Microfluidic Production of Polymeric Functional Microparticles

This dissertation focuses on applying droplet-based microfluidics to fabricate new classes of polymeric microparticles with customized properties for various applications. The integration of microfluidic techniques with microparticle engineering allows for unprecedented control over particle size, shape, and functional properties. Specifically, three types of microparticles are discussed here: (1) Magnetic and fluorescent chitosan hydrogel microparticles and their in-situ assembly into higher-order microstructures; (2) Polydimethylsiloxane (PDMS) microbeads with phosphorescent properties for oxygen sensing; (3) Macroporous microparticles as biological immunosensors. First, we describe a microfluidic approach to generate monodisperse chitosan hydrogel microparticles that can be further connected in-situ into higher-order microstructures. Microparticles of the biopolymer chitosan are created continuously by contacting an aqueous solution of chitosan at a microfluidic T-junction with a stream of hexadecane containing a nonionic detergent, followed by downstream crosslinking of the generated droplets by a ternary flow of glutaraldehyde. Functional properties of the microparticles can be easily varied by introducing payloads such as magnetic nanoparticles and/or fluorescent dyes into the chitosan solution. We then use these prepared microparticles as "building blocks" and assemble them into high ordered microstructures, i.e. microchains with controlled geometry and flexibility. Next, we describe a new approach to produce monodisperse microbeads of PDMS using microfluidics. Using a flow-focusing configuration, a PDMS precursor solution is dispersed into microdroplets within an aqueous continuous phase. These droplets are collected and thermally cured off-chip into soft, solid microbeads. In addition, our technique allows for direct integration of payloads, such as an oxygen-sensitive porphyrin dye, into the PDMS microbeads. We then show that the resulting dye-bearing beads can function as non-invasive and real-time oxygen micro-sensors. Finally, we report a co-flow microfluidic method to prepare uniform polymer microparticles with macroporous texture, and investigate their application as discrete immunological biosensors for the detection of biological species. The matrix of such microparticles is based on macroporous polymethacrylate polymers configured with tailored pores ranging from hundreds of nanometers to a few microns. Subsequently, we immobilize bioactive antibodies on the particle surface, and demonstrate the immunological performance of these functionalized porous microbeads over a range of antigen concentrations

Koseido purasuchikku maikuro nano kozotai sakusei to kagaku seikagaku maikurochippu eno oyo

制度:新 ; 報告番号:甲3060号 ; 学位の種類:博士(工学) ; 授与年月日:2010/3/15 ; 早大学位記番号:新532

Recent advances on open fluidic systems for biomedical applications: A review

Microfluidics has become an important tool to engineer microenvironments with high precision, comprising devices and methods for controlling and manipulating fluids at the submillimeter scale. A specific branch of microfluidics comprises open fluidic systems, which is mainly characterized by displaying a higher air/liquid interface when compared with traditional closed-channel setups. The use of open channel systems has enabled the design of singular architectures in devices that are simple to fabricate and to clean. Enhanced functionality and accessibility for liquid handling are additional advantages inputted to technologies based on open fluidics. While benchmarked against closed fluidics approaches, the use of directly accessible channels decreases the risk of clogging and bubble-driven flow perturbation. In this review, we discuss the advantages of open fluidics systems when compared to their closed fluidics counterparts. Platforms are analyzed in two separated groups based on different confinement principles: wall-based physical confinement and wettability-contrast confinement. The physical confinement group comprises both open and traditional microfluidics; examples based on open channels with rectangular and triangular cross-section, suspended microfluidics, and the use of narrow edge of a solid surface for fluid confinement are addressed. The second group covers (super)hydrophilic/(super)hydrophobic patterned surfaces, and examples based on polymer-, textile- and paper-based microfluidic devices are explored. The technologies described in this review are critically discussed concerning devices' performance and versatility, manufacturing techniques and fluid transport/manipulation methods. A gather-up of recent biomedical applications of open fluidics devices is also presented.European Research Council grant agreement ERC-2012-ADG 20120216-321266 for project ComplexiTE and ERC-2014-ADG-669858 for project “ATLAS”. N. M. Oliveira acknowledges the financial support from Portuguese Foundation for Science and Technology − FCT (Grant SFRH/BD/73172/2010), from the financial program POPH/FSE from QREN. The work was developed within the scope of the project CICECO Aveiro Institute of Materials, POCI-01-0145-FEDER-007679 (FCT Ref. UID/CTM/50011/2013). Sara Vilabril acknowledges the financial support from national funds through the FCT/MEC and when appropriate co-financed by FEDER under the PT2020 Partnership Agreementinfo:eu-repo/semantics/publishedVersio

