Biomedical Engineering Reference
In-Depth Information
10
Filtration
I wish all teenagers can filter through songs instead of turning to drugs and
alcohol.
Taylor Swift
Except for steel meshes in bulk manufacturing of nonsterile dosage forms,
filters are rarely reused in the pharmaceutical industry. They take varied
forms—from muslin cloth to paper filters to membrane cartridges. Disposable
filter devices in biological manufacturing were the earliest changes that went
disposable mainly because of the problems with cleaning them; the cost of
these parts has always been reasonable.
There are a multitude of filter designs and mechanisms utilized within
the biopharmaceutical industry. Prefilters are commonly pleated or wound
filter fleeces manufactured from melt-blown random fiber matrices. These
filters are used to remove a high contaminant content within the fluid.
Prefilters have a large band of retention ratings and can be optimized to
all necessary applications. The most common application for prefilters is
to protect membrane filters that are tighter and more selective than pre-
filters. Membrane filters are used to polish or sterilize fluids. These fil-
ters need to be integrity testable to assess whether or not they meet the
performance criteria. Cross-flow filtration can be utilized with micro or
ultrafiltration membranes. The fluid sweeps over the membrane layer and
therefore keeps it unblocked. This mode of filtration also allows diafiltra-
tion or concentration of fluid streams. Nanofilters are commonly used as
viral removal filters. The most common retention rating of these filters is
20 or 50 nm.
Dead-End Filtration
Dead-end filtration operates on the principle of passing a fluid feed stream
through a filter device by means of a pressure drop, usually applied by either
a pump or compressed gas pressure before the filter device. All contami-
nants larger in size than the pore size of the filter media are retained by the
filter material and will finally cause a filter blockage by plugging its channels
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