Preparation of high internal phase emulsions utilizing hyaluronic acid and elucidation of its structure-stabilizing effect

Abstract Oil-in-water (O/W) high internal phase emulsions (HIPEs) are emulsions with an internal phase (oil phase) volume ratio of 0.74 or higher and can be used as cosmetics, pharmaceutical dosage forms, and reaction fields for porous material fabrication. However, the preparation of HIPEs requires a large amount of surfactant (5 to 50 vol%) to disperse the oil phase stably, posing significant environmental concerns. In this study, hyaluronic acid (HYA) was focused on as a naturally derived stabilizer for emulsion, and highly concentrated emulsions were prepared based on the high viscosity and water retention of HYA. Highly concentrated emulsions, including HIPEs, were obtained with a lower amount of surfactants using HYA than without HYA. Furthermore, rheological measurements exhibited that the range of viscosity where emulsions could be obtained and the correlation between emulsion viscosity and the viscosity of the aqueous phase were clarified. These results showed the same tendency as the molecular weight and structure of HYA were changed. Our research exhibited new insights into the mechanism of stabilizing effects on the emulsions by HYA.