Name: reconfigurable microfluidic channel with pin-discretized sidewalls
Uploaded: 2018-04-12T15:00:00.000+00:00
Duration: 10 min 39 s
Description: Watch this Scientific Journal Video about Reconfigurable Microfluidic Channel with Pin-discretized Sidewalls at JoVE.com

This research was supported by KAKENHI (20800048, 23700543).

1. Etching of Pins (Figure 2A)
<ol>
	<li>Degrease rectangular pins by immersion in acetone.</li>
	<li>Passivate the pins by immersing in 4 mL of 10% nitric acid, then heat the solution at 65 &#176;C for 30 min in an oven.</li>
	<li>Sonicate the pins in deionized water for 5 min to remove residual acid and dry with a paper towel. Immerse the pins in 0.5 mL of mold release agent for 2 h.Sonicate the pins in deionized water for 5 min.</li>
	<li>Fabricate an etching dish (Figure 2C).
	<ol>
		<li>Draw or inscribe two parallel lines with a 4 mm gap on a glass slide using a ruler.</li>
		<li>Apply a chemical-resistant and low viscosity adhesive to one surface of two rectangular cut coverglasses.</li>
		<li>Bond the two cut coverglasses on the glass slide at a 4 mm gap. Use the parallel line as a guide.</li>
	</ol>
	</li>
	<li>Dispense two lines of silicone adhesive on the etching dish (see Figure 2C for the position and the size of the contour). 
	NOTE: A 3D-printed template (a STL model file is included as a supplemental material) will help draw lines easily and accurately.</li>
	<li>Put the pins on the etching dish so that the 2 mm-long tips on their straight ends are immersed into the adhesive line pattern. Dispense the adhesive again to ensure that the pins are completely covered and to draw a contour. Transfer the etching dish to a humidified fermenter heated to 38 &#176;C.&#160;Wait overnight to cure the adhesive.</li>
	<li>Add 0.2 mL of 0.5 M nitric acid to 0.2 mL of 5.0 M hydrochloric acid slowly in a glass vial. 
	CAUTION: The mixture, also known as Aqua regia, is very corrosive and potentially explosive. Wear acid-proof rubber gloves and safety goggles, and exercise extreme caution when handling acids. Never store the solution. Reduce nitric acid as possible to decrease its aggressiveness.</li>
	<li>Put the etching dish on a hotplate heated to 65 &#176;C. Pour 0.4 mL of the acid mixture over the uncovered region of the pins. Wait 10 min and transfer the acid to a beaker.</li>
	<li>Neutralize all the remaining acid including the etched region of the pins with 5 mL of 0.8 M sodium bicarbonate solution in deionized water.</li>
	<li>Remove the pins from the etching dish by pulling the pins longitudinally with tweezers. Sonicate the pins in deionized water for 5 min followed by sonication in acetone for 5 min.</li>
	<li>Passivate the etched region of the pins as in step 1.2.</li>
	<li>Check the width of the etched pins with a shop microscope with a reticle. Adjust the etching time described in 1.7 so that the width of the etched region is 0.2 &#177; 0.02 mm.</li>
	<li>Transfer the pins to a glass vial containing 5 ml of 70% ethanol. Bring the vial to a laminar hood. Pick up the pins out of the vial and allow them to dry.</li>
</ol>
2. Fabrication of Silicone slab with Reservoirs and a Space for Pins.
<ol>
	<li>Fabricate a mold for a space for pins and a fixed sidewall by typical lithographic processes.
	<ol>
		<li>Coat a degreased glass slide with 1 mL of negative epoxy photoresist using a spin coater at 1,000 rpm. Dry the photoresist on a 95 &#176;C hot plate for 15 min. Repeat this step once.</li>
		<li>Spin coat the third layer of the same photoresist at 2,000 rpm on the glass slide with coated photoresist. Dry the photoresist on a 95 &#176;C hotplate for 30 min.</li>
		<li>Expose the photoresist layer to 450 mJ/cm2 of 365-nm ultraviolet light from a UV spot light source through a photoplotted film. Bake the exposed photoresist on a 95 &#176;C hotplate for 15 min. Develop the photoresist by spraying a solvent (2-methoxy-1-methylethyl acetate) using a hand sprayer, and blow-dry with nitrogen gas.</li>
		<li>Place the glass slide with patterned photoresist at the bottom of a plastic dish.</li>
	</ol>
	</li>
	<li>Pour prepolymer of polydimethylsiloxane (PDMS) onto the mold to a thickness of 3 mm.Debubble the PDMS prepolymer in a vacuum desiccator at -800 kPa for 10 min.</li>
	<li>Cure the PDMS prepolymer in an oven at 65 &#176;C for 1 h. Demold the partially cured PDMS slab using a scalpel. Fully cure the PDMS in an oven at 120&#176;C for 1 h.</li>
	<li>Along the guideline pattern, trim away irregular edges from the PDMS slab with the same scalpel. Make as precise and clean a cut as possible, particularly at the surface that defines the insertion slot (See Figure 1A) for the pins.</li>
	<li>Perforate 2 mm-diameter holes for the inlet/outlet into the ends of the main channel of the PDMS slab using biopsy punches. Similarly, perforate 1 mm-dimeter holes at the ends of the air vent channel. See Figure 1A for the channel layout and the position of these holes.</li>
</ol>
3. Assembly of the Device with In-Place Fabrication of Gap Filler and Barrier.
<ol>
	<li>Fabricate a microchannel assembly.
	<ol>
		<li>Immerse a 10 &#215; 20 mm No. 4 coverglass in a cleaning solution heated to 60 &#176;C for 10 min.</li>
		<li>Rinse the coverglasses with deionized water twice and dry at 120 &#176;C for 10 min.</li>
		<li>Plasma-bond the PDMS slab to a coverglass:
		<ol>
			<li>Place the PDMS slab (channel feature side up) and the cleaned 10 &#215; 20 mm No. 4 coverglass in the vacuum chamber of a sputter coater.</li>
			<li>Start pumping down the chamber to 60 Pa. Generate air vacuum plasma (20 mA) for 30 s.</li>
			<li>Immediately vent the chamber. Bond the channel feature side of the PDMS slab to the coverglass with their edges aligned.</li>
