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

Monodisperse ZnO Micro and Nanoparticles Obtained by Micro Segmented Flow Synthesis

Mikro- und Nanopartikel aus Zinkoxyd (ZnO) besitzen bemerkenswerte Eigenschaften für Applikationen im Bereich der Elektronik, Optik und Photonic. Als ein Halbleitermaterial mit großer Bandlücke ist ZnO ebenfalls für die Entwicklung von Sensoren, Light Emitting Diodes (LEDs) und Solarzellen von hohem Interesse. Die Herstellung definierter Materialien mit einheitlicher Morphologie und enger Partikel-Größenverteilung ist hierzu eine wichtige Voraussetzung. Verschiedene Verfahren zur Herstellung entsprechender Partikel sind in der Vergangenheit untersucht worden. Die tropfenbasierte Mikrofluidik bietet die Möglichkeit einer exzellenten Reaktionskontrolle durch die Verwendung eines Tropfens als Reaktionsgefäß. Kurze Mischzeiten, hohe Heiz-/Kühlraten sowie eine definierte Verweilzeit ermöglichen so neben stöchiometrischen Parametern eine exakte Reaktionsführung. Ziel der hier vorliegenden Dissertationsschrift ist die Untersuchung der ZnO-Präzipitation in entsprechenden mikrofluidischen Systemen sowie die Charakterisierung der hergestellten Materialien.ZnO micro and nanoparticles have attracted considerable interest because of their remarkable performance in electronics, optics and photonics. As a wide band gap semiconductor material, ZnO is also a potential candidate for various applications including gas sensing, light emitting devices and solar cells. Although some technologies have been developed to produce well-defined ZnO particles of different shapes and sizes, ZnO particles prepared by micro segmented flow synthesis have been rarely reported. The aim of this work was to develop a microfluidic system based on the micro segmented flow method and to test whether the microfluidic components are suitable for the generation and investigation of ZnO particles with improved homogeneity.In order to optimize the experimental conditions, ZnO particles were first synthesized in batch. The optimized batch conditions were then adapted to two microfluidic arrangements for continuous synthesis of ZnO particles below 100°C. The set-ups included computer-controlled syringe pumps, T-injectors, PTFE tubings and PTFE knot mixers in a thermostat water bath. The ZnO particles were obtained under strong alkaline conditions at elevated temperature in aqueous solution and DMSO solution. Needle-like, flower-like and compact ZnO particles were obtained. In nearly all cases, a strong effect of the flow conditions on the homogeneity of the formed particles was observed. The higher quality of the particles can be attributed to the fast mixing and enhanced heat transfer caused by segment-internal convection.In addition, two other microfluidic set-ups were developed to control the ZnO formation reaction at temperature up to 150°C. A static micromixer was used for mixing the reactants at room temperature. The formation of segmented flow was realized by injection of the reaction mixture into a carrier stream. The particle growth took place in PTFE tube coils inside a thermostat, which allowed to heat up to 150°C. By using this set-up, flower-like, star-like, and spherical ZnO particles were successfully synthesized. The shape and size of the formed particles were strongly dependent on the reactant concentration and the molar ratio of NaOH/Zn(Ac)2. The total residence time for preparation of these particles was only 9.3s, which is very short compared to the most conventional methods.The effect of the solvent on the formation of ZnO particle has also been investigated using this microfluidic set-up. Two different experimental conditions were applied to prepare ZnO particles, where Zn(Ac)2 and NaOH in ethylene glycol (EG) were mixed with water or water/EG mixing solvent to achieve different water contents in the final mixture solution. The formation of homogeneous particles was characterized by SEM and TEM. A stronger dependence of the particle size and shape on the water content was observed. Furthermore, the water content can be used for tuning the optical absorption spectra of the formed ZnO particles. Besides the ZnO microparticles, ZnO nanoparticles with an average diameter around 4-5nm have been synthesized using Zn(Ac)2 and LiOH in ethanol. The prepared nanoparticles exhibited green and blue emission under excitation at 325nm. In order to understand the size-dependent optical properties of ZnO nanoparticles, extended X-ray absorption fine structure (EXAFS) spectroscopy was applied to study their local structure properties and compared with that of ZnO flower-like microparticles. The EXAFS measurements revealed higher vacancies and a higher degree of structural disorders in the nanoparticles than the microparticles. These disorders and vacancies could contribute to the blue shift of the visible emission from ZnO nanopartilces.Due to the potential applications of semiconductor-metal composite particles in diverse areas, the flower-like ZnO microparticles obtained by micro segmented flow synthesis were used to fabricate ZnO/4-MBA/Au composite particles using a simple strategy. The formed composite particles were very homogeneous in shape and size. The surface coverage of Au nanoparticles on ZnO/4-MBA particles can be adjusted by changing the molar ratio of ZnO/4-MBA to Au. In order to study the interaction of 4-MBA molecules with ZnO and Au particles, Raman spectra of ZnO/4-MBA and ZnO/4-MBA/Au particles were analysed.In summary, the segmented flow technique is suitable to generate ZnO particles with controlled size and morphology. Compared to most conventional methods, this technique offers several advantages, and it provides a new insight into material synthesis under environmentally friendly conditions

