Thesis (Ph. D.)--Electrical and Computer Engineering, Georgia Institute of Technology, 2006. / Michaels, Thomas E., Committee Member ; LaPlaca, Michelle, Committee Member ; Frazier, A. Bruno, Committee Member ; DeWeerth, Stephen P., Committee Member ; Allen, Mark G., Committee Chair.

Thesis (M.S.)--University of Missouri-Columbia, 2004. / Typescript. Includes bibliographical references (leaves 99-102). Also available on the Internet.

Microfluidic devices are emerging as an attractive technology for automatically orchestrating the reactions needed in a biological computer. Thousands of microfluidic primitives have already been integrated on a single chip, and recent trends indicate that the hardware complexity is increasing at rates comparable to Moore's Law. As in the case of silicon, it will be critical to develop abstraction layers--such as programming languages and Instruction Set Architectures (ISAs)--that decouple software development from changes in the underlying device technology.Towards this end, this paper presents BioStream, a portable language for describing biology protocols, and the Fluidic ISA, a stable interface for microfluidic chip designers. A novel algorithm translates microfluidic mixing operations from the BioStream layer to the Fluidic ISA. To demonstrate the benefits of these abstraction layers, we build two microfluidic chips that can both execute BioStream code despite significant differences at the device level. We consider this to be an important step towards building scalable biocomputers.

This thesis includes three stages of experiments. The goal of the thesis was to prepare nanoparticle-encapsulated curcumin for the purpose of drug delivery. The first step was the nanoparticle preparation. The self-assembly of block copolymer (poly(ε- caprolactone)-b-poly(ethylene oxide)) and curcumin was conducted on a gas-liquid two phase microfluidic reactor. During preparation, various chemical parameters and flow rates were tested. The nanoparticles showed flow variability; the size decreased and the loading efficiency increased with increased flow rates. Increasing the water content and drug-to-polymer loading ratio also proved to increase loading efficiency and decrease the size of the nanoparticles. The release profiles, however, showed fast release rates under various preparation conditions, with a nearly complete release after ~5 h. In the next stage of the research, we considered release optimization in preparation for future pharmacokinetic studies. Increasing the flow rate had a greater influence on slowing down release rates than changing other parameters, such as decreasing the drug-to- polymer loading ratio or increasing the water content. A procedure to extract and quantify curcumin from mouse blood was also developed in this stage. In the final stage of the research, nanoparticle-encapsulated curcumin was tested on a human breast cancer cell line, MDA-MB-231. The result showed that the nanoparticle formulation had a growth inhibition effect on MDA-MB-231, although the cytotoxicity was compromised by encapsulation in the nanoparticles. / Graduate / 2019-01-13

University of Macau / Faculty of Science and Technology / Department of Electrical and Computer Engineering

Encapsulating cells within semi-permeable hydrogel material has been shown to boost the therapeutic effectiveness of stem cell therapy in certain applications. Cell encapsulation promotes high retention and engraftment rates, and protects against attack from the immune system of the host, as these are challenges often seen in utilizing stem cells in suspension alone. Leveraging droplet-based microfluidics has yielded a platform capable of producing monodispersed microcapsules embedded with cells at high throughput, typically achieved by mixing an aqueous hydrogel solution that contains cells with an immiscible liquid (oil) in a flow focusing geometry. However, encapsulation using microfluidics results in randomized generation of empty and cell-laden microcapsules, following Poisson statistics, raising the need to institute a successful sorting mechanism, thereby increasing occupancy and ultimately purifying the desired sample. In this thesis we propose a sorting strategy by combining two conceptual mechanisms of electrophoresis (EP) and deterministic lateral displacement (DLD). Different varieties of microcapsules were characterized for EP and DLD respectively. Leveraging these differences was used in a device combining both of the concepts towards sorting of empty and cell-laden microcapsules.

