Browsing by Subject "Microfluidics"

Now showing 1 - 20 of 20

3D Printing Multifunctional Optoelectronic and Microfluidic Devices
(2020-10) Su, Ruitao
Functional materials encompass different classes of materials possessing intrinsic or synthetic properties that are responsive to external stimuli. A few examples include semiconducting polymers/crystals, electroluminescent polymers, polymers with controlled cross-linking mechanisms and printable metallic inks with tunable sintering mechanisms and conductivity. The technology of additive manufacturing, or 3D printing, has been extensively investigated with structural plastics and metals to realize rapid prototyping of irregular/customized geometries, demonstrating a few successful examples of commercialization. Yet, a further systematic study is demanded to investigate the methodologies to incorporate multiple functional materials in the 3D printed multifunctional devices. This will lay important foundations for the fabrication of a range of devices under ambient conditions that were conventionally accessible exclusively to the cleanroom-based microfabrication. More importantly, the capability of 3D printing to integrate materials in a freeform manner will facilitate novel device form-factors and functionalities that are challenging to realize with microfabrication. In this work, the methodologies of 3D printing optoelectronic and microfluidic devices were investigated with an emphasis on material selection, device configuration, alignment, performance optimization and scalable fabrication. To this end, a custom-built 3D printing system was utilized to accurately pattern functional materials that possess varying rheological properties. Over the past several decades, 3D printing has demonstrated an array of electronic devices such as batteries, capacitors, sensors, wireless transmitters etc. This progress renders an expectation for fully 3D printed integrated circuits that can be rapidly prototyped and adopt more complicated spatial architectures. However, fully 3D printed optoelectronic devices are still a relatively unexplored paradigm. One major challenge of 3D printed optoelectronics is to optimize the device performance by controlling the thickness and uniformity of the solution-processed layers. An optimized layer thickness maintains the balance between charge injection and light extraction for light emitting diodes (LEDs) or light absorption and charge separation for photodetectors. Layer uniformity affects the contact between adjacent layers and therefore the charge carrier transport. In this work, electroluminescent semiconductors, including silicon nanocrystals (SiNCs) and conjugated polymers, were 3D printed as the active layers of LEDs and photodetectors. The effect of printed layer thickness on the device performance was investigated for the extrusion-based printing. A spray printing method was integrated in the 3D printing system and an improved device performance was observed. Significantly, for the 3D printed polymer photodetectors, an external quantum efficiency (EQE) of 25.3%, comparable to that of spin-coated devices, was achieved by controlling the concentration of the active ink. For the device integration, photodetector arrays were printed on flexible and spherical substrates for a freeform and wide field-of-view image sensing. Novel multifunctional optoelectronic devices consisting of integrated LEDs and photodetectors in a side-by-side layout was printed on the same platform, demonstrating potential applications of wearable physiological sensors. Next, for the 3D printed microfluidic devices, this work demonstrates that yield-stress fluids, such as viscoelastic gels, can be extruded to construct self-supporting hollow microstructures that are highly flexible and stretchable. Several additive manufacturing methods, such as stereolithography and multi-jet printing, have demonstrated 3D printed microfluidic devices with improved automation compared to the conventional soft lithography. However, it remains a challenge to directly incorporate electrical and biological sensing elements in the microfluidic devices. In this study, because of the yield strength of the viscoelastic ink, mechanical equilibrium states were found to exist for the inclined standing walls. Self-supporting microfluidic channels and chambers were 3D printed by stacking silicone filaments according to prescribed toolpaths. Since no sacrificial material was demanded to realize the hollow structures, the microfluidic structures can be directly aligned and printed onto microfabricated circuits without contaminating the electrodes. The high modeling precision of this method was demonstrated via fully 3D printed chemical species mixers that were embedded with herringbone ridges. In addition, automation components, including microfluidic valves and peristaltic pumps, were also 3D printed with overlapping silicone channels that were encapsulated by UV-curable resins. Most compellingly, microfluidic networks integrated with valves transcended the conventional planar form-factors and were directly printed on 3D surfaces. The 3D microfluidics suggests a potential application of microfluidics-based physiological sensors that can be directly printed onto freeform surfaces such as human bodies. Lastly, this work demonstrates that the above two distinct systems can be seamlessly integrated together via 3D printing, yielding fully encapsulated and flexible LED matrices. Liquid metals such as eutectic GaIn are promising candidates for soft and stretchable electronics. As the cathode material of 3D printed optoelectronic devices, it has the desired work function and a high mechanical compliance. However, current challenge of patterning liquid metals lies in the design of a robust encapsulation for the cathodes and simultaneously creating an effective interface with interconnects. To this end, self-supporting microfluidic networks that are highly adaptable and aligned to the layout of LED matrices were printed to encapsulate the liquid metal. The 3D printed liquid metal microfluidics enabled the scalable fabrication of flexible and individually addressable LED matrices. In summary, this research expanded the scope of ink composition for 3D printed multifunctional devices. Transferring these materials from microfabrication to 3D printing significantly improves the manufacturability of optoelectronic and microfluidic devices. The intrinsic capabilities of 3D printing to pattern 3D structures in a freeform manner facilitated novel functionalities for both types of devices, including spherical image sensors, 3D microfluidic networks, flexible organic LED matrices etc.
