Control and measurement of oxygen in microfluidic bioreactors. (2009)
Type of ContentTheses / Dissertations
Thesis DisciplineElectrical Engineering
Degree NameDoctor of Philosophy
PublisherUniversity of Canterbury. Electrical and Computer Engineering
Bioartificial Liver (BAL) is a term for medical devices designed to replace natural liver functions. The idea behind the use of artificial livers is to either externally support an injured liver to recovery or bridge a patient with a failing liver to transplantation. Central to all BAL systems is a bioreactor for culturing liver cells. The main function of this reactor is to provide a cell adhesion matrix and supply the necessary nutrient solution. A high cellular oxygen uptake rate combined with low solubility in aqueous media makes oxygen supply to the liver cells the most constraining factor in current reactor designs. Devices with parallel-plate channel geometry promise high efficiency for blood detoxification and liver metabolism. However, due to their specific flow regime oxygen depletion in the medium is a major problem in these devices. This thesis explores a unique method of controlling and measuring dissolved oxygen in BAL cell-culture bioreactors and lab-on-a-chip devices. Testing is performed using simulations, prototype bioreactor devices and in-vitro measurement of dissolved oxygen. Several strategies developed to fabricate the bioreactors and integrate oxygen sensing are presented. Emphasis is placed on techniques that provide compatibility with commonly used microfabrication processes, while allowing for laterally-resolved measurement of oxygen in a re-usable, low-cost setup. The most significant contribution presented is the development and assessment of the tapered cell-culture bioreactor with integrated PtOEPK/PS oxygen sensor. The combination adopts a unique approach to oxygen control. Bioreactor shape is used to modulate the oxygen supplied to cells via the resulting shear-stress function. By linearly increasing the shear-stress oxygen concentration can be maintained constant over the length of the reactor. Using the integrated oxygen sensor, the resulting concentration profile can be monitored in real-time with high lateral resolution. The advantage of the device over existing techniques is that no additional oxygenation inside the reactor chamber is required to maintain a certain concentration profile and that oxygen concentration can be mapped in-situ without having to introduce further chemicals into the perfusion medium. This thesis presents a number of other contributions: a grayscale mask process, development of the PtOEPK/PS sensor patterning method and signal optimization regime, demonstration of the multi-stream flow application, an experimental setup for sensor calibration and a process to pattern cell-adhesion proteins simultaneously with the oxygen sensor, a multi-layer BAL prototype and the results of a brief experiment to test an approach using vertically aligned carbon nanotube bundles as fluidic conduits for bile drainage.
Keywordsmicrofluidics; bioreactor; oxygen sensor; cell culture; microfabrication
RightsCopyright Volker Michael Nock
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Nock, V.; Blaikie, R.J.; David, T. (University of Canterbury. Electrical and Computer EngineeringUniversity of Canterbury. Mechanical Engineering, 2009)Dissolved oxygen (DO) is an important parameter in biomedical and cell-culture applications. Several studies have found cell survival and function to be intimately linked to oxygen concentration. Laminar flow, as observed ...
Nock, V.; Blaikie, R.J. (University of Canterbury. Electrical and Computer Engineering, 2010)Dissolved oxygen (DO) is an important parameter with significant effect on cellular development and function. Micron-scale laminar flow and hydrodynamic focusing provide ideal tools for the generation of controlled chemical ...
Nock, V.; Murray, L.; Alkaisi, M.M.; Evans, J.J. (University of Canterbury. Electrical and Computer Engineering, 2011)In this paper we will demonstrate spatially-resolved visualization of oxygen dissolved in a liquid medium and introduce two microfluidic devices for cell-culture experiments with integrated oxygen control. We will further ...