CETONI Elements now supports precision scales!

Integration of a high-resolution precision balance in your application offers you precise information at every point in your process and thus additional security. With the help of our flexible laboratory automation software CETONI Elements You can now integrate precision scales into your process and use them for targeted control of your high-precision dosing, automation of processes or permanent process monitoring.

Simply install the latest QmixElements update and getting started!

The CETONI Elements software now supports the integration of laboratory balances via the balance plug-in. A device driver for Sartorius scales (Entris, ED, GK and GW scales) is already included with the release of the plugin. This means that you can easily integrate your existing Sartorius laboratory balance into the CETONI Elements software. Thus you not only extend your CETONI system with the possibility to weigh substances, substances or dosed liquids, but you can also synchronise or completely automate processes as you wish in interaction with other CETONI hardware and your own analysis.

CETONI Elements with two Nemesys syringe pumps and a scale

The configuration of the scale devices is carried out, as you are used to from the CETONI Elements software, via the device configurator. Simply create a new configuration or add the scale to an existing configuration and save it. After activating the configuration, the scale is available in the software.

Elements Device Configurator

In the software, the scale is then displayed as a normal analogue input channel in the list of I/O channels ❶. There you can see the current value at any time and tare the scale via the context menu of the channel. Like all other analogue channels, you can also record this channel in the graphic logger ❷ or in the CSV logger and use it to create control channels. Due to the real-time recording of the measured value in the graphic logger, dynamic weight changes, e.g. when dosing into a sample vessel, can be visualised and followed very well.

List of I/O channels with scale channel

The measuring channel of the scale can be read via the script system and taring of the scale is also possible via a script function. This allows the scale to be easily integrated into more complex analyses and automated processes.

Cell-on-Chip: More and more research fields aim to miniaturize and transfer cell cultures and complete assays to a lab-on-a-chip system. On the one hand, the reduced analysis areas mean that less sample is required, and on the other hand, it is possible to observe cell behaviour in real time. High-precision and pulsation-free dosing systems are the key to successful implementation of such lab-on-a-chip procedures. Our CETONI nemesys syringe pumps are used in numerous laboratories for the realization of microfluidic analyses.

We have therefore compiled 10 tips from which beginners and experienced researchers can benefit in their work.

1. The right chip material

The demands on the chip material for cell cultivation are high. The material should not only be biocompatible, but also have a high transmission property. For this reason, most of the work is based on the polymers PDMS (polydimethylsiloxane) or COC (cycloolefin copolymers). Nevertheless, PDMS also has some disadvantages due to its gas permeability and it is not resistant to chemicals, which means that COC or glass are becoming more and more important.

2. CO2-independent cell culture media

CO2-independent media are ready-to-use formulations which independently build up HEPES-(2-(4-(2-hydroxyethyl)-1-piperazinyl)-ethanesulfonic acid)- a buffer system, e.g. based on mono- and di-basic sodium phosphate and β-glycerophosphate. Therefore, the supply of CO2 is not necessary to maintain the buffer system.

3. Separated cell reservoirs

The use of cavities (lowered cell reservoirs) can both create a microclimate within the cell reservoir and protect the cells from shear stress, both of which are otherwise disadvantages of flow cell cultivation.

4. Coating favours cell adhesion

Many different wet chemical coating substances are known to promote cell adhesion. Collagen, gelatine or the substance mixture Matrigel® are most commonly used. Depending on the cell culture used, the suitability must be investigated on the basis of a time-dependent growth profile.

5. Exact control of the flow

A too high flow rate can not only prevent the adhesion of the cells, but can even detach them, both of which are a consequence of the shear stress that is too high in this case. A flow rate that is too low, on the other hand, would not mean a sufficient supply of nutrients for the cells. Ultimately, a compromise must be chosen in which the flow rate is adapted to the glucose consumption of the cells.