Advancements In Microfluidics For Biotechnology Applications
(2018-10) Agrawal, Pranav
Microfluidic technology has made a huge impact in the field of biotechnology and life sciences. The advancements can be categorized into three aspects: understanding of physical phenomena at the microscale; development of tools for easy integration of different phenomena; and devising systems for various applications. This thesis highlights the ability of microfluidic technology in manipulating different biological entities by fabricating small feature sizes. In particular, we have focused on the development of new processes for three biotechnology applications – (i) long DNA sample preparation for genomic; (ii) delivery of genetic delivery vehicles for gene and cell therapy; and (iii) an in vitro model to study human gut. Each of these systems is developed in close collaboration with potential users and is aimed towards easy integration with the existing workflow. Long-read genomic applications such as genome mapping in nanochannels require long DNA that is free of small-DNA impurities. Chapter 2 reports a chip-based system based on entropic trapping that can simultaneously concentrate and purify a long DNA sample under the alternating application of an externally applied pressure (for sample injection) and an electric field (for filtration and concentration). In contrast, short DNA tends to pass through the filter owing to its comparatively weak entropic penalty for entering the nanoslit. The single-stage prototype developed here, which operates in a continuous pulsatile manner, achieves selectivity of up to 3.5 for λ-phage DNA (48.5 kilobase pairs) compared to a 2 kilobase pair standard based on experimental data for the fraction filtered using pure samples of each species. The device is fabricated in fused silica using standard clean-room methods, making it compatible for integration with long-read genomics technologies. Non-viral delivery vehicles are becoming a popular choice to deliver genetic materials for various therapeutic purposes, but they need engineering solution to improve and control the delivery process. In Chapter 3, we demonstrate a highly efficient method for gene delivery into clinically relevant human cell types, such as induced pluripotent stem cells (iPSCs) and fibroblasts, reducing the protocol time by one full day. To preserve cell physiology during gene transfer, we designed a microfluidic strategy, which facilitates significant gene delivery in short transfection time (<1 minute) for several human cell types. This fast, optimized and generally applicable cell transfection method can be used for rapid screening of different delivery systems and has significant potential for high-throughput cell therapy applications. Microfluidic in vitro models are being developed to mimic individual or combination of various human organ functions for systematic studies, and for better predictive models for clinical studies. In Chapter 4, we outline a microfluidic-based culture system to study host-pathogen interaction in the human gut. We demonstrate that the infection of Enterohemorrhagic Escherichia coli (EHEC) in epithelial cells are oxygen dependent and can be used to prolong co-culture of bacterial and epithelial cells. This work presents a large scope to study the factors influencing the infection, especially the commensal microbiome in the human gut. Overall, this thesis shows how the microfluidic system can be useful in solving real-life problems and envision further advancements in the field of biotechnology.
Complex droplet interfaces at the microscale: Surfactant and hydrodynamic effects in the separation of water-in-oil emulsions
(2020-08) Narayan, Shweta
Complex, surfactant-stabilized emulsions are relevant to various technological applications, such as the removal of dispersed water from diesel fuel in engines. Due to chemical stabilization of micrometer-sized dispersed droplets by surfactant molecules, emulsions can be challenging to separate, especially because surfactant transport to the interface is enhanced by the small droplet size and large interfacial curvature. The main goal of this work is to measure fundamental emulsion properties affecting their stability, such as dynamic interfacial tension and interfacial rheological properties, on the microscale, and relate these properties to droplet dynamics and coalescence behavior in water-in-fuel emulsions. First, dynamic interfacial tension (IFT) of water-in-diesel fuel systems containing surface-active additives such as monoolein and poly(isobutyl) succinimide (PIBSI), relevant to fuel filtration, is measured using a microfluidic tensiometer with contraction-expansion geometries. Microfluidic dynamic IFT measurements are compared with pendant drop tensiometry measurements employing millimeter-sized droplets. It is found that the dynamic interfacial tension decreases on orders of magnitude faster timescales on the microscale due to enhanced diffusive flux to curved microscale interfaces. This result has implications for fuel-water separation testing in the filtration industry. Next, a microfluidic hydrodynamic ‘Stokes’ trap is used to trap droplets in a cross-slot geometry. A four-channel hydrodynamic trap is applied towards studying drop shape relaxation as well as binary droplet coalescence of water droplets in mineral oils, stabilized by SPAN 80. It is found that the film drainage time for coalescence increases with droplet radius and surfactant concentration, while it decreases with incoming drop velocity. Critical conditions for flocculation and rebound of droplets are identified in terms of the capillary number. Finally, interfacial dilatational rheological properties of water-in-diesel fuel systems are measured using a capillary pressure microtensiometer. PIBSI and monoolein are added to the diesel fuel, and the dependence of the dilatational modulus on oscillation frequency and surfactant concentration is investigated. The dilatational modulus is found to increase with oscillation frequency and decrease with surfactant concentration. PIBSI-laden interfaces have higher modulus than monoolein-laden interfaces. Collectively, these experiments enhance our understanding of the intricate relationship between surfactant transport on the microscale, and droplet coalescence leading to emulsion separation.
