Name: solvent bonding for fabrication of pmma and cop microfluidic devices
Uploaded: 2017-01-17T15:00:00.000+00:00
Duration: 4 min 54 s
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, injection molding).</li>
	<li>Visually inspect device layers to ensure that edges are &#34;clean&#34; (i.e., no burrs or ridges of leftover material from the fabrication process). For best results, check all machined micro-feature edges in addition to the outside edges of the device under an optical microscope.</li>
	<li>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.</li>
	<li>Clean device surfaces with laboratory soap and water and dry with compressed air. Submerge device layers in 2-propanol for 2 min and dry with compressed air.</li>
</ol>
2. Solvent Bonding
<ol>
	<li>Prepare heated press (for PMMA) or hotplate (for COP).
	<ol>
		<li>For PMMA (cast acrylic, glass transition temperature of ~100-110 &#176;C)18 preheat press to 70 &#176;C, and allow temperature to stabilize.</li>
		<li>For COP (glass transition temperature of 102 &#176;C, from manufacturer), preheat hotplate to 25 &#176;C, and allow temperature to stabilize.</li>
	</ol>
	</li>
	<li>Prepare solvent for bonding process.
	<ol>
		<li>For PMMA, measure 0.5 ml of ethanol per square inch of bonding area.</li>
		<li>For COP, prepare a 65:35 mixture of 2-propanol and cyclohexane, with a total volume of 0.5 ml of the mixture per square inch of bonding area. 
		NOTE: For COP, use glass pipettes and containers, as cyclohexane will dissolve common polypropylene labware. Perform all mixing and bonding in a fume hood, as cyclohexane is toxic.</li>
	</ol>
	</li>
	<li>Dispense 0.1 ml of solvent per square inch of bonding area between cleaned plastic layers and bring the layers together. Visually inspect for air bubbles at the bonding interface, which are common, and should be removed as much as possible. 
	NOTE: It is beneficial to work quickly once the solvent has been dispensed, as volatile solvents will begin to evaporate (and hence, solvent mixtures will change in composition).
	<ol>
		<li>If bubbles are present, slide the two plastic layers along the bonding interface so that they nearly come apart (but remain in contact), and then slide them back together.</li>
	</ol>
	</li>
	<li>Align the layers of the device with alignment pins, a custom jig, or simply by hand (see Discussion section for further details).
	<ol>
		<li>If using alignment pins, align the holes for the pins, and insert the pins into the device stack.</li>
		<li>If using a custom jig, insert the device stack into the jig and tighten around the device.</li>
		<li>If aligning by hand, use fingers to align the outer edges of the device.</li>
	</ol>
	</li>
	<li>Place the device with solvent into the pre-heated press (for PMMA) or onto the pre-heated hotplate (for COP).
	<ol>
		<li>For PMMA, apply 2,300 kPa of pressure for 2 min.</li>
		<li>For COP, apply 350 kPa of pressure. Increase the temperature from 25 &#176;C to 70 &#176;C at a rate of 5 &#176;C/min. After reaching 70 &#176;C (after 9 min), bond for an additional 15 min.</li>
	</ol>
	</li>
	<li>Use tweezers to safely remove the hot device for inspection. Bonding is now complete.</li>
	<li>Remove any remaining liquid in the device (in microchannels or other features).
	<ol>
		<li>For PMMA, remove any remaining liquid with compressed air. For COP, place bonded device on hotplate and bake at 45 &#176;C for 24 hr to remove any remaining cyclohexane.</li>
	</ol>
	</li>
</ol>