6. Constant temperatures

Miniaturized cell-based sensors allow the holistic statement on cell physiological processes in real time through incubator-independent observation. However, this requires the maintenance of 37 °C for the cultivation of human cells. In this respect, different approaches are taken when heating an incubator-independent system. Peltier elements, heating foils or slides, which have been provided with an ITO (Indium Tin Oxide) coating. The ITO coating offers an even temperature distribution and an excellent optical transparency for simultaneous light microscopic examinations of the cell culture.

7. Eliminating gas bubbles

In addition to the general aim of air-free filling of the system, the greatest challenge in microfluidics is to reduce remaining gas bubbles in the chip system. Very often media are degassed beforehand or so-called “bubble traps” (degasser) are used in the process. These not only represent an expense in terms of equipment and a potential risk of contamination, but also make pulsation-free conveying more difficult. Another approach makes use of Henry’s law, where the proportion of gas dissolved in a liquid is proportional to the pressure. In a figurative sense, the increase in pressure in the system favours the solubility of the smallest gas bubbles in the system, which thus lose their disturbing effect. This effect can be exploited by the correct placement of a back-pressure regulator (BPR), which provides a fluidic resistance and thus ensures the desired pressure increase depending on the set flow rate.

8. Continuous-flow

In order to expose cells to conditions as homogeneous as possible and to supply them continuously with nutrients, a continuous and low-pulsating flow is essential. Subsequent incubation with appropriate test substances allows meaningful and reproducible results to be generated afterwards.

9. Reduce the risk of contamination

A contaminated cell culture is a nightmare for every cell researcher. Especially in incubator-independent cell-on-chip research, the risk of contamination is correspondingly high and should be monitored particularly carefully. The use of special sterile filters before and after the chip system supports contamination-free cultivation. Special attention should of course be paid to the fluid connection technology and the conveyor system. Through the targeted use of disposable or autoclavable components such as syringes and valves, the modular nemesys syringe pumps are ideally suited for this purpose.

10. The cell seeding

The cell seeding process in the chip system is particularly critical because the uniform cell distribution has a decisive influence on the validity of the experiment. The introduction of the cells into a fully assembled microfluidic system requires either some fingertip sensitivity or constructive mechanisms that ensure an even cell distribution. The following methods for cell trapping can be distinguished: hydrodynamic, optical, magnetic, electrical or acoustic.

In their latest publication, a team from the laboratory of Mohammad A. Qasaimeh, at New York University Abu Dhabi, set a new milestone for open space microfluidics in the field of cell biology. The researchers developed a new kind of open-space microfluidic system for the sequential cell separation and patterning based on dielectrophoresis, and are able to reach a cell purity of ~90 %.

The syringe pumps were used to generate flow from the injection to aspiration aperture of their device, in order to generate a hydrodynamic flow confinement within which cell separation occurred.

Laboratory Setup:

For the research work it was necessary to use specially developed and 3D-printed microfluidic chips. Based on the Hele-Shaw-cell approximation, the flow was generated between two parallel flat plates by simultaneous injection and aspiration of fluids from the microelectrofluidic probe. Dielectrophoresis forces were then used to isolate target cells out of the flow stream and sequentially pattern them on the bottom substrate. Based on this method, cell purity of up to ~90 % was reached, characterized by fluorescence microscopy.

With their publication in Lab on a Chip last year, Qasaimeh et al. provide new tools to separate specific cells from heterogeneous cell population without need of any microchannels and have thus laid important foundations for this field of research.

Laboratory setup cell separation

The setup for the investigation of open space microfluidics for cell separation could be realized with a modular and high-precision CETONI dosing system. In order to generate continuous multipoles to separate cells with a high isolation efficiency, an extremely uniform and pulsation-free fluid flow is required. The nemesys precision syringe pumps are ideally suited for precise and smooth dosing of smallest fluid quantities. Thanks to its modularity, the setup can also be extended at any time, giving the research team complete flexibility in their work.

