Name: multi-step variable height photolithography for valved multilayer microfluidic devices
Uploaded: 2017-01-27T15:00:00
Description: Watch this Scientific Journal Video about Multi-step Variable Height Photolithography for Valved Multilayer Microfluidic Devices at JoVE.com

The authors thank Scott Longwell for helpful comments and edits to the manuscript and Robert Puccinelli for device photography. The authors acknowledge generous support from a Beckman Institute Technology Development Grant. K.B. is supported by a NSF GFRP fellowship and the TLI component of the Stanford Clinical and Translational Science Award to Spectrum (NIH TL1 TR 001084); P.F. acknowledges a McCormick and Gabilan Faculty Fellowship.

1. Multi-layer Device Design
NOTE: Features of different heights and/or photoresists must be added sequentially to the wafer during different fabrication steps to create final composite features. Therefore, designs for each separate height and photoresist to be included on a wafer must be printed on their own mask (Figure 4).
<ol>
	<li>Download a computer-assisted design (CAD) drafting program (e.g., AutoCAD Educational Version).</li>
	<li>Define the 4&#34; wafer ar...

<ol>
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R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Microfluidic+Large-Scale+Integration.">Microfluidic Large-Scale Integration.</a> Science. 298 (5593), (2002).</li><li>Li, N., Sip, C., Folch, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Microfluidic+Chips+Controlled+with+Elastomeric+Microvalve+Arrays.">Microfluidic Chips Controlled with Elastomeric Microvalve Arrays.</a> JoVE. (8), e296 (2007).</li><li>Kim, 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=Soft+lithography+for+microfluidics:+a+review.">Soft lithography for microfluidics: a review.</a> Biochip. J. 2 (1), 1-11 (2008).</li><li>Studer, V., Hang, G., Pandolfi, A., Ortiz, M., Anderson, W. F., Quake, S. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Scaling+properties+of+a+low-actuation+pressure+microfluidic+valve.">Scaling properties of a low-actuation pressure microfluidic valve.</a> J. Appl. Phys. 95 (1), 393-398 (2004).</li><li>Kartalov, E. P., Scherer, A., Quake, S. R., Taylor, C. R., Anderson, W. F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Experimentally+validated+quantitative+linear+model+for+the+device+physics+of+elastomeric+microfluidic+valves.">Experimentally validated quantitative linear model for the device physics of elastomeric microfluidic valves.</a> J. Appl. Phys. 101 (6), 064505 (2007).</li><li>Gerver, R. E., G&#243;mez-Sj&#246;berg, R., 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=Programmable+microfluidic+synthesis+of+spectrally+encoded+microspheres.">Programmable microfluidic synthesis of spectrally encoded microspheres.</a> Lab. Chip. 12 (22), 4716-4723 (2012).</li><li>Fordyce, P. M., Diaz-Botia, C. A., DeRisi, J. L., G&#243;mez-Sj&#246;berg, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Systematic+characterization+of+feature+dimensions+and+closing+pressures+for+microfluidic+valves+produced+via+photoresist+reflow.">Systematic characterization of feature dimensions and closing pressures for microfluidic valves produced via photoresist reflow.</a> Lab. Chip. 12 (21), 4287-4295 (2012).</li><li>Li, C. -. W., Cheung, C. N., Yang, J., Tzang, C. H., Yang, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=PDMS-based+microfluidic+device+with+multi-height+structures+fabricated+by+single-step+photolithography+using+printed+circuit+board+as+masters.">PDMS-based microfluidic device with multi-height structures fabricated by single-step photolithography using printed circuit board as masters.</a> The Analyst. 128 (9), 1137-1142 (2003).</li><li>Romanowsky, M. B., Abate, A. R., Rotem, A., Holtze, C., Weitz, D. A. <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+production+of+single+core+double+emulsions+in+a+parallelized+microfluidic+device.">High throughput production of single core double emulsions in a parallelized microfluidic device.</a> Lab. Chip. 12 (4), 802-807 (2012).</li><li>Mata, A., Fleischman, A. 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This work demonstrates a complete multi-step photolithography protocol for a multilayer microfluidic device with valves and variable height geometry that can be tuned for any application with simple modifications to fabrication parameters based on our online tool26 and manufacturer instructions25. This protocol is intended to demystify multilayer photolithography for researchers wishing to construct microfluidic devices beyond simple, passive one-layer molds.
<p class="...

