Name: solvent bonding for fabrication of pmma and cop microfluidic devices
Uploaded: 2017-01-17T15:00:00
Description: Watch this Scientific Journal Video about Solvent Bonding for Fabrication of PMMA and COP Microfluidic Devices at JoVE.com

We acknowledge financial support from the Natural Sciences and Engineering Research Council of Canada (NSERC, #436117-2013), the Cancer Research Society (CRS, #20172), Myeloma Canada, and Grand Challenges Canada.

Note that all of the steps described below have been developed and performed in a non-cleanroom environment. The solvent bonding steps can certainly be performed in a cleanroom, if available, but this is not required.
1. Preparation of Thermoplastic Microfluidic Device Layers
<ol>
	<li>Design and fabricate microfluidic device layers from the thermoplastic of choice, using an appropriate fabrication method (e.g., micromilling15, embossing16-18</s...

<ol>
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The feasibility of potential bonding strategies depends on available equipment. While hotplates are relatively common and free weights can be purchased inexpensively, high pressure strategies will require the use of a heated press. For example, our optimal PMMA bonding recipe requires high pressure to bond with ethanol (see Table 1), and the required pressure is not attainable for typical device sizes using free weights. Thus, if only a hotplate and weights are available, PMMA can instead be bonded with ...

Microfluidics has emerged over the past twenty years as a technology well suited for studying chemistry and physics at the microscale1, and with growing promise to significantly contribute to biology research2-4. The majority of microfluidic devices have historically been made from poly(dimethylsiloxane) (PDMS), a silicone elastomer that is easy to use, inexpensive, and offers high quality feature replication5. However, PDMS has well-documented shortcomings and is incompatible with high-volume fabrication processes6,7, and as such, there has been a growing trend toward fabricating microfluidic devices from thermoplastic materials, because of their potential for mass manufacturing and thus commercialization.
One of the major barriers to wider adoption of plastic microfabrication has been achieving easy, high quality bonding of plastic devices. Current strategies employ thermal, adhesive, and solvent bonding techniques, but many suffer from significant challenges. Thermal bonding increases autofluorescence8 and often deforms microchannel geometries9-11, while adhesive techniques require stencils, careful alignment, and ultimately leave the thickness of the adhesive exposed to the microchannel10. Solvent bonding is attractive due to its simplicity, tunability, and low cost10,12-14. In particular, its tunability enables optimization for a variety of plastics, which can yield consistent, high quality bonding that minimizes deformation of microfeatures14.
During solvent bonding, solvent exposure increases the mobility of polymer chains near the surface of the plastic, which enables inter-diffusion of chains across the bonding interface. This causes entanglement via mechanical interlocking of the diffusing chains, and results in a physical bond10. Thermal bonding works in a similar manner, but relies on elevated temperature alone to increase chain mobility. Thus, thermal methods require temperatures near or above the glass transition of the polymer, whereas the use of solvents can significantly reduce the temperature needed for bonding, and thus reduce unwanted deformation.
We provide a specific protocol for bonding both PMMA and COP devices. However, this protocol and method describes a simple, generic approach for solvent bonding of thermoplastic microfluidic devices that can be tailored for other plastic materials, solvents, and available equipment. We describe numerous methods for assessing the quality of bonds (e.g., bond coverage, bond strength, bond durability, and deformation of microfeature geometries), and provide troubleshooting approaches to address these common challenges.

<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>COP</td>
			<td>Zeonor</td>
			<td>604Z1020R080</td>
			<td>20 kg COP Pellets - 1020R. Multiple suppliers can be used, but may affect bonding characteristics.</td>
		</tr>
		<tr>
			<td>PMMA</td>
			<td>McMaster Carr</td>
			<td>8560K173</td>
			<td>1.5 mm sheet thickness for our typical applications. Multiple suppliers can be used, but may affect bonding characteristics.</td>
		</tr>
		<tr>
			<td>Cyclohexane</td>
			<td>Sigma-Aldrich</td>
			<td>227048</td>
			<td>Cyclohexane, anhydrous, 99.5%. Multiple suppliers can be used. Toxic, requires fumehood.</td>
		</tr>
		<tr>
			<td>Ethanol</td>
			<td>Sigma-Aldrich</td>
			<td>24102</td>
			<td>Ethanol, absolute, &#8805;99.8% (GC). Multiple suppliers can be used.</td>
		</tr>
		<tr>
			<td>Acetone</td>
			<td>Sigma-Aldrich</td>
			<td>179124</td>
			<td>Acetone, ACS reagent, &#8805;99.5%. Multiple suppliers can be used.</td>
		</tr>
		<tr>
			<td>2-Propanol</td>
			<td>Sigma-Aldrich</td>
			<td>278475</td>
			<td>2-Propanol, anhydrous, 99.5%. Multiple suppliers can be used.</td>
		</tr>
		<tr>
			<td>Hot plate(s)</td>
			<td>Torrey Pines Scientific</td>
			<td>HP60</td>
			<td>Fully programmable digital hotplate. Multiple suppliers can be used.</td>
		</tr>
		<tr>
			<td>Free weights</td>
			<td>Cap Barbell</td>
			<td>RPG#2</td>
			<td>Standard cast iron plate. Multiple suppliers and different weights can be used.</td>
		</tr>
		<tr>
			<td>Heated press</td>
			<td>Carver</td>
			<td>Auto CH</td>
			<td>Auto series heated hydraulic press. Multiple suppliers can be used. A press that fits in a fumehood would allow the most flexibility (this model does not).</td>
		</tr>
		<tr>
			<td>CNC Milling Machine</td>
			<td>Tormach</td>
			<td>PCNC 770</td>
			<td>3 Axis CNC mill. Multiple suppliers can be used.</td>
		</tr>
		<tr>
			<td>Endmills</td>
			<td>Various</td>
			<td>Various</td>
			<td>Required sizes depend on designs. Multiple suppliers can be used.</td>
		</tr>
	</tbody>
</table>

