Introduction

This article covers some tips for setting up microfluidic systems. Flow resistance is a crucial parameter for flow stability, and effective optimization of flow resistance and pressures during setup will help you achieve the best performance from your microfluidic flow control system.

Modifying Flow Resistance

Higher flow resistances improve flow stability and flow rate resolution – however, increasing flow resistance also increases the pressure required to obtain the required flow rate.

Hence, it is important to be careful while increasing the resistance to avoid exceeding the maximum pressure allowed inside the microfluidic chip, as this can change the experiment parameters or even create leaks or bursts.

This risk can be best avoided by changing the external resistance upstream from the microchip. Using this method, no increase in pressure will take place in the chip and the integrity of the experiment is preserved.

The example shows the manner in which, by increasing the external flow resistance, the flow control performance can be increased. It is possible to obtain an improvement in the flow control performance of microfluidic set-up #1 by adding external resistance before the chip (microfluidic set-up #2) or after the chip (microfluidic set-up #3).

Figure 1. Schematics of the microfluidic setups

The pressure controller used for flow control is a microfluidic flow control system from Fluigent (MFCS™) with the technical properties given in the below table (Table 1).

Table 1. Pressure flow controller performance

The three setups are explained in Table 2. For all three setups, the same chip design has been used. In setup #2 and #3, identical tubing characteristics have been used. Only the positioning has been changed, i.e whether the resistance is added before or after the chip.

Table 2. Description of the microfluidic setups

Results

Table 3 shows the impact on flow control performance and pressure in the chip.

Table 3. Flow control performances

It can be seen from the results that improving the resistance enhances flow control by:

• Enhancing the flow rate resolution– it is seen here that the resolution is 3.5 times higher than with an increased flow resistance
• Enhancing the flow rate stability– it can be seen from the above table that the flow rate variation is 3.5 times better with higher flow resistance

Also, external flow resistance management helps maintain the pressure in the chip at a minimal value, even if there is an increase in the pressure provided by the pressure actuator.

Conclusion

Flow resistance management is a powerful tool to increase the flow control performances of a flow control device based on pressure actuation.

Fluigent offers pressure actuation systems with highest stability and resolution (0.03% of the full scale pressure range) that helps achieve optimum performances without resistance management. In addition, the pressure ranges of the MFCS™ (from -345mbar to 7bar) cover a broad range of applications in rheology, chemistry or biology studies.