For the past 15 years, microfluidics as a field has undergone rapid growth, with an explosion of new technologies enabling the manipulation of fluids at the micrometer scale1. Microfluidic systems are attractive platforms for wet laboratory functionality because the small volumes have the potential to realize increased speed and sensitivity while at the same time dramatically increasing throughput and reducing cost by leveraging economies of scale2,3. Multilayer microfluidic systems have made particularly significant impacts in high-throughput biochemical analysis applications such as single cell analysis4,5,6, single molecule analysis (e.g., digital PCR7), protein crystallography8, transcription factor binding assays9,10, and cellular screening11.
A central goal of microfluidics has been the development of &#34;lab on a chip&#34; devices capable of performing complex fluidic manipulations within a single device for total biochemical analysis12. The development of multi-layer soft lithography techniques has helped realize this goal by enabling creation of on-chip valves, mixers, and pumps for actively controlling fluids within small volumes13,14,15. Despite their advantages and demonstrated applications, many of these microfluidic technologies remain largely unharnessed by non-specialist users. Widespread adoption has been challenging in part due to limited access to microfabrication facilities, but also due to inadequate communication of fabrication techniques. This is especially true for multilayer microfluidic devices featuring structures for valves or complex geometries: the paucity of detailed, practical information about important design parameters and fabrication techniques often deters new researchers from embarking on projects involving the design and creation of these devices.
This article aims to address this knowledge gap by presenting a complete protocol for making multilayer microfluidic devices with valves and variable height features, starting from design parameters and moving through all fabrication steps. By focusing on the initial photolithography steps of fabrication, this protocol complements other microfluidics protocols16 that describe downstream steps of casting devices from molds and running specific experiments.
Microfluidic devices with monolithic on-chip valves are composed of two layers: a &#34;flow&#34; layer, where the fluid of interest is manipulated in microchannels, and a &#34;control&#34; layer, where microchannels containing air or water can selectively modulate fluid flow in the flow layer14. These two layers are each fabricated on a separate silicon molding master, which is subsequently used for polydimethylsiloxane (PDMS) replica molding in a process called &#34;soft lithography17.&#34; To form a multilayer device, each of the PDMS layers are cast on their respective molding masters and then aligned to one another, thereby forming a composite PDMS device with channels in each layer. Valves are formed at locations where flow and control channels cross one another and are separated by only a thin membrane; pressurization of the control channel deflects this membrane to occlude the flow channel and locally displace the fluid (Figure 1).
Active on-chip valves can be fabricated in multiple ways, depending on the desired final application. Valves can be configured in either a &#34;push down&#34; or &#34;push up&#34; geometry, depending on whether the control layer is above or below the flow layer (Figure 1)15. &#34;Push up&#34; geometries allow for lower closing pressures and higher device stability against delamination, while &#34;push down&#34; geometries allow for the flow channels to be in direct contact with the bonded substrate, conferring the advantage of selective functionalization or patterning of the substrate surface for later functionality18,19.
Valves can also be either intentionally leaky &#34;sieve&#34; valves or fully sealable, depending on the cross-sectional profile of the flow channel. Sieve valves are useful for trapping beads, cells or other macroanalytes1, and are fabricated via the use of typical negative photoresists (i.e., SU-8 series), which have rectangular profiles. When a control channel is pressurized over these valve regions, the PDMS membrane between the control and flow layer deflects isotropically into the rectangular profile of the valve without sealing the corners, permitting fluid flow but trapping macro scale particles (Figure 1). Conversely, fully-sealable microfluidic valves are fabricated by including a small patch of rounded photoresist at valve locations. With this geometry, pressurization of the control channel deflects the membrane against the rounded flow layer to completely seal the channel, halting fluid flow. Rounded profiles in the flow layer are generated via the melting and reflow of positive photoresist (e.g., AZ50 XT or SPR 220) after typical photolithography steps. We have previously demonstrated that post-reflow heights of valve regions depend on chosen feature dimensions21. This protocol demonstrates the fabrication of both valve geometries within a bead synthesis device.
