Name: fabricating high-viscosity droplets using microfluidic capillary device with phase-inversion co-flow structure
Uploaded: 2018-04-17T14:00:00
Description: Watch this Scientific Journal Video about Fabricating High-viscosity Droplets using Microfluidic Capillary Device with Phase-inversion Co-flow Structure at JoVE.com

This work was supported by the National Natural Science Foundation of China (Nos. 51420105006 and 51322501). We thank Daniel for his helpful discussion on the high viscosity ideas.

1. Producing a Phase-Inversion Co-Flow Capillary Device for Observing the Generation Process of Aqueous, High-Viscosity Droplets with a Diameter of ~500 &#956;m.
NOTE: The square outer tube used here is for taking images of the generation process of the high-viscosity droplets. If there is no need to take images, a simplified version of the device can be made according to protocol step 2.
<ol>
	<li>Prepare three glass tubes with different sizes for the assembly of the capillary devic...

<ol>
	<li>Shah, R. K., Shum, H. C., Rowat, A. C., Lee, D., Agresti, J. J., Utada, A. S., Chu, L. Y., Kim, J. W., Fernandez-Nieves, A., Martinez, C. J., 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=Designer+emulsions+using+microfluidics.">Designer emulsions using microfluidics.</a> Mater. Today. 11, 18-27 (2008).</li><li>Park, J. I., Saffari, A., Kumar, S., G&#252;nther, A., Kumacheva, E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Microfluidic+synthesis+of+polymer+and+inorganic+particulate+materials.">Microfluidic synthesis of polymer and inorganic particulate materials.</a> Annu. Rev. Mater. Res. 40, 415-443 (2010).</li><li>Heath, J. R., Ribas, A., Mischel, P. 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The phase-inversion co-flow device provides a simple and straight forward method to generate monodisperse high-viscosity droplets. This device has a similar structure to common co-flow devices, as the basic co-flow structure consists of an inner tube inserted in the middle tube, the exit of which is connected to outlet tubing. However, there are two main differences between the phase-inversion co-flow device and common co-flow device for the generation of high-viscosity droplets with a viscosity of &#951;&#160;&...

The generation of droplets is becoming a key technology in a variety of applications, such as drug delivery, materials synthesis, 3D bioprinting, cell assays, and food engineering1,2,3,4,5,6. Microfluidic devices with T-junction7,8, co-flow1,9, or flow-focusing10,11 structures are widely used to generate monodisperse single emulsion droplets. Selection of a more viscous continuous phase will facilitate the formation of droplets12, and the viscosities of both the continuous and dispersed fluids are commonly below 0.1 Pas in droplet microfluidics13. However, in many applications, the dispersed phase may have a viscosity several hundred times higher than that of water, such as glycerol14, solutions containing nanoparticles15, proteins16, or polymers17,18,19, while it is difficult to achieve monodisperse droplets directly from high-viscosity fluids in a stable dripping regime11 in microfluidic devices, especially for fluids with a viscosity of &#951;&#160;&#62;&#160;1&#160;Pa&#183;s14,17,18,19. Furthermore, it has been reported13,18 that typical microfluidic methods for droplet formation require fluids with a relatively low viscosity and moderate interfacial tension to form uniform droplets in a stable dripping regime.
For a dispersed phase with a viscosity slightly larger than 0.1 Pas, there are several possible approaches to facilitate the droplet formation with typical T-junction, co-flow, or flow-focusing microfluidic devices: (1) decrease the viscosity of the dispersed phase by diluting it in an volatile solvent11,20; (2) decrease the dispersed-to-continuous viscosity ratio by increasing the viscosity of the continuous phase1,11; (3) decrease the flow rate of the dispersed phase to an extremely low value, while keeping a high continuous-to-dispersed flow rate ratio 14,19. However, these approaches are not practical for fluids with much higher viscosity, as they will significantly lower the production rate while dramatically raising the consumption of the volatile solvent or the continuous phase. In addtion, it has been reported that some high viscosity polymer solutions with &#951;&#160;&#62;&#160;1&#160;Pa&#183;s still did not break up into droplets with the approaches mentioned above17,19.
There are also several improved designs of microfluidic devices which introduce a third phase of fluid into the system, which facilitates the generation of high-viscosity droplets. Innovations include: bubbles introduced to cut a jetting thread into droplets21, an immiscible chaperoning fluid with moderate viscosity, introduced as the middle phase between the dipsersed phase and the continuous phase18, and microreactors introduced to generate high-viscosity droplets from two low-viscosity precursors21,22,23. However, as one more fluid is involved in the process, the system becomes more complicated, and the devices usually work in a much narrower flow regime than the typical devices for the generation of single emulsion droplets.
To generate monodisperse droplets directly from a high-viscosity fluid with &#951;&#160;&#62;&#160;1&#160;Pa&#183;s, surface-controlled phase-inversion methods have been investigated24. As the generation of low-viscosity droplets is much easier than that of high-viscosity droplets12, elongated low-viscosity droplets in a high-viscosity continuous phase are first generated using a typical co-flow structure, and then are broken up due to the change of surface wettability downstream of the co-flow structure. The released low-viscosity fluid inversely encapsulates the downstream high-viscosity fluid into droplets so that phase inversion is completed. According to the phase inversion mechanism, monodisperse high-viscosity droplets can be generated based on a typical co-flow device, while the exit of the co-flow device is treated to be wetted by the low-viscosity fluid, and then connected to a wider tube24,25.