Understanding Flow-Induced Phase Inversion Of Emulsions Using Microfluidics

Phase inversion emulsification (PIE) is a process of generating emulsions by inverting the continuous and dispersed phases of precursor emulsions. PIE is particularly useful when it is challenging to generate the target emulsions by conventional emulsification methods. One such case is the synthesis of polymeric nanoparticles, which requires production of very small droplets of viscous oils. Currently most, if not all, PIE processes in industry are performed as batch processes. Many studies have demonstrated considerable reductions in operation time/cost by changing a batch system to a continuous system. One way of inducing phase inversion in continuous processing is by flowing emulsions through precisely engineered channels and pore-arrays i.e. by flow-induced phase inversion emulsification (FIPIE). A clear advantage of this mechanism is that it can be simulated in microfluidic channels and thus direct observation and fundamental investigation of the PIE process is possible. It is shown that preferential wetting between the dispersed phase of the precursor emulsions and the channel surfaces is crucial for FIPIE. This means, O/W emulsions require hydrophobic channels for FIPIE and vice versa. A tapered design of the phase inversion channels (PICs) with homogeneous surface treatments is used to induce FIPIE. It is found that FIPIE is very sensitive to the amount of taper and is suppressed if taper angle increases above 5 degrees. The dynamic factors affecting FIPIE are investigated in terms of dimensionless parameters – Capillary number, which denotes the relative importance of surface tension and viscous effects and D/W, which is the ratio of size of droplets to the minimum width of the tapered PICs. Lower Ca and higher D/W are found to favor FIPIE. A mechanism of FIPIE is proposed based on the real-time visualization of FIPIE. As droplets passed through narrow channels, the continuous aqueous phase is sheared into a thin film surrounding the oil droplets. Rupture of this aqueous film is found to be the most critical mechanistic step of the process. The underlying physical phenomena driving film rupture are studied based on a balance of interfacial stresses. Finally, the effect of composition and molecular mass of surfactants on the stability of emulsions against FIPIE is studied. It is shown that surfactants, which provide thicker and more viscoelastic films at emulsion interfaces result in emulsions that are more resistant to FIPIE. The insights developed in this thesis can further the prospects of enabling continuous PIE on a larger scale

Fabrication of Microfluidic Devices for Emulsion Formation by Microstereolithography

Droplet microfluidics—the art and science of forming droplets—has been revolutionary for high-throughput screening, directed evolution, single-cell sequencing, and material design. However, traditional fabrication techniques for microfluidic devices suffer from several disadvantages, including multistep processing, expensive facilities, and limited three-dimensional (3D) design flexibility. High-resolution additive manufacturing—and in particular, projection micro-stereolithography (PµSL)—provides a promising path for overcoming these drawbacks. Similar to polydimethylsiloxane-based microfluidics 20 years ago, 3D printing methods, such as PµSL, have provided a path toward a new era of microfluidic device design. PµSL greatly simplifies the device fabrication process, especially the access to truly 3D geometries, is cost-effective, and it enables multimaterial processing. In this review, we discuss both the basics and recent innovations in PµSL; the material basis with emphasis on custom-made photopolymer formulations; multimaterial 3D printing; and, 3D-printed microfluidic devices for emulsion formation as our focus application. Our goal is to support researchers in setting up their own PµSL system to fabricate tailor-made microfluidics

