Stability of freestanding lung surfactant films under simulated breathing conditions

Whether alveolar pores in the lungs are stably covered by freestanding liquid films or prone to rupture during breathing remains an open question, despite their potential importance for collateral ventilation and immune cell transport. In this study, we examine the stability of freestanding lung surfactant films under relevant pressure variations using an in vitro setup that mimics film thinning across alveolar pores. Experiments with the natural surfactant extract Infasurf demonstrate sustained film stability under simulated breathing conditions. Additionally, we compare a model lipid mixture with and without 1% of the key hydrophobic surfactant protein SP-B or SP-C. The presence of either protein enhances the stability of thicker freestanding films at equivalent applied pressures. These findings suggest that, in healthy lungs, interalveolar pores remain spanned by stable thin liquid films throughout the respiratory cycle, supporting continuous mechanical and biological connectivity between adjacent alveoli.