Optical feedback interferometry is a sensing technique with relative recent implementation for the interrogation of fluidic systems. The sensing principle is based on the perturbation of the laser emission parameters induced by the reinjection in the laser cavity of light back-scattered from a distant target. The technique allows for the development of compact and noninvasive sensors that measure various parameters related to the motion of moving targets. In particular, optical feedback interferometers take advantage of the Doppler effect to measure the velocity of tracers in flowing liquids. These important features of the optical feedback interferometry technique make it wellsuited for a variety of applications in chemical engineering and biomedical fields, where accurate monitoring of the flows is needed. This thesis presents the implementation of optical feedback interferometry based sensors in multiple fluidic systems where local velocity or flow rate are directly measured. We present an application-centered study of the optical feedback sensing technique used for flow measurement at the microscale with focus on the reliability of the signal processing methods for flows in the single and the multiple scattering regimes. Further, we present experimental results of ex vivo measurements where the optical feedback sensor is proposed as an alternative system for myography. In addition we present a real-time implementation for the assessment of non-steady flows in a millifluidic configuration. A semi-automatized system for single particle detection in a microchannel is proposed and demonstrated. Finally, an optical feedback based laser sensor is implemented for the characterization of the interactions between two immiscible liquid-liquid flowing at the microscale, and the measurement is compared to a theoretical model developed to describe the hydrodynamics of both fluids in a chemical microreactor. The present manuscript describes an important contribution to the implementation of optical feedback sensors for fluidic and microfluidic applications. It also presents remarkable experimental results that open new horizons to the optical feedback interferometry.

Li, Yuefang. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2010. / Includes bibliographical references (leaves 46-48). / Abstracts in English and Chinese. / Abstract --- p.i / 摘要 --- p.ii / Acknowledgement --- p.iii / Table of contents --- p.iv / Chapter Chapter 1 --- Introduction --- p.1 / Chapter 1.1 --- Introduction to protein crystallization --- p.1 / Chapter 1.1.1 --- Principles of protein crystallization --- p.2 / Chapter 1.1.2 --- Classical methods to crystallize protein --- p.4 / Chapter 1.2 --- Crystal growth in unique environments: the pursuit of better crystals --- p.6 / Chapter 1.2.1 --- Protein crystallization in space --- p.6 / Chapter 1.2.2 --- Crystallization in gel and capillary --- p.7 / Chapter 1.3 --- Microfluidic methods for protein crystallization: high through-put screenings --- p.9 / Chapter 1.3.1 --- Valve-controlled methods --- p.10 / Chapter 1.3.2 --- Droplet-based methods --- p.11 / Chapter 1.3.3 --- Microwell-based methods --- p.11 / Chapter 1.4 --- Objective of the project --- p.13 / Chapter Chapter 2 --- Rehydratable hydrogel in nanoliter microwells --- p.15 / Chapter 2.1 --- Introduction --- p.15 / Chapter 2.2 --- Experimental --- p.17 / Chapter 2.2.1 --- Fabrication of SU-8 mould --- p.17 / Chapter 2.2.2 --- Fabrication of the PDMS device --- p.19 / Chapter 2.2.3 --- Liquid dispensing in PDMS device --- p.20 / Chapter 2.2.4 --- Polymerization of PA gel --- p.21 / Chapter 2.2.5 --- Drying and Rehydration of PA gel --- p.22 / Chapter 2.3 --- Results and discussions --- p.23 / Chapter 2.3.1 --- Preparation of PA gel in PDMS device --- p.23 / Chapter 2.3.2 --- Immobilization of PA gel in microwells --- p.25 / Chapter 2.3.3 --- Dehydration and Rehydration of PA gel --- p.25 / Chapter 2.3.4 --- Liquid dispensing in the gel-preloaded microwells --- p.29 / Chapter 2.4 --- Conclusion --- p.31 / Chapter Chapter 3 --- Protein crystallization by gel-based FID --- p.32 / Chapter 3.1 --- Introduction --- p.32 / Chapter 3.2 --- Experimental --- p.34 / Chapter 3.2.1 --- Conditions used for crystallize proteins --- p.34 / Chapter 3.2.2 --- Protein crystallization by microbatch method --- p.34 / Chapter 3.2.3 --- Protein crystallization in microchip --- p.35 / Chapter 3.3 --- Results and discussions --- p.35 / Chapter 3.3.1 --- Crystallization in microplate --- p.36 / Chapter 3.3.2 --- Crystallization in microwells --- p.38 / Chapter 3.4 --- Conclusion --- p.41 / Chapter Chapter 4 --- Conclusions --- p.43 / Chapter 4.1 --- Summary of the work --- p.43 / Chapter 4.2 --- Future perspectives --- p.44 / Reference --- p.46

