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Microfluidics application note

Microfluidic pressure-driven flow control

What is microfluidic pressure-driven flow control?

Recently, researchers switched to microfluidic pressure-driven flow control systems because of their unique performances for microfluidic experiments. However, for historical reasons syringe pump were the most used system in microfluidics.

In this application note, you should learn:

  • How pressure-driven flow control works
  • The advantages / disadvantages of the different technologies
  • How to choose between a syringe pump & pressure-driven flow controller depending of your experimental requirements

Applications

Pressure-driven flow controlled microfluidics is used for many applications that require an accurate control over parameters such as size, shape, generation rate, mixing…

Notably, emulsion and foam applications demonstrate a real need to control very precisely the microfluidic bubble or droplet generation to obtain a stable emulsion or foam.

For more insight into these work, please check the following notes & related short reviews:

Pressure-driven flow controlled microfluidics is also very useful for any biological applications that require a fine tuning of the forces acting on the cells, bacterias or any living systems contained within the microfluidic device.

How to perform ultra-precise & responsive pressure-driven flow control?

List of components

Setup diagram: pressure-driven flow controlled microfluidic system

A pressure driven flow controller is a smart alternative to syringe pump. It allows pulseless flow within subsec response time. It consists in using a gas input pressure within a hermetic liquid tank in order to flow liquid from the tank to your microfluidic device.

Pressure driven flow control

Pressure-driven flow control principle

A pressure controller pressurizes a tank, such as Eppendorf, Falcon or a bottle containing the sample, which is then smoothly and quasi-instantly injected into a microfluidic chip.

Figure 3 : The reservoir is pressurized, the gas pushes on the fluid surface, the fluid will flow through the outlet. Thus, controlling the input gas pressure of the tank willallow to control the liquid that flows out of the tank. Thanks to piezoelectric pressure regulation, Elveflow’s systems are able to regulate flow within 40 ms with a 0.005 % stability. One advantage of pressure-driven flow control lies in the ability to handle fluid volumes of several hundreds of mL. You can thus turn your system into a powerful syringe pump.

By coupling our pressure controller with one of our flow sensors, you can perform ultra precise and responsive pressure-driven flow control. You can request a flow rate value in the Elveflow Software and the pressure controller will automatically adjust pressure to reach the requested value thanks to a customizable PID Feedback loop.

microfluidic reservoir principle zoom

Figure 3: pressurized reservoir

Advantages / Weaknesses

Syringe Pump

  • Fast setup for fluidic experiments.
  • The amount of dispensed liquid can be known for long term experiment.
  • Maximum pressure generated by a syringe pump can be of several hundred bars.

Pressure Control

  • Fast response time (down to 40ms)
  • High stability and pulseless flow
  • Possibility to handle fluid volumes of several liters
  • Possibility to control fluids in dead-end channels
  • Enable both flow and pressure control when used with a flow meter

Technical comments:

  1. Response time can vary from seconds to hours depending on the fluidic resistance and compliance.
  2. Without flow meters, users cannot know the real flow rate during the transient period (seconds to hours).
  3. The amount of fluid dispensed by the syringe pump is limited in volume.
  4. Even pulseless syringe pumps require to carefully choose the syringe size depending on your experimental conditions to avoid periodic pulsations on the flow rate due to the step-by-step motor of the syringe pump.
  5. If channels are clogging (due to dust for example) the pressure increases without limit and can lead to device destruction.
  6. Knowing the pressure inside the fluidic system requires a pressure sensor.
  7. Flow control of fluids in dead-end channels (like integrated valves) is impossible using syringe pumps.
  8. When pressure is unbalanced, it is possible to have backflows, when doing flow switches with multiple inputs (association with valves is required to solve that problem).

Performance: response time & stability

The main advantage of syringe pumps is that they are easy to use, and but they present slow response time when setting a new flow rate and flow oscillations due to motor steps.

Flow changes inside chips can take seconds to hours (see the tutorial on syringe pump responsiveness in microfluidics). This lack of reactivity is one of the main limitations of syringe pumps for numerous applications notably for droplet-based microfluidics as described in this short video:

Modern microfluidic pressure controllers also enable you to control both pressure and flow rate by integrating a flow meter with a feedback loop. Microfluidic researchers mainly use pressure controllers when they require high flow responsiveness and high flow stability and precision, as well as when they work with dead-end channels or require large sample volumes. More informations about response timestability in microfluidic systems.

Conclusion

Syringe pumps are convenient and have been used for a long period. However, performances are limited (response time, oscillations) when the setup is complex or when a fine control is requested as it is usually the case in microfluidics.

Pressure-driven flow control was developed for microfluidics and perfectly meets users’ expectations (responsiveness, stability, reproducibilty…).

Feel free to contact our team of experts for any additional information!

Want to run a similar experiment? Feel free to contact us at: contact@elveflow.com
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