<p>  </p> <p>High-resolution enclosed channels/fibers are highly demanded by different disciplines such as microfluidic channels for chemical synthesis, bioreactors for drug metabolism, magnetic locomotor for drug delivery, and wearable devices for motion detection. However, the current fabrication techniques for enclosed channels/fibers are restricted to a few millimeters in size. Their manufacturing often involves time and energy-consuming multi-step processes with insufficient resolution. In this work, we demonstrate a novel co-flow-enabled fabrication method to resolve the technological restrictions in the fabrication of high-resolution enclosed channels/fibers with efficient production time, controllable morphologies, and high throughput manner.</p> <p>An epoxy-based enclosed microfluidic channel was first built. A non-reactive paraffin oil and a liquid resin were pumped into a 3D-printed co-flow generator and worked as core and shell fluids, respectively. The epoxy resin was cured by external heat stimulus. As a result, the reaction region was limited between the generator wall surface and the boundary of core flow, eliminating the need for precise control over the curing system. The experiment was successfully conducted to cure build resin channel inside copper and resin tubes with good shell thickness.</p> <p>Conductive hollow hydrogel microfibers were also fabricated by this method. Sodium Alginate and Calcium Chloride were chosen as the shell and core flows, respectively. The ionic crosslinking happens at the boundary of two flows and expands outwards across the radial direction. Thus, the diameter of the hollow channel can be easily adjusted by tuning the flow rate and the size of the core flow injection needle. PEDOT: PSS, a conductive polymer, was mixed with Sodium Alginate to impart fibers with excellent electrical conductivity. The synthesized hollow microfibers have shown their functionality in stretching movement detection by serving as a fundamental building element of motion sensors. </p>

Research on bacteria in their biofilm form is limited by the ability to artificially culture bacterial biofilms in a system that permits the visualization of individual cells. The experiments comprising this thesis research are on-going investigations of bacterial culture systems engineered to provide an environment that mimics biofilms while enabling real-time microscopy. Specifically, the microfluidic systems developed and assessed as part of this thesis permit the visualization of individual bacteria cells within consortia growing within a narrow space provided by a microfluidic device. This research demonstrates the versatility of these microfluidic systems across potentially high-throughput microbiological experiments utilizing genetically engineered Escherichia coli. Before demonstrating the efficacy of these systems, the development of the field of synthetic biology over the past half century is reviewed, focusing on synthetic genetic circuits and their applications (Chapter 2). The first and main microfluidic device explored in this research was developed to mimic the nutrient-deficient conditions within biofilms by forcing media to enter the culture area through a narrow, torturous channel. The microfluidic channel was thin enough (0.97 μm) to prevent the motility of 1-μm-wide E. coli cells, enabling visualization of individual cells. The bacteria cultured in the device contained either a simple Plux-driven quorum sensing receiver (Chapters 3 and 5) or a LacI- and TetR-driven genetic toggle switch (Chapter 4). Under the culture conditions, the quorum sensing reporter signal was detected even without addition of the signaling molecule (Chapter 3). The genetic toggle switch was stable when the system began in the high-LacI expression state, but after 5 days of culture, >5% of high-TetR expression cells began to consistently express the high-LacI state (Chapter 4). This system was also employed to track lineages of cells using real-time microscopy, which successfully characterized the inheritance of aberrant, enlarged cell phenotypes under stress (Chapter 5). Another microfluidic device, a droplet bioreactor, was also developed to culture small numbers of cells in an aqueous bubble suspended in oil (Chapter 6). Quorum sensing receiver cellswere cultured in this device, demonstrating that it is well suited for testing the effects of compounds on biofilms within water-in-oil droplets. / Ph. D. / Bacteria are the most abundant organisms globally, yet relatively little is understood about the basic biology of biofilms, one of the most common natural states of bacteria. Biofilms are ubiquitous consortia of individual microbial cells that send and received chemical signals from one another to carry out group behaviors such as quorum sensing. The impacts of biofilms range from the contamination of food processing equipment to antibiotic resistant bacterial infections. The vast majority of microbiological research has been conducted on bacteria in their planktonic state as individual cells cultured in a liquid medium. This form of culture does not permit the types of research that can help address the impacts of biofilms on human health and economic activities, never mind examine the biological mechanism of random gene and morphological expression within bacterial biofilm. This thesis presents research utilizing two microfluidic devices that will enable further large-scale studies to unravel the mechanisms that create biofilms as well as permit high-throughput testing of chemical compounds to control the growth and development of biofilms. Moreover, these devices permit the use of real-time microscopy to track cells and their growth over time. The first microfluidic device utilized in this research mimics the nutrient-limiting conditions of biofilms. This biofilm-mimicking device was used to culture a common research bacteria, Escherichia coli, with one of two engineered genetic circuits (reviewed in Chapter 2): a quorum sensing receiver (Chapters 3 and 5) or genetic toggle switch (Chapter 4). Both of these genetic circuits demonstrated stochasticity in their gene expression states under the culture conditions in the biofilm-mimicking device. The second microfluidic device successfully permitted the culture of small numbers of isolated cells within a small bubble of bacterial media suspended in oil (Chapter 6). Additionally, this device enabled the addition of chemical compounds to influence the growth and metabolism of the trapped cells. Collectively, these microfluidic devices provide the ability to effectively study both the mechanisms underlying random gene expression within biofilms as well as explore the chemical factors that can be used to control and mitigate biofilm formation and growth.

