Bioreactor characterization allows evaluating mixing capacity and homogeneity inside the bioreactor. It simulates parameter
evolutions while regulations are ongoing during a process.
Oxygen transfers. The oxygen transfer coefficient (KLa) was measured with air at the previous working flow rate and at the maximum flow rate allowed by the equipment. The air-flow
rates applied during the process were representatives to 1,250 L production bioreactor flow rates.
Stirred and paddle mixing bioreactors have a sparger to introduce air and oxygen during dissolved oxygen regulation, while
an orbital shaking bioreactor regulates oxygen concentration by injecting air and oxygen only in the headspace.
The agitation speed was the same as the one applied during the production process (see Table 2).
Table 2. Comparison of KLa measured at working flow rate and maximum flow rate between disposable bioreactors, a 1,250 L MSB production bioreactor,
and a 3.6 L process development bioreactor.
The cells studied did not require a lot of oxygen. A low KLa (0.44h–1) was sufficient to run the process.
The air-flow rates applied in the orbital shaking bioreactor during the process were defined according to Merck Serono Biodevelopment
and supplier experiences. These flow rates should have been decreased as KLa was above traditional bioreactors.
The stirred mixing disposable bioreactor obtained the maximum oxygen transfer. Despite air injection only through the headspace,
the orbital shaking bioreactor had a KLa close to the stirred mixing bioreactor.
The paddle mixing bioreactor had a maximum KLa close to the traditional bioreactor.
Mixing time. Mixing time was also measured in phosphate saline buffer at the maximum working volume and the agitation speed applied during
Mixing time was measured by injecting concentrated sodium hydroxide from the top of the bag (mixing down) and from the bottom
of the bag (mixing up) (Table 3).
Table 3 : Comparison of mixing time measured in seconds between disposable bioreactors, 1,250 L MSB production bioreactor,
and 3.6L process development bioreactor.