Cancer remains a leading cause of death worldwide, with no signs of slowing down. In 2023 alone, the projected number of deaths from cancer is 600,000, with projected incidences at almost 2 million. Mortality rates have improved recently, but a cancer diagnosis still burdens patients and their families. This burden weighs on patients not only financially but also emotionally. For example, the average out-of-pocket patient cost is more than $2,000 and can be even higher for more aggressive types of cancer. Additionally, 2 in 3 cancer patients experience significant psychological stress due to their diagnosis. As such, cancer research is an increasingly important field that will only become more needed as birthrates rise and the population continues to live longer.

The current in vitro cancer models generally rely on 2D monolayer cell growth conformation that lacks the sophistication required to represent physiological tissues accurately. As such, many therapeutic screening studies that employ these models fail to translate well to clinical trials. Furthermore, the xenografted nude mouse model, the most commonly used in vivo animal model, lacks many critical immune components to represent drug response and survival rates correctly. Also, as anticancer strategies are moving away from cytotoxic styles of drugs and toward inhibitory and immunotherapeutic drugs, the use cases for the nude mouse model have diminished greatly. Thus, the need for novel 3D physiologically accurate in vitro cancer research models is apparent. Bioreactors, specifically flow-perfusion bioreactors, are uniquely poised to fill this void as exceptionally useful tools for cell culture that can create 3D macro-scale cultures for tissue engineering applications. They offer unique cell culture monitoring facilities through modular sensors, particularly in the liquid phase, which leaves a gap for creating an analytical sensor for gas phase volatile metabolite detection.

As such, the abovementioned deficiencies with current 2D in vitro models and the lack of proper gas phase metabolite analysis pose the guiding questions for this manuscript: 1) “How can we use novel mid-IR laser spectrometry to monitor cell cultures in bioreactors?” and 2) “In what ways does hypoxia affect the proliferation and oxygen uptake rates of cancer cells in 3D in vitro flow-perfusion bioreactor models?”. These questions will be answered by modifying the previously established flow-perfusion bioreactor system to incorporate 3D collagen hydrogel scaffolds as a more physiologically representative in vitro solid tumor model. The verification of successful cell culture was determined using cell growth and viability. Furthermore, cell culture within the solid tumor model was monitored using a novel Mid-IR laser spectrometer to detect acetaldehyde, a gas-phase metabolite, as a potential biomarker for cancer diagnosis. Further exploring the novel 3D in vitro solid tumor model illuminated the need to add hypoxia, a critical component of solid tumor pathophysiology, to create a better biomimetic model. The hypoxic component was added by directing the flow of the bioreactor such that media flowed through each chamber without reoxygenation in a series way, thus lowering the oxygen saturation stepwise. The following chapters of this investigation will focus on answering each of these questions in succession.