Comprehensive Multidimensional Separations of Biological Samples using Capillary Electrophoresis coupled with Micro Free Flow Electrophoresis
(2017-12) Johnson, Alexander
Micro free-flow electrophoresis (μFFE) is a continuous separation technique in which analytes are streamed through a perpendicularly applied electric field in a planar separation channel. Analyte streams are deflected laterally based on their electrophoretic mobilities as they flow through the separation channel. The continuous nature of µFFE separations makes it uniquely suitable as the second dimension for multidimensional separations. The focus of this work is the development of coupling capillary electrophoresis (CE) to µFFE as a high speed two-dimensional (2D) separation platform, followed by an investigation of orthogonality of the two techniques, and finally a novel label-free detection method for µFFE separations. A new µFFE device was fabricated and coupled to CE via capillary inserted directly into the µFFE separation channel. High peak capacity separations of trypsin digested BSA and small molecule bioamines demonstrated the power of CE × µFFE. Since both methods rely on electrophoretic mobility to separate, an investigation on the orthogonality of the two techniques was carried out. µFFE can operate in many different separation modes to increase the orthogonality CE × µFFE. Lastly, fluorescent labeling of the analytes can cause the sample to lose its dimensionality affecting 2D separation peak capacity and coverage. A novel absorption detector was studied to demonstrate the first ever label free absorption detection on a µFFE device. A separation was performed on visible dyes and their detection limits quantified.
Development of a microfluidic, segmented-flow, single molecule, enzyme activity assay and improvement of separation efficiency of basic proteins by application of a water- proofing agent as a coating in capillary electrophoresis
(2012-08) Castro Barahona, Eric Rigoberto
A novel, microfluidic platform for segmented flow assays has been developed using commercially available Teflon tubing and PEEK connectors. Such a system can be used to generate arrays of nano to pico liter sized droplets separated from each other by plugs of a fluourous solvent. Each droplet becomes an individual reaction vessel suitable for high-throughput applications. We have applied this method to the development of a single enzyme molecule fluorescence assay. Characterization of the droplet generation platform was done with the use of a 100 μm ID PEEK T-junction connector. When two immiscible streams, such as water and a fluorous solvent, meet at the T-junction an array of aqueous droplets separated by plugs of the solvent is generated inside the Teflon tubing. Experiments have shown that, like previous microfabricated segmented flow devices, our system can control the size of the droplets generated solely by changing the ratio of the flow rates of the two phases. Using this approach droplets can be produced with good reproducibility (better than 6% in all cases and better than 3% in most) over a wide range of flow rates. Rates of droplet generation of 10.37 ± 0.17 drops/s are easily achieved for good high-throughput potential. Fast on-line mixing of reagents and long term droplet stability of up to 7 days has also been demonstrated. The discovery of the heterogeneity of enzyme molecules with respect to activity has resulted in the development of a variety of single enzyme molecule assays, with the aim of investigating the prevalence and origin of this phenomenon. The segmented flow platform we have developed is well suited to the application of single enzyme assays. It has the advantage of high-throughput, as well as ease of fabrication compared to PDMS or silica based devices and elimination of exposure of the enzyme analyte to the walls of the channel or well. A segmented flow, single molecule assay has been developed for the enzyme alkaline phosphatase (AP). Single AP molecules were sequestered inside 100 pL droplets generated in a PEEK tee and stored in a length of 50 μm ID Teflon tubing. The droplet array was allowed to incubate for a suitable time period, during which the AP molecules converted the weakly fluorescent substrate AttoPhos® into a strongly fluorescent product. AP molecules were found, as in previous studies, to display heterogenous activity with up to a 9-fold difference between individual enzymes In the last section of this work we have used the commercial glass treatment Aquapel as a capillary wall coating agent to reduce protein absorption in capillary electrophoresis (CE). Due to their large number of potential sites for interactions with the fused-silica wall, protein separations with CE can often be difficult. For this reason, much effort is expended on the development on wall coating agents for the prevention of such interactions. Aquapel is a fluorous polymer used commercially to render glass surfaces hydrophobic. The efficacy of the coating was investigated using a suite of three basic proteins: lysozyme, cytochrome c and α-chymotrypsinogen. Separation efficiencies of up to 130,000 theoretical plates were achieved over a pH range of 4.0 to 7.0, a significant improvement over bare fused silica capillary. Electroosmotic flow (EOF) was reduced by the Aquapel coating but not entirely suppressed. The stability of the coating was also examined. 62 protein injections were performed over a two day period during which analyte migration times varied by less than 3.5%. Due to the ease of application and low cost, coating with Aquapel is an attractive alternative to available capillary coatings.