L’objet de ce travail expérimental est l’étude de la mécanique de films de mousses dont la structure est confinée par leur faible épaisseur. A partir d’une méthode de moussage de dispersion de particules de polyuréthane, nous sommes parvenus à contrôler, de façon indépendante, la fraction d’air (ou la densité) de ces films, leur épaisseur e et la distribution des tailles de leurs pores (de diamètre moyen D ̅_b). Pour ce dernier paramètre, nous nous sommes intéressés au cas de distributions monodisperse, bidisperse et polydisperses. Les différentes structures obtenues ont été étudiées par tomographie aux rayons X, de manière à quantifier l’ordre induit par le confinement (profils de densité, position des centres de pores, tailles des éléments structuraux,…). Nous nous sommes intéressés à la mécanique de ces films de mousse en tension (dans le plan du film) et en compression (dans le plan orthogonal au film). Un travail spécifique mené sur la matrice de polymère nous a permis de déterminer des grandeurs adimensionnées (modules et contraintes caractéristiques) permettant une comparaison avec les données et les modèles de la littérature. Nous montrons qu’en plus de l’effet classique de la densité, le nombre moyen de bulles à travers l’épaisseur, i.e. e⁄D ̅_b , est un paramètre déterminant pour les deux directions de sollicitation. En élongation, les couches pariétales contribuent à augmenter le module élastique des films par rapport à une mousse non-confinée. Ce renforcement est d’autant plus important (jusqu’à deux fois) lorsque e⁄D ̅_b est faible, quel que soit le type de distribution des tailles de pores. En compression, les couches pariétales ne contribuent pas directement, mais le confinement joue également un rôle important, avec cette fois-ci un impact déterminant de la distribution des tailles de pores. Ainsi, un film de mousse monodisperse est ordonné comme un polycristal et présente des caractéristiques mécaniques nettement plus élevées qu’un film de mousse polydisperse, comportant de nombreuses zones de faiblesse mécanique engendrées par les défauts d’empilement des bulles initiales. Les films de mousse bidisperses ont une réponse mécanique qui se rapproche soit des mousses monodisperses, pour de relativement grands rapports e⁄D ̅_b , soit des mousses polydisperses, pour de relativement petits rapports( e)⁄D ̅_b / The subject of this experimental work is the study of foam films mechanics with a confined structure because of their low thickness. With our foaming method using polyurethane particles dispersion, we generated foam films with independent control over the gas fraction (or the density), the thickness e or the pore size distribution (with a mean diameter D ̅_b). For this last parameter, we focused on monodisperse, bidisperse and polydisperse distributions. Obtained structures were studied using X-ray tomography to quantify confinement-induced order (density profiles, pore center spatial position, structural elements size,…). The mechanics of such foam films was studied in both uniaxial tension (in-plane) and compression (orthogonal plan). A particular work was done on the polymer matrix in order to determine reduced values (moduli and characteristic stress) to compare our results with models in the literature. We show that in addition to the classic density effect, the mean number of bubbles across the thickness, i.e. e⁄D ̅_b is a determinant parameter for both stress directions. In tension, parietal walls contribute to increase the elastic modulus of films with respect to non-confined foam. This effect on the mechanical strength is even more important (up to two times) when e⁄D ̅_b is small without any effect regarding the pore size distribution. In compression, parietal walls do not contribute directly to the measured values but the confinement still has an important role, this time depending on the pore size distribution. Indeed, monodisperse foam films are organized in polycrystals with much better mechanical characteristics compared to polydisperse foam films that present numerous mechanical weak spots caused by initial bubble packing defects. Bidisperse foam films mechanical behavior is either close to monodisperse or polydisperse foam films respectively for high or small e⁄D ̅_b ratio

