The fractal hologram and elucidation of the structure of liposomal carriers in aqueous and biological media.

The present study deals with the physicochemical characterization (size, polydispersity, ζ-potential) of dipalmitoylphosphatidylcholine (DPPC) liposomes and DPPC:cholesterol (chol) (9:1 molar ratio) liposomes, and the determination of their fractal dimension (mass fractal (d(f)) and surface fractal (d(s))), in an aqueous (HPLC grade water) and in a biological (fetal bovine serum - FBS) medium. Dynamic, static and electrophoretic light scattering and fluorescence spectroscopy are used as experimental techniques to elucidate the structure and physicochemical parameters of liposomes in an ageing study in two different media, as well as their structural response in changes in concentration and temperature. The extended DLVO theory would be the tool to explain the phenomenology of the colloidal behavior in these systems and of their aggregation process. The fractal dimensionality of DPPC liposomes was decreased while for DPPC:cholesterol (9:1) it remained unaffected in the two dispersion media. The structure of the liposomal systems, the process kinetics, and the fractal dimension are consistent with the diffusion-limited cluster aggregation (DLCA) and reaction-limited cluster aggregation (RLCA) models. On the contrary, hydrodynamic radius (R(h)) was found to be stable during the variations of colloidal system conditions, especially due to concentration changes. Finally, we suggest that this study can be a rational road map to design advanced Drug Delivery nano Systems (aDDnSs) with improved pharmacokinetic profile which could be considered as crucial for their effectiveness.