A bioreactor may refer to any device or system
that supports a biologically active environment. In one case, a
bioreactor is a vessel in
which is carried out a chemical process which involves organisms or
biochemically active substances
derived from such organisms. This process can either be aerobic or
anaerobic. These bioreactors are commonly cylindrical, ranging
in size from some liter to cube meters,and are often made of stainless
steel.
A bioreactor may also refer to a
device or system meant to grow cells or
tissues in the
context of cell
culture. These
devices are being developed for use in tissue engineering.
On the basis of mode of operation, a bioreactor may be classified as batch, fed batch or
continuous.
An example of a bioreactor is the
chemostat....more
Bioreactor design
Bioreactor design is quite a
complex engineering task. Under optimum conditions the microorganisms or
cells are able to perform their desired function with great efficiency.
The bioreactor's environmental conditions like gas (i.e., air, oxygen,
nitrogen, carbon dioxide) flowrates, temperature, pH and
dissolved oxygen levels, and agitation speed/circulation rate need to be
closely monitored and controlled.
Most industrial bioreactor
manufacturers use vessels, sensors,
controllers, and a control system, networked together for their bioreactor system, see programmable logic controller (PLC).
Fouling can
harm the overall sterility and efficiency of the bioreactor, especially
the heat
exchangers. To avoid
it the bioreactor must be easily cleanable and must be as smooth as
possible (therefore the round shape).
A heat exchanger is needed to maintain the bioprocess at a constant
temperature. Biological fermentation is a major source of heat,
therefore in most cases bioreactors need water refrigeration. They can be refrigerated with an external jacket
or, for very large vessels, with internal coils.
In an aerobic process, optimal
oxygen transfer is perhaps the most difficult task to accomplish.
Oxygen is poorly soluble in water -and even less in fermentation broths-
and is relatively scarce in air (20.8%). Oxygen transfer is usually helped by
agitation, that is also needed to mix nutrients and to keep
the fermentation homogeneous. There are however limits to the speed of
agitation, due both to high power consumption (which is proportional to
the cube of the speed of the electric motor) and the damage to organisms
due to excessive tip speed.
Industrial bioreactors usually
employ bacteria or other simple organisms that can withstand the forces of
agitation. They are also simple to sustain, requiring only simple nutrient
solutions and can grow at astounding rates.
In bioreactors where the goal is
grow cells or tissues for experimental or therapeutic purposes, the design
is significantly different from industrial bioreactors. Many cells and
tissues, especially mammalian, must have a surface or other structural
support in order to grow, and agitated environments are often destructive
to these cell types and tissues. Higher organisms also need more complex
growth medium.
