Name: preparation and structural evaluation of epithelial cell monolayers in a physiologically sized microfluidic culture device
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Description: Watch this Scientific Journal Video about Preparation and Structural Evaluation of Epithelial Cell Monolayers in a Physiologically Sized Microfluidic Culture Device at JoVE.com

The authors acknowledge Alan Shepardson for designing the cutting pattern for the 3M adhesive and mylar sheet used in microfluidic channel construction and for testing the cell culture media flow rate and syringe pump programming. Funding was supplied by NIH R01 HL0142702, NSF CBET 1706801, and the Newcomb-Tulane College Dean&#39;s Grant.

The NCI-H441 human epithelial lung cell line was used for the present study (see Table of Materials).
1. Cell culture in the microfluidic channel
<ol>
	<li>Fabricate the microfluidic channel and perform the pre-treatment following the steps below.
	<ol>
		<li>Obtain a single-channel flow array (see Table of Materials) and separate the upper portion from the polycarbonate base plate.</li>
		<li>Obtain a #1.5 rectangular coverglass (thickness ...

<ol>
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S., Katara, G., Hemvani, N., Chitnis, S., Chitnis, V. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Surface+disinfection+by+exposure+to+germicidal+UV+light.">Surface disinfection by exposure to germicidal UV light.</a> Indian Journal of Medical Microbiology. 26 (3), 241 (2008).</li><li>Sandell, L., Sakai, D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Mammalian+cell+culture.">Mammalian cell culture.</a> Current Protocols Essential Laboratory Techniques. 5 (1), 4 (2011).</li><li>New Era Pump Systems. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Multi-Phaser+Programmable+Syringe+Pump:+NE-1000+Series+User+Manual.">Multi-Phaser Programmable Syringe Pump: NE-1000 Series User Manual.</a> New Era Pump Systems. , (2014).</li><li>Thermo Fisher Scientific. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Safety+Data+Sheet:+Image-iT+Fixative+Solution+(4%+formaldehyde,+methanol-free).">Safety Data Sheet: Image-iT Fixative Solution (4% formaldehyde, methanol-free).</a> Thermo Fisher Scientific. , (2018).</li><li>Thavarajah, R., Mudimbaimannar, V. 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C., Oliver, C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Permeabilization+of+cell+membranes.">Permeabilization of cell membranes.</a> Immunocytochemical Methods and Protocols. 588, 63-66 (2009).</li><li>Thermo Fisher Scientific. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=ActinGreen+488+ReadyProbes+Reagent+Protocol.">ActinGreen 488 ReadyProbes Reagent Protocol.</a> Thermo Fisher Scientific. , (2022).</li><li>Slowfade Glass soft-set Antifade Mountant. 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The presented protocol describes the culture, crosslinking fixation, staining, permeabilization, and confocal microscopic visualization of NCI-H441 human lung epithelial cells in the dynamic environment of a single-channel microfluidic flow array, as well as in the static environment of a traditional eight-well chambered coverglass. With any microfluidic cell culture protocol, the flow conditions of the cell culture media are of paramount importance, as the high-rate flow has the potential to wash away the cells or inter...

