Application note How to avoid air bubbles during your microfluidic experiments
Video: Bubble trap at work! The liquid enters on the right and exits on the left. All the air bubbles are removed
Air bubbles are a very common issue for microfluidic experiments. They are very difficult to avoid, and they can be really difficult to remove from the microfluidic device. Moreover, they can be really detrimental for the experiment.
For more information about the cause of air bubbles and the issues they can create, check our dedicated review. But here, this application note will focus on two methods allowing you to remove air bubbles from your experiments.
1st method: take advantage of your flow control system
When filling your microfluidic device with fluid, air bubbles are almost inevitable. These air bubbles can be difficult to detach, especially with complex chip designs. Moreover, air bubbles can appear during the experiment. Indeed, temperature changes, for example, can result in the formation of air bubbles.
In most cases, a smart use of your flow control system can help you to remove air bubbles. In the following examples, we will see how to use the OB1 Mk3 pressure controller to remove air bubbles.
Pressure pulses to remove bubbles
In order to remove air bubbles trapped inside your microfluidic device, one of the easiest method is to apply pressure pulses to detach them. The Elveflow Smart Interface software has pressure patterns already integrated. You can use a square pattern in order to create pressure pulses.
The frequency and amplitude can be adjusted for a better result.
Set up diagram
To best fit your needs, Elveflow developed three different types of bubble traps, having different size therefore different internal volume. It allows to choose the best trade of between an optimal bubble absorption and a low dead volume in a range suited for microfluidics applications. You can see all the characteristics on the attached graph and on the product datasheet. Don’t hesitate to ask our expert for advices!
Use pressure to dissolve air bubbles
Another solution to remove the bubbles trapped inside your chip is to pressurize both the inlet and outlet of the chip. Indeed this high pressure applied to the bubbles will enable a faster dissolution of the air inside the liquid. This technique will be more efficient with porous chips, such as PDMS devices, since the air will go through the porous material.
The setup used to dissolve air bubbles inside the chip is presented in the following scheme:
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Video: Air bubbles are dissolved inside a microfluidic chip by pressurizing the liquid.
2nd method: use a bubble trap
Air traps use a membrane permeable to gas and not permeable to aqueous liquids in order to remove air bubbles from your experiments. This kind of bubble trap can be placed in line, just before the chip, removing all the bubbles which could be inserted in the fluidic path before, during a change of sample for example.
This bubble trap can be used in two modes: a passive mode, and an active mode where a vacuum line can be added. In this second mode, a vacuum outlet of a pressure generator, such as the OB1 Mk3, can be used to maximize the bubble trap’s efficiency. This bubble trap enables to achieve a 100% debubbling for a flow up to 60ml/min.
The following video shows the in line bubble removing performed with the bubble trap in passive mode.
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