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Researchers’ Insights on Droplet Generation in Microfluidics: Syringe Pumps vs. Pressure Control

 

 

Microchannel flowIntroduction to droplet generation in microfluidics

Droplet generation in microfluidics: the aim of this technology is to create fluid-fluid dispersion into channels (principally water-in-oil emulsion). During the recent years, researchers have shown a greater interest in droplet-based microfluidics. There are many applications in domains as diverse as chemistry or biotechnology [1].

Also see: A short introduction to digital microfluidics

Analogy with AN electrical circuit

There are two main ways to generate flows.

In the field of microfluidics, flow behavior is quite similar to electrical current behavior. Just like a current source and voltage source are the two main ways to generate an electrical current, microfluidic researchers have to choose between flow controller and pressure controller to command their flow in their experiments (For instance Darwin Microfluidics offers syringe pumps for microfluidics)

In microfluidics, the most widely used technology is the syringe pump. This method is strongly relevant for a lot of applications and is appreciated for its fast setup, simplicity and affordability. Pressure control is used for experiments requiring a short response time or a high level of stability and accuracy.

Micro-droplet generation and control

There are several ways to generate droplets.

3 categories of geometries are most commonly used [2]:

  • Co-flowing streams
  • Cross-flowing streams (T or cross-shaped junction)
  • Elongational flow in a flow focusing geometry

Most of the time, micro-droplet generation are performed in capillary tubes & junction or in on-chip channels. To shape droplets successfully, it is necessary to precisely control the flows of continuous phase and dispersed phase no matter the geometry chosen.

Microfluidic droplets generation

       


Researchers’ opinion

We asked a hundred of researchers from laboratories working on droplet-based microfluidics which technology they used to control their flows in their latest papers, and their opinion about it.

Choice of technology for droplet-based microfluidics

A significant majority of researchers uses syringe pump technology to control flows in their experiments related to droplet generation. Their choice of technology mainly depends on their opinion on syringe pumps, their habits of experimentation and equipment of their laboratory.

In the 1/4th of pressure control users, several of them have recently moved to pressure-driven control technology, or are still using the two technologies at the same time.

Lastly, some of researchers interviewed built their own homemade system using hydrostatic pressure or pressurized containers with valves.

Technologies used for microdroplet generation and control

(*)This study is based on the kind answers given by researchers in the field of droplets-based microfluidics [3-30]

 

Pros and Cons of flow control and pressure control for droplet generation

PROS

Syringe pump

    • Ease of setup and control
    • Using a syringe pump allows to know and specify the flow rate
    • Commercial availability: variety of providers

Pressure control

CONS

Syringe pump

    • Long response time of the flow rate (seconds to minutes)
    • The piston of the syringe pump generates oscillations at low flow rate: droplets are irregularly dispersed [4]
    • Fluidic resistance rises could lead to pressure increase and burst the device
    • The amount of dispensed fluid is usually reduced around tens of mL
    • Incompatible with a valve-based closing system

Pressure control

    • Using a pressure controller does not allow to know the flow rate (*)
    • The flow rate varies with fluidic resistance when controlling flow in pressure [3] (*)

(*) can be overcome with pressure source including flow rate feedback loop

You can also check out a detailed review by one of our distributors, Elexan, comparing syringe pumps and pressure controllers for droplet generation in microfluidics.

Reviews on droplets generation:

How to generate droplets in capillary tubes & junction step by step
How to generate droplets in on-chip channels step by step

For more details about flow control in microfluidics, also see this document.

This review about droplet generation in microfluidics have been written by Thomas Grandry.

  1. Seemann R et al, Rep. Prog. Phys., 2012, 75 016601
  2. Christopher G F et al., J. Phys. D: Appl. Phys., 2007, 40 R319
  3. Glawdel T et al., Microfluidics and Nanofluidics, 2012, 13, 469-480
  4. Korczyk P M et al., Lab Chip, 2011,11, 173-175
  5. Resto P J et al., Lab Chip, 2010, 10(1):23-6
  6. Waegli P et al., Anal. Chem., 2013, 85 (15), 7558–7565
  7. Zec H C et al., MEMS, 2013, 263-266
  8. Tarchichi N et al., Microfluidics and Nanofluidics 14 (2013) 45-51
  9. Basu A S et al., Lab Chip, 2013,13, 1892-1901
  10. Strain M C et al. ,PLoS ONE, 2013, 8(4): e55943
  11. Churski K et al., Lab Chip, 2012,12, 1629-1637
  12. Rotem A et al., Lab Chip, 2012, 12(21):4263-8
  13. Chang C et al., Lab Chip, 2013, 13, 1817-1822
  14. Eastburn D J et al., PLoS ONE, 2013, 8(4): e62961
  15. Whitesides GM et al., Optics Express, 2011, 2204-2215
  16. Sjostrom S L et al., Lab Chip, 2013,13, 1754-1761
  17. Shum H C et al., Biomicrofluidics, 2012, 6, 012808
  18. Li X B et al., Chemical Engineering Science, 2012, 340-351
  19. Guo F et al., Anal Chem., 2012, 84(24), 10745-9
  20. Smith C A et al., Anal. Chem., 2013, 85 (8), 3812–3816
  21. Leptihn S et al., Nature Protocols, 2013, 1048–1057
  22. addala J et al., AIChE Journal, 2012, 2120-2130
  23. Thompson S C et al., Lab Chip, 2013, 13, 632-635
  24. Wang Y et al., Lab Chip, 2013, 13, 2547-2553
  25. Schoeman R M et al., Electrophoresis, 2013
  26. Theberge A B et al., Angew. Chem. Int. Ed., 2010, 49: 5846–5868
  27. Han Z et al., Chem. Commun., 2012,48, 1601-1603
  28. Wehking JD et al., Microfluidics and Nanofluidics, 2013
  29. Arayanarakool R et al., Int. Conf. of microTAS, 2012
  30. KĂĽster SK et al., Anal. Chem., 2013, 85(3), 1285-1289

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Microfluidics knowledge

Do you want tips on how to best set up your microfluidic experiment? Do you need inspiration or a different angle to take on your specific problem? Well, we probably have an application note just for you, feel free to check them out!

  • #Organ on a chip
  • #Droplets
  • #Micromixers
  • #Enhanced Oil Recovery
Show all Droplet & digital microfluidics
Show all Droplet & digital microfluidics
Show all Droplet & digital microfluidics

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