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Bench-Top Thawing
The usual way to thaw a microplate is to
place it on the laboratory bench … and wait! To illustrate
this thawing bottleneck, the deep-well
microplate in the figure below was filled with filtered water (and subsequently
with the chemical solvent, DMSO), and fitted with two K- type thermocouples that extend
approximately halfway down in a center and a side well, as shown. The filled microplate was placed overnight in a
freezer, having a temperature of about minus 10°C, with the two
thermocouples frozen in place. Then, the plate was removed from the
freezer, placed on a laboratory bench, and allowed to thaw. The
ambient room temperature varied from 24°C at the start, to 26°C at the
end for the test with water, and from 27°C to 29°C for the test with DMSO. The results are shown in
the figure  below where the blue symbols
are data for the center-well thermocouple, and the red symbols
are for the side-well; circles refer to the test with water, and the
diamonds to DMSO.
For the water test, it is seen that the
two instrumented wells remain at the thawing temperature (0°C) for a
long time, which means that the wells stayed partly frozen for this
time period; the reason is that the bench-top heat transfer is very
poor. Thus, the side well was not fully thawed until ~1½ hours
after the start, when its temperature starts to increase above zero,
as seen from the red circles in the figure above. The central well continued as
partly frozen at 0°C, even after 3 hours; indeed, removal of the
center thermocouple at 2 hrs showed it to be covered with ice about 5
mm in diameter and 15 mm in length, indicating less than 50% thawing,
and this is starting with the ice in the freezer at only -10°C!
For the DMSO test, thawing did
not begin until about 40 minutes, where the center-well thermocouple
in the figure above read +10°C. Then, thawing progressed slowly until after 2
hrs when the thermocouple was totally in liquid and read +17°C;
however, even at this time, there was frozen DMSO in the bottom ¼ of
the well (solid DMSO is more dense that its liquid and, so, remains at
the bottom unless stirred). Hence, for DMSO as well as for water
solutions, an inordinate amount of time is required for thawing on the
bench.
Clearly, the Rapid Thaw System (RTS) is badly needed –
as described in further detail.
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