Bidirectional surface analysis of monomolecular membrane harboring nanoscale reversible collapse structures

Area of Science:

• Surface science
• Materials science
• Biophysics

Background:

• Determining the orientation of nanoscale collapse structures in Langmuir films at the air-aqueous interface is challenging with current experimental methods.
• Understanding this orientation is crucial for pulmonary surfactant films, which form reversible surface-associated reservoirs (SARs) during dynamic compression and expansion.
• The orientation of SARs relative to the interface has remained uncertain.

Purpose of the Study:

• To develop a novel methodological approach to investigate the directionality of SARs.
• To determine the orientation of SARs in a functional analogue of the pulmonary surfactant lining.

Main Methods:

• A new technique was designed involving the transfer of a compressed film onto a holey substrate.
• Bidirectional surface imaging was performed on the hole-spanning monomolecular membrane containing SARs.

Main Results:

• The study unambiguously demonstrated the association of SARs with the membrane.
• The orientation of SARs was found to be toward the air-side of the interface.
• This finding contrasts with the previously accepted view of an aqueous phase orientation.

Conclusions:

• The developed methodological approach successfully determined the orientation of SARs.
• Pulmonary surfactant SARs are oriented toward the air-side of the interface.
• This provides critical new insights into the structure and function of pulmonary surfactant films.