How to control the flow while flow line changing with a Mux Distributor ?

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Setup : OB1 flow controller + Mux Distributor

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Maintain a controlled flow rate?

This application note aims to help you maintain a controlled flow rate during a flow line switch thanks to the Mux Distributor. This valve allows to switch between up to 10 lines to inject several fluids sequentially in your system. It has many applications such as sequential sample injection for biochemistry and flow chemistry, or medium switch for cell biology on chip.

Because the flow switch introduce temporary flow rate diminution, it is important to tune the parameters of the PID flow rate control to have the optimal performances for your set-up. The following sections will walk you through the steps to easily perform this optimal regulation.

Mux Distributor working principle

The Mux Distributor is a 10 to 1 valve that can be used in both direction: to distribute your liquid sample in different lines or to inject in your setup different liquids samples. Thanks to the Elveflow® Smart Software, you will be able to command the Mux Distributor and even to choose how much time you want each connection to be on. Another advantage of the Mux Distributor, is the guaranty to have no back flow and thus no contamination between samples.

We will here focus on how to regulate the flow after a sample switch. Indeed, although the swith occurs in a few hundred of ms, it induces a flow rate fall.

One can use any method to generate the flow. In order to get to a quick and precise flow control we will use the OB1® pressure controller. One advantage of using this instrument is the integrated flow control system provided in the software.

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PID tuning for a fast flow regulation

In this set-up is the flow settled by an OB1 and measured thanks to a microfluidic flow sensor. A PID algorithm determines the OB1 pressure output value according to the flow measurement. This algorithm has two parameters- the gain parameter and the integration time parameter- that can be tuned by the user (the D parameter is fixedà. According to your set-up behavior, you may change these parameters to find the best combination to have both a good response time and stability.

If you want to go further in the comprehension of this algorithm, check-out our dedicated tutorial: how-to- choose-flow-regulation-parameters.

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Applications

  • Cell culture on chip
  • Live cell imaging
  • Cell response to medium change
  • Drug screening
  • Toxicity tests
  • Stem cells assays

Setup

This section explains how to inject sequentially several fluids at a controlled flow rate in the device of your choice (microfluidic device, perfusion chamber etc…)

Material

Components list

Setup Diagram

For this setup, the following Elveflow® devices are needed:

  • Elveflow® pressure & flow control instrument (OB1)
  • Microfluidic Tubing for the fluidic connection of the setup elements
  • Microfluidic Fittings & Connectors
  • Bronkhorst flow sensor

We here use the Flow Sensor with the OB1 MkIII in pressure control mode and a MUX Distributor.

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Tips : For a fastest switch, place your microfluidic chips as close as possible from the Mux Distributor. It also allows a more accurate volume control with less liquids in the tubing.

Setting the right parameters

Once the circuit mounted, the next step is to optimize the flow regulation. The algorithm can be tuned in accordance to your needs in order to find the right balance between responsiveness and accuracy.

In order to find the best relation between both flow regulation parameters (gain and integration time), you can use the “auto-tune” functionality”. If it is not enough, go to this tutorial which explain exactly how to choose flow regulation parameters.

The optimal parameters can be different from one lines to another (depending of the properties of your fluids). The Elveflow® software allows you to save different configurations and to load them easily : you can create configurations for all your lines, the algorithm parameters will also be saved.

Tips : To minimize the perturbations caused by the mechanical switch, plug as far as possible your samples in neighbor lines of the Mux distributor. It will reduce the switch time.

Step by step control with Elveflow® smart software

Make sure that all the cables and tubing are well connected to your Elveflow® instruments (USB cable, 24V DC, Flow sensor data cable, etc). Perform leakage tests and remove any air bubbles before starting your experiment.

The flow sensor is very sensitive to vibrations and movement perturbations so it is recommended to fix it to a stable surface as often as possible.

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1) Launch Elvefow® smart interface and
add the OB1® pressure controller and
the Mux Distributor.

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2) Connect the flow sensor on the used
pressure channel of your OB1®.

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3) Launch the OB1® and the Mux distributor. To switch manually which line is connected to the output, simply click on the line you want to select.

It is also possible to rename the lines as in neighboring screenshot.

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4) Go to the sensor controlled mode and set the parameters as explained in the previous section.

You may have to do several test to find the best parameters. The optimal parameters can be different from one line to another.

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5)  Launch the regulation. You can follow the flow rate evolution on a graph.

In this example at time t=27s, a line switch was performed.

When switching the flow rate first decreases when the flow is blocked. To compensate this stop, the pressure increases and makes the flow rate overshoot the set value before going back to this value in less than 1s.

Perform line switch manually

This example shows how to switch between sample when a specific volume of liquid is reached. It is not the most precise way to control experiment because even if the computer gives the volume of liquid, the switch has to be done manually.

However, it can be very useful if you want to use the Mux Distributor to perform injections in your microfluidic device and this process is particularly easy to follow.

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1) Launch the flow regulation with the OB1® pressure controller and open the Mux Distributor control panel.

You may change the name of the Mux Distributor lines.

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2) Connect the flow sensor with the Mux Distributor using the panel on the right of the screen.

You will now see for each line, the volume of liquid which went through
the line. If you don’t need to much precision, you can switch manually between the lines when the volume of a sample reached the one you wanted to inject.

Perform switches using Elveflow® smart interface sequence planer

Connect the flow sensor with the Mux Distributor using the panel on the right of the screen.

You will now see for each line, the volume of liquid which went through the line.

If you don’t need to much precision, you can switch manually between the lines when the volume of a sample reached the one you wanted to inject.

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1) First, for each line create a configuration with the adapted flow rate and flow control parameters. Save these configurations.

Tips : You can also create a “finish” configuration to stop the flow rate at the end of the experiment.

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2) Go back to the main panel and launch the sequence planer.

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3) Add to the sequence planer the event corresponding to the line switches and the load of the different configurations in the OB1 ®.

Then set the time you want to stay in each configuration using the “wait” command.

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4) You can now play the sequence ! If the response of one of the channel does not correspond to your need, go back to the configuration and adapt the flow controls parameters.

Do not forget that, even if you can’t avoid a little bit of disturbance during a line switch because of the flow rate brief stop, you can minimize it by switching between neighboring lines.

Congratulations, you can now run your experiment and control up to 10 lines with a low switch time and an accurate flow regulation!

Stop by the Bronkhorst® flow sensor product webpage.

FLOW REGULATION

Related tutorials

Mux Distributor basics, a simple tutorial if you want to perform a switch with no flow control constraint :

Microfluidic-Valve-Rheodyne

A complete tutorial on the PID control in a more general case :

Microfluidic-flow-control-Full-Setup-image

Mux Distributor product page where you can find the datasheet and all the technical specifications :

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Explore other ways to perform switches with all the Elveflow® Mux range, and find the solution that fit the bet for your set-up! Mux Wire for fast switch in a microfluic device with multiple inputs :

Microfluidic-Valves-Controler

A comparison between multiples ways to perform switches :

Microfluidic-fast-medium-switch2

WORLD LEADER IN HIGH PERFORMANCE MICROFLUIDIC FLOW CONTROL

We  provide the only microfluidic flow control system using Piezo technology that enables a blazing fast flow change in your microdevice.

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