Low temperature co-fired ceramic (LTCC) electronic packaging materials are applied for their electrical and mechanical properties, high reliability, chemical stability and ease of fabrication. Three dimensional features can also be prepared allowing integration of microfluidic channels and cavities inside LTCC modules. Mechanical, optical, electrical, microfluidic functions have been realized in single LTCC modules. For these reasons LTCC is attractive for biomedical microfluidics and Lab-on-a-Chip systems. However, commercial LTCC systems, optimized for microelectrics applications, have unknown cytocompatibility, and are not compatible with common surface functionalization chemistries. The first goal of this work is to develop biocompatible LTCC materials for biomedical applications. In the current work, two different biocompatible LTCC substrate materials are conceived, formulated and evaluated. Both materials are based from well-known and widely utilized biocompatible materials. The biocompatibilities of the developed LTCC materials for in-vitro applications are studied by cytotoxicity assays, including culturing endothelial cells (EC) both in LTCC leachate and directly on the LTCC substrates. The results demonstrate the developed LTCC materials are biocompatible for in-vitro biological applications involving EC. The second goal of this work is to develop functional capabilities in LTCC microfluidic systems suitable for in-vitro and biomedical applications. One proposed application is the evaluation of oxygen tension and oxidative stress in perfusion cell culture and bioreactors. A Clark-type oxygen sensor is successfully integrated with LTCC technique in this work. In the current work, a solid state proton conductive electrolyte is used to integrate an oxygen sensor into the LTCC. The measurement of oxygen concentration in Clark-type oxygen sensor is based on the electrochemical reaction between working electrode and counter electrode. Cyclic voltammetry and chronoamperometry are measured to determine the electrochemical properties of oxygen reduction in the LTCC based oxygen sensor. The reduction current showed a linear relationship with oxygen concentration. In addition, LTCC sensor exhibits rapid response and sensitivity in the physiological range 1─9 mg/L. The fabricated devices have the capabilities to regulate oxygen supply and determination of local dissolved oxygen concentration in the proposed applications including perfusion cell culture and biological assays.

Microfluidic devices have found applications in a number of areas, such as medical analysis, chemical synthesis, biological study, and drug delivery. Because of the small channel dimensions used in these systems, most microchannels exhibit laminar flow due to their low Reynold’s number, making mixing of fluids very challenging. Mixing at this size scale is diffusion-limited, so inducing chaotic flow patterns can increase the interface surface area between two fluids, thereby decreasing overall mixing time. One method to create a chaotic flow within the channel is through the introduction of internal protrusions into the channel. In such an application protrusions that create a rotational flow within the channel are preferred due to their effectiveness in folding the two fluids over one another. The novel mixer outlined in this paper uses a Ti-Ni shape memory alloy for the creation of protrusions that can be turned controlled through material temperature. Controllability of the alloy allows users to turn the chaotic flow created by the protrusions off and on by varying the temperature of the mixer. This ability contributes to the idea of a continuous microfluidic system that can be turned on only when necessary as well as recycle unmixed fluids while turned off.

This thesis seeks to address the critical bottlenecks of current technologies that have slowed the neuroscience research in C. elegans. The objective of this research is to enhance the currently developed systems through the design and construction of simple microdevices and quantitative analytical tools for high-throughput phenotyping C. elegans to investigate functions of nervous systems. First, we developed and used the integrated system combining user-friendly single-layer microfluidics and quantitative analytical tools to study the genetic regulation of target gene expression. We found several putative mutants based on large-scale screens, which would have previously been too labor-intensive to attempt. Second, we developed a simple mathematical model that describes the regulation of a target gene expression. Using the model developed, we simulated phenotypical space of hypothetical mutants to suggest plausible genetic pathways some isolated mutants may affect. Lastly, we developed a high-density multichannel device for rapid trapping, parallel selective stimulating, long-term culturing, and (often repeatedly). We used this integrated system to study the neurodegenerative process based on selective ablation of multiple animals using an optogenetic tool, which would have been taken at least 1 order of magnitude longer. Taken together, we expect that these developments will greatly facilitate a broad range of fundamental, and application studies including aging, neurodegeneration, circuit and behavior.

No description available.

This thesis describes the development of microfluidic (MF) platforms for the study of biological and chemical processes. In particular the thesis is divided into two distinct parts: (i) development of a MF methodology to generate tunable cell-laden microenvironments for detailed studies of cell behavior, and (ii) the design and fabrication of MF reactors for studies of chemical reactions. First, this thesis presented the generation of biopolymer microenvironments for cell studies. In the first project we demonstrated a high-throughput MF system for generating cell-laden agarose microgels with a controllable ratio of two different types of cells. The MF co-encapsulation system was shown to be a robust method for identifying autocrine and/or paracrine dependence of specific cell subpopulations. In the second project we studied the effect of the mechanical properties on the behavior of acute myeloid leukemia (AML2) cancer cells. Cell-laden macroscopic agarose gels were prepared at varying agarose concentrations. A modest range of the elastic modulus of the agarose gels were achieved, ranging from 0.62 kPa to 20.21 kPa at room temperature. We observed a pronounced decrease in cell proliferation in stiffer gels when compared to the gels with lower elastic moduli. The second part of the thesis focuses on the development of MF platforms for studying chemical reactions. In the third project presented in this thesis, we exploited the temperature dependent solubility of CO2 in order to: (i) study the temperature mediated CO2 transfer between the gas and the various liquid phases on short time scales, and (ii) to generate bubbles with a dense layer of colloid particles (armoured bubbles). The fourth project involved the fabrication of a multi-modal MF device with integrated analytical probes. The MF device comprised a pH, temperature, and ATR-FTIR probes for in-situ analysis of chemical reactions in real-time. Furthermore, the MF reactor featured a temperature controlled feedback system capable of maintaining on-chip temperatures at flow rates up to 50 mL/hr.

