Effects of oils, surfactants and cosurfactants on physicochemical properties and permeation of Centella Asiatica extract in microemulsions

Abstract

The purposes of the study were to develop the preparation of Centella asiatica microemulsions and investigate the effect of composition of microemulsions on the pseudoternary phase diagram and permeation through shed snake skin membrane. The microemulsions were prepared using either isopropyl myristate (IPM) or caprylic/capric triglyceride as oil phase and various surfactants, including Brij 30, Brij 97, Arlatone T, and mixture of Tween 80 and Span 80 of 1:1 and 2:1 ratios. Propan-2-ol and propylene glycol were employed as cosurfactants to design microemulsions by constructing pseudoternary phase diagrams. The microemulsion system containing IPM as oil, Brij 30 : propan-2-ol and Brij 97 : propan-2-ol at the ratio of 2:1 presented the highest percentage of isotropic area at 36.11. The physicochemical properties of microemulsion were evaluated such as conductivity, viscosity, pH, optical property under polarized light microscopy and droplet size. Selected fifteen formulations of microemulsion containing Centella triterpene extract with different surfactants and cosurfactants were prepared and evaluated. the permeationprofiles of microemulsions containing Centella triterpene extract were explored using Franz diffusion cells and the samples were analyzed for asiaticoside, madecassic acid and asiatic acid by high-performance liquid chromatography with gradient system. It was found that the microemulsion comprised of isopropyl myristate: Tween 80: Span 80: propan-2-ol: water as 30: 20: 10: 30: 10, showed the highest permeation rate. Additionally, the microemulsions containing Centella extract showed a good stability, regarding asiaticoside, madecassic acid and asiatic acid under the stress condition of heating-cooling cycle.