Nanostar self-assemblies of spherical nanoparticles inside lipid vesicles.

Curvature deformations of lipid membranes resulting from the adhesion of nanoparticles (NPs) often lead to effective interactions between the NPs, resulting in their self-assembly. Many studies have shown that this interaction is attractive in the case of NPs with uniform surfaces adhering to the outer leaflet of lipid vesicles. This interaction leads to the NPs' self-assembly into in-plane or out-of-plane linear chains in which they are uni-dimensionally close-packed. In this article, we show, through coarse-grained molecular dynamics simulations, that spherical NPs with uniform surfaces adhering to the inner leaflet of lipid vesicles experience repulsive interactions, resulting in NP configurations in which they are apart. Systematic simulation sets with respect to the number of NPs inside vesicles and the strength of their adhesion to the membrane show an interesting phase diagram with different adhesion modes. These include a three-dimensional clustering mode, which is fairly dynamic at low adhesion strength and rigid at moderately high adhesion strength. These two regimes are separated by an intriguing two-dimensional clustering mode at moderate values of the adhesion strength. In this mode, the NPs form ordered planar nanostars with geometries determined by the number of NPs. In contrast to the three-dimensional mode, in the two-dimensional clustering mode, the NPs are anisotropically wrapped by the NPs with the largest degree of wrapping along the plane normal to the nanostar plane and the lowest degree of wrapping along the plane of the nanostar.