Flow Control Technologies
To perform effective experiments in microfluidics, one needs to master the different flow control technologies available to use the most suitable way to control microfluidic flows. This article aims at presenting a short review of the existing techniques.
The main microfluidic flow control technologies are listed below.
- Applying pressure to fluids in a sealed container with a fluid outlet. The fluids will move because of the pressure difference, according to a simple relation, similar to Ohm’s law for electricity (V=RI): In the case of fluid flow, P=RQ. The fluidic resistance is a function of the geometry of the channel and the viscosity of the fluid. For more information on the microfluidic resistance .
- Using volumetric control as syringe pumps or peristaltic pumps. Here the principle is to use a mechanical movement that modifies a volume to apply a flow-rate. For syringe pumps, modifying the syringe volume and the infusion rate enable to achieve different flow-rates.
- Other techniques as electro-osmotic pumps or integrated micropumps are more specific and are described below.
To make the best, it is important to consider the following elements:
- The flow-rate or the pressure range you need.
- How quickly you need to set or change the flow-rate.
- How stable you need the flow-rate to be.
Based on these methods, different flow control techniques and technologies are available to manage microfluidic flows.
1. Using hydrostatic pressure
This is the simplest way to move fluids: the basic idea is to put the inlet reservoir higher than the outlet reservoir in order to let the gravity force move the fluid from the inlet to the outlet, just like a water tower.
2. Pressure regulator or pressure pump
The working principle of such pumps is to pressurize the sample reservoirs in order to control the pressure drop between the inlet and the outlet of the microfluidic
system. The responsiveness of the generated flow-rate depends on the responsiveness of the pressure pump. For instance, all our MFCS™ series offer a settling time down to 100ms and a resolution of 0.03% full scale (pressure sensor resolution) as well as a stability of 0.1% CV on measured values.
3. Syringe pump
Widely used in standard laboratories, syringe pumps are based on a mechanical system usually actuated by an electric stepper motor that pushes a syringe at a fixed rate.
The liquid is contained in a flexible tube and alternative compressions and relaxations will draw in the liquid and result in flow.
4. Electroosmotic pump
The main idea is to create an electro-osmotic flow in a porous media.
4. Integrated micropump
Several kinds of integrated micropumps exist: there are mostly based on a peristaltic principle with flexible membrane made of PDMS.