One of the major challenges with curcumin is its poor solubility in water, which limits its absorption and bioavailability in the body. This study aimed to develop and characterize stable microemulsions (MEs) as MEs increase the dispersibility of curcumin in water and aid its absorption in the body. Curcumin-loaded MEs were developed with the goal of enhancing topical delivery and its pharmacological activity (antioxidant, antibacterial, anticancer activity, and anti-inflammatory). The pseudoternary phase diagram was constructed to find out the desired microemulsion region. The prepared MEs (ME1-ME5) were evaluated for pH, viscosity, size of the particle, electrical conductivity, zeta potential, and ex vivo permeation of the drug. The optimized ME formulation was selected based on particle size and was further evaluated for biological activity (in vitro/vivo). In vitro cytotoxic effects of formulations were checked on the human liver cancer cell line, HEPG2 (a cell line exhibiting epithelial-like morphology that was isolated from a hepatocellular carcinoma). Geranium oil, Tween 80 (as a surfactant), and propylene glycol (as a cosurfactant) were screened out based on solubility to formulate MEs. The optimized ME formulation (ME5), with a composition of 20:50:30 (geranium oil:Tween 80:propylene glycol), exhibited pH 4.36 ± 0.057, conductivity of 40.06 ± 0.05 μS/cm, viscosity of 165 ± 0.37 mPa·s, and droplet diameter of 199.39 ± 0.017 nm. The ex vivo permeation study demonstrated a significant cumulative amount of curcumin permeated in 24 h and had a flux of 130.91 ± 0.02 μg/cm²/h. Antioxidant activity demonstrated that curcumin-loaded microemulsion (ME5) exhibited higher scavenging activity (99.27 ± 0.021%) than blank microemulsion (94.67 ± 0.001%). Optimized curcumin-loaded microemulsion (ME5) exhibited zones of inhibition of 25.18 and 28.37 mm against Escherichia coli and Staphylococcus aureus, respectively. Among the cell lines tested, a higher concentration of ME5 showed the greatest cytotoxicity with a % viability of 8.22 ± 1.09%. Evidently, it also revealed significant in vivo anti-inflammatory effects with 93.29 ± 0.030% inhibition by the carrageenan-induced paw edema model (6 h study) and 88.39 ± 0.002% inhibition by the formalin-induced paw edema model (14 day study). In conclusion, microemulsion was safe and effective for effective delivery of curcumin with the potential for antioxidant, antibacterial, cytotoxic, and in vivo anti-inflammatory activities.

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