			<li>Place the bonded layers in a 65 &#176;C oven for 10 min.</li>
		</ol>
		</li>
		<li>Bring the bonded layers to a laminar hood using a sterile container. Sterilize them with UV light for 30 min.</li>
		<li>In the laminar hood, insert the pins into the slot so that their ends form the other sidewall of the microchannel. Adjacent pins should be different in length to avoid contact of both vertical ends (See Figure 1B). Large spacing between the vertical ends is preferable. A space of (N-1) &#215; (pin width) is possible when N kinds of pins with different pin lengths (L in Figure 2A) are prepared.</li>
	</ol>
	</li>
	<li>Fabricate a base ( Figure 2B).
	<ol>
		<li>Make or read a part file of the base and make two numerical control (NC) files (containing toolpaths; included as supplemental material) using CAD/CAM software. The first supplemental NC file uses a 4 mm-diameter end mill and the second a 1 mm-diameter end mill.</li>
		<li>Clamp a 3 mm-thick clear polymethylmethacrylate (PMMA) board onto a CNC mill.</li>
		<li>Open the first NC file on the controller of a computer NC (CNC) mill. Install a 4 mm end mill to the CNC mill and locate part zero by touching the end mill to the PMMA board. Run the NC code to cut the board. 
		NOTE: Occasionally blow the end mill tip with compressed air for cooling and chip removal.</li>
		<li>Repeat 3.2.3 using the second NC file and a 1 mm end mill.</li>
		<li>Degrease the machined parts with detergent and dry with a paper towel. Spray the parts with 70 % ethanol and bring them to a laminar hood.</li>
	</ol>
	</li>
	<li>Fabricate a pin gap filler and elastomeric barrier: 
	&#8203;NOTE: Steps 3.3.1 - 3.3.7 should be performed aseptically in a laminar hood.
	<ol>
		<li>Prepare gap filler by mixing white petrolatum and polytetrafluoroethylene powder at a 2:1 ratio by weight. Homogenize the mixture using an ultrasonic homogenizer.</li>
		<li>Pour gap filler into a dispenser syringe. Insert a plunger and push it to fill the tip of the syringe. Attach a needle and push the plunger again until the needle tip is filled. Likewise, prepare a dispenser syringe with a plunger and a needle, and fill with silicone adhesive.</li>
		<li>Connect each syringe to a pneumatic dispenser using an adapter tube. Adjust the dispense pressures for silicone adhesive and filler to 250 kPa and 280 kPa.</li>
		<li>Dispense silicone adhesive to the edge of a pocket of the base. Place a 10 &#215; 20 mm No.4 coverglass on the pocket and press it firmly to bond.</li>
		<li>Dispense silicone adhesive to a depth of approximately 1 mm to draw two segments along two outer slots of the base. Dispense gap filler to a depth of approximately 1 mm, to draw segments along the other slot.</li>
		<li>Dispense silicone adhesive to the edge of another pocket. Place a microchannel assembly (3.1) on the pocket and press it firmly to bond.</li>
		<li>Repeat 3.3.5 to ensure that both gap filler and silicone adhesive fully embed the pins and that there is no opening at the slots.</li>
		<li>Put the device in a sterile container such as a stainless steel box with lid. Transfer the container to a humidified fermenter heated to 38 &#176;C. In the laminar hood, cure&#160;the elastomeric barrier for one day.</li>
		<li>Move each pin up to 1 mm along adjacent pins to release the pins from the cured elastomeric barrier.</li>
		<li>Sterilize the device with UV light for 30 min.</li>
	</ol>
	</li>
</ol>
4. Evaluation of the Microfluidic Device
<ol>
	<li>Detect leakage using fluorescence
	<ol>
		<li>Open the microchannel using a fine tool or a desktop robot. Make the channel width as consistent throughout the channel as possible.</li>
		<li>Dilute a green fluorescent dye with deionized water at 10 &#181;M to make fluorescence solution.</li>
		<li>Add fluorescence solution to one of the end ports of the microchannel with a micropipettor. This step will fill the channel with the solution.</li>
		<li>Put the microfluidic device and two pieces of absorbent paper wet with deionized water in a large plastic dish. Incubate the dish at 37 &#176;C and 5% CO2 for at least 24 h.</li>
		<li>Record green fluorescence images of the microchannel with an inverted fluorescent microscope with a microscope camera.</li>
		<li>Open the fluorescent images with an appropriate image analysis software and confirm there is no leakage (green fluorescence) at the interface of the gap filler and the pins.</li>
	</ol>
	</li>
	<li>Seed cells to the microchannel.
	<ol>
		<li>Prepare a cell culture vessel containing 70 - 80% confluent cells (depending on cell types). Detach and suspend the cells in growth medium.</li>
		<li>Centrifuge the cells (the speed and time depend on cell types), and aspirate the medium.</li>
		<li>Resuspend the cells with a small amount of medium. Count the cells with a cell counter and adjust the cell density from 1.5 &#215; 106 to 1.5 &#215; 107 cells/mL.</li>
		<li>Open the microchannel using a fine tool or a desktop robot (Figure 1B) to make a straight 400-&#181;m-wide channel. Adjust pin positions to make the sidewall as flat throughout the channel as possible. Add cell suspension to one of the end port of the microchannel and fill the channel.</li>
		<li>Locate one of the pins that defines the sidewall of the region to start culture. Under an inverted microscope, close the two adjacent pins to enclose cells in the cell culture region.</li>
		<li>Close all pins from in order from inner to outer to expel all cells from the channel. Gently aspirate suspension from the end ports, and add medium to them.</li>
		<li>Incubate the device as described in 4.1.4. When cells are about 70 - 80% confluent, slowly open a pin to widen the culture area.</li>
	</ol>
	</li>
</ol>

