Biomedical Engineering Reference
In-Depth Information
Fig. 13.2
Device for controlled-rate freezing of stem cells
prevent or reduce the degree of cell thermal damages. As stated, the first applied
cryoprotectant was glycerol [
2
]. Later on, numerous substances with high-level
cryoprotective capacity were described [
27-
31
]. One of them is DMSO which has
demonstrated specific efficiency in the cryopreservation of SCs, platelets, lympho-
cytes, and granulocytes. DMSO is a transparent (colorless) fluid with a sulfur-like
smell. It is a very polar molecule, which dissolves many water-soluble and lipid-
soluble substances. DMSO has exothermic properties and should be mixed slowly
with the cell suspension to dissipate the generated heat. Given intravenously (even
in small concentrations) DMSO may cause certain unwanted effects such as nausea,
vomiting, local vasospasm, etc. [
22,
32-
43
]
Generally, cryoprotectants can be classified into nonpenetrating or extracellular
and penetrating or intracellular compounds [
29-
31
]. Mechanisms of their action are
complex and only partially recognized. Due to the differences in its chemical and
other properties, it is not possible to discover a cryoprotective mechanism common
for all cryoprotectants. In a nutshell, extracellular agents could protect cells during
high-rate freezing, reducing the intracellular ice crystal formation. However, intra-
cellular cryoprotectants could provide protection in the course of low-rate freezing,
decreasing the degree of cell dehydration [
10,
22,
31
] . Penetrating cryoprotectants
increase intracellular solute concentration, and lower the temperature at which ice
crystals form (reduced or “delayed” ice crystallization). Applied cryoprotectants, in
higher concentration (but below the critical cytotoxicity) as well as reduced tem-
perature, will increase intracellular viscosity. That is why the mobility of the water
molecules and ice crystal formation and/or growth are slowed down. They decrease
intracellular vs. extracellular osmotic gradient (reduced “solution effect”) too [
5-
10
] .
Finally, certain cryoprotectants can change directly the cell membrane permeability
for water, thus influencing the degree of cell dehydration [
22,
29-
33
] .
