Biomedical Engineering Reference
In-Depth Information
Fig. 13.1
Cryoinjuries: low-rate vs. rapid freezing procedures
the one which causes intracellular crystallization [
10,
22
]. Optimal freezing rate is
the function of the ratio between cell surface and volume as well as of cell mem-
brane permeability for water and its corresponding temperature coefficient—but it
also depends on what type of cryopreservation strategy is applied [
4-
9
] . Fig.
13.1
.
Last but not the least, a higher degree of cell destruction has occurred when transi-
tion period from liquid to solid phase (fusion heat releasing) is prolonged. The
released heat of fusion—if not considered during controlled-rate freezing—could
result in additional temperature fluctuation. That is why the period of transformation
from liquid to solid phase is prolonged, and its duration directly related to the degree
of cryoinjury [
5-
12,
22
]. Finally, in the course of rapid freezing, as stated, the quan-
tity of “free” intracellular water can be increased as a result of “bound” water desorp-
tion. In accordance with this thermodynamic fact, more recently, a small second peak
of heat release was detected between −30°C and −40°C [
17
]. We think that this “sec-
ond heat release” might be partially caused by water desorption and additional crys-
tallization. Consequently, there is potential need for revision of some cryodynamic
parameters specific for controlled-rate cryobiosystems (Fig.
13.2
).
The Use of Cryoprotectant Agents
Determination of the optimal freezing approach is essential, but it cannot solve all
problems related to cell cryoinjury. Precisely, postthaw cell recovery and viability
are high only when cryoprotectants are present in the cryobiosystem. They efficiently