INTEGRATION AND CHARACTERIZATION OF TOBACCO MOSAIC VIRUS BASED NANOSTRUCTURED MATERIALS IN THREE-DIMENSIONAL MICROBATTERY ARCHITECTURES

The realization of next-generation portable electronics, medical implants and miniaturized, autonomous microsystems is directly linked with the development of compact and efficient power sources and energy storage devices with high energy and power density. As the components of these devices are continuously scaled down in size, there is a growing demand for decreasing the size of their power supply as well, while maintaining performance comparable to larger assemblies. This dissertation presents a novel approach for the development of microbattery electrodes that is based on integrating both micro and nano structured components for the formation of hierarchical electrodes. These electrodes combine both high energy density (enabled by the high surface area and mass loading) with high power density (due to the small thickness of the active battery materials). The key building block technologies in this work are the bottom-up self-assembly and metallization of a biological template and the top-down microfabrication processes enabled by Microelectromechanical Systems (MEMS) technology. The biotemplate used is the Tobacco mosaic virus (TMV), a rod-like particle that can be genetically modified to express functional groups with enhanced metal binding properties. In this project, this feature is combined with standard microfabrication techniques for the synthesis of nanostructured energy-related materials as well as their hierarchical patterning in device architectures. Specifically, synthesis of anode (TiO2) and cathode (V2O5) materials for Li-ion batteries in a core/shell configuration is presented, where the TMV biomineralization is combined with atomic layer deposition of the active material. These nanostructured electrodes demonstrate high energy storage capacities, high rate capabilities and superior performance to electrodes with planar geometries. In addition, a toolbox of biofabrication processes for the defined patterning of virus-templated structures has been developed. Finally, the nanocomposite electrodes are integrated with three-dimensional micropillars to form hierarchical electrodes that maintain the high rate performance capabilities of nanomaterials while exhibiting an increase in energy density compared to nanostructures alone. This is in accordance with the increase in surface area added by the microstructures. Investigation of capacity scaling for varying active material thickness reveals underlying limitations in nanostructured electrodes and highlights the importance of this method in controlling both energy and power density with structural hierarchy. These results present a paradigm-shifting technology for the fabrication of next-generation microbatteries for MEMS and microsystems applications

Development of a laser foaming process for high throughput three-dimensional tissue model devices

