The interaction of bilayer vesicles with hard nanoparticles is of great relevance to the field of nanotechnology, e.g., its impact on health and safety matters, and also as vesicles are important as delivery vehicles. In this work we describe hybrid systems composed of zwitterionic phospholipid vesicles (DPPC), which are below the phase transition temperature, and added silica nanoparticles (SiNPs) of much smaller size. The initial DPPC unilamellar vesicles, obtained by extrusion, are rather unstable and age but the rate of ageing can be controlled over a large time range by the amount of added SiNPs. For low addition they become destabilized whereas larger amounts of SiNPs enhance the stability largely as confirmed by dynamic light scattering (DLS). z-Potential and DSC measurements confirm the binding of the SiNPs onto the phospholipid vesicles, which stabilizes the vesicles against flocculation by rendering the z-potential more negative. This effect appears above a specific SiNP concentration, and is the result of the adsorption of the negatively charged nanoparticles onto the outer surface of the liposome leading to decorated vesicles as proven by cryogenic transmission electron microscopy (cryo-TEM). Small amounts of surface-adsorbed SiNPs initially lead to a bridging of vesicles thereby enhancing flocculation, while higher amounts render the vesicles much more negatively charged and thereby longtime stable. This stability has an optimum at neutral pH and for low ionic strength. Thus we show that the addition of the SiNPs is a versatile way to control the stability of gel-state phospholipid vesicles and also to modulate their surface structure in a systematic fashion. This is not only of importance for understanding the fundamental interaction between SiNPs and bilayer vesicles, but also with respect to using silica particles as formulation aids for phospholipid dispersions.

The formation of hybrid materials consisting of membrane‐coated silica nanoparticles (SiNPs) concentrated within small unilamellar vesicles (SUVs) of 1,2‐dioleoyl‐sn‐glycero‐3‐phosphocholine (DOPC) is described. They are formed by a simple self‐assembly process resulting from invagination of the SiNPs into the SUVs and subsequent vesicle fusion, thereby retaining an almost constant size. This process was followed under conditions where it proceeds slowly and could be analyzed in structural detail. The finally formed well‐defined SiNP‐filled vesicles are long‐time stable hybrid colloids and their structure is conveniently controlled by the initial mixing ratio of SiNPs and vesicles.

The formation of hybrid materials consisting of membrane-coated silica nanoparticles (SiNPs) concentrated within small unilamellar vesicles (SUVs) of 1,2-dioleoyl-snglycero-3-phosphocholine (DOPC) is described. They are formed by a simple self-assembly process resulting from invagination of the SiNPs into the SUVs and subsequent vesicle fusion, thereby retaining an almost constant size. This process was followed under conditions where it proceeds slowly and could be analyzed in structural detail. The finally formed well-defined SiNP-filled vesicles are long-time stable hybrid colloids and their structure is conveniently controlled by the initial mixing ratio of SiNPs and vesicles.

Liposome-nanoparticle hybrid colloids … … were obtained by internalization of silica nanoparticles into fluid liposomes. In their Communication on page 12441 ff., M. Gradzielski, R. Michel et al. show that the structure of these long-time stable hybrid colloids is conveniently controlled by the initial mixing ratio of nanoparticles to liposomes. The internalization can be followed under conditions under which the process proceeds slowly, allowing for the observation of the different steps of the mechanism.

Liposom‐Nanopartikel‐Hybridkolloide wurden durch Internalisierung von Quarznanopartikeln in fluide Liposome erhalten. In ihrer Zuschrift auf zeigen M. Gradzielski, R. Michel et al., dass die Struktur dieser langzeitstabilen Hybridkolloide durch das anfängliche Mischverhältnis von Nanopartikeln zu Liposomen geprägt ist. Die Internalisierung kann unter Bedingungen verfolgt werden, unter denen der Prozess langsam verläuft, was die Beobachtung der einzelnen mechanistischen Schritte möglich macht.