Biomedical Engineering Reference
In-Depth Information
The practice of integrating bags, tubing, and filters into preassembled,
ready-to-use bioprocess solutions is optimized if noninvasive sensing of crit-
ical process parameters is part of the package instead of using sensors that
may require sterilization and cleaning validation, the core processes which
are obviated in the use of disposable bioreactors.
Even though these obstacles do not always preclude the use of traditional
measurement technologies, single-use solutions for monitoring process
parameters eliminate the need for equipment cleaning and autoclaving small
parts, reduce the risk and cost involved with making process connections,
and may be more cost-effective than tracking and maintaining traditional
technologies. For example, a sanitary, autoclavable pressure transducer that
is qualified for a certain number of autoclave cycles and requires recalibra-
tion may be more expensive to use versus a single-use pressure sensor.
The adoption of disposable sensors requires a keen understanding of their
need and utilization. Their suitability would be determined by their mate-
rial properties, sensor manufacturing, process compatibility, performance
requirements, control system integration, compatibility with treatments
before use, and regulatory requirements.
Several companies, including Finesse and Fluorometrix (recently acquired
by Sartorius-Stedim), have created single-use, membrane biosensors that can
be added to or directly incorporated (during manufacturing) into single-use
bioreactor bags.
There are two options in using disposable sensors: one where the sen-
sors are placed in situ in contact with the liquid, and the other where the
external sensors contact the medium either optically (ex situ) or via a sterile
(and disposable) sample removal system (on line). Disposable sensors must
be sterilizable if they come in contact with media; these must also be cost-
effective and reliable. Better designs using inexpensive sensing elements
can be located inside a disposable bioreactor and combined with reusable
(and more expensive) analytical equipment outside the reactor. Inexpensive,
single-use sensors can also be placed on transistors and placed either in the
headspace, inlet, outlet, or into the cultivation broth for liquid-phase analysis
(temperature, pH, pO 2 ). These can also be optical sensors that allow noninva-
sive monitoring through a transparent window.
Sampling Systems
Continuous sampling from a bioreactor can be accomplished using a sterile
filter and a peristaltic pump to obtain a cell-free sample and, where the dead
volume of a sample is of concern (as in smaller bioreactors), microfiltration
membranes can be used that may be placed inside the bioreactor; disposable
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