A three-dimensional (3D) porous structure on biodegradable or biocompatible polymers have attracted tremendous attention in numerous bio-related areas including 3D cell culturing and tissue engineering because of their microenvironment similar to ones in vivo. In this study, a novel fabrication process, named selective laser foaming, was developed to create localized 3D porous structure on a polymer chip. The effects of laser power and lasing time on the porous structure were studied both experimentally and through finite element modeling. A high throughput two-chamber tissue model platform was developed using the proposed selective laser foaming process. For comparison, cell culture studies were conducted with both selective laser foamed and unfoamed polylactic acid (PLA) samples using T98G cells. The results show that by laser foaming gas-impregnated polylactic acid it is possible to generate an array of inverse cone-shaped wells with porous walls. The size of the foamed region can be controlled with laser power and exposure time, while the pore size of the scaffold can be manipulated with the saturation pressure. The finite element modeling results showed good agreement with the experimental data; therefore, the model could be used to optimize and control the selective foaming process. T98G cells grew well in the foamed scaffolds, forming clusters that have not been observed in 2D cell cultures. Cells were more viable in the 3D scaffolds than in the 2D cell culture cases, suggesting that the 3D porous microarray could be used for parallel studies of drug toxicity, guided stem cell differentiation, and DNA binding profiles. As an example, a high-throughput two-chamber 3D tissue model platform driven by the centrifugal force was developed for drug screening. The selective laser foaming process was calibrated to fabricate 3D scaffold on a commercially available compact disc (CD) made of polycarbonate (PC). Laser foaming of gas saturated polycarbonate created inverse cone-shaped wells with micro-sized porous structure underneath the surface. The open pores were hundreds of micrometers in diameter and depth. The pore size of the underneath porous structure was several tens of micrometers. The size of the well was dependent on the laser power and laser exposure time. Two laser-foamed scaffolds were fabricated in tandem and two mechanically-machined chambers were placed adjacent to the scaffolds, respectively. All scaffolds and chambers were in line and all of them were connected with micro-channels. The surface was coated with polydopamine (PDA) in order to increase the hydrophilicity and biocompatibility. After sterilization, human glioblastoma multiforme (M059K) and hepatoblastoma (C3A sub28) were seeded in the two 3D scaffolds separately and cultured for up to four weeks. These cells grew well in the scaffolds and cell aggregates were observed, suggesting that the developed two-chamber tissue model array could be useful for high-throughput biochemical assays.Mechanical Engineerin

New Trends and Applications in Femtosecond Laser Micromachining

This book contains the scientific contributions to the Special Issue entitled: "New Trends and Applications in Femtosecond Laser Micromachining". It covers an array of subjects, from the basics of femtosecond laser micromachining to specific applications in a broad spectra of fields such biology, photonics and medicine

Acoustofluidic self-assembly of colloidal materials for additive manufacturing

Additive manufacturing techniques like 3D printing are being used extensively to produce custom-designed products in all walks of life- from household items to human organs to space shuttle parts. However, most additive manufacturing platforms use single materials or use extremely complicated processes to print multi-material products. Also, the microstructure of the materials cannot be controlled in many cases. The 3D printing sector is a USD 7 Billion market and is expected to grow at a rate of 25% per annum. At this rate of development, the use of printing multi-material components and creating programmable material structures will be crucial for the already booming market. In order to create programmable materials, it has been shown extensively that nano- and micro-material inclusions can produce customized material properties. Bottom-up material fabrication techniques like external-field directed self-assembly have been used to create programmable materials using colloidal particles, just like building a Lego structure. However, these self-assembled materials have been manufactured at the micro-scale and are often batch-produced, that makes it difficult to create bulk materials. Also, most self-assembled materials require clean-room and high-end equipment to fabricate the materials, which makes it highly expensive, inaccessible to common man and high complicated to integrate with additive manufacturing systems. I intend to use a combination of bottom-up colloidal self-assembly techniques with additive manufacturing platforms to create programmable, smart-materials that can be fabricated using 3D printing multi-material platforms and create portable additive manufacturing platforms to make it accessible for all. A high-throughput, continuous flow self-assembled material platform where colloidal particles, are self-assembled to create colloidal crystals in an acoustic field is developed. The colloidal crystals are embedded in a polymer, creating continuous colloidal particle-polymer composites fibers that can be 3D printed. Since the concentration of the colloidal solution and the acoustic field can be controlled, precise and programmable structures with varying mechanical, electrical and magnetic composite materials are developed. Our preliminary results show increased mechanical properties in PMMA-UV cured resin composites compared to randomly distributed composites and we demonstrate a graphene monolayer-polymer composite that can conduct selectively in particular regions. Similarly, we are working on creating a magnetic monolayer-polymer composite that can be used in robotic actuators. I am working on assembling the acoustic self-assembly platform on a CNC machine to 3D print the composited to form bulk materials. In addition, I worked on understanding the effect of acoustic and fluid fields on the assembly process to understand and the assembly kinetics using Force-biased Monte Carlo simulations to obtain defect-free materials. I have used various quantitative techniques like micro-Particle Image Velocimetry (PIV), order parameter analysis and image processing to analyze the experiments and correlate and compare them with the Monte Carlo simulations

