a pre-screening for best conditions at a smaller scale like shake flasks

(SF) or spin tubes prior to advancing to the bioreactor stage [15]

(see Note 5).

Furthermore, it is often necessary to provide additional nour-

ishment in the form of a concentrated glucose (e.g., 45% w/v)

solution to keep this nutrient from being fully depleted (see Note

6). Several CHO-derived cells require the addition of glutamine.

Depending on the cell type and the way the gene of interest was

introduced, additional metabolic supplements may be required

(HAT medium, Folate).

Due to the additional stress that the cells may be exposed to in

bioreactors, supplementation of the media with a shear protectant

such as Pluronic might be required [16].

2.4

Antifoam

Generally, antifoaming agents need to be added to the bioreactor to

control the level of foam generated by stirring and gas addition

through the sparger [17]. As these chemicals can have a negative

impact on the cells and downstream purification steps, their addi-

tion should be limited to the minimum necessary [18] (see Note 7).

2.5

Controller

Controllers are available from many different manufacturers and

can often be combined with equipment (bioreactor units, probes)

from another supplier. While these devices can be operated in

different modes with various degrees of complexity and automa-

tion, their core function is to integrate readouts from the bioreac-

tor, like vessel temperature and amount of dissolved oxygen

(DO) and adjust outputs to reach a particular setpoint. To provide

an example, a specific setpoint in DO can be maintained by chang-

ing the rotation speed of the impeller or the amount or composi-

tion of the injected gasses (or both), until the desired DO has been

reached. Furthermore, controllers allow for the automatic addition

of feeds and other additives and the control of the pH as well as

changes in cultivation temperature at a pre-defined time or based

on process data (see Note 8). Table 1 is meant to serve as a general

guideline and starting point for operation parameters.

2.6

Probes

Levels of dissolved oxygen (DO) and pH are typically measured by

probes inserted into the bioreactor. They are available using differ-

ent technologies and in single- and multi-use format. The latter

need to be cleaned and sterilized prior to use and might require

additional calibration and quality control steps at regular intervals.

Conditions for long-term storage also need to be considered. Some

manufacturers of single-use bioreactors now also offer pre-installed

measurement capabilities which however usually require dedicated

equipment [19]. In addition, a number of other technologies

Benchtop Bioreactors in Mammalian Cell Culture: Overview and Guidelines

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