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Water in Oil Emulsions

Water in oil emulsions (W/O) form the basis manufacturing techniques widely used in the industrial and R&D environments to manufacture droplets (e.g., for compartmentalization applications), hydrogel beads (e.g., alginate, agarose, or polyacrylamide), and polymer beads (e.g., acrylic, vinyl, and ethyl-based). Of particular importance is the ability to produce high-quality, monodisperse droplets and the ability to do so reproducibly and at a viable production rate.

The combination of Fluigent pressure pump units and Raydrop microfluidic devices enable smooth fluid delivery, precision flowrate control, automation, and reproducibility necessary to generate high-quality water in oil emulsions.

In this application note, we present droplet generation data obtained using one of the most widely used water in oil emulsion systems – water in decane. We demonstrate the ability of Fluigent equipment coupled with Raydrop microfluidic devices to generate high-quality emulsions with controlled droplet sizes and with high throughput.

We kindly thank of SMALL Biotechnologies for this collaboration.

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Materials and Methods

Reagents

Droplet Phase: Water (Mili Q) 

Continuous phase: Decane + 2% (wt) SPAN 80  

Reagent
Supplier
Catalogue number
CAS Number
Water
Ultrapure 18.2 MΩ – cm
-
7732-18-5
Decane
Sigma Aldrich
D901
124-18-5
SPAN 80
Sigma Aldrich
8.40123
1338-43-8

Microfluidic Setup

The microfluidic setup was composed of:

2x Flow EZ (2000 mbar) pressure pumps

Microfluidic flow controller

2x Flow Units enabling flowrate control

Flow sensor

RayDrop chip

Droplet generator

 

Optical microscope

FlowUnit
RayDrop microfluidic droplet generator
Digital high-speend microscope 7092 fps

The Flow EZ is the most advanced flow controller for pressure-based fluid control. It can be combined with a Flow Unit to control pressure or flow rate. It can be used without a PC. Two Flow EZ with 2 bar of full-scale pressure are used in the setup presented here.

The Flow Unit is a flow sensor that allows real-time flow rate measurement. By combining a Flow Unit with the Flow EZ, it is possible to switch from pressure control to flow rate control, allowing for the generation of highly monodispersed droplets over a long time. Two Flow Units M are used here to monitor and control the flow rates of the dispersed and continuous phase during the run.

The RayDrop droplet and emulsion chip is used to control the generation of alginate droplet. The RayDrop is based on the alignment of two capillaries immersed in a pressurized chamber containing the continuous phase. The dispersed phase exits one of the capillaries through a 3D-printed nozzle, placed in front of the extraction capillary for collecting the droplets. This non-embedded implementation of an axisymmetric flow-focusing is referred to co-flow-focusing.

Fluigent high-speed camera is a package that contains all necessary instruments to have a good optical device.

It contains:

  • Microscope
  • High-speed camera
  • Light controller

This package is connected with a USB 3.0 wire to a PC where the user can visualize its microfluidic device with the Pixelink Capture Software together with other Fluigent Software (MAT, A-i-O). The camera has been selected to reach rates up to 7028 fps, ideal for droplet experiments. 

Figure 1: Scheme of the fluidic setup

Figure 2: Pictures of the Fluigent equipment

Results

Continuous phase flowrate
(μl/min)
Droplet phase flowrate
(μl/min)
Droplet diameter
(μm)
Production rate
(Hz)
100
5
71
445
100
10
75
754
100
15
87
725
50
5
85
259
50
10
91
422
50
15
92
613
25
5
89
225
25
10
93
396
25
15
94
575
15
15
94
575

Figure 3: Droplet phase diagram

 

Figure 4: Images of water droplets in decane generated using Fluigent equipment and Raydrop microfluidic device

 

 

Conclusion

Fluigent pressure based flow controller units and Raydrop microfluidic device were successfully used to generate high-quality, monodisperse droplets of water in hydrocarbon oil. The droplet size was controlled in the range of 75 – 94 μm by adjusting the continuous and dispersed phase flowrates. Peak stable droplet production rate was recorded for 75 μm droplets at 754 Hz. The production techniques developed here can be extended to the generation of hydrogel, protein, or polymer beads by adding appropriate post-processing steps.

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