Development of Biomimetic Microfluidic Platforms for Cellular Interaction Studies
(2016-08) Wu, Xiaojie
Achieving a better understanding of cellular interactions with other critical components in physiological microenvironments is an urgent challenge due to the fact that critical cellular behaviors are delicately regulated by the complexity of the biological system. Factors influencing cellular behaviors include interactions with the surrounding cell types and biological molecules, as well as a range of biophysical factors, such as pressure, flow, and chemical gradients. With a better understanding of environmental impacts on cellular behaviors, mechanistic insights on the pathogenesis of diseases and advances in medical treatment will be provided. Because the technical difficulties of traditional cell assays have limited the systematic study of cellular interactions, novel platforms with the ability to represent cellular interactions in a quick, spatiotemporal-resolved, and biomimetic manner would be welcomed by the research community. Microfluidics, one of the novel techniques used frequently for cell biology studies, is able to introduce the cellular interactions into an in vivo-like microenvironment with high spatiotemporal resolution, also allowing the quantification of cellular behaviors at the single cell level. The aim of this thesis is to develop biomimetic microfluidic platforms to mechanistically study cellular interactions in the context of different biological processes. First, Chapter 1 of this thesis reviews the application of microfluidics in the field of cellular interactions with focus on advances of microfluidics in single cell analysis and in vivo-like microenvironment generation. The following chapters separately discuss the topics including cell-drug interactions (Chapter 2), cell migration within complex gradient patterns (Chapter 3), the interactions between iii cell migration and angiogenesis growth (Chapter 4), heterotypic cellular interactions in a biomimetic environment (Chapter 5), and the effects of shear rates on cellular adhesion behaviors (Chapter 6). In Chapter 2, we developed a microfluidic platform containing stable chemical gradients to assess the drug effects on neutrophil migration, which is the key characteristic of inflammatory diseases. By tracking the migration of single neutrophils, we achieved quantification of various parameters, including average velocity, orientation, and overall effectiveness of migration. In addition to examining neutrophil migratory behaviors, the cytotoxicity of drug candidates was also evaluated to reveal a comprehensive understanding about the drug effects on neutrophil function. In Chapter3 and 4, we continued to study neutrophil migration in more complicated in vivo-like microenvironments. To be specific, a three-dimensional endothelial cell layer was cultured in the microfluidic channel, and neutrophil transendothelial migration was monitored under various chemical gradient patterns such that the competitive and synergistic effects among different cytokine molecules were determined. Furthermore, the interactions between neutrophil migration and endothelial angiogenesis were studied by inducing angiogenic growth of the endothelial cell layer in the microfluidic channel. We found that larger endothelial cell angiogenic growth area induced significantly more neutrophil migration while the process of neutrophil migration was able to stabilize the endothelial cell structure even in the presence of an angiogenesis inhibitor that decreases the angiogenic growth of endothelial cells. After detailed evaluation of neutrophil migration in different conditions, a biomimetic microfluidic model was used in Chapter 5 to study heterotypic cellular interactions between endothelial cells and HeLa cancer cells. Three critical environmental factors, including chemical gradients, flow rate, and hypoxia, were separately introduced into the microfluidic model to determine the effect of each factor on cellular interactions. Also, all these three factors were combined together into a single microfluidic device to investigate the overall effects on cellular interactions, which provides an in vitro approach to predict the cellular behaviors in the context of cancer. In the last chapter (Chapter 6), a simple microfluidic system was established to explore the relationship between shear rates and cell adhesion behaviors. Two major blood cell types, platelets and neutrophils, were injected through the endothelial cell covered-microfluidic channels with different dimensions, and the results suggest that the expression of receptor molecules participating in the cell adhesion is selective to the dimension of microfluidic channel. This conclusion reveals the novel insights on the mechanisms of cell adhesion in various shear rate conditions and provides deeper understandings about the pathogenesis of blood-based diseases. Overall, the research presented in this thesis focuses on using microfluidic platforms to characterize cellular interactions with biological complexity, in hopes of advancing our understanding about cellular behaviors in the pathogenesis of relevant diseases. All the findings reported in this thesis indicate that the application of microfluidic platform enables the recapitulation of in vivo physiological microenvironments and predicts the cellular behaviors occurring in human body, successfully bridging the gap between current in vitro and in vivo approaches.
Development of High Fidelity Digital Inline Holographic Particle Tracking Velocimetry for 3D Flow Measurements
(2016-03) Toloui, Mostafa
Three-dimensional non-invasive measurement capability is often a necessity to unravel the physical phenomenon in fluid mechanic problems such as flow field characterization in wall-bounded turbulent flows and microfluidic devices. Among all the 3D optical flow diagnostic techniques, digital inline holographic particle tracking velocimetry (DIH-PTV) provides the highest spatial resolution with low cost, simple and compact optical setups. Despite these advantages, DIH-PIV suffers from major limitations including poor longitudinal resolution, human intervention (i.e. requirement for manually determined tuning parameters during tracer field reconstruction and extraction), limited tracer concentration, small sampling volume and expensive computations. These limitations have prevented this technique from being widely implemented for high resolution 3D flow measurements. In this study, we present our novel high-fidelity DIH-PTV algorithm with the goal of overcoming all the above mentioned limitations. Specifically, the proposed particle extraction method consists of multiple steps including 3D reconstruction, 3D deconvolution, automatic signal-to-noise ratio enhancement and thresholding, particle segmentation and centroid cacluation, and inverse iterative particle extraction. In addition, the processing package is enriched with a multi-pass 3D tracking method and a cross-correlation based longitudinal displacement refinement scheme. The entire method is implemented using GPU-based algorithm to increase the computational speed significantly. Validated with synthetic particle holograms, the proposed method can achieve particle extraction rate above 95% with ghost particles less than 3% and maximum position error below a particle diameter for holograms with particle concentration above 3000 particles/mm3 within sampling volumes of ~1 mm longitudinal length. Such improvements will substantially enhance the implementation of DIH-PTV for 3D flow measurements and enable the potential commercialization of this technique. The applicability of the technique is validated using the experiment of laminar flow in a microchannel and the synthetic tracer flow fields generated using a DNS turbulent channel flow database. In addition, the proposed method is applied to smooth- and rough-wall turbulent channel flows under two different settings of high-resolution near-wall and whole-channel measurements (i.e. sampling volume is extended to the entire depth of the channel). In the first case, using a microscopic objective and local seeding mechanism, DIH-PTV resolves near-wall flow structures within a sampling volume of 1 × 1.5 × 1 mm3 (streamwise × wall-normal × spanwise) with velocity resolution of ~100 μm (vector spacing). In the second case, the measurement volume is extended to the whole-channel depth by seeding the entire channel. Under this setting, the 3D velocity fields are obtained within a sampling volume of 14.7 × 50.0 × 14.4 mm3 with a velocity resolution of ~ <1.3 mm per vector, comparable to other the-state-of-the-art 3D whole-field flow measurement techniques. Overall, the presented DIH-PTV measurements under two different settings highlight the potential of DIH-PTV to obtain 3D characterization of the turbulent structures over a full range of scales, covering both the near wall and the out-layer regions of wall-bounded turbulent flows.
