Name: procedure for the development of multi-depth circular cross-sectional endothelialized microchannels-on-a-chip
Uploaded: 2013-10-21T19:45:00
Description: Watch this Scientific Journal Video about Procedure for the Development of Multi-depth Circular Cross-sectional Endothelialized Microchannels-on-a-chip at JoVE.com

This research was partially supported by National Science Foundation (NSF 1227359), WVU EPSCoR program funded by the National Science Foundation (EPS-1003907), WVU ADVANCE office sponsored by the National Science Foundation (1007978), and WVU PSCoR, respectively. The microfabrication work was done in WVU Shared Research Facilities (Cleanroom facilities) and Microfluidic Integrative Cellular Research on Chip Laboratory (MICRoChip Lab) at West Virginia University. The confocal imaging was done at WVU Microscope Imaging Facility.

1. Photolithography Fabrication of Photoresist Master Mold
The following protocol shows the process to fabricate the microchannels with diameters between 30-60 &#956;m. To get a microchannel with a smaller diameter (less than 30 &#956;m), a single spin-coating of photoresist is needed.
<ol>
	<li>Transfer the reflow photoresist from the refrigerator at 4 &#176;C to the cleanroom 24 hr prior to use and allow it to warm to room temperature.</li>
	<li>Clean a silicon wafer and bake it for one hr...

1. Master mold fabrication
One of the designing and guiding principles for vascular morphometry is known as Murray&#39;s law16, which states that the distribution of vessel diameters throughout the network is governed by minimum energy consideration. It also states that the cube of the diameters of a parent vessel at a bifurcation equals the sum of the cubes of the diameters of the daughter vessels (<img alt="Equation 1" fo:content-width="0.9in" fo:src="/files/ftp_upload/50771/50771eq1...

Microvessels, as a part of the circulation system, mediate the interactions between blood and tissues, support metabolic activities, define tissue microenvironment, and play a critical role in many health and pathological conditions. Recapitulation of functional microvessels in vitro could provide a platform for the study of complex vascular phenomena. However, conventional in vitro microvessel assays, such as endothelial cell migration assays, endothelial tube formation assays, and rat and mouse aortic ring assays, are unable to recreate the in vivo microvessels with respect to three-dimensional (3D) geometry and continuous flow control1-8. Studies of microvessels using animal models and in vivo assays, such as corneal angiogenesis assay, chick chorioallantoic membrane angiogenesis assay, and Matrigel plug assay, are more time-consuming, high in cost, challenging with respect to observation and quantifications, and raise ethical issues1, 9-13.
Advances in micromanufacturing and microfluidic chip technologies have enabled a variety of insights into biomedical sciences while curtailing the high experimental costs and complexities associated with animals and in vivo studies14, such as easily and tightly controlled biological conditions and dynamic fluidic environments, which would not have been possible with conventional macroscale techniques.
Here, we present an approach to construct an endothelialized microchannels-on-a-chip which mimics the 3D geometry of in vivo microvessels and runs under controlled continuous perfusion flow by using the combination of photolithographic reflowable photoresist technique, soft lithography, and microfluidics.