Used CETONI devices:

• Base 120
• 6x CETONI nemesys Low Pressure Syringe Pumps 290N

Literature:
A. T. Brimmo, A. Menacherya, M. A. Qasaimeh: Microelectrofluidic probe for sequential cell separation and patterning. 2019, (19), 4052-4063. DOI: 10.1039/C9LC00748B

In the second part of this tutorial you will learn how to create sinusoidal flow profiles using JavaScript functions. To do this, you modify the script from the first part so that a sinusoidal profile is generated instead of a sawtooth profile. Before you start with this second part, you may want to read the first part of the tutorial here.

Important
For this tutorial, you need QmixElements version v20191121 or a newer version. If you are still using an older version, please update to the latest QmixElements version.

Latest QmixElements Version

Preparation

Configure your system as described in the first part of the tutorial and then connect to your devices. If you do not have the appropriate devices, you are welcome to follow the tutorial with simulated devices. The QmixElements project with simulated devices and the script created in the first tutorial can be downloaded here.

Now open the script Tutorial_Sawtooth_Profile.qsc that you created in the first part of the tutorial and save it under a new name. You should then see the following program in script editor.

Part 2 – Script for generating a sinusoidal profile

The goal of this script is to generate a flow profile in the form of a sine wave from 0 to the defined target flow rate with one pump and to supplement the flow of the first pump with the second pump in such a way that the sum of the two flows results in a constant flow with a defined flow rate.

To generate the profile, the flow rate of the pump must be changed step by step so that a sinusoidal profile is created over time. The number of steps for generating the sine profile, i.e. the resolution, should be set to 100 steps for one sine. In the previous sawtooth script you had set the number of steps to 20. Therefore change the value of the variable $GradientSteps to 100.

Adjusting the resolution (number of steps) for a sine profile

Now delete the two Generate Flow functions as shown in the figure below. To do this, select both functions and then delete them using the context menu (right mouse button) or by pressing the Delete key.

Now insert a new variable before the two existing variables in the counting loop. Name the variable $Sinus and select JavaScript Expression in the Type field.

The $Sine variable is used to store the calculation of the sine value for further processing. To calculate the sine value, use the JavaScript function Math.sin() together with the constant Math.PI. Enter the following into the input field for the JavaScript expression:

Math.sin(2 * Math.PI / ($GradientSteps – 1) * $i)

The loop counter $i runs from 0 to the number of $GradientSteps – 1. To calculate the current sine value, the period 2π is divided by the number of steps – 1 and then multiplied by the current step $i.

To check the calculated value of the $Sine variable, you can display its value in the graphical logger. To do this, you have already created the virtual I/O channel Script Value 1 in the first part of the tutorial and added it to the graphical logger. Now insert the function Write Device Property ❶ into the script. Then configure the function as shown in the figure below.

In the field Value to be written ❷ enter the variable name $Sinus. In the Device Property area ❸ select in the Devicefield the virtual channel Script Value 1. In the Property field select the property ActualValue. You can now read the function as follows:

Write the value of the variable $Sinus into the property ActualValue of the virtual channel Script Value 1.

Now delete all data from the graphical logger and activate automatic scaling. Now start your script. If you have entered everything correctly, you should see how the following sine function is generated in the graphical logger:

The sine oscillates between 1 and -1 as expected. For the sinusoidal flow profile to be generated, the flow rate should oscillate between 0 and the target flow rate. In a first step, the sine value should be adjusted so that it oscillates between 0 and 1. You can achieve this by shifting the sine on the Y-axis upwards by 1 and then halve the amplitude. To store the new value, we use the existing variable $Flow1 ❶. This can now be calculated like this:

❷ $Flow1 = ($Sine + 1) / 2

Now change the Write Device Property function so that the value of the variable $Flow1 is displayed instead of the value of the variable $Sine. Then delete the graphical logger and reactivate automatic scaling. You should now see the following function in the graphic logger – a sine function oscillating between 0 and 1:

To make the sine oscillate between 0 and the target flow rate, you now only have to multiply by the target flow rate $TargetFlow. Extend the calculation of the variable $Flow1 by this step:

$Flow1 = ($Sine + 1) / 2 * $TargetFlow

The flow rate $Flow1 will now oscillate sinusoidally between 0 and the target flow rate. The flow rate $Flow2 of the second pump should complement the first flow rate in such a way that a constant flow with a constant flow rate $TargetFlow is created. You can therefore calculate the flow rate of the second pump in the variable $Flow2 as follows:

$Flow2 = $TargetFlow – $Flow1

Now insert two Generate Flow functions in front of the Write Device Property function and then delete the Write Device Property function as it is no longer needed.