Development of an autonomous lab-on-a-chip system with ion separation and conductivity detection for river water quality monitoring

This thesis discusses the development of a lab on a chip (LOC) ion separation for river water quality monitoring using a capacitively coupled conductivity detector (C⁴D) with a novel baseline suppression technique.Our first interest was to be able to integrate such a detector in a LOC. Different designs (On-capillary design and on-chip design) have been evaluated for their feasibility and their performances. The most suitable design integrated the electrode close to the channel for an enhanced coupling while having the measurement electronics as close as possible to reduce noise. The final chip design used copper tracks from a printed circuit board (PCB) as electrodes, covered by a thin Polydimethylsiloxane (PDMS) layer to act as electrical insulation. The layer containing the channel was made using casting and bonded to the PCB using oxygen plasma. Flow experiments have been conduced to test this design as a detection cell for capacitively coupled contactless conductivity detection (C⁴D).The baseline signal from the system was reduced using a novel baseline suppression technique. Decrease in the background signal increased the dynamic range of the concentration to be measured before saturation occurs. The sensitivity of the detection system was also improved when using the baseline suppression technique. Use of high excitation voltages has proven to increase the sensitivity leading to an estimated limit of detection of 0.0715 μM for NaCl (0.0041 mg/L).The project also required the production of an autonomous system capable of operating for an extensive period of time without human intervention. Designing such a system involved the investigation of faults which can occur in autonomous system for the in-situ monitoring of water quality. Identification of possible faults (Bubble, pump failure, etc.) and detection methods have been investigated. In-depth details are given on the software and hardware architecture constituting this autonomous system and its controlling software

Towards rapid 3D direct manufacture of biomechanical microstructures

The field of stereolithography has developed rapidly over the last 20 years, and commercially available systems currently have sufficient resolution for use in microengineering applications. However, they have not as yet been fully exploited in this field. This thesis investigates the possible microengineering applications of microstereolithography systems, specifically in the areas of active microfluidic devices and microneedles. The fields of micropumps and microvalves, stereolithography and microneedles are reviewed, and a variety of test builds were fabricated using the EnvisionTEC Perfactory Mini Multi-Lens stereolithography system in order to define its capabilities. A number of microneedle geometries were considered. This number was narrowed down using finite element modelling, before another simulation was used to optimise these structures. 9 × 9 arrays of 400 μm tall, 300 μm base diameter microneedles were subjected to mechanical testing. Per needle failure forces of 0.263 and 0.243 N were recorded for the selected geometries, stepped cone and inverted trumpet. The 90 μm needle tips were subjected to between 30 and 32 MPa of pressure at their failure point - more than 10 times the required pressure to puncture average human skin. A range of monolithic micropumps were produced with integrated 4 mm diameter single-layer 70 μm-thick membranes used as the basis for a reciprocating displacement operating principle. The membranes were tested using an oscillating pneumatic actuation, and were found reliable (>1,000,000 cycles) up to 2.0 PSIG. Pneumatic single-membrane nozzle/diffuser rectified devices produced flow rates of up to 1,000 μl/min with backpressures of up to 375 Pa. Another device rectified using active membrane valves was found to self-prime, and produced backpressures of up to 4.9 kPa. These devices and structures show great promise for inclusion in complex, fully integrated and active microfluidic systems fabricated using microstereolithography alone, with implications for both cost of manufacture and lead time

