This work is supported by a fund from Bourns College of Engineering of University of California, Riverside. BK received a scholarship from the Lung-Wen Tsai Memorial Award in Mechanical Design.

1. Planar 4-layer Device (Stacked Layers) Construction
<ol>
	<li>Print arrays of each layer of the device9 onto each piece of filter paper using a solid ink printer.11,12 Place each filter paper on a hotplate at 170 &#176;C for 2 min. This will melt the wax-based ink and allow it to fully penetrate the thickness of the paper, forming hydrophobic barriers. 
	NOTE: The exact designs used are available as supplemental files.</li>
	<li>Remove filter paper from hotplate and allow it to cool to RT....

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	<li>Li, X., Ballerini, D. R., Shen, W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+perspective+on+paper-based+microfluidics:+Current+status+and+future+trends.">A perspective on paper-based microfluidics: Current status and future trends.</a> Biomicrofluidics. 6, 11301-11313 (2012).</li><li>Yetisen, A. K., Akram, M. S., Lowe, C. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Paper-based+microfluidic+point-of-care+diagnostic+devices.">Paper-based microfluidic point-of-care diagnostic devices.</a> Lab Chip. 13, 2210-2251 (2013).</li><li>Cate, D. M., Adkins, J. A., Mettakoonpitak, J., Henry, C. S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Recent+developments+in+paper-based+microfluidic+devices.">Recent developments in paper-based microfluidic devices.</a> Anal Chem. 87, 19-41 (2015).</li><li>Martinez, A. W., Phillips, S. T., 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=Three-dimensional+microfluidic+devices+fabricated+in+layered+paper+and+tape.">Three-dimensional microfluidic devices fabricated in layered paper and tape.</a> Proc Natl Acad Sci U S A. 105, 19606-19611 (2008).</li><li>Fu, E., Ramsey, S. A., Kauffman, P., Lutz, B., Yager, P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Transport+in+two-dimensional+paper+networks.">Transport in two-dimensional paper networks.</a> Microfluid Nanofluidics. 10, 29-35 (2011).</li><li>Govindarajan, A. V., Ramachandran, S., Vigil, G. D., Yager, P., Bohringer, K. F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+low+cost+point-of-care+viscous+sample+preparation+device+for+molecular+diagnosis+in+the+developing+world;+an+example+of+microfluidic+origami.">A low cost point-of-care viscous sample preparation device for molecular diagnosis in the developing world; an example of microfluidic origami.</a> Lab Chip. 12, 174-181 (2012).</li><li>Schilling, K. M., Jauregui, D., Martinez, A. W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Paper+and+toner+three-dimensional+fluidic+devices:+programming+fluid+flow+to+improve+point-of-care+diagnostics.">Paper and toner three-dimensional fluidic devices: programming fluid flow to improve point-of-care diagnostics.</a> Lab Chip. 13, 628-631 (2013).</li><li>Liu, H., Crooks, R. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Three-dimensional+paper+microfluidic+devices+assembled+using+the+principles+of+origami.">Three-dimensional paper microfluidic devices assembled using the principles of origami.</a> J Am Chem Soc. 133, 17564-17566 (2011).</li><li>Lewis, G. G., DiTucci, M. J., Baker, M. S., Phillips, S. T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=High+throughput+method+for+prototyping+three-dimensional,+paper-based+microfluidic+devices.">High throughput method for prototyping three-dimensional, paper-based microfluidic devices.</a> Lab Chip. 12, 2630-2633 (2012).</li><li>Kalish, B., Tsutsui, H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Patterned+adhesive+enables+construction+of+nonplanar+three-dimensional+paper+microfluidic+circuits.">Patterned adhesive enables construction of nonplanar three-dimensional paper microfluidic circuits.</a> Lab Chip. 14, 4354-4361 (2014).</li><li>Carrilho, E., Martinez, A. W., Whitesides, G. 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The authors have nothing to disclose.

The above protocols use perforated metal sheets as stencils for applying aerosol adhesives to construct planar and nonplanar 3D paper microfluidic devices. In planar devices, this has the advantage of allowing devices to be completely unfolded after the adhesive has dried without destroying the device. In other adhesive based construction techniques, this is almost impossible, although, some designs allow for partial destructive disassembly by unpeeling two halves held together with a removable adhesive.14 Adh...

