(755c) Lung Surfactant Microbubbles

Lipid monolayers form an essential barrier between the atmosphere and the aqueous environment inside our body and are present on the eyes, ears and lungs. Traditionally, such films have been studied on planar surfaces, such as the Langmuir trough, or on millimeter-scale pendant drops and bubbles. Such techniques have proved invaluable for studying monolayer composition, phase behavior and microstructure. But how does one study the interfacial properties of lipid monolayers in high throughput? Microbubbles provide a facile platform to study populations of lipid monolayers and their interactions with biological molecules. Experimental results highlighting the properties of microbubbles coated with a common lung surfactant replacement formula are given as an example. Our results show that lung surfactant readily stabilizes microbubbles. This corroborates previous clinical work on the Microbubble Stability Test, by which a negative diagnosis for respiratory distress syndrome in neonates is evident by the presence of stable microbubbles in processed gastric aspirate. The resulting lung-surfactant microbubble suspensions were characterized by particle sizing and counting techniques, zeta potential measurement, fluorescence microscopy and flow cytometry. These techniques allowed determination of the effects of environmental conditions on surfactant function. For example, surface charge was found to reverse sign from positive to negative as the suspension medium became more basic. The ability of serum albumin to inactivate surfactant function, and the ability of polyethylene glycol to restore function, was confirmed. These results illustrate how microbubbles can serve as a platform for studying lipid monolayers and their interactions with biological milieu.