An Innovative Natural Eutectic Solvents-Based Emulsion Examined through the Lens of the Safe and Sustainable by Design Framework

Natural eutectic solvents (NESs) are promising alternatives to conventional organic solvents, yet their use as structuring media in emulsified systems remains largely unexplored. This study reports the first fully eutectic solvents-based emulsion, in which both phases are exclusively composed of NESs. The formulation consists of a hydrophilic NES (glycerol/glucose/betaine/water, 4:1:1:11 mol/mol) as the continuous phase and a hydrophobic NES (oleic acid/1,2-octanediol, 5:4 mol/mol) as the dispersed phase, stabilized with a bio-based non-ionic surfactant (lauryl glucoside). Designed using conventional emulsion engineering principles, the system exhibits high physical stability and well-controlled physicochemical and rheological properties. As a functional demonstration, the emulsion significantly enhances the stability and dermal penetration of retinyl palmitate, a model compound highly sensitive to oxidation, photodegradation, and extreme pH. Within a Safe and Sustainable by Design (SSbD) framework, ecotoxicological assessment using Daphnia magna revealed no adverse effects on survival or inflammatory pathways. The formulation process is compatible with existing industrial emulsification equipment. This work establishes eutectic solvents as viable and scalable media for sustainable emulsion systems, coupling performance with reduced environmental impact.