Essential Physics of Low Temperature and Freezing - Freeze-drying of Pharmaceuticals and Biopharmaceuticals - page 45

Figure 18 Photomicrographs of emulsified cells in undercooled water: left, human eryth-
rocytes and right, yeast (S. cerevisiae). The mean diameter of empty water
droplets is 7 mm
they were examined for survival by signs of haemolysis and growth of
bacterial activity, respectively. 166 Neither preparation showed signs of
deterioration. Similar success was achieved (Mathias & Franks, unpub-
lished results) with tobacco embryos, grown in tissue culture, and stored
at 201C. They were successfully grown into healthy plants. In the
preparations shown in Figure 18, analysis by differential scanning calo-
rimetry (DSC) during cooling of the emulsions indicated two freezing
events: one of the intracellular water and the second one at a lower
temperature, close to 401C, i.e. at T h . The ratios of the signal amplitudes
corresponded exactly to the concentration ratios of intracellular water to
empty water droplets.
The undercooling technique can be considerably refined and is thus a
useful means of storing live material or clinical fluid specimens for
prolonged periods. The technique is not useful or commercially attractive
for the long-term storage and transport of large quantities of material,
mainly because of the stringent temperature limits imposed, either by
inadvertent freezing below the nucleation temperature of water in the
material on the one hand, and an upper temperature, usually o 101C, on
the other hand, at which the emulsion will become unstable and break.