<table>
	<tbody>
		<tr>
			<td>VitroTubes Glass Tubing</td>
			<td>VitroCom</td>
			<td>8240</td>
			<td>Square - Miniature Hollow Glass Tubing, I.D.=0.4mm, OD=0.8mm</td>
		</tr>
		<tr>
			<td>VitroTubes Glass Tubing</td>
			<td>VitroCom</td>
			<td>CV2033</td>
			<td>Round - Miniature Hollow Glass Tubing, I.D.=0.2mm, O.D.=0.33mm</td>
		</tr>
		<tr>
			<td>VitroTubes Glass Tubing</td>
			<td>VitroCom</td>
			<td>CV1017</td>
			<td>Round - Miniature Hollow Glass Tubing, I.D.=0.1mm, O.D.=0.17mm</td>
		</tr>
		<tr>
			<td>VitroTubes Glass Tubing</td>
			<td>VitroCom</td>
			<td>Q14606</td>
			<td>Square - Miniature Hollow Glass Tubing, I.D.=1.05mm+0.1/-0, OD=1.5mm</td>
		</tr>
		<tr>
			<td>Standard Glass Capillaries</td>
			<td>WPI</td>
			<td>1B100-6</td>
			<td>Round - Glass Tubing, I.D.=0.58mm, O.D.=1.00mm</td>
		</tr>
		<tr>
			<td>Glycerol</td>
			<td>Sinopharm Chemical Reagent Beijing</td>
			<td>10010618</td>
			<td></td>
		</tr>
		<tr>
			<td>Paraffin Liquid</td>
			<td>Sinopharm Chemical Reagent Beijing</td>
			<td>30139828</td>
			<td></td>
		</tr>
		<tr>
			<td>Poly(vinyl alcohol), PVA-124</td>
			<td>Sinopharm Chemical Reagent Beijing</td>
			<td>30153084</td>
			<td></td>
		</tr>
		<tr>
			<td>Span 80</td>
			<td>Sigma-Aldrich</td>
			<td>85548</td>
			<td></td>
		</tr>
		<tr>
			<td>Starch</td>
			<td>Sigma-Aldrich</td>
			<td>S9765</td>
			<td></td>
		</tr>
		<tr>
			<td>Trichloro(octadecyl)silane</td>
			<td>Sigma-Aldrich</td>
			<td>104817</td>
			<td></td>
		</tr>
		<tr>
			<td>Toluidine Blue O</td>
			<td>Sigma-Aldrich</td>
			<td>T3260</td>
			<td></td>
		</tr>
		<tr>
			<td>Honey</td>
			<td></td>
			<td></td>
			<td>Chaste tree honey, common food product purchased from supermarket</td>
		</tr>
		<tr>
			<td>DEVCON 5 Minute Epoxy</td>
			<td>ITW&#160;</td>
			<td></td>
			<td>Epoxy glue</td>
		</tr>
		<tr>
			<td>Blunt Tip Stainless Steel Dispensing Needles (Luer Lock)</td>
			<td>Suzhou Lanbo Needle, China</td>
			<td>LTA820050</td>
			<td>20G x 1/2&#34;&#160;</td>
		</tr>
		<tr>
			<td>Tungsten/Carbide Scriber</td>
			<td>Ullman</td>
			<td>1830</td>
			<td>For cutting glass tubing</td>
		</tr>
		<tr>
			<td>Microscope Slides</td>
			<td>Sail Brand</td>
			<td>7101</td>
			<td>76.2 mm x 25.4 mm, Thickness 1 - 1.2 mm</td>
		</tr>
		<tr>
			<td>Polyethylene Tubing</td>
			<td>Scientific Commodities</td>
			<td>BB31695-PE/5</td>
			<td>I.D. = 0.86 mm, O.D. = 1.32 mm</td>
		</tr>
		<tr>
			<td>Syringe Pumps</td>
			<td>Longer Pump, China</td>
			<td>LSP01-1A</td>
			<td>3 pumps needed for the experiments</td>
		</tr>
	</tbody>
</table>