<ol>
	<li>Nge, P. N., Rogers, C. I., Woolley, A. T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Advances+in+microfluidic+materials,+functions,+integration,+and+applications.">Advances in microfluidic materials, functions, integration, and applications.</a> Chem Rev. 113 (4), 2550-2583 (2013).</li><li>Araci, I. E., Brisk, P. <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+microfluidic+large+scale+integration.">Recent developments in microfluidic large scale integration.</a> Curr Opin Biotechnol. 25, 60-68 (2014).</li><li>Gu, W., Chen, H., Tung, Y. -. C., Meiners, J. -. C., Takayama, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Multiplexed+hydraulic+valve+actuation+using+ionic+liquid+filled+soft+channels+and+Braille+displays.">Multiplexed hydraulic valve actuation using ionic liquid filled soft channels and Braille displays.</a> Appl Phys Lett. 90 (3), 033505 (2007).</li><li>Konda, A., Taylor, J. M., Stoller, M. A., Morin, 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=Reconfigurable+microfluidic+systems+with+reversible+seals+compatible+with+2D+and+3D+surfaces+of+arbitrary+chemical+composition.">Reconfigurable microfluidic systems with reversible seals compatible with 2D and 3D surfaces of arbitrary chemical composition.</a> Lab Chip. 15 (9), 2009-2017 (2015).</li><li>Hahn, Y., Hong, D., Kang, J., Choi, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+Reconfigurable+microfluidics+platform+for+microparticle+separation+and+fluid+mixing.">A Reconfigurable microfluidics platform for microparticle separation and fluid mixing.</a> Micromachines. 7 (8), 139 (2016).</li><li>Kintses, B., van Vliet, L. D., Devenish, S. R. A., Hollfelder, F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Microfluidic+droplets:+new+integrated+workflows+for+biological+experiments.">Microfluidic droplets: new integrated workflows for biological experiments.</a> Curr Opin Chem Biol. 14 (5), 548-555 (2010).</li><li>Jebrail, M. J., Bartsch, M. S., Patel, K. D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Digital+microfluidics:+a+versatile+tool+for+applications+in+chemistry,+biology+and+medicine.">Digital microfluidics: a versatile tool for applications in chemistry, biology and medicine.</a> Lab Chip. 12 (14), 2452-2463 (2012).</li><li>Frey, O., Misun, P. M., Fluri, D. A., Hengstler, J. G., Hierlemann, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Reconfigurable+microfluidic+hanging+drop+network+for+multi-tissue+interaction+and+analysis.">Reconfigurable microfluidic hanging drop network for multi-tissue interaction and analysis.</a> Nat Commun. 5, 4250 (2014).</li><li>Futai, N. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Reconfigurable+microchannels+with+discretized+moving+sidewalls.">Reconfigurable microchannels with discretized moving sidewalls.</a> Chem Micro-Nano Syst. 10 (1), 24-25 (2011).</li><li>Oono, 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=Reconfigurable+microfluidic+device+with+discretized+sidewall.">Reconfigurable microfluidic device with discretized sidewall.</a> Biomicrofluidics. 11 (3), 034103 (2017).</li></ol>