Precise manipulation of heterogeneous droplets on an open droplet microfluidic platform could have numerous practical advantages in a broad range of applications, from proton exchange membrane (PEM) fuel cells and microreactors, to medical diagnostic platforms capable of assaying complex biological analytes. Toward the aim of developing electrically controllable micropost arrays for use in open droplet manipulation, custom-designed titanium dioxide (TiO2)- loaded poly(dimethylsiloxane) (PDMS) micropost arrays were developed in this work and indirectly mechanically actuated by applying an electric field. Initial experiments explored the bulk properties of TiO2-loaded PDMS films, with scanning electron microscopy (SEM) confirming a uniform TiO2 particle distribution in the PDMS, and tensile testing of bulk films showing an inverse relationship between TiO2 % (w/w) and Young’s Modulus with the Young’s Moduli quantified as 4.22 ± 0.51 MPa for unloaded PDMS, 2.27 ± 0.18 MPa for 10 % (w/w) TiO2, and 1.39 ± 0.20 MPa for 20 % (w/w) TiO2. Following bulk material evaluation, soft lithography methods were developed to fabricate TiO2- loaded PDMS micropost arrays. Mathematical predictions were applied to design microposts of varying shape, length, and gap spacing to yield super-hydrophobic surfaces actuatable by an electric field. Visual inspection and optical microscopy of the resulting arrays confirmed a non- collapsed micropost geometry. Overall, round microposts that were 100, 200, and 300 μm in length, 15 μm in diameter, and spaced 50 μm apart were produced largely free of defects, and used in contact angle measurements and micropost deflection experiments. Droplet contact angles measured on the arrays remained above 120° indicating the arrays successfully provided super- hydrophobic surfaces. Individual microposts deflected most notably above an electric field strength of 520 kV/m (12.5 kV nominal voltage). The ability to mechanically deflect customized microposts using an electric field demonstrated by this work is promising for translating this technology to precise droplet manipulation applications. Indirect actuation of droplets could enable the manipulation of liquids with varying electrical properties, which is a limitation of current micropumping technologies. Once optimized, electrically actuated micropost arrays could significantly contribute to the micro- handling of heterogeneous, highly ionic, and/or deionized fluids. / Thesis (Master, Chemical Engineering) -- Queen's University, 2013-03-03 17:25:49.785

The goal of this research was to develop acoustic sensors and actuators for microfluidic applications. To this end, capacitive micromachined ultrasonic transducers (cMUTs) were developed which generate guided acoustic waves in fluid half-spaces and microchannels. An interdigital transducer structure and a phased excitation scheme were used to selectively excite guided acoustic modes which propagate in a single lateral direction. Analytical models were developed to predict the geometric dispersion of the acoustic modes and to determine the sensitivity of the modes to changes in material and geometric parameters. Coupled field finite element models were also developed to predict the effect of membrane spacing and phasing on mode generation and directionality. After designing the transducers, a surface micromachining process was developed which has a low processing temperature of 250C and has the potential for monolithically integrating cMUTs with CMOS electronics. The fabrication process makes extensive use of PECVD silicon nitride depositions for membrane formation and sealing. The fabricated interdigital cMUTs were placed in microfluidic channels and demonstrated to sense changes in fluid sound speed and flow rate using Scholte waves and other guided acoustic modes. The minimum detectable change in sound speed was 0.25m/s, and the minimum detectable change in flow rate was 1mL/min. The unique nature of the Scholte wave allowed for the measurement of fluid properties of a semi-infinite fluid using two transducers on a single substrate. Changes in water temperature, and thus sound speed, were measured and the minimum detectable change in temperature was found to be 0.1C. For fluid pumping, interdigital cMUTs were integrated into microchannels and excited with phase-shifted, continuous wave signals. Highly directional guided waves were generated which in turn generated acoustic streaming forces in the fluid. The acoustic streaming forces caused the fluid to be pumped in a single, electronically-controlled direction. For a power consumption of 43mW, a flow rate of 410nL/min was generated against a pressure of 3.4Pa; the thermodynamic efficiency was approximately 5x10-8%. Although the efficiency and pressure head are low, these transducers can be useful for precisely manipulating small amounts of fluid around microfluidic networks.

