The alveoli, in which the oxygen and carbon dioxide are exchanged with the blood, are very small, less than 1/10 of a millimeter in diameter, and are lined by a thin layer of liquid. When air and liquid are in contact, a strong force known as surface tension tends to compress the alveoli. The primary function of lung surfactant is to form a monolayer at the alveolar air/water interface capable of lowering the surface tension to near zero values, said Ding. The physical and chemical properties of the monolayer determine how low the surface tension can be.
That way premature babies don't have to use so much of their energy to breathe. The lower the surface tension between the liquid and the gas, the easier it is to breathe, said Zasadzinski.
The minimum surface tension upon expiration is limited by monolayer collapse, said Ding. The mechanical properties of the monolayer, especially the shear viscosity, are directly related to the mechanism of monolayer collapse.
Ding explained the use of a magnetic needle viscometer along with fluorescence microscopy, Brewster Angle Microscopy and Atomic Force Microscopy to study model surfactant systems, as well as natural surfactants, to determine the relationship between lung surfactant components and monolayer viscosity.
He reported the systematic measurements of monolayer viscosity as a function of lipid chain length, protein concentration, and temperature.
"You want the monolayer to spread easily," said Ding, "to flow and coat the alveolar surface during breathing in and out."
The research leads to questions like, "Why did nature select only a particular lipid with a 16-length carbon chain to be the main component of natural surfactant?" asked Ding. "Mother nature chose it because it's the right viscosity for expanding and contracting."
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