Embedded resistance wire as a heating element for temperature control in microbioreactors

This paper presents the technical realization of a low-cost heating element consisting of a resistance wire in a microbioreactor, as well as the implementation and performance assessment of an on/off controller for temperature control of the microbioreactor content based on this heating element. The microbioreactor (working volume of 100 mu L) is designed to work bubble-free, and is fabricated out of the polymers poly(methylmethacrylate) (PMMA) and poly(dimethylsiloxane) (PDMS). The temperature is measured with a Pt 100 sensor, and the resistance wires are embedded in the polymer such that they either surround the reactor chamber or are placed underneath it. The latter can achieve an even temperature distribution across the reactor chamber and direct heating of the reactor content. We show that an integrated resistance wire coupled to a simple on/off controller results in accurate temperature control of the reactor ( plus or minus 0.1 degree C of the set point value) and provides a good disturbance rejection capability (corrective action for a sudden temperature drop of 2.5 degree C at an operating temperature of 50 degree C takes less than 30 s). Finally, we also demonstrate the workability of the established temperature control in a batch Saccharomyces cerevisiae cultivation in a microbioreactor.