An Active Microscaffold System with Fluid Delivery and Stimulation/Recording Functionalities for Culturing 3-D Neuronal Networks Laura Elizabeth Rowe 215 Pages Directed by Dr. A. Bruno Frazier An active microscaffold system with fluid delivery and electrical stimulation/recording functionalities for 3-D neuronal culture studies is presented. The microscaffolds presented in this dissertation consist of an array of microfabricated towers with integrated microfluidic channels, fluid ports, and electrodes. The microfluidic channels and ports allow for perfusion of nutrients, gas exchange, and biochemical control of the extracellular environment throughout the 3-D culture, while the electrodes allow for active stimulation/recording of the 3-D neuronal network. In essence, the microscaffold serves as an artificial circulatory system to enable 3-D in vitro growth and proliferation of re-aggregate neuronal cell cultures. Increased cell survival on microscaffolds with nutrient perfusion at 14 and 21 days in vitro (DIV) is presented. Additionally, the microtower scaffold is built upon a substrate that is compatible with the Multi Channel Systems preamplifier setup to enable electrical stimulation/recording of the cultured network in a 3-D mutilelectrode array (MEA) environment. Impedance measurements on the functioning microtower electrodes were obtained. The overall goal of this research was to develop a BioMEMS technology to provide neuroscientists with a better investigative tool for studying 3-D in vitro neuronal networks than is currently available.

Nanobelts are a new class of semiconducting metal oxide nanowires with great potential for nanoscale devices. The present research focuses on the manipulation of SnO₂ nanobelts suspended in ethanol using microfluidics and electric fields. Dielectrophoresis (DEP) was demonstrated for the first time on semiconducting metal oxide nanobelts, which also resulted in the fabrication of a multiple nanobelt device. Detailed and direct real-time observations of the wide variety of nanobelt motions induced by DEP forces were conducted using an innovative setup and an inverted optical microscope. High AC electric fields were generated on a gold microelectrode (~ 20 µm gap) array, patterned on glass substrate, and covered by a ~ 10 µm tall PDMS (polydimethylsiloxane) channel, into which the nanobelt suspension was introduced for performing the DEP experiments. Negative DEP (repulsion) of the nanobelts was observed in the low frequency range (< 100 kHz) of the applied voltage, which caused rigid body motion as well as deformation of the nanobelts. In the high frequency range (~ 1 MHz - 10 MHz), positive DEP (attraction) of the nanobelts was observed. Using a parallel plate electrode arrangement, evidence of electrophoresis was also found for DC and low frequency (Hz) voltages. The existence of negative DEP effect is unusual considering the fact that if bulk SnO₂ conductivity and permittivity values are used in combination with ethanol properties to calculate the Clausius Mossotti factor using the simple dipole approximation theory; it predicts positive DEP for most of the frequency range experimentally studied. A fluidic nanobelt alignment technique was studied and used in the fabrication of single nanobelt devices with small electrode gaps. These devices were primarily used for conducting impedance spectroscopy measurements to obtain an estimate of the nanobelt electrical conductivity. Parametric numerical studies were conducted using COMSOL Multiphysics software package to understand the different aspects of the DEP phenomenon in nanobelts. The DEP induced forces and torques were computed using the Maxwell Stress Tensor (MST) approach. The DEP force on the nanobelt was calculated for a range of nanobelt conductivity values. The simulation results indicate that the experimentally observed behavior can be explained if the nanobelt is modeled as having two components: an electrically conductive interior and a nonconductive outer layer surrounding it. This forms the basis for an explanation of the negative DEP observed in SnO₂ nanobelts suspended in ethanol. It is thought that the nonconductive layer is due to depletion of the charge carriers from the nanobelt surface regions. This is consistent with the fact that surface depletion is a commonly observed phenomenon in SnO₂ and other semiconducting metal oxide materials. The major research contribution of this work is that, since nanostructures have large surface areas, surface dominant properties are important. Considering only bulk electrical properties can predict misleading DEP characteristics.

