Thesis (Ph. D.)--West Virginia University, 2010. / Title from document title page. Document formatted into pages; contains xii, 124 p. : ill. (some col.). Includes abstract. Includes bibliographical references.

Thesis (Ph. D.)--University of Washington, 2006. / Vita. Includes bibliographical references (leaves 66-80).

Thesis (Ph. D.)--University of Washington, 2007. / Vita. Includes bibliographical references (leaves 140-155).

Thesis (Ph. D.)--Oregon State University, 2008. / Printout. Includes bibliographical references (leaves 133-137). Also available on the World Wide Web.

The present thesis includes a series of studies on microfluidic technology from novel microfabrication methods in polymers to diverse microfluidic applications. Specifically, this study focuses on some key issues in microfluidics, regarding the development of microfluidic fabrication strategy, material selection for microfabrication, and applications, in particularly controllable reactions of novel polymer-based microfluidic devices. We have developed novel methods, which hold completely different idea/ concept with conventional approaches', for fabrication of microfluidic chips with polymer materials. While for the microfluidic applications, the thesis exhibits cell perfusion experiments with freestanding 3D microchannels made of alginate hydrogel, convenient and sensitive lead(Ⅱ) ions detection on a plastic membrane microfluidic chip which was fabricated by the proposed novel one-step strategy, as well as and microfluidic controllable synthesis of enzyme-embedded metal-organic frameworks in a laminar flow;In the first part, we proposed an inside-out fabrication strategy using a copper scaffold as the sacrificial template to create freestanding 3D microvascular structures containing branched tubular networks with alginate hydrogel. The microvascular structures produced with this method are strong enough to allow handling, biocompatible for cell culture, appropriately porous to allow diffusion of small molecules, while sufficiently dense to prevent blocking of channels when embedded in various types of gels. In addition, other materials and biomolecules could be pre-loaded in our hydrogel tubular networks by mixing them with alginate solution, and the thickness of tubule wall is tunable. Compared to other potential strategies of fabricating free-standing gel channel networks, our method is parallel processing using an industrially mass-producible template, making our method rapid, low-cost and scalable. We demonstrated cell culture in a nutrition gradient based on a microfluidic diffusion device made of agar, a hydrogel traditionally hard to microfabricate, by embedding the synthesized tubules into the agar gel. In this way, the freestanding hydrogel vascular network we produced is a universal functional unit that can be integrated with other gel-based devices to build up the supporting matrix for 3D cell culture outside the hydrogel vascular structure; allowing great convenience and flexibility 3D culture. The method is readily implementable to have broad applications in biomedicine and biology, such as vascular tissue regeneration, drug discovery, and delivery system in 3D culture.;The second part, we developed a one-step method to mass produce microfluidic chip with thermal plastic membranes. We used a perfluoropolymer perfluoroalkoxy (often called Teflon PFA) negative mold, which is very nonsticky and has ultrahigh melting point, as solid stamp to thermal-bond two pieces of plastic membranes, low density polyethylene (LDPE) and polyethylene terephthalate (PET) coated with ethylene-vinyl acetate copolymer (EVA), which have different coefficients of thermal expansion. During the short period of contact with the heated Teflon stamp, the pressed area of the membranes permanently bonded, while the LDPE membrane spontaneously rose up at the area not pressed, forming microchannels automatically. These two regions were clearly distinguishable even at micrometer scale so that we were able to fabricate microchannels with width down to 50 microns. By using thermal-bonding, the pattern of Teflon mold will be transferred to the plastic membrane forming channels while two membranes will be bonded at the same time. The method enables generation of microchannels and bonding process to accomplish in a single step without sophisticated instruments. One Teflon mold can be used to mass replicate many plastic membrane chips in a short time because each round needs only a few seconds. Our method can fabricate a plastic microfluidic chip rapidly (within 12 seconds per piece) at an extremely low price (less than 0.02{dollar} per piece). We also showed some identical microfluidic manipulations with the flexible plastic membrane chips including droplet formation, microfluidic capillary electrophoresis and squeezing-pump for quantitative injection. In addition, we demonstrated convenient on-chip detection of lead ion by a peristaltic-pumping design, as an example of the applications of the plastic membrane chips in resource-limited environment. Due to the fast production method and low-cost of plastic materials, this one-step method will hopefully lead to new opportunities for the commercial implementations of microfluidic technologies.;Finally, on the basis of preliminary study of microfluidic laminar flow synthesis of MOFs in aqueous system in Chapter 4, we successfully synthesized and investigated formation of enzyme-embedded metal-organic frameworks (MOFs) in a continuous laminar flow on a microfluidic chip. Resultant enzyme-MOF composites displayed higher enzymatic activity than enzyme-MOF composites from bulk solution synthesis. A possible reason was that the precisely controlled and yet changeable reaction conditions such as reaction time and diffusive mixing of reagents allowed the fast reaction to be isolated into controllable processes and studied with predesigned yet changing conditions. This, in return, led to distinct morphological characteristics and activities of the enzyme-MOF composites compared to those from bulk synthesis. The results indicated that the highest activity of enzyme-MOF composites was obtained when metal ions and organic ligands were first gradually mixed within a few seconds before enzyme molecules joined the gradual mixing process. We found that the crystallinity degree of as-produced enzyme-MOF composites was reduced via the microfluidic flow synthesis, containing more structural defects compared to those with high degree of crystallinity from bulk synthesis. The reduced crystallinity allowed more effective approaching of substrates with enzyme embedded in composites and therefore an increased enzyme activity compared to enzyme-MOF composites from bulk synthesis. We further demonstrated that enzyme-MOF composites showed enhanced stability against elevated temperature and protease digestion compared with free enzymes, allowing their wider utility in biotechnology.

