Low Frequency Rheology of Mixed Lipid-Nanoparticle Monolayers

The study of the rheological properties of lipid Langmuir monolayers have undergone an intense development in recent years because these relative simple systems can be utilised as models for the study of biological systems or complex systems with physiological implications, like the lung surfactant (LS). In this comunication the effect of nanoparticles of different chemical nature (hydrophilic and hydrophobic silica, carbon, titania) on the rheological properties of 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) monolayers is analysed, DPPC being the essential component of LS. The information about the mechanical response of the layers was obtained by two complementary techniques: the oscillatory barrier method in a Langmuir balance and the oscillating drop method in a drop shape tensiometer. Both techniques allow obtaining information of the interfacial mechanical behaviour in a range of frequencies around 10-3 - 0.2 Hz.. This information allows evaluating the reorganization processes of the lipid molecules in the monolayer at different packing state. The presence of nanoparticles modifies the dynamic response of the monolayer affecting the surface packing of the molecules, their lateral redistribution and, consequently the monolayer phase behaviour. These modifications are driven by the nanoparticle-lipid interaction and, consequently, presents different characteristics depending on the nanoparticles chemical and geometrical features [1]. The combination of the present rheological study with the previous ones on the thermodynamic and structure [2] of these systems allows proposing a scenario where the incorporation of nanosized particulate materials may induce important changes in the composition and mechanical properties of the LS. These modifications may have potential toxicological implications related to the inhibition of the LS functionality. Literature: 1. E. Guzmán, L. Liggieri, E. Santini, M. Ferrari, F. Ravera. 2011. Effect of Hydrophilic and Hydrophobic Nanoparticles on the Surface Pressure Response of DPPC Monolayers. J. Phys. Chem. C 115:21715-21722. 2. E. Guzmán, L. Liggieri, E. Santini, M. Ferrari, F. Ravera. 2012. Influence of silica nanoparticles on phase behavior and structural properties of DPPC--Palmitic acid Langmuir monolayers. Colloids Surf. A doi: 10.1016/j.colsurfa.2011.11.023.