Formulation and Optimization of a Melissa officinalis Loaded Nanoemulgel for Anti-Inflammatory Therapy Using Design of Experiments (DoE)

This research explores the use of a Design of Experiments (DoE) framework for the development and systematic refinement of a nanoemulsion comprising Melissa officinalis essential oil for transdermal drug delivery applications. Fourier-transform infrared spectroscopy (FTIR) confirmed the presence of characteristic phytochemical groups such as hydroxyl (–OH), carbonyl (C=O), and ether (C–O–C), pointing to the oil’s phytochemical makeup. To examine the effect of various formulation factors, a Central Composite Design (CCD) was implemented. This strategy aimed to minimize droplet size and enhance emulsion stability by evaluating the influence of Tween 80 concentration and homogenization time. The optimized formulation resulted in an average droplet diameter of 127.31 nm, a polydispersity index of 17.7%, 88.3% transmittance, and a zeta potential of –25.0 mV, indicating favorable colloidal stability and uniformity. The drug release study revealed that the release pattern adhered to the Higuchi model (R² = 0.900; k = 4.63), which suggests a diffusion-driven mechanism. Further kinetic analysis based on the Korsmeyer–Peppas equation (n = 0.88) indicated a non-Fickian, or anomalous, release behavior. In vitro antimicrobial testing showed that Staphylococcus aureus (MIC = 250 µg/mL) was more sensitive to the formulation compared to Escherichia coli (MIC = 500 µg/mL). Evaluation of anti-inflammatory efficacy in vivo, using a carrageenan-induced paw edema model, showed that the formulation significantly decreased inflammation (p = 0.005 at 60 minutes), with full reduction by 240 minutes. These outcomes highlight the therapeutic value of Melissa officinalis oil-based nanoemulgel as a promising carrier for transdermal management of microbial infections and inflammatory conditions.