Surface engineering the cellular microenvironment via patterning and gradients

Cell organization, proliferation, and differentiation are impacted by diverse cues present in the cellular microenvironment. As a result, the surface of a material plays an important role in cellular function. Synthetic surfaces may be augmented by physical as well as chemical means. In particular, patterning and interfacial gradients may be utilized to mitigate the cellular response. Patterning is advantageous as it affords control over a range of feature sizes from several nanometers to millimeters. Gradients exist in vivo , for instance in stem cell niches, and the ability to create interfacial gradients in vitro can provide valuable insights into the influence of a series of minute surface changes on a single sample. This review focuses on fabrication methods for generating micro‐ and nanoscale surface patterns as well as interfacial gradients, the impact of these surface modifications on the cellular response, and the advantages and challenges of these surfaces in in vitro applications. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys., 2013 The influence of patterning and interfacial gradients on the cellular response has numerous applications in tissue engineering and basic cell science. Various methods for fabricating small‐scale patterns and interfacial gradients as well as their potential and limitations are described. Furthermore, the impact of patterns and gradients on cellular function for numerous cell types and the use of these techniques to address biological questions in in vitro environments are illustrated. Future perspectives are also provided.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/97492/1/23275_ftp.pd

Rapid detection of theophylline using an aptamer-based nanopore thin film sensor

This paper reports, for the first time, an aptamer-based nanopore thin film sensor for detecting the ophylline in buffer and complex fluids. In my experiments, I created the sensor and found that it could help us to better test theophylline than an antibody-based detection sensor. The following is a detailed explanation of the sensor creation and the experimental process. Anodic aluminum oxide (AAO) has been investigated and applied in numerous products since the 1970s. It is a highly-arrayed porous nanostructure as shown in Figure 1. The pore size normally ranges from tens to hundreds of nanometers, and the aspect ratio could be higher than 40:1. Application areas of AAO include biomedical sensing, energy storage, template-based nanofabrication, electronics, etc. In my experiment, I applied AAO to the process of creating a sensor. In my experiments, I chose RNA aptamer rather than antibodies because its molecules overcome the weakness of antibodies. The 33 nts RNA aptamer sequences used were found to recognize and selectively bind theophylline (Figure 2) [1]. Moreover, aptamers are easy to synthesize, have both excellent heat stability and a wide tolerance range of PH and salt concentration, and is much less costly than antibodies. The first study used an aptamer-based nanopore thin film sensor to detect theophylline in the buffer and complex fluids. I first fabricated the nanopore thin film sensors with a microfluidic interface, then demonstrated the surface functionalization procedure of the sensor. I then used optical transducing signals to detect the fringes followed by using the sensor as a reference sensor to further cancel out the non-specific binding effect; theophylline in low concentration (0.2μM), caffeine, theobromine, and plant extract were successfully detected. The experiment showed that this aptamer-based sensor had good specificity and selectivity, allowing me to further test theophylline in serum. The second study used an optical aptamer-based plant hormone sensor with a microfluidics capillary interface. I adopted the exact same methodology and sensor from themy first study and further designed an optical aptamer-based sensor with a microfluidics capillary interface to upgrade the testing process. Such a microfluidics capillary interface film censor was created and how my two successful experiments were performed. The research outcome is that an aptamer-based label-free sensor for optically detecting theophylline has been demonstrated for the first time. It performs much better than its competitors and has a promising future in further applications in similar experiments

Controlling Surface-Induced Platelet Activation by Modulation of Contacting Interfaces

