Implementation of a high resolution optical feedback interferometer for microfluidics applications

Recent progress of interferometric sensors based on the optical feedback in a laser diode have demonstrated possibility for measurement of flow rates and flow-profiles at the micro-scale. That type of compact and embedded sensors is very promising for a research and industrial field –microfluidics – that is a growing domain of activities, at the frontiers of the physics, the chemical science, the biology and the biomedical. However, the acquisition of flow rate or local velocity at high resolution remains a very challenging issue, and the sensors that have been proposed so far did not have been giving sufficient information on the nature of the particles flowing. The present thesis is driven to the implementation, validation and evaluation of the sensing performances of the optical feedback interferometry technology in both chemical and biomedical fields of applications. The elaboration of a new generation of sensors that will provide both a high spatial resolution for 2D Doppler imaging is presented, as well as a methodology that gives further information on the flowing particles concentration and/or dimensions. Then, a new embedded optical feedback interferometry imager for flowmetry has been realized using a 2-axis beamsteering mirror mounted on Micro-Electro-Mechanical Systems (MEMS) thus taking the full advantage of the compactness offered by the optical feedback interferometry sensing scheme. While previous works on optical feedback interferometry flowmetry have been limited to high particle densities fluids in single or multiple scattering regimes, we present also a sensing technique based on the optical feedback interferometry scheme in a laser diode that enables single particle detection at micro and nanoscales through the Doppler-Fizeau effect. Thanks to the proposed signal processing, this sensing technique can detect the presence of single spherical polystyrene micro/nanospheres seeded in watery suspensions, and measure their flow velocity, even when their diameter is below half the laser wavelength. It discriminates particle by their diameter up to a ratio of 5 between large and small ones while most of the technologies for particle characterization is bulk and requires manipulation of the fluid with small volume handling, precise flow and concentration control. Altogether, the results presented in this thesis realize a major improvement for the use of optical feedback interferometry in the chemical engineering or biomedical applications involving micro-scale flows

Two new types of laser doppler flowmeters prototypes validation

A fluxometria laser Doppler (LDF) é uma técnica para avaliação em tempo real do fluxo microcirculatório em tecidos biológicos. Esta técnica pode ser usada para monitorização não invasiva da microcirculação (por exemplo, avaliação da perfusão na pele), ou para monitorização da perfusão de forma invasiva (por exemplo, avaliação da perfusão no cérebro). Nesta tese, pretende-se acrescentar ao estado da arte da LDF, quando aplicada à monitorização não invasiva da perfusão na pele, a capacidade de discriminação em profundidade. Para isso, foi desenvolvido um protótipo de um fluxómetro laser Doppler com vários comprimentos de onda e diferentes separações entre as fibras emissora e receptora. Tendo em vista a monitorização de perfusão de cérebro de rato construiu-se um protótipo de um fluxómetro laser Doppler baseado na técnica self-mixing utilizando micro-fibras ópticas de forma invasiva. Para validar estes dois novos protótipos, fizeram-se simulações Monte Carlo do transporte de luz em tecidos. Realizaram-se simulações num fantoma (constituído por seis camadas de fluido a diferentes profundidades), e num modelo da pele para a validação do protótipo não invasivo. Os resultados demonstraram que o primeiro momento do especto de potência (M1), assim como, a profundidade atingida pelos fotões, aumentam com o incremento da distância entre as fibras emissora e receptora. Para além disso, os resultados evidenciaram que o acréscimo do comprimento de onda da luz laser traduz-se numa maior profundidade média amostrada. Medições realizadas com o protótipo não invasivo no fantoma e na pele foram comparados com os resultados das simulações. As simulações aproximam-se bastante dos resultados das medições Para a validação do protótipo invasivo, foram efectuadas simulações Monte Carlo num modelo de cérebro de rato. Foi demonstrado que a profundidade média medida com a sonda construída é de 0.15 mm

