DSC measures the heat flow of a sample during the cooling and/or
heating scans. The curve of heat flow plotted against temperature
or time, called “a thermogram,” shows the release or absorption of
heat energy by the sample or the change of heat capacity at different
temperatures or given times. By analyzing thermograms of
biological samples treated with cryopreservation solutions, one
gains insight into the nature of the thermophysical and/or thermochemical events that occur during cooling and/or warming. Such
information is needed for successful development of protectant
formulations and cooling/warming protocols for cells and tissues.
Similarly, by analyzing thermograms of biological samples treated
with lyoprotectant formulations and freeze-dried products that are
produced by a given freeze-drying process, one obtains the necessary information for reformulation and optimization of freezedrying process parameters, as well as information about shelf stability of the final products.
The principle of calorimetrical analysis for biological materials,
cryopreservation solution, and freeze-drying formulations is that,
on the one hand, the thermal changes of water and their
corresponding quantities of energy are greatly affected by the presence of solutes and solvents or other biological materials and that,
on the other hand, the thermal behavior of solutes and biological
materials in the system is affected by the presence of water. For
example, as water content decreases and/or the solute concentration increases, the onset freezing and melting temperature of water
decreases, while at the same time, the glass transition temperature
increases due to the reduced plasticizing effect of water.
A complete DSC instrument consists of several subsystems:
(a) a temperature controller, (b) cooling and heating elements,
(c) a gas flow rate controller, (d) a signal amplification module,
(e) a differential scanning detector, and (f) a data collection system.
The temperature controller regulates the cooling and heating rates
during a given measurement as specified by researchers. The cooling and heating elements provide the cooling or heating capabilities
for temperature control. The gas flow regulator controls the gaseous environment in which the measurement is made. The signal
amplification module amplifies the very small thermal difference
detected by the thermal couples and increases the sensitivity and
accuracy for thermal measurements. The differential scanning
detector is the most critical core component that includes sample
cells and thermal couples for temperature measurement and signal
transduction. The data collection system (a computer) automatically records and stores the measurement data and allows data
retrieval for subsequent analysis. Cryopreservation and freezedrying research generally use low-temperature DSC models, typically in the temperature range between À170 and 250
C. The
subzero temperature range is used for freezing and thawing investigation (i.e., ice formation and melting, eutectic precipitation,
glass transition, devitrification, recrystallization, etc.), whereas the
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heating scans. The curve of heat flow plotted against temperature
or time, called “a thermogram,” shows the release or absorption of
heat energy by the sample or the change of heat capacity at different
temperatures or given times. By analyzing thermograms of
biological samples treated with cryopreservation solutions, one
gains insight into the nature of the thermophysical and/or thermochemical events that occur during cooling and/or warming. Such
information is needed for successful development of protectant
formulations and cooling/warming protocols for cells and tissues.
Similarly, by analyzing thermograms of biological samples treated
with lyoprotectant formulations and freeze-dried products that are
produced by a given freeze-drying process, one obtains the necessary information for reformulation and optimization of freezedrying process parameters, as well as information about shelf stability of the final products.
The principle of calorimetrical analysis for biological materials,
cryopreservation solution, and freeze-drying formulations is that,
on the one hand, the thermal changes of water and their
corresponding quantities of energy are greatly affected by the presence of solutes and solvents or other biological materials and that,
on the other hand, the thermal behavior of solutes and biological
materials in the system is affected by the presence of water. For
example, as water content decreases and/or the solute concentration increases, the onset freezing and melting temperature of water
decreases, while at the same time, the glass transition temperature
increases due to the reduced plasticizing effect of water.
A complete DSC instrument consists of several subsystems:
(a) a temperature controller, (b) cooling and heating elements,
(c) a gas flow rate controller, (d) a signal amplification module,
(e) a differential scanning detector, and (f) a data collection system.
The temperature controller regulates the cooling and heating rates
during a given measurement as specified by researchers. The cooling and heating elements provide the cooling or heating capabilities
for temperature control. The gas flow regulator controls the gaseous environment in which the measurement is made. The signal
amplification module amplifies the very small thermal difference
detected by the thermal couples and increases the sensitivity and
accuracy for thermal measurements. The differential scanning
detector is the most critical core component that includes sample
cells and thermal couples for temperature measurement and signal
transduction. The data collection system (a computer) automatically records and stores the measurement data and allows data
retrieval for subsequent analysis. Cryopreservation and freezedrying research generally use low-temperature DSC models, typically in the temperature range between À170 and 250
C. The
subzero temperature range is used for freezing and thawing investigation (i.e., ice formation and melting, eutectic precipitation,
glass transition, devitrification, recrystallization, etc.), whereas the
286
Wendell Q. Sun