Acute respiratory distress syndrome (ARDS) is an acute condition arising from insult to and propagation of injury in the lung parenchyma, resulting in pulmonary edema of the alveoli, inadequate gas exchange, and subsequent hypoxemia1. This initiates a cycle of pro-inflammatory cytokine release, neutrophil recruitment, toxic mediator release, and tissue damage, which itself incurs a further inflammatory response2. Additionally, pulmonary surfactant, which stabilizes the airways and prevents damage caused by repetitive recruitment/derecruitment (R/D), may be inactivated or otherwise rendered dysfunctional by the chemical processes occurring during ARDS, resulting in further stress and injury to the surrounding parenchyma3. If sufficient damage is sustained, mechanical ventilation may be necessary to ensure adequate systemic oxygenation4. However, mechanical ventilation imposes its own challenges and traumas, including the possibility of ventilator-induced lung injury (VILI), characterized as injury to the lung parenchyma caused by the mechanical stresses imposed during overinflation (volutrauma) and/or the R/D of the air-liquid interface in the fluid-occluded airway (atelectrauma)5. The pressure gradient experienced by epithelial cells exposed to an air-liquid interface (as in a fluid-occluded bronchiole) in the atelectrauma model can result in a permeability-originated obstructive response (POOR), leading to a POOR-get-POORer virtuous cycle of injury6,7,8.
In vitro experimentation can provide micro-scale insights into these phenomena, but current studies in microfluidic channel environments with physiologically relevant dimensions face several challenges9. For one, optimizing cell culture conditions poses a significant barrier to entry for cell culture research in microfluidic environments, as there exists a narrow intersection within which media flow parameters, culture duration, and other culture conditions permit optimal cell layer formation. This includes the diffusion limitations imposed by the oxygen-impermeable nature of the microfluidic culture channel enclosure. This necessitates careful consideration of media flow parameters, as low flow rates can deprive cells of oxygen, especially those farthest from the inlet; on the other hand, high flow rates can push cells out of the culture channel or result in improper or uneven layer development. Diffusion limitations may be addressed by using oxygen-permeable materials such as polydimethylsiloxane (PDMS) in an air-liquid interface (ALI) culture apparatus; however, many conventional microfluidic culture channels, such as those of the electric cell-substrate impedance sensing (ECIS) system, are inherently oxygen-impermeable, given the nature of the manufactured enclosure10. This protocol aims to provide a technique for analyzing cell layers cultured in an oxygen-impermeable enclosure.
When comparing the viability of culture conditions, observations of specific layer characteristics, such as the presence of a monolayer, surface topology, confluency, and layer-thickness uniformity, are necessary to determine whether the cell layer produced by a particular set of culture conditions meets the desired specifications and are indeed relevant to the experimental design. A limited evaluation may be performed by methods such as ECIS, which utilizes measurements of electric potential (voltage) created by resistance to high-frequency alternating current (AC) (impedance) imposed by electrically-insulating membranes of cells cultured on gold electrodes within the flow array. By modulating the frequency of AC applied to cells, specific frequency-dependent cellular properties of the cells and cell layers such as surface adherence strength, tight-junction formation, and cell proliferation or confluency may be targeted and examined11. However, these indirect forms of measurements are somewhat difficult to interpret at the onset of an experiment, and may not quantify all relevant aspects of the cell layer. Simply observing the cell layer under a phase-contrast microscope may reveal the nature of certain qualities such as confluency; however, many relevant characteristics such as the presence of a monolayer and layer-thickness uniformity require a three-dimensional (3D) evaluation that is not possible with brightfield, phase-contrast, or fluorescent microscopic imaging12.
The objective of this study was to develop a filamentous-actin staining technique to allow for imaging-based verification of a monolayer and the evaluation of cell layer uniformity using confocal laser scanning microscopy (CLSM). Filamentous-actin (F-actin) was deemed an appropriate target for the fluorophore conjugate, due in part to the way that F-actin tightly follows the cell membrane, allowing for a visual approximation of the entire cell volume13. Another important benefit of targeting F-actin is the manner in which staining of F-actin visually elucidates cytoskeletal disruptions or alterations imposed by the stresses and strains experienced by the cells. Crosslinking fixation with methanol-free formaldehyde was used to preserve the morphology of the cells and the cell layer, as dehydrating fixatives such as methanol tend to flatten cells, grossly distorting the cell layer and altering its properties14,15.
To determine the ability of the layer evaluation technique to mitigate these challenges, cells were cultured in traditional eight-well culture chambers as well as in microfluidic channels to evaluate the differences, if any, in the cell layers that were produced. For fixed culture wells, eight-well chambered coverglass units were used. For microfluidic culture, flow arrays (channel length 50 mm, width 5 mm, depth 0.6 mm) were optimized to culture immortalized human lung epithelial (NCI-H441) cells in an environment with dimensions physiologically relevant to the terminal bronchioles present in the respiratory zone of the human lung16. While this protocol was developed with the culture environment of ECIS flow arrays in mind, it may apply to any oxygen-impermeable dynamic-culture environment for which evaluation of cultured cell layer characteristics or culture conditions is necessary.

