**6. How Do the Particle Physico-Chemical Properties Affect Their Interaction with LS Layers?**

Once particles are deposited on the LS layer, their specific physico-chemical properties define the particle-LS interactions, and their consequences. Furthermore, it is very important to control the particle dose that interacts with the LS film because in most cases the harmful effects associated with inhaled particles present a strong dose dependence [70,193,212–214]. It should be noted that in general, particles' affects to the respiratory function are at two different levels: (i) LS biological function and (ii) LS metabolism [7]. Therefore, a deep understanding of the impact of particles on the physico-chemical properties of LS layers requires examination of the specific characteristics of the probed particles [65,128]. Figure 7 summarized the potential impact of particles with different physicochemical properties in the interfacial properties of layers formed by LS models.

**Figure 7.** Schematic representation of the effect of different types of particles in the interfacial organization of LS layers, and the surface pressure-area per molecule isotherms. Reprinted from Arick et al. [65], with permission from Elsevier, Copyright 2015.