In recent years, paper microfluidics has garnered considerable popularity for its potential to provide low-cost point of care (POC) diagnostic devices.1-3 POC devices offer functionality similar to those of lab-based tests in a format that allows results to be obtained relatively quickly. POC devices made from paper are low-cost, lightweight, and easy-to-use alternatives to expensive microfluidic chips and miniaturized laboratories, making them ideal for use in resource-limited settings. The most common paper microfluidic devices are one-dimensional lateral flow devices, but planar three-dimensional (3D) paper microfluidic devices hold promise to provide multiplexed diagnostic devices4 that take up a much smaller footprint than would be required by a 2D device5 and correspondingly use a smaller sample volume.
Initially, planar 3D paper microfluidic devices were assembled individually, layer-by-layer with patterned paper layers alternating with laser-cut double-sided tape. Carefully aligned holes cut in the tape layer were filled with cellulose powder to ensure inter-layer fluid transport.4 A number of alternate methods were subsequently developed,6-9 each improving different aspects of the devices. In particular, by eschewing adhesives, devices could be folded via origami techniques with layers held together by an external clamp.8 This eliminates any potential adhesive interference in a diagnostic test and allows the device to be unfolded post-use, potentially allowing even smaller sample volumes by displaying results internally. Alternatively, by using an aerosol adhesive applied between each paper layer, sheets of devices could be assembled simultaneously, without time-consuming patterning and alignment of tape.9
However, by applying an aerosol adhesive through a stencil, it is possible to gain the benefit of both of these techniques. By spraying the adhesive through a stencil, only a fraction of the adhesive is applied to the device, minimizing any potential interference with interlayer fluid transfer. Additionally, with careful stencil selection, a pattern of adhesive can be applied that results in semi-permanent adhesive bonding, allowing devices to be unfolded after use, while still providing sufficient interlayer contact to allow fluid to wick between layers.
Finally, applying aerosol adhesives through a stencil eases the construction of nonplanar 3D paper microfluidic devices, by minimizing the amount of adhesive applied to adjacent faces that may require frequent folding and unfolding during construction.10 Additionally, the use of patterned adhesive enables device to be unfolded after use for more convenient storage. Nonplanar 3D paper microfluidic devices are expected to be used for tasks that would otherwise be impossible in a planar 3D device. Figure 1 depicts the general process flow used to construct both planar and nonplanar 3D devices.

<table border="0" cellpadding="0" cellspacing="0" width="585">
	<tbody>
		<tr height="22">
			<td height="22" style="height:22px;width:165px;">Camera</td>
			<td style="width:143px;">Nikon</td>
			<td style="width:119px;">D5100</td>
			<td style="width:160px;"></td>
		</tr>
		<tr height="22">
			<td height="22" style="height:22px;width:165px;">Solid-ink printer</td>
			<td style="width:143px;">Xerox</td>
			<td style="width:119px;">ColorQube 8880</td>
			<td style="width:160px;"></td>
		</tr>
		<tr height="22">
			<td height="22" style="height:22px;width:165px;">Hotplate</td>
			<td style="width:143px;">Torrey Pines</td>
			<td style="width:119px;">HS60</td>
			<td style="width:160px;"></td>
		</tr>
		<tr height="22">
			<td height="22" style="height:22px;width:165px;">Humidity chamber</td>
			<td style="width:143px;">Electro-Tech Systems</td>
			<td style="width:119px;">5503-E</td>
			<td style="width:160px;"></td>
		</tr>
		<tr height="22">
			<td height="22" style="height:22px;width:165px;">Spray adhesive</td>
			<td style="width:143px;">3M</td>
			<td style="width:119px;">62497749309</td>
			<td style="width:160px;">Super 77 (16.75 oz can)</td>
		</tr>
		<tr height="22">
			<td height="22" style="height:22px;width:165px;">Filter paper</td>
			<td style="width:143px;">Whatman</td>
			<td style="width:119px;">Grade 4</td>
			<td style="width:160px;"></td>
		</tr>
		<tr height="22">
			<td height="22" style="height:22px;width:165px;">Perforated steel sheet</td>
			<td style="width:143px;">MetalsDepot</td>
			<td style="width:119px;">PS16116</td>
			<td style="width:160px;"></td>
		</tr>
		<tr height="22">
			<td height="22" style="height:22px;width:165px;">Tartrazine</td>
			<td style="width:143px;">Sigma-Aldritch</td>
			<td style="width:119px;">T0388</td>
			<td style="width:160px;"></td>
		</tr>
		<tr height="22">
			<td height="22" style="height:22px;width:165px;">Allura Red</td>
			<td style="width:143px;">Sigma-Aldritch</td>
			<td style="width:119px;">458848</td>
			<td style="width:160px;"></td>
		</tr>
		<tr height="22">
			<td height="22" style="height:22px;width:165px;">Erioglaucine disodium salt</td>
			<td style="width:143px;">Sigma-Aldritch</td>
			<td style="width:119px;">861146</td>
			<td style="width:160px;"></td>
		</tr>
	</tbody>
</table>