<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>A1R HD25 Confocal Microscope System</td>
			<td>Nikon</td>
			<td>A1R HD25</td>
			<td>https://www.microscope.healthcare.nikon. 
			com/products/confocal-microscopes/a1hd25-a1rhd25/specifications</td>
		</tr>
		<tr>
			<td>ActinGreen 488 ReadyProbes Reagent (AlexaFluor 488 phalloidin)</td>
			<td>Invitrogen</td>
			<td>R37110</td>
			<td>https://www.thermofisher.com/order/catalog/product/R37110</td>
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			<td>Adhesive Transfer Tape Double Linered</td>
			<td>3M</td>
			<td>468MP</td>
			<td>https://gizmodorks.com/3m-468mp-adhesive-transfer-tape-sheet-5-pack/</td>
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			<td>Air-Tite&#160;HSW Soft-Ject Disposable Syringes</td>
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			<td>BAISDY 4 mil (0.1 mm) Thick Mylar Sheet</td>
			<td>BAISDY</td>
			<td>AS022</td>
			<td>https://www.amazon.ca/Stencil-Perfect-Silhouette-Machines-BAISDY/dp/B07RJJ9BNC</td>
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			<td>Branson Ultrasonics&#160;M Series Ultrasonic Cleaning Bath</td>
			<td>Branson Ultrasonics</td>
			<td>15-336-100</td>
			<td>https://www.fishersci.com/shop/products/m-series-ultrasonic-cleaning-bath/15336100</td>
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			<td>Corning&#160;Fibronectin, Human</td>
			<td>Fisher Scientific</td>
			<td>CB-40008</td>
			<td>https://www.fishersci.com/shop/products/corning-fibronectin-human-3/CB40008?keyword=true</td>
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			<td>DPBS, calcium, magnesium</td>
			<td>Gibco</td>
			<td>14040133</td>
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			<td>ECIS Cultureware Disposable Electrode Arrays 8 x 10 ECIS Flow Array</td>
			<td>Applied BioPhysics</td>
			<td>1F8x10E PC</td>
			<td>https://www.biophysics.com/cultureware.php#1F8x10E</td>
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			<td>Enterprise Technology Solutions UV Sterilizer Cabinet, White</td>
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			<td>Fetal Bovine Serum (FBS)</td>
			<td>Gibco</td>
			<td>26140079</td>
			<td>https://www.thermofisher.com/order/catalog/product/26140079</td>
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			<td>Finnpipette F2 Variable Volume Pipettes</td>
			<td>Thermo Scientific</td>
			<td>4642090</td>
			<td>https://www.thermofisher.com/order/catalog/product/4642090</td>
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			<td>Fisherbrand 50mL Easy Reader Plastic Centrifuge Tubes</td>
			<td>Fisher Scientific</td>
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			<td>Fisherbrand&#160;Cover Glasses: Rectangles (#1.5)</td>
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			<td>Fisherbrand&#160;Sterile Syringes for Single Use</td>
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			<td>https://www.fishersci.com/shop/products/sterile-syringes-single-use-12/14955458</td>
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			<td>Gibco RPMI 1640 Medium</td>
			<td>Gibco</td>
			<td>11875093</td>
			<td>https://www.thermofisher.com/order/catalog/product/11875093</td>
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			<td>Image-iT Fixative Solution (4% formaldehyde, methanol-free)</td>
			<td>Invitrogen</td>
			<td>FB002</td>
			<td>https://www.thermofisher.com/order/catalog/product/FB002</td>
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			<td>ImageJ Fiji</td>
			<td>ImageJ</td>
			<td>ImageJ Fiji</td>
			<td>https://imagej.net/downloads</td>
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		<tr>
			<td>Immersion Oil F 30 cc</td>
			<td>Nikon</td>
			<td>MXA22168</td>
			<td>https://www.microscope.healthcare.nikon. 
			com/products/accessories/immersion-oil/specifications</td>
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			<td>Large-Capacity Reach-In CO2&#160;Incubator, 821 L, Polished Stainless Steel</td>
			<td>Thermo Scientific</td>
			<td>3950</td>
			<td>https://www.thermofisher.com/order/catalog/product/3950</td>
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			<td>Laxco LMC-3000 Series Brightfield Compound Microscope System</td>
			<td>Laxco</td>
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			<td>https://www.fishersci.com/shop/products/lmc-3000-series-brightfield-compound-microscope-system-8/LMC3BF1</td>
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			<td>Masterflex Fitting, Nylon, Straight, Male Luer Lock to Hose Barb Adapters, 1/16&#34; ID; 25/PK</td>
			<td>Masterflex</td>
			<td>ZY-45505-31</td>
			<td>https://www.masterflex.com/i/masterflex-fitting-nylon-straight-male-luer-lock-to-hose-barb-adapters-1-16-id-25-pk/4550531?PubID=ZY&#38;persist=true&#38;ip=no&#38; 
			gclid=Cj0KCQiA3rKQBhCNARIsAC 
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			udmwaAuDHEALw_wcB</td>
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			<td>Microsoft Excel</td>
			<td>Microsoft</td>
			<td>0016</td>
			<td>https://www.microsoft.com/en-us/download/details.aspx?id=56547</td>
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			<td>National Target All-Plastic Disposable Syringes</td>
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			<td>03-377-24</td>
			<td>https://www.fishersci.com/shop/products/national-target-all-plastic-disposable-syringes/0337724#tab8</td>
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			<td>NCI-H441 Human Epithelial Lung Cells</td>
			<td>American Type Culture Collection (ATCC)</td>
			<td>HTB-174</td>
			<td>https://www.atcc.org/products/htb-174</td>
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			<td>NE-1600 Six Channel Programmable Syringe Pump</td>
			<td>New Era Pump Systems</td>
			<td>NE-1600</td>
			<td>https://www.syringepump.com/NE-16001800.php</td>
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			<td>NIS Elements AR</td>
			<td>Nikon</td>
			<td>NIS Elements AR</td>
			<td>https://www.microscope.healthcare.nikon. 
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			<td>NucBlue Live ReadyProbes Reagent (Hoechst 33342)</td>
			<td>Invitrogen</td>
			<td>R37605</td>
			<td>https://www.thermofisher.com/order/catalog/product/R37605?SID=srch-srp-R37605</td>
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			<td>Nunc Lab-Tek Chambered Coverglass</td>
			<td>Thermo Scientific</td>
			<td>155411</td>
			<td>https://www.thermofisher.com/order/catalog/product/155361</td>
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			<td>Parafilm M Wrapping Film</td>
			<td>Fisher Scientific</td>
			<td>S37441</td>
			<td>https://www.fishersci.com/shop/products/parafilm-m-wrapping-film-3/S37441</td>
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			<td>PendoTech 3-Way Stopcock, Polysulfone, Male/Female Luer Inlet x Female Luer Branch</td>
			<td>PendoTech</td>
			<td>ZY-19406-49</td>
			<td>https://www.masterflex.com/i/pendotech-3-way-stopcock-polysulfone-male-female-luer-inlet-x-female-luer-branch/1940649</td>
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			<td>Phosphate Buffered Solution (PBS), pH 7.4</td>
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			<td>https://www.thermofisher.com/order/catalog/product/10010023</td>
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			<td>https://www.thermofisher.com/order/catalog/product/A3890401#/A3890401</td>
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			<td>https://www.sigmaaldrich.com/US/en/product/sigma/47036</td>
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			<td>https://www.thermofisher.com/order/catalog/product/S36917-5X2ML</td>
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			<td>13-100-752PM</td>
			<td>https://www.fishersci.com/shop/products/1300-series-class-ii-type-a2-biological-safety-cabinet-package-promo/p-9049003#?keyword=biosafety%20hood</td>
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			<td>Tygon Transfer Tubing, BioPharm Platinum-Cured Silicone, 1/16&#34; ID x 1/8&#34; OD; 50 Ft</td>
			<td>Cole-Parmer</td>
			<td>EW-95702-01</td>
			<td>https://www.coleparmer.com/i/tygon-transfer-tubing-biopharm-platinum-cured-silicone-1-16-id-x-1-8-od-50-ft/9570201?searchterm=95702-01</td>
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preparation and structural evaluation of epithelial cell monolayers in a physiologically sized microfluidic culture device

