A novel standalone microfluidic device for local control of oxygen tension for intestinal‐bacteria interactions

Abstract

The intestinal environment is unique because it supports the intestinal epithelial cells under a normal oxygen environment and the microbiota under an anoxic environment. Due to importance of understanding the interactions between the epithelium and the microbiota, there is a strong need for developing representative and simple experimental models. Current approaches do not capture the partitioned oxygen environment, require external anaerobic chambers, or are complex. Another major limitation is that with the solutions that can mimic this oxygen environment, the oxygenation level of the epithelial cells is not known, raising the question whether the cells are hypoxic or not. We report standalone microfluidic devices that form a partitioned oxygen environment without the use of an external anaerobic chamber or oxygen scavengers to coculture intestinal epithelial and bacterial cells. By changing the thickness of the device cover, the oxygen tension in the chamber was modulated.We verified the oxygen levels using several tests: microscale oxygen sensitive sensors which were integrated within the devices, immunostaining of Caco-2 cells to determine hypoxia levels, and genetically encoded bacteria to visualize the growth.Collectively, these methods monitored oxygen concentrations in the devices more comprehensively than previous reports and allowed for control of oxygen tension to match the requirements of both intestinal cells and anaerobic bacteria. Our experimental model is supported by the mathematical model that considered diffusion of oxygen into the top chamber. This allowed us to experimentally determine the oxygen consumption rate of the intestinal epithelial cells under perfusion. K E Y W O R D Sanaerobe, barrier function, colon, hypoxic intestine, intestine-bacteria interaction, microfluidics, organ-on-chip, oxygen sensor, partitioned oxygen environment 2 of 15 | WANG et Al.

Patient-derived pancreatic cancer-on-a-chip recapitulates the tumor microenvironment

“…The two-layer microfluidic device was fabricated using a method published previously 52 , 53 . To create the polydimethylsiloxane (PDMS) layers, a SYLGARD 184 elastomer containing silicone precursors was used as a base along with a curing agent (Dow Chemical, Midland, MI) at a 9:1 ratio.…”

“…The device chambers were cleaned and sterilized with 70% isopropyl followed by a 15-min exposure under UV light before use. The device has been characterized for the absence of hypoxia and was found to pose no obstacle to drug delivery to cultured cells 52 .…”

“…Membranes with pore sizes of 3 and 8 µm are commonly used for Transwell migration assays 55 . The smaller pore-size membrane used in our chips reduced the unwanted spontaneous migration of cells into the other channel, while the delivery of cell culture medium and drugs and waste material disposal were still possible 52 , 56 , 57 . Additionally, Matrigel at a 50% dilution has an average pore size of 2 µm, which is much smaller than the cell dimension, thus allowing the Matrigel to hold cells without hindering molecule transportation 58 .…”

Oxygen control: the often overlooked but essential piece to create betterin vitrosystems

“…The gut oxygen conditions were also emulated in a two-compartment device separated by a porous membrane. 141 Caco-2 cells were grown on the membrane with their basal side facing O 2 flow and the facultative anaerobic bacteria Escherichia coli and the anaerobic Bifidobacterium adolescentis were added on the apical side. On the top of the device a thick 5 mm extra layer of PDMS was added as a cap to slow down oxygen diffusion.…”

Microfluidic Techniques for Next‐Generation Organoid Systems

“…[17] Subsequently, Wang et al developed a novel standalone microfluidic device to create a dual-oxygen environment for local control of oxygen tension without using an external anaerobic chamber to model intestinal-bacteria interactions. [57] Besides, a gut-brain axis-on-a-chip was developed to study microbial byproducts responses between the gut and blood-brain barrier (BBB) (Figure 2D). [39] Based on those studies, future research on the microbiome in the human body is likely to integrate the microfluidic chip with organoids in order to enable the characterization of microbial communities in physiologically relevant human organoids.…”