The design and characterization of a positively charged submicron emulsion containing a sunscreen agent

Abstract Stable monodispersed positively charged submicron emulsions were prepared and characterized using appropriate emulsification and homogenization processing conditions. Only the emulsions prepared with a combination of phospholipids (phosphatidylcholine (PC) and phosphatidylethanolamine (PE)), poloxamer and stearylamine, were stable enough to resist the thermic shock induced by autoclave sterilization or excessive shaking. The results suggested that a mixed interfacial film comprising the phospholipids, poloxamer and stearylamine molecules was formed at the o/w interface with an overall positive surface charge. The occurrence of the molecular interactions of stearylamine with at least the anionic phospholipidic component, PE, is revealed by the zeta potential values obtained in the experiments where the PC/PE ratio was varied. Indeed, decreasing the concentration of PE at the o/w interface led to an increase in the positive zeta potential value of the emulsions. In the presence of octyl methoxycinnamate, a sunscreen agent in the oil phase, a substantial increase in positive zeta potential was noted at 0.3% stearylamine. It appears that octyl methoxycinnamate enhanced the molecular interactions occurring between stearylamine and the phospholipidic components at the o/w interface. TEM analysis showed that most of the fractured oil droplets seemed to be surrounded by emulsifier monolayers showing the typical characteristics of an ideal submicron emulsion. Although some of the particle cores exhibited layered structures on the surfaces, no large multilamellar bilayers could be detected. Nevertheless, the formation of multilayer structures is likely to occur in the present emulsion as already reported in the investigation of negatively charged i.v. fat emulsions.