Snežana Cupara

Background/Objectives: Cinnamon bark essential oil (CEO) possesses antimicrobial, antioxidant, and anti-inflammatory properties. However, its topical application is limited by poor aqueous solubility, volatility, and chemical instability. The aim of this study was to develop gelled oil-in-water microemulsions stabilized with Decyl Glucoside for the cutaneous delivery of CEO and to evaluate their physicochemical and pharmaceutical characteristics. Methods: Pseudoternary phase diagrams were constructed to identify the microemulsion regions using Decyl Glucoside, propylene glycol, CEO, isopropyl myristate, and water. Selected CEO-loaded microemulsions were characterized in terms of droplet size, polydispersity index, zeta potential, refractive index, viscosity, and apparent pH, and were subsequently gelled with Aerosil^® 200. The resulting gelled microemulsions were evaluated for CEO content, apparent pH, rheological and textural properties, spreadability, in vitro release and skin permeation studies. The short-term stability of both liquid and gelled microemulsions was also assessed over 45 days. Results: Three CEO-loaded oil-in-water microemulsions were selected from the isotropic regions of the pseudoternary phase diagrams and successfully transformed into homogeneous gelled systems without phase separation. CEO incorporation increased the storage modulus and yield stress of the gelled formulations compared with the corresponding blank systems. The surfactant-to-cosurfactant ratio markedly influenced the rheological properties, mechanical strength, and in vitro release and skin permeation of CEO. Among the investigated formulations, MEG-CEO-2 provided the best balance between mechanical properties, CEO release, and skin permeation. Both liquid and gelled microemulsions maintained their principal physicochemical characteristics during the 45-day stability assessment. Conclusions: Decyl Glucoside-stabilized gelled microemulsions exhibited physicochemical and pharmaceutical properties supporting their further investigation as topical delivery systems for CEO. The results demonstrate that the surfactant-to-cosurfactant ratio can be used to tailor formulation performance, supporting a rational approach for the development of CEO-loaded dermal delivery systems. However, preservation of the biological activities of CEO following incorporation into these systems remains to be experimentally established.

Background/Objectives: Basil essential oil exhibits a wide range of biological activities, including strong antimicrobial and anti-inflammatory effects. Considering the health benefits of basil essential oil (BEO) and the favorable properties of alkyl polyglucoside emulsifiers, novel Montanov™-68-based O/W creams containing BEO were developed and characterized. Additionally, the influence of the emulsifier content on the cream’s properties was evaluated. Methods: The physicochemical properties were evaluated by organoleptic examination, physical stability test, and pH and electrical conductivity measurement. The mechanical properties were investigated by rheological, textural, and consistency analyses. In addition, a sensory evaluation protocol was applied. Results: The cream formulations containing 5% and 7% Montanov™ 68 demonstrated physical stability, with no evidence of phase separation during the observation period or following accelerated aging. The pH values remained within the acceptable range for topical use, and a gradual decrease in electrical conductivity over time was observed. The rheological analyses confirmed the non-Newtonian pseudoplastic behavior with thixotropic flow characteristics. The textural analyses demonstrated that the higher emulsifier content led to increased firmness, consistency, cohesiveness, and index of viscosity. The sensory analysis revealed differences between the alkyl polyglucoside (APG)-based cream formulations only in terms of the elasticity and stickiness. Conclusions: Although the rheological analyses suggested the better spreadability of the formulation with 5% emulsifier, this was not confirmed by the sensory analysis. However, the APG-based formulations performed significantly better than the synthetic surfactant-based formulation in terms of the absorption, stickiness, and greasiness (during and after application). These results are encouraging for the further evaluation of APG-based creams containing basil essential oil for topical application.