The script should now look like the figure below ❶. Configure the two Generate Flow functions to start the first pump at flow rate $Flow1 ❷ and the second pump at flow rate $Flow2 (see figure below). Make sure that the Run to completion option ❸ is disabled.

Now delete all data from the graphical logger again and activate automatic scaling. Before starting the script, check that the syringes of both pumps are filled. Then start your script. If you have entered everything correctly, you should see how the following flow profiles are generated in the graphical logger:

You have now learned the basics of how to use JavaScript in the script functions – e.g. to perform mathematical calculations. Apply what you have learned, for example by programming a script that generates two sinusoidal flows, where the sine of the second flow has twice the period of the sine of the first flow. Use the graphical logger to check the results.

In the third part of the tutorial you will learn how to add an initialization routine to the script, how to wind up the syringes and get tips on how to improve the readability of your script and how to document your script.

The QmixElements project with simulated devices and the scripts created in the first and second part of the tutorial can be downloaded here.

Nowadays, medical science needs to be more innovation-driven and personalized than ever. That’s why microfluidics play a critical role in researching new therapeutic approaches. CETONI has a clear mission: with innovative solutions, we not only empower our customers to be part of the development process, we even allow them to take charge.

Unlike conventional methods, individualized medicine focuses on humans instead of diseases. The primary goal is patient-oriented interventions without time loss or side effects. The establishment of in-vitro assays, as a first step toward authoritative effectiveness tests, has paved the way for developing personalized therapies in a way that is sensible and available to the masses.

Conventional processes are reaching their limits

Cell cultivation is usually done in standardized cell culture flasks in a regulated CO2 environment. The enclosed incubation unit maintains a constant temperature, high humidity and sterility. But there is a problem caused by spatial separation between cell cultures and the analysis unit, which makes it impossible to arrive at a holistic conclusion about the real-time physiological process inside the cells. Microfluidic systems, on the other hand, are perfectly suited to the simultaneous analysis of different test substances. Therefore, the development of an automated cell culture for the purpose of reducing costs and time-consuming tasks, as well as the real-time observation of cells, becomes very interesting, particularly with respect to developing personalized therapies.

After a short implementation phase, the miniaturization of laboratory processes, from standardized in-vitro assays in well designs to lab-on-a-chip systems, becomes extremely lucrative in terms of time and cost-savings. Due to the reduced analysis areas inside the chip, the required samples are very small. This technology offers new possibilities, particularly when it comes to cell cultivation. These systems can not only automate cell seeding and supply nutrients to the cell culture. They also allow for toxic stimulation of cells in real time. Since the cell culture areas are very small, only a small number of cells are needed, which can be analyzed in real time, while ensuring a controlled supply of cells through an automatic pump and supply system with a heating unit. In addition, the pump system allows for automated cultivation.

Gold nanoparticles have recently become very important in different application fields. The reproducible synthesis of such nanoparticle is quite difficult due to many reaction parameters, which affect the optical and electrical properties of the particles. The size, shape and dispersity can also affect these properties.

Chow et al. In their scientific article Chow et al. report about a new flow-controlled method for the synthesis of gold nanoparticles using a liquid-liquid membrane-based separation technology.

Laboratory Setup

The flow-controlled synthesis of nanoparticles has a lot of convincing advantages. Mainly because of the precise control of the reaction parameters and surrounding conditions, i.e. mixing ratio, residence times and temperatures. Finally, flow-controlled synthesis minimizes batch-to-batch variability while benefitting yield and quality of the gold nanoparticles.

