Influence of Film Composition on the Morphology, Mechanical Properties, and Surfactant Recovery of Phase-Separated Phospholipid-Perfluorinated Fatty Acid Mixed Monolayers

摘要

Monolayer surfactant films composed of a mixture of phospholipids andnperfluorinated (or partially fluorinated) surfactants are of potential utility for applications innpulmonary lung surfactant-based therapies. As a simple, minimal model of such a lungnsurfactant system, binary mixed monolayer films composed of 1,2-dipalmitoyl-sn-glycero-3-nphosphocholine (DPPC) and perfluorooctadecanoic acid (C18F) prepared on a simplifiednlung fluid mimic subphase (pH 7.4, 150 mM NaCl) have been characterized in terms of mixingnthermodynamics and compressibility (measured through π−A compression isotherms), filmnmorphology (via atomic force, fluorescence, and Brewster angle microscopy), as well asnspreading rate and hysteresis response to repeated expansion−contraction cycles for a varietynof compositions of mixed films. Under all mixing conditions, films and their components werenfound to be completely immiscible and phase-separated, though there were significant changesnin the aforementioned film properties as a function of composition. Of particular note was the existence of a maximum in thenextent of immiscibility (characterized by ΔGexnπ values) and enhanced surfactant recovery during hysteresis experiments at χC18F ≥n0.30. The latter was attributed to the relatively rapid respreading rate of the perfluorinated amphiphile in comparison with DPPCnalone at the air−water interface, which enhances the performance of this mixture as a potential pulmonary lung surfactant.nFurther, monolayer film structure could be tracked dynamically as a function of compression at the air−water interface vianBrewster angle microscopy, with the C18F component being preferentially squeezed out of the film with compression, butnreturning rapidly upon re-expansion. In general, addition of C18F to DPPC monolayers resulted in improvements to mechanical,nstructural, and respreading properties of the film, indicating the potential value of these compounds as additives to pulmonarynlung surfactant formulations.