Fabrication of a microfluidic platform for impedance analysis of cultured endothelial cell monolayers.

Assessing the functionality of the endothelium can provide insight into the initiation and formation of arterial diseases. One of the most important functions of the endothelial layer is its permeability. The integrity of the cell monolayer and its ability to transport molecules can be assessed in vitro by investigating the electrical impedance. In this study, a microfluidic platform was created using an electrode-patterned glass substrate and microfluidic poly(dimethyl siloxane) (PDMS) substrate. The electrode glass base of the structure was fabricated with platinum square electrodes of various sizes ranging from 10x10 ìm2 to 160x160 ìm2 and a larger, common counter electrode. Master microfluidic molds for PDMS casting were created by micro-milling Lexan® and photolithographically patterning SU-8. The microfluidic PDMS substrates reversibly and conformally bonded to the glass-electrode substrate. The microfluidic platforms were characterized by loading the microchannels with cell growth media alone, cell growth media and fibronectin, and cell growth media, fibronectin and human umbilical vein endothelial cells and obtaining impedance spectra. The experiments were performed under both no flow and flow conditions. Fibronectin did not significantly alter the collected impedance spectrum compared to media alone under no flow conditions. Under no flow conditions, impedance spectra measurements were able to detect the presence of cultured cells on the electrodes. The presence of fibronectin and various tested flow rates did not alter the impedance spectrum compared to media alone under static conditions. After further investigations, the microfluidic platform will become a versatile means of characterizing endothelial cell layer behavior

Silicon carbide epitaxial growth using methylsilanes as gas sources

Large area and high quality SiC substrates are required for many applications. The goal of this research is to develop novel methods of growing epitaxial silicon carbide (SiC) on 6H-SiC and silicon (Si) substrates while extending our understanding of the growth mechanisms and the effects of key growth parameters. High temperature hydrogen-etching procedures for preparing atomically-stepped 6H-SiC substrates suitable for epitaxial growth were also developed.;This dissertation presents results of both homoepitaxial SiC growth on 6H-SiC substrates and heteroepitaxial growth on Si substrates by gas source molecular beam epitaxy. The experimental variables included gas species, molecular flux, growth time, and substrates growth temperature. In particular, the growth species considered here were methylsilane and dimethylsilane, and the substrate temperatures were 700°C and 800°C. The thin films grown in these studies were characterized by Auger electron spectroscopy, reflection high Energy electron diffraction, field emission scanning electron microscopy, and atomic force microscopy.;Homoepitaxial films grown on 6H-SiC substrates showed little to no change in surface chemical composition, surface crystal structure, and RMS roughness. Compared to the substrates, reductions in step height were detected consistent with previous observations for chemical vapor desposition of SiC. Thick heteroepitaxial films could be grown on Si using methylsilane as the gas source at 800°C, but voids caused by Si out-diffusion from the substrate were a problem still. Dimethylsilane produced thick epitaxial films at 800°C without substrate voids. In this case, however, the surface was terminated by C-C bonds

Towards the manufacturing of microfluidic devices : fluid flow in multilayer devices as a test case

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2006.Includes bibliographical references (p. 154-158).In this work, the area of microfluidics is analyzed for advances that could be made in the manufacturing of a microfluidic device, and then one area - the alignment of multilayer devices - is selected for greater focus. Microfluidics is an emerging technology receiving much attention to date for its potential in biological, chemical, and medical applications. It could bring costs savings and contamination-reducing disposable parts, but only if certain hurdles relating to the design and fabrication of the devices are overcome. In order to better understand the manufacturing issues, a survey of the applications is presented, with a focus on the functional requirements for the fabrication of the devices. Then, a survey of the techniques currently in use to create microfluidic devices is presented, again focusing on the issues related to their fabrication and scalability to large-volume manufacturing. In order to address the issues that arise during the surveys, two new directions are submitted. First, a "test device" is proposed. This test device will consist of a variety of sample features characteristic of many different types of microfluidic devices, in a range of carefully selected dimensions.(cont.) The test device serves as a tool for evaluating different processes for relative capabilities in creating the microfluidic structures. Second, multilayer devices, an area of concern that will arise as the field moves forward, is explored further. Specifically, the impact on fluid flow parameters of alignment of the two layers, a process currently performed manually, is investigated. A theoretical model of the scenario, which acts as a pressure barrier to laminar flow in a rectangular channel, is established, identifying the parameter of interest, the coefficient of pressure loss across the multilayer joint between layers. Then a series of sample multilayer parts with target dimensions of 100 gm x 100 pm x 3 mm is constructed. The pressure loss coefficients were obtained as a function of the cross-sectional area of the joint, from as small as 0.71 for very large joints up to over 1000 for joints that are only 30 gm of the channel in width. Failure pressure for the devices was found to be on the order of 140 kPa.by Samuel N. Korb.S.M

