Formation and physicochemical properties of non-ionic oil-in-water nanoemulsions containing liquid and solid triglycerides

Abstract

With the increasing attention in nanoemulsions (NE) formulation as drug delivery vehicles in recent years, in this study, the formation and physicochemical properties of the oil-in-water NE stabilized by the nonionic C18:1E10 surfactant containing either liquid triglycerides (soybean oil and trioctanoin) or solid triglycerides (tripalmitin and trilaurin) were investigated. The extent of NE formation was influenced by triglyceride molecular weight in that the intermediate molecular weight triglyceride, trilaurin, which is approximate equal to molecular weight of surfactant formed NE over the greatest range of compositions followed by the higher molecular weight triglycerides, (tripalmitin, soybean oil) and a lower molecular weight triglyceride (trioctanoin), respectively. The NE existence was divided into Regions A, B and C based on their appearances which were clear, translucent and cloudy, respectively. The results showed that the properties of NE in Regions A and B were similar and had advantages on improved solubilisation of lipophilic drug, testosterone proprionate (TP), while NE in Region C had different properties and had no advantages on drug solubilisation. Phase inversion temperature and small angle neutron scattering studies suggested that soybean oil, tripalmitin and trilaurin formed a core in the NE droplets, while trioctanoin both formed a core in droplet and penetrated through the surfactant hydrophobic tail. The solubility of TP in NE was influenced by the nature and melting point of triglyceride. The drug would solubilise to the greater extent in NE containing either liquid triglycerides (soybean oil and trioctanoin) or a lower melting point solid triglyceride (trilaurin) which was in “liquid-like” state in NE. In contrast, solubilisation of TP was limited in NE containing higher melting point solid triglyceride, tripalmitin, owing to “solid-like” state of triglyceride inside NE. Conclusively, the information obtained from this study will help ultimately design NE as drug carrier as well as provide more understanding about the effect of the triglyceride nature on the properties and drug solubilisation capacity of NE.