Biology Reference
In-Depth Information
17. The pO
2
electrode is calibrated in terms of percentage of oxy-
gen saturation, after sterilization, with culture medium at
operating conditions (temperature, airflow, and stirrer). To
be sure that the electrode is good to be used is necessary to
check its response. Connect the pH cable of the correct unit
(where the bioreaction is going to run) to the electrode.
Connect the temperature sensor cable to the unit. Observe
the pO
2
value obtained with the electrode in the atmospheric
air. Place the electrode in a container enriched with N
2
envi-
ronment (can be obtained by supplying N
2
by the gas flow of
the unit to the inside of a small cup covered with parafilm)
and observe the decrease in pO
2
values of the electrode. A
good electrode response corresponds to a decrease of pO
2
to
10 % in less than 1 min and to lower than 1 % in less than
10 min. If this criteria is not meet than verify the probe.
18. There are several types of aerations systems. In STBs with
microcarrier cultures, cells at low densities or with low O
2
demanding, the aeration is performed via the headspace. The
oxygen transfer in this case is affected by the surface area and
the stirrer speed. The operation parameter ranges are
0.1-1 vvm. For higher cell densities and higher O
2
demanding
cells, one of the systems used is the direct sparging of air or
oxygen with ring spargers (drilled holes >0.5 mm diameter)
placed below the stirrer. This allows better dispersion and lon-
ger residence times of gas bubbles in the culture liquid result-
ing in improved gas transfer rates. The operation ranges from
0.005 to 0.4 vvm.
19. The probes of the bioreactor should be submerged in liquid in
order to avoid any damage by drying during sterilization. The
liquid can be MilliQ water (resistivity of 18.2 MΩ cm) or
D-PBS.
20. The number of the impellers assembled depends of the vol-
ume/size of the bioreactor and the type of the impeller on the
type cell culture to be performed. The most common impel-
lers for mammalian cells are 3-blade impellers (or marine
impellers). These impellers allow less shear stress and are ideal
for maintaining microcarriers in suspension. Other impellers
also used are the rushton turbine with 4 or 6 bladed versions.
21. The probes should be placed separately and distributed along
the bioreactor to avoid nonhomogeneous fluid distribution
due to the electrodes interference. The pO
2
probe should be
placed far from the entry ports since adding liquid to the bio-
reactor can create air bubbles that can be trapped under the
electrode membrane an interfere with the measurements. If
bubble trapping is observed, increase stirring rate for a moment
to remove them.