This thesis focuses on applying microfluidic techniques to analyze two carbon management methods; underground carbon sequestration and enhanced oil recovery. The small scale nature of microfluidic methods enables direct visualization of relevant pore-scale phenomena, enabling elucidation of parameters such as diffusion coefficients and critical compositions. In this work, a microfluidic platform was developed to control a two-phase carbon dioxide (CO2)-water interface for diffusive quantification with fluorescent techniques. It was found that the diffusion coefficient of CO2 in pure water was constant (1.86 [± 0.26] x10-9 m2/s) over a range of pressures. The effects of salinity on diffusivity were also measured in solutions, it was found that the diffusion coefficient varied up to 3 times. A microfluidic technique able to determine the critical composition of a model ternary mixture was also successfully implemented. Results indicate potential application of this approach to minimum miscibility pressure measurements used in enhanced oil recovery.

In this thesis I present a microfluidic platform developed to control dissolved gases and monitor dissolved oxygen concentrations within the microenvironment of isolated small blood vessels. Dissolved gas concentrations are controlled via permeation through the device substrate material using a 3D network of gas and liquid channels. Dissolved oxygen concentrations are measured on-chip via fluorescence quenching of an oxygen sensitive probe embedded in the device. Dissolved oxygen control was validated using the on-chip sensors as well as a 3D computational model. The platform was used in a series of preliminary experiments using olfactory resistance arteries from the mouse cerebral vascular bed. The presented platform provides the unique opportunity to control dissolved oxygen concentrations at high temporal resolutions (<1 min) and monitor dissolved oxygen concentrations in the microenvironment surrounding isolated blood vessels.

Microfluidic techniques have allowed for fast, sensitive, and low cost applications of the Polymerase Chain Reaction (PCR) through the use of small reaction volumes, rapid amplification speeds, and the on-chip integration of upstream and downstream sample handling processes including purification and electrophoretic separation functionality. While such systems are capable of measuring the expression levels of thousands of genes simultaneously, or in hundreds of cells, or with sample-in and answer-out capability, none of these systems are easily scalable in the time domain. Because of this, the field of gene expression measurement has yet to fully utilize the advantages of microfluidic PCR in developing systems to measure changes in gene expression in increments of hours rather than days. In this project, we developed a microfluidic RT-qPCR system that utilizes infrared heating and open-loop control to reliably reverse transcribe, amplify, and detect samples in a single 1 μl polymer chip. Optimized power profiles were created that allow for fast heating and cooling rates while minimizing undershoot and overshoot from the desired hold temperatures. By utilizing repeatable microfluidic chip manufacturing techniques, and by controlling the environment around the chip, the same open loop program can repeatedly amplify multiple samples without any need for temperature feedback or recalibration between runs. Furthermore, the system was designed to operate on top of a fluorescence microscope to enable real-time fluorescence detection and quantification of starting copy number. By eliminating complicated setup procedures and calibration runs, this system increases the practicality of measuring gene expression at a high temporal frequency.

The polymerase chain reaction (PCR) is an extremely powerful tool for viral detection and screening because it can detect specific infectious agents with great sensitivity and specificity. It works by exponentially amplifying a target viral DNA sequence to high enough concentrations through the use of specific reagents and thermal cycling. It has surpassed culture based methods as the gold standard for viral detection because of the increased speed and sensitivity. Microfluidic approaches to PCR have focused on decreasing the time to thermally cycle, the volumes used for reactions, and they have also added upstream and downstream processes that are of benefit for on-chip viral detection. While these improvements have made great strides over commercially available products in terms of speed, cost, and integration, a major limitation that has yet to be explored is the throughput associated with running PCR. Since each PCR reaction relies on primers with a unique annealing temperature to detect specific viral DNA, only a single virus can be screened for at a time. The device presented here uses two infrared laser diodes that are driven identically by the same laser driver to independently thermally cycle two chambers on the same microfluidic chip. Different temperatures are achieved in the two chambers by modulating the radiation reaching one of those chambers with an optical shutter. Closed loop temperature feedback in both chambers is done with a Labview program and thermocouples embedded in the polymer chip. This allows for accurate temperature measurement without inhibiting the reaction. To demonstrate the capabilities of this device, two different reactions were simultaneously amplified successfully on the same device that have annealing temperatures that differ by 15°C.

Thesis (Ph.D.). / Written for the Dept. of Biomedical Engineering. Title from title page of PDF (viewed 2008/01/12). Includes bibliographical references.