<ol>
	<li>Beebe, D. J., Mensing, G. A., Walker, G. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Physics+and+applications+of+microfluidics+in+biology.">Physics and applications of microfluidics in biology.</a> Annual Review of Biomedical Engineering. 4, 261-286 (2002).</li><li>Situma, C., Hashimoto, M., Soper, S. a. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Merging+microfluidics+with+microarray-based+bioassays.">Merging microfluidics with microarray-based bioassays.</a> Biomolecular Engineering. 23 (5), 213-231 (2006).</li><li>Paguirigan, A. L., Beebe, D. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Microfluidics+meet+cell+biology:+Bridging+the+gap+by+validation+and+application+of+microscale+techniques+for+cell+biological+assays.">Microfluidics meet cell biology: Bridging the gap by validation and application of microscale techniques for cell biological assays.</a> BioEssays. 30 (9), 811-821 (2008).</li><li>Young, E. W. K., Beebe, D. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Fundamentals+of+microfluidic+cell+culture+in+controlled+microenvironments.">Fundamentals of microfluidic cell culture in controlled microenvironments.</a> Chemical Society Reviews. 39 (3), 1036-1048 (2010).</li><li>Duffy, D. C., McDonald, J. C., Schueller, O. J. A., Whitesides, G. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Rapid+Prototyping+of+Microfluidic+Systems+in+Poly(dimethylsiloxane).">Rapid Prototyping of Microfluidic Systems in Poly(dimethylsiloxane).</a> Analytical Chemistry. 70 (23), 4974-4984 (1998).</li><li>Berthier, E., Young, E. W. K., Beebe, D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Engineers+are+from+PDMS-land,+Biologists+are+from+Polystyrenia.">Engineers are from PDMS-land, Biologists are from Polystyrenia.</a> Lab on a Chip. 12 (7), 1224-1237 (2012).</li><li>Sackmann, E. K., Fulton, A. L., Beebe, D. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+present+and+future+role+of+microfluidics+in+biomedical+research.">The present and future role of microfluidics in biomedical research.</a> Nature. 507 (7491), 181-189 (2014).</li><li>Young, E. W. K., Berthier, E., Beebe, D. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Assessment+of+enhanced+autofluorescence+and+impact+on+cell+microscopy+for+microfabricated+thermoplastic+devices.">Assessment of enhanced autofluorescence and impact on cell microscopy for microfabricated thermoplastic devices.</a> Analytical Chemistry. 85 (1), 44-49 (2013).</li><li>Wallow, T. I., Morales, A. M., 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=Low-distortion,+high-strength+bonding+of+thermoplastic+microfluidic+devices+employing+case-II+diffusion-mediated+permeant+activation.">Low-distortion, high-strength bonding of thermoplastic microfluidic devices employing case-II diffusion-mediated permeant activation.</a> Lab on a Chip. 7 (12), 1825-1831 (2007).</li><li>Tsao, C. W., DeVoe, D. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Bonding+of+thermoplastic+polymer+microfluidics.">Bonding of thermoplastic polymer microfluidics.</a> Microfluidics and Nanofluidics. 6 (1), 1-16 (2009).</li><li>Young, E. W. K., Berthier, 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=Rapid+prototyping+of+arrayed+microfluidic+systems+in+polystyrene+for+cell-based+assays.">Rapid prototyping of arrayed microfluidic systems in polystyrene for cell-based assays.</a> Analytical Chemistry. 83 (4), 1408-1417 (2011).</li><li>Truckenm&#252;ller, R., Henzi, P., Herrmann, D., Saile, V., Schomburg, W. K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Bonding+of+polymer+microstructures+by+UV+irradiation+and+subsequent+welding+at+low+temperatures.">Bonding of polymer microstructures by UV irradiation and subsequent welding at low temperatures.</a> Microsystem Technologies. 10 (5), 372-374 (2004).</li><li>Tsao, C. W., Hromada, L., Liu, J., Kumar, P., DeVoe, D. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Low+temperature+bonding+of+PMMA+and+COC+microfluidic+substrates+using+UV/ozone+surface+treatment.">Low temperature bonding of PMMA and COC microfluidic substrates using UV/ozone surface treatment.</a> Lab on a Chip. 7 (4), 499-505 (2007).</li><li>Wan, A. M. D., Sadri, A., Young, E. W. K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Liquid+phase+solvent+bonding+of+plastic+microfluidic+devices+assisted+by+retention+grooves.">Liquid phase solvent bonding of plastic microfluidic devices assisted by retention grooves.</a> Lab on a Chip. 15 (18), 3785-3792 (2015).</li><li>Guckenberger, D. J., de Groot, T. E., Wan, A. M. D., Beebe, D. J., Young, E. W. K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Micromilling:+a+method+for+ultra-rapid+prototyping+of+plastic+microfluidic+devices.">Micromilling: a method for ultra-rapid prototyping of plastic microfluidic devices.</a> Lab on a Chip. 15 (11), 2364-2378 (2015).</li><li>Cameron, N. S., Roberge, H., Veres, T., Jakeway, S. C., John Crabtree, H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=High+fidelity,+high+yield+production+of+microfluidic+devices+by+hot+embossing+lithography:+rheology+and+stiction.">High fidelity, high yield production of microfluidic devices by hot embossing lithography: rheology and stiction.</a> Lab on a Chip. 6 (7), 936 (2006).</li><li>Yang, S., Devoe, D. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Microfluidic+device+fabrication+by+thermoplastic+hot-embossing.">Microfluidic device fabrication by thermoplastic hot-embossing.</a> Methods in Molecular Biology. 949, 115-123 (2013).</li><li>Konstantinou, D., Shirazi, A., Sadri, A., Young, E. W. K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Combined+hot+embossing+and+milling+for+medium+volume+production+of+thermoplastic+microfluidic+devices.">Combined hot embossing and milling for medium volume production of thermoplastic microfluidic devices.</a> Sensors and Actuators B: Chemical. 234, 209-221 (2016).</li><li>Maszara, W. P., Goetz, G., Caviglia, A., McKitterick, J. B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Bonding+of+silicon+wafers+for+silicon-on-insulator.">Bonding of silicon wafers for silicon-on-insulator.</a> Journal of Applied Physics. 64 (10), 4943 (1988).</li><li>Bhattacharyya, A., Klapperich, C. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Mechanical+and+chemical+analysis+of+plasma+and+ultraviolet-ozone+surface+treatments+for+thermal+bonding+of+polymeric+microfluidic+devices.">Mechanical and chemical analysis of plasma and ultraviolet-ozone surface treatments for thermal bonding of polymeric microfluidic devices.</a> Lab on a Chip. 7 (7), 876-882 (2007).</li></ol>