Blood vessel detection in medical procedures using laser Doppler flowmetry

The needle procedures such as coronary angioplasty and coronary artery bypass graft installation are the most common surgical interventions performed in medical practice, and the accuracy of the catheter needle placement defines the success of the whole operation. Due to anatomical variations in patients, finding and puncturing the correct blood vessel is a challenging step, and the needle guidance might significantly simplify the process. Therefore, the primary aim of this work was to develop a novel blood vessel detection system based on laser Doppler flowmetry (LDF) technology that will improve the quality of medical needle procedures. In this work, LDF measurement setup was designed, assembled and evaluated. The setup includes custom laser-detector system, two invasive measurements probes, two experimental phantoms and data acquisition software. The optical properties of human tissue and blood were examined in order to define the required laser characteristics and relevant tissue-mimicking materials. The data processing was based on the power spectrum analysis, from which the perfusion parameter was extracted. The measurement range of the system was assessed in respect to the various criteria such as penetration angle, depth and site. The applicability of LDF in the needle procedures was evaluated. The experimental results demonstrated that the blood vessel can be successfully detected in the wide angles range and at different penetration sites. The differentiation between low and high blood flow speeds is also possible. Moreover, the potential of the measurements in tissue was demonstrated. However, certain limitations need to be addressed. It was discovered, that the distinction between the arteria and the vein is challenging, and the penetration depth inside the tissue is restricted. Nevertheless, the proposed technology can be implemented in the needle procedures and a number of other medical applications, such as laparoscopic surgeries and biopsies

Bioreactor technologies to support liver function in vitro

Liver is a central nexus integrating metabolic and immunologic homeostasis in the human body, and the direct or indirect target of most molecular therapeutics. A wide spectrum of therapeutic and technological needs drives efforts to capture liver physiology and pathophysiology in vitro, ranging from prediction of metabolism and toxicity of small molecule drugs, to understanding off-target effects of proteins, nucleic acid therapies, and targeted therapeutics, to serving as disease models for drug development. Here we provide perspective on the evolving landscape of bioreactor-based models to meet old and new challenges in drug discovery and development, emphasizing design challenges in maintaining long-term liver-specific function and how emerging technologies in biomaterials and microdevices are providing new experimental models.National Institutes of Health (U.S.) (R01 EB010246)National Institutes of Health (U.S.) (P50-GM068762-08)National Institutes of Health (U.S.) (R01-ES015241)National Institutes of Health (U.S.) (P30-ES002109)5UH2TR000496-02National Science Foundation (U.S.). Emergent Behaviors of Integrated Cellular Systems (CBET-0939511)United States. Defense Advanced Research Projects Agency. Microphysiological Systems Program (W911NF-12-2-0039

Aerospace medicine and biology: A continuing bibliography with indexes (supplement 287)

This bibliography lists 346 reports, articles and other documents introduced into the NASA scientific and technical information system in July 1986

Gastrointestinal injury following cardiopulmonary bypass

The gastrointestinal (GI) tract may be the source of a number of bacterial and non-bacterial mediators, which may contribute to the development of morbidity and mortality following episodes of gut hypoperfusion/ ischaemia. The aim of this thesis has been to identify the changes in gut blood flow, oxygenation and function following cardiopulmonary bypass (CPB) and their relationship to the development of post-CPB morbidity. The findings are summarised below: The retrospective study identified age (>65 yr) and CPB time as risk factors for the development of post-CPB intra-abdominal complications . Tonometrically determined values for intramucosal pH (pHi) need temperature correction to avoid calculation of erroneously high values during hypothermic CPB. Considerable hypoperfusion occurs during hypothermic CPB, with laser Doppler flowmetry (LDF) falling to approximately 45% of pre-CPB values. The gastric and colonic pHi becomes acidotic (<7.35) during the re-warming and immediate post-CPB period. Intramucosal acidosis occurs at a time when mucosal LDF blood flow is normal or supranormal. CPB increases gut permeability and reduces the absorption of the monosaccharides, 3-O-m-D-glucose, D-xylose & L-rhamnose. Post-CPB gut permeability has a temporal relationship with the CPB time. Pulsatile flow attenuates the increase in post-CPB gut permeability. Endotoxaemia occurs during CPB but is not associated with the production of TNFα; pulsatile flow attenuates this endotoxaemia. When examining perfusion and patient factors, the best predictor for a protracted ventilation & ICU stay for patients was a low gastric pHi (<7.35). A canine model of CPB supported the clinical findings, but also found that: (a) changes in large vessel blood flow do not indicate more dynamic alterations in small vessel blood flow (b) blood flow is prioritised to the mucosa at the expense of the serosal aspects of the bowel wall (c) in the re-warming phase of hypothermic CPB & the immediate post-CPB period, when intramucosal acidosis occurs, there is a disparity between gut oxygen consumption & delivery (b) increased expression of vasoactive intestinal peptide was found in the neural plexus of the submucosa post-CPB, which may indicate a role in preserving mucosal blood flow during periods of hypoperfusion