solvent bonding for fabrication of pmma and cop microfluidic devices

Thermoplastic microfluidic devices offer many advantages over those made from silicone elastomers, but bonding procedures must be developed for each thermoplastic of interest. Solvent bonding is a simple and versatile method that can be used to fabricate devices from a variety of plastics. An appropriate solvent is added between two device layers to be bonded, and heat and pressure are applied to the device to facilitate the bonding. By using an appropriate combination of solvent, plastic, heat, and pressure, the device can be sealed with a high quality bond, characterized as having high bond coverage, bond strength, optical clarity, durability over time, and low deformation or damage to microfeature geometry. We describe the procedure for bonding devices made from two popular thermoplastics, poly(methyl-methacrylate) (PMMA), and cyclo-olefin polymer (COP), as well as a variety of methods to characterize the quality of the resulting bonds, and strategies to troubleshoot low quality bonds. These methods can be used to develop new solvent bonding protocols for other plastic-solvent systems.

A schematic of the general solvent bonding procedure is shown in Figure 1. The easiest way to assess bond quality is to visually inspect bond coverage, since poor bond coverage is easily visible as regions of unbonded plastic, and is indicative of weak bonding. Such regions are typically near free edges (e.g., periphery of device, or near open ports or microchannels), and can also often appear around any particles of dirt or dust at the bonding interface. Poor bo...

Watch this Scientific Journal Video about Solvent Bonding for Fabrication of PMMA and COP Microfluidic Devices at JoVE.com

Solvent Bonding for Fabrication of PMMA and COP Microfluidic Devices

Solvent bonding is a simple and versatile method for fabricating thermoplastic microfluidic devices with high quality bonds. We describe a protocol to achieve strong, optically clear bonds in PMMA and COP microfluidic devices that preserve microfeature details, by a judicious combination of pressure, temperature, an appropriate solvent, and device geometry.

Thermoplastic microfluidic devices offer many advantages over those made from silicone elastomers, but bonding procedures must be developed for each ...

The overall goal of this technique is to provide a simple and versatile method for fabricating thermoplastic microfluidic devices with high quality bonds. This solvent bonding procedure will allow us to fabricate well bonded and durable thermoplastic microfluidic devices for a variety of applications from microfluidic cell culture systems to prototypes for point of care diagnostic tools. The main advantage of this technique is that it allows us to quickly and easily bond thermoplastic device layers.The procedure can be easily adapted to bond different thermoplastic materials. Design and fabricate microfluidic device layers from the thermoplastic of choice, using an appropriate fabrication method. Visually inspect the device layers to ensure that edges are clean without burrs or ridges of leftover material from the fabrication process.For best results, check all machined microfeature edges, in addition to the outside edges of the device, under an optical microscope. If leftover material is found during visual inspection, use a razor blade or scalpel to carefully remove any material that prevents the device layers from lying flat against one another so that the interfaces of the layers come into conformal contact. Then, clean the device surfaces with laboratory soap and water.And, dry with compressed air. After submerging the device layers in 2-propanol for two minutes, dry them with compressed air. This video is demonstrated with poly methyl methacrylate, abbreviated PMMA.Please see the text protocol for slight alterations in the procedure when using cyclic olefin polymer, or COP. Preheat, a heated press to 70 degrees celsius and allow the temperature to stabilize. To prepare the solvent for bonding process, measure 0.5 milliliters of ethanol, per square inch of bonding area for PMMA.It's important that an appropriate volume of solvent is applied to the device layers because too much solvent can lead to challenges in aligning layers. Dispense 0.1 milliliters of solvent per square inch of bonding area between cleaned plastic layers and bring the layers together. Visually inspect the bonding interface for air bubbles, which are common and should be removed as much as possible.If bubbles are present, slide the two plastic layers along the bonding interface so that they nearly come apart. And, then, slide them back together. To align the layers of the device by hand, use fingers to align the outer edges of the device.If more accurate alignment is required, include L shaped corner brackets to hold the device layers together. Next, place the device with solvent into the preheated press and apply 2, 300 kPa of pressure for two minutes. Use tweezers to safely remove the hot device for inspection.Bonding is now complete. Finally, remove any remaining liquid in the device using compressed air. Shown here are representative results of a pair of device layers before cleaning and after cleaning.The device layers have been milled to remove burrs. A representative image of a device with solvent added shows bubbles present through the bonding surface that can inhibit bonding. Conversely, well distributed solvent that is free of bubbles leads to strong, high quality bonds.Rapid solvent evaporation, during heating, can lead to regions of unbonded material near free edges of the device, resulting in poor bond coverage, leaky microfluidic features, and low overall bond strength. These regions are visible as lighter patches with colored interference fringes. An optimized solvent plastic system achieves good bond coverage and strength and minimizes damage to microfeatures, while still properly sealing them.Once mastered, a new thermoplastic device design can be fabricated in as little as two hours if the bonding technique is done properly. Remember that working with cyclohexane can be hazardous and should be handled in a fume hood and while wearing personal protective equipment. After watching this video, you will have a simple and versatile method for fabricating thermoplastic microfluidic devices with high quality bonds that are leak free and appropriate for use in cell culture, in point of care diagnostic applications.

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