Mayassa, M. (2018). Experimental and in-silico characterization of microfluidic concentration gradient generators [Diploma Thesis, Technische Universität Wien]. reposiTUm. https://doi.org/10.34726/hss.2018.60782
Due to importance of gradients in chemistry and biology, stable and controllable gradient concentrations in microfluidics has significance for analysis of cell migration, cancer metastasis, drug screening, chemotaxis as well as chemical synthesis and mixing. Microfluidic devices offer the possibility of generating complex and well-defined gradient profiles. Fluid streams at the micron scale can provide a tool to recreate and control these gradients over space and time. Furthermore, besides advantages like deterministic flow (i.e. low Reynolds number), reduced costs and ease of manufacturing, microfluidics gives the possibility to observe cell-related processes at the same scale at which they take place. One of the most popular methods for generating chemical gradients is to leverage the tree-shaped design, where two or more fluids are mixed in different ratios by a channel network, forming a gradient in the main channel by laminar flow. Because of the laminar regime that is inherent to fluid flow in microchannels, the geometry of the microdevice and the flow rates can be tuned to subject for instance cultured cells to well-defined concentration profiles. In this thesis, a diffusion-dependent microfluidic concentration gradient generator was designed and fabricated using the photo and soft lithography. Three different channel heights were produced (30 m, 45 m, 90 m) and tested at different flow rates (100 L/min - 0.5 L/min). Concentration gradient splitting and fluid dynamics were simulated using Computational Fluid Dynamic (CFD) simulation tools (Gambit and Fluent) for the three different channel heights at different flow rates. These results were compared to experimental, gravimetric and spectroscopic measurements to evaluate the chip performance and the best operating range with respect to flow rate.
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