Rheological study of biobased structured emulsions for pharmaceutical and cosmetic applications

This study introduces HOSBM-MA, a biobased amphiphilic alternating copolymer derived from high-oleic soybean oil-based acrylic monomer and maleic anhydride, as a polymeric surfactant for structured emulsions —an application that has not previously been explored for this material. In combination with sucrose palmitate (SP), HOSBM-MA was used to formulate biobased formulations encapsulating oleic acid (OA) and fish oil (FO), with the aim of optimizing rheological performance, structural stability, and texture. Surfactant ratios, cargo compositions, and thermal conditions were systematically varied and analyzed through steady-shear flow, oscillatory rheology, thermal analysis, and microstructural evaluation. All formulations exhibited shear-thinning behavior, confirming their suitability for topical applications requiring controlled spreading. The most robust formulation was achieved with a 6:1 wt% SP: HOSBM-MA ratio containing 33 wt% OA/FO cargo, maintaining high viscosity and G′ dominance over G″ at both 22 and 40 °C—demonstrating stability under skin-temperature conditions. Higher OA content (30–33 wt%) produced thicker, more elastic creams suited for adhesive, occlusive applications, whereas lower OA content (15–25 wt%) yielded softer, more spreadable textures. Partial substitution of OA with FO produced intermediate viscosities and enhanced formulation versatility. These results highlight the novel functionality of HOSBM-MA as a bio-based polymeric surfactant capable of forming structured emulsions when paired with a high hydrophilic lipophilic balance (HLB) co-surfactant. By enabling precise tuning of texture, adhesion, and thermal stability through surfactant ratio and cargo selection, this system establishes a sustainable platform for pharmaceutical and cosmetic cream products, particularly in wound care and sensitive skin applications where balancing spreadability and structural integrity is essential.