The authors declare that they have no competing financial interests.

The pin-discretized microchannel is a full-featured microfluidic channel, and we believe that it has obviously high reconfigurability in channel shape compared with any existing microfluidic channels. The protocol we provided here will enable microfluidic devices capable of cell culture with gradually expanding cell culture surface area to keep the cultures under confluency for a long duration. The device will also provide in-channel patterning of cells without patterning proteins on the substrate beforehand or any other consideration at the time of design or fabrication. In addition, this reconfigurable microfluidic device easily generates strong in-channel displacement flow, which would help implement handling of such difficult-to-flow materials that very few existing microfluidic devices can handle. This means that the interaction between the cells and other microorganisms, gases, and other non-fluids can be evaluated using this device without large modifications in device design.
We have considered applying Laplace pressure or hydrostatic pressure to one inlet of the channel as external flow control methods. We do not recommend pushing liquid at a dead end because it will generate flow toward the air vent channel through the gaps between pins and the ceiling/floor of the channel. Many fluid operations do not require such pin operations. For example, mixing can be accomplished by mashing liquid by one pin (i.e., moving only one pin back and forth several times).
The most critical parts of the device are the pins. Precision in length, parallelism, perpendicularity and surface quality are required for the pins, as they must form a microchannel, must move smoothly, and must guide the movement of adjacent pins. Therefore, we recommend that the pins should be ordered from a company that specializes in precision machining by submitting a drawing similar to Figure 2A. There may be companies that require additional geometric dimensioning and explicit surface roughness directions. However, the pins are reusable if they are handled with care and occasionally passivated with nitric acid.
The elastomeric barrier is another critical feature, and its formation is the most critical step in the fabrication processes of the device. A precisely machined base will be needed to obtain repeatable and reliable results. Placing the pins on the uncured barrier is also a critical step. The pins should be kept well aligned, and embedded in the gap filler and the barrier without air bubbles. These steps prevent leakage through the pins, which is a common problem with this microfluidic device.
Other common issues in using this device are a) frictionally restrained pins, and b) cell death, and low growth rate. Possible causes for these in a) include uneven (tapered or wavy) etching of the pin middle, poor quality of the etched surface, and dimensional misfit between the pin tip height and the height of the photoresist layer on a mold for silicone slabs. Adjustment of etchant formulation, temperature, and agitation may help improve the pin movement. In addition, trial fitting without using wax or adhesive will provide hints to solve the problem. Possible factors in b) are insufficient passivation of the pins, errors in selection of adhesives for elastomeric barriers, and incomplete curing of the adhesives. Some cells may require coating inside the microchannel with fibronectin or other proteins or polymers that promote cell adhesion. In addition, optimization in cell culture practice such as trypsinization and centrifugation will decrease dead cells in the microchannel.
One of the limitations of the presented fabrication protocol is that only one of the sidewalls is discretized. The reconfigurability of the channel will further improve if the both sidewalls are built by pin arrays. Although it requires double the amount of pins and longer fabrication steps, this is a technically viable option.