The authors declare that they have no competing financial interests.

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><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, &amp;ge;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, &amp;ge;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 ...

solvent-bonding-for-fabrication-of-pmma-and-cop-microfluidic-devices

Research

JoVE Journal

Engineering

16.2K Views.  University of Toronto. 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.

Video: Solvent Bonding for Fabrication of PMMA and COP Microfluidic Devices

Non-plasma Bonding of PDMS for Inexpensive Fabrication of Microfluidic Devices

In this video, we demonstrate how to use the neuron microfluidic device without plasma bonding.  In some cases it may be desirable to reversibly bond devices to the Corning No. 1 cover glass.  This could be due, perhaps, to a plasma cleaner not being available.  In other instances, it may be desirable to remove the device from the glass after the culturing of neurons for certain types of microscopy or for immunostaining, though it is not necessary to remove the device for immunostaining since the neurons can be stained in the device.  Some researchers, however, still prefer to remove the device.  In this case, reversible bonding of the device to the cover glass makes that possible.  There are some disadvantages to non-plasma bonding of the devices in that not as tight of a seal is formed.  In some cases axons may grow under the grooves rather than through them.  Also, because the glass and PDMS are hydrophobic, liquids do not readily enter the device making it necessary at times to force media and other reagents into the device.  Liquids will enter the device via capillary action, but it takes significantly longer as compared to devices that have been plasma bonded.  The plasma cleaner creates temporary hydrophilic charges on the glass and device that facilitate the flow of liquids through the device after bonding within seconds.  For non-plasma bound devices, liquid flow through the devices takes several minutes.  It is also important to note that the devices to be used with non-plasma bonding need to be sterilized first, whereas plasma treated devices do not need to be sterilized prior to use because the plasma cleaner will sterilize them.

In this video we demonstrate how to use the neuron microfluidic device without plasma bonding.

In this video, we demonstrate how to use the neuron microfluidic device without plasma bonding.  In some cases it may be desirable to reversibly bond ...

Biology

Fabrication of the Thermoplastic Microfluidic Channels

In our lab, we have successfully isolated nucleic acids directly from microliter and submicroliter volumes of human blood, urine and stool using polymer/nanoparticle composite microscale lysis and solid phase extraction columns. The recovered samples are concentrated, small volume samples that are PCRable, without any additional cleanup. Here, we demonstrate how to fabricate thermoplastic microfluidic chips using hot embossing and heat sealing. Then, we demonstrate how to use in situ light directed surface grafting and polymerization through the sealed chip to form the composite solid phase columns. We demonstrate grafting and polymerization of a carbon nanotube/polymer composite column for bacterial cell lysis. We then show the lysis process followed by solid phase extraction of nucleic acids from the sample on chip using a silica/polymer composite column. The attached protocols contain detailed instructions on how to make both lysis and solid phase extraction columns.

