archives@tulane.edu / Structural changes in the cytoskeleton during metastatic transformation make cancer cells more deformable, and recent experimental studies confirm a direct correlation between cell invasiveness and cell deformability. Several microfluidic approaches have recently developed to exploit this cellular property for high-throughput assessment of metastatic risk from small samples of patient’s blood. While demonstrating feasibility in the lab, these technologies often lack a solid theoretical foundation or do not show adequate sensitivity to cellular mechanical properties (“mechanotype”). The long-term goal of this project is to optimize microfluidic tests for metastatic risk assessment, including circulating tumor cell (CTC) isolation and mechanotype analysis, through predictive computational modeling. Specific aims of the presented study are 1) to expand the capability of our custom computational algorithm for viscoelastic cell deformation and migration to simulate cell sorting and CTC isolation in channels with complex geometry, including channels with pillars and bifurcations, and 2) to demonstrate the capability of our algorithm to optimize microfluidic methods for cancer cell mechanotype measurement. / 1 / Scott J. Hymel

The purpose of this research is to explore and investigate the biophysical properties of living cells using microfluidics based electrical impedance sensing (EIS) technique. It provides a non-invasive approach to detect label-free biological markers in the regulation of cellular activities even at a molecular level. We specifically focus on the development, testing, and theoretical modeling of electrical impedance spectroscopy for neuroblastoma cells and endothelial cells. First, we demonstrate that the EIS technique can be used to monitor the progressive mitochondrial fission/fusion modification in genetically modified human neuroblastoma cell lines. Our results characterize quantitatively the abnormal mitochondrial dynamics through the variations in cytoplasm conductivity. Secondly, we employ a real time EIS method to determine the biophysical properties of the junctions which join one endothelial cell with one another in a monolayer of endothelial cells. In particular, we examine the role of the protein, c-MYC oncogene, in the barrier function. Our results show that the downregulation of c-MYC oncogene enhances the endothelial barrier dysfunction associated with inflammation. Finally, we measure and find that the electrical admittance (the reciprocal of the impedance) of the monolayer of endothelial cellular networks exhibits an anomalous power law of the form, Y ∝ ωα, over a wide range of frequency, with the value of the exponent, α, depending on the severity of the inflammation. We attribute the power law to the changes of the intercellular electric permeability between neighboring endothelial cells. Thus, the inflammation gives rise to relatively smaller values of α compared to that of the no-inflammation group. Furthermore, we propose a simple percolation model of a large R-C network to confirm the emergent of power law scaling behavior of the complex admittance, suggesting that the endothelial network behaves as a complex microstructural network and its electrical properties may be simulated by a large R-C network. / Includes bibliography. / Dissertation (Ph.D.)--Florida Atlantic University, 2020. / FAU Electronic Theses and Dissertations Collection

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In this dissertation, we examine how advective and diffusive flows are created in the insect respiratory system, using a combination of direct biological studies and computational fluid dynamics simulations. The insect respiratory system differs significantly from the vertebrate respiratory system. While mammals use oxygen-carrying molecules such as hemoglobin, insects do not, favoring the direct delivery of oxygen to the tissues. An insect must balance advective flow with diffusive flux in order to sustain the appropriate oxygen concentrations at the tissue level. To better understand flow creation mechanisms, we studied the Madagascar hissing cockroach. In Chapter One, we used x-ray imaging to identify how tracheal tube compression, spiracular valving, and abdominal pumping coordinate to produce unidirectional flow during active respiration. In Chapter Two, we altered the environmental conditions by exposing the animals to various levels of hypoxia and hyperoxia, then examined how they changed their respiratory behaviors. In Chapter Three, we used our previous findings to construct a simulated insect respiratory system to parametrically study the effects of network geometry and valve timing on the creation of unidirectional advective flow and diffusive flux. These results can be used to inform future studies of the insect respiratory system, as well as act as the basis for bio-inspired microfluidic devices. / Doctor of Philosophy / The insect respiratory system works through the direct delivery of oxygen to the tissues. This occurs via a complex network of pumps, tubes, valves, and other structures that facilitate flow. These mechanisms allow insects to survive and prosper under a wide range of environmental and physiological conditions. While these structures have been studied extensively in a wide range of insect species, there are still many aspects of the respiratory system that remain unexplored. Here, we use the Madagascar hissing cockroach to examine how both bulk flow and diffusion are created in some types of insect respiratory systems. First, in Chapter One, we studied the animal under normal environmental conditions in order to determine how abdominal pumping, tracheal tube collapse, and spiracular valving are coordinated. Then, in Chapter Two, we exposed the animals to a range of oxygen concentrations to identify how the animals respond to varying environmental conditions. Finally, in Chapter Three, we constructed a simulated insect respiratory system to parametrically study the effects of network geometry and valve timing on the creation of advective and diffusive flow. By combining these three studies, we were able to improve our understanding of flow creation in the insect respiratory system.