<img alt="Figure 1" src="/files/ftp_upload/55276/55276fig1.jpg" /> 
Figure 1: Multilayer Microfluidic Valve Geometries. Typical &#34;push up&#34; device architectures for sieve and fully sealable valves before (top) and after (bottom) pressurization. <a href="http://cloudflare.jove.com/files/ftp_upload/55276/55276fig1large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
Devices can also include complex passive features such as chaotic mixers13 and on-chip resistors20 that require features of multiple different heights within a single flow layer. To achieve a variable height flow layer, different groups have employed many methods including printed circuit board etching22, multilayer PDMS relief alignment23, or multi-step photolithography24. Our group has found multi-step photolithography on a single molding master to be an effective and reproducible method. To do this, a simple photolithography technique of building thick channels of negative photoresist (e.g., SU-8 series photoresists) in layers without development in between application of each layer is employed. Each layer is spun in negative photoresist according to its thickness using manufacturer instructions25 on the silicon master. Features of this height are then patterned onto the layer using a specific transparency mask (Figure 2) affixed to a glass mask plate and aligned to the previously spun layer before exposure. In multi-step photolithography, precise alignment between layers is critical in forming a complete variable height flow channel. After alignment, each layer is subjected to a thickness-dependent post-exposure bake. Without development, the next layer is similarly patterned. In this way, tall features can be built up on a single flow wafer layer-by-layer via the use of multiple masks. By skipping development between each step, previous photoresist layers can be used to generate composite height features (i.e., two 25 &#181;m layers can make a 50 &#181;m feature)24. Additionally, channel floor features such as chaotic mixer herringbone grooves13 can be made using layers with previously exposed features. A final development step completes the process, creating a single flow wafer with features of variable height (Figure 3).
Here, a complete protocol for multi-step photolithography that includes examples of all procedures necessary to fabricate on-chip valves and flow channels with multiple heights is provided. This fabrication protocol is presented in the context of a multi-layer microfluidic bead synthesizer that requires valves and variable-height features for its functionality. This device includes T-junctions for generating water droplets in an oil sheath, on-chip resistors to modulate flow rates through controlling Poiseuille resistance, a chaotic mixer for homogenizing droplet components, and both fully sealing and sieve valves to enable automated workflows involving multiple reagent inputs. Using multi-step photolithography, these features are each fabricated on a different layer according to height or photoresist; the following layers are constructed in this protocol: (1) Flow Round valve layer (55 &#181;m, AZ50 XT) (2) Flow Low layer (55 &#181;m, SU-8 2050) (3) Flow High layer (85 &#181;m, SU-8 2025, 30 &#181;m additive height), and (4) Herringbone Grooves (125 &#181;m, SU-8 2025, 40 &#181;m additive height) (Figure 3).
Hydrogel beads can be used for a variety of applications including selective surface functionalization for downstream assays, drug encapsulation, radiotracing and imaging assays, and cell incorporation; we previously used a more complex version of these devices to produce spectrally encoded PEG hydrogel beads containing lanthanide nanophosphors20. The designs discussed here are included in Additional Resources for any lab to use in their research efforts if desired. We anticipate that this protocol will provide an open resource for specialists and non-specialists alike interested in making multi-layer microfluidic devices with valves or complex geometries to lower the barrier to entry in microfluidics and increase the chances of fabrication success.