Microfluidic devices - micro-sized devices that control small amounts of liquid and their flows - offer miniaturization of biomedical procedures into a &#34;chip&#34; format with increased portability and, often, affordability. As described in a recent review1, various microfluidic components consisting of spaces and positive features have been developed to realize basic and key fluidic functions such as mixing, separation, particle trapping, or reactions.
While the behavior of many microfluidic devices is determined at the design stage, some kinds of microfluidic devices allow post-fabrication changes of their structure or behavior. Here we refer to this feature as &#34;reconfigurability&#34;. The reconfigurability of microfluidic systems generally reduces the time and cost required to design a device, and/or enables customization of the microfluidic layout or functions over time.
Previously described reconfigurable microfluidic devices fall into the following three categories. In the first, deformation of elastomeric channels allows flow rates and directions to be changed during use. To gain reconfigurability, elastomeric channels are deformed by various external and controllable forces such as pneumatic pressure sources2, Braille actuators3, or compression sealing4. In the second, reconfigurable devices rely on modular designs, such as multi-layer fluidic circuits, modular channels with magnetic interconnects, and tubing-based microfluidics5. In the third, the device itself is not reconfigurable, but microdroplet transportation on electrode arrays (often referred to as digital microfluidics)6,7 and hanging drop-based microfluidic devices8 enable on-demand switching of the flow or the route of fluid.
Nonetheless, many of these reconfigurations are limited at the topological and macroscopic levels. For example, many integrated microfluidic devices stop flow or change the flow direction by collapsing microchannels in predefined regions. However, the position and number of regions to be collapsed are not reconfigurable. Although the digital microfluidics has a variety of fluid handling abilities, possible flows should be largely limited by the volume of each droplet. In addition, when cells are cultured in such droplets of cell culture media, extra effort is needed to prevent evaporation and gas dissipation from droplets and avoid osmolality shock and sudden pH change.
To realize channel feature-level reconfigurability, we proposed a microfluidic device with movable sidewalls that consisted of arrays of machine elements to dynamically reconfigure them when in use9. To form a deformable sidewall, small rectangular pins were lined up so that each end of the pins defined a segment of the sidewall. Sliding the pins allowed the deformation of the sidewall which allowed transport or patterning of cells, bubbles, and particles inside the channel. To minimize dead volume and maximize reconfigurability, the distance between the adjacent pins had to be minimized. However, strong capillary action acting on the small gaps between pins connecting the inside and outside of the microchannel causes leakage of any liquid entering the pin gap, causing media evaporation, bacterial or cytotoxic contamination, and eventually cell death. Therefore, we have developed leak-free discretized sidewall-type reconfigurable microfluidic channels that withstand cyclic pin actions and long-term cell culture10.
In this article, we provide a protocol to build microfluidic cell culture device with a discretized sidewall that can be reconfigured following the gradual increase in the cell culture area. Airtightness of the discrete channel sidewalls is tested using fluorescence imaging. The cell-culture compatibility and the ability of cell patterning are evaluated using on-chip cell culture.
This microfluidic system is suitable whenever appropriate channel design cannot be predetermined and must be changed on demand. For example, this system could be used to adjust the channel width and flow rate based on the cell growth or migration, to flow or trap active nematodes or other small objects that behave unexpectedly in the channel, or to accept various raw samples or bioproducts that were not yet conceived at the time of design.

<table><tbody><tr><td>Oven</td><td>Yonezawa</td><td>MI-100</td><td></td></tr><tr><td>10% Nitric Acid</td><td>Wako Chemicals</td><td>149-06845</td><td></td></tr><tr><td>Stainless steel pins</td><td>Micro Giken</td><td>N/A</td><td>0.3 mm crosssection, Grade 316L stainless steel, wire-cut EDM</td></tr><tr><td>Mold release agent</td><td>Fluoro Technology</td><td>FG-5093SH</td><td></td></tr><tr><td>Polydimethylsiloxane (PDMS)</td><td>Shin-Etsu Chemicals</td><td>KE-106</td><td></td></tr><tr><td>Negative epoxy photoresist</td><td>Nippon Kayaku</td><td>SU-8 3050</td><td></td></tr><tr><td>Coverglasses (Rectangular)</td><td>Matsunami Glass</td><td>26 x 60mm No.4</td><td></td></tr><tr><td>Acetone</td><td>Kanto Chemicals</td><td>01060-79</td><td></td></tr><tr><td>Glass slides (Large)</td><td>Matsunami Glass</td><td>76 x 52mm No.1</td><td></td></tr><tr><td>Silicone adhesive</td><td>Shin-Etsu Chemicals</td><td>KE-41</td><td></td></tr><tr><td>White petrolatum</td><td>Nikko Rica</td><td>Sun White P-1</td><td></td></tr><tr><td>Polytetrafluoroethylene (PTFE) powder</td><td>Power House Accele</td><td>Microfluon II</td><td></td></tr><tr><td>Clear acrylic plate (3 mm-thick)</td><td>Various</td><td>N/A</td><td></td></tr><tr><td>Pneumatic dispenser</td><td>Musashi Engineering</td><td>ML-5000XII</td><td></td></tr><tr><td>Hydrochloric acid</td><td>Kanto Chemicals</td><td>180768-00</td><td></td></tr><tr><td>Computer numerical control (CNC) mill</td><td>Pro Spec Tools</td><td>PSF240-CNC</td><td></td></tr><tr><td>End mill (4 mm diameter)</td><td>Mitsubishi Materials</td><td>MS2MSD0400</td><td></td></tr><tr><td>End mill (1 mm diameter)</td><td>Mitsubishi Materials</td><td>MS2MSD0100</td><td></td></tr><tr><td>Adhesive (chemical-resistant and low viscosity )</td><td>Cotronics</td><td>Duralco 4460</td><td></td></tr><tr><td>Borisilicate glass vials</td><td>Various</td><td></td><td>To prepare HNO3+HCl solution (Aqua regia). Always select borosilicate glass.</td></tr><tr><td>Sodium bicarbonate</td><td>Kanto Chemicals</td><td>37116-00</td><td></td></tr><tr><td>Ultrasonic cleaner</td><td>AS ONE</td><td>AS12GTU</td><td></td></tr><tr><td>Ultrasonic drill</td><td>Shinoda Tools</td><td>SOM-121</td><td>Used as a ultrasonic homogenizer.</td></tr><tr><td>Spin coater</td><td>Active</td><td>ACT-220DII</td><td></td></tr><tr><td>Hotplate</td><td>AS ONE</td><td>ND-1</td><td></td></tr><tr><td>Photoplotted film (12,700 dpi)</td><td>Unno Giken</td><td>N/A</td><td>Negative image of the recess at the bottom of a PDMS slab are plotted.</td></tr><tr><td>2-methoxy-1-methylethyl acetate</td><td>Wako Chemicals</td><td>130-10505</td><td></td></tr><tr><td>UV spot light source</td><td>Hamamatsu</td><td>L8327</td><td>Ultraviolet source</td></tr><tr><td>Nitrogen</td><td>Various</td><td>N/A</td><td></td></tr><tr><td>Vacuum desiccator and pump</td><td>AS ONE</td><td>MVD-100, GM-20S</td><td></td></tr><tr><td>Scalpels</td><td>Various</td><td>No.11</td><td></td></tr><tr><td>Biopsy punches (1.0mm and 2.0mm)</td><td>Kai Medical</td><td>BP-10F(1.0m), BP-20F(2.0mm)</td><td></td></tr><tr><td>Glass engraving pen</td><td>Various</td><td>N/A</td><td></td></tr><tr><td>Cleaning solution</td><td>Tama Chemicals</td><td>TMSC</td><td>Dilute 1:100 with deionized water</td></tr><tr><td>Sputter coater</td><td>San-yu Electron</td><td>SC-708</td><td>For plasma bonding.</td></tr><tr><td>Dispenser syringe (5 ml)</td><td>Musashi Engineering</td><td>PSY-5E</td><td></td></tr><tr><td>Plunger</td><td>Musashi Engineering</td><td>FLP-5E</td><td></td></tr><tr><td>Blunt needle (21G)</td><td>Musashi Engineering</td><td>PN-21G-B</td><td></td></tr><tr><td>Adapter tube</td><td>Musashi Engineering</td><td>AT-5E</td><td></td></tr><tr><td>Fermenter</td><td>Japan Kneader</td><td>PF100</td><td></td></tr><tr><td>Green fluorescent dye (Alexa Fluor 488 carboxylic acid)</td><td>Thermo Fisher</td><td>A33077</td><td></td></tr><tr><td>Large plastic dish</td><td>Greiner bio-one</td><td>688161</td><td></td></tr><tr><td>Absorbent paper</td><td>Asahi Kasei</td><td>BEMCOT M-1</td><td></td></tr><tr><td>Inverted microscope</td><td>Leica</td><td>DMi8</td><td></td></tr><tr><td>Microscope camera</td><td>Qimaging</td><td>Retiga 2000R</td><td></td></tr><tr><td>Dulbecco modified Eagle medium (DMEM)</td><td>GE Health Care</td><td>SH30021.01</td><td></td></tr><tr><td>Antibiotic-antimycotic solution</td><td>Thermo Fisher</td><td>15240-062</td><td></td></tr><tr><td>Trypsin/EDTA solution</td><td>Thermo Fisher</td><td>25200-056</td><td></td></tr><tr><td>Phosphate buffered saline (PBS)</td><td>GE Health Care</td><td>SH30256.01</td><td></td></tr><tr><td>Fetal bovine serum (FBS)</td><td>Biowest</td><td>S1820</td><td></td></tr><tr><td>Cell counter</td><td>FPI</td><td>OC-C-S02</td><td></td></tr><tr><td>Cell culture vessel</td><td>VIOLAMO</td><td>VTC-D100</td><td></td></tr><tr><td>15 ml conical tube</td><td>Corning</td><td>352095</td><td></td></tr><tr><td>Shop microscope</td><td>PEAK</td><td>2034-20</td><td></td></tr><tr><td>Hand sprayer</td><td>FURUPLA</td><td>No.3530</td><td></td></tr><tr><td>Coverglasses (Rectangular)</td><td>Matsunami Glass</td><td>10 x 20mm No.4</td><td></td></tr><tr><td>CAD/CAM software</td><td>Autodesk</td><td>Inventor HSM</td><td></td></tr><tr><td>Nitrogen gas pressure regulator</td><td>AS ONE</td><td>GF1-2506-RN-V</td><td>Set to 0.1 MPa</td></tr></tbody></table>