Microchemical systems for singlet oxygen generation

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2008.Includes bibliographical references (p. 153-158).Chemical Oxygen-Iodine Lasers (COIL) are a technology of interest for industrial and military audiences. COILs are flowing gas lasers where the gain medium of iodine atoms is collisionally pumped by singlet delta oxygen molecules, which are created through the catalyzed multiphase reaction of hydrogen peroxide and chlorine. Currently the use of COIL technology is limited by size and efficiency issues. This thesis seeks to use MEMS technology towards the development of more compact and efficient COIL systems, with a focus on the singlet oxygen generator (SOG) stage. Based on success in other applications, MEMS technology offers opportunities for improved reactant mixing, product separation, and heat transfer in SOGs. A MEMS singlet oxygen generator (or microSOG) is built and demonstrated. The chip features 32 multiplexed packed bed reaction channels and utilizes capillarity effects to separate the gas and liquid products. Cooling channels are arranged on the chip such that they form a cross-flow heat exchanger with the reaction channels. Spontaneous optical emission measurements and mass spectroscopy are used to confirm singlet oxygen production in the chip. A singlet delta oxygen molar flow rate corresponding to a power of 1.37 W was measured in the chip. The singlet oxygen molar flow rate per unit of hardware volume is 6.7x10-2 mol/L/sec, which represents an order of magnitude improvement over sparger and rotary SOG designs. A detailed physical model is developed to understand the behavior of the microSOG. This model is used along with the experimental results to gain insights into the poorly characterized singlet oxygen deactivation coefficients. Clogging and nonlinear hydraulic behavior prevented the first-generation microSOG from performing as well as the models originally suggested. These issues are addressed in a proposed second generation design, which simulations indicate will produce 50% more singlet oxygen per unit of hardware volume than its predecessor.by Tyrone Frank Hill.Ph.D

A thin monocrystalline diaphragm pressure sensor using silicon-on-insulator technology.

The sensors market is huge and growing annually, of this a large sector is pressure sensors. With increasing demands on performance there remains a need for ultraminiature, high performance pressure sensors, particularly for medicai applications. To address this a novel capacitive pressure sensor consisting of an array of parallel connected diaphragms has been designed and fabricated from SIMOX substrates. The benefits of this include single crystal silicon diaphragms, small, well controlled dimensions, single sided processing and the opportunity for electronics integration. Theoretical modelling of this structure predicts a high sensitivity and low stress device with opportunities for scaling to suit alternative applications. A novel, process technology was developed to achieve the required structure with the inclusion of procedures to address the specific issues relating to the SIMOX material. The sensor was fully characterised and the results demonstrated high performance compared with similar reported devices. Alternative structures such as cantilevers, bridges and resonators were fabricated as a demonstrative tool to show the feasibility of this technology in a wider field of applications

Dissection of Affective Catecholamine Circuits Using Traditional and Wireless Optogenetics

Parsing the complexity of the mammalian brain has challenged neuroscientists for thousands of years. In the early 21st century, advances in materials science and neuroscience have enabled unprecedented control of neural circuitry. In particular, cell-type selective manipulations, such as those with optogenetics and chemogenetics, routinely provide answers to previously intractable neurobiological questions in the intact, behaving animal. In this two-part dissertation, I first introduce new minimally invasive, wireless technology to perturb neural activity in the ventral tegmental area dopaminergic system of freely moving animals. I report a series of novel devices for studying and perturbing intact neural systems through optogenetics, microfluidic pharmacology, and electrophysiology. Unlike optogenetic approaches that rely on rigid, glass fiber optics coupled to external light sources, these novel devices utilize flexible substrates to carry microscale, inorganic light emitting diodes (μ-ILEDs), multimodal sensors, and/or microfluidic channels into the brain. Each class of device can be wirelessly controlled, enabling studies in freely behaving mice and achieving previously untenable control of catecholamine neural circuitry. In the second part of this dissertation, I apply existing cell-type selective approaches to dissect the role of the locus coeruleus noradrenergic (LC-NE) system in anxiety-like and aversive behaviors. The LC-NE system is one of the first systems engaged following a stressful event. While LC-NE neurons are known to be activated by many different stressors, the underlying neural circuitry and the role of this activity in generating stress-induced anxiety has not been elucidated until now. I demonstrate that increased tonic activity of LC-NE neurons is both necessary and sufficient for stress-induced anxiety; a behavior which is driven by LC projections to the basolateral amygdala. Furthermore, this activity and behavior is elicited by corticotropin releasing hormone-containing afferent inputs into the LC from the central amygdala. These studies position the LC-NE system as a critical mediator of acute stress-induced anxiety and offer a potential intervention for preventing stress-related affective disorders. Together these two objectives provide a rich technological toolbox for neuroscientists and yield important knowledge of how small catecholamine structures with widespread forebrain innervation can selectively mediate higher order behaviors

High Throughput Methods in the Synthesis, Characterization, and Optimization of Porous Materials

Porous materials are widely employed in a large range of applications, in particular, for storage, separation, and catalysis of fine chemicals. Synthesis, characterization, and pre- and post-synthetic computer simulations are mostly carried out in a piecemeal and ad hoc manner. Whilst high throughput approaches have been used for more than 30 years in the porous material fields, routine integration of experimental and computational processes is only now becoming more established. Herein, important developments are highlighted and emerging challenges for the community identified, including the need to work toward more integrated workflows

Advances in Condition Monitoring, Optimization and Control for Complex Industrial Processes

The book documents 25 papers collected from the Special Issue “Advances in Condition Monitoring, Optimization and Control for Complex Industrial Processes”, highlighting recent research trends in complex industrial processes. The book aims to stimulate the research field and be of benefit to readers from both academic institutes and industrial sectors