Continuous progress in the nanotechnology field has allowed for the emergence of powerful, nanopore-based detection technology. Solid-state nanopores were developed for next-generation sequencing and single-molecule detection. They are advantageous over their biological counterpart because they offer robustness, stability, tunable pore size and the ability to be integrated within a microfluidic device. With all of these attractive attributes, solid-state nanopores are a top contender for point-of-care diagnostic technologies. However, hindering their performance is an inability to distinguish between small molecules, pore-clogging, and the detection rate's dependence on sample concentration. The concentration-dependent detection rate becomes particularly evident at low sample concentrations (<1 nM), sometimes taking hours for the nanopore to sense a single molecule because of diffusion. The inability to distinguish between small molecules can be addressed using DNA nanostructures; however, pore-clogging and variable detection rates hinder its potential in a clinical setting. This thesis proposes a microfluidic device design and methodology that seeks to mitigate pore-clogging and improve the detection rate for dilute samples. DNA coated microbeads will create a bead column within the microfluidic device and confine the target molecules to an extremely small (20 nL) volume. The sample can be washed, ridding the contaminants, and eluted on-chip, so the sample is purified and concentrated, affording a more reliable sensing performance. First, a magnetic microbead DNA assay was optimized off-chip, and the capture and release efficiencies were monitored using a Biotek™ Epoch™ 2 spectrophotometer (Chapter 2). Next, a novel microfluidic device design was optimized and validated to ensure precise sample manipulation (Chapter 3). Finally, the microbead assay was incorporated into the microfluidic device for sample concentration (Chapter 4). Fluorescence microscopy results suggest successful DNA elution from the microbeads within the microfluidic device, allowing for a 28.5 X concentration increase. This platform shows promise for sample preconcentration by reducing the starting DNA sample volume of 25 µL to 20 nL, which could improve the speed of solid-state nanopore sensing.

Microfluidics have been created to acquire, operate, and process complex fluids in extremely tiny volumes with high efficiency and high speed, and without the requirement for an experienced operator. In addition, microfluidic systems also enable miniaturization and incorporation of different complex functions, which can help bring intricate diagnostic tools out of the laboratories. Ideally, these systems should be inexpensive, precise, reliable, robust, and well-suited to the medical diagnostic systems. Most of the microfluidic devices reported previously were based on devices made of polydimethylsiloxane (PDMS). PDMS is a material that dissolves in many common organic solvents. Meanwhile, it is also prone to absorb small molecules like the proteins, which is detrimental to a stable and reliable result. Current work focuses on bioassays that are badly needed in our life and these bioassays are addressed based on microfluidic platform with different materials. The translation of microfluidic technology into large scale implementations highly relies on new materials that address the limitations of PDMS. Firstly, we fabricated two different microfluidic platforms for rapid antimicrobial susceptibility testing (AST). One was made of hydrogel, and the bacterial cells were cultured on the top of the device; the other was of polypropylene (PP), and bacterial cells were cultured inside the microchannels. Meanwhile, we developed a novel "barcode" sensor, a microscope-free method for cell accumulation and cell counting, as the downstream of the PP-based chips. As a result, AST can be accomplished simply through an application on a mobile phone rather than using an expensive and sophisticated microscope. Secondly, we presented a self-contained paper-based system for lead(II) ion detection based on G-quadruplex-based luminescence switch-on assay, comprising a novel type of paper-based chip and a matching portable device. Different from the reported paper-based devices, the paper substrate we chose was art paper, which is used for printing magazines. This type of paper could prevent the absorption of liquid into the paper matrix and hold the liquid in place for a period of time; and it could also be used for temporary liquid containing like a plastic substrate (such as polypropylene (PP) and polystyrene (PS)), but the surface of the paper is inherently hydrophilic. In such a design, liquid drops are suspended on the surface of the device in designed reservoirs, rather than absorbed into the paper; when the chip is tilted, the liquid drops will move to other reservoirs according to the guidance of channels defined on the surface. To differentiate it from reported μPAD devices that are fabricated with water-permeable paper, we name this new type of paper-based devices suspending-droplet mode paper-based microfluidic devices (SD-μPAD). Different from the conventional μPADs that use capillary force to drive liquid, our SD-μPADs uses wetting and gravity as driving force. To fabricate the superhydrophobic pattern on the paper device, we developed a new microcontact printing-based method to produce inexpensive and precisely patterned superhydrophobic coating on paper. The coating material is poly(dimethylsiloxane) (PDMS), a hydrophobic and transparent silicone that has long been used for fabricating microfluidic devices. Importantly, the negative-relief stamp we used is made of Teflon, a non-stick polymer, so that the PDMS-coated paper could be peeled from the stamp flawlessly. After such fabrication process, the stamped area of the paper is coated with a textured PDMS layer that is decorated with arrays of micropillars, which could provide superhydrophobic effect and most effectively hold the droplets in place; the remaining area of the paper is still hydrophilic. As a demonstration of this new design, we developed a method using the reaction characteristics of iridium(III) complex for rapid, onsite detection of lead(II) ions in liquid samples. As the reagents have already been loaded onto the paper device during fabrication, the only reagent the users need to add is water. Because of the large Stokes shift of the iridium(III) complex probe, inexpensive optical filters can be employed, and we were able to make an inexpensive, battery-powered compact device for routine portable detection using a smartphone as a detector, allowing the rapid analysis and interpretation of results on site as well as the automatic dissemination of data to professional institutes, including tests even in poor rural areas in developing countries. Thirdly, we upgraded our suspending-droplet mode paper-based microfluidic device (SD-μPAD), which is used for the detection of lead(II) ions in liquid solution. The reason is that our paper-based SD chips are not suitable for long reaction process (> 20 min) detection of biomolecules due to the potential permeation and contaminating problems of art papers. Hence, we chose polypropylene (PP), a hydrophobic, cheap, and thermal stable material (< 110°C), as the material for the fabrication of the SD microfluidic chip. We established a convenient, low-cost, portable and reliable platform for monitoring VEGF165 accurately, which can be applied for point-of-care (POC) testing. In this project, we also employed the label-free oligonucleotide-based luminescence switch-on assay on the microfluidic platform, which possesses the advantages of high sensitivity and high selectivity. Based on the detection of VEGF165 in a three-step reaction process, we adopted a new design for the droplet transfer throughout the channels. This design could migrate the droplet through the chambers via controlling the orientation of the chip, which systematically combined the superhydrophobic force of the coating, the gravity of the droplet and the surface tension between PP and droplet. Therefore, traditional micro pump could be avoided and the total cost for the device could be substantially reduced. In addition, we developed an automatic, matched and portable device for the detection of VEGF165, which assembled by a rotatable chip holder, a UV lamp, a filter, and a camera. Finally, we developed a new whole Teflon membrane-based chip for the aptamer screening. Our article "Whole-Teflon microfluidic chips" introduced the fabrication of a microfluidic device entirely using Teflon materials, one group of the most inert materials in the world. It was a successful and representative introduction of new materials into the fabrication of microfluidic devices, which show dramatically greater anti-fouling performance. However, even such device was inadequate for current purpose, as it is rigid and lacks convenient valve control functions for particle suspensions used in systematic evolution of ligands by exponential enrichment (SELEX). For this project, we propose a SMART screening strategy based on a highly integrated microfluidic chip. This new type of whole-Teflon devices, which are made of flexible Teflon membranes, offering convenient valving control for the whole SELEX process to be performed on chip and fulfilling the anti-fouling requirement in the meantime. The SELEX cycles including positive and negative selections could be automatically performed inside tiny-size microchambers on a microchip, and the enrichment is real-time monitored. The selection cycles would be ended after the resulted signal of the aptamers with high specificity reached a plateau, or no target aptamer is captured after a number of cycles of enrichment. Owning to the antifouling property of the chip materials, the loss of the sample is tremendously reduced. The SMART platform therefore is not only free of complicated manual operations, but also high-yield and well reproducible over conventional methods

