Quercetin crystal-stabilized pickering emulsions: altering droplet shape via oil polarity

Pickering emulsions are emulsions stabilized by solid particles. These particles serve as an alternative to conventional synthetic surfactants, which may raise concerns related to toxicity, irritation, and environmental impact. In this study, the active pharmaceutical ingredient-traditionally solubilized or encapsulated within emulsion droplets-is instead used in its crystalline form to stabilize the droplets. Quercetin, a natural flavonoid with attractive pharmacological properties, is selected as a model compound. The effect of oil polarity on oil-in-water emulsions stabilized by size-reduced commercial quercetin dihydrate crystals is investigated. Oils of increasing polarity-PDMS, Miglyol, castor oil, a mixture of Miglyol and castor oil, and a eutectic solvent (C8:C12)-are employed. Droplet formation follows the limited coalescence phenomenon characteristic of Pickering emulsions. Increasing oil polarity leads to more deformed droplets, which nevertheless remain remarkably stable. Confocal and cryo-scanning electron microscopy (cryo-SEM) imaging confirm dense crystal coverage at the droplet interfaces for all emulsions, which remain stable for at least 28 days. This work highlights a novel strategy for the design of pharmaceutical emulsions in which natural active ingredients, in crystalline form, act as stabilizing agents, offering new perspectives for tailoring emulsion physicochemical properties.