withdrawn through the underflow pipe at the bottom of the insert bag [52]. As no seals

are required for connection of the single use insert bag and the conical rotor, and the

inserts have been approved by the FDA, these systems are attractive for large-scale

virus production [19,43]. To our knowledge no published study reported details re-

garding the use of centrifuges for the cultivation of viruses in perfusion mode, so far.

However, they have been routinely used in commercial perfusion processes for

production of labile proteins [19]. Drawbacks of the Centritech® system as well as the

other centrifuges are the high investment costs. Furthermore, long residence times of

the cells inside the centrifuge (up to 9 min) and high wall shear stress in the insert bags

are disadvantageous. Moreover, reliability and robustness of the perfusion process is

solely dependent on the quality of the insert bag, which has to be replaced at every 20

million revolutions or 31 days of continuous operation [19,53]. Compared to a

filtration-based perfusion system, usage of the Centritech® system has been shown to

reduce the productivity in MAb production by 30% [79].

Centrifuges can also be used as separate external “pseudo” retention devices for

small-scale screening systems. Particularly for research purposes including initial

process development and high-throughput screening, small-scale semi-perfusion

shake flask cultivations are a convenient alternative to full perfusion processes

[11,19]. Using small-scale systems (shake flasks or spin tubes), total medium usage

is significantly reduced, while even for HCD cultures, cell viabilities similar to

bioreactor perfusion systems can be achieved [11]. In semi-perfusion, cells are

Feed pump

Centrifuge

Balance

Weight control

Permeate pump

Spent medium

Feed

medium

FIGURE 6.7 Schematic illustration of a disc centrifuge setup for perfusion processes. The

main streams of the centrifuge can be divided into three parts: The feed stream containing

cells is pumped from the bioreactor into the centrifuge. Centrifugal forces push the cells

outward and separate them as the underflow, which can be pumped back into the bioreactor.

Cell-free supernatant is constantly removed from the overflow, allowing fresh medium to be

added to the bioreactor. Figure adapted from [ 65].

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Bioprocessing of Viral Vaccines