Review: Electric field driven pumping in microfluidic device

Pumping of fluids with precise control is one of the key components in a microfluidic device. The electric field has been used as one of the most popular and efficient nonmechanical pumping mechanism to transport fluids in microchannels from the very early stage of microfluidic technology development. This review presents fundamental physics and theories of the different microscale phenomena that arise due to the application of an electric field in fluids, which can be applied for pumping of fluids in microdevices. Specific mechanisms considered in this report are electroosmosis, AC electroosmosis, AC electrothermal, induced charge electroosmosis, traveling wave dielectrophoresis, and liquid dielectrophoresis. Each phenomenon is discussed systematically with theoretical rigor and role of relevant key parameters are identified for pumping in microdevices. We specifically discussed the electric field driven body force term for each phenomenon using generalized Maxwell stress tensor as well as simplified effective dipole moment based method. Both experimental and theoretical works by several researchers are highlighted in this article for each electric field driven pumping mechanism. The detailed understanding of these phenomena and relevant key parameters are critical for better utilization, modulation, and selection of appropriate phenomenon for efficient pumping in a specific microfluidic application

Flow Through Nanoporous Electrodes in a Microfluidic Fuel Cell

ABSTRACT In this paper we present how advection in the electric double layer (EDL) affects the kinetic performance of electrochemical cells. To accomplish this we use a laminar flow fuel cell model based on the Poisson-NernstPlanck and Frumkin-Butler-Volmer equations. The model contains nonlinear physics with very disparate length scales due to the complex 3-dimensional nature of the nano-porous device. To account for these difficulties, the full mathematical model is solved numerically using a novel numerical algorithm developed based on domain decomposition method. Numerical results show that the presence of an advection flux through nano-pores on the order of the EDL width yields some novel physics that affect the structure of electrode-electrolyte interface. We also show that electrolyte advection within the EDL can be used to enhance the kinetic performance of electrodes in electrochemical cells. In the device presented the peak power density can be increased significantly with flow velocity

Hypoxic behavior in cells under controlled microfluidic environment

Depleted oxygen levels, known as hypoxia, causes considerable changes in the cellular metabolism. Hypoxia-inducible factors (HIF) act as the major protagonist in orchestrating manifold hypoxic responses by escaping cellular degradation mechanisms. These complex and dynamic intracellular responses are significantly dependent on the extracellular environment. In this study, we present a detailed model of a hypoxic cellular microenvironment in a microfluidic setting involving HIF hydroxylation. We have modeled the induction of hypoxia in a microfluidic chip by an unsteady permeation of oxygen from the microchannel through a porous polydimethylsiloxane channel wall. Extracellular and intracellular interactions were modeled with two different mathematical descriptions. Intracellular space is directly coupled to the extracellular environment through uptake and consumption of oxygen and ascorbate similar to cells in vivo. Our results indicate a sharp switch in HIF hydroxylation behavior with changing prolyl hydroxylase levels from 0.1 to 4.0μM. Furthermore, we studied the effects of extracellular ascorbate concentration, using a new model, to predict its accumulation inside the cell over a relevant physiological range. In different hypoxic conditions, the cellular environment showed a significant dependence on oxygen levels in resulting intracellular response. Change in hydroxylation behavior and nutrient supplementation can have significant potential in designing novel therapeutic interventions in cancer and ischemia/reperfusion injuries. The hybrid mathematical model can effectively predict intracellular behavior due to external influences providing valuable directions in designing future experiments

Tsun-kay Jackie Sze Numerical Modeling of Flow Through Phloem Considering Active Loading

Transport through phloem is of significant interest in engineering applications, including self-powered microfluidic pumps. In this paper we present a phloem model, combining protein level mechanics with cellular level fluid transport. Fluid flow and sucrose transport through a petiole sieve tube are simulated using the Nernst-Planck, Navier-Stokes, and continuity equations. The governing equations are solved, using the finite volume method with collocated storage, for dynamically calculated boundary conditions. A sieve tube cell structure consisting of sieve plates is included in a two dimensional model by computational cell blocking. Sucrose transport is incorporated as a boundary condition through a six-state model, bringing in active loading mechanisms, taking into consideration their physical plant properties. The effects of reaction rates and leaf sucrose concentration are investigated to understand the transport mechanism in petiole sieve tubes. The numerical results show that increasing forward reactions of the proton sucrose transporter significantly promotes the pumping ability. A lower leaf sieve sucrose concentration results in a lower wall inflow velocity, but yields a higher inflow of water due to the active loading mechanism. The overall effect is a higher outflow velocity for the lower leaf sieve sucrose concentration because the increase in inflow velocity outweighs the wall velocity. This new phloem model provides new insights on mechanisms which are potentially useful for fluidic pumping in self-powered microfluidic pumps

A Review of Nanofluidic Patents

Abstract: Nanofluidics is a relatively new area of research, generally viewed as the study of the behavior, manipulation, and control of fluids at nanometer (<100 nm) scales. At nanometer scales, fluids exhibit unique physical behaviors which are not present in larger structures. Nanofluidic structures have been successfully applied to technologies including analytical separations and the manipulation of proteins, RNA and DNA. There are increasing numbers of applications emerging, as well as innovative fabrication methods enabling the development of these applications. This review covers some of the recent and significant patents relating to nanofluidic devices and methods. We particularly focus on nanofluidic patents targeted to separate, sense and manipulate biofluids and the presence of macromolecules therein. Moreover, several important fabrication methods are reviewed relating to forming microscale and nanoscale fluidic structures. This study found that a majority of the current nanofluidic patents are intended for bioengineering and biotechnology applications, and none of these patents used gas as a working fluid. To date, the number of nanofluidic patents has been very limited, though it is expected that the nanofluidic area will grow in the near future

Parallel implementation of finite volume based method for isoelectric focusing

A message passing interface (MPI) based parallel simulation algorithm is developed to simulate protein behavior in non-linear isoelectric focusing (IEF). The mathematical model of IEF is formulated based on mass conservation, charge conservation, ionic dissociation-association relations of amphoteric molecules and the electroneutrality condition. First, the concept of parallelism is described for isoelectric focusing, and the isoelectric focusing model is implemented for 96 components: 94 ampholytes and 2 proteins. The parallelisms were implemented for two equations (mass conservation equation and electroneutrality equation). The CPU times are presented according to the increase of the number of processors (1, 2, 4 and 8 nodes). The maximum reduction of CPU time was achieved when four CPUs were employed, regardless of the input components in isoelectric focusing. The speed enhancement was defined for comparison of parallel efficiency. Computational speed was enhanced by maximum of 2.46 times when four CPUs were used with 96 components in isoelectric focusing

DRIVEN FLOWS IN NANOCHANNELS Abstract

I would like to thank my advisor Dr. Prashanta Dutta for the research guidance, patience and understanding during the past four years. He has been making a difference of my life ever since the day I took his undergraduate heat transfer class. I am especially grateful for his great emotional and technical support during my internship period at Technip USA. To write a thesis while being a full time engineer is nothing like doing research while being the teaching assistant at school. Without him, this thesis is not possible. I would also like to thank Washington State University for providing me the financial support. Thirdly, many thanks go to my fellow lab mates for their mental support. In the end, I want to give the greatest appreciation to my parents. iii MOLECULAR DYNAMICS SIMULATION OF ELECTROOSMOTIC & PRESSUR