Determination of respiration and acidification rates in dynamic cell cultures and organ-on-chips

Constant monitoring of culture parameters like oxygen, pH, and glucose is needed to ensure physiological conditions in microfluidic cell cultures or micro physiological systems. Furthermore, the measurement of these parameters can give valuable information on the viability and metabolic state of the cultured cells. Despite the large improvement of the systems and stem cell technology in the recent years there is a lack in the development of proper readout techniques for OoC. Especially, metabolic monitoring would be crucial to understand the cells response to different stimuli inside the chip. However, most systems do not offer possibilities for metabolic monitoring. Miniaturized luminescent sensors spots for oxygen and pH are integrated into various microfluidic cell and tissue culture devices using inkjet printing technique. The sensor spots in a size from 300 to 800 µm can be read out with a miniaturized multi-channel phase fluorimeter. Our sensors can be excited with red-light and emit light in the near infra-red range (<700 nm). This suppresses background fluorescence or scattering from biological material. Various cell types were cultured in the different systems and their metabolic response was monitored using integrated sensor spots. Oxygen consumption rates and extracellular acidification rates of cells are assessed in stop-flow experiments. We perform standard mitochondrial and glycolysis stress tests using model drugs to assess the ATP production of human-induced pluripotent stem cells (hiPSC) insidea microfluidic chip. We perform similar assays in the Seahorse™ system for validation. This system is the gold standard for determination of cell metabolism in static culture. Both methods yield similar results in both assays. Similar methods are used to create a microfluidic assay for cell viability and nanotoxicity. In addition, the determination of respiration rates in a heart on chip system is shown. These results will pave the way for assessment of cell metabolism in complex microfluidic systems like Organ-on-Chips with the same precision and relevance as in the current standard for static cell cultures.