Passive Micromixers

Micro-total analysis systems and lab-on-a-chip platforms are widely used for sample preparation and analysis, drug delivery, and biological and chemical syntheses. A micromixer is an important component in these applications. Rapid and efficient mixing is a challenging task in the design and development of micromixers. The flow in micromixers is laminar, and, thus, the mixing is primarily dominated by diffusion. Recently, diverse techniques have been developed to promote mixing by enlarging the interfacial area between the fluids or by increasing the residential time of fluids in the micromixer. Based on their mixing mechanism, micromixers are classified into two types: active and passive. Passive micromixers are easy to fabricate and generally use geometry modification to cause chaotic advection or lamination to promote the mixing of the fluid samples, unlike active micromixers, which use moving parts or some external agitation/energy for the mixing. Many researchers have studied various geometries to design efficient passive micromixers. Recently, numerical optimization techniques based on computational fluid dynamic analysis have been proven to be efficient tools in the design of micromixers. The current Special Issue covers new mechanisms, design, numerical and/or experimental mixing analysis, and design optimization of various passive micromixers

Electrohydrodynamic focusing and light propagation in 2-dimensional microfluidic devices for preconcentration of low abundance bioanalytes

This thesis presents work on electrohydrodynamic focusing (EHDF) and photon transmission to aid the development of species preconcentration and identification. EHDF is an equilibrium focusing method, where a target ion becomes stationary under the influence of a hydrodynamic force opposed by an electromigration force. To achieve this one force must have a non-zero gradient. In this research a novel approach of using a 2-dimensional planar microfluidic device is presented with an open 2D-plane space instead of conventional microchannel system. Such devices can allow pre-concentration of large volume of species and are relatively simple to fabricate. Fluid flow in these systems is often very complex making computer modelling a very useful tool. In this research, results of newly developed simulations using COMSOL Multiphysics® 3.5a are presented. Results from these models were compared to experimental results to validate the determined flow geometries and regions of increased concentration. The developed numerical microfluidic models were compared with previously published experiments and presented high correspondence of the results. Based on these simulations a novel chip shapes were investigated to provide optimal conditions for EHDF. The experimental results using fabricated chip exceeded performance of the model. A novel mode, named lateral EHDF, when test substance was focused perpendicularly to the applied voltage was observed in the fabricated microfluidic chip. As detection and visualisation is a critical aspect of such species preconcentration and identification systems. Numerical models and experimental validation of light propagation and light intensity distribution in 2D microfluidic systems was examined. The developed numerical mode of light propagation was used to calculate the actual light path through the system and the light intensity distribution. The model was successfully verified experimentally in both aspects, giving results that are interesting for the optimisation of photopolymerisation as well as for the optical detection systems employing capillaries

A PDMS Sample Pretreatment Device for the Optimization of Electrokinetic Manipulations of Blood Serum

This project encompasses the design of a pretreatment protocol for blood serum and adaption of that protocol to a microfluidic environment in order to optimize key sample characteristics, namely pH, conductivity, and viscosity, to enable on-chip electrokinetic separations. The two major parts of this project include (1) designing a pretreatment protocol to optimize key parameters of the sample solution within a target range and (2) designing /fabricating a microchip that will effectively combine the sample solution with the appropriate buffers to replicate the same bench-scale protocol on the micro-scale. Biomarker detection in complex samples such as blood necessitates appropriate sample “pretreatment” in order for specific markers to be isolated through subsequent separations. This project, though using conventional mixing techniques and buffer solutions, is one of the first to observe the effects of the combination of micro-mixing and sample pretreatment in order to create an all-in-one “pretreatment chip”. Using previous literature related to capillary electrophoresis, a bench-scale pretreatment protocol was developed to tune these parameters to an optimal range. A PDMS device was fabricated and used to combine raw sample with specific buffer solutions. Off-chip electrodes were used to induce electrokinetic micro-mixing in the mixing chamber, where homogeneous analyte mixing was achieved in less than one second using an 800V DC pulse wave. Ultimately, we wish to incorporate this device with pre-fabricated electrokinetic devices to optimize certain bioseparations

Microscale methods to investigate and manipulate multispecies biological systems

The continuing threats from viral infectious diseases highlight the need for new tools to study viral interactions with host cells. Understanding how these viruses interact and respond to their environment can help predict outbreaks, shed insight on the most likely strains to emerge, and determine which viruses have the potential to cause significant human illness. Animal studies provide a wealth of information, but the interpretation of results is confounded by the large number of uncontrolled or unknown variables in complex living systems. In contrast, traditional tissue culture approaches have provided investigators a valuable platform with a high degree of experimental control and flexibility, but the static nature of flask-based cell culture makes it difficult to study viral evolution. Serial passaging introduces un-physiological perturbations to cell and virus populations by drastically reducing the number of species with each passage. Low copy, high fitness viral variants maybe eliminated, while in vivo these variants would be essential in determining the virus’ evolutionary fate. Bridging technologies are urgently needed to mitigate the unrealistic dynamics in static flask-based cultures, and the complexity and expense of in vivo experiments. This thesis details the development of a continuous perfusion platform capable of more closely mimicking in vivo cell-virus dynamics, while surpassing the experimental control and flexibility of standard cell culture. First, a microfluidic flow through acoustic device is optimized to enable efficient and controllable separation of cells and viruses. Repeatable isolation of cell and virus species is demonstrated with both a well-characterized virus, Dengue Virus (DENV), and the novel Golden Gate Virus. Next, a platform is built around this device to enable controllable, automated, continuous cell culture. Beads are used to assess system performance and optimize operation. Subsequently, the platform is used to culture both murine hybridoma (4G2) and human monocyte (THP-1) cell lines for over one month, and demonstrate the ability to manipulate population dynamics. Finally, we use the platform to establish a multispecies culture with THP-1 cells and Sindbis Virus (SINV). This work integrates distinct engineering feats to create a platform capable of enhancing existing cell virus studies and opening the door to a variety of high-impact investigations

