Structures of surfactant films: a scanning force microscopy study.

Area of Science:

• Pulmonary physiology
• Surface chemistry
• Biophysics

Background:

• The alveolar lining layer is traditionally viewed as a simple aqueous hypophase covered by a dipalmitoyl-phosphatidylcholine (DPPC) monolayer.
• Emerging evidence from electron microscopy and in vitro studies suggests a more intricate structure for pulmonary surfactant films.

Purpose of the Study:

• To investigate the complex structure of pulmonary surfactant films.
• To explore the relationship between film compression, surface pressure, and film morphology.
• To challenge the established hypothesis of a homogeneous phospholipid monolayer.

Main Methods:

• Spreading of four distinct surfactants on a Langmuir-Wilhelmy balance.
• Transfer of surfactant films onto mica substrates using the Langmuir-Blodgett technique.
• Imaging of surfactant films in air using scanning force microscopy (SFM) in contact mode.

Main Results:

• Scanning force microscopy revealed that surfactant films are heterogeneous and exhibit phase transitions at varying surface pressures.
• Different surfactants displayed distinct surface patterns even at similar surface pressures.
• Inclusion of surfactant proteins (SP-B and SP-C) resulted in observable differences in film surface structure.

Conclusions:

• The widely accepted model of a regular phospholipid monolayer governing surface tension is likely an oversimplification.
• The structure-function relationship of surface-active surfactant films is more complex than previously understood.
• SFM provides valuable insights into the nanoscale architecture of pulmonary surfactant films.