Droplet Generation and Manipulation via Silicon Microfluidics, Remote Stimulation of Electrogenetic Cells, and Microcraters Characterization
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Date
2023
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Doctoral Thesis
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Abstract
Microfabrication techniques such as photolithography, etching, and thin film deposition provide the foundation for creating integrated circuits, microelectromechanical systems, and microfluidic devices. Advancements in the microfabrication technology have boosted device miniaturization and enhanced microsystems functionalization, leading to many new applications in fields ranging from electronics and robotics to chemistry and biomedicine. For instance, the field of microfluidics inherited some microfabrication methods, originally developed for the semiconductor industry, to engineer microsystems that manipulate fluids in channels at the micrometers scale. Despite the popularity of polymeric materials in microfluidic research, properties of silicon such as mechanical compliance, chemical inertness, and manufacturing accuracy make it a preferable choice for certain applications.
The first part of this doctoral thesis is focused on leveraging microfabrication techniques to develop novel recipes to fabricate silicon microfluidic devices for the generation and manipulation of droplets. A microfabrication route is presented to create 3D microfluidic architectures by stacking glass and silicon layers, and used to build microfluidic devices with several droplet generation junctions in parallel. Moreover, the influence of the fluid flow in such parallelized systems is investigated (Chapter 2). Likewise, a novel microfabrication procedure is developed to integrate electrodes into silicon-based microfluidic devices for droplet manipulation by means of electric fields. In addition, optical transmission windows are opened through the devices to overcome silicon opacity. Using this procedure, picoinjection and fluorescence-activated droplet sorting microfluidic devices are created, leading to operation at low voltages (Chapter 3).
Electrogenetics consists of introducing genetic modifications into cells or organisms to make them responsive to electrical signals, allowing for precise control and manipulation of their activity. In the second part of this thesis, silicon-based microelectrode arrays are fabricated to stimulate electrogenetic cells which secrete insulin upon exposure to electric fields. An implant device prototype, aimed to be subcutaneously implanted and remote-controlled with a smartphone app, is assembled to
regulate the secretion of insulin from electrogenetic cells (Chapter 4).
Laser ablation is a process to remove or vaporize material from a solid surface using a laser beam. Besides being used as a high precision microfabrication technique, laser ablation is also employed as a sampling method to accurately extract a very small amount of material, leaving a microcrater behind, in order to study its chemical composition with a mass analyzer. In the last part of this thesis, a novel characterization method is presented to reconstruct the microcraters created on a material surface due to the laser ablation process. This method consists of X-ray computed tomography of the microcraters’ negative polydimethylsiloxane molds, and it is exemplarily demonstrated with a silicon sample (Chapter 5). Finally, this method is applied to reconstruct the microcraters created on a single crystal ruthenium sample and the results are combined with other characterization methods to
conduct a comprehensive study of the ablation process (Chapter 6).
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Examiner : Fussenegger, Martin
Examiner : Panke, Sven
Examiner : Lörtscher, Emanuel
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ETH Zurich
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Subject
Microfluidics; Electrogenetics; FADS; X ray computed tomography; Laser ablation
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03694 - Fussenegger, Martin / Fussenegger, Martin