THE REASON WHY:
Because KryoVueTM is made from two layers of
plastics adhered to each other, the strength of KryoVueTM as a
fluid container is limited by the strength of the bond between
the two layers. This bond is weak enough to be readily
peeled apart by human hands. The polyimide portion, the
orange colored portion, does not stretch. Accordingly, if
fluids are frozen in the KryoVueTM pouch, it is likely that the
expansion of ice will cause parting of the bond between the Kapton and the FEP. On the other hand, this system is
exceedingly strong in the opposite direction; even extremely
high pressures will not cause an "implosion" of this pouch. It
is a very reliable overpouch.
SAFETY? Liquid nitrogen freezers cryopreserve everything
that enters the freezer. This includes the yeasts and
molds that fall into the freezer when the door is open, and it
includes materials that exit broken vessels that are stored
within the liquid nitrogen as well as from the fingerprints and
such from handling specimens that are placed into the freezer.
Accordingly everything that enters a liquid nitrogen freezer
must be considered contaminated. That is why there are
KryoVueTM overpouches. These protect the valuable items from
being contaminated.
Will FEP bags break in immersion liquid nitrogen storage?
No, the reason that most plastic bags break in liquid
nitrogen is
because they become brittle in the cold, and rather then bend,
they break. FEP remains flexible in liquid nitrogen. Even
if bent, bashed, or flexed, FEP bends and springs back the same
as at room temperature, accordingly it will not break.
Is it necessary to get all the air out of the fluid stored
in the bag when placing it into liquid nitrogen?
Desirable but not necessary. Any air in the fluid will
make a bubble when the rest of the fluid freezes. As the
temperature drops to -182 even the oxygen in the air will
condense to a liquid leaving a vacuum in the bubble. This
vacuum space will become filled with nitrogen. When
warmed, the oxygen and nitrogen expand fracturing the ice.
The FEP bag will expand and stretch because it is still flexible
and stretchable. The swollen bag may cause the cassette to
be hard to open but the bag will not break.
Why are FEP bags better than t-flasks for culture?
They are a closed system.
What is a closed system?
A container (system) which prevents outside contamination
from entering and inside materials from escaping.
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