<table border="1">
	<tbody>
		<tr>
			<td>Reagent/Material</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Reflow Photoresist</td>
			<td>AZ Electronic Materials</td>
			<td>AZP4620</td>
			<td></td>
		</tr>
		<tr>
			<td>Developer</td>
			<td>AZ Electronic Materials</td>
			<td>AZ 400K</td>
			<td></td>
		</tr>
		<tr>
			<td>PDMS</td>
			<td>Dow Corning Corporation</td>
			<td>Sylgard 184</td>
			<td></td>
		</tr>
		<tr>
			<td>MCDB 131 Culture Medium</td>
			<td>Invitrogen</td>
			<td>10372-019</td>
			<td></td>
		</tr>
		<tr>
			<td>NacBlue Nuclei Staining</td>
			<td>Invitrogen</td>
			<td>H1399</td>
			<td></td>
		</tr>
		<tr>
			<td>PKH Red Stain</td>
			<td>Sigma</td>
			<td>MINI26 and PKH26GL</td>
			<td></td>
		</tr>
		<tr>
			<td>Fibronectin</td>
			<td>Gibco</td>
			<td>PHE0023</td>
			<td></td>
		</tr>
		<tr>
			<td>L-Glutamine</td>
			<td>Sigma</td>
			<td>G7513</td>
			<td></td>
		</tr>
		<tr>
			<td>Phosphate Buffered Saline</td>
			<td>Invitrogen</td>
			<td>14040-133</td>
			<td></td>
		</tr>
		<tr>
			<td>HEPES Buffered Saline Solution</td>
			<td>Lonza</td>
			<td>CC-5024</td>
			<td></td>
		</tr>
		<tr>
			<td>Trypsin/EDTA</td>
			<td>Invitrogen</td>
			<td>25300-062</td>
			<td></td>
		</tr>
		<tr>
			<td>Trypsin Neutralizing Solution</td>
			<td>Lonza</td>
			<td>CC-5002</td>
			<td></td>
		</tr>
		<tr>
			<td>PDMS Curing Agent</td>
			<td>Dow Corning Corporation</td>
			<td>Sylgard 184</td>
			<td></td>
		</tr>
		<tr>
			<td>Primary Human Umbilical Vein Endothelial Cells</td>
			<td>Lonza</td>
			<td>CC-2517</td>
			<td></td>
		</tr>
		<tr>
			<td>Fetal Bovine Serum</td>
			<td>Lonza</td>
			<td>14-501F</td>
			<td></td>
		</tr>
		<tr>
			<td>Diluent C</td>
			<td>Sigma</td>
			<td>CGLDIL</td>
			<td></td>
		</tr>
		<tr>
			<td>Hoechst33342</td>
			<td>Invitrogen, Molecular Probes</td>
			<td>R37605</td>
			<td></td>
		</tr>
		<tr>
			<td>Dextran</td>
			<td>Sigma</td>
			<td>95771</td>
			<td></td>
		</tr>
		<tr>
			<td>3.5% Paraformaldehyde</td>
			<td>Electron Microscopy Science</td>
			<td>15710-S</td>
			<td></td>
		</tr>
		<tr>
			<td>Equipment</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Spinner</td>
			<td>Laurell Technologies Corporation</td>
			<td>WS-400BZ-6NPP/LITE</td>
			<td></td>
		</tr>
		<tr>
			<td>Desiccator</td>
			<td>BelArt Products</td>
			<td>999320237</td>
			<td></td>
		</tr>
		<tr>
			<td>Inverted Microscope</td>
			<td>Nikon</td>
			<td>Eclipse Ti</td>
			<td></td>
		</tr>
		<tr>
			<td>Syringe Pump System</td>
			<td>Harvard Apparatus</td>
			<td>PHD Ultra</td>
			<td></td>
		</tr>
		<tr>
			<td>Laminar Biosafety Hood</td>
			<td>Thermo Scientific</td>
			<td>1300 Series A2</td>
			<td></td>
		</tr>
		<tr>
			<td>Planetary Centrifugal Mixer</td>
			<td>Thinky</td>
			<td>ARE-310</td>
			<td></td>
		</tr>
		<tr>
			<td>Isotemp Oven</td>
			<td>Fisher Scientific</td>
			<td>13-246-516GAQ</td>
			<td></td>
		</tr>
		<tr>
			<td>Optical Microscope</td>
			<td>Zeiss</td>
			<td>Invertoskop 40C</td>
			<td></td>
		</tr>
		<tr>
			<td>Plasma Cleaner</td>
			<td>Harrick Plasma</td>
			<td>PDC-32G</td>
			<td></td>
		</tr>
		<tr>
			<td>Hotplate</td>
			<td>Barnstead/Thermolyne Cimarec</td>
			<td>SP131635</td>
			<td></td>
		</tr>
		<tr>
			<td>Laser Scanning Confocal Microscope</td>
			<td>Zeiss</td>
			<td>LSM 510</td>
			<td></td>
		</tr>
	</tbody>
</table>

procedure for the development of multi-depth circular cross-sectional endothelialized microchannels-on-a-chip

Efforts have been focused on developing in vitro assays for the study of microvessels because in vivo animal studies are more time-consuming, expensive, and observation and quantification are very challenging. However, conventional in vitro microvessel assays have limitations when representing in vivo microvessels with respect to three-dimensional (3D) geometry and providing continuous fluid flow. Using a combination of photolithographic reflowable photoresist technique, soft lithography, and microfluidics, we have developed a multi-depth circular cross-sectional endothelialized microchannels-on-a-chip, which mimics the 3D geometry of in vivo microvessels and runs under controlled continuous perfusion flow. A positive reflowable photoresist was used to fabricate a master mold with a semicircular cross-sectional microchannel network. By the alignment and bonding of the two polydimethylsiloxane (PDMS) microchannels replicated from the master mold, a cylindrical microchannel network was created. The diameters of the microchannels can be well controlled. In addition, primary human umbilical vein endothelial cells (HUVECs) seeded inside the chip showed that the cells lined the inner surface of the microchannels under controlled perfusion lasting for a time period between 4 days to 2 weeks.

Our approach to fabricate the multi-depth microchannel network mimics the complex 3D geometries of in vivo microvessels, in which the microchannels have rounded cross sections15. Additionally, the diameters of parent branching channels and the daughter channels approximately obey Murray&#39;s law for maintaining the fluid flow at a required level so that the overall channel resistance is low and flow velocities are more uniform throughout the network16-18. The processes and results for the ...

Watch this Scientific Journal Video about Procedure for the Development of Multi-depth Circular Cross-sectional Endothelialized Microchannels-on-a-chip at JoVE.com

Procedure for the Development of Multi-depth Circular Cross-sectional Endothelialized Microchannels-on-a-chip

A microchannels-on-a-chip platform was developed by the combination of photolithographic reflowable photoresist technique, soft lithography, and microfluidics. The endothelialized microchannels platform mimics the three-dimensional (3D) geometry of in vivo microvessels, runs under controlled continuous perfusion flow, allows for high-quality and real-time imaging&#160;and can be applied for microvascular research.

Efforts have been focused on developing in vitro assays for the study of microvessels because in vivo animal studies are more time-consuming, expensive, ...

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