Biocompatible Emulsions Stabilized by Natural Silk Fibroin

Due to its amphiphilicity, the natural fibrous structural protein, silk fibroin (SF), can adsorb at the oil/water interface, form protective viscoelastic layers, and stabilize emulsions. Biocompatible SF-stabilized emulsions can be used in different fields of cosmetics, food, drug delivery, and biomedicine. Depending on the silk processing method, various emulsion types can be obtained, such as film-stabilized emulsions stabilized by SF molecules and Pickering emulsions stabilized by nanostructured SF or SF particles. Nanostructured SF and SF particles, with β-sheet dominated secondary structures, can overcome the drawback of SF molecules with unstable conformation transition during application, and thus endow higher emulsion stability than SF molecules. The emulsions