Microfluidics is a constantly evolving area of research. The implementation of new technologies and fabrication processes offers novel methodologies to solve existing problems. There are currently a large number of established techniques to address issues associated with microscale mixing and valving. We present mixing and valving techniques that utilize simplified and inexpensive techniques. The first technique addresses issues associated with microscale mixing. Exercising control over animal locomotion is well known in the macro world but in the micro-scale world, control requires more sophistication. We present a method to artificially magnetize microorganisms and use external permanent magnets to control their motion in a microfluidic device. This effectively tethers the microorganisms to a location in the channel and controls where mixing occurs. We use the bulk and ciliary motion of the microswimmers to generate shear flows, thus enhancing cross-stream mixing by supplementing diffusion. The device is similar to an active mixer but requires no external power sources or artificial actuators. The second technique examines a methodology involving the integration of electroactive polymers into microfluidic devices. Under the influence of high applied voltages, electroactive polymers with fixed boundary conditions undergo out-of-plane deformation. We use this finding to create a valve capable blocking flow in microchannels. Electrolytic fluid solutions are used as electrodes to carry the voltage signal to the polymer surface. Currently we have demonstrated this methodology as a proof of concept, but aim to optimize our system to develop a robust microvalve technology. / Master of Science

Generally, dielectrophoresis (DEP) analysis of biological cell samples relies on the differing electrical parameters between the cells and the surrounding fluid medium. To achieve effective positive DEP manipulation and sorting of mammalian cells in suspension, it is required to resuspend the cells into a low-conductivity fluid buffer. The use of a low conductivity buffer also aids in minimizing the effects of Joule heating, which can cause cell death and ineffective cell trapping. The common method to prepare the sample relies on centrifugation of sensitive cells, a time-consuming and tedious process that may result in decreased sample viability. Herein is presented a microfluidic device that passively moves cells from a high-conductivity growth media into a low-conductivity DEP buffer. It is comprised of con- verging rows of pillars and uses mechanical filtration to force cells into the new buffer while allowing for the old fluid to flow through the posts and out of separate outlets. Because this device is intended to be used upstream of a contactless dielectrophoresis (cDEP) device, the buffer exchange device must have an outlet flow rate that is within the range necessary for direct integration with the cDEP device, maintain a low shear stress that will not affect the integrity of the sample and achieve sufficiently high cell recovery. Methods of this project included optimizing the shape, size, and orientation of the posts, determining the flow rate for maintaining an ideal DEP buffer conductivity, numerical modeling of shear stress, and determining the cell recovery rate. It is anticipated that this device can be extended to physiological media sample processing such as for liquid biopsy. / Master of Science / In order to accomplish numerous biomedical experiments, cells must be transferred from their native fluid growth media into a different fluid solution, through a process referred to as buffer exchange. The current method for buffer exchange is time consuming, tedious, and affects the number of cells left alive for experimentation. In this work, we present a microfluidic device that can accomplish the buffer exchange process by simply flowing in the cells in their media in parallel with the new buffer solution. The results of this research work can be extended to aid in the process of buffer exchange for various biological experiments. The proposed device utilizes mechanical filtration to force cells into the new buffer while allowing for the old fluid to flow through the posts and out of separate outlets. The design of the device was optimized through computational analysis of the concentration and fluid shear stress in conjunction with experimental tests of devices for outlet conductivity and cell retention.