In the article Chow et al. describe a flow-controlled study for the synthesis of DMAP stabilized gold nanoparticles split into 3 synthesis stages. Based on the modular neMESYS syringe pump system and CETONI’s automation software QmixElements, a novel flow setup for the gold nanoparticle synthesis could be realized. A setup of six CETONI neMESYS Mid Pressure syringe pumps were used to generate the exact and pulsation-free flow stream to allow the formation of TOAB-Au stabilized nanoparticles using sodium borohydride as a reducing agent. In addition, a modular peristaltic pump (peRISYS-S, CETONI) was used to deliver three lines of solution for the washing of TOAB-Au stabilized nanoparticles in a 2 m mixing coil. For effective diffusion and advective mixing a glass-silicon split and recombine KombiMix micromixer (CETONI) was used in the third stage.

To separate the organic and aqueous phases a liquid-liquid membrane has been used, too. In order to balance the pressure on both sides for an efficient separation, precise pressure measurements are essential. CETONI’S pressure module QmixP was used to monitor any pressure-build up upstream due to nanoparticle aggregation which may cause a blockage of the T-mixer.

Within the scope of this brilliant research work a liquid-liquid membrane-based separation of gold nanoparticles could be demonstrated for the first time. A versatile and easy-to-use software tool in combination with various off-the-shelf plug and play components (neMESYS syringe pumps, peRISYS-S peristaltic pump, pressure measurement module etc.) from a single source had a decisive influence on the research progresses and success.

Used CETONI devices:

• Base 600
• Syringe pumps: 6x neMESYS Mid Pressure modules 1000N
• Peristaltic pump: 1x peRISYS-S
• Pressure controller: 1x QmixP
• Micromixer: KombiMix
• Software: CETONI Elements (QmixElements)

Literature:
Chow E., Raguse B., Della Gaspera E., Barrow S. J., Hong J., Hubble L. J., Chai R., Cooper J. S., Sosa Pintos A., Flow-controlled synthesis of gold nanoparticles in a biphasic system with inline liquid–liquid separation. React. Chem. Eng., 2020, 5, 356. DOI: 10.1039/c9re00403c

The syringe pump offers enormous advantages for microfluidic applications due to its volumetric delivery principle and minimized pulsation. However, it also has a major disadvantage compared to other pumps: the delivery naturally ends as soon as the syringe is empty. This is why the syringe pump is often used in applications where this is irrelevant because the process is paused from time to time and the syringe can be refilled, such as filling individual cavities during pipetting.

In many applications – especially in flow chemistry – an interruption would not be possible, as this would disturb the steady state that has already been set at the beginning of the process by the flow of eluents (chemicals that react with one another).

This problem can be solved by using two syringe pumps per dosing channel, working alternately. This means that when the first syringe is empty, the second syringe takes over the delivery, while a 3/2-way valve refills the first pump from a reservoir. The first syringe then resumes delivery and the second syringe is refilled.

In order not to generate hard impulses when switching the pumps, flatter acceleration and deceleration ramps (crossflow) must be used instead of abrupt stopping when switching from one pump to the other. For applications at higher pressures, however, this is not sufficient to avoid all pressure or flow rate impulses, since the entire mechanical-fluidic system (including the pump that is currently pumping) is pressurized, while the replenished pump – waiting to be used – is under atmospheric pressure. If you now connect this refilled pump to the application by switching the 3/2-way valve, a pressure compensation takes place, which results in a compensation stream. As a result, a certain volume flows from the pressurized application into the unpressurized pump. This reduces the flow rate in the application and, in the worst case, can even become negative for a short time. This must be avoided.

We solve this problem by increasing the pressure of the refilled pump to the same pressure as in the application before connecting it to the application. We achieve this by using two pressure sensors, several valves and an intelligent software implementation. The refilled pump is first run against closed valves and a pressure comparison is made between the two pumps. Based on the parameters defined by the user, the acceptance criterion is reached after a short time, which assumes that the pressure is equal and the valve can therefore be opened for the application.

