Mechanically adjustable chemostats based on stimuli-responsive polymers

A method for a mechanical operating point adjustment of hydrogel-based devices performing closed loop control has been developed. These so-called chemostats automatically control certain chemical and energy-based conditions of a liquid. The adjustment of the controlled condition is provided by a defined change of the triggering point by the activation unit of the device and the hydrogel actuator determining the basic functional relationship. The antagonistic principles of automatic valve chemostats were introduced, which can alternatively realize a normally open or a normally closed function. Using the hydrogel poly(N-isopropylacrylamide) the chemostatʹs switching concentration of ethanol in aqueous solution can be adjusted in the range of 5 and 20 wt.% with a practically relevant precision of 1 wt.%. The controllability of an energy-based condition by the chemostat was investigated on the process temperature control. We found that this temperature can be mechanically adjusted in a range of 25 and 35 °C with a standard deviation below 0.75 K.