Characteristics
of PFCs
The utility of perfluorocarbon products was first recognized in World War II when the
Manhattan Project (development of the atom bomb) required a chemically inert molecule for
use with highly sensitive components. Scientists discovered that replacing hydrogen atoms
of carbohydrates with fluorine produces fluorocarbons that are resistant to any kind of
reaction with other molecules. Because fluorocarbon molecules are chemically inert, their
reactions with surrounding molecules are limited to interactions of their physical
properties such as relatively high vapor pressure and low boiling point, low surface
tension, low viscosity, very low solubility in water, low solubility in oil, and increased
solubility of gasses. The medical world was attracted to these characteristics because
gaseous molecules seemed to stay imbedded in chemically inert PFCs significantly more than
in corresponding carbohydrates. The volatility of some of the PFC molecules precluded use
with humans. Compatible molecules, however, demonstrated the ability to convey oxygen at
twice the rate of whole blood at normal body temperature. Retention of other gasses (CO2,
N2, NO, and CO) are also significantly increased in PFCs and this suggest some interesting
applications other than their oxygen-retention capabilities. PFCs are also of interest for
medical uses because they are chemically inert, and thus do not react with other
molecules. PFC products can also be sterilized and thus made completely free of
contaminants, such as infectious viruses and bacteria. |
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Perfluorocarbons are not soluble in
water, and therefore not soluble in blood. In order to be blood compatible, PFCs must be
combined with a surfactant to form an emulsion that can be conveyed safely by the blood
stream. Emulsions however, are not without problems. An emulsion can alter the PFCs’
properties. A clinically usable product requires development of a stable emulsion.
Additionally, emulsions have only limited concentrations of PFC, meaning that the total
PFC carried in the bloodstream is reduced, and therefore, the total volume of gas carried
is also reduced. As attractive as PFCs are, they remain less efficient carriers of oxygen
than hemoglobins (red blood cells) because their oxygen carrying ability is directly
related to the inspired fraction of oxygen, nominally 20% of air taken into the lungs.
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