Acoustic Standing Wave Manipulation of Particles and Cells in Microfluidic Chips

The rise of MEMS and µTAS techniques has created a whole new family of microfluidic devices for a wide range of chemical and biomedical analyses to be performed on small Lab-on-a-chip platforms. The operations often include small samples of particle or cell suspensions on which separation, mixing, trapping or sorting is performed. External fields and forces are used for these operations, and this thesis is specifically focused the development of ultrasonic standing wave technology and the use of acoustic force fields to perform bioanalytical unit operations. The combination of acoustic standing waves and the laminar flow in microfluidics has proven to be well suited for performing particle and cell separation. The fundamental acoustic separator used in this thesis consists of a microfluidic flow channel with a three way flow splitter (trifurcation) in the end of the channel. An acoustic standing wave field is applied to the main flow channel by attaching the transducer underneath the chip. The acoustic standing wave is however obtained perpendicular to the axial propagation of the wave field and the direction of the flow. The half wavelength resonance affects rigid particles or cells driving them into the acoustic pressure node while liquid spheres having other density and compressibility properties may move to the pressure antinode. This enables acoustic separation of different particle types. Blood has proven to be very suitable for acoustic cell manipulation. An application where lipid particles can be removed acoustically from shed blood from open heart surgery is demonstrated. An application for acoustic plasmapheresis is also shown where high quality blood plasma is generated. Different separator designs, device material, and the influence of the separation channel cross-section design are also investigated

Design, test and biological validation of microfluidic systems for blood plasma separation

Sample preparation has been described as the weak link in microfluidics. In particular, plasma has to be extracted from whole blood for many analysis including protein analysis, cell-free DNA detection for prenatal diagnosis and transplant monitoring. The lack of suitable devices to perform the separation at the microscale means that Lab On Chip (LOC) modules cannot be fully operated without sample preparation in a full-scale laboratory. In order to address this issue, blood flow in microchannels has been studied, and red blood cells behaviours in different geometrical environments have been classified. Several designs have been subsequently proposed to exploit some natural properties of blood flow and extract pure plasma without disturbing the cells. Furthermore, a high-level modelling method was developed to predict the behaviour of passive microfluidic networks. Additionally, the technique proposed provides useful guidance over the use of systems in more complex external environments. Experimental results have shown that plasma could be separated from undiluted whole blood in 10μm width microchannels at a flow rate of 2mL/hr. Using slightly larger structures (20μm) suitable for mass-manufacturing, diluted blood can be separated with 100% purity efficiency at high flow rate. An extensive biological validation of the extracted plasma was carried out to demonstrate its quality. To this effect Polymerase Chain Reaction (PCR) was performed to amplify targeted human genomic sequence from cell-free DNA present in the plasma. Furthermore, the influence of the sample dilution and separation efficiency on the amplification was characterised. It was shown that the sample dilution does have an influence on the amplification of house-keeping gene, but that amplification can be achieved even on high diluted samples. Additionally amplification can also be obtained on plasma samples with a range of separation efficiencies from 100% to 84%. In particular, two main points have been demonstrated (i) the extraction of plasma using combination of constrictions and bifurcations, (ii) the biological validation of the extracted plasma

Microfluidics and Nanofluidics Handbook

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

BioMEMS

As technological advancements widen the scope of applications for biomicroelectromechanical systems (BioMEMS or biomicrosystems), the field continues to have an impact on many aspects of life science operations and functionalities. Because BioMEMS research and development require the input of experts who use different technical languages and come from varying disciplines and backgrounds, scientists and students can avoid potential difficulties in communication and understanding only if they possess a skill set and understanding that enables them to work at the interface of engineering and biosciences. Keeping this duality in mind throughout, BioMEMS: Science and Engineering Perspectives supports and expedites the multidisciplinary learning involved in the development of biomicrosystems. Divided into nine chapters, it starts with a balanced introduction of biological, engineering, application, and commercialization aspects of the field. With a focus on molecules of biological interest, the book explores the building blocks of cells and viruses, as well as molecules that form the self-assembled monolayers (SAMs), linkers, and hydrogels used for making different surfaces biocompatible through functionalization. The book also discusses: Different materials and platforms used to develop biomicrosystems Various biological entities and pathogens (in ascending order of complexity) The multidisciplinary aspects of engineering bioactive surfaces Engineering perspectives, including methods of manufacturing bioactive surfaces and devices Microfluidics modeling and experimentation Device level implementation of BioMEMS concepts for different applications. Because BioMEMS is an application-driven field, the book also highlights the concepts of lab-on-a-chip (LOC) and micro total analysis system (μTAS), along with their pertinence to the emerging point-of-care (POC) and point-of-need (PON) applications