3.1.1 Mixing time in 2 L STR
Figure 2A shows the mixing time variation in the 2 L STR with varying
stirrer speeds and two different working volumes, 1.5 L and 1.8 L, to
account for changes upon addition of induction agents. As expected, the
graph shows that mixing time was inversely proportional to the stirrer
speed. It can also be seen that for the two fill volumes evaluated, the
mixing times were comparable as demonstrated by the overlapping error
bars. The mixing time ranged from 7 – 17 s for 1.5 L and 7 – 24 s for
1.8 L. At higher agitation rates (i.e. ≥ 225 rpm), the mixing time
values were less than 10 s, which is necessary to maintain a homogenous
culture environment (Amanullah et al., 2004; Alvin W. Nienow, 2006;
Silk, 2014). With respect to the 2 L STR LVV production process model,
the platform operating stirrer speed fell in the range of higher
agitation rates, hence, was sufficient to maintain the required
homogeneity for optimal HEK293T growth and LVV productivity. In
addition, the mixing time values from this work was comparable with
those found in literature for other bench-scale bioreactors as
summarised in Table 1. From the table, we observe that the variety of
mixing time methods used by different groups all produced consistent
datasets for a similar range of Reynolds numbers as evaluated in this
study.