(595h) Dynamics of Monolayer Collapse and Folding

Choi, S. Q., University of Minnesota
Zasadzinski, J. A., University of Minnesota

When subjected to a large compression, a two-dimensional thin film collapses. To date, several collapse mechanisms are known for lipid monolayers: fracture, solubilization, and folds. We present a novel method that enables us to distinguish “folds” from other mechanisms and, furthermore, quantify folds. We simply measure fluctuations of the surface tension when the collapse occurs, and compute the mean squared fluctuation, which provides various properties of folds (e.g. a size and time that folds remain). We validate this technique using mixed lipid monolayers of DPPC and POPG, which exhibit the different mechanisms of collapses by varying POPG fraction. Moreover, visualization of such monolayers with the measurements reveals that formation of folds occurs randomly, and depends strongly on compression rates and a composition of POPG, showing that collapse is governed by a kinetic, rather than an equilibrium process.

   By understanding the nature of monolayer collapse, we can begin to design optimized replacement lung surfactants for the treatment of neonatal respiratory distress syndrome (nRDS).  Monolayer collapse determines the minimum surface tension at an air-water interface, which must be  10 mN/m for an effective lung surfactant.  We expect that the various lipid and protein components of lung surfactant act to modify the kinetics of collapse by modifying the activation energy of the kinetic process of monolayer folding.  We also know that saturated dipalmitoylphosphatidylcholine (DPPC) is necessary for a low surface tension monolayer; we also know that DPPC adsorbs slowly to the interface without assistance from the other lipid and protein species of lung surfactant.  By studying the relationship between the fluctuations and the chemical composition of the surfactant, we hope to determine the roles of the various components of lung surfactant on our way to creating an entirely synthetic lung surfactant for treatment of nRDS.