Developing an electrochemical tissue perfusion sensor

This thesis focuses on the development of an electrochemical tissue perfusion sensor. Tissue perfusion is the cellular level mass transport mechanism which describes the movement of nutrients and metabolites within in tissue and is a measure of tissue health. Our understanding of tissue perfusion is still limited because current measurement tools are inadequate. The tissue perfusion measurement technique developed overcomes the limitation of current methods in that continuous and cellular level measurements are possible. This is achieved using a platinum ring-disc microelectrode operated in the collector-generator mode. This electrode pair is placed in tissue where one electrode generates hydrogen whilst the other collects it. Tissue perfusion will strongly influence the movement of H2 between the two closely spaced electrodes. The ratio of collector to generator current can thus be used to quantify tissue perfusion. To make the micron size ring-disc electrodes, a novel fabrication method was used. It relies on hollow cylindrical sputter coating and produces sensors with diameter as small as 28 μm. A number of numerical models of the sensor under diffusion and convection mass transport modes were constructed to assist the design process and to further our understanding of the behaviour of the electrodes in different situations. Experimental characterisation of the sensor was also carried out under diffusion and convection mass transport modes. These experiments also improved the design of the sensor and often agreed with numerical predictions. Finally the sensor was tested in a number of animal and human tissues as well as perfusion models. These were used as a proof of principle to confirming the capability of the sensor to continuously measure changes in tissue perfusion at the cellular level

Tailoring vessel morphology in vivo

Tissue engineering is a rapidly growing field which seeks to provide alternatives to organ transplantation in order to address the increasing need for transplantable tissues. One huge hurdle in this effort is the provision of thick tissues; this hurdle exists because currently there is no way to provide prevascularized or rapidly vascularizable scaffolds. To design thick, vascularized tissues, scaffolds are needed that can induce vessels which are similar to the microvasculature found in normal tissues. Angiogenic biomaterials are being developed to provide useful scaffolds to address this problem. In this thesis angiogenic and cell signaling and adhesion factors were incorporated into a biomimetic poly(ethylene glycol) (PEG) hydrogel system. The composition of these hydrogels was precisely tuned to induce the formation of differing vessel morphology. To sensitively measure induced microvascular morphology and to compare it to native microvessels in several tissues, this thesis developed an image-based tool for quantification of scale invariant and classical measures of vessel morphology. The tool displayed great utility in the comparison of native vessels and remodeling vessels in normal tissues. To utilize this tool to tune the vessel response in vivo , Flk1::myr-mCherry fluorescently labeled mice were implanted with Platelet Derived Growth Factor-BB (PDGF-BB) and basic Fibroblast Growth Factor (FGF-2) containing PEG-based hydrogels in a modified mouse corneal angiogenesis assay. Resulting vessels were imaged with confocal microscopy, analyzed with the image based tool created in this thesis to compare morphological differences between treatment groups, and used to create a linear relationship between space filling parameters and dose of growth factor release. Morphological parameters of native mouse tissue vessels were then compared to the linear fit to calculate the dose of growth factors needed to induce vessels similar in morphology to native vessels. Resulting induced vessels did match in morphology to the target vessels. Several other covalently bound signals were then analyzed in the assay and resulting morphology of vessels was compared in several studies which further highlighted the utility of the micropocket assay in conjunction with the image based tool for vessel morphological quantification. Finally, an alternative method to provide rapid vasculature to the constructs, which relied on pre-seeded hydrogels encapsulated endothelial cells was also developed and shown to allow anastamosis between induced host vessels and the implanted construct within 48 hours. These results indicate great promise in the rational design of synthetic, bioactive hydrogels, which can be used as a platform to study microvascular induction for regenerative medicine and angiogenesis research. Future applications of this research may help to develop therapeutic strategies to ameliorate human disease by replacing organs or correcting vessel morphology in the case of ischemic diseases and cancer

Implementation of optical feedback interferometry for sensing applications in fluidic systems

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