Development of silica-based physical confinement models to isolate and study dormancy-prone cancer cells
(2021-03) Preciado, Julian
Metastatic cancers account for the majority of cancer-related deaths. Some metastatic tumors arise after a latent, disease-free period. The latency is attributed to cancer cells being in a dormant state that is eventually overcome, leading to metastatic progression. The ability to isolate dormant cancer cells to study and develop treatments to prevent relapse has remained an elusive goal. In this dissertation, a novel process to isolate and study dormancy-prone cells is presented. The process involves immobilizing cancer cells within a highly porous silica-poly(ethylene glycol) gel that physically confines cells. Two separate gelation models are presented. In the first model (SPEG), a distinct viability response was observed in which MCF-7, a dormancy-prone cell line, survived physical confinement significantly better than dormancy-resistant cell lines (MDA-MB-231, MDA-MB-468). Surviving MCF-7 cells were demonstrated to be in a reversible cell cycle arrested state akin to clinically observed single-cell dormancy. It was also found that tumor cells from breast and ovarian cancers that survived physical confinement were in a cell cycle arrested state. The second model, MSPEG, was developed as an improved system that allows efficient and viable cell extraction. In the MSPEG model, cells are first coated individually in a thin layer of agarose using flow-focusing microfluidic devices before encapsulation in a silica-PEG gel for protection during the extraction process. The microfluidic system conditions such as microfluidic device dimensions, flow rates, agarose concentration, oil, and surfactants were optimized to produce individually coated cells with high viability at high throughput levels. The agarose coating could be degraded to recover cells or in situ while in silica to awaken dormant cells. The silica-PEG composition was also re-engineered for better disintegration and facile silica separation from cells by modifying the molecular weight and type of PEG used and introducing iron oxide nanoparticles stabilized with fumed silica, respectively. The MSPEG model was evaluated as a clinically relevant dormancy model by examining the protein expression of p38 and ERK, the RNA expression of CDK2, cyclin D1, and cyclin E1. Additionally, we confirmed the cell cycle arrest observed was reversible by examining Ki-67 expression, senescence-associated factors, and proliferation of cells before and after physical confinement. The two models presented in this thesis can therefore be used to isolate and study dormancy-prone cells.
Development, Characterization, and Applications of a 3D Printed micro Free-Flow Electrophoresis Device
(2017-02) Anciaux, Sarah
Micro free-flow electrophoresis (μFFE) is a unique separation technique because of its continuous nature. Analytes are pressure driven through a planar separation channel, and an electric field applied laterally to the flow producing a spatial separation. Fabrication methods associated with μFFE devices hinder our ability to address the limitations of μFFE. This work focuses on a novel fabrication method to reduce the overall fabrication cost and time, followed by validating and characterizing the device. A novel μFFE device is fabricated in acrylonitrile butadiene styrene (ABS) by 3D printing two sides of the device and then acetone vapor bonding them while simultaneously inserting electrodes and clarifying the device. Fluorescent dyes are separated, and their limit of detection determined. After validation of the new fabrication method, a new device design is made with the sample inlet modified so that 2D nLC × μFFE separations can be performed. 2D nLC × μFFE separations of fluorescent dyes, proteins, and tryptic BSA digest are demonstrated. These samples allow comparison between the surface properties of glass and 3D printed devices. Peak asymmetries, widths, and the interface were investigated. Minimal surface adsorption is observed for fluorescent dyes, proteins, and peptides, unlike in glass devices. After investigating surface properties, an open edge device for coupling to mass spectrometry is designed and compared to its glass counterpart. A novel ionization method is demonstrated from a hydrophobic membrane and the open edge device is shown to have stable flow.
Experimental data of biofilm development experiments under fluctuating flow conditions taken and processed at SAFL in 2022
(2023-05-04) Wei, Guanju; Yang, Judy Q; judyyang@umn.edu; Yang, Judy; University of Minnesota, Saint Anthony Falls Laboratory, Environmental Transport Lab
This dataset consists of the Matlab codes, experimental data, and raw images of the biofilm development experiments under fluctuating flow conditions. They are all collected in the Saint Anthony Falls Laboratory at the University of Minnesota. The codes are used for processing the raw images to calculate the biofilm thickness and biofilm area coverage. The experimental data file contains the data after processing. The image file contains the raw images collected during the experiments using the Nikon confocal microscope.