A microfluidic device was created for single-cell capture and analysis using polydimethylsiloxane (PDMS) channels and a glass substrate to develop a microfluidic single-cell impedance sensor for cell diagnostics. The device was fabricated using photolithography to create a master mold which in turn will use soft lithography to create the PDMS components for constant device production. The commercial software, COMSOLTM Multiphysics, was used to quantify the fluid dynamics in shallow micro-channels. The device will be able to capture a cell and sequester it long enough to enable measurement of the impedance spectra that can characterize cell. The proposed device will be designed to capture a single cell and permit back-flow to flush out excess cells in the chamber. The device will be designed to use syringe pumps and the syringe-controlled channel will also be used to capture and release the cell to ensure cell control and device reusability. We hypothesize that these characteristics along with other proposed design factors will result in a unique microfluidic cell-capture device that will enable single-cell impedance sensing and characterization.

Silk fibroin from silkworm cocoons is found in numerous applications ranging from textiles to medical implants. Its recent adoption as a biomaterial is due to the material's strength, biocompatibility, self-assembling behavior, programmable degradability, optical clarity, and its ability to be functionalized with antibodies and proteins. In the field of bioengineering it has been utilized as a tissue scaffolding, drug delivery system, biosensor, and implantable electrode. This work suggests a new application for porous silk in a microscale chromatography column. We demonstrate in situ cryotropic polymerization of highly porous structures in microscale geometries by freezing aqueous silk with a solvent. The resulting cryogels are experimentally characterized using flow parameters common in chromatography design; tortuosity, global pressure drop, pore diameter, and porosity. These empirical parameters are put into porous flow models to calculate an order-of-magnitude increase in functional surface area over the blank capillaries and packed-sphere columns used in traditional designs. Additionally, the pressure requirements to produce relevant flow rates in these structures are found not to threaten the integrity of microfluidic seals or connectors.

When confined within containers or conduits, drops and bubbles migrate to regions of minimum energy by the combined effects of surface tension, surface wetting, system geometry, and initial conditions. Such capillary phenomena are exploited for passive phase separation operations in micro-fluidic devices on earth and macro-fluidic devices aboard spacecraft. Our study focuses on the migration and ejection of large inertial-capillary drops confined between tilted planar hydrophobic substrates. In our experiments, the brief nearly weightless environment of a drop tower allows for the study of such capillary dominated behavior for up to 10 mL water drops with migration velocities up to 12 cm/s. We control ejection velocities as a function of drop volume, substrate tilt angle, initial confinement, and fluid properties. We then demonstrate how such geometries may be employed as passive no-moving-parts droplet generators for very large drop dynamics investigations. The method is ideal for hand-held non-oscillatory drop generation for fun, educational, and insightful astronaut demonstrations aboard the International Space Station.

