New perspectives in shake flask pH control using a 3D-printed control unit based on pH online measurement

•We investigated the possibility to perform online pH control in shake flask.•A combination of a SLS printed case and micropumps was tested.•pH measurement was achieved by pH chemosensors “sensorspots”.•pH is controlled very precisely during cultivation for at least 24h.•The progressive miniaturization prevents a severe top-heaviness of the system. Online pH control during microbial shake flask cultivation has not been established due to the lack of a practical combination of an online sensor system and an appropriate control unit. The objective of this investigation was to develop a minimum scale dosage apparatus, namely shake flask controller (“SFC”), which can control the pH during a complete cultivation and serves as technical example for the application of small liquid dispensing lab devices. A well evaluated optical, chemosensor based, noninvasive, multisensory platform prototype for online DO (dissolved oxygen)-, pH- and biomass measurement served as sensor. The SFC was designed as cap-integrated, semi-autarkical control unit. Minimum scale working parts like the commercial mp6 piezoelectric micropumps and miniature solenoid valves were combined with a selective laser sintering (SLS) printed backbone. In general it is intended to extend its application range on the control of enzymatic assays, polymerization processes, cell disruption methods or the precise dispense of special chemicals like inducers or inhibitors. It could be proved that pH control within a range of 0.1pH units could be maintained at different cultivation conditions. A proportional-integral-derivative- (PID) controller and an adaptive proportional controller were successfully applied to calculate the balancing solution volume. SLS based 3D printing using polyamide combined with state-of-the-art micro pumps proved to be perfectly adaptable for minimum size, autoclavable lab devices.