Biomedical Engineering Reference
In-Depth Information
used during large-scale production because of economic reasons (e.g., shelf life),
storage, and shipment concerns. At the large scale, the culture medium is typi-
cally prepared by the addition of base powder or liquid concentrate mixtures to
appropriate grade water. These base media mixtures usually contain amino acids,
vitamins, cell membrane precursors, antioxidants, and growth factors. Additional
components such as lipids and proteins may be added separately. Media may
also contain poorly characterized ingredients such as yeast extract or protein
hydrolysates. It is important that media be identical in terms of composition.
One major issue that needs to be monitored when using powdered media is the
issue of blend uniformity or homogeneity of powdered mediums from different
drums [20].
INOCULUM EXPANSION Inoculum expansion increases the number of cells avail-
able for inoculation of the large-scale production fermenters or bioreactors. Cells
are cultured in successively larger flasks by adding fresh medium during their
growth phase, so a vigorously growing culture can be used for start of commer-
cial production. Inoculum expansions are typically carried out in T-flasks and
shake flasks for smaller volumes at the beginning of expansion, and subsequently
roller bottles or spinner flasks are used for larger volumes (10-20l). For volumes
greater than 10-20l, bioreactors of successively large scale can be used for expan-
sion of cells until the working volume of the production fermenter/bioreactor is
reached [20].
BIOREACTOR OPERATIONS The choice and scale of any fermenter or bioreactor
will depend upon the needs of the process, product, and the market demand. At a
minimum, at commercial scale, fermenter/bioreactor vessels should be capable of
being operated aseptically for a number of days, reliable in long-term operations,
and meet containment requirements. In addition, vessels should be capable of
providing adequate mixing, agitation, and aeration to meet the metabolic require-
ments of the microorganisms or cells.
Cell culture and fermentation processes are often considered the most difficult
to scale up, partly because causal links between culture conditions (e.g., aeration,
mixing, dissolved oxygen and carbon dioxide, and nutrient concentrations) and
product characteristics are often poorly understood, and also because not all
critical process parameter values can be kept the same during scale-up.
HARVEST OPERATIONS Biotechnology-derived products can be either intracellu-
lar or extracellular (or secreted). As mentioned in Section 12.3.4, in the initial
stages of recovery and purification, a product needs to be purified from the
accompanying cells, cell debris, and other large particles or contaminants. Typ-
ical unit operations employed for this clarification step include centrifugation,
filtration, etc. To ensure a successful scale-up strategy, it is important to select a
method that is robust, readily scalable, efficient, and can provide high processing
rates.
Search WWH ::




Custom Search