using adhesive patterning to construct 3d paper microfluidic devices

We demonstrate the use of patterned aerosol adhesives to construct both planar and nonplanar 3D paper microfluidic devices. By spraying an aerosol adhesive through a metal stencil, the overall amount of adhesive used in assembling paper microfluidic devices can be significantly reduced. We show on a simple 4-layer planar paper microfluidic device that the optimal adhesive application technique and device construction style depends heavily on desired performance characteristics. By moderately increasing the overall area of a device, it is possible to dramatically decrease the wicking time and increase device success rates while also reducing the amount of adhesive required to keep the device together. Such adhesive application also causes the adhesive to form semi-permanent bonds instead of permanent bonds between paper layers, enabling single-use devices to be non-destructively disassembled after use. Nonplanar 3D origami devices also benefit from the semi-permanent bonds during folding, as it reduces the likelihood that unrelated faces may accidently stick together. Like planar devices, nonplanar structures see reduced wicking times with patterned adhesive application vs uniformly applied adhesive.

The 4-layer device tests were performed in a sealed chamber, shielding them from any wind or breezes that might cause excessive evaporation of the limited deposited fluid volume. The majority of the wicking in the 4-layer devices is in the middle layers of the device, so differences in wicking speeds due to evaporation were expected to be minimal. Additionally, there is minimal lateral wicking, with only 13 mm between the inlet and any individual outlet, suggesting that variations in wick...

Watch this Scientific Journal Video about Using Adhesive Patterning to Construct 3D Paper Microfluidic Devices at JoVE.com

Using Adhesive Patterning to Construct 3D Paper Microfluidic Devices

We demonstrate the use of patterned aerosol adhesives to construct 3D paper microfluidic devices. This method of adhesive application forms semi-permanent bonds between layers, enabling single-use devices to be non-destructively disassembled after use and to ease folding complex nonplanar structures.

We demonstrate the use of patterned aerosol adhesives to construct both planar and nonplanar 3D paper microfluidic devices. By spraying an aerosol ...