reconfigurable microfluidic channel with pin-discretized sidewalls

Microfluidic components need to have various shapes to realize different key microfluidic functions such as mixing, separation, particle trapping, or reactions. A microfluidic channel that deforms even after fabrication while retaining the channel shape enables high spatiotemporal reconfigurability. This reconfigurability is required in such key microfluidic functions that are difficult to achieve in existing "reconfigurable" or "integrated" microfluidic systems. We describe a method for the fabrication of a microfluidic channel with a deformable sidewall consisting of a laterally aligned array of the ends of rectangular pins. Actuating the pins in their longitudinal directions changes the pins' end positions, and thus, the shape of discretized channel sidewalls.Pin gaps can cause unwanted leakage or adhesion to adjacent pins caused by meniscus forces. To close the pin gaps, we have introduced hydrocarbon-fluoropolymer suspension-based gap filler accompanied by an elastomeric barrier. This reconfigurable microfluidic device can generate strong temporal in-channel displacement flow, or can stop the flow in any region of the channel. This feature will facilitate, on demand, the handling of cells, viscous liquids, gas bubbles, and non-fluids, even if their existence or behavior is unknown at the time of fabrication.

The construction of the reconfigurable microchannel is shown in Figure 1. Multiple rectangular pins were placed on a glass substrate and were lined up so that the long side of the pins were in contact. A PDMS sheet with punched holes and a recess of the same depth as the pin height covered the ends of the pins to form the channel inlet/outlet reservoirs, channel ceiling, and another sidewall opposite to the channel wall that consisted of the pins. The region surrounded by pins, a wall (one of the faces of the PDMS sheet), and the glass substrate form one microfluidic channel.
As previously described, the reconfigurability of the proposed microfluidic system is achieved by many small pins placed in parallel with very small but non-zero gaps. The problem in previous reports was the strong flow generated through the gaps by the capillary effect. To overcome this problem, the gaps were first filled with a gap filler. In this protocol, a disperse mixture of viscous hydrocarbon and fluoropolymer powder was used as a gap filler. However, the gap filler itself is also subject to the capillary effect. Therefore, as shown in Figure 1, the resulting reconfigurable microchannel has both hydrocarbon/fluoropolymer gap filler and an elastomeric barrier formed around the outer perimeter of the gap filler. Thinning the middle of the pins is needed to accommodate a sufficient amount of gap filler to ensure the thickness and strength of the elastomeric barrier between two pins.
Figure 2A shows a drawing of a pin that forms a sidewall segment. Stainless steel grade 316L was selected as the material due to its corrosion-resistant and low leaching properties. However, an extra passivation process was required to make pins cell culture compatible. A pin must have a precisely rectangular tip without burrs to successfully form a sidewall segment. In addition, a pin must have a &#34;handle&#34; so that the pin can easily be moved by pushing the handle. Because each pin has a narrow middle, the thickness of elastomer between pins was enough to withstand shear caused by pin movement. Unlike other parts comprising the device, the fabrication of pins, except middle thinning, should be ordered from a company specializing in electrical discharge machining (EDM) because it is one of the most precise and cost-effective methods of machining small parts made of hard metals. Performing middle thinning by etching yourself reduces the cost of machining and the risk of bending or breaking during machining.
To confirm that the gap filler, the elastomeric barrier, and eventually the watertightness of the reconfigurable microchannel function properly, leak detection by fluorescence was used. Figure 3 shows a fluorescence image of the area near the edge of the elastomeric barrier 3 days after the microchannel was filled with water containing fluorescent tracer dye. The fluorescence image shows that the liquid filling the channel reached a depth of about 200 &#181;m from the visible edge of the elastomeric barrier. However, the liquid did not reach the gap filler. Additionally, no leakage of gap filler through the elastomeric barrier was observed. This observation indicates that the tight fit between the narrow middle of the pins and elastomeric barrier prevented the migration of liquid through the gaps.
Finally, we performed long-term cell culture with the culture area adapted by gradually expanding the sidewall of the reconfigurable microfluidic device as shown in Figure 4A. At 0 d, a small number of cells were confined within a space equal to one pin-width and other cells were aspirated. At 2 d, the cells were attached to the bottom surface and started proliferating. Two pins were retracted so that all cells were clearly visible, although the confluency was still low. At 5 d, the cells continued to proliferate and the confluency increased. At 6 and 9 d, two other pins were retracted to keep the cells underconfluent. The effect of gradual expansion of the culture area is shown in Figure 4B. There were sudden changes in the cell density on the day the pin(s) were retracted. However, the growth rate of the cell count was kept constant, while that seen in typical cell culture is exponential.
<img alt="Figure 1" class="xfigimg" src="/files/ftp_upload/57230/57230fig1.jpg" /> 
Figure 1: Reconfigurable microfluidic device with one pin-discretized sidewall.&#160;(A) Parts and construction of a reconfigurable microfluidic device. The device has one straight channel with one sidewall formed by the ends of 10 stainless steel pins inserted into PDMS/glass microchannel features. Gap filler and an elastomeric barrier prevents liquid from leaking through the pin gaps. Coverglasses, gap filler, and the elastomer barrier are fixed to a polymethylmethacrylate (PMMA) base. (B) Automated pin manipulator. An end effector made from a sheet of metal is fixed to a 3-axis desktop robot. To move one pin, the end effector pushes its vertical end. Pins with different lengths are placed at an interval of three times the pin width. The interval ensures that the end effector mates one pin at one time with enough clearance. <a href="https://cloudflare.jove.com/files/ftp_upload/57230/57230fig1large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 2" class="xfigimg" src="/files/ftp_upload/57230/57230fig2.jpg" /> 
Figure 2: Mechanical drawing of machined parts used in the protocol. Units are in millimeters; R indicates a radius dimension; the square symbol (&#9633;) indicates square features; t indicates thickness. (A) A 316L stainless steel pin as a part of the sidewall. Pins can be ordered and machined as described. Thinning of the pin middle to make dog bone-like shapes is not reflected in this drawing because this was not ordered as part of the machining but was performed as part of the protocol. (B) A polymethylmethacrylate (PMMA) base that holds the coverglasses, gap filler and elastomeric barrier in place against pin movement. (C) An etching dish that is used to etch the middle of pins. To build an etching dish, four pieces of glass are bonded using silicone adhesive. A contour pattern of silicone adhesive is drawn on the dish followed by placement of the pins on the dish as shown in the drawing. <a href="https://cloudflare.jove.com/files/ftp_upload/57230/57230fig2large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 3" class="xfigimg" src="/files/ftp_upload/57230/57230fig3.jpg" /> 
Figure 3: Fluorescence detection of leakage from a reconfigurable microchannel through pin gaps. Fluorescence image of green fluorescent dye filling the reconfigurable microchannel is overlaid on a phase contrast image of the seal structure, which consists of a gap filler (opaque) and elastomeric barrier (translucent). An edge of the elastomer barrier is visible as meniscus-like features and is denoted by an upper dotted line; the interface between elastomer barrier and gap filler is shown as meniscus-like features that contact the black area and is indicated by the lower dotted line. <a href="https://cloudflare.jove.com/files/ftp_upload/57230/57230fig3large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 4" class="xfigimg" src="/files/ftp_upload/57230/57230fig4.jpg" /> 
Figure 4: Progressive and continuous cell growth with variable cell culture area in a reconfigurable microchannel. (A) COS-7 cell growth in a cell culture area confined by moving sidewalls. (B) Growth curve and time evolution of the density of COS-7 cells confined in variable-size culture areas in the reconfigurable microchannel shown in A). Three vertical arrows denote expansion of the cell culture area at 2, 5, and 6 d, respectively. In addition to cell count, cell densities are shown for the same culture areas, fitted individually to each exponential growth curve, and used to estimate the local doubling time (td [h]) shown in the frames. <a href="https://cloudflare.jove.com/files/ftp_upload/57230/57230fig4large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>

Watch this Scientific Journal Video about Reconfigurable Microfluidic Channel with Pin-discretized Sidewalls at JoVE.com

Reconfigurable Microfluidic Channel with Pin-discretized Sidewalls

A microfluidic channel with deformable sidewalls offers flow control, particle handling, channel dimension customization and other reconfigurations while in use. We describe a method for fabricating a microfluidic channel with sidewalls made of an array of pins that allows their shape to change.

Microfluidic components need to have various shapes to realize different key microfluidic functions such as mixing, separation, particle trapping, or ...

reconfigurable-microfluidic-channel-with-pin-discretized-sidewalls

Research

JoVE Journal

Bioengineering

7.5K Views.  Shibaura Institute of Technology. A microfluidic channel with deformable sidewalls offers flow control, particle handling, channel dimension customization and other reconfigurations while in use. We describe a method for fabricating a microfluidic channel with sidewalls made of an array of pins that allows their shape to change.