Microfluidic based miniature lab-on-a-chip devices integrate different laboratory functionality in microscale. Microarray technology is evolving as a powerful tool for biomedical and pharmaceutical applications to identify gene sequences or to determine gene expression levels. Preparation of samples and spotting the arrays are the two major steps required for making microarrays. The microfluidic components developed in this research would facilitate performing the above-mentioned steps by a single lab-on-a-chip. Three microfluidic modules were developed: a non-contact microdispenser, an interface connecting the microdispenser with planar Electrowetting on Dielectric (EWOD) sample manipulator and a microvalve that controls the flow at the interface. An electrostatically actuated non-contact type drop-on-demand based microdispenser was developed. The dispenser was designed using finite element modeling technique that solved electrostatically actuated dispensing process. Prototypes were fabricated and tested verifying stable droplet dispensing with error in subsequent droplet generation was less than 15% between each droplet. The frequency of stable generation was 20 Hz and the average volume of dispensed droplet was 1 nL. A closed-channel EWOD actuated interface was developed that allowed a series of droplets to merge inside at the interface converting droplet flow to a continuous flow. An innovative design modification allowed series of droplet merging inside closed-channel. The interface allows integration of pressure driven devices such as: pumps, dispensers, and valves with droplet based planar EWOD devices. A novel EWOD based microvalve was developed that utilizes a thermo-responsive polymer to block and unblock a pressurized continuous flow. EWOD actuation was used to control the positioning of the valving polymer at location of interest. The valve also isolated a pressurized flow from an integrated planar EWOD device. Valves with zero leak rates were demonstrated. Such a valve will be useful in controlling microflows in EWOD to pressure driven flows such as dispensers.

Microfluidic based miniature lab-on-a-chip devices integrate different laboratory functionality in microscale. Microarray technology is evolving as a powerful tool for biomedical and pharmaceutical applications to identify gene sequences or to determine gene expression levels. Preparation of samples and spotting the arrays are the two major steps required for making microarrays. The microfluidic components developed in this research would facilitate performing the above-mentioned steps by a single lab-on-a-chip. Three microfluidic modules were developed: a non-contact microdispenser, an interface connecting the microdispenser with planar Electrowetting on Dielectric (EWOD) sample manipulator and a microvalve that controls the flow at the interface. An electrostatically actuated non-contact type drop-on-demand based microdispenser was developed. The dispenser was designed using finite element modeling technique that solved electrostatically actuated dispensing process. Prototypes were fabricated and tested verifying stable droplet dispensing with error in subsequent droplet generation was less than 15% between each droplet. The frequency of stable generation was 20 Hz and the average volume of dispensed droplet was 1 nL. A closed-channel EWOD actuated interface was developed that allowed a series of droplets to merge inside at the interface converting droplet flow to a continuous flow. An innovative design modification allowed series of droplet merging inside closed-channel. The interface allows integration of pressure driven devices such as: pumps, dispensers, and valves with droplet based planar EWOD devices. A novel EWOD based microvalve was developed that utilizes a thermo-responsive polymer to block and unblock a pressurized continuous flow. EWOD actuation was used to control the positioning of the valving polymer at location of interest. The valve also isolated a pressurized flow from an integrated planar EWOD device. Valves with zero leak rates were demonstrated. Such a valve will be useful in controlling microflows in EWOD to pressure driven flows such as dispensers.

