Characterization of Lung Surfactant Behavior on Curved Interfaces using Microtensiometer Combined with Confocal Fluorescence Microscopy

Abstract

Lung surfactants are a mixture containing proteins and phospholipids that play a critical role in reducing the surface tension of the liquid-air interface within the alveoli, which eases respiratory function. While clinical surfactants like Survanta and Curosurf are often employed to treat neonatal respiratory distress syndrome (NRDS), the underlying mechanism behind acute respiratory distress syndrome (ARDS) and the impact of alveolar curvature on surfactant function remains underexplored. The Langmuir trough is commonly employed to investigate lung surfactant morphology—often in conjunction with confocal microscopy—and to measure surface pressure–area isotherms. However, the influence of alveolar curvature on surfactant behavior remains underexplored. Recent study (Sachan and Zasadzinksim PNAS, 2018) suggests that curvature introduces a circle-to-strip phase transition of liquid condensed (LC) domains . Therefore, we aim to further investigate how surfactant monolayers behave under curvature variations, temperature, and compositional changes. A controlled-pressure microtensiometer, integrated with a confocal fluorescence microscope, was employed to analyze adsorption dynamics and also image the interface on alveolar-sized microbubbles (~ 60 um) simultaneously. We observed unreported liquid-liquid coexistence in the absence of cholesterol and further examined the relationship between the stripe width and the bubble radius. The line tension is extracted from analyzing the Brownian motion of small domains and the relaxation of distorted liquid domains. By refining our understanding of surfactant behavior in curved environments, this study will enhance the knowledge of the stability and effectiveness of therapeutic surfactants, improving treatment outcomes for patients with respiratory disorders.