Thermo-pneumatic, single-stroke micropump

Abstract

A novel single-stroke, pipette-like micropump capable of delivering discrete amounts of liquid in the µL range free of pulsations was developed and fabricated. No moving parts are required for device operation, so that low-cost polymer fabrication is possible, e.g., casting of poly(dimethyl siloxane) (PDMS). By implementing a dead-end channel with an inlet port on one end and a sealed chamber on the other, thermal gas expansion of the trapped air in the chamber is used to manipulate the liquid, similar to a pipette. The air in the chamber is heated in a controlled way by an external heater, e.g., a resistive or Peltier element. With a heater temperature variation of 50 K, the pumped liquid volume is around 2 µL for a 16-µL chamber, which is approximately equal to the air volume change caused by this temperature change. If required, the liquid flow can be electronically controlled by maintaining a constant heating or cooling rate of the heater. Flow rates for liquid uptake on the order of 0.34 µL min−1 were obtained by cooling the heater at the rate of 10 K min−1. For optimization of the pump design, mathematical models have been developed to predict the static and dynamic behavior of the pump. The resulting data compare well with the experimental values. Different from most flow-through pumps with inlet and outlet, this low-cost, thermo-pneumatic micropump allows us to draw in and to eject liquids from the chip without priming. Also hydrophilic surfaces are not required if certain design rules are followed. An additional advantage of this thermo-pneumatic principle is its absolutely pulsation-free operation, which can be useful for the formation of concentration gradients.