Thesis (Ph. D.) -- California Institute of Technology, 2010. / Title from home page (viewed 02/25/2010). Advisor and committee chair names found in the thesis' metadata record in the digital repository. Includes bibliographical references.

Delivery vehicles that can encapsulate and release active ingredients of pre-determined volumes at the target site on-demand present a challenge in biomedical field. Due to their tunable physiochemical properties and degradation rate, polymeric particles are one of the most extensively employed delivery vehicles. Generally they are fabricated from emulsion templates. Conventional bulk emulsification technique provides little control over the characteristics of droplets generated. Thus the properties of the subsequent particles cannot be controlled. The advance of droplet microfluidics enables the generation and manipulation of designer single, double or higher-order emulsion droplets with customizable structure. These droplets are powerful and versatile templates for fabricating polymeric delivery vehicles with pre-determined properties. Due to the monodispersity of droplet templates by microfluidics, the relationship between size, size distribution, shape, architecture, elastic responses and release kinetics can be systematically studied. These understandings are of key importance for the design and fabrication of the next generation polymeric delivery vehicles with custom-made functions for specific applications. In the present work, we engineer the droplet templates generated from microfluidics to fabricate designer polymeric microparticles as delivery vehicles. We investigate and obtain the relationship between the particle size, size distribution, structure of microparticles and their release kinetics. Moreover, we also identify an innovative route to tune the particle shape that enables the investigation of the relationship between particle shape and release kinetics. We take advantage of the dewetting phenomena driving by interfacial tensions of different liquid phases to vary the droplet shape. We find that the phase-separation-induced shape variation of polymeric composite particles can be engineered by manipulating the kinetic barriers during droplet shape evolution. To predict the performance of our advanced polymer particles in practical applications, for instance, in narrow blood vessels in vivo, we also develop a novel capillary micromechanics technique to characterize the linear and non-linear elastic response of our polymer particles on single particle level. The knowledge of the mechanical properties enables the prediction as well as the design of the mechanical aspects of polymer particles in different applications. The ability to control and design the physical, chemical, mechanical properties of the delivery vehicles, and the understanding between these properties and the biological functionalities of delivery vehicles, such as the release kinetics, lead towards tailor-designed delivery vehicles with finely-designed functionalities for various biomedical applications. Our proposed electro-microfluidic platform potentially enables generation of submicron droplet templates with a narrow size distribution and nanoscaled delivery vehicles with well-controlled properties, leading to a next generation of intracellular delivery vehicles. Microfluidic-based technique has the potential to be scaled up by parallel operation. Therefore, we are well-equipped for the massive production of custom-made droplet templates of both micron-size and nanosized, and we can design the physiochemical properties and biological functionalities of the delivery vehicles. These abilities enable us to provide solutions for applications and fundamental topics where encapsulation, preservation and transportation of active ingredients are needed. / published_or_final_version / Mechanical Engineering / Doctoral / Doctor of Philosophy

Thesis (M. S.. in Biomedical Engineering)--Vanderbilt University, Dec. 2009. / Title from title screen. Includes bibliographical references.

Thesis (M.S.)--Oregon State University, 2009. / Printout. Includes bibliographical references (leaves 62-63). Also available on the World Wide Web.

University of Macau / Institute of Chinese Medical Sciences

Tang, Xiaoju. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2008. / Includes bibliographical references (leaves 45-50). / Abstracts in English and Chinese. / Abstract --- p.1 / 摘要 --- p.iii / Acknowledgement --- p.iii / Table of Contents --- p.iv / Chapter 1. --- Introduction --- p.1 / Chapter 1.1 --- Introduction to microfluidics --- p.1 / Chapter 1.2 --- Aqueous two phase system (ATPS) --- p.4 / Chapter 1.3 --- Emulsion --- p.7 / Chapter 1.4 --- Objective of the research --- p.9 / Chapter 2. --- Two-Phase Emulsion --- p.10 / Chapter 2.1 --- Emulsions in microfluidic channels --- p.10 / Chapter 2.2 --- Fabrication of the microfluidic device --- p.12 / Chapter 2.3 --- Generation of water-in-oil emulsion --- p.15 / Chapter 2.3.1 --- Generation of water-in-oil emulsion --- p.15 / Chapter 2.3.2 --- Formation conditions of water in oil emulsions.........................................................: --- p.16 / Chapter 2.4 --- Generation of emulsion with aqueous two phase system --- p.22 / Chapter 2.4.1 --- Introduction and application of emulsions of ATPS --- p.22 / Chapter 2.4.2 --- Generation of emulsion with aqueous two phase system --- p.23 / Chapter 2.4.3 --- Forming conditions of ATPS emulsions --- p.24 / Chapter 2.5 --- Generation of emulsions with flow focusing device --- p.30 / Chapter 2.5.1 --- Fabrication of the flow-focusing device --- p.30 / Chapter 2.5.2 --- Generation of emulsions --- p.31 / Chapter 2.5.3 --- Results and discussion --- p.32 / Chapter 2.6 --- Conclusion --- p.34 / Chapter 2.6.1 --- Generation of emulsions with coaxial device --- p.34 / Chapter 2.6.2 --- Generation of emulsions with flow focusing device --- p.34 / Chapter 3. --- Double Emulsion --- p.35 / Chapter 3.1 --- Double emulsion in microfluidic channels --- p.35 / Chapter 3.2 --- Fabrication of the microfluidic device --- p.36 / Chapter 3.3 --- Generation of double emulsion --- p.36 / Chapter 3.4 --- Results and discussion --- p.37 / Chapter 3.5 --- Conclusion --- p.42 / Chapter 4. --- Conclusion --- p.43 / Chapter 4.1 --- Microfluidic device --- p.43 / Chapter 4.2 --- Two phase emulsion --- p.43 / Chapter 4.3 --- Double emulsion --- p.44 / Reference --- p.45