Experimental data of Pseudomonas putida biofilm development experiments in flat and rough microfluidic channels
(2022-05-09) Wei, Guanju; Yang, Judy Q; judyyang@umn.edu; Yang, Judy; University of Minnesota, Saint Anthony Falls Laboratory, Environmental Transport Lab
This dataset consists of the codes, experimental data, and raw images of the Pseudomonas putida biofilm development experiments. They are all collected in the Saint Anthony Falls Laboratory at the University of Minnesota. The codes are used for processing the raw images to calculate the biofilm thickness. The experimental data file contains the experiment parameters and the data after processing. The image file contains the raw images collected using the Nikon confocal microscope.
High Speed Separations of Complex Mixtures using nano-Liquid Chromatography Coupled with micro Free Flow Electrophoresis
(2016-03) Geiger, Matthew
Micro free flow electrophoresis (µFFE) is a separation technique which can be used for unique applications due to its continuous nature. Separations are performed in space, as opposed to time, as laminar flow drives analytes down the separation chamber and are separated laterally by an electric field. This continuous nature makes it an attractive option to be used as a second dimension in multidimensional separations. The major focus of this work will be the development of a 2D separation platform coupling a commercial nano-liquid chromatography (nLC) instrument with an all glass µFFE device followed by investigating factors which could affect the efficiency of the technique. A new µFFE device was designed and fabricated for coupling with nLC. High peak capacity separations of tryptic peptides of BSA demonstrated the power of the technique. Broadening in temporal and spatial dimensions were investigated since peak capacity is calculated using analyte peak width. The observation that the adsorption of analytes only affects broadening in the temporal dimension is critical for maximizing peak capacity. Finally, the effect of using fluorescent labels in 2D nLC × µFFE separations will be demonstrated. The impact of label choice can be seen in the peak capacity and orthogonality of separations of amino acids and peptides.
High-Throughput Method for Microfluidic Placement of Cells in Micropatterned Tissues
(2013-04-20) Sevcik, Emily
Recent studies have shown that cell shape and tissue structure can dictate functional behavior in engineered tissues (1). One method for controlling tissue structure in vitro is microcontact printing, where extracellular matrix proteins are patterned on a substrate to construct arrays of single cells or multicellular tissues. This technique is used to create tissues that mimic in vivo architecture which can be used to study tissue properties and disease mechanisms (2). Traditional seeding of cells on the substrate is imprecise, but our group has developed a microfluidic device for spatial control of cell seeding, which creates more replicable high-fidelity tissues. However, the current method is low-throughput and labor intensive. Here, we present a scalable system of multiple microfluidic devices for parallel cell seeding. This high-throughput, precise approach reduces experimental variation, making biochemical assays on single cell arrays possible in future work. We will use this system to create large arrays of single cells of various shapes for phenotypic studies and to create arrays of tissues with varying cellular organization. 1)Alford, P. W., Nesmith, A. P., Seywerd, J. N., Grosberg, A., & Parker, K. K. (2011). Vascular smooth muscle contractility depends on cell shape. Integrative Biology, 3(11), 1063-1070. 2)Ruiz, S. A., & Chen, C. S. (2007). Microcontact printing: A tool to pattern. Soft Matter, 3(2), 168-177.
Label-Free, Microfluidic Biosensors with Printed, Floating-Gate Transistors
(2017-12) White, Scott
Printed electronics and microfluidics are two emerging and developing technologies with the common attractive feature of scalability. Advancements in fabrication capabilities have evolved research questions from, “What can we build?” to, “What should we build?”. This work focuses on the combination of these two technologies and their application to biosensing. The motivating theme is to understand how integrated, functional materials interact, elucidate the underlying molecular phenomena, then utilize the emergent advantages to address the outstanding limitations of conventional biosensing strategies. Printed electronics have recently been applied to biological detection with a variety of techniques1 while microfluidics, since their inception, have been used to handle biological fluids.2 The work presented here outlines a patented sensing strategy based off Floating-Gate Transistors (FGTs). The FGT design physically separates the electronic materials and biological fluids and thus bypasses various compatibility obstacles limiting other next-generation sensor technologies.3 The specific changes in interfacial properties that lead to robust signal transduction are derived empirically.4 This is followed by a mechanistic investigation into the molecular origin of sensor operation when FGTs are used in biomolecular detection. Finally, the versatility and scalability engendered by facile prototyping of FGTs is exemplified by successful iterations to DNA,3 ricin,5 and gluten proteins. The first proof-of-principle experiments incorporated printed electronics with an elementary biological system of DNA oligonucleotides. The results successfully demonstrated the potential of FGTs but failed to solidify their concrete value. Systematic investigation into the complex dynamics at the interface of chemically functionalized electrodes and electrolytes uncovered the most attractive features of the FGT technology. The chemistry was tuned with molecules that range in complexity from simple, short-chain alkyl-thiols to reversible protein-protein interactions. The observed responses with well-controlled systems were generalized to real systems like protein capture in food matrices (e.g. ricin in milk, orange juice). The resulting versatility originated from the label-free, electronic sensing mechanism and opened a range of possibilities for FGTs’ impact. The fundamental insights into interfacial dynamics, device operation, and biomolecular interactions were made possible by the advancements in the materials science and fabrication techniques underlying the presented results. Future avenues of development are hypothesized along with the most promising strategies. The continued elucidation of the physical mechanism and engineering upgrades justify the proposed strategies and inspire the continued effort to fully realize the potential of FGT biosensors.