Since both pressures are the same at the moment of switching on, there is no pressure compensation and therefore no volume compensation flow. The pressure and volume conditions in the application remain constant as desired. The result is a continuous pulsation-free flow (Conti Flow).

The QmixElements software has a powerful script system to automate processes and procedures quickly and easily. This tutorial will give you an insight and many useful hints on some of the advanced features of QmixElements. Techniques, such as the use of variables, the use of JavaScript and the use of virtual channels for recording values in the graphical logger.

In this tutorial, you will create two scripts that generate flow gradients or flow profiles based on mathematical functions.

Preparation

Before you can start programming the scripts, you must configure your system. If you do not have the appropriate devices, you are welcome to follow the tutorial with simulated devices. You can download the QmixElements project with simulated devices and the script created in the tutorial here.

Important
For this tutorial you need the QmixElements version v20191121 or a newer version. If you are still using an older version, please update to the latest QmixElements version.

Latest QmixElements Version

For this tutorial we used two neMESYS low pressure syringe pumps with 5 ml glass syringes ❶. You can do this tutorial with other neMESYS syringe pumps or syringes, but you may have to adjust the flow rates. To switch the valves automatically during the generation of the flow profiles, activate the valve automation for both pumps ❷. Please configure ml/min ❸ as the unit for the flow rate.

To visualize calculated values from the script graphically, create a virtual channel ❹in the list of I/O channels. A virtual channel is an I/O channel that can be used for entering and outputting values.

To record and visualize the generated flow profiles graphically in real time, use the graphical logger and configure it according to the figure below. The current flow rate of both pumps should be displayed as well as the current value of the virtual channel ❶. As Log Interval❷ set a value of 0.1 seconds. Now you can start programming the first script.

Part 1 – Script for generating a sawtooth profile

The aim of this script is to generate a flow profile in the form of a sawtooth with one pump and to supplement the flow of the first pump with the second pump so that the sum of the two flows leads to a constant flow with a defined flow rate but with a mixing ratio that changes over time.

The sawtooth is generated by increasing the flow rate stepwise in a fixed interval from 0 to the desired target flow rate. The following parameters can be identified for the script:

• Number of steps for a single sawtooth ($GradientSteps)
• Duration of a step in milliseconds ($StepDuration)
• Target flow rate ($TargetFlow)

You create three variables for these parameters in your script. So you can change the parameters later quickly and easily in one place, without having to navigate through the complete script all the time. For each variable you assign a meaningful and unique name.

For the gradient, use 20 steps ($GradientSteps = 20) with a duration of 100 milliseconds each ($StepDuration = 100). The resolution of 100 ms is a reasonably fast time base for many applications. You can change these values later at any time. You can enter a fixed value for the target flow rate, or you can calculate the target flow rate based on the maximum flow rate of the first pump. To do this, you can insert the device property (Insert device property) for the maximum flow rate of the pump into the JavaScript field and use it for calculations. In this example we want to dose with one tenth of the maximum flow rate and therefore simply divide it by 10. You can also use other values or your own calculations:

$TargetFlow = $neMESYS_Low_Pressure_1.MaxFlow / 10

To create a single sawtooth, you now need a Counting Loop ❶. Two parameters can be configured for a counting loop: the number of Loop Cycles ❷ and the name of the variable (Counter Variable) in which the counter value for the current loop cycle is stored ❸. The input field for the loop cycles ❷ is marked with an orange V, i.e. you can use variables in this input field. At this point you can simply enter the previously defined variable $GradientSteps.

Within the loop you can now calculate the flow rate for the first pump and save it in a variable. The loop counter $i takes the values 0 – 19 for the 20 loop passes. You can therefore calculate the flow rate with the following formula:

❶ $Flow1 = $TargetFlow / ($GradientSteps – 1) * $i

I.e. the flow rate is 0 in the first loop pass and reaches the value $TargetFlow in the last loop pass. The sum of the flow rates of both pumps should give the value $TargetFlow. Therefore, in a second variable, you can calculate the flow rate of the second pump as follows:

❷ $Flow2 = $TargetFlow – $Flow1

You can now use these two values to start the dosing of the two pumps with the function Generate Flow ❶. To configure the Generate Flow function, simply select the appropriate pump and enter the calculated value $Flow1 or $Flow2 in the Flow field ❷. It is important that the unit for the flow rate is set to the same value as configured for the pump – in this case ml/min ❸. You have to deactivate the Run to completition checkbox ❹. If this field is active, the next function will not be started until the pump has finished dosing. In the case of the Generate Flow function, this would be when the pump is fully wound or drained. Since this is not desired here, but the script is to be continued immediately, deactivate the field.