Prostate cancer presents a significant paradox: it is very common, yet rarely fatal. To wit, the prostate is the most common non-skin tissue for cancer diagnosis in men in the United States. Despite its high incidence, fatal malignancy occurs in only a small fraction of diagnosed men. The fatal cases are characteristically defined by distant spread in the body, also known as metastasis. In order to metastasize a cancer cell must complete several sequential steps. These include degradation of and invasion through the epithelial basement membrane, typically through the loss of static intracellular adhesions with fellow epithelial cells; entrance into the blood stream (intravasation); survival within circulation; exit from the blood stream upon arrival at a new tissue (extravasation); and survival and colonization at the secondary site. At the time of diagnosis, it is not currently possible to accurately predict future metastasis and thereby clinicians cannot delineate those men at high risk for fatal disease from the vast majority of men who are likely to experience an indolent disease course. Consequently, we examined the behavior of cancer cells in several steps of the metastatic cascade. In doing so, we uncovered both molecular and biophysical characteristics of cancer cells that may facilitate successful metastatic dissemination and tumor outgrowth. Epithelial-to-mesenchymal transition (EMT) is physiological process of transdifferentiation that is normally initiated during vertebrate development, but has recently been implicated in tumor development, progression, and metastases. The EMT program results in dramatic changes, including the exchange of epithelial for mesenchymal markers, altered cellular morphology, and gain of motility. EMT-like cellular alterations have been implicated most strongly in the metastasis steps of invasion and survival of cells at primary tumors sites. How EMT-like changes may facilitate survival and growth in the microenvironment of a micrometastatic niche has been less clearly elucidated. Consequently, we evaluated how EMT-like changes may affect the survival and subsequent outgrowth of prostate cancer cell lines following restrictive growth conditions. We observed that EMT-like cells as compared to their more epithelial counterparts displayed enhanced maintenance of their proliferative potential following extended culture in nutrient restriction. This phenotype depended on an EMT-associated increase in autophagy. Notably, the post-stress outgrowth phenotype could be conferred through a paracrine signaling mechanism that may involve autophagy-derived exosome-like extracellular vesicles. These studies demonstrated that EMT-like cells have a resistance to nutrient restriction through enhanced autophagy and may have uncovered a novel autophagy-dependent exosomal secretion pathway. Metastatic efficiency is thought to be strongly limited by the destruction of circulating tumor cells by the hemodynamic shear forces within the vasculature. However, such a persistent belief has little appropriate published experimental evidence. We developed an in vitro assay to expose cells to fluid shear stress (FSS). By monitoring the viability of the cells, we determined that transformed cells had a highly conserved ability to resist even very high FSS. The mechanism depended on the capacity to patch membrane defects, extracellular calcium, and a dynamic cytoskeleton. We also observed a stiffening of cancer cell membranes after exposure to FSS. Taken together, these studies expand the understanding of how cancer cells survive in circulation and indicate that metastatic efficiency is less limited by hemodynamic forces than previously thought. The steps of hematogenous metastasis between intravasation and extravasation necessitate the existence of circulating tumor cells (CTCs). Collection, enumeration, and study of CTCs have the potential to serve as a "liquid biopsy" of the metastatic cascade. In prostate cancer, the enumeration of CTCs by detection of the expression of epithelial markers has displayed limited clinical utility. We hypothesized that the prognostic value of CTC number may be enhanced by detection of cells which have undergone the pro-metastatic EMT-like program. We developed a flow cytometry-based experimental assay for enumeration of CTCs using epithelial (EpCAM) and mesenchymal-like (N-cadherin) surface proteins. We detected from prostatectomy patients before and after surgery events expressing EpCAM, N-cadherin, and both. However, the detection of background events from healthy control subjects was unacceptably high. These studies support the idea of mesenchymal-like tumor cells in circulation, but will require further assay development for reliable conclusions to be drawn. In sum, the work described above has provided descriptive and mechanistic insight to molecular and biophysical properties that may facilitate prostate cancer metastasis. It is our hope that these data will result in the development of relevant preventative, diagnostic, and therapeutic clinical strategies for prostate cancer.

This research utilizes Electrical Impedance Spectroscopy, a technique classically used for electrochemical analysis and material characterization, as the basis for a non-destructive, label-free assay platform for three dimensional (3D) cellular spheroids. In this work, a linear array of microelectrodes is optimized to rapidly respond to changes located within a 3D multicellular model. In addition, this technique is coupled with an on chip micro-pH sensor for monitoring the environment around the cells. Finally, the responses of both impedance and pH are correlated with physical changes within the cellular model. The impedance analysis system realized through this work provides a foundation for the development of high-throughput drug screening systems that utilize multiple parallel sensing modalities including pH and impedance sensing in order to quickly assess the efficacy of specific drug candidates. The slow development of new drugs is mainly attributed to poor predictability of current chemosensitivity and resistivity assays, as well as genetic differences between the animal models used for tests and humans. In addition, monolayer cultures used in early experimentation are fundamentally different from the complex structure of organs in vivo. This requires the study of smaller 3D models (spheroids) that more efficiently replicate the conditions within the body. The main objective of this research was to develop a microfluidic system on a chip that is capable of deducing viability and morphology of 3D tumor spheroids by monitoring both the impedance of the cellular model and the pH of their local environment. This would provide a fast and reliable method for screening pharmaceutical compounds in a high-throughput system.

