We sincerely thank Dr. Javier Rodr&#237;guez, Dr. Mar&#237;a Luisa L&#243;pez, Carlos Matell&#225;n, and Juan Francisco Rodr&#237;guez for very helpful suggestions, discussions, and/or preliminary data. We also kindly thank the contributions of Sergio F&#233;rnandez, Pedro Herreros, and Lara Stolzenburg to this project. Special thanks go to Dr. Marta Garc&#237;a for GFP-labelled hFBs and hKCs. Finally, we recognize the excellent technical assistance of Guillermo Vizca&#237;no and Ang&#233;lica Corral. This work was supported by the &#34;Programa de Actividades de I+D entre Grupos de Investigaci&#243;n de la Comunidad de Madrid&#34;, Project S2018/BAA-4480, Biopieltec-CM. This work was also supported by the &#34;Programa de excelencia&#34;, Project EPUC3M03, CAM. CONSEJER&#205;A DE EDUCACI&#211;N E INVESTIGACI&#211;N.

1. Chip design and micromachining parameters
<ol>
	<li>Design the microfluidic chip layers with FreeCAD open-source design software; refer to Table 1 for the dimensions of the channels. Include four 2.54 mm diameter holes in the design to use a custom-made aligner for a correct layer superposition.</li>
</ol>
<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td></td>
			<td>Length (&#956;m)</td>
			<td>Width (&#956;m)</td>
		</tr>
		<tr>
			<...

<ol>
	<li>McNamee, P., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+tiered+approach+to+the+use+of+alternatives+to+animal+testing+for+the+safety+assessment+of+cosmetics:+Eye+irritation.">A tiered approach to the use of alternatives to animal testing for the safety assessment of cosmetics: Eye irritation.</a> Regulatory Toxicology and Pharmacology. 54 (2), 197-209 (2009).</li><li>Mathes, S. H., Ruffner, H., Graf-Hausner, U. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+use+of+skin+models+in+drug+development.">The use of skin models in drug development.</a> Advanced Drug Delivery Reviews. 69-70, 81-102 (2014).</li><li>Abd, E., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Skin+models+for+the+testing+of+transdermal+drugs.">Skin models for the testing of transdermal drugs.</a> Clinical Pharmacology: Advances and Applications. 8, 163-176 (2016).</li><li>Flaten, G. 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W., Evaniew, N., Ghert, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Lost+in+translation:+animal+models+and+clinical+trials+in+cancer+treatment.">Lost in translation: animal models and clinical trials in cancer treatment.</a> American Journal of Translational Research. 6 (2), 114-118 (2014).</li><li>Pronko, P. P., VanRompay, P. A., Zhang, Z., Nees, J. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Pronko+et+al.+Reply.">Pronko et al. Reply.</a> Physical Review Letters. 86 (7-12), 1387 (2001).</li><li>H.R.2858 - Humane Cosmetics Act. 114th Congress Available from: <a target="_blank" href="https://congress.gov/bill/114th-congress/house-bill/2858">https://congress.gov/bill/114th-congress/house-bill/2858</a> (2016)</li><li>. 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The authors declare that they have no competing financial interests.

The motivation to develop this method was the desire to model skin diseases and study the effects of new and innovative therapies in a high-throughput platform. To date, this laboratory produces these dermo-epidermal equivalents by casting-either manually or with the help of the 3D bioprinting technology-the fibrin gel with fibroblasts into a cell culture insert plate and seeding the keratinocytes on top of it. Once the keratinocytes reach confluence, the 3D culture is exposed to the air-liquid interface, which induces k...

