Curcumin-loaded microemulsion: formulation, characterization, and in vitro skin penetration

Objective: Formulation of curcumin in a microemulsion with a high loading capacity and that favors its penetration into the skin.SignificanceTake advantage of the properties of microemulsions to promote the penetration of curcumin into the skin, with the aim of enhancing its therapeutic effects. Methods: Curcumin was formulated in microemulsions based on oleic acid (oil phase), Tween((R)) 80 (surfactant), and Transcutol((R)) HP (cosurfactant). The microemulsion formation area was mapped by constructing pseudo-ternary diagrams for surfactant:co-surfactant ratios 1:1, 1:2, and 2:1. Microemulsions were characterized through measurements of specific weight, refractive index, conductivity, viscosity, droplet size, and in vitro skin permeation studies. Results: Nine microemulsions were prepared and characterized, showing clear, stable formulations with globule size dependent on the proportion of the components. The microemulsion with the highest loading capacity (60 mg/mL), based on Tween((R)) 80, Transcutol((R)) HP, oleic acid, and water (40:40:10:10) was able to penetrate the viable epidermis, finding a total amount of curcumin in the receptor medium at 24 h of 10.17 +/- 9.7 mu g/cm(2). The distribution of curcumin in the skin, visualized by confocal laser scanning microscopy, showed that the maximum amount was located between 20 and 30 mu m. Conclusion: The inclusion of curcumin in a microemulsion allows its passage into and through the skin. The localization of curcumin, especially in the viable epidermis, would be important for those cases where local conditions are sought to be treated.