Organ-on-a-chip membrane layer

It is possible to couple Micronit OOC devices to commercial optical readers for dissolved gases in the culture medium. This option allows for applications such as the monitoring of oxygen in the culture chamber.

Have a look at this document about imaging systems.

Always check that there’s no blockage in one of the flow paths, this can be verified by checking the amount of collected liquid in a specific time frame and compare it with the expected amount for the flow rate used. If this isn't the case, droplet formation on the end of the tubing is the problem. Each falling droplet affects the flow a bit, resulting in changes in flow rates. Resolve this by keeping the end of the tubing in the collection reservoir submerged in liquid.

Cleaning Resealable flowcells are produced in cleanroom facilities and clean areas to prevent physical impurities. After use, cleaning might be required to remove organic residues. Please use distinguished cleaning processes for glass slides with and without a gasket. Glass slides with gasket: Can be cleaned with ethanol, isopropanol and acetone. The glass slides could be either immersed in the solvents or rinsed with them. Immersion might lead to diffusion of solvents into the gasket. Therefore, it is recommended to rinse the glass slide with the gasket thoroughly with water or buffer to remove residues. Only wipe with lint free tissue, otherwise the sealing might be affected negatively or completely lost. It is advised to not wipe the gasket as this might damage it and reduce its sealing abilities. Physical cleaning of the surface by either heat (with a maximum temperature of 140 °C) or oxygen plasma is possible. Cleaning with acids or bases has not been fully tested. Glass slides without gasket: Can be cleaned with organic solvents. Can be gently wiped with tissue. Physical cleaning of the surface by either heat up to 400 °C or oxygen plasma treatment is possible. Alkaline solution can be used to clean the surface, e.g. 1 M sodium hydroxide in water. Concentrated sulfuric acids could dissolve organic material, but are extremely corrosive, therefore it is not advised to use those. Hydrochloric acid could be used for cleaning, as well as bleach.

Sterilization Resealable flowcells are not sterilized when delivered. Please use distinguished sterilization processes for glass slides with and without a gasket. Glass slides with gasket: Can be sterilized with ethanol. Dry heat of up to 140 °C can be applied. Can be autoclaved. Glass slides without gasket: Can be sterilized with ethanol. Can be autoclaved.

Kulthong K, Duivenvoorde L, Mizera BZ, Rijkers D, Dam GT, Oegema G, Puzyn T, Bouwmeester H, Van Der Zande M. Implementation of a dynamic intestinal gut-on-a-chip barrier model for transport studies of lipophilic dioxin congeners. RSC Advances. 2018; 8(57): 32440-32453 Abstract Novel microfluidic technologies allow the manufacture of in vitro organ-on-a-chip systems that hold great promise to adequately recapitulate the biophysical and functional complexity of organs found in vivo. In this study, a gut-on-a-chip model was developed aiming to study the potential cellular association and transport of food contaminants. Intestinal epithelial cells (Caco-2) were cultured on a porous polyester membrane that was tightly clamped between two glass slides to form two separate flow chambers. Glass syringes, polytetrafluoroethylene tubing and glass microfluidic chips were selected to minimize surface adsorption of the studied compounds (i.e. highly lipophilic dioxins), during the transport studies. Confocal microscopy studies revealed that, upon culturing under constant flow for 7 days, Caco-2 cells formed complete and polarized monolayers as observed after culturing for 21 days under static conditions in Transwells. We exposed Caco-2 monolayers in the chip and Transwell to a mixture of 17 dioxin congeners (7 polychlorinated dibenzo-p-dioxins and 10 polychlorinated dibenzofurans) for 24 h. Gas chromatography-high resolution mass spectrometry was used to assess the cellular association and transport of individual dioxin congeners across the Caco-2 cell monolayers. After 24 h, the amount of transported dioxin mixture was similar in both the dynamic gut-on-a-chip model and the static Transwell model. The transport of individual congeners corresponded with their number of chlorine atoms and substitution patterns as revealed by quantitative structure–property relationship modelling. These results show that the gut-on-a-chip model can be used, as well as the traditional static Transwell system, to study the cellular association and transport of lipophilic compounds like dioxins.