We have investigated and implemented several general strategies in the development of microfluidics-based chemical/biochemical sensing systems. The research in this dissertation covers the immobilization of biological reagents inside microfluidic channels using polystyrene (PS) microbeads and photopolymerizable hydrogel, electrochemical sensing via electrochemiluminescence (ECL) reporting with bipolar and two-electrode configurations, and integration of these general functions to realize multiplexing and networking on-chip. Photopolymerizable hydrogel based on Poly(ethylene glycol) (PEG) and streptavidin-coated polystyrene (PS) microbeads were employed as building blocks as well as functional components in microfluidic system. PEG hydrogels can be used to define local microenvironments at different locations in the same microchannel, which enables the introduction of multiple sensing events on the same device. Monitoring of DNA hybridization and enzyme/substrate interaction were realized thereafter by using either fluorescence or electrochemistry as the detection method. Electrogenerated chemiluminescence based on Ru(bpy)32+ (bpy = 2,2??-bipyridine) and tripropylamine (TPA) was used to photonically report various redox events in microfluidic systems. By using microfluidic electrochemical cells based on either two-electrode or bipolar electrode (one-electrode), electroactive species that undergo reduction can be electrically linked to this anodic ECL process and thus be reported by the latter. This ECL sensing scheme essentially broadens the spectrum of redox compounds that can be detected by ECL since the analytes are not required to directly participate into the light-generating processes. Microfluidics offers some unique technical advantages of performing electrochemistry over conventional methods. In particular, laminar flow allows multiple analyte streams to be brought together in parallel with little mixing. Moreover, electrochemical signals can be generally utilized as a convenient means to link individual microchannels together hence to realize microfluidic networking and cross-communication. Electrochemical microfluidic devices can be used to mimic general functions of microelectronic devices such as diodes, transistors, and logic gates. These novel functions rendered by electrochemistry are believed to bring us closer to the final goals of micro total analysis systems and lab-on-a-chip.

Novel microscale velocity and temperature measurement techniques were studied based on confocal laser scanning microscopy (CLSM) and optical serial sectioning microscopy (OSSM). Two microscopic measurement systems were developed, 1) a CLSM micro particle image velocimetry (PIV) system with a dual Nipkow disk confocal unit (CSU-10), a CW argon-ion laser and an upright microscope, and 2) an OSSM micro- particle tracking velocimetry (PTV) system with an epi-fluorescence microscope and a non-designed specimen to make a three-dimensional (3-D) diffraction particle image. The CLSM micro-PIV system shows a unique optical slicing capability allowing true depth-wise resolved vector field mapping. A comparative study is presented between the CLSM micro-PIV and a conventional epi-fluorescence micro-PIV. Both have been applied to the creeping Poiseuille flows in two different microtubes of 99-µm (Re = 0.00275) and 516-µm ID diameters (Re = 0.021). The CLSM micro-PIV consistently shows significantly improved particle image contrasts, the definition of "optical slicing" and measured flow vector fields more accurately agreeing with predictions based on the Poiseuille flow fields, compared to the conventional micro-PIV. The OSSM micro-PTV technique is applied for a 3-D vector field mapping in a microscopic flow and a Brownian motion tracking of nanoparticles. This technique modifies OSSM system for a micro-fluidic experiment, and the imaging system captures a diffracted particle image having numerous circular fringes instead of an in-focus particle image. The 3-D particle tracking is based on a correlation between the 3-D diffraction pattern of a particle and the defocus distance from a focal plane. A computational program is invented for the OSSM micro-PTV, and provides a 3-D velocity vector field with a spatial resolution of 5.16 µm. In addition, a concept of nonintrusive thermometry is presented based on the correlation of the Brownian motion of suspended nanoparticles with the surrounding fluid temperature. Detection of fully three-dimensional Brownian motion is possible by the use of the OSSM, and the measured value of mean square displacement (MSD) is compared fairly well with Einstein's predictions.

Pancreatic islets are heavily vascularized micro-organs containing insulin secreting beta-cells coupled with endothelial cells (EC). These EC slowly deteriorate in static culture, precluding long term study of beta-cell-EC interaction, and likely limiting tissue revascularization post-transplantation. We postulate this EC deterioration is due to an absence of hemodynamics, blood movement. We created a microfluidic device to mimic aspects of hemodynamics, delivering a range of media flow to ex vivo islets. With our resulting desk-top system, we have conducted long term incubations (72 hrs), fixed tissue treatments (maintaining endothelial cell morphology) and real-time live tissue imaging (glucose-stimulated Ca2+-response). Our data show that flow in a microfluidic device maintains EC morphology in ex vivo islets better than non-flowing culture, providing an improved platform to study ex vivo islets and to examine the interaction between beta-cells and EC. Our data also suggest an opportunity to prime islet EC for revascularization using microfluidic flow prior to transplantation.

The specific membrane capacitance (SMC) of biological cell membranes correlates with cells’ electrical activity and morphology, which are physiological markers for cellular phenotype and health. Conventionally, SMC measurements are conducted using electro-rotation and Patch-clamping, which entail long time training and stringent operation skills. Both techniques also suffer from limited throughput and lengthy measurement time. In this study, a microfluidic device, which enables impedance spectroscopy measurements, was developed to quantify the SMC of single biological cells. The device has a testing speed of approximately one cell per minute and is relatively easy to operate. Three-dimensional finite element simulations of the microfluidic device confirm the feasibility of this approach. SMC measurement of two AML (Acute Myeloid Leukemia) subtypes and two UCC (Urothelium Cell Carcinoma) subtypes were conducted. Measured SMC results were found to lie in the comparable range with previously reported publications.