Effect of hydrophilic and hydrophobic nanoparticles on the surface pressure response of DPPC monolayers

The study of the interaction between Langmuir monolayers of 1,2-dipalmitoyl-sn-glycerol-3-phosphocholine (DPPC), as the major component of lung surfactant (LS), and nanoparticles of different nature, hydrophilic silica (SiO2) and hydrophobic carbon black (CB), has been carried out by measuring the compression Pi-A isotherms and the response of the surface pressure to harmonic variations of the interfacial area simulating respiratory cycles in a Langmuir trough. The change of the monolayer interfacial structure induced by nanoparticles was monitored by Brewster angle microscopy. The results point out that nanoparticles incorporating into the monolayers influence the interfacial organization of the molecule's and induce important modifications in both the phase behavior and the mechanical properties. Silica has stronger effects on DPPC phase behavior, compared to carbon black, while both affect the monolayer elasticity, the collapse conditions, and the nonlinearity of the surface pressure response to area expansion-compression simulating the respiratory cycles. With DPPC being the major component of pulmonary surfactant, the results here obtained are relevant in the framework of wider studies on the effect of nanoparticles on the pulmonary surfactant interfacial properties.