Here we demonstrate how to fabricate thermoplastic microfluidic chips using hot embossing and heat sealing. Then we demonstrate how to use in situ light directed surface grafting and polymerization through the sealed chip to form the composite solid phase columns.

In our lab, we have successfully isolated nucleic acids directly from microliter and submicroliter volumes of human blood, urine and stool using ...

Microfluidic Pneumatic Cages: A Novel Approach for In-chip Crystal Trapping, Manipulation and Controlled Chemical Treatment

The precise localization and controlled chemical treatment of structures on a surface are significant challenges for common laboratory technologies. Herein, we introduce a microfluidic-based technology, employing a double-layer microfluidic device, which can trap and localize in situ and ex situ synthesized structures on microfluidic channel surfaces. Crucially, we show how such a device can be used to conduct controlled chemical reactions onto on-chip trapped structures and we demonstrate how the synthetic pathway of a crystalline molecular material and its positioning inside a microfluidic channel can be precisely modified with this technology. This approach provides new opportunities for the controlled assembly of structures on surface and for their subsequent treatment.

Herein, we describe the fabrication and operation of a double-layer microfluidic system made of polydimethylsiloxane (PDMS). We demonstrate the potential of this device for trapping, directing the coordination pathway of a crystalline molecular material and controlling chemical reactions onto on-chip trapped structures.

The precise localization and controlled chemical treatment of structures on a surface are significant challenges for common laboratory technologies. ...

Chemistry

Creating Sub-50 Nm Nanofluidic Junctions in PDMS Microfluidic Chip via Self-Assembly Process of Colloidal Particles

Polydimethylsiloxane (PDMS) is the prevailing building material to make microfluidic devices due to its ease of molding and bonding as well as its transparency. Due to the softness of the PDMS material, however, it is challenging to use PDMS for building nanochannels. The channels tend to collapse easily during plasma bonding. In this paper, we present an evaporation-driven self-assembly method of silica colloidal nanoparticles to create nanofluidic junctions with sub-50 nm pores between two microchannels. The pore size as well as the surface charge of the nanofluidic junction is tunable simply by changing the colloidal silica bead size and surface functionalization outside of the assembled microfluidic device in a vial before the self-assembly process. Using the self-assembly of nanoparticles with a bead size of 300 nm, 500 nm, and 900 nm, it was possible to fabricate a porous membrane with a pore size of ~45 nm, ~75 nm and ~135 nm, respectively. Under electrical potential, this nanoporous membrane initiated ion concentration polarization (ICP) acting as a cation-selective membrane to concentrate DNA by ~1,700 times within 15 min. This non-lithographic nanofabrication process opens up a new opportunity to build a tunable nanofluidic junction for the study of nanoscale transport processes of ions and molecules inside a PDMS microfluidic chip.

We propose a simple self-assembly technique of silica colloidal nanoparticles to create a nanofluidic junction between two microchannels in polydimethylsiloxane (PDMS). Using this technique, a nanoporous bead membrane with a pore size down to ~45 nm was built inside a microchannel and applied to electrokinetic preconcentration of DNA samples.

Polydimethylsiloxane (PDMS) is the prevailing building material to make microfluidic devices due to its ease of molding and bonding as well as its ...

Microfluidic-based Synthesis of Covalent Organic Frameworks (COFs): A Tool for Continuous Production of COF Fibers and Direct Printing on a Surface

Covalent Organic Frameworks (COFs) are a class of porous covalent materials which are frequently synthesized as unprocessable crystalline powders. The first COF was reported in 2005 with much effort centered on the establishment of new synthetic routes for its preparation. To date, most available synthetic methods for COF synthesis are based on bulk mixing under solvothermal conditions. Therefore, there is increasing interest in developing systematic protocols for COF synthesis that provide for fine control over reaction conditions and improve COF processability on surfaces, which is essential for their use in practical applications. Herein, we present a novel microfluidic-based method for COF synthesis where the reaction between two constituent building blocks, 1,3,5-benzenetricarbaldehyde (BTCA) and 1,3,5-tris(4-aminophenyl)benzene (TAPB), takes place under controlled diffusion conditions and at room temperature. Using such an approach yields sponge-like, crystalline fibers of a COF material, hereafter called MF-COF. The mechanical properties of MF-COF and the dynamic nature of the approach allow the continuous production of MF-COF fibers and their direct printing onto surfaces. The general method opens new potential applications requiring advanced printing of 2D or 3D COF structures on flexible or rigid surfaces.

