**6. Conclusions**

The results reported here indicate the possibility to get "*hybrid*" colloid composites from the interactions between *LYS-NPs* complexes and vesicles. The reported results refer to the phenomenological aspects of the interaction process, as it was inferred from *DLS*. Very

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presumably, the observed features are related to structural rearrangements and to eventual rupture of vesicle-*NP* adducts with time. In one case, apparently, the sedimentation of adducts takes place after some time. In others, large floating objects are present in the dispersing medium.

Depending on the forces active between vesicles and *LYS-NPs*, it is possible that the kinetics of adducts formation follows different pathways. In the case of *SDS*-*CTAB* cat-anionic vesicles (bearing a substantial negative charge), the interaction mechanism obeys a pseudo first-order mechanism, controlled by the number ratio between the components. In the interaction between *DDAB* vesicles and *LYS-NPs*, conversely, the situation is more cumbersome to be rationalized. In this latter case, it is presumed that the interaction mechanism implies the formation of a transient state (characterized by a maximum in *DLS*  plots); after some time the mixed colloid particles rearrange and change in size and shape. It is also possible that the large increase in size observed in this system is due to the incipient nucleation of particles, which precipitate after some time.

Some questions are still under debate on the biological implications of the above systems. However, when *LYS-ABOP* particles interact with cells, it is expected that the reactive behavior (mostly the one relative to surface adsorption) will be close to that reported in case of cat-anionic surfactant mixtures. In fact, cells are negatively charged and are generally composed by mixtures of oppositely charged lipids. On this regard, thus, catanionic systems are much more effective as bio-mimetic models compared to other currently used lipid dispersions. It must be also considered that the mechanisms controlling the pynocytosis of particles adsorbed onto cells require the deformation of the latter. In fact, vesicles made by different lipids are more prone to be deformed and envaginate (25), as a consequence of local changes in composition associated to adsorption of charged and bulky entities onto them. This implies the migration of the lipid components in the bi-layer and induces a local deformation of vesicles, making possible particles uptake into cells. More dedicated investigation is required to clarify such aspects.

Another relevant question deals with use of the above systems in modeling bio-mimetic processes. In nature there are cases of interactions between "*hard*" and "*soft*" particles, as, for instance, in the interactions between viruses and other viral vectors and cells (26,27). From such a point of view, the ones presented here are excellent mimetic models of the above interactions, because viruses are generally covered with enzymes attaching onto the surface of cells and tissues. Preparing nano-particles sharing some properties in common to viruses (having, for instance, a similar surface coverage) would help understanding the physical grounds underlying the interactions between viruses and cells.