Recently, advances have been made toward the development and production of in vitro human skin models for the analysis of the toxicity of cosmetic and pharmaceutical products1. Researchers in pharmaceutical and skin care industries have been using animals, mice being the most common, to test their products2,3,4,5. However, testing products on animals is not always predictive of the response in humans, which frequently leads to drug failure or adverse effects in humans and consequently to economic losses5,6. The UK was the first country that prohibited the use of animals for cosmetic testing in 1998. Later, in 2013, the EU banned the testing and approbation of cosmetics in animals (EU Cosmetics Regulation No. 1223/2009)7.
This prohibition is also being considered by other countries such as in &#39;The Humane Cosmetics Act&#39; in the USA8. In addition to ethical concerns, the anatomical differences between animal and human skin make animal testing time-consuming, expensive, and often ineffective. Furthermore, the global in vitro toxicology testing market size is expected to reach USD 26.98 billion by 20259. For these reasons, there is a need to develop new methods and alternatives for those in vitro studies, such as bioengineered human skin models, that enable testing for safety and toxic effects of cosmetics and drugs without the use of animals.
There are two different kinds of commercially available, in vitro, human skin models. The first type consists of stratified epidermal equivalents containing multiple layers of differentiating keratinocytes that are seeded on different materials. Some of them have been approved by the Organization for Economic Co-operation and Development (OECD) and validated by the (European Centre for the Validation of Alternative Methods (ECVAM) for skin corrosion and irritation testing, such as EpiDerm or SkinEthic10,11,12. The second type are full-skin equivalents with a layer of differentiating human keratinocytes seeded on a three-dimensional (3D) scaffold that contains fibroblasts, such as T-Skin and EpiDerm-FT. However, these models are cultured under static conditions, which makes them unable to accurately represent human physiological conditions.
Recent interest has focused on generating in vitro 3D skin models in cell culture-insert (CCI) formats with dynamic perfusion13,14,15,16,17,18,19. However, these systems cannot be considered stricto sensu as microfluidic skin-on-chips as per their classical definition in the field. Ingber&#39;s definition for organs-on-a-chip states that the organ must be placed inside the microfluidic channels, which is a condition that only a few devices fulfil20,21. Skin-on-chips have so far modelled mostly simple epithelia as single-cell layers and/or dermal cell layers separated by a porous membrane22,23. Although there have been some advances modeling skin in microfluidic systems16,24, there is currently no literature showing an organ-on-a-chip system that fits Ingber&#39;s definition, capable of producing a multilayered skin in situ and including both epithelial and stromal components.
In this work, a new, cost-effective, robust, vinyl-based microfluidic platform for skin-on-a-chip applications is presented. This platform was produced by micro-machining, which provides more simplicity in the fabrication process, as well as increased flexibility and versatility in the layout of the device, overcoming some of the limitations of PDMS25. A way to introduce a simplified skin construct through a parallel flow controlled with syringe pumps was also designed. Parallel flow allows two fluids with very different viscosities (a buffer and fibrin pre-gel in this case) to be perfused through a channel without mixing with each other. As a proof of concept, a dermo-epidermal construct containing fibroblasts embedded in a fibrin matrix mimicking the dermis was introduced in the device, on top of which a monolayer of keratinocytes was loaded to emulate the undifferentiated epidermis. The dermal compartment height can be modulated by modifying the flow rates. The main novelty of this work, compared to previously described models22,26,27,28,29, is the development of a 3D construct inside a microchamber by means of microfluidics. Although this article presents a simplified undifferentiated skin, the long-term goal is to generate and characterize a fully differentiated skin construct to demonstrate its viability and functionality for drug and cosmetic testing purposes.