No description available.

Physical trauma is responsible for over six million deaths annually, and of these roughly 40 percent result from acute traumatic coagulopathy (ATC) occurring in the first few hours of incidence. Patients who have developed ATC have significantly improved survivability when treated with tranexamic acid (TXA), a chemical inhibitor of the clot lysing enzyme plasmin. Current methods of detecting ATC are inadequate, lacking in either efficient speed, sensitivity, or cost. Hyperfibrinolysis (HF) is a key component of ATC and can be a result of excess plasmin activity. The following study observes effects of plasmin on hemostasis, and explores the use of silicon-based polydimethylsiloxane (PDMS) microfluidics measuring changes in electrical resistance as a method to detect HF. Coagulation was characterized by measuring turbidity of solutions containing fibrinogen and thrombin, and plasmin was incorporated to observe fibrinolysis and other plasmin-induced effects. It was found that high concentrations of plasmin caused a delay in the turbidity increase during coagulation. This lag phase may be a contributing factor to HF and ultimately ATC. Finally, the use of PDMS microfluidics to measure changes in electrical resistance to detect coagulation and fibrinolysis activity was supported. Resistance change adhered closely to traditional substrate-enzyme kinetics and plasmin-induced effects mimicked those which were observed in turbidity measurements. Further investment and development of this method of measurement could provide a faster, more accurate, and more inexpensive alternative to current techniques for measuring fibrinolysis.