Complex fluid-fluid interfaces are ubiquitous in many industries such as biomedical, food, personal care and, petroleum. At fluid-fluid interfaces surface-active species adsorb to the interface, sometimes forming microstructures, altering the surface energy and mechanical properties. Understanding these interfacial properties is critical for industrial product design and processing. Each surfactant system investigated in this project are motivated by pharmaceutical applications. The objective for studying each surfactant system is to measure and correlate properties such as surface tension, surface rheology, and monolayer structure to monolayer composition. One system explored in this project is lung surfactant (LS) modeled under conditions associated with acute respiratory distress syndrome (ARDS), the most severe form of acute lung injury. During the progression of ARDS, LS is said to be ‘inactivated,’ meaning that it increasingly loses its ability to reduce surface tension, but the mechanism for inactivation remains unknown. This investigation focuses on the role of the enzyme phospholipase (PLA<sub>2</sub>) in LS inactivation. The objective is to measure mechanical and morphological changes in a model LS monolayer as it is degraded by PLA<sub>2</sub> and correlate observed changes to its evolving composition. Using interfacial microbutton microrheometry coupled with fluorescence microscopy, we track the stiffness and morphology of the actively degrading monolayer. These results are compared to the stiffness and morphology of mixtures of model LS and its degradation products, simulating the evolving monolayer composition.

Understanding interfacial composition and structure of lipid-based surfactant monolayers for pharmaceutical applications

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