Chemical stability and phase distribution of all-trans-retinol in nanoparticle-coated emulsions

The influence of silica nanoparticle coating on the chemical stability and phase distribution of all-trans-retinol in submicron oil-in-water emulsions is reported. The chemical stability was studied as a function of UVA + UVB irradiation, and storage temperature (4 °C, ambient temperature, and 40 °C) for emulsions stabilised with lecithin and oleylamine as the initial emulsifier with and without silica nanoparticle layers. The chemical stability of all-trans-retinol was highly dependent on the emulsifier type and charge, with negligible influence of the initial loading phase of silica nanoparticles. A significant stability improvement (∼2-fold increase in the half-life of the drug) was observed by nanoparticle incorporation into oleylamine-stabilised droplets (i.e. electrostatically coated), with no considerable effect for partially coated lecithin-stabilised droplets. The chemical stability of all-trans-retinol incorporated into nanoparticle-coated emulsions was well-correlated to the phase distribution of the active agent, and the interfacial structure of emulsions as determined by freeze fracture-SEM. Specifically engineered nanoparticle layers can be used to enhance the chemical stability of active ingredients in emulsion carriers.