In vitro microfluidic experimentation holds great potential to reveal many insights into the microphysiological phenomena occurring in conditions such as acute respiratory distress syndrome (ARDS) and ventilator-induced lung injury (VILI). However, studies in microfluidic channels with dimensions physiologically relevant to the terminal bronchioles of the human lung currently face several challenges, especially due to difficulties in establishing appropriate cell culture conditions, including media flow rates, within a given culture environment. The presented protocol describes an image-based approach to evaluate the structure of NCI-H441 human lung epithelial cells cultured in an oxygen-impermeable microfluidic channel with dimensions physiologically relevant to the terminal bronchioles of the human lung. Using phalloidin-based filamentous-actin staining, the cytoskeletal structures of the cells are revealed by confocal laser scanning microscopy, allowing for the visualization of individual as well as layered cells. Subsequent quantification determines whether the cell culture conditions being employed are producing uniform monolayers suitable for further experimentation. The protocol describes cell culture and layer evaluation methods in microfluidic channels and traditional fixed-well environments. This includes channel construction, cell culture and requisite conditions, fixation, permeabilization and staining, confocal microscopic imaging, image processing, and data analysis.

The presented method allows for the visualization of epithelial cell layers cultured in microfluidic culture channels and uses a demonstration in traditional fixed-well cell culture environments as validation. Images acquired will exist on a spectrum of quality, signal intensity, and cellular target specificity. Successful images will demonstrate high contrast, allowing for image analysis and quantification of data for subsequent statistical evaluation. Unsuccessful images will be dim, fuzzy, blurry, or otherwise unusabl...

Watch this Scientific Journal Video about Preparation and Structural Evaluation of Epithelial Cell Monolayers in a Physiologically Sized Microfluidic Culture Device at JoVE.com

Preparation and Structural Evaluation of Epithelial Cell Monolayers in a Physiologically Sized Microfluidic Culture Device

The presented protocol describes the development and use of a phalloidin-based filamentous-actin staining technique with confocal laser scanning microscopy (CLSM) to visualize adherent cell layer structure in microfluidic dynamic-culture channels and traditional fixed-well static-culture chambers. This approach aids in evaluating cell layer confluency, monolayer formation, and layer-thickness uniformity.

In vitro microfluidic experimentation holds great potential to reveal many insights into the microphysiological phenomena occurring in conditions such as ...

Research

JoVE Journal

Bioengineering

Microfluidic Device for Recreating a Tumor Microenvironment in Vitro

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