Researchers’ opinion on droplet generation in microfluidics: syringe pumps or pressure control?

droplet generation in microfluidics - researchers opinion about syringe pumps and pressure control
Introduction

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 about digital microfluidics

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Analogy with electrical circuit

There are two main ways to generate flows.

In the field of microfluidics flow behavior is quite similar to electrical current behavior. As well as 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.

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 droplet successfully it is necessary to control precisely flows of continuous phase and dispersed phase whatever the geometry chosen.

Microfluidic droplets generation

Researchers’ opinion

I asked to 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 quarter 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 I interviewed built their own home made 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

PROS

Syringe pump

  • Ease of setup and control
  • Using a syringe pump enables 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 minute)
  • 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 enable to know the flow rate (*)
  • The flow rate varies with fluidic resistance when controlling flow in pressure [3] (*)

Related tutorials about 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.

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

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Article written by Thomas Grandry

References:

[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

Study also based on instrumentation of:

[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] Maddala 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] Küster SK et al., Anal. Chem., 2013, 85(3), 1285-1289