Micro-injection moulding of three-dimensional integrated microfluidic devices

This thesis investigates the use of micro-injection moulding (μIM), as a high-volume process, for producing three-dimensional, integrated microfluidic devices. It started with literature reviews that covered three topics: μIM of thermoplastic microfluidics, designing for three-dimensional (3-D) microfluidics and functional integration in μIM. Research gaps were identified: Designing 3-D microfluidics within the limitations of μIM, process optimisation and the integration of functional elements. A process chain was presented to fabricate a three-dimensional microfluidic device for medical application by μIM. The thesis also investigated the effect of processing conditions on the quality of the replicated component. The design-of-experiments (DOE) approach is used to highlight the significant processing conditions that affect the part mass taking into consideration the change in part geometry. The approach was also used to evaluate the variability within the process and its effect on the replicability of the process. Part flatness was also evaluated with respect to post-filling process parameters. The thesis investigated the possibility of integrating functional elements within μIM to produce microfluidic devices with hybrid structures. The literature reviews highlighted the importance of quality control in high-volume micromoulding and in-line functional integration in microfluidics. A taxonomy of process integration was also developed based on transformation functions. The experimental results showed that μIM can be used to fabricate microfluidic devices that have true three-dimensional structures by subsequent lamination. The DOE results showed a significant effect of individual process variables on the filling quality of the produced components and their flatness. The geometry of the replicated component was shown to have effect on influential parameters. Other variables, on the other hand, were shown to have a possible effect on process variability. Optimization statistical tools were used to improve multiple quality criteria. Thermoplastic elastomers (TPE) were processed with μIM to produce hybrid structures with functional elements.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Laser-induced forward transfer (LIFT) of water soluble polyvinyl alcohol (PVA) polymers for use as support material for 3D-printed structures

The additive microfabrication method of laser-induced forward transfer (LIFT) permits the creation of functional microstructures with feature sizes down to below a micrometre [1]. Compared to other additive manufacturing techniques, LIFT can be used to deposit a broad range of materials in a contactless fashion. LIFT features the possibility of building out of plane features, but is currently limited to 2D or 2½D structures [2–4]. That is because printing of 3D structures requires sophisticated printing strategies, such as mechanical support structures and post-processing, as the material to be printed is in the liquid phase. Therefore, we propose the use of water-soluble materials as a support (and sacrificial) material, which can be easily removed after printing, by submerging the printed structure in water, without exposing the sample to more aggressive solvents or sintering treatments. Here, we present studies on LIFT printing of polyvinyl alcohol (PVA) polymer thin films via a picosecond pulsed laser source. Glass carriers are coated with a solution of PVA (donor) and brought into proximity to a receiver substrate (glass, silicon) once dried. Focussing of a laser pulse with a beam radius of 2 µm at the interface of carrier and donor leads to the ejection of a small volume of PVA that is being deposited on a receiver substrate. The effect of laser pulse fluence , donor film thickness and receiver material on the morphology (shape and size) of the deposits are studied. Adhesion of the deposits on the receiver is verified via deposition on various receiver materials and via a tape test. The solubility of PVA after laser irradiation is confirmed via dissolution in de-ionised water. In our study, the feasibility of the concept of printing PVA with the help of LIFT is demonstrated. The transfer process maintains the ability of water solubility of the deposits allowing the use as support material in LIFT printing of complex 3D structures. Future studies will investigate the compatibility (i.e. adhesion) of PVA with relevant donor materials, such as metals and functional polymers. References: [1] A. Piqué and P. Serra (2018) Laser Printing of Functional Materials. Weinheim, Germany: Wiley-VCH Verlag GmbH & Co. KGaA. [2] R. C. Y. Auyeung, H. Kim, A. J. Birnbaum, M. Zalalutdinov, S. A. Mathews, and A. Piqué (2009) Laser decal transfer of freestanding microcantilevers and microbridges, Appl. Phys. A, vol. 97, no. 3, pp. 513–519. [3] C. W. Visser, R. Pohl, C. Sun, G.-W. Römer, B. Huis in ‘t Veld, and D. Lohse (2015) Toward 3D Printing of Pure Metals by Laser-Induced Forward Transfer, Adv. Mater., vol. 27, no. 27, pp. 4087–4092. [4] J. Luo et al. (2017) Printing Functional 3D Microdevices by Laser-Induced Forward Transfer, Small, vol. 13, no. 9, p. 1602553