Influence of oil content on physicochemical properties and skin distribution of Nile red-loaded NLC

The aims of this study were to investigate the effect of the oil content on the physicochemical properties of NLC and to elucidate the potential of NLC for skin targeting. The obtained results showed that an increase in the oil content did not affect the mean particle size of NLC but impacted on the zeta potential. The inner structure of NLC was influenced by the increasing proportion of oil towards the less ordered structure as confirmed by differential scanning calorimetry (DSC) and X-ray diffraction (XRD), particularly for the higher medium chain triglycerides (MCT) loading. The data from proton nuclear magnetic resonance (¹H NMR) revealed that cetyl palmitate nanoparticles did not completely recrystallize after cooling down to room temperature. ¹H NMR and DSC results indicate that MCT molecules were restricted in the NLC as compared to the nanoemulsions (NE). Nile red distribution and penetration into skin from NLC were pronounced as compared to NE and dependent on the MCT loading. The deep penetration and high amount of Nile red were related to the occlusion factor. Moreover, the epidermal targeting was achieved by NLC applications, particularly those containing 5% MCT (NLC-5) depending on the amount of MCT loading.