*6.3. Impact of Particle Shape on the Interactions with LS Layers*

Particle shape, and in particular shape anisotropy, emerges as a very important parameter controlling the physico-chemical properties of colloidal particles, and their ability for self-organizing at the fluid interface [231], and hence it may be expected that it plays a very important role in the modification of the LS performance as a result of the particle incorporation [232]. This is clear by comparing the modifications of the phase behavior of DPPC layers upon the incorporation of three different types of particles, two surface inactive anisotropic clays (plate-like bentonite and halloysite nanotubes) and spherical silicon dioxide particles. The results found that the increase of the particle anisotropy facilitates the particle clearance upon compression [229]. However, there are no systematic experimental studies evaluating the impact of the particle anisotropy on LS layers. However, some simulations (molecular dynamics) evidenced that the length-to-diameter aspect ratio of the particles plays a very important role on the control of their penetration and disturbance of LS function [233].

The influence of the particle anisotropy on the modification of LS layers was further explored by Kondej and Sosnowski [161]. They studied how carbon particles with different geometry (nanotubes and nanohorns) modify the performance of LS layers and found that the increase of the surface area of the particles induces a stronger frustration in the LS behavior. It should be stressed that most of the effect on LS behavior associated with particle anisotropy can be ascribed to the influence of the capillary forces [234].

#### *6.4. Does the Particle Chemistry Matter in Their Interactions with Lung Surfactant Films?*

The impact of the particle chemical nature on LS performance is difficult to systematize [59,65], and only some general aspects will be included about the impact of particle chemistry in LS layers. Silicon dioxide particles alter the LS performance in such a way that it is strongly dependent on the number of SiOH groups on the particle surface. Thus, the increase of the surface density of silanol groups leads to the emergence of silicosis and other lung diseases associated with the inhalation of silicon dioxide particles [235]. The importance of the chemistry of the particles in the modification of LS properties is also found by comparing the effect of carbon black and fumed silicon dioxide in the interfacial

properties of DPPC layers [128]. Despite the physical characteristic of the particles possibly being very similar, the specific chemical nature of the particles governs the balance of interactions occurring within the interface, and that consequently modifies the degree of interfacial disruption and the aggregation of the particles at the interface.

Figure 9 presents a summary of the impact of different physico-chemical properties of the particles in the LS function.

**Figure 9.** Impact of different physico-chemical properties of the particles in the LS performance. General perspective of the main effects and interactions of particles upon contact with LS. Reprinted from García-Mouton et al. [7], with permission from Elsevier, Copyright 2019.
