Characterization of the permeability of sealing tapes and development of a viscosity measuring technique in shaken reactors

摘要

The first part of this work deals with the characterization of 12 commercially available sealing tapes for microtiter plates with regard to their oxygen and water vapor permeability. Special attention was given to the influence of the evaporation on the liquid temperature in the well. The results of the experimental analysis showed that three of the investigated sealing tapes do not permit oxygen transport and are therefore unsuitable for aerobic cultivation. With respect to water vapor permeability, the remaining sealing tapes exhibit vast differences. On average, the water loss was 40% of the initial volume after 24 hours at 37°C and 45% humidity. This immense liquid loss led to differences of up to 3.8°C from to the desired temperature due to evaporative cooling. Accordingly, none of the 12 sealing tapes met the requirements of the user. To address this optimization potential, a mathematical model was developed. With the help of the model, it was shown that, contrary to oxygen supply, the evaporation rate is linearly dependent on the size of the diffusion area. A reduction of the diffusion area can therefore reduce evaporation without affecting oxygen transport. The second part focused on the development of a measurement technique for the quantitative, non-invasive detection of viscosity in shake flasks. The measurement technique is based on detecting the position of the rotating bulk liquid as it changes with respect to the direction of centrifugal acceleration dependent on the viscosity. It is possible to correlate this offset in the liquid motion with the viscosity. For non-invasive detection of the liquid position, a fluorescence as well as a transmission measurement were developed. To convert the information about the liquid’s position in the shake flask into a viscosity signal, a calibration was established using model fluids of known viscosity. The developed 8-flask-device was validated by the cultivation of the bacteria Paenibacillus polymyxa and Xanthomonas campestris. The comparison of the online measurement technique with a conventional measurement on a rheometer showed that the viscosity can be measured with an accuracy of 3.11 mPa·s ± 0.6 mPa·s up to 120 mPa·s.