Xiao, Zigang. / "October 2010." / Thesis (M.Phil.)--Chinese University of Hong Kong, 2011. / Includes bibliographical references (leaves 62-66). / Abstracts in English and Chinese. / Abstract --- p.i / Acknowledgement --- p.vi / Chapter 1 --- Introduction --- p.1 / Chapter 1.1 --- Microfluidic Technology --- p.2 / Chapter 1.1.1 --- Continuous Flow Microfluidic System --- p.2 / Chapter 1.1.2 --- Digital Microfluidic System --- p.2 / Chapter 1.2 --- Pin-Constrained Biochips --- p.4 / Chapter 1.2.1 --- Droplet-Trace-Based Array Partitioning Method --- p.5 / Chapter 1.2.2 --- Broadcast-addressing Method --- p.5 / Chapter 1.2.3 --- Cross-Referencing Method --- p.6 / Chapter 1.2.3.1 --- Electrode Interference in Cross-Referencing Biochips --- p.7 / Chapter 1.3 --- Computer-Aided Design Techniques for Biochip --- p.8 / Chapter 1.4 --- Placement Problem in Biochips --- p.8 / Chapter 1.5 --- Droplet Routing Problem in Cross-Referencing Biochips --- p.11 / Chapter 1.6 --- Our Contributions --- p.14 / Chapter 1.7 --- Thesis Organization --- p.15 / Chapter 2 --- Literature Review --- p.16 / Chapter 2.1 --- Introduction --- p.16 / Chapter 2.2 --- Previous Works on Placement --- p.17 / Chapter 2.2.1 --- Basic Simulated Annealing --- p.17 / Chapter 2.2.2 --- Unified Synthesis Approach --- p.18 / Chapter 2.2.3 --- Droplet-Routing-Aware Unified Synthesis Approach --- p.19 / Chapter 2.2.4 --- Simulated Annealing Using T-tree Representation --- p.20 / Chapter 2.3 --- Previous Works on Routing --- p.21 / Chapter 2.3.1 --- Direct-Addressing Droplet Routing --- p.22 / Chapter 2.3.1.1 --- A* Search Method --- p.22 / Chapter 2.3.1.2 --- Open Shortest Path First Method --- p.23 / Chapter 2.3.1.3 --- A Two Phase Algorithm --- p.24 / Chapter 2.3.1.4 --- Network-Flow Based Method --- p.25 / Chapter 2.3.1.5 --- Bypassibility and Concession Method --- p.26 / Chapter 2.3.2 --- Cross-Referencing Droplet Routing --- p.28 / Chapter 2.3.2.1 --- Graph Coloring Method --- p.28 / Chapter 2.3.2.2 --- Clique Partitioning Method --- p.30 / Chapter 2.3.2.3 --- Progressive-ILP Method --- p.31 / Chapter 2.4 --- Conclusion --- p.32 / Chapter 3 --- CrossRouter for Cross-Referencing Biochip --- p.33 / Chapter 3.1 --- Introduction --- p.33 / Chapter 3.2 --- Problem Formulation --- p.34 / Chapter 3.3 --- Overview of Our Method --- p.35 / Chapter 3.4 --- Net Order Computation --- p.35 / Chapter 3.5 --- Propagation Stage --- p.36 / Chapter 3.5.1 --- Fluidic Constraint Check --- p.38 / Chapter 3.5.2 --- Electrode Constraint Check --- p.38 / Chapter 3.5.3 --- Handling 3-pin net --- p.44 / Chapter 3.5.4 --- Waste Reservoir --- p.45 / Chapter 3.6 --- Backtracking Stage --- p.45 / Chapter 3.7 --- Rip-up and Re-route Nets --- p.45 / Chapter 3.8 --- Experimental Results --- p.46 / Chapter 3.9 --- Conclusion --- p.47 / Chapter 4 --- Placement in Cross-Referencing Biochip --- p.49 / Chapter 4.1 --- Introduction --- p.49 / Chapter 4.2 --- Problem Formulation --- p.50 / Chapter 4.3 --- Overview of the method --- p.50 / Chapter 4.4 --- Dispenser and Reservoir Location Generation --- p.51 / Chapter 4.5 --- Solving Placement Problem Using ILP --- p.51 / Chapter 4.5.1 --- Constraints --- p.53 / Chapter 4.5.1.1 --- Validity of modules --- p.53 / Chapter 4.5.1.2 --- Non-overlapping and separation of Modules --- p.53 / Chapter 4.5.1.3 --- Droplet-Routing length constraint --- p.54 / Chapter 4.5.1.4 --- Optical detector resource constraint --- p.55 / Chapter 4.5.2 --- Objective --- p.55 / Chapter 4.5.3 --- Problem Partition --- p.56 / Chapter 4.6 --- Pin Assignment --- p.56 / Chapter 4.7 --- Experimental Results --- p.57 / Chapter 4.8 --- Conclusion --- p.59 / Chapter 5 --- Conclusion --- p.60 / Bibliography --- p.62