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Development of microfluidic devices for the separation and capture of circulating tumor cells

Development of microfluidic devices for the separation and capture of circulating tumor cells
Yousang Yoon
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The separation of cells from a complex biological solution such as blood is a frequently required task in the biomedical analysis where particular cells can serve as a clinical marker. One of the highlighted objectives in cell separation is circulating tumor cell (CTC) which is known as the main cause of metastasis, forming a secondary tumor on a distant organ. Possessing high clinical potential, efforts have been made to separate CTCs from peripheral blood. Among various methods, separation of CTCs using their distinct biophysical properties is highly regarded with the ability to separate CTCs regardless of their heterogeneous phenotypes. This thesis presents three microfluidic devices developed for the separation and capture of CTCs, and discusses what each device was aimed at and what should be considered to further contribute to CTC applications. The first device to be presented is a flow-restricted trap array which is capable of hydrodynamically induced single-cell capture of CTCs. To achieve high capture efficiency as well as high single-cell capture rate, the extent of flow restriction to the capture sites, correlating with the bypass geometry, was optimized. Since cells were able to be captured individually at intended positions on the same focal plane, the flow-restricted trap array shows high prospects for an automated quantification of the targeted CTCs. The second device to be presented is a microfluidic sieving (μ-sieving) device which was developed to overcome the clogging issue that most filter based microfluidic separators suffer. By applying a low-frequency oscillation to the fluid flow, μ-sieving was able to keep the filter pores from being blocked by cell accumulation which causes the filtering of unintended contaminants, loss of targeted cells, and even device failure. Consequently, μ-sieving achieved high separation efficiency as well as high purity and retrieval rate, which was demonstrated by polymer microparticles and fixed tumor cells spiked blood. The final device to be presented is a slanted weir microfluidic device that was developed to separate CTCs from the unprocessed whole blood by utilizing both size and deformability. The addition of cell deformability in the separation strategy enabled the improved selectivity of CTCs which show the overlapped size variation with leukocytes. Rather than using a common cancer cell line, the slanted weir device was optimized by using a highly invasive breast cancer cell line that underwent in vivo lung metastasis twice. As a result, the slanted weir device was able to separate viable tumor cells with high separation efficiency and purity, even from the slight difference in deformability with leukocytes. Furthermore, by testing its ability using the clinical samples, the separation of CTCs, as well as a cancer stem cell and a tumor infiltrating leukocyte, was verified.
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