The Biostat CultiBag RM is shown to reach KLa values of 43.2 h-1, and 12.9 h-1, respectively, at small scale for 2-L and 20-L
systems. The reactor easily provides oxygen transfer rates sufficient for medium cell densities in seed stage microbial fermentation.
E. coli, still the preferred microbial host for recombinant protein production, was shown to be successfully cultivated to medium
cell densities. In addition, growth of the C. diphtheria reached an OD590 of 4.95 in the CultiBag RM and 7.26 in the stainless-steel fermenter after an 8 h cultivation period, indicating
that it was successfully cultured in preparation of a seed inoculum despite a drop in dissolved oxygen concentration. A second
trial confirmed these results. Despite the high demand for aeration and agitation in microbial cultures, we have demonstrated
that the Biostat CultiBag RM is suitable for microbial seed stage cultivation. The superior gas mixing capability optimizes
headspace aeration and creates a suitable vessel for microbial cultivation.
When comparing a rocking bioreactor with and without process control as demonstrated by the CHO-A process, a different cell
culture performance is demonstrated. The rocking device with control was the CultiBag system with feedback control loops for
pH and DO to disposable sensors, and the rocking device without any pH and DO control was the Wave bioreactor. Both systems
exhibit similar rocking motion mixing. The Wave bioreactor exhibits a rocking motion, which starts and stops, forcing the
culture to create turbulent waves for mixing. The Wave bioreactor was gassed with a constant flow rate of air and CO2, without any feedback control mechanisms. A constant flow of CO2 can cause pH fluctuations to occur as the uncontrolled CO2 dissolves into the media and converts to carbonic acid. The CultiBag offers a gentler and continuous rocking motion with
an inbuilt feedback control mechanism, adding CO2 on demand and only when the culture needs it. The constant flow of air at the liquid surface prevents CO2 accumulation and pH fluctuation. Both systems had similar rocking and temperature control. The Wave bioreactor was shown
to have a higher final CVC value, a lower RP HPLC titer, and a lower average specific productivity, thereby indicating that
process control offers many advantages for cell cultivation.
When comparing the CultiBag side-by-side with a conventional stirred-tank bioreactor system in the CHO-A process, the overall
cell culture performance of the CultiBag bioreactor was comparable to the STR. In this case, both systems had good control
systems in place, but the STR used reusable sensors and the CultiBag used disposable sensors. This demonstrates the comparability
between conventional and disposable sensor technology in a live process. Additionally there was no oxygen limitation in the
rocking bioreactor compared with the stirred tank. In fact, the final RP HPLC titer value and the average specific productivity
of CultiBag were higher than that of the STR.
This is further demonstrated by the CHO-S and CHO-K1 process, which also shows comparable growth and productivity to the STR.
Additionally, real time data plots show the online process control of the disposable sensors in the CHO-X evaluation, demonstrating
that the process control of disposable sensors are similar to reusable sensors. We can therefore conclude that, not only do
disposable sensors provide adequate control of processes, but that these rocking bioreactors can exhibit cell growth productivities
similar to a traditional STR and, in some cases, even higher. With the added benefit of disposable systems in terms of cleaning,
sterilizing, reduced cross contamination, and flexibility, it is obvious to see why the industry is focused on disposable
Millie Ullah, PhD, is a product manager, disposable bioreactors, at Sartorius Stedim North America, Edgewood, NY, 631.254.4249, firstname.lastname@example.org
Terry Burns is a senior technology scientist at Wyeth Vaccines, Sanford, NC. Amardeep Bhalla, PhD, is a senior scientist at Schering-Plough, Summit, NJ. Hans-Wilhelm Beltz is manager of recombinant technology at CSL Behring, Preclinical R&D, Marburg, Germany. Gerhard Greller, PhD, is a scientist of R & D pharma process and Thorsten Adams, PhD, is an application specialist of fermentation technology, both at Sartorius Stedim Biotech GmbH, Goettingen, Germany.