Laboratoire Matière et Systèmes Complexes

Fanny Mousseau Equipe Physique du Vivant

Lung fluid : a natural protection against inhaled nanoparticles ?

Abstract : Pulmonary surfactant, the fluid lining the epithelium of the lungs, is a complex surface-active medium that contains phospholipidic vesicles and proteins. Toxicity studies have shown that inhaled nanoparticles reach the alveoli and interact with the pulmonary surfactant (Fig. 1a). As a result, the particle properties such as surface activity, stability, and cellular uptake may be modified and perturb the lung physiology. In this work, clinically approved lung surfactant (Curosurf®, Chiesi, Italia) is investigated with different types of oxide particles (size below 100 nm), including alumina, silica, and titania. Light scattering, electrophoretic mobility, electron and optical microscopy show that vesicles and particles co-assemble into micron-sized aggregates via electrostatic interaction (Fig. 1b, c) [1]. Contrary to the models of lipoprotein corona or nanoparticle wrapping [2,3], our work indicates that the vesicles remain intact, and that particles are trapped at their surfaces. Viability assays (WST) were performed on alveolar epithelial cells (A549) using particles both with and without surfactant. In the presence of lung fluid, a net decrease of the toxicity is observed for silica particles. This result is attributed to the formation of aggregates that hampers the particle adsorption and internalization by the cells.

in collaboration with D. Nguyen, R. Leborgne, E. Seyrek and J.F. Berret

[1] F. Mousseau, R. Le Borgne, E. Seyrek and J.-F. Berret, Langmuir (2015), in revision [2] Le Bihan et al., J. Struct. Biol. 2009, 168 (3), 419-425. [3] Gradzielski, M. et al., T. R. Adv. Colloids Interface Sci. 2014, 208 (0), 214-224

Figure : a) Schematic representation of particles reaching an alveolus b) TEM picture of nanoparticles-vesicles aggregates c) cartoon of nanoparticles-vesicles aggregates

Simon Merminod Equipe DSHE

Order-disorder transitions in a driven magnetic granular monolayer.

Abstract : In an experiment at the human scale, we can observe with the naked eye phenomena involved in the shaping of matter at the molecular scale, resulting from the competition between thermal disordered motion and non-contact interactions between particles. Soft ferromagnetic particles are placed inside a horizontal, quasi-two-dimensional cell and are vertically vibrated, so that they perform a horizontal Brownian motion. When immersed in an external vertical magnetic field, the particles become magnetized and thus interact according to a dipolar repulsive law. Ordered and disordered phases are observed depending on the particle area fraction and on the ratio of the magnetic energy to the kinetic energy. In all the experiments that will be presented, the shaking strength is fixed and the magnetic field is increased. At low particle area fraction, we show that, prior to the complete solidification of the disordered granular gas into a crystalline state, the typical properties of this dissipative out-of-equilibrium granular gas are progressively lost, to approach those expected for a usual gas at thermodynamic equilibrium [1]. Surprisingly, when the area fraction is higher, the system solidifies into a large-scale disordered labyrinthine phase mostly constituted of randomly orientated short chains of particles in contact, despite the magnetic repulsion [2]. We characterize quantitatively this transition and explain the formation of these chains using a simple model. Moreover, by studying the aging properties of the labyrinthine phase, we show that it exhibits slow dynamics, which occurs typically in out-of-equilibrium disordered systems such as structural glasses.

[1] S. M., M. Berhanu and E. Falcon, EPL 106, 44005 (2014). [2] S. M., T. Jamin, E. Falcon and M. Berhanu, accepted PRE (ArXiv : 1507.06950v3)