Numerical Simulations Of Manipulation Of Microparticles By Droplets In Digital Microfluidics

Manipulation of microparticles by droplets is a very useful and important technique for many microfluidics applications. Due to the large specific surface necessary for chemical binding and easy recovery from a dispersion, utilization of nanospheres or microspheres has become more and more popular for different medical, biological, and optical applications. The goal of this research is to understand the mechanism for the manipulation of microparticles by droplets. Dissipative particle dynamics (DPD), which is extensively used to model mesoscale flow phenomena, is applied as the numerical tool for this study. A model for solid microparticles is designed to study the interactions among microparticles, liquid droplets, and solid substrates. A spherical shell is used to represent the microparticle, and the shell surface is packed by dense enough beads to avoid undesired penetration of liquid beads into solid microparticles, conserving the momentum automatically. After that, the interaction between a rigid microparticle and a solid substrate is modeled based on contact mechanics, including adhesion forces, normal forces, and friction forces. After the model for microparticles is built, a baseline case simulating the pickup and transport of a hydrophobic microparticle by a droplet is demonstrated and compared with experimental observations. Then, the flow structures within a droplet containing a hydrophobic microparticle are revealed. With this developed numerical tool, parametric studies are conducted to investigate the effect on the manipulation processes (including pickup, transport, and drop off) of a microparticle by droplet sizes, wetting properties of microparticles, and particle-substrate friction coefficients. The increase of droplet size can speed up the transport of microparticles. However, the increase of particle-substrate friction coefficients can lead to drop-off of a hydrophobic microparticle. The mechanism for the drop-off, or delivery, is analyzed by checking the development of the friction force and driving force on the microparticle during the transport process. The critical velocity, defined as the instantaneous velocity of the microparticle right before the occurrence of delivery, is measured, and it is found that the critical velocity is about same for different sizes of droplets. Based on the numerical results, two different designs, namely passive delivery and active delivery, have been demonstrated to be capable of controlling the location for the delivery of single hydrophobic microparticle without any trap design or external field forces. These numerical results provide a fundamental understanding of interactions among the microparticle, the droplet and the substrate to facilitate the optimal experimental design of digital microfluidic system utilizing microparticles.

Droplet and Digital Microfluidics: Ideation to Implementation is a detailed introduction to the dynamics of droplet and digital microfluidics, also featuring coverage of new methods and applications. The explosion of applications of microelectromechanical systems (MEMS) in recent years has driven demand for expertise and innovation in fluid flow in the microchannels they contain. In this book, detailed descriptions of methods for biological and chemical applications of microfluidics are provided, along with supporting foundational knowledge. In addition, the principles of droplet and digital microfluidics are explained, along with their different applications and governing physics. New additions to the technological knowledgebase that enable advances in droplet and digital microfluidics include machine learning and exciting future avenues for research. Provides step-by-step fabrication, testing, and characterization instructions in each chapter to support implementation Includes explanations of applications and methods in biological and chemical settings Describes the path to automation of digital and droplet microfluidic platforms

The Microfluidics and Nanofluidics Handbook: Two-Volume Set comprehensively captures the cross-disciplinary breadth of the fields of micro- and nanofluidics, which encompass the biological sciences, chemistry, physics and engineering applications. To fill the knowledge gap between engineering and the basic sciences, the editors pulled together key individuals, well known in their respective areas, to author chapters that help graduate students, scientists, and practicing engineers understand the overall area of microfluidics and nanofluidics. Topics covered include Finite Volume Method for Numerical Simulation Lattice Boltzmann Method and Its Applications in Microfluidics Microparticle and Nanoparticle Manipulation Methane Solubility Enhancement in Water Confined to Nanoscale Pores Volume Two: Fabrication, Implementation, and Applications focuses on topics related to experimental and numerical methods. It also covers fabrication and applications in a variety of areas, from aerospace to biological systems. Reflecting the inherent nature of microfluidics and nanofluidics, the book includes as much interdisciplinary knowledge as possible. It provides the fundamental science background for newcomers and advanced techniques and concepts for experienced researchers and professionals.

