Surface micromachined polymer actuators as valves in PDMS microfluidic system

To control flows in microfluidic systems there is a need of valves. Desirable properties of such valves are in general low cost, low dead-volume, fast response and low power-consumption. For bioanalytical purposes the requirements also include biocompatibility and ability to function in biological fluids. One way to address these problems is to use surface-fabricated actuators, and then bonding the actuator chip with high aspect-ratio flow-channels in a thick polymer cover. A suitable cover structure can be made in elastomeric poly(dimethylsiloxane) (PDMS) which can be joined to a silicon surface. The active valve structures can be micromuscles, i.e. actuators based on conjugated polymer such as polypyrrole (PPy), which can be electrochemically doped. The reversible doping of PPy forces counterions to flow into or out of the polymer to balance the charge, resulting in a volume change. This volume change can be used in a bilayer actuator, where a metal can serve as constant volume layer as well as electrical contact to the polymer layer changing volume under reversible doping.