The alveolar sacs in mammalian species are coated by a lipid/protein complex known as pulmonary surfactant (PS). This system minimizes the surface stress at the alveolar air-liquid interface and its lack or dysfunction leads to pulmonary collapse and respiratory failure. As the lungs must respond to dilatational and compressional deformations occurring as a consequence of inhalation and exhalation, it has been proposed that surfactant mechanics can be optimized through the formation of sub-surface reservoirs of material connected to phospholipid-based interfacial films by action of the hydrophobic surfactant proteins SP-B and SP-C. However, the presence of these interfacial three-dimensional structures is still being interrogated and the mechanisms by which they would sustain surfactant performance are still not fully understood. In this study, to investigate the conditions required for multilayer formation and the subsequent influence on interfacial rheological properties, physiological-like compression/expansion cycles were applied to different PS-mimicking interfaces in the presence of different concentrations of hydrophobic surfactant proteins SP-B and SP-C in a custom-made symmetric trough capable of performing pure dilation/compression of the surface (Quadrotrough). In parallel, the changes in composition and thickness of the interface and associated multilayer structures were measured by neutron reflectometry at physiological temperatures. In this way, with the unique combination of dilatational rheology and neutron reflectivity, we investigated the biophysical relevance of these reservoirs of material and the conditions defining their formation.
Collada et al. (Sun,) studied this question.