A new vesicle-loaded hydrogel system suitable for topical applications: preparation and characterization.

Aim of this research was to prepare and study drug release from a new formulation consisting of non ionic surfactant vesicular structures, niosomes (NSVs), loaded with model molecules calcein (CALC), nile red (NR), ibuprofen (IBU) or caffeine (CAFF), and embedded in a hydrogel matrix. Methods. The system locust bean gum/xanthan (1:1), prepared at 60 degrees C, was used to entrap the vesicles (Tween 20/cholesterol 1:1), loaded with guest molecules and the release profiles were detected at 32 C. The hydrogel systems were characterized by means of scanning electron microscopy; niosomes were characterized by means of size and zeta-potential measurements. Results. Size measurements showed that a slight increase in vesicle dimensions occurs after inclusion of CALC or CAFF (hydrophilic molecules) in the vesicular structures. zeta-potential measurements showed that the inclusion of these molecules did not significantly modify the surface charge of empty vesicles. This was probably related to an almost negligible drug adsorption on the vesicle surface. The release from the niosomes- gel systems of two probes (CALC and NR) showed that the diffusion of CALC through the gel was not affected by the niosome entrapment while for NR, the presence of vesicles was crucial. The release profiles from niosomes- gel systems and from the hydrogel alone of model drugs, CAFF and IBU, showed an appreciable difference between the two drugs: the more hydrophilic CAFF was released much faster than IBU. In all release studies turbidity, dimension and zeta-potential analyses indicated that the loaded niosomes were released by the hydrogel matrix without being damaged. Conclusions. The reported in vitro experiments show the capability of the novel formulation to combine the qualities of both chosen single systems, i.e. the niosomes and the polymeric network. The hydrogel shows a protective effect on vesicle integrity and leads to a slow release of the loaded model molecules from the polysaccharidic system.