Natural-Based Microparticles as Sole Stabilizers of High Internal Phase Pickering Emulsions

Designing a water-reduced emulsion is a technical approach to creating more sustainable cosmetic products and reducing the strain on global water resources. This study explores the structuration of highly concentrated O/W emulsions solely stabilized by particles, also known as "high internal phase Pickering emulsions" (HIPPEs). It focuses especially on particles from natural origins with a micrometric scale instead of the highly modified nanometric ones commonly used (which may raise health issues). Highly concentrated O/W emulsions were formulated with different lipid phases (regarding the chemical nature and polarity) of up to 80%. A comprehensive array of particle natural sources (plant, mineral, etc.), micrometric sizes (from 3 to 45 μm), and geometries were screened. Parameters such as droplet size distribution, microstructure, relative stability (backscatter level changes), and pH were systematically monitored over 2 weeks. An experimental design approach was carried out on three particles to determine their stability domains in various formulation combinations, dissecting complex parameter interactions that pilot emulsion characteristics. Micrometric particles demonstrated excellent efficacy in structuring HIPPEs. A wide spectrum of systems can be engineered, exhibiting a wide range of microstructures (droplets ranging from micrometers to several millimeters), stabilities, and intrinsic properties (with pH values extending from approximately 6 to 10). Emulsions displaying resistance to coalescence in W/O systems were also successfully formulated by using hydrophobic natural particles. Waterless emulsions (less than 20% (w/w) water) stabilized exclusively with naturally derived microparticles represent promising architectures for designing future clean-label cosmetic prototypes. By meticulously selecting particle parameters, including their chemical composition, size, or origin, we can tailor the architecture of HIPPEs to obtain the targeted characteristics and functionalities. Beyond particle constituents, other ingredients influence the structural arrangement such as the lipid phase chemistry.