Optical biosensors are increasingly being considered for lab-on-a-chip applications due to their benefits such as small size, biocompatibility, passive behaviour and lack of the need for fluorescent labels. The light guiding mechanisms used by many of them result in poor overlap of the optical field with the target molecules, reducing the maximum sensitivity achievable. This thesis presents a new platform for optical biosensors, namely slotted photonic crystals, which engender higher sensitivities due to their ability to confine, spatially and temporally, the peak of optical mode within the analyte itself. Loss measurements showed values comparable to standard photonic crystals, confirming their ability to be used in real devices. A novel resonant coupler was designed, simulated, and experimentally tested, and was found to perform better than other solutions within the literature. Combining with cavities, microfluidics and biological functionalization allowed proof-of-principle demonstrations of protein binding to be carried out. High sensitivities were observed in smaller structures than most competing devices in the literature. Initial tests with cellular material for real applications was also performed, and shown to be of promise. In addition, groundwork to make an integrated device that includes the spectrometer function was also carried out showing that slotted photonic crystals themselves can be used for on-chip wavelength specific filtering and spectroscopy, whilst gas-free microvalves for automation were also developed. This body of work presents slotted photonic crystals as a realistic platform for complete on-chip biosensing; addressing key design, performance and application issues, whilst also opening up exciting new ideas for future study.

Micro-assembly processes suffer from some breaches due to the continuing trend towards an increase in the production capabilities as well as in the size reduction of the components manipulated. Usual manipulating schemes have reached their limit and capillary forces constitute a valuable alternative strategy.<p><p>The goal of this work is to describe the dynamics of liquid bridges in the application of micro-assembly processes. The description is obtained using the Kelvin-Voigt model, with a spring, a damper, and a mass connected in parallel, supported by numerical simulations, analytical approximations and experiments.<p><p>The works is divided into three parts. First we present important aspects of microfluidics, as well as the constitutive equations and an overview of numerical approaches used to describe fluid flow problems with moving interfaces.<p><p>The second part is devoted to the capillary rise case, intended to validate and to compare the numerical approaches to analytical laws and experimental results. The implementation of the slipping and the dynamic contact angles is discussed.<p><p>The last part focuses on the dynamics of the liquid bridge. The liquid bridge is confined between two circular and parallel plates and presents an axial symmetry. The description reveals that the stiffness depends on the surface tension and on the shape of the air/liquid interface, the damping coefficient depends on the viscosity and the volume of liquid and the equivalent mass depends on the density and the volume.<p> / Doctorat en Sciences de l'ingénieur / info:eu-repo/semantics/nonPublished

Sepsis, commonly referred to as blood poisoning, is a serious medical condition characterized by a whole-body inflammatory state caused by microbial infection. Rapid treatment is crucial, however, traditional culture-based diagnostics usually takes 2-5 days.  The overall aim of the thesis is to develop microfluidic based sample preparation strategies, capable of isolating bacteria from whole blood for rapid sepsis diagnostics.  Although emerging technologies, such as microfluidics and “lab-on-a-chip” (LOC) devices have the potential to spur the development of protocols and affordable instruments, most often sample preparation is performed manually with procedures that involve handling steps prone to introducing artifacts, require skilled technicians and well-equipped, expensive laboratories.  Here, we propose the development of methods for fast and efficient sample preparation that can isolate bacteria from whole blood by using microfluidic techniques with potential to be incorporated in LOC systems. We have developed two means for high throughput bacteria isolation: size based sorting and selective lysis of blood cells. To process the large blood samples needed in sepsis diagnostics, we introduce novel manufacturing techniques that enable scalable parallelization for increased throughput in miniaturized devices. The novel manufacturing technique uses a flexible transfer carrier sheet, water-dissolvable release material, poly(vinyl alcohol), and a controlled polymerization inhibitor to enable highly complex polydimethylsiloxane (PDMS) structures containing thin membranes and 3D fluidic networks. The size based sorting utilizes inertial microfluidics, a novel particles focusing method that operates at extremely high flow rates. Inertial focusing in flow through a single inlet and two outlet, scalable parallel channel devices, was demonstrated with filtration efficiency of &gt;95% and a flowrate of 3.2 mL/min. Finally, we have developed a novel microfluidic based sample preparation strategy to continuously isolate bacteria from whole blood for downstream analysis. The method takes advantage of the fact that bacteria cells have a rigid cell wall protecting the cell, while blood cells are much more susceptible to chemical lysis. Whole blood is continuously mixed with saponin for primary lysis, followed by osmotic shock in water. We obtained complete lysis of all blood cells, while more than 80% of the bacteria were readily recovered for downstream processing. Altogether, we have provided new bacteria isolation methods, and improved the manufacturing techniques and microfluidic components that, combined offer the potential for affordable and effective sample preparation for subsequent pathogen identification, all in an automated LOC format. / QC 20120611

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