Nanoparticles and biomembranes as models for aggregation in the biological environment

Nanoparticles are ever more present in our bodies, both as devices engineered for biomedical applications and as incidental intruders. Moreover, nanoparticles can be exploited as biomimetic devices, able to reproduce specific properties of relevant biological macromolecules, such as proteins, thanks to their design flexibility at the synthesis level. In each case, their fate in the biological environment is determined, among other properties, by their aggregation behavior. For this reason, it is crucial to understand the physical driving forces that underlie their aggregation, whether in water or at the biomembrane interface. When the aggregation takes place at the scale of a few nanometers, complex molecular mechanisms, detectable by high-resolution computer simulations, mediate the interactions. Coarse grained force fields offer a sweet spot in modeling these systems: while maintaining a relevant portion of molecular detail, they allow the study of the collective behavior of nanosized objects and large patches of lipid bilayers. This thesis uses coarse grained simulations to study the aggregation of nanoparticles with hydrophobic or functionalized amphiphilic surfaces in water and in membranes. In both environments, we find that the reshaping of the soft interfaces of these systems (NP-membrane and NP-NP) is the common factor driving the formation of unexpected aggregates, which assume peculiar, non-isotropic configurations. Our results pave the way to the rational design of nanoparticles with targeted aggregation properties due to the tunability of their ligand shell composition, core shape, and size. Moreover, many of the observed mechanisms can be generalized to understand the interactions of similar relevant biological macromolecules, such as proteins.