Effects of Hydrophilic Natural Deep Eutectic Solvents on the Rheological, Textural, and Sensory Properties of Carboxymethylcellulose-Based Cosmetic Hydrogels

Natural deep eutectic solvents (NaDES), a category of sustainable solvents made from biorefinery ingredients, are an eco-friendly alternative to organic solvents in solubilization of active pharmaceutical or cosmetic ingredients. Biocompatible NaDES can be introduced in final products but are prone to modify their properties thanks to their hydrogen bonding capacities. The present study focuses on the impact of the incorporation of two hydrophilic NaDES made of betaine and glycerol (BG) or citric acid and glucose (CG), on the properties of a carboxymethylcellulose (CMC)-based hydrogel. Differential scanning calorimetry revealed that NaDES did not affect the endothermic peak of water but eliminated an endothermic peak associated with CMC polymer chain loosening. Rheological analysis displayed shear-thinning behavior, while the addition of 10% wt NaDES led to a significant increase in the viscosity at rest. CG introduction led to a shift from viscous-dominant behavior to elastic-dominant behavior, strengthening cohesion in the gel structure. Texture analyses revealed that NaDES-containing gels exhibit higher hardness and elasticity. Sensory evaluations highlighted differences in five sensory attributes among gels with NaDES concentrations and types playing significant roles. This research underscores the intricate interplay between NaDES and hydrogel properties, offering insights into the formulation of innovative cosmetic products that achieve both solubility and sensory appeal.