fabricating high-viscosity droplets using microfluidic capillary device with phase-inversion co-flow structure

The generation of monodisperse droplets with high viscosity has always been a challenge in droplet microfluidics. Here, we demonstrate a phase-inversion co-flow device to generate uniform high-viscosity droplets in a low-viscosity fluid. The microfluidic capillary device has a common co-flow structure with its exit connecting to a wider tube. Elongated droplets of the low-viscosity fluid are first encapsulated by the high-viscosity fluid in the co-flow structure. As the elongated low-viscosity droplets flow through the exit, which is treated to be wetted by the low-viscosity fluid, phase inversion is then induced by the adhesion of the low viscosity droplets to the tip of the exit, which results in the subsequent inverse encapsulation of the high-viscosity fluid. The size of the resultant high-viscosity droplets can be adjusted by changing the flow rate ratio of the low-viscosity fluid to the high-viscosity fluid. We demonstrate several typical examples of the generation of high-viscosity droplets with a viscosity up to 11.9 Pas, such as glycerol, honey, starch, and polymer solution. The method provides a simple and straightforward approach to generate monodisperse high-viscosity droplets, which may be used in a variety of droplet-based applications, such as materials synthesis, drug delivery, cell assay, bioengineering, and food engineering.

A microfluidic capillary device with a phase-inversion, co-flow structure was designed to generate monodisperse aqueous high-viscosity droplets, as shown in Figure 1A. In Figure 1, the high-viscosity aqueous phase was glycerol, which has a viscosity of &#951;w = 1.4 Pas; the low-viscosity oil phase was liquid paraffin, which has a viscosity of &#951;o = 0.029 Pas; the surface tension betwee...

Watch this Scientific Journal Video about Fabricating High-viscosity Droplets using Microfluidic Capillary Device with Phase-inversion Co-flow Structure at JoVE.com

Fabricating High-viscosity Droplets using Microfluidic Capillary Device with Phase-inversion Co-flow Structure

A phase-inversion co-flow device is demonstrated to generate monodisperse high-viscosity droplets above 1 Pas, which is difficult to realize in droplet microfluidics.

The generation of monodisperse droplets with high viscosity has always been a challenge in droplet microfluidics. Here, we demonstrate a phase-inversion ...

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