<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>Amchafibrin</td>
			<td>Rottafarm</td>
			<td></td>
			<td>Tranexamic acid</td>
		</tr>
		<tr>
			<td>Antibiotic/antimycotic</td>
			<td>Thermo Scientific HyClone</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Calcium chloride</td>
			<td>Sigma Aldrich</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Culture plates</td>
			<td>Fisher</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>DMEM</td>
			<td>Invitrogen Life Technologies</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Double-sided tape vynil</td>
			<td>ATP Adhesive Systems</td>
			<td></td>
			<td>GM 107CC, 12 &#181;m thick</td>
		</tr>
		<tr>
			<td>Edge plotter</td>
			<td>Brother</td>
			<td></td>
			<td>Scanncut CM900</td>
		</tr>
		<tr>
			<td>FBS</td>
			<td>Thermo Scientific HyClone</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Fibrinogen</td>
			<td>Sigma Aldrich</td>
			<td></td>
			<td>Extracted from human plasma</td>
		</tr>
		<tr>
			<td>Glass slide</td>
			<td>Thermo Scientific</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>GFP-Human dermal fibroblasts</td>
			<td>-</td>
			<td></td>
			<td>Primary. Gift from Dr. Marta Garc&#237;a</td>
		</tr>
		<tr>
			<td>H2B-GFP-HaCaT cell line</td>
			<td>ATCC</td>
			<td></td>
			<td>Immortalized keratinocytes. Gift from Dr. Marta Garc&#237;a</td>
		</tr>
		<tr>
			<td>Live/dead kit</td>
			<td>Invitrogen</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>PBS</td>
			<td>Sigma Aldrich</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Polycarbonate membrane</td>
			<td>Merk TM</td>
			<td></td>
			<td>5 &#181;m pore size</td>
		</tr>
		<tr>
			<td>Polydimethylsiloxane</td>
			<td>Dow Corning</td>
			<td></td>
			<td>Sylgard 184</td>
		</tr>
		<tr>
			<td>Sodium chloride</td>
			<td>Sigma Aldrich</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Syringes</td>
			<td>Terumo</td>
			<td></td>
			<td>5 mL</td>
		</tr>
		<tr>
			<td>Thrombin</td>
			<td>Sigma Aldrich</td>
			<td></td>
			<td>10 NIH/vial</td>
		</tr>
		<tr>
			<td>Transparent adhesive vinyl</td>
			<td>Mactac</td>
			<td></td>
			<td>JT 8500 CG-RT, 95 &#181;m thick</td>
		</tr>
		<tr>
			<td>Trypsin/EDTA</td>
			<td>Sigma Aldrich</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Tubing</td>
			<td>IDEX</td>
			<td></td>
			<td>Teflon, 1/16&#8221; OD, 0.020&#8221; ID</td>
		</tr>
	</tbody>
</table>

generation of a simplified three-dimensional skin-on-a-chip model in a micromachined microfluidic platform

This work presents a new, cost-effective, and reliable microfluidic platform with the potential to generate complex multilayered tissues. As a proof of concept, a simplified and undifferentiated human skin containing a dermal (stromal) and an epidermal (epithelial) compartment has been modelled. To accomplish this, a versatile and robust, vinyl-based device divided into two chambers has been developed, overcoming some of the drawbacks present in microfluidic devices based on polydimethylsiloxane (PDMS) for biomedical applications, such as the use of expensive and specialized equipment or the absorption of small, hydrophobic molecules and proteins. Moreover, a new method based on parallel flow was developed, enabling the in situ deposition of both the dermal and epidermal compartments. The skin construct consists of a fibrin matrix containing human primary fibroblasts and a monolayer of immortalized keratinocytes seeded on top, which is subsequently maintained under dynamic culture conditions. This new microfluidic platform opens the possibility to model human skin diseases and extrapolate the method to generate other complex tissues.

The designed chip is composed of two fluidic chambers separated by a 5 &#181;m pore size PC membrane that allows the growth of the cell by allowing the passage of growth-promoting molecules from the lower chamber. The upper chamber holds the tissue construct, in this case, a monolayer of hKCs on a fibrin hydrogel containing hFBs.
The height of the channels is determined by the number of adhesive sheets added to each channel. The lower chamber is composed of 4 layers (380 &#181;m) and the upper...

Watch this Scientific Journal Video about Generation of a Simplified Three-Dimensional Skin-on-a-chip Model in a Micromachined Microfluidic Platform at JoVE.com

Generation of a Simplified Three-Dimensional Skin-on-a-chip Model in a Micromachined Microfluidic Platform

Here, we present a protocol to generate a three-dimensional simplified and undifferentiated skin model using a micromachined microfluidic platform. A parallel flow approach allows the in situ deposition of a dermal compartment for the seeding of epithelial cells on top, all controlled by syringe pumps.

This work presents a new, cost-effective, and reliable microfluidic platform with the potential to generate complex multilayered tissues. As a proof of ...