Microfluidic assays for assessing oligonucleotide catalyst abundance and monitoring biomolecule concentration in real time
(2023-10) Douma, Cecilia
Microfluidic platforms control and manipulate very small volumes of liquid, typically at the microliter or nanoliter scale. By replacing pipettes and flasks with microfluidic channels and chambers, routine laboratory processes can be scaled down and sped up. Microfluidic platforms can mix, react, incubate, separate, extract, and detect solutions with high throughput and reproducibility, measuring the natural world at physical scales and timescales that would be inaccessible using traditional laboratory techniques. This thesis describes the development of microfluidic assays to address two bioanalytical challenges. First, a droplet microfluidic platform was developed to quantify the abundance of catalytic molecules in pools of random-sequence DNA. Although catalytic oligonucleotides are attractive as sensors and therapeutic agents, the full scope of their catalytic activity is largely unknown. The microfluidic platform described here encapsulates a library of DNA sequences in droplets with a fluorogenic substrate. Droplets that contain a catalytic sequence will become fluorescent after a period of incubation, while droplets without a catalyst will remain dark. The frequency of catalysts in the original library can be calculated from the ratio of fluorescent and non-fluorescent droplets. This thesis describes the technical design of a droplet microfluidic platform, its performance in library screening experiments, and its application for the detection of a known DNA catalyst. A versatile microfluidic platform for oligonucleotide library screening could assess catalyst abundance across a wide variety of reactions and conditions, creating a new framework for understanding the catalytic potential of oligonucleotides. Second, an aptamer affinity assay was developed for continuous cytokine quantification using micro free-flow electrophoresis (µFFE). Affinity assays are a prominent tool for biomolecule quantification because of their excellent sensitivity and specificity. However, traditional affinity assays use discrete samples and are poorly suited for measuring dynamic changes in an analyte’s concentration. The ultimate aim of the aptamer assay is to continuously quantify cellular cytokine secretion in real time using µFFE, a continuous separation technique that can detect free aptamer and bound aptamer complexes in a flowing sample stream. This thesis describes the characterization of µFFE devices fabricated in cyclic olefin copolymer as well as initial development of a µFFE aptamer assay for continuous quantification of tumor necrosis factor α (TNFα).
Microfluidic studies of temperature dependent phase transitions in aerosol droplets
(2021-06) Roy, Priyatanu
Atmospheric aerosols are suspensions of microscopic chemically complex solid or liquid particles in the atmosphere. The composition and phase of aerosols play important roles in determining radiative forcing, cloud formation, atmospheric chemistry, visibility and human health. Temperature and relative humidity (RH) dependent aerosol particle phase states and phase transitions control interactions with the surrounding gas phase as well as with other particles, and the way the particles evolve with age. Due to acceleration of global warming, there is an urgent need to develop more accurate particle-resolved climate models to improve climate prediction. Aerosols remain the largest source of uncertainty in climate predictions. The main goal of this dissertation is to develop microfluidic instrumentation to measure aerosol droplet phase transitions such as liquid-liquid phase separation and ice nucleation as a function of temperature and relative humidity. First, liquid-liquid phase separation (LLPS) similar to that observed in atmospheric aerosol droplets is investigated with aqueous droplets containing organic and inorganic solutes in a static trap based microfluidic device. LLPS in an aerosol particle directly affects aerosol water uptake and formation of cloud drops. Temperature and RH dependence of LLPS and crystallization for model aerosol droplets with varying composition is explored. It is observed that temperature has a significant effect on some systems while having no effect on others depending on the organic to inorganic ratio (OIR) as well as the identity of the organic and inorganic phases. Second, a high-throughput droplet freezing counter based on flow-through droplet microfluidics was developed to estimate ice nucleation (IN) in liquid samples relevant to atmospheric cloud droplets. Automated detection and classification of frozen droplets from liquid drops was implemented through machine learning with a deep neural network. A case study with an ideal biological ice nucleating particle (INP), Snomax, was performed. Heating and aging of the sample were also performed to identify the molecular nature of ice nucleation. The device benchmarked well against literature data and provided the highest throughput of any existing INP counters. Finally, a large array based static trap microfluidic device was implemented to study both RH dependent phase and temperature dependent INP concentration of the same sample in situ using bulk sea water and sea surface microlayer (SSML) from a simulated waveflume experiment (SeaSCAPE). This study has implications in identifying origins of INPs in sea spray which make up a significant portion of atmospheric aerosols. Correlation between ice nucleation temperature and residual dry particle morphology showed that the bulk sample had lower INPs than SSML and the residual particles were significantly different between the samples. In this dissertation, instrumentation development and case studies have been performed to show the suitability of microfluidics as versatile, adaptable and highly customizable devices, which are applicable to studying phases of aerosols and has broad implications in climate science.