The application of microfluidics to biotechnology is an exciting new area that has already begun to revolutionize how researchers study and manipulate macromolecules like DNA, proteins and cells in vitro and within living organisms. Now in a newly revised and expanded second edition, the Artech House bestseller, Microfluidics for Biotechnology brings you to the cutting edge of this burgeoning field. Among the numerous updates, the second edition features three entirely new chapters on: non-dimensional numbers in microfluidics; interface, capillarity and microdrops; and digital, two-phase and droplet microfluidics.Presenting an enlightening balance of numerical approaches, theory, and experimental examples, this book provides a detailed look at the mechanical behavior of the different types of micro/nano particles and macromolecules that are used in biotechnology. You gain a solid understanding of microfluidics theory and the mechanics of microflows and microdrops. The book examines the diffusion of species and nanoparticles, including continuous flow and discrete Monte-Carlo methods.This unique volume describes the transport and dispersion of biochemical species and particles. You learn how to model biochemical reactions, including DNA hybridization and enzymatic reactions. Moreover, the book helps you master the theory, applications, and modeling of magnetic beads behavior and provides an overview of self-assembly and magnetic composite. Other key topics include the electric manipulation of micro/nanoparticles and macromolecules and the experimental aspects of biological macromolecule manipulation.

After spending over 12 years developing new microsystems for biotechnology – especially concerned with the microfluidic aspects of these devices – Jean Berthier is considered a leading authority in the field. Now, following the success of his book, Microfluidics for Biotechnology, Dr. Berthier returns to explain how new miniaturization techniques have dramatically expanded the area of microfluidic applications and microsystems into microdrops and digital microfluidics. Engineers interested in designing more versatile microsystems and students who seek to learn the fundamentals of microfluidics will all appreciate the wide-range of information found within Microdrops and Digital Microfluidics. The most recent developments in digital microfluidics are described in clear detail, with a specific focus on the computational, theoretical and experimental study of microdrops. Over 500 equations and more than 400 illustrations Authoritative reporting on the latest changes in microfluidic science, where microscopic liquid volumes are handled as "microdrops" and separately from "nanodrops" A methodical examination of how liquid microdrops behave in the complex geometries of modern miniaturized systems and interact with different morphological (micro-fabricated, textured) solid substrates A thorough explanation of how capillary forces act on liquid interfaces in contact with micro-fabricated surfaces Analysis of how droplets can be manipulated, handled, or transported using electric fields (electrowetting), acoustic actuation (surface acoustic waves), or by a carrier liquid (microflow) A fresh perspective on the future of microfluidics

Digital microfluidics is a new technology that permits manipulation of liquid droplets on an array of electrodes. Using this technology, nanoliter to microliter size droplets of different samples and reagents can be dispensed from reservoirs, moved, split, and merged together. Digital microfluidics is poised to become an important and useful tool for biomedical applications because of its capacity to precisely and automatically carry out sequential chemical reactions. In this thesis, a set of tools is presented to accelerate the integration of digital microfluidics into Lab-on-a-Chip platforms for a wide range of applications.An important contribution in this thesis is the development of three rapid prototyping techniques, including the use of laser printing to pattern flexible printed circuit board (PCB) substrates, to make the technology accessible and less expensive. Using these techniques, both digital and channel microfluidic devices can be produced in less than 30 minutes at a minimal cost. These rapid prototyping techniques led to a new method for manipulating liquid droplets on non-planar surfaces. The method, called All Terrain Droplet Actuation (ATDA), was used for several applications, including DNA enrichment by liquid-liquid extraction. ATDA has great potential for the integration of different physico-chemical environments on Lab-on-a-Chip devices.A second important contribution described herein is the development of a new microfluidic format, hybrid microfluidics, which combines digital and channel microfluidics on the same platform. The new hybrid device architecture was used to perform biological sample processing (e.g. enzymatic digestion and fluorescent labeling) followed by electrophoretic separation of the analytes. This new format will facilitate complete automation of Lab-on-a-Chip devices and will eliminate the need for extensive manual sample processing (e.g. pipetting) or expensive robotic stations.Finally, numerical modeling of droplet actuation on single-plate digital microfluidic devices, using electrodynamics, was used to evaluate the droplet actuation forces. Modeling results were verified experimentally using an innovative technique that estimates actuation forces based on resistive forces against droplet motion. The results suggested a list of design tips to produce better devices. It is hoped that the work presented in this thesis will help introduce digital microfluidics to many of the existing Lab-on-a-Chip applications and inspire the development of new ones.