Video: Reconfigurable Microfluidic Channel with Pin-discretized Sidewalls

A Microfluidic-based Hydrodynamic Trap for Single Particles

The ability to confine and manipulate single particles in free solution is a key enabling technology for fundamental and applied science. Methods for particle trapping based on optical, magnetic, electrokinetic, and acoustic techniques have led to major advancements in physics and biology ranging from the molecular to cellular level. In this article, we introduce a new microfluidic-based technique for particle trapping and manipulation based solely on hydrodynamic fluid flow. Using this method, we demonstrate trapping of micro- and nano-scale particles in aqueous solutions for long time scales. The hydrodynamic trap consists of an integrated microfluidic device with a cross-slot channel geometry where two opposing laminar streams converge, thereby generating a planar extensional flow with a fluid stagnation point (zero-velocity point). In this device, particles are confined at the trap center by active control of the flow field to maintain particle position at the fluid stagnation point. In this manner, particles are effectively trapped in free solution using a feedback control algorithm implemented with a custom-built LabVIEW code. The control algorithm consists of image acquisition for a particle in the microfluidic device, followed by particle tracking, determination of particle centroid position, and active adjustment of fluid flow by regulating the pressure applied to an on-chip pneumatic valve using a pressure regulator. In this way, the on-chip dynamic metering valve functions to regulate the relative flow rates in the outlet channels, thereby enabling fine-scale control of stagnation point position and particle trapping. The microfluidic-based hydrodynamic trap exhibits several advantages as a method for particle trapping. Hydrodynamic trapping is possible for any arbitrary particle without specific requirements on the physical or chemical properties of the trapped object. In addition, hydrodynamic trapping enables confinement of a "single" target object in concentrated or crowded particle suspensions, which is difficult using alternative force field-based trapping methods. The hydrodynamic trap is user-friendly, straightforward to implement and may be added to existing microfluidic devices to facilitate trapping and long-time analysis of particles. Overall, the hydrodynamic trap is a new platform for confinement, micromanipulation, and observation of particles without surface immobilization and eliminates the need for potentially perturbative optical, magnetic, and electric fields in the free-solution trapping of small particles.

In this article, we present a microfluidic-based method for particle confinement based on hydrodynamic flow. We demonstrate stable particle trapping at a fluid stagnation point using a feedback control mechanism, thereby enabling confinement and micromanipulation of arbitrary particles in an integrated microdevice.

The ability to confine and manipulate single particles in free solution is a key enabling technology for fundamental and applied science.  Methods for ...

Microfluidic Chips Controlled with Elastomeric Microvalve Arrays

Miniaturized microfluidic systems provide simple and effective solutions for low-cost point-of-care diagnostics and high-throughput biomedical assays. Robust flow control and precise fluidic volumes are two critical requirements for these applications. We have developed microfluidic chips featuring elastomeric polydimethylsiloxane (PDMS) microvalve arrays that: 1) need no extra energy source to close the fluidic path, hence the loaded device is highly portable; and 2) allow for microfabricating deep (up to 1 mm) channels with vertical sidewalls and resulting in very precise features.

The PDMS microvalves-based devices consist of three layers: a fluidic layer containing fluidic paths and microchambers of various sizes, a control layer containing the microchannels necessary to actuate the fluidic path with microvalves, and a middle thin PDMS membrane that is bound to the control layer. Fluidic layer and control layers are made by replica molding of PDMS from SU-8 photoresist masters, and the thin PDMS membrane is made by spinning PDMS at specified heights. The control layer is bonded to the thin PDMS membrane after oxygen activation of both, and then assembled with the fluidic layer. The microvalves are closed at rest and can be opened by applying negative pressure (e.g., house vacuum). Microvalve closure and opening are automated via solenoid valves controlled by computer software.

Here, we demonstrate two microvalve-based microfluidic chips for two different applications. The first chip allows for storing and mixing precise sub-nanoliter volumes of aqueous solutions at various mixing ratios. The second chip allows for computer-controlled perfusion of microfluidic cell cultures.

The devices are easy to fabricate and simple to control. Due to the biocompatibility of PDMS, these microchips could have broad applications in miniaturized diagnostic assays as well as basic cell biology studies.

We demonstrate protocols for manufacturing and automating elastomeric polydimethylsiloxane (PDMS)-based microvalve arrays that need no extra energy to close and feature photolithographically defined precise volumes. A parallel subnanoliter-volume mixer and an integrated microfluidic perfusion system are presented.

Miniaturized microfluidic systems provide simple and effective solutions for low-cost point-of-care diagnostics and high-throughput biomedical assays.  ...

Biology

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

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

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

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

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

Microfluidic Fabrication of Polymeric and Biohybrid Fibers with Predesigned Size and Shape

A &#8220;sheath&#8221; fluid passing through a microfluidic channel at low Reynolds number can be directed around another &#8220;core&#8221; stream and used to dictate the shape as well as the diameter of a core stream.&#160;Grooves in the top and bottom of a microfluidic channel were designed to direct the sheath fluid and shape the core fluid.&#160;By matching the viscosity and hydrophilicity of the sheath and core fluids, the interfacial effects are minimized and complex fluid shapes can be formed.&#160;Controlling the relative flow rates of the sheath and core fluids determines the cross-sectional area of the core fluid.&#160;Fibers have been produced with sizes ranging from 300 nm to ~1 mm, and fiber cross-sections can be round, flat, square, or complex as in the case with double anchor fibers. Polymerization of the core fluid downstream from the shaping region solidifies the fibers.&#160;Photoinitiated click chemistries are well suited for rapid polymerization of the core fluid by irradiation with ultraviolet light.&#160;Fibers with a wide variety of shapes have been produced from a list of polymers including liquid crystals, poly(methylmethacrylate), thiol-ene and thiol-yne resins, polyethylene glycol, and hydrogel derivatives. Minimal shear during the shaping process and mild polymerization conditions also makes the fabrication process well suited for encapsulation of cells and other biological components.

Two adjacent fluids passing through a grooved microfluidic channel can be directed to form a sheath around a prepolymer core; thereby&#160;determining both shape and cross-section. Photoinitiated polymerization, such as thiol click chemistry, is well suited for rapidly solidifying the core fluid into a microfiber with predetermined size and shape.

A &#8220;sheath&#8221; fluid passing through a microfluidic channel at low Reynolds number can be directed around another &#8220;core&#8221; stream and ...

