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Quality aspects / reproducibility:
For many R&D projects, the amounts of biomass and cell products generated in Erlenmeyer shake flasks far exceed the amounts required for subsequent analysis or bioassay. Researchers in many areas have - of course - realised this for quite some time, but were hesitant to use miniaturised growth systems such as microplates because of the worry for quality loss. This concern was justified by the following problems:
- wells were not adequately closed so that evaporation rates were too high and cross-contamination could occur
- well-to-well variability: wells in the outside rows received more oxygen and lost more water
- oxygen transfer rates were often more than 10 fold lower than in shake flasks because of too low shaking frequencies and amplitudes (high shaking frequencies would have caused cross-contamination).
In our system, all of these problems have been adequately addressed; the wells of microtiter plates covered with our sandwich covers are now a fully mature alternative to Erlenmeyer flasks:
- all wells are hermetically closed by our sandwich covers; evaporation is reduced 20-fold (1-2% per well per day at 30 ºC) while still a sufficient degree of exchange of headspace air with the surroundings is maintained.
- at a working volume of 500 ul culture (in a well from a 96-square deepwell plate), the oxygen transfer rate at 300 rpm and a shaking amplitude of 50 mm is 38 mmol O2/l/h, which is at the high end of that obtainable in Erlenmeyer flasks. Also for the three other types of microtiter plates, suitable incubation conditions resulting in OTRs of 30-50 mmol O2/l/h are achievable (for more details see hydrodynamics, oxygen transfer rates).
- all wells behave as individual - exactly identical - mini-reactors; identical hydrodynamics are secured by i) the well defined shape of the wells, ii) the exactly identical mixing force (the centrifugal force), and iii) the individual connections of the wells with the outer air.
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