Electrochemical Focal Hypoxia for Cell Models

For the last few decades, there has been increasing attention to hypoxia’s (low oxygen) contribution to poor prognosis and ineffective treatments. Despite existing physiologically, hypoxia is a pathological accompaniment in a myriad of diseases, including tumour, stroke, dementia and cardiovascular diseases, that causes damage locally and to surrounding tissues. The inflicted damage is particularly significant in the brain which uses 20% of the body’s total oxygen supply and has limited energy storage. Currently common hypoxia models such as low oxygen incubators, hypoxia chambers and chemical hypoxia have two major flaws: no spatial control and long equilibration time. It is not possible to induce hypoxia focally such that these approaches have very limited translatability and resemblance to the physiology and pathophysiology of the local tissue. Thus, our ability to focus on the geography of events emerging from hypoxia has been limited. This thesis addressed the spatiotemporal limitation of existing hypoxia models and investigated oxygen removal by electrochemical reduction in culture media. The platinum/graphite (Pt/C) electrode had a large surface area and showed promising catalytic properties for the oxygen reduction reaction in the culture media. The oxygen scavenging system effectively generated hypoxia at the base of the electrochemical cell in 7 minutes from normoxia, contrasting with hours needed by conventional methods. Its flexibility in reshaping and positioning were also beneficial to generating patterns of hypoxia gradient. Upon application to human cells, the electrochemical oxygen scavenging system was proven to induce spatiotemporal response of HIF-1α transcription factor in neural progenitor cells. The system was also applied in a human cerebral microchannel model which was the first known in vitro model to demonstrate that 10-minute focal hypoxic stress on the axons caused the induction of apoptosis in human cortical neurons, observed in the distant cell bodies.Croucher Cambridge International Scholarship; Cambridge Trus