An oxygen-controlled in vitro model of the gastrointestinal human-microbiome interface

Abstract

The gastrointestinal system plays a vital role in the functioning of the human body, processing food into useable energy, controlling homeostasis, and serving as the front line of the immune system. The intestines are aided in their many functions by the gut microbiome, a collection of 100 trillion anaerobic bacteria cells that live inside the GI tract. Although they play an essential part in the organ system, they remain little-represented in in vitro gastrointestinal models because of the difficulty of replicating the anaerobic conditions of the intestines. We constructed an in vitro model capable of growing aerobic epithelial intestinal cells along with anaerobic microbes in the same bioreactor. A device called the apical flow module seals a 12-well transwell and provides an inlet and outlet port into the apical chamber. Media is deoxygenated using nitrogen bubbles before it is pumped using a nitrogen-actuated pneumatic pump block. Microbes are injected into the anaerobic fluid through a rubber septum injection port before the fluid flows into the sealed transwell. Effluent is collected in sterile tubes at a controlled height so as to regulate the apical side pressure. Oxygen is provided to the basolateral human epithelial cells through basolateral circulation achieved using a pneumatic circulation plate. Preliminary testing confirms our ability to control the oxygen in all parts of the system and to grow cocultures of human and bacteria cells. Epithelial cells grown in our bioreactor show signs of behaving more similarly to cells in vivo when exposed to the conditions present in our system, providing researchers with an oxygen-controlled gastrointestinal in vitro model.