To achieve the desired step duration for each loop cycle, add a Delayfunction ❶ as the last function in the loop. You can directly enter the variable $StepDuration in the configuration area of the function in the input field Milliseconds ❷. The Delay function delays the further execution of the script for the configured time period.

At the end of your short script, now add the Stop All Pumps ❶ to stop all pumps. To synchronize the recording of the flow rates in the graphical logger with the script flow, add the function to start the logger (Start Plot Logger) ❷ before the counting loop and the function to stop the recording (Stop Plot Logger) ❸ at the end of the script.

When your syringes are completely filled, you can now start the first test run. If the script has run without errors, you should see the following graphs in the graphical logger.

In the next step, extend the script to repeat the generation of the sawtooth cyclically until the user presses the Request Script Stop ❶ button. To do this, insert a Conditional Loop ❷ in front of the sawtooth loop. In the configuration area of the function, switch to the JavaScript area ❸ and enter the following condition:

❹ $StopRequested == false

This means that this loop is repeated continuously as long as the condition is fulfilled, i.e. as long as the global variable $StopRequested has the value false. The variable $StopRequested is a global script variable that is always present. After starting the script this variable always has the value false. Only when the user presses the button Request Script Stop ❶, the value of the variable is set to true.

Now you can insert the sawtooth loop into the conditional loop. Click on the Counting Loop ❺ and drag it to the Conditional Loop ❷. The counting loop is then inserted into the conditional loop. Now restart the script. The generation of the sawtooth is now repeated until you press the button Request Script Stop ❶.

After a few cycles, press the Request Script Stop ❶ button to end the script. If the script has run without errors, you should see the following graphs in the graphical logger.

Your flow profile script is almost finished. To improve the clarity, you can combine the variables you declared at the beginning of the script in a variable group (Variable Declarations). Insert a Variable Declarations function as the first function in the script. Then select all variables. Click on the first Create Variable function and then click on the last Create Variable function while holding down the Shift key – just as you would select several files in your file explorer.

Afterwards you can move all marked variables with the mouse into the variable group. With this you have grouped the variables and improved the clarity and readability of the script. In addition, it is now easier to move this group of variables to another position. Your script should now look like this:

In the second part of the tutorial you will learn how to modify the script so that sinusoidal flow profiles can be generated with the help of JavaScript functions. You will also learn how to add an initialization routine to the script that pulls up the syringes and how to record calculated values using virtual I/O channels in the graphical logger. Finally, you will receive tips on how to improve the readability of your script and document your script.

The QmixElements project with simulated devices and the script created in the tutorial can be downloaded here.

When Sir Alexander Fleming discovered penicillin in 1928, it was by coincidence, more than anything else. He had forgotten to take a bacterial culture from the lab and later notice that a fungus had grown on it. Apparently, this fungus was able to keep the bacteria in its environment at bay. Being a researcher, Fleming wanted to find out how the fungus managed to do this and extract the active substance it produced.

Penicillin made it possible to heal bacterial infections, often caused by minor wounds, that previously killed people in large numbers. But the discovery of penicillin and its first widespread application happened a long time ago. Over the years, other antibiotically active substances were found and used. Meanwhile, humanity has reached a point at which new agents are desperately needed, since various strains of bacteria have become resistant to antibiotics.