Microfluidic-based Synthesis of Covalent Organic Frameworks COFs: A Tool for Continuous Production of COF Fibers and Direct Printing on a Surface

We present a novel microfluidic-based method for synthesis of covalent organic frameworks (COFs). We demonstrate how this approach can be used to produce continuous COF fibers, and also 2D or 3D COF structures on surfaces.

Covalent Organic Frameworks (COFs) are a class of porous covalent materials which are frequently synthesized as unprocessable crystalline powders. The ...

Fabrication of Refractive-index-matched Devices for Biomedical Microfluidics

The use of microfluidic devices has emerged as a defining tool for biomedical applications. When combined with modern microscopy techniques, these devices can be implemented as part of a robust platform capable of making simultaneous complementary measurements. The primary challenge created by the combination of these two techniques is the mismatch in refractive index between the materials traditionally used to make microfluidic devices and the aqueous solutions typically used in biomedicine. This mismatch can create optical artifacts near the channel or device edges. One solution is to reduce the refractive index of the material used to fabricate the device by using a fluorinated polymer such as MY133-V2000 whose refractive index is similar to that of water (n = 1.33). Here, the construction of a microfluidic device made out of MY133-V2000 using soft lithography techniques is demonstrated, using O2 plasma in conjunction with an acrylic holder to increase the adhesion between the MY133-V2000 fabricated device and the polydimethylsiloxane (PDMS) substrate. The device is then tested by incubating it filled with cell culture media for 24 h to demonstrate the ability of the device to maintain cell culture conditions during the course of a typical imaging experiment. Finally, quantitative phase microscopy (QPM) is used to measure the distribution of mass within the live adherent cells in the microchannel. This way, the increased precision, enabled by fabricating the device from a low index of refraction polymer such as MY133-V2000 in lieu of traditional soft lithography materials such as PDMS, is demonstrated. Overall, this approach for fabricating microfluidic devices can be readily integrated into existing soft lithography workflows in order to reduce optical artifacts and increase measurement precision.

This protocol describes the fabrication of microfluidic devices from MY133-V2000 to eliminate artifacts that often arise in microchannels due to the mismatching refractive indices between microchannel structures and an aqueous solution. This protocol uses an acrylic holder to compress the encapsulated device, improving adhesion both chemically and mechanically.

The use of microfluidic devices has emerged as a defining tool for biomedical applications. When combined with modern microscopy techniques, these devices ...

Double Emulsion Generation Using a Polydimethylsiloxane (PDMS) Co-axial Flow Focus Device

Double emulsions are useful in a number of biological and industrial applications in which it is important to have an aqueous carrier fluid. This paper presents a polydimethylsiloxane (PDMS) microfluidic device capable of generating water/oil/water double emulsions using a coaxial flow focusing geometry that can be fabricated entirely using soft lithography. Similar to emulsion devices using glass capillaries, double emulsions can be formed in channels with uniform wettability and with dimensions much smaller than the channel sizes. Three dimensional flow focusing geometry is achieved by casting a pair of PDMS slabs using two layer soft lithography, then mating the slabs together in a clamshell configuration. Complementary locking features molded into the PDMS slabs enable the accurate registration of features on each of the slab surfaces. Device testing demonstrates formation of double emulsions from 14 &#181;m to 50 &#181;m in diameter while using large channels that are robust against fouling and clogging.

Double Emulsion Generation Using a Polydimethylsiloxane PDMS Co-axial Flow Focus Device

Microfluidic double emulsions generation typically involves devices with patterned wettability or custom-fabricated glass components. Here we describe the fabrication and testing of an all polydimethylsiloxane (PDMS) double emulsion generator that does not require surface treatment or complicated fabrication processes, and is capable of producing double emulsions down to 14 &#181;m.

Double emulsions are useful in a number of biological and industrial applications in which it is important to have an aqueous carrier fluid. This paper ...