Blutplättchen, auch Thrombozyten genannt, sind ein wesentlicher Bestandteil des menschlichen Blutgerinnungssystems. Die Hauptaufgabe der Thrombozyten innerhalb des Körpers besteht in der Blutstillung. Außerhalb des Körpers neigen Thrombozyten jedoch dazu, nach kurzem Kontakt mit synthetischen, nicht physiologischen Oberflächen zu aktivieren, was für viele Anwendungen unerwünscht sein kann, einschließlich der Lagerung von Thrombozyten und der Erforschung der Wechselwirkungen zwischen Thrombozyten und Arzneimitteln. Normalerweise werden Thrombozyten-Konzentrate in handelsüblichen Plastikbeuteln aufbewahrt, die eine große Menge an Weichmachern enthalten, um die Flexibilität des Beutels zu erhöhen und die Möglichkeit eines Bruchs während der Handhabung und des Transports zu vermeiden. Bei längerer Exposition können die giftigen Weichmacher in das Thrombozyten-Konzentrat entweichen. Aktivierte Thrombozyten setzen eine Vielzahl von Proteinen frei, die den Prozess der oberflächeninduzierten Thrombozytenaktivierung (SIPA) weiter unterstützen. SIPA ist eines der Hauptprobleme von Medizinprodukten mit Blutkontakt und Transfusionsgeräten, und ein entscheidender Faktor für die verkürzte Haltbarkeit gelagerter Thrombozyten. Um SIPA zu vermeiden, werden den Thrombozyten-Konzentraten Antikoagulantien zugesetzt, so dass sie bis zu 5 Tage gelagert werden können. Diese Antikoagulantien greifen in die Aktivierungswege der Thrombozyten ein und beeinträchtigen so ihre Funktionalität. Das häufigste Problem bei der Lagerung von Thrombozyten ist schließlich die Gefahr einer bakteriellen Kontamination. Um dieses Problem zu lösen, werden verschiedene UV-Behandlungen eingesetzt, um das Risiko einer Kontamination mit Krankheitserregern zu minimieren. Studien zeigen jedoch, dass diese Strahlung mit kurzer Wellenlänge die Bestandteile der Thrombozytenmembran zerstören und zu einer Aktivierung der Thrombozyten führen kann. Diese zahlreichen, oft miteinander verknüpften Probleme verdeutlichen den dringenden Bedarf an einer effizienten Lösung zur Optimierung der Lagerungsbedingungen für Thrombozyten und zur Maximierung ihrer Lagerfähigkeit. Ziel dieser Doktorarbeit ist es, Oberflächen zu entwickeln, die die Adhäsion von Thrombozyten hemmen und somit ihre Aktivierung und Aggregation verhindern - ohne dass der Zusatz von Antikoagulantien erforderlich ist. Für die Veränderung der Oberflächeneigenschaften stehen drei verschiedene Ansätze zur Verfügung: Biophysikalische, physikochemische oder biochemische Strategien können Verwendet werden, um eine plättchenfreundliche Oberfläche zu gestalten. In der ersten Phase dieses Projekts wurde eine Kombination aus physikochemischen und biophysikalischen Ansätzen angewandt, um Hydrogele aus Gelatine und Agarose herzustellen, die anschließend durch Integration von Eisennanopartikeln zu Nanokompositen verarbeitet wurden. Agarose-basierte Hydrogel-Filme erwiesen sich dabei durch die Kombination von Oberflächenbenetzbarkeit und besseren mechanischen Eigenschaften als ideale Oberflächen. Mikroskopaufnahmen zeigten, dass die Anzahl der Blutplättchen, die an solchen Oberflächen adhärieren, deutlich reduziert und die Ausbreitung der Blutplättchen verhindert wurde. Hergestellte Agarose-Filme und ihre Nanokomposite konnten darüber hinaus bakterielles Wachstum erfolgreich hemmen: Von allen getesteten Proben wurde der höchste Prozentsatz an toten Bakterien auf den Nanokomposit-Filmen gemessen. Die Topographie des Substrats spielt eine entscheidende Rolle für das Verhalten der Zellen und die Kontrolle ihrer Physiologie und Morphologie. Für die Veränderung der Oberflächentopografie stehen zahlreiche komplexe Techniken zur Verfügung. In dieser Arbeit wurden zwei Techniken mit individuellen Vorteilen zur Herstellung von Nanostrukturen eingesetzt. Bei der ersten handelt es sich um ein auf der Rasterkraftmikroskopie (AFM) basierendes Fluidiksystem namens FluidFM, bei dem eine Monomere enthaltende Tinte aus der Öffnung des Cantilever Spitze auf die Oberfläche extrudiert wird. Nach dem Druckvorgang wird die Tinte polymerisiert, um 3D-Strukturen zu erhalten. Mit Hilfe von kontinuierlichen und