Review: Fast medium switch OB1 vs. OB1+MUX

Introduction

Fast medium switch in microfluidic channels is generally a required technique to perform a wide range of biomedical and chemical microfluidic assays, such as the analysis of living cells in vitro, particle washing, etc.

For this reason, Elveflow® proposes two different configurations of its microfluidic instruments to perform ultrafast flow changes.

- Configuration A: Elveflow® OB1 + MUX Flow switch (consult its corresponding Application Note)

- Configuration B: Elveflow® OB1 (consult its corresponding Application Note)

In this review the medium change speed of these two configurations are measured, analysed and compared in order to help our clients finding the best configuration to perform their particular assays.

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Experimental

To measure the medium change speed, the two configurations have been set and several medium flow switches have been carried out (see figure below) and recorded using a frame rate of 30fps for each configuration.

Microfluidic fast medium switch

Secondly, each video has been analyzed using “ImageJ” software and sliced into a stack of images (one image every 0.003 seconds). Finally, the changes in intensity have been monitored through each stack and the average intensity at a fixed position has been calculated giving different results for each configuration.

Results and interpretation:

a) Configuration A: Elveflow OB1 + MUX

- Switch each 4 seconds: Average time= 0.2897

- Switch each 8 seconds: Average time= 0.2933

- Switch each 12 seconds: Average time = 0.2833s

- Switch each 16 seconds: Average time = 0.3007s

- Switch each 24 seconds: Average time = 0.2793s

b) Configuration B: Elveflow OB1

– Switch each 4 seconds: Average time = 0.3337s

- Switch each 8 seconds: Average time = 0.6893s

- Switch each 12 seconds: Average time = 1.0927s

- Switch each 16 seconds: Average time = 1.5757s

- Switch each 24 seconds: Average time = 2.4970s

Microfluidic fast medium switch configuration speed comparison graphic

The results show that the Configuration A (OB1+MUX) can perform a faster medium switch than the Configuration B (OB1). This observation remains true even when the switch frequency time between each of the three tested mediums becomes longer: the Configuration A shows a constant average time whereas the Configuration B shows an increment directly proportional to the switch frequency time (see the figure below).

Microfluidic fast medium switch switch frequency graphic

The reason for this increment is that some flow always comes back from the main channel and passes through the other two channels. The longer this flow carries on flowing the longer it will take to come back through the main channel.

There is an alternative way to perform the medium switch with this configuration which allows to reduce the average switch time: when a little residual laminar flow of the other two mediums is allowed on the edges of the main channel, we avoid any back flow. As a result no extra time will be needed by the medium to come back on every switch.

Conclusion:

As every assay or experiment is different, the best configuration will depend on its objectives and conditions. The following SWOT analysis expects to be helpful to decide which configuration is more suitable in each case.

Microfluidic fast medium switch SWOT configurations analysis

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