<table border="0" cellpadding="0" cellspacing="0" width="1709">
	<tbody>
		<tr height="21">
			<td height="21" style="height:21px;width:459px;">Materials</td>
			<td style="width:332px;"></td>
			<td style="width:259px;"></td>
			<td style="width:659px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Mylar Transparency Masks, 5&#34;</td>
			<td>FineLine Plotting</td>
			<td></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">5&#34; Quartz Plates</td>
			<td>United Silica&#160;</td>
			<td>Custom</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">4&#34; Silicon Wafers, Test Grade</td>
			<td>University Wafer</td>
			<td>452</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">SU8 2005, 2025, 2050 photoresist</td>
			<td>Microchem</td>
			<td>Y111045, Y111069, Y111072</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Az50XT&#160;</td>
			<td>Integrated Micromaterials</td>
			<td>AZ50XT-Q</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">SU8 Developer</td>
			<td>Microchem</td>
			<td>Y020100</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">AZ400K 1:3 Developer</td>
			<td>Integrated Micromaterials</td>
			<td>AZ400K1:3-CS</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Pyrex 150 mm glass dish</td>
			<td>Sigma-Aldrich</td>
			<td>CLS3140150-1EA</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Wafer Petri Dishes, 150 mm</td>
			<td>VWR</td>
			<td>25384-326</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Wafer Tweezers&#160;</td>
			<td>Electron Microscopy Sciences (EMS)</td>
			<td>78410-2W</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Trichloro(1H,1H,2H,2H-perfluorooctyl)silane (PFOTS)</td>
			<td>Sigma-Aldrich</td>
			<td>448931-10G</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">2&#34; x 3&#34; glass slides</td>
			<td>Thomas Scientific&#160;</td>
			<td>6686K20</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">RTV 615 elastomeric base and curing agent PDMS set</td>
			<td>Momentive&#160;</td>
			<td>RTV615-1P</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Tygon Tubing, 0.02&#34; O.D.&#160;</td>
			<td>Fischer Scientific&#160;</td>
			<td>14-171-284</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Capillary PEEK tubing,&#160; 510 um OD, 125 um ID</td>
			<td>Zeus</td>
			<td>Custom</td>
			<td>360 um PEEK is readily available by Idex (catalog number: 1571)</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Cyro 4 mL tube</td>
			<td>Greiner Bio-One</td>
			<td>127279</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Epoxy, 30-minute</td>
			<td>Permatex</td>
			<td>84107</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Metal Pins, 0.025&#34; OD, .013&#34; ID</td>
			<td>New England Small Tube</td>
			<td>NE-1310-02</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Poly(ethylene glycol) diacrylate, Mn 700</td>
			<td>Sigma-Aldrich</td>
			<td>455008-100ML</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Lithium Phenyl(2,4,6-trimethylbenzoyl)phosphinate photoinitator&#160;</td>
			<td>Tokyo Chemical Industry Co.</td>
			<td>L0290</td>
			<td>We typically synthesize LAP in-house.&#160;</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">HEPES</td>
			<td>Sigma-Aldrich</td>
			<td>H4034-25G</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Light mineral oil</td>
			<td>Sigma-Aldrich</td>
			<td>330779-1L</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Span-80</td>
			<td>Sigma-Aldrich</td>
			<td>85548</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">ABIL EM 90</td>
			<td>UPI Chem</td>
			<td>420095</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Name&#160;</td>
			<td>Company</td>
			<td>Catalog Number</td>
			<td>Comments</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:459px;">Equipment</td>
			<td>Equivalent equiptment or homebuilt setups will work equally as well</td>
			<td></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Mask Aligner</td>
			<td>Karl Suss</td>
			<td>MA6</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Profilometer</td>
			<td>KLA-Tencor</td>
			<td>Alpha-Step D500</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Spin Coater</td>
			<td>Laurell Technologies</td>
			<td>WS-650-23</td>
			<td>Any spincoater can be used that accepts 100 mm wafers</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Vacuum Dessicator, Bell-Jar Style</td>
			<td>Bel-Art</td>
			<td>420100000</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Oven</td>
			<td>Cole-Palmer</td>
			<td>WU-52120-02</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">UV Spot Curing System with 3 mm LLG option</td>
			<td>Dymax</td>
			<td>41015</td>
			<td>UV LEDs, Xenon Arc Lamps, or other UV sources of the same intensity work equally as well</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">MFCS Microfluidic Fluid Control System</td>
			<td>Fluidgent</td>
			<td>MFCS-EZ</td>
			<td>Syringe pumps, custom pneumatics or other control systems can also be used</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Automated control scripting</td>
			<td>MATLAB</td>
			<td></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Hotplate</td>
			<td>Tory Pines Scientific</td>
			<td>HP30</td>
			<td>Any hotplate with uniform heating (i.e. aluminum or ceramic plates) will suffice.&#160;</td>
		</tr>
	</tbody>
</table>