One-Step Approach to Fabricating Polydimethylsiloxane Microfluidic Channels of Different Geometric Sections by Sequential Wet Etching Processes

Polydimethylsiloxane (PDMS) materials are substantially exploited to fabricate microfluidic devices by using soft lithography replica molding techniques. Customized channel layout designs are necessary for specific functions and integrated performance of microfluidic devices in numerous biomedical and chemical applications (e.g., cell culture, biosensing, chemical synthesis, and liquid handling). Owing to the nature of molding approaches using silicon wafers with photoresist layers patterned by photolithography as master molds, the microfluidic channels commonly have regular cross sections of rectangular shapes with identical heights. Typically, channels with multiple heights or different geometric sections are designed to possess particular functions and to perform in various microfluidic applications (e.g., hydrophoresis is used for sorting particles and in continuous flows for separating blood cells6,7,8,9). Therefore, a great deal of effort has been made in constructing channels with various sections through multiple-step approaches like photolithography using several photoresist layers and assembly of different PDMS thin sheets. Nevertheless, such multiple-step approaches usually involve tedious procedures and extensive instrumentation. Furthermore, the fabricated devices may not perform consistently and the resulted experimental data may be unpredictable. Here, a one-step approach is developed for the straightforward fabrication of microfluidic channels with different geometric cross sections through PDMS sequential wet etching processes, that introduces etchant into channels of planned single-layer layouts embedded in PDMS materials. Compared to the existing methods for manufacturing PDMS microfluidic channels with different geometries, the developed one-step approach can significantly simplify the process to fabricate channels with non-rectangular sections or various heights. Consequently, the technique is a way of constructing complex microfluidic channels, which provides a fabrication solution for the advancement of innovative microfluidic systems.

Several methods are available for the fabrication of channels of non-rectangular sections embedded in polydimethylsiloxane microfluidic devices. Most of them involve multistep manufacturing and extensive alignment. In this paper, a one-step approach is reported for fabricating microfluidic channels of different geometric cross sections by polydimethylsiloxane sequential wet etching.

Polydimethylsiloxane (PDMS) materials are substantially exploited to fabricate microfluidic devices by using soft lithography replica molding techniques. ...

Engineering

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.

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 ...

Soft Lithographic Procedure for Producing Plastic Microfluidic Devices with View-ports Transparent to Visible and Infrared Light

Infrared (IR) spectro-microscopy of living biological samples is hampered by the absorption of water in the mid-IR range and by the lack of suitable microfluidic devices. Here, a protocol for the fabrication of plastic microfluidic devices is demonstrated, where soft lithographic techniques are used to embed transparent Calcium Fluoride (CaF2) view-ports in connection with observation chamber(s). The method is based on a replica casting approach, where a polydimethylsiloxane (PDMS) mold is produced through standard lithographic procedures and then used as the template to produce a plastic device. The plastic device features ultraviolet/visible/infrared (UV/Vis/IR) -transparent windows made of CaF2 to allow for direct observation with visible and IR light. The advantages of the proposed method include: a reduced need for accessing a clean room micro-fabrication facility, multiple view-ports, an easy and versatile connection to an external pumping system through the plastic body, flexibility of the design, e.g., open/closed channels configuration, and the possibility to add sophisticated features such as nanoporous membranes.

A protocol for the fabrication of plastic microfluidic devices with transparent view-ports for visible and infrared light imaging is described.

Infrared (IR) spectro-microscopy of living biological samples is hampered by the absorption of water in the mid-IR range and by the lack of suitable ...

Generation of Dynamical Environmental Conditions using a High-Throughput Microfluidic Device

Mimicking in vivo environmental conditions is crucial for in vitro studies on complex life machinery. However, current techniques targeting live cells and organs are either highly expensive, like robotics, or lack nanoliter volume and millisecond time accuracy in liquid manipulation. We herein present the design and fabrication of a microfluidic system, which consists of 1,500 culture units, an array of enhanced peristaltic pumps and an on-site mixing modulus. To demonstrate the capacities of the microfluidic device, neural stem cell (NSC) spheres are maintained in the proposed system. We observed that when the NSC sphere is exposed to CXCL in day 1 and EGF in day 2, the round-shaped conformation is well maintained. Variation in the input order of 6 drugs causes morphological changes to the NSC sphere and the expression level representative marker for NSC stemness (i.e., Hes5 and Dcx). These results indicate that dynamic and complex environmental conditions have great effects on NSC differentiation and self-renewal, and the proposed microfluidic device is a suitable platform for high throughput studies on the complex life machinery.

We present a microfluidic system for high throughput studies on complex life machinery, which consists of 1500 culture units, an array of enhanced peristaltic pumps and an on-site mixing modulus. The microfluidic chip allows for the analysis of the highly complex and dynamic micro-environmental conditions in vivo.

Mimicking in vivo environmental conditions is crucial for in vitro studies on complex life machinery. However, current techniques targeting live cells and ...

Setup of a Microfluidic Device for Combinatorial Plug  Production

Bilayer Microfluidic Device for Combinatorial Plug Production

Droplet microfluidics is a versatile tool that allows the execution of a large number of reactions in chemically distinct nanoliter compartments. Such systems have been used to encapsulate a variety of biochemical reactions - from incubation of single cells to implementation of PCR reactions, from genomics to chemical synthesis. Coupling the microfluidic channels with regulatory valves allows control over their opening and closing, thereby enabling the rapid production of large-scale combinatorial libraries consisting of a population of droplets with unique compositions. In this paper, protocols for the fabrication and operation of a pressure-driven, PDMS-based bilayer microfluidic device that can be utilized to generate combinatorial libraries of water-in-oil emulsions called plugs are presented. By incorporating software programs and microfluidic hardware, the flow of desired fluids in the device can be controlled and manipulated to generate combinatorial plug libraries and to control the composition and quantity of constituent plug populations. These protocols will expedite the process of generating combinatorial screens, particularly to study drug response in cells from cancer patient biopsies.

Author Spotlight: Integrating Computational and Experimental Approaches in Precision Oncology

The fabrication of a polydimethylsiloxane (PDMS)-based bilayer device for the production of combinatorial libraries in water-in-oil emulsions (plugs) is presented here. The necessary hardware and software required to automate plug production are detailed in the protocol, and the production of a quantitative library of fluorescent plugs is also demonstrated.

Droplet microfluidics is a versatile tool that allows the execution of a large number of reactions in chemically distinct nanoliter compartments. Such ...