This is a novel, lithography-free protocol for modeling a 3D skin-on-chip using micromachined, adhesive vinyl layers and a parallel-flow methodology for the dermal compartment generation. Micromachined vinyl provides more simplicity in the fabrication process and versatility in the layout of the device, overcoming some of the limitations of PDMS and traditional lithography approaches. This multilayered skin-on-a-chip can be used for drug and cosmetic testing approaches, since it allows high-throughput screening at lower costs and could be used to model several diseases.Begin by designing a microfluidic chip using Brother Canvas Workspace software. Create a 30-by-30 centimeter workspace, and fill it with the design patterns for the different layers of the chip before storing it in a svg file. Cut the 30-by-30 centimeter vinyl sheets.Stick it to a low-tack adhesive mat and eliminate all air bubbles, as necessary. Using a USB drive, upload the svg file to the edge plotter, and set the cutting parameters as cutting pressure at level zero, cutting blade at level three, and level one for the cutting speed. When parameters are set, place the adhesive mat with the vinyl into the plotter and start the process of cutting the channel patterns on 95-micrometer-thick vinyl.Assemble the whole device by using an aligner for proper adjustment channels, inlets, and outlets. Pile up for vinyl layers with a corresponding micromachine design for assembling the lower channel, keeping the cover tape of the bottom layer to avoid sticking to the aligner. Cut and place the polycarbonate porous membrane on top of the lower channel without covering the inlets.Add 10 vinyl layers with the upper-chamber design and stick a double-sided tape final layer on top. Remove the chip from the aligner to stick it on the glass slide. Place a two-millimeter-thick PDMS sheet on top of the double-sided tape vinyl layer.To ensure that the chip is completely watertight, leave a weight on top of the chip overnight. On the next day, sterilize the chip by flushing it with 70%ethanol for five minutes, followed by a wash with distilled water. Connect pump one and pump two to the upper chamber inlet one and the upper chamber inlet two, respectively.Connect pump three to the lower chamber inlet, then connect the upper chamber and lower chamber outlets to a waste tub. Connect the syringes to each inlet using PTFE tubes and 18-gauge stainless steel connectors. Pump PBS with pump three through the lower chamber inlet at 50 microliters per minute, and with pump two through the upper chamber inlet two at 100 microliters per minute.Then, load the syringe with the fibrinogen pre-gel, immediately place it into pump one, and run it at 200 microliters per minute. Once the pre-gel exits the upper chamber outlet, stop pumps one and two, then, without removing the tubing, leave the chip to allow gellation at 37 degrees Celsius for 10 minutes. After gellation, block the upper chamber inlet one with a cap, and pump the culture medium through the upper chamber inlet two with pump three at 50 microliters per hour overnight.24 hours after the generation of the dermal compartment, check that human primary fibroblast cells are spread in the assembly, then introduce five times 10 to the 6 HKCs per milliliter through the upper channel inlet two at 40 microliters per minute for one minute. For cell attachment, place the chip overnight at 37 degrees Celsius in a humidity-saturated incubator. Start pumping fresh culture medium with pump three only through the lower chamber inlet at 50 microliters per minute.In the representative analysis, the height of the hydrogel along the upper chamber of the assembly is displayed. An average height of 550 micrometers was optimum for the functioning of the gel at the flow rates of 100 and 200 microliters per minute for the sacrificial PBS and the pre-gel, respectively. Failure to flush PBS through the lower channel led to discrepancies between the theoretical height of the gel and the one measured, with a difference of 40%After 24 hours from initiation of the parallel-flow protocol, the human primary fibroblasts were found to be successfully spread in the fibrin gel in the upper chamber of the assembly, following which, green fluorescent protein-expressing HKCs could be effectively seeded on top of the hydrogel.Removal of tubing without keeping the system closed overnight to allow the HKCS to sediment resulted in a non-uniform, confluent monolayer of cells. 3D confocal analysis of the undifferentiated skin model in the microfluidic chip clearly showed the surface of the hydrogel separating HKCs in the top from the fibroblast embedded at the bottom. The generated skin could be exposed to the air/liquid interface to obtain a mature and differentiated epidermis, and further be characterized using several dermal and epidermal markers.This technique allows for a faster and cheaper device fabrication, and the generation of multilayered skin using microfluidics, providing a more realistic approach for drugs and cosmetics testing.

generation-simplified-three-dimensional-skin-on-chip-model

Research

JoVE Journal

Bioengineering

3.8K visualizações.  Universidad Carlos III de Madrid (UC3M). Este é um novo protocolo, livre de litografia para modelar um skin-on-chip 3D usando camadas de vinil micromachined, adesivo e uma metodologia de fluxo paralelo para a geração de compartimentos dérmicos. O vinil micromaquinado proporciona mais simplicidade no processo de fabricação e versatilidade no layout do dispositivo, superando algumas das limitações do PDMS e das abordagens tradicionais de litografia. Este skin-on-a-chip multicamadas pode ser usado para abordagens de testes medi...