Recent advances in computing technology have highlighted deficiencies with electrical interconnections at the motherboard and card-to-backplane levels. The CPU speeds of computing systems are drastically increasing with on-chip local clock speeds expected to approach 6 GHz by 2010. Yet, card-to-backplane communication speeds have been unable to maintain the same pace. At speeds beyond a few gigahertz the implementation of electronic interconnects gets increasingly complex, thus, alternative optical interconnection techniques are being extensively researched to relieve the expected CPU to data bus bottleneck. Despite the advantages afforded by optical interconnects there are still demands for improved packaging, enhanced signal tapping, and reduced cost expenditures. In this dissertation, we present a novel array waveguide evanescent coupling (AWEC) technology for card-to-backplane applications. The interconnection scheme is based on waveguide directional coupling between a backplane waveguide and a flexible waveguide connected to the access card or daughter board. To gain access to the shared bus media, coupling of evanescent waves is exploited to tap optical signals from the backplane waveguide to the corresponding card waveguide. The approach results in the elimination of micro-mirror out of plane deflectors and local waveguide termination obstacles present in other reported optical interconnect schemes. Most importantly, the AWEC method can yield efficient multi-drop bus architectures, not possible through free-space, fiber, or traditional guided wave approaches, that only achieve point-to-point topologies. The AWEC concept for optical interconnection was introduced through coupled mode theory, numerical simulations and BeamPROP aided CAD models. Subsequent experimental waveguide analysis was performed and shown to reasonably agree with the simulation results. Likewise, a high-resolution, cost-effective, and rapid prototyping approach for AWEC fabrication has been formulated. Significantly, when compared to other soft lithographic methods, the novel vacuum assisted microfluidic (VAM) technique results in improved waveguide structures, polymer background residue elimination and lower propagation losses. Moreover, experimental results show that our evanescent coupling approach facilitates high-speed coupling between card and backplane waveguides at speeds of 10 Gbps per channel; currently limited only by our testing electronics. In addition, satisfactory eye diagram performance comparable to that of a conventional fiber link, was also observed for the AWEC, alluding to possible aggregate speeds of 100 Gbps. Similarly, we implemented an elementary AWEC shared bus architecture and demonstrate a microprocessor-to-memory interconnect prototype through the proposed AWEC link. Notably, we expect that the AWEC scheme will be significant for high-speed optical interconnects in advanced computing systems.

AC Electrokinetics (ACEK) has attracted much research interest for microfluidic manipulation for the last few years. It shows great potential for functions such as micropumping, mixing and concentrating particles. Most of current ACEK research focuses on AC electroosmosis (ACEO), which is limited to solutions with conductivity less than 0.02 S/m, excluding most biofluidic applications. To solve for this problem, this dissertation seeks to apply AC electrothermal (ACET) effect to manipulate conductive fluids and particles within, and it is among the first demonstration of ACET devices, a particle trap and an ACET micropump. The experiments used fluids at a conductivity of 0.224 S/m that is common in bio-applications. Pumping and trapping were demonstrated at low voltages, reaching ~100 um/s for no more than 8 Vrms at 200 kHz. The flow velocity was measured to follow a quadratic relationship with applied voltage which is in accordance with theory. This research also studies ACET effect on low ionic strength microfluidics, since Joule heating is ubiquitous in electrokinetic devices. One contribution is that our study suggested ACET as one possible reason of flow reversal, which has intrigued the researchers in ACEK field. Electrically, a microfluidic cell can be viewed as an impedance network of capacitances and resistors. Heat dissipation in those elements varies with AC frequency and fluid properties, so changes the relative importance of heat generation at the electrode/electrolyte interface and in the resistive fluid bulk, which could change the temperature gradient in the device, hence changing the flow direction. Another contribution of this dissertation is the reaction enhanced ACET micropumping. A dramatic improvement in flow rate over conventional ac micropumps is achieved by introducing a thin fluid layer of high ionic density near the electrodes. Such an ionic layer is produced by superimposing a DC offset on AC signal that induces Faradaic reaction. The velocity improvement, in some cases, is over an order of magnitude, reaching a linear velocity of up to 2.5 mm/s with only 5.4Vrms. This discovery presents an exciting opportunity of utilizing ACET effect in microfluidic applications.