Fleming once commented his discovery by saying, “One sometimes finds, what one is not looking for.” Now, the time has come to actively look for such new agents, instead of hoping for their discovery. But where to begin? In the ground! A cubic centimeter of soil contains about a billion lifeforms. If one could cultivate and examine the various species, the chances of finding one or even several promising candidates would be pretty good. Applied to an agar plate (a petri dish with a culture medium), microorganisms multiply and form colonies. However, a small number of fast-growing species usually impede many of the slower species by suppressing their growth. This means that the slower-growing species never register. They do exist in soil, however, apparently because there they find habitats conducive to their growth. So, if you wanted to cultivate them, you would have to offer them those same habitats.

And this is where microfluidics come into play. The so-called segmented flow is one of the wonderful tools in the microfluidic toolbox. This flow is generated in micro-reactors featuring channels with a diameter of 100 to 200 µm. A polar liquid (water) is introduced to an intersection point of a nonpolar carrier flow (oil). Since the two liquids will not mix, individual water droplets will be torn away and join the oil flow. The droplet sizes are very defined and constant and they happen at defined intervals, while being separated from each other by the oil between them. Large amounts of these droplets can be created in a very short time. If the soil concentration in the water is correct, each droplet contains just one individual or very few organisms, existing in their own habitat, where they can procreate and form cultures. Arranged on a coil of narrow tubing, similar to beads on a pearl necklace, they can now be taken to an incubator offering the appropriate growing environment.

Generating such small, defined and segmented flows requires highly precise, pulsation-free and controllable pumps, such as the neMESYS 290N low-pressure pump made by CETONI. Thanks to its excellent dosing properties, substances, such as nutrients, can be dosed into the individual droplets. Also, it is possible to detect clouding and separate promising droplets. The CETONI Elements (QmixElements) software allows users to operate the system comfortably and intuitively. Maybe, this method will lead to a breakthrough one day. While it is the proverbial search for a needle in a haystack, microfluidic methods and high-quality equipment make it possible to miniaturize and automate this process.

In their latest publication, a team from the laboratory of Thomas Gervais, at École Polytechnique de Montréal set the foundations of “microfluidic multipoles”, a new kind of open-space microfluidic systems. The experimental demonstration of the principles exposed required the use of up to 12 Low Pressure Syringe Pumps neMESYS 290N. The pumps powered microfluidic multipoles were further used to automate an immunofluorescence assay on an antibody array.

Laboratory Setup

Specially developed and 3D-printed sample heads were used, which were positioned in close proximity with the surface to be processed. By simultaneous injection and aspiration of fluids from the numerous apertures, periodic patterns of confined reagents could be formed on the surface. The flow under these devices could be modeled by using a direct analogy with electromagnetic theory (so-called multipoles). Under this analogy, the neMESYS pumps impose a flow rate which is analogous to a constant charge in an electrostatic field. The flow streamlines generated are, in turn, mathematically analogous to the electric field distribution around charges and can be modeled easily. By using the fluorescent dyes, the patterns could be further visualized and analyzed by fluorescence microscopy.

With their publication in Nature Communications this year, Goyette, Boulais, et al. provide new tools to design and perform surface processing and biological assays to further the development of open-space microfluidics. The setup for the investigation of multipoles could be realized with a modular and high-precision CETONI dosing system. In order to generate continuous multipoles with sub-millimetre accuracy while minimizing reagent consumption, an extremely uniform and pulsation-free fluid flow is required. The neMESYS precision syringe pumps are ideally suited for precise dosing of smallest fluid quantities.

Microfluidic multipoles

The PID-regulated drive unit of the syringe pump ensures an extremely even drive of the syringe piston, prevents stick-slip effects and thus guarantees the high accuracy and pulsation-free flow of the generated fluid, which was a prerequisite for this application. Due to the modularity, the setup can also be extended at any time.

Used CETONI devices:

• Base 120
• 12 x neMESYS Low Pressure module 290N

Literature:

Goyette P.-A., Boulais E., Normandeau F., Laberge G., Juncker D., Gervais T. Microfluidic multipoles theory and applications. Nature Communications. 2019, (10), 1781. DOI: 10.1038/s41467-019-09740-7