The overall goal of this technique is to create planar and nonplanar three-dimensional paper microfluidic devices that are able to be unfolded during construction and after use through the patterning of aerosol adhesive. This method opens up a brand new design space for paper microfluidics, by removing constraints which previously kept researchers from fabricating out of plain channel networks. The primary advantages of this technique are that it significantly reduces the amount of adhesive applied during the fabrication of paper microfluidic devices, and that it enables the construction of nonplanar three-dimensional paper microfluidic circuits.First, print an array of each layer for the device onto filter paper using a solid ink printer. Place each filter paper on a hot plate at 170 degrees Celsius for two minutes, to melt the wax-based ink, and allow it to fully penetrate into the paper, forming hydrophobic barriers. Once the paper has cooled, put a different dye color in each of the branches of layer three using a micropipette.Four microliter aliquots of five millimolar dyes will suffice. Now, begin the construction. First, clamp the bottommost layer between the stencil and a stiff backing, such as a piece of plate glass.Ensure that the stencil is flat against the paper to minimize spray shadows. Then, set a metronome to 180 beats per minute and spray adhesive from approximately 24 centimeters away for four beats. Move the can across the stencil in four even motions.If the can is moved too slowly, the adhesive will accumulate on the stencil itself, clogging the stencil. If the can is moved too rapidly, not enough adhesive will be applied. Next, remove the stencil and position the next layer of the device over the freshly-sprayed layer, carefully aligning them at the edges.Firmly press the layers together. Then, spray the adhesive again. Continue this process until all the layers are tightly adhered.Onto the four-layer stack, stick a strip of packing tape across the bottom layer to prevent fluid from leaking out. Then, individual devices can be cut from the stack following the printed pattern. Like the previous procedure, print the device onto filter paper using a solid ink printer and melt the ink on a hot plate at 170 degrees Celsius for two minutes.For this procedure, also print the crease pattern in the same manner, but on regular printer paper. Once the prints have cooled, align the lines of the crease pattern to the edges of the channel patterns. Then, secure them using tape.Next, trace the crease pattern with a blunt stylus. Apply enough force to mark the device sheet but do not tear the paper. If a tear occurs, start over.This pre-creasing technique increases the accuracy and precision of the folding. Now, begin folding the device using mountain and valley folds according to the crease pattern. Folding before application of the adhesive helps speed the device assembly.Once folded, unfold it to expose the portions that require adhesive. Then, with a blade, cut out masks to limit where adhesive will get applied. Now, clamp the device flatly between the stencil with the mask and a stiff backing.Use a metronome to time out 1.3 seconds and apply the adhesive as before. If the ambient humidity is low, apply the adhesive in a humidity-controlled area so the adhesive doesn't dry too quickly. Next, remove the stencil and mask and turn the sheet over.Then, spray the back side of the paper in the same manner. Immediately remove the device from the stencil and begin folding the device. Once the device is completely folded, apply continuous pressure to the adhesive-containing portion until it is dried.To perform a wicking test on the four-layer devices, randomly select 20 devices. Place the devices where they are shielded from air currents to minimize evaporation. Then, deposit 40 microliters of water at the inlet of each device.Record the time it takes for each device to have all of its outlets completely filled with dye. For the origami devices, compare two origami peacocks, one made as previously described, and the other made without using the stencil while applying the adhesive. Then, insert one end of a small paper lead into the body of the peacock.Under controlled relative humidity, above 90%place each leg and the paper lead of each peacock into a container filled with five millimolar dye. Average wicking times and success rates for four-layer devices constructed with different amounts of applied adhesive were compared. Uniform adhesive coverage resulted in relatively high success rates that decreased with increasing quantities of adhesive.Success rates were also much higher with faster wicking times when the patterned adhesive was applied to both sides, than only one side. Failures occurred more frequently when adhesive was only applied to one side. Typical stacked device failure was characterized by outlets that failed to completely fill with dye or took longer than five minutes to fill.In origami folded devices, device failure was characterized by outlets that failed to fill with any amount of dye. These outlets were exclusively located along the two edges of the device that contained the creases. By doubling the size of the border around the channels, the success rates for both single and dual-sided adhesive applications increased.Both methods of adhesive application resulted in devices that successfully routed liquid the length of their channels and without mixing. However, the device with uniformly-applied adhesive was noticeably slower. While attempting this procedure, it's important to ensure even and consistent adhesive application.Do note that aerosol adhesive should only be applied in well-ventilated areas. After watching this video, you should have a good understanding of how to apply and use patterned adhesives to construct planar and nonplanar 3D paper microfluidic devices. This technique will allow researchers to explore the use of nonplanar structures to achieve functionality not previously found in planar devices, such as integrated actuation and sensing.

using-adhesive-patterning-to-construct-3d-paper-microfluidic-devices

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Bioengineering

7.5K Views.  University of California, Riverside. The overall goal of this technique is to create planar and nonplanar three-dimensional paper microfluidic devices that are able to be unfolded during construction and after use through the patterning of aerosol adhesive. This method opens up a brand new design space for paper microfluidics, by removing constraints which previously kept researchers from fabricating out of plain channel networks. The primary advantages of this technique are that it significantly reduces the amount of adhesive a...