The high throughput capabilities and low sample volume requirements of microfluidic technology make it an attractive prospect for the pharmaceutical industry. This thesis concerns the development of microfluidic devices to investigate two important challenges to the pharmaceutical industry: to interface microchannel systems with electrospray ionisation mass spectrometry, an extensively used technique in drug discovery and development, and to investigate drug precipitation and its prevention through formulation. A microfluidic electrospray ionisation mass spectrometry interface was developed which could be placed within the source enclosure of a Waters ZQ mass spectrometer with little requirement for modification. The microfluidic interface showed a signal improvement of 38% over a capillary voltage of 4 - 4.75 kV when compared to the commercial probe which was operated at a desolvation gas flow rate of 120 L hr-1. Under typical desolvation temperatures of 350 ºC, the commercial probe outperformed the microfluidic interface which was operated at a desolvation temperature of 60 ºC, however, only an 18% improvement in signal intensity was observed for a 290 ºC increase in temperature, and there is scope to increase the operating desolvation temperature of the microfluidic interface. A novel droplet-based microfluidic light scattering detection system was developed to monitor drug precipitation of weakly basic poorly water soluble drugs. These drugs frequently exhibit poor bioavailability and variability due to precipitation in the GI tract. A pH-shift method was used to simulate gastric emptying conditions and generate a supersaturated state. Ketoconazole was used as the model drug in this study and was found to precipitate rapidly upon supersaturation. The extent of precipitation was shown to have a linear dependence on the degree of supersaturation for physiologically relevant supersaturations. This thesis also reports the first example of microfluidic screening of precipitation inhibitors. The inhibitory effect of two water soluble polymers, polyvinylpyrrolidone (PVP) and hydroxypropyl methylcellulose (HPMC) on ketoconazole precipitation was evaluated. HPMC was found to be a more potent precipitation inhibitor than PVP, with just 0.05 mM HPMC resulting in approximately a 75% decrease in ketoconazole precipitation, outperforming that of 1.7 mM PVP, which only decreased precipitation by approximately 60%. These findings corroborate results obtained from macroscale experiments employing dynamic light scattering detection. The onset time of precipitation for a range of ketoconazole supersaturations was measured using the scattered light intensity observed from the initial 22 seconds of ketoconazole precipitation. Onset times of between 0.24 – 2.45 seconds were determined for ketoconazole supersaturations of between 30 – 65.

No description available.

We design actuated cilia that can maneuver microscopic particles normal to a microfluidic channel wall and transport microscopic particles parallel to the channel wall. For identifying the design specifications, we employ a hybrid LBM/LSM computational model, to simulate hydrodynamic interactions between oscillating elastic cilia and microscopic particles in a microfluidic channel. The oscillating synthetic cilia are elastic filaments tethered to the channel wall and actuated by sinusoidal force acting at their free ends. The cilia are arranged in a square pattern. The microscopic particle is a neutrally buoyant solid sphere, which is sufficiently small compared to the cilium length and inter-cilium distances, so that the particle can move freely inside the ciliated layer. We study the effect of actuation frequency on the particle motion inside the ciliated layer. We show that depending on the frequency, particles can be either driven away from the ciliated channel wall or drawn towards the wall. We also examine how to use inclined cilia to transport particles along the ciliated layer. We show that the particle transport along the ciliated layer can be regulated by the frequency of cilium oscillation. The results uncover a new route for regulating particle position and transport in microfluidic devices.

The lymphatic system has three primary roles: transporting lipids, transporting immune cells, and maintaining fluid balance. Each one of these roles are influenced by the presence of flow. Inflammation increases lymph flow, lipid uptake is enhanced by flow, cancer cell migration increases in the presence of flow, and lymphatic permeability and lymphatic contractility respond to changes in flow. Flow is very important to lymphatic function, and yet, there are no in vitro models that incorporate both luminal (flow along cell lumen) and transmural (flow through cell lumina) flow for lymphatics. To address this need, a microfluidic device has been developed that can incorporate both of these types of flow. This is achieved by driving flow through a channel which creates a pressure gradient that drives fluid through a porous membrane into an adjacent channel. Following several design iterations, the device can be easily fabricated, imaged, and cells can grow and survive in it. Permeability experiments have been performed in static and flow, 0.175 mL/min (0.5 dyne/cm²), cases. The effective permeability of dextran in the static and flow cases was calculated to be 0.0083 μm/s and 2.05 μm/s respectively. While the effective permeability of bodipy in the static and flow cases was calculated to be 0.0053 μm/s and 2.57 μm/s respectively. The static values are similar to values obtained in a transwell study by Dixon et al. As mentioned, lipid uptake is increased in the presence of flow and these numbers suggest the same. In addition to permeability studies, experiments were performed with cancer cells suspended in a collagen gel. Two image processing techniques were used to quantify cancer cell migration. The first technique was used to calculate the number of cells present at the beginning of the experiment and the number of cells that were ever present during the experiment in that particular z slice. The static case yielded a cell flux of 15 additional cells. While the two flow cases, within interstitial flow range, had a flux of 24 and 40 cells. This suggests that flow increases migration in cancer cells and is in agreement with the literature. The second technique was used to show that the cells in the static and flow cases are similarly motile, but the flow case is more directed in the z direction towards the membrane. The future work for this device is quite extensive, but a strong foundation centered around basic capabilities like inducing flow, seeding cells, and imaging has been formed.

No description available.