The application of Micro Electro Mechanical Systems (MEMS) in the biomedical field is leading to a new generation of medical devices. MEMS for biomedical applications reviews the wealth of recent research on fabrication technologies and applications of this exciting technology.The book is divided into four parts: Part one introduces the fundamentals of MEMS for biomedical applications, exploring the microfabrication of polymers and reviewing sensor and actuator mechanisms. Part two describes applications of MEMS for biomedical sensing and diagnostic applications. MEMS for in vivo sensing and electrical impedance spectroscopy are investigated, along with ultrasonic transducers, and lab-on-chip devices. MEMS for tissue engineering and clinical applications are the focus of part three, which considers cell culture and tissue scaffolding devices, BioMEMS for drug delivery and minimally invasive medical procedures. Finally, part four reviews emerging biomedical applications of MEMS, from implantable neuroprobes and ocular implants to cellular microinjection and hybrid MEMS.With its distinguished editors and international team of expert contributors, MEMS for biomedical applications provides an authoritative review for scientists and manufacturers involved in the design and development of medical devices as well as clinicians using this important technology. Reviews the wealth of recent research on fabrication technologies and applications of Micro Electro Mechanical Systems (MEMS) in the biomedical field Introduces the fundamentals of MEMS for biomedical applications, exploring the microfabrication of polymers and reviewing sensor and actuator mechanisms Considers MEMS for biomedical sensing and diagnostic applications, along with MEMS for in vivo sensing and electrical impedance spectroscopy

"Understanding the dynamics of fluids has enabled humans to devise strategies for a myriad of global challenges on a wide range of scales, from nanotechnology to space exploration. By designing and developing systems for manipulating fluid flows, researchers not only constantly optimize many of the conventional approaches to older engineering tasks, but also establish novel methods to tackle new and unsolved problems in science and technology. The advent of microfabrication and microfluidics along with improvements in numerical methodologies and computational power have equipped researchers with unprecedented resources to address these problems. In this work, I aim to investigate two areas where fluids engineering plays a critical role: droplet generation in microfluidic systems and fluid drag reduction of microtextured surfaces. In the first part, I study a relatively new area - droplet generation in microchannels using a high-speed gas phase flow. The use of microdroplets has become ubiquitous in many Lab-on-a-Chip applications ranging from material synthesis to biochemical sensing and testing. Droplet-microfluidics offers a promising approach for controlled generation and manipulation of uniform fluid entities. Despite the versatility and unparalleled control of the droplet formation and transport, the range of droplet microfluidic applications could be greatly expanded by enhancing the per-channel throughput and improving the interaction of droplets and jets with the continuous flow and the microchannel. I investigate a new class of droplet-based systems that uses a high-speed gaseous flow to generate uniform liquid droplets in a flow-focusing geometry. The interaction of the liquid and gas inside the microchannel creates distinct flow patterns. By characterizing the operation extent of resulting flow maps, I then focus on the Dripping and Jetting modes of droplet formation. To improve the performance of the droplet generation, I design and fabricate a three-dimensional microchannel architecture to facilitate formation of a contact-less liquid jet within the air flow inside the microchannel. Droplet generation frequency in this non-planar microchannel increase by at least one order of magnitude in comparison to conventional liquid-liquid droplet systems. The high-speed nature of the flows in this system, however, poses new challenges, namely inertial and compressibility effects on precise control of the jets and droplets. I use numerical simulations to further investigate the flow dynamics and determine the local pressure and velocity of the air inside the microchannel. The knowledge gained from this discussion of the fundamentals and physics is subsequently leveraged in applications that can benefit from this system. I propose a novel technique to use droplets as isolated micro-reactors for absorbing and detecting airborne targets and provide a proof-of-concept for sensing gaseous ammonia using sample digitization with microdroplets. In addition, I present the potential of using gas-liquid droplets as a template for polymer particle fabrication by showing experimental results that demonstrate the generation of calcium alginate microgels purely in air. At the end of this part, I discuss the current challenges in each application and suggest possible solutions towards effective implementation of this system for next generation microfluidic systems in particle synthesis and biochemical diagnostics. In the second part, I revisit a relatively old problem - understanding the dynamics of the laminar flow over textured surfaces for drag reduction applications. Inspired by the natural skins of certain plants and animals, introducing surface corrugations is a proven strategy to reduce the fluid drag and create a superhydrophobic effect, which has potential environmental and economic benefits. I examine the effects of periodic transverse grooves on the laminar boundary layer flow for mid- to high-Reynolds numbers (1000-25000). The width-to-depth aspect ratio of the grooves (AR) is a critical parameter that determines flow behavior near the grooves. Using finite element simulations, I study the local and temporal pressure and velocity fields in rectangular grooves for a wide range of aspect ratios (0.2