Kulthong K, Duivenvoorde L, Sun H, Confederat S, Wu J, Spenkelink B, de Haan L, Marin V, van der Zande M, Bouwmeester H. Microfluidic chip for culturing intestinal epithelial cell layers: Characterization and comparison of drug transport between dynamic and static models. Toxicol In Vitro. 2020 Jun;65:104815 Abstract Dynamic flow in vitro models are currently widely explored for their applicability in drug development research. The application of gut-on-chip models in toxicology is lagging behind. Here we report the application of a gut-on-chip model for biokinetic studies and compare the observed biokinetics of reference compounds with those obtained using a conventional static in vitro model. Intestinal epithelial Caco-2 cells were cultured on a porous membrane assembled between two glass flow chambers for the dynamic model, or on a porous membrane in a Transwell model. Confocal microscopy, lucifer yellow translocation, and alkaline phosphatase activity evaluation revealed that cells cultured in the gut-on-chip model formed tight, differentiated, polarized monolayers like in the static cultures. In the dynamic gut-on-chip model the transport of the high permeability compounds antipyrine, ketoprofen and digoxin was lower (i.e. 4.2-, 2.7- and 1.9-fold respectively) compared to the transport in the static Transwell model. The transport of the low permeability compound, amoxicillin, was similar in both the dynamic and static in vitro model. The obtained transport values of the compounds are in line with the compound Biopharmaceuticals Classification System. It is concluded that the gut-on-chip provides an adequate model for transport studies of chemicals.

Kulthong K, Hooiveld GJEJ, Duivenvoorde L, Miro Estruch I, Marin V, van der Zande M, Bouwmeester H. Transcriptome comparisons of in vitro intestinal epithelia grown under static and microfluidic gut-on-chip conditions with in vivo human epithelia. Sci Rep. 2021 Feb 5;11(1):3234. doi: 10.1038/s41598-021-82853-6. Abstract Gut-on-chip devices enable exposure of cells to a continuous flow of culture medium, inducing shear stresses and could thus better recapitulate the in vivo human intestinal environment in an in vitro epithelial model compared to static culture methods. We aimed to study if dynamic culture conditions affect the gene expression of Caco-2 cells cultured statically or dynamically in a gut-on-chip device and how these gene expression patterns compared to that of intestinal segments in vivo. For this we applied whole genome transcriptomics. Dynamic culture conditions led to a total of 5927 differentially expressed genes (3280 upregulated and 2647 downregulated genes) compared to static culture conditions. Gene set enrichment analysis revealed upregulated pathways associated with the immune system, signal transduction and cell growth and death, and downregulated pathways associated with drug metabolism, compound digestion and absorption under dynamic culture conditions. Comparison of the in vitro gene expression data with transcriptome profiles of human in vivo duodenum, jejunum, ileum and colon tissue samples showed similarities in gene expression profiles with intestinal segments. It is concluded that both the static and the dynamic gut-on-chip model are suitable to study human intestinal epithelial responses as an alternative for animal models.

Duivenvoorde LPM, Louisse J, Pinckaers NET, Nguyen T, van der Zande M. Comparison of gene expression and biotransformation activity of HepaRG cells under static and dynamic culture conditions. Sci Rep. 2021 May 14;11(1):10327. Abstract Flow conditions have been shown to be important in improving longevity and functionality of primary hepatocytes, but the impact of flow on HepaRG cells is largely unknown. We studied the expression of genes encoding CYP enzymes and transporter proteins and CYP1 and CYP3A4 activity during 8 weeks of culture in HepaRG cells cultured under static conditions (conventional 24-/96-well plate culture with common bicarbonate/CO2 buffering) and under flow conditions in an organ-on-chip (OOC) device. Since the OOC-device is a closed system, bicarbonate/CO2 buffering was not possible, requiring application of another buffering agent, such as HEPES. In order to disentangle the effects of HEPES from the effects of flow, we also applied HEPES-supplemented medium in static cultures and studied gene expression and CYP activity. We found that cells cultured under flow conditions in the OOC-device, as well as cells cultured under static conditions with HEPES-supplemented medium, showed more stable gene expression levels. Furthermore, only cells cultured in the OOC-device showed relatively high baseline CYP1 activity, and their gene expression levels of selected CYPs and transporters were most similar to gene expression levels in human primary hepatocytes. However, there was a decrease in baseline CYP3A4 activity under flow conditions compared to HepaRG cells cultured under static conditions. Altogether, the present study shows that HepaRG cells cultured in the OOC-device were more stable than in static cultures, being a promising in vitro model to study hepatoxicity of chemicals upon chronic exposure.

Our OOC chips and resealable flow cells are designed for low-pressure applications, up to 300–400 mbar. The large channels allow for effective flow with minimal pressure, making it crucial to use a pump system that can control and limit pressure within this range. We recommend using a pressure-based system for optimal performance. If a syringe pump is preferred, please ensure that each liquid path includes a pressure relief valve to maintain leak free operating conditions. This setup will allow for cost effective flow control while preventing leakage. An example of such a valve is this.