This research is a contribution of our previous works aim to introducing and developing of eco-friendly microemulsion drug delivery systems based on herbal oils for poorly soluble celecoxib drug. Since the antioxidant properties of both herbal oils and celecoxib have been proven, the synergistic effect of the proposed formulations containing sunflower, sesame, and olive oils has been investigated. In order to introduce suitable formulations, pseudo-ternary phase diagrams of the systems containing surfactant/cosurfactant of Tween 80/ ethanol and three mentioned herbal oils were constructed. Then, four different formulations were prepared and some of their physicochemical properties such as electrical conductivity, viscosity, density, refractive index, surface tension, and pH were measured. The size and morphology of the microemulsion systems were determined using dynamic light scattering and transmission electron microscope. The results showed spherical nanoparticles of oil-in-water microemulsion with low polydispersity index. Skin permeation and accumulation of celecoxib for the microemulsion as well as their microemulgel formulations have been evaluated during 24 h at 37 ◦C. The permeation kinetics of all formulations was also investigated with different models, which Higuchi and Korsmeyer-Peppas models showed better correlation. On the other hand, investigated antioxidant activity of three types of microemulsions and microemulgels without and with celecoxib, interestingly, indicated the synergistic effect of oil and celecoxib. It is also verified that formulations containing olive oil has significantly higher antioxidant activity compared to the other two oils. Finally, the sun protection factor was evaluated for all formulations, demonstrating a good potential to prevent the harmful effects of ultraviolet rays.
