PDMS Quake valves and co: a review
Introduction to PDMS multilayer valve
PDMS pneumatic microvalves have been introduced for the first time in 2000 almost simultaneously by Stephen’s Quake group (Quake microvalves) and by Hosokawa and Maeda («doormat» microvalves). Since then, similar systems listed here from Au’s excellent review  have been designed using different geometry.
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Each of them involves different advantages and drawbacks but they are all based on the same principle: the pressure-driven deformation of a soft material (generally PDMS) that clogs or releases liquid flows into microsystems.
Quake PDMS bilayer micro-valve
Figure 2 :Microscopy image of activated Quake valve from 
The Quake microvalve is the most commonly used pneumatic microvalve. It involves a bilayer PDMS microfluidic chip. Liquid flows inside the bottom layer while the upper layer integrates an air network. When activated, the latter can selectively compress and clog channels of the fluidic layer, which enables fluid motion control. Quake valves show high potential for some microfluidic applications.
«Doormat» style bilayer micro-valves
Figure 3 : Scheme and microscopy image of ”doormat” microvalves, from .
Like Quake microvalves, «doormat» style microvalves involve a bilayer structure with a liquid network and an air network. But unlike the Quake microvalves, these ones are normally-closed valves, i.e. in rest state, the liquid channel is blocked by a PDMS barrier. In order to open the valve, a depressure must be applied in the air network. That depressure deforms the wall between the two networks, enabling the fluid to overpass the PDMS barrier.
Figure 4 : 3D representation of closed and opened plunger valves, from .
Plunger microvalves involve a multilayer design where the fluidic inlet and outlet are on different layers and separated by a holed layer. A fourth pneumatic layer enables to control the deformation of PDMS, hence enabling or disabling fluid flow through the holed layer. Plunger microvalves can be considered as complex systems that imply many microfabrication steps. Nevertheless, that complexity enables to tune the valves features (e.g. the max operating pressure).
«Curtain» style micro-valves
«Curtain» style microvalves are a variation of «doomat» style microvalves. They involve a bilayer (liquid-pneumatic) structure and a barrier in the middle of the channel alike the previously described ‘‘doormat’’ valves. But unlike these ones, the «Curtain» style microvalves directly deflect the barrier when the vacuum is applied on the pneumatic layer, hence enabling liquid to flow through the channel.
Figure 5 : Schematic representations of a closed and opened check valves, from .
Different sorts of check valves have been created using membranes of PDMS (or similar soft polymer). As in commonly used check valves, a membrane can deflect in one direction enabling the liquid to flow. But if the flow direction is inverted, the membrane is mechanically constrained which prevents back flow. This check valve does not involve a pneumatic actuator.
Lateral deflection membrane micro-valve
Figure 6 : Design of lateral deflection microvalve, from .
The lateral deflection valve is the only microvalve described here that requires a single PDMS layer. As suggested by the name, these valves are activated by a lateral deflection of the PDMS membrane, and not from above or below like in other microvalves. Nevertheless, this design involves rectangular channels that cannot be totally sealed. Therefore, lateral-deflection valves are more tunable flow restrictors than real valves.
Pneumatic PDMS micropumps
Figure 7 : Quake valve based peristalsis micropump, from .
Pneumatic micropumps generally correspond to a series of pneumatic valves actuated simultaneously to generate a peristalsis motion. Depending on the microvalves, the corresponding pumps have different flow rate features. The basis of generating a peristalsis motion generally involves high speed sequencing of the air distribution in the pneumatic layer. Nevertheless, some specific designs allow to activate pumps with a single pressure line.
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For more tutorials about microfluidics, please visit our other tutorials here: «Microfluidics tutorials». The photos in this article come from the Elveflow® data bank, Wikipedia or elsewhere if specified. Article written by Christophe Horvath, Luke Lutchanah and Timothée Houssin.
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