My adventures in microfluidics: exploration of novel modes for sized-based DNA separation
(2014-06) Thomas, Joel Daniel Pierson
DNA separation is ubiquitous in biological research. The common technique for performing these separations, gel electrophoresis, leaves much to be desired. The separations are slow, taking hours to separate. There can also be huge variations in quality between gels, due to the randomness of the gel. Gels are limited to DNA smaller than about 15 kbp, unless pulsed fields are used that take even longer to separate. Performing these separations in microfluidic devices overcomes some of these problems. Two common geometries used to separate DNA are the slit-well geometry and the post array geometry. Using the understanding gained using these geometries, researchers have been able to create continuous separation devices.We have tested novel operations modes, initially predicted by theory and simulations, within these well understood geometries. We achieved bi-directional migration using an asymmetric pulsed electric field in the slit well geometry. This created a non-clogging DNA filter. We achieved improved separation in a hexagonal post array by rotating the array. We were able to separate DNA in a shorter array, 4 mm, and at a higher electric field, 50 V/cm, than seen before. We also tried to create a continuous DNA separation device using proximity field nano-patterning, but were ultimately unsuccessful. While the work done to develop microfluidic DNA separation devices by a multitude of researchers ultimately did not change how DNA separations are performed in biology labs, the advances and insights gained from those performing the work led to great advancements in DNA manipulation techniques, including genomic and sequencing techniques. In fact, a genomic technique called DNA barcoding, which is performed by stretching DNA in very small channels, or nanochannels, would not have been possible without the initial microfluidic work in DNA separation techniques.
Protein crystallization using micro-fluidic devices
(2009-08) Sugiyama, Masano
X-ray diffraction is the most common way to determine protein structure at an atomic level. To determine the protein structure, a high-quality crystal of sufficient size is required. Obtaining such a crystal is difficult due to the multi-parametric phase space that needs to be screened to determine the best conditions for growth of a suitable crystal. In this work two microfluidic protein crystallization techniques have been developed and tested: the continuous-feed crystallization chamber and the phase diagram visualizer. The continuous-feed crystallization chamber (CCC) allows for kinetic path control through the crystallization phase diagram during crystallization. The CCC operates similarly to a continuously stirred tank reactor, where protein, salt, and buffer are fed at desired flow rates and concentrations to maintain desired conditions inside the chamber. A lumped kinetic model was developed, and parameters for heterogeneous nucleation kinetics were determined. Heterogeneous nucleation was found to have faster nucleation kinetics and slower growth kinetics than homogeneous nucleation, as expected. The lumped-model analysis gives a method to quantifying the effect of various crystallization variables by extraction of kinetic parameters. The phase diagram visualizer (PDV) determines the solution phase diagram for protein-precipitant systems in one experiment rather than many lengthy experiments as required for traditional methods. Laminar flow and diffusion in the PDV create significant gradients in concentration, so crystals form in only part of the chamber. By combining observation of the location of the crystal-rich regions with a computer simulation of flow and transport in the chamber, a solution phase diagram is generated. This PDV has been tested for the lysozyme-sodium chloride and lysozyme-soidum nitride system. Modeling results where used to design an improved PDV with grooves. This device has been fabricated and is to be tested in the next phase of experiments. These two microfluidic devices together can be used together to determine and execute an optimized growth strategy for a given protein or a condition change. The PDV will give a general road map of the phase space that will be traveled using the CCC.
Supporting data for "3D Printed Self-Supporting Elastomeric Structures for Multifunctional Microfluidics"
(2020-07-30) Su, Ruitao; Wen, Jiaxuan; Su, Qun; Wiederoder, Michael S; Koester, Steven J; Uzarski, Joshua R; McAlpine, Michael C; mcalpine@umn.edu; McAlpine, Michael C; University of Minnesota McAlpine Research Group
Microfluidic devices fabricated via soft lithography have demonstrated compelling applications in areas such as rapid biochemical assays, lab-on-a-chip diagnostics, DNA microarrays and cell analyses. These technologies could be further developed by directly integrating microfluidics with electronic sensors and curvilinear substrates as well as reducing the human-centric fabrication processes to improve throughput. Current additive manufacturing methods, such as stereolithography and multi-jet printing, tend to contaminate substrates due to uncured resins or supporting materials that are subsequently evacuated to create hollow fluid passages. Here we present a printing methodology based on precisely extruding viscoelastic inks into self-supporting structures, creating elastomeric microchannels and chambers without requiring sacrificial materials. We demonstrate that, in the sub-millimeter regime, the yield strength of the as-extruded silicone ink is sufficient to prevent creep under the gravitational loading within a certain angular range. Printing toolpaths are specifically designed to realize leakage-free connections between channels and chambers, T-shaped intersections and overlapping channels. The self-supporting microfluidic structures enable the automatable fabrication of multifunctional devices, including multi-material mixers, microfluidic-integrated sensors, automation components and 3D microfluidics.
Understanding DNA Electrophoresis in Colloidal Crystals
(2014-08) King, Scott
The electrophoretic separation of DNA (deoxyribose nucleic acid) has been a target of engineering and optimization since its inception. In the following pages, I describe an engineering investigation into the physics of DNA separation in colloidal crystals. Colloidal crystals are formed through self-assembly of micron-sized spheres, suspended as a colloidal suspension. In this work, we follow the pioneering separation work of Zeng and Harrison, seeking to better understand the properties that allow for the observed enhanced separations of small, <1 kilo base-pair (kbp) DNA and large (>10 kbp) DNA. I demonstrate some key insights required to fabricate these devices, then move on to evaluating their performance. In the first section I tackle the quality of the crystal and its potential effects on separation performance. In the second section, I attempt to explain the order of magnitude better separation behavior between agarose gels and colloidal crystals by evaluating the mobility regimes for large DNA. At the end of this work, I have included a discussion on the future place of colloidal crystals as a separation medium.

University Digital Conservancy

Browse by Subject

Browsing by Subject "Microfluidics"