multi-step variable height photolithography for valved multilayer microfluidic devices

Microfluidic systems have enabled powerful new approaches to high-throughput biochemical and biological analysis. However, there remains a barrier to entry for non-specialists who would benefit greatly from the ability to develop their own microfluidic devices to address research questions. Particularly lacking has been the open dissemination of protocols related to photolithography, a key step in the development of a replica mold for the manufacture of polydimethylsiloxane (PDMS) devices. While the fabrication of single height silicon masters has been explored extensively in literature, fabrication steps for more complicated photolithography features necessary for many interesting device functionalities (such as feature rounding to make valve structures, multi-height single-mold patterning, or high aspect ratio definition) are often not explicitly outlined. 
Here, we provide a complete protocol for making multilayer microfluidic devices with valves and complex multi-height geometries, tunable for any application. These fabrication procedures are presented in the context of a microfluidic hydrogel bead synthesizer and demonstrate the production of droplets containing polyethylene glycol (PEG diacrylate) and a photoinitiator that can be polymerized into solid beads. This protocol and accompanying discussion provide a foundation of design principles and fabrication methods that enables development of a wide variety of microfluidic devices. The details included here should allow non-specialists to design and fabricate novel devices, thereby bringing a host of recently developed technologies to their most exciting applications in biological laboratories.

Here, we demonstrate the fabrication of valved, variable height multilayer microfluidic molds by making devices capable of generating poly ethylene glycol (PEG) hydrogel beads from droplets (Figure 2). An overview of the complete fabrication process is included in Figure 3. Using design elements from previous work, the bead synthesizer employs 4 heights in its flow layer including (1) rounded AZ50 XT valves for laminar flow modulation (55...

Watch this Scientific Journal Video about Multi-step Variable Height Photolithography for Valved Multilayer Microfluidic Devices at JoVE.com

Multi-step Variable Height Photolithography for Valved Multilayer Microfluidic Devices

Multilayer microfluidic devices often involve the fabrication of master molds with complex geometries for functionality. This article presents a complete protocol for multi-step photolithography with valves and variable height features tunable to any application. As a demonstration, we fabricate a microfluidic droplet generator capable of producing hydrogel beads.

Microfluidic systems have enabled powerful new approaches to high-throughput biochemical and biological analysis. However, there remains a barrier to ...

Research

JoVE Journal

Bioengineering

Separating Beads and Cells in Multi-channel Microfluidic Devices Using Dielectrophoresis and Laminar Flow

Microfluidic devices have advanced cell studies by providing a dynamic fluidic environment on the scale of the cell for studying, manipulating, sorting ...

Fabrication of Micropatterned Hydrogels for Neural Culture Systems using Dynamic Mask Projection Photolithography

Increasingly, patterned cell culture environments are becoming a relevant technique to study cellular characteristics, and many researchers believe in the ...

Simple Microfluidic Devices for in vivo Imaging of C. elegans, Drosophila and Zebrafish

Simple Microfluidic Devices for in vivo Imaging of C. elegans, Drosophila and Zebrafish

Micro fabricated fluidic devices provide an accessible micro-environment for in vivo studies on small organisms. Simple fabrication processes are ...

Multi-step Preparation Technique to Recover Multiple Metabolite Compound Classes for In-depth and Informative Metabolomic Analysis

Metabolomics is an emerging field which enables profiling of samples from living organisms in order to obtain insight into biological processes. A vital ...

Polymeric Microneedle Array Fabrication by Photolithography

This manuscript describes the fabrication of polymeric microneedle (MN) arrays by photolithography. It involves a simple mold-free process by using a ...

Layer-by-layer Collagen Deposition in Microfluidic Devices for Microtissue Stabilization

Although microfluidics provides exquisite control of the cellular microenvironment, culturing cells within microfluidic devices can be challenging. 3D ...

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 ...

Designing Microfluidic Devices for Studying Cellular Responses Under Single or Coexisting Chemical/Electrical/Shear Stress Stimuli

Microfluidic devices are capable of creating a precise and controllable cellular micro-environment of pH, temperature, salt concentration, and other ...

Fabrication of Three-dimensional Paper-based Microfluidic Devices for Immunoassays

Paper wicks fluids autonomously due to capillary action. By patterning paper with hydrophobic barriers, the transport of fluids can be controlled and ...

Polydimethylsiloxane-polycarbonate Microfluidic Devices for Cell Migration Studies Under Perpendicular Chemical and Oxygen Gradients

This paper reports a microfluidic device made of polydimethylsiloxane (PDMS) with an embedded polycarbonate (PC) thin film to study cell migration under ...