Penetration enhancer-containing vesicles: composition dependence of structural features and skin penetration ability

In this work, we focused on how composition and preparation method of vesicles might affect their morphological features and delivery performances. Penetration Enhancer-containing Vesicles, PEVs, vesicles containing a water miscible penetration enhancer (Transcutol® P; 10%, 20%, 30% v/v) and encapsulating diclofenac sodium, were formulated and compared with conventional liposomes. A cheap and unpurified commercial mixture of phospholipids, fatty acids, and triglycerides (Phospholipon® 50) was used, and the effects of this heterogeneous composition (along with the presence or absence of transcutol and the production method) on vesicle morphology, size, surface charge, drug loading, and stability were investigated. The variations in vesicle structure, bilayer thickness, and number of lamellae were assessed by TEM and Small and Wide Angle X-ray Scattering, which also proved the liquid state of the vesicular bilayer. Further, vesicles were evaluated for ex vivo (trans)dermal delivery, and their mode of action was studied performing a pre-treatment test and confocal laser scanning microscopy analyses. Results showed the formation of multi- and unilamellar vesicles that provided improved diclofenac delivery to pig skin, influenced by vesicle lipid composition and structure. Images of the qualitative CLSM analyses support the conclusion that PEVs enhance drug transport by penetrating intact the stratum corneum, thanks to a synergic effect of vesicles and penetration enhancer.