and biochemical processing
Abstract:   In the past few years, interdisciplinary science and technologies have converged to create exciting challenges and opportunities, which involve a new generation of integrated microfabricated devices. These new devices are referred to as 'lab-on-a-chip' or Micro Total Analysis Systems. Their development involves both established and evolving technologies, which include microlithography, micromachining, Micro Electro Mechanical Systems technology, microfluidics and nanotechnology. This review summarizes the key device subject areas and the basic interdisciplinary technologies, and gives a better understanding of how these technologies can be used to provide appropriate technical solutions to fundamental problems. Important applications for this novel 'synergized' technology in chemical and biotechnological processing, in addition to the application of simulation methods in the development of microfabricated devices, will also be discussed.

Microfluidic systems in proteomics
Abstract:   We present the state-of-the-art in miniaturized sample preparation, immunoassays, one-dimensional and multidimensional analyte separations, and coupling of microdevices with electrospray ionization-mass spectrometry. Hyphenation of these different techniques and their relevance to proteomics will be discussed. In particular, we will show that analytical performances of microfluidic analytical systems are already close to fulfill the requirements for proteomics, and that miniaturization results at the same time in a dramatic increase in analysis throughput. Throughout this review, some examples of analytical operations that cannot be achieved without microfluidics will be emphasized. Finally, conditions for the spreading of microanalytical systems in routine proteomic labs will be discussed.

Microscale separation and analysis
Abstract:   There is a recent and growing interest in microscale separation and analysis, a result of advantages of miniaturization such as rapid separation times, high performance and throughput, reduced costs, and the possibility of system integration and multiplexing. Adopting the concepts of conventional capillary electrophoresis, capillary electrochromatography, micellar electrokinetic chromatography and various sample preparation techniques to microchip format, in conjunction with the integration of different analysis steps into a monolithic system, have opened new levels in performance, functionality and throughput. This review summarizes the recent advances in the field of microfabricated separation devices for genomics, proteomics and high-throughput screening applications, also addressing system integration and micropreparative functionalities.

Introduction: mixing in microfluidics
Abstract:   In this paper we briefly review the main issues associated with mixing at the microscale and introduce the papers comprising the Theme Issue.



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        ©2004 Dr. Orlin Velev and Jeremy Schwartz
        ©2004 Dr. Orlin Velev and Jeremy Schwartz
        Last Updated: 12:24 PM 10/5/2004