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 The
Novaferm cell-cultivation systems are designed for optimal reliable
growth of animal and plant cells in an easy, controllable way. The
product program includes systems for cells in suspension and/or on
microcarrier support. The cultivation volume range is laboratory scale
3—20 l, pilot plant scale 5—75 I and industrial scale 20—1 000 I utile
volumes.
The basic concept is gently stirred reactors, a well-defined and
controlled environment and aseptic design for safe operation over long
cultivation periods.
Cultivation of sensitive cells requires advanced control, which is
achieved with the Novaferm
Fermenter Control System connected to the
fermenter via the supply cabinet. Sterilisation, temperature control,
agitation, gassing and other functions are controlled by this
combination.
Most cells are very fragile and sensitive to gas bubbles and
gentle agitation and oxygenation systems are therefore necessary. If the
cell is anchorage-dependent, this means special requirements for the
vessel. For cultures in suspension, the conventional fermenter vessel
with certain modifications can often be used. Conversion kits with bottom-mounted,
magnetically coupled agitators, are available for the Novaferm standard
fermenters.
For cultivation of anchorage-dependent cells, we have developed a
special conical vessel with a top-mounted, magnetically coupled agitator.
This means that there are no bearings below the liquid level that may
cause grinding of beads and cells. The conical shape results in good
distribution of beads at slow agitation speed and the possibility of
growing small or large culture batches in the same vessel. The internal
parts may be selected for the process conditions required.
The vessel, sensors and process piping are sterilisable in situ.
Materials are selected with respect to the sensitive requirements of the
cells. A broad selection of accessories is available, such as different
gassing systems, perfusion systems, incinerators for exit gas and
clean-steam generators. Future upgradings regarding both control
functions and vessel configurations are permitted by the modular design
and easily carried out by the user.
VESSELS
 The
fermenter vessel, made of high-quality, acid proof stainless steel, is in
its laboratory version mounted directly on the drive unit by means of a
quick connector. The pilot version is mounted on a mobile stand (total
volume up to 200 I) and may be tiltable to facilitate cleaning and
maintenance. The industrial vessel type is mounted on a fixed stand, may
be tiltable and is often skid-mounted together with the piping and
control cabinet. All vessels are jacketed and sterilisation is carried
out in situ.
Connection between vessel and supply unit is achieved by flexible
tubing for easy detachment and prevention of external influence when
using load sensors. The process gas is fed to the culture through a
sterile filter directly attached to the vessel. The top mounted agitator
is magnetically coupled to minimize the risk of contamination. All
process connections are 25 mm, sealed with 0-rings and sterilisable in
situ. Steam-sealed lid and connections are available as options, e.g. for
pathogenic processes.
A viewing glass is mounted in the side of laboratory fermenters
and in the lid or top of pilot and industrial vessels.
All internal components, such as gassing system, agitator and
perfusion sieves, can easily be removed to facilitate cleaning or
replaced for changing processes.
The basic set-up includes filters, propeller, inlet and outlet
tubes, valves for aseptic sampling, membrane penetrators, extra filters,
basic spares and a set of tools.
OXYGENATION SYSTEMS
 Oxygenation
of cell cultures is sometimes a problem because of the sensitive nature
of the cell and foaming due to serum in the culture media.
Novaferm AB has developed oxygenation methods available as various
products in the Novaferm program.
In small vessels and in process with moderate oxygen demand,
surface aeration/oxygenation may be the best solution. The head space gas
is continuously changed for a suitable gas mixture. To increase
diffusion, a special surface-braking "comb" may be mounted on
the agitator shaft.
In some cases, gentle sparging of pure oxygen (or air) is possible
if the cells are not too sensitive and serum content of the medium is
low. Sparging is, in these cases, done via a sintered sparger.
For microcarrier cultures, sparging can be done inside a rotating
sieve cage. The sieve mesh allows the medium to pass and prevents the
microcarriers (with attached cells) from coming into contact with the gas
bubbles. Rotation of the sieve prevents clogging.
Oxygenation can also be achieved by diffusion through membranes
made from e.g. silicone.
SUPPLY CABINET
The supply cabinet/drive unit contains tubing, valves, pumps etc.
for distribution of thermostated water, steam, process gases and
electricity and is controlled by the Novaferm Fermenter Control System .
The drive unit for the laboratory system also contains the
agitator drive motor. Larger vessels are connected to a floor-standing
cabinet. The tubing for steam, that is in contact with culture media, is
made of stainless steel. Gas flow-meters for air N2, O2
and CO2 are supplied as standard. In the basic version, flow
control is achieved manually, but mass flowmeters with valves controlled
from the control system can be provided. Manometers at the front indicate
the pressure of inlet media. The electric unit mounted in the cabinet
contains agitator motor control, contactors, fuses etc. Agitator motor
control allows agitator speeds down to 10 rpm.
The supply unit is easily installed by the connection of in-coming
media to the rear side of the unit.
The laboratory fermenter vessel is installed via a quick connector
on top of the drive unit, and the larger vessels are installed via
flexible tubes to the left of the cabinet.
PUMP UNIT
Addition of different chemicals, such as alkali/acid or anti-foam
agent, can be provided by fixed-speed pumps (or pressurised vessels).
The pump unit consists of 3 peristaltic pumps with silicones
rubber tubing. The pumps are automatically controlled by the Novaferm
Fermenter Control System.
Accessories, such as glass containers, injection needles, filters
and silicone hoses, are supplied along with the unit.
In cell cultivation, pH control is often performed by means of
changes in the CO 2 content in the supply gas. This can be done
by the control system if an automatic CO2 flow control or a CO2
dosing valve is mounted. Rough pH adjustment can be effected through the
pump unit, by addition of alkali or acid.
CONTROL UNIT
The Novaferm Fermenter Control System is described here.
A variety of measurement systems in addition to the basic control
modules are available, e.g. for gas analysis, turbidity, etc. The control
system confers considerable advantages in cell cultivation by its ability
to cascade-control different parameters and by sequence control. When
starting a cultivation using microcarriers, the agitator can be
programmed to stop or run very slowly during the attachment phase. Speed
can be programmed to change with time, i.e. to compensate for increasing
cell density. Control of O2 flow according to pO2
value and CO2 according to pH is possible. Cascade in chains
can be done, e.g. by first increasing air flow supply, then increasing
the O2 supply and finally increasing pressure.
The sequence control makes it possible to stop the process or
change the set points after a certain time or on a set limit value of any
measured parameter.
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