Bioengineering

Window on a Microworld: Simple Microfluidic Systems for Studying Microbial Transport in Porous Media

Microbial growth and transport in porous media have important implications for the quality of groundwater and surface water, the recycling of nutrients in the environment, as well as directly for the transmission of pathogens to drinking water supplies. Natural porous media is composed of an intricate physical topology, varied surface chemistries, dynamic gradients of nutrients and electron acceptors, and a patchy distribution of microbes. These features vary substantially over a length scale of microns, making the results of macro-scale investigations of microbial transport difficult to interpret, and the validation of mechanistic models challenging. Here we demonstrate how simple microfluidic devices can be used to visualize microbial interactions with micro-structured habitats, to identify key processes influencing the observed phenomena, and to systematically validate predictive models. Simple, easy-to-use flow cells were constructed out of the transparent, biocompatible and oxygen-permeable material poly(dimethyl siloxane). Standard methods of photolithography were used to make micro-structured masters, and replica molding was used to cast micro-structured flow cells from the masters. The physical design of the flow cell chamber is adaptable to the experimental requirements: microchannels can vary from simple linear connections to complex topologies with feature sizes as small as 2 &mu;m. Our modular EcoChip flow cell array features dozens of identical chambers and flow control by a gravity-driven flow module. We demonstrate that through use of EcoChip devices, physical structures and pressure heads can be held constant or varied systematically while the influence of surface chemistry, fluid properties, or the characteristics of the microbial population is investigated. Through transport experiments using a non-pathogenic, green fluorescent protein-expressing Vibrio bacterial strain, we illustrate the importance of habitat structure, flow conditions, and inoculums size on fundamental transport phenomena, and with real-time particle-scale observations, demonstrate that microfluidics offer a compelling view of a hidden world.

Microfluidic devices can be used to visualize complex natural processes in real time and at the appropriate physical scales. We have developed a simple microfluidic device that mimics key features of natural porous media for studying growth and transport of bacteria in the subsurface.

Microbial growth and transport in porous media have important implications for the quality of groundwater and surface water, the recycling of nutrients in ...

Computer Numerical Control Micromilling of a Microfluidic Acrylic Device with a Staggered Restriction for Magnetic Nanoparticle-Based Immunoassays

Microfluidic systems have greatly improved immunoassay techniques. However, many microfabrication techniques require specialized, expensive, or complicated equipment, making fabrication costly and incompatible with mass production, which is one of the most important preconditions for point-of-care tests (POCT) to be adopted in low-resource settings. This work describes the fabrication process of an acrylic (polymethylmethacrylate, PMMA) device for nanoparticle-conjugated enzymatic immunoassay testing using the computer numerical control (CNC) micromilling technique. The functioning of the microfluidic device is shown by performing an immunoassay to detect a commercial antibody using lysozyme as a model antigen conjugated to 100 nm magnetic nanoparticles. This device integrates a physical staggered restriction of only 5 &#181;m in height, used to capture magnetic microparticles that make up a magnetic trap by placing an external magnet. In this way, the magnetic force on the immunosupport of conjugated nanoparticles is enough to capture them and resist flow drag. This microfluidic device is particularly suitable for low-cost mass production without the loss of precision for immunoassay performance.

Microfluidics is a powerful tool for the development of diagnostic tests. However, expensive equipment and materials, as well as laborious fabrication and handling techniques, are often required. Here, we detail the fabrication protocol of an acrylic microfluidic device for magnetic micro- and nanoparticle-based immunoassays in a low-cost and simple-to-use setting.

Microfluidic systems have greatly improved immunoassay techniques. However, many microfabrication techniques require specialized, expensive, or ...

Rapid Fabrication of Custom Microfluidic Devices for Research and Educational Applications

Microfluidic devices allow for the manipulation of fluids, particles, cells, micro-sized organs or organisms in channels ranging from the nano to submillimeter scales. A rapid increase in the use of this technology in the biological sciences has prompted a need for methods that are accessible to a wide range of research groups. Current fabrication standards, such as PDMS bonding, require expensive and time consuming lithographic and bonding techniques. A viable alternative is the use of equipment and materials that are easily affordable, require minimal expertise and allow for the rapid iteration of designs. In this work we describe a protocol for designing and producing PET-laminates (PETLs), microfluidic devices that are inexpensive, easy to fabricate, and consume significantly less time to generate than other approaches to microfluidics technology. They consist of thermally bonded film sheets, in which channels and other features are defined using a craft cutter. PETLs solve field-specific technical challenges while dramatically reducing obstacles to adoption. This approach facilitates the accessibility of microfluidics devices in both research and educational settings, providing a reliable platform for new methods of inquiry.

Here we present a protocol to design and fabricate custom microfluidic devices with minimal financial and time investment. The aim is to facilitate the adoption of microfluidic technologies in biomedical research laboratories and educational settings.