(112h) Relating Interfacial Morphology, Curvature, and Dilatational Modulus for Surfactant Films

Acute respiratory distress syndrome (ARDS) affects over 150,000 people each year in the United States alone and has a mortality rate of 40%. A major reason for this high mortality rate is a poor understanding of the underlying cause of the disease. To gain a better understanding of ARDS, we posit the following feedback mechanism in which inflammation products in the lung lead to mechanical instabilities in breathing.

After an initial injury or infection in the lung, inflammation occurs, allowing proteins and phospholipases from the blood to enter the lungs. These components of the innate immune system then interact with lung surfactant (LS) and disrupt the interfacial properties required for breathing. The resulting Laplace instability (which occurs when the dilatational modulus(d/dlnA) is greater than half the surface tension leads to alveolar flooding and decreased lung compliance, further exacerbating lung injury. Improved ARDS treatment requires a better understanding of how these inflammation products affect the morphological and physical properties of the LS film. In this work, we examine how one of the inflammation products found in the lungs of ARDS patients, lysolipids, which are formed by the phospholipase 2 catalyzed breakdown of bacterial and viral membrane lipids.

Confocal microscopy is used in conjunction with Langmuir-Blodgett dilatational measurements and capillary bubble microtensiometry to simultaneously observe interfacial morphology and measure dilatational modulus and surface tension on flat and curved interfaces. The structure and properties of the interface are also measured as lysopalmityol-phosphatidylcholine (Lyso-PC) is introduced in the subphase solution. We observe the contaminants entering the interfacial layer and disrupting the morphology. This coincides with orders of magnitude changes in the surface dilatational modulus with little effect on the measured surface tension. These changes can induce the Laplace instability at normal breathing frequencies. We also provide theoretical insights on how concentration, interfacial curvature, breathing rate (oscillation frequency), and micellar exchange kinetics affect the way surfactants adsorb to the interface.