diskontinuierlichen Topografien wurden hexagonale Bienenstock- bzw. halbkugelförmige Gitterstrukturen hergestellt. Dabei zeigte sich, dass die Thrombozyten diese Strukturierung mechanisch wahrnehmen und ihr Zytoskelett umorganisieren, was zu einer geringeren Ausbreitung der Blutplättchen führt. Darüber hinaus wurde die Technik zum Drucken einer modifizierten biofunktionalisierten Tinte verwendet, die so modifiziert wurde, dass Moleküle mit unterschiedlichen funktionellen Gruppen in die Basistinte integriert wurden. Diese Modifikation führte nur zu einer geringfügigen Veränderung der mechanischen Eigenschaften der gedruckten Strukturen, während ihre Funktionalität erhalten blieb. Die Möglichkeit, Bindungsmotive für spezifische Wechselwirkungen zu integrieren, demonstriert die Vielseitigkeit der FluidFM und ebnet den Weg für die weitere Erforschung des biochemischen/topographischen Ansatzes im Bereich der Entwicklung plättchenfreundlicher Oberflächen. Das Drucken von Mikro- und Nanostrukturen stellt eine schnelle, kostengünstige und effiziente Methode zur Herstellung verschiedener geometrischer Prototypen dar und kann nicht nur zur Untersuchung verschiedener Strukturformen, sondern auch ihrer Größe und anderer topografischer Parameter eingesetzt werden. Die zweite verwendete Technik war die thermische Nanoimprint-Lithografie (T-NIL), mit der ein breiteres Spektrum an Oberflächentopologien untersucht werden konnte, einschließlich Punkt, Kette, Pille und Quadrat-förmiger. Diese Nanomuster wurden auf Siliziumscheiben geätzt und auf einen PDMS-basierten Stempel übertragen, der so zum Prägen von Hydrogelen verwendet werden konnte. Verschiedene Topologien wurden auf die Oberfläche von Agarosegelen geprägt, um ihre zuvor beobachtete, hemmende Wirkung auf die Thrombozytenadhäsion zu verbessern. Das pillenförmige Nanomuster war dabei am besten geeignet, um die Thrombozytenadhäsion zu hemmen, was auf die Höhe der Struktur zurückgeführt werden kann. Zusammenfassend lässt sich festhalten, dass in diesem Projekt Hydrogelfilme auf Agarosebasis, insbesondere in Form von Nanokompositen mit integrierten antibakteriellen Eisennanopartikeln, entwickelt wurden, die Lagerungsbedingungen für Thrombozyten deutlich verbessern, indem sie die SIPA und das Risiko einer bakteriellen Kontamination verringern. UV-Behandlungen von Thrombozyten-Konzentraten werden dadurch überflüssig. Durch die Einführung verschiedener Oberflächentopologien kann die Adhäsion von Thrombozyten gehemmt werden: Das FluidFM-basierte vielseitig einsetybare Nanodrucksystem wurde für die Erforschung und Entwicklung von Prototypen effektiver Geometrien eingesetzt, während T-NIL für die Prägung ausgewählter Strukturen auf die Oberfläche von Agarose-Filmen verwendet werden kann, um eine einheitliche Oberflächentopographie zu schaffen

Microfluidics and Nanofluidics Handbook

The Microfluidics and Nanofluidics Handbook: Two-Volume Set comprehensively captures the cross-disciplinary breadth of the fields of micro- and nanofluidics, which encompass the biological sciences, chemistry, physics and engineering applications. To fill the knowledge gap between engineering and the basic sciences, the editors pulled together key individuals, well known in their respective areas, to author chapters that help graduate students, scientists, and practicing engineers understand the overall area of microfluidics and nanofluidics. Topics covered include Finite Volume Method for Numerical Simulation Lattice Boltzmann Method and Its Applications in Microfluidics Microparticle and Nanoparticle Manipulation Methane Solubility Enhancement in Water Confined to Nanoscale Pores Volume Two: Fabrication, Implementation, and Applications focuses on topics related to experimental and numerical methods. It also covers fabrication and applications in a variety of areas, from aerospace to biological systems. Reflecting the inherent nature of microfluidics and nanofluidics, the book includes as much interdisciplinary knowledge as possible. It provides the fundamental science background for newcomers and advanced techniques and concepts for experienced researchers and professionals