Impact of Nanoparticles in the Interfacial Properties of Pulmonary Surfactant-Like Monolayers: Equilibrium and Dynamical Features

The study of the interactions between nanoparticles and surfactants is of fundamental interest in many fields of the physical-chemistry of interfaces. Among the systems composed by nanoparticles and surfactants, special attention is increasingly posed on surfactant-lipid mixture simulating the pulmonary surfactant in presence of different kind of solid nanoparticles. The study of nanoparticle-surfactant interactions is important in this field being at the basis of the potential impact of the presence of nanoparticles in the environment on the respiratory physiology [1]. The pulmonary surfactant is a complex mixture of lipid and proteins (1,2-dipalmitoyl-sn-glycero-3-phosphocholine, DPPC is the essential component) that coats, as liquid layer, the alveolar walls, and ensures the mechanical stability of the alveoli during the respiratory cycle [2]. This work presents a comparative study on the effect of different hydrophilic and hydrophobic nanoparticles on the interfacial properties and structure of pulmonary surfactantlike monolayers with different lipid compositions [3]. The experimental results show important changes in the phase behavior of the lipid monolayers due to the interaction with nanoparticles and their likely incorporation into the interfacial layer. These changes are related to a disturb effect on the ordering and selforganization of the lipid molecules, as confirmed by the Brewster Angle Microscopy (BAM) images, and a key role is played by the nature of the nanoparticles (hydrophilicityhydrophobicity). This effect on the structural properties of the monolayer leads also to changes in the dynamic response to area perturbation as found out by oscillatory barrier experiments in the range of 10-3 - 10-1 Hz. This impact on the mechanical properties of the interfacial layer is related to the interactions between the nanoparticles and the different lipidic components of the monolayer which provides a more complex surface dynamics as result of the heterogeneous composition (lipids, nanoparticles and/or lipid-nanoparticle complexes). The effects on the dynamic response under respiratory cycle-like conditions (? ~ 40 mN/m, ? ~ 0.05 Hz, u ~ 30 - 40 %) have also been investigated because cause allow for a first definition of potential damages induced by nanoparticles on the mechanical response of lung surfactant in physiology relevant conditions. From the results obtained by rheological investigation and structural characterization (BAM, AFM) it is possible to conclude that the interfacial behaviour of the pulmonary surfactant may be affected by the presence of nanoparticles in the environment [1] C. Mühlfeld, B. Rothen-Rutishauser, F. Blank, D. Vanhecke, M. Ochs, P. Gehr,. Am. J. Phys. 294 (2008) L817. [2] S. Rugonyi, S.C. Biswas, S.B. Hall, Resp. Phys. Neurobiol. 163 (2008) 244. [3] E. Guzmán, L. Liggieri, E. Santini, M. Ferrari, F, Ravera, Influence of Silica Nanoparticles on Thermodynamic and Rheological Properties of DPPC - Palmitic Acid Langmuir Monolayers, Langmuir submitted (2011).