Design and Optimization of a Continuous Bioreactor for Enhanced Cell Production
Type of DegreePhD Dissertation
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This research investigated a novel continuous bioreactor which can be operated both in batch and chemostat modes. The bioreactor showed significant improvement in cell growth due to addition of a spiroid which increased gas-liquid contact areas. The bioreactor consists of a cylindrical wall and is horizontally rotated on a roller bed. The spiroid is embedded in the cylindrical wall of the bioreactor to increase oxygen transfer to the liquid phase which fills two-thirds of the bioreactor. The bioreactor has two rotary inlets and outlets for batch, continuous or fed-batch operation and real-time sampling. The rotation rate of the reactor can be adjusted to control the flow of gas and liquid in the spiroid. When the partially filled reactor is rotating, the spiroid picks up slugs of gas and liquid near the reactor exit and delivers them to the reactor entrance. The flow though spiroid at different rotation rates, spiroid diameter and spiroid length was studied using computational fluid dynamics (CFD) to determine conditions for optimum operation. As flow through spiroid is a complex phenomenon, the CFD model was simplified to a straight tube and different parameters (shear stress, velocity vectors, wall turbulence, turbulence parameters) for different dimensions were studied to determine the optimum size of the spiroid. To test the viability of the reactor for cellular production and growth, biological tests using Saccharomyces cerevisiae (yeast) were conducted at different rotation rates, operation modes (batch, continuous) and steady state levels. Cell growth monitoring and metabolite concentration (glucose) measurements in the bioreactor with and without the spiroid demonstrated the advantage of the bioreactor in increased cell production (57% increased cells and 27% less operating time). The bioreactor was further used to optimize the cell line production. Higher cell production was seen at 8 RPM for yeast at a flow rate of 0.6 ml/min. 3D printing techniques were used to prototype the reactor to reduce the degradation of the material with continued use of various cell lines and make it biocompatible and autoclavable. Mammalian cell culture using Chinese hamster ovary (CHO) cells showed promising results for producing high cell densities of 2.4 x 106 cells/ml for a period of 14 days. Cell viabilities could be maintained up to 90% with the use of spiroid in the reactor. Higher CHO cell densities were obtained at higher rotation rate of 10rpm and high medium flow rate of 4ml/min. These results show the potential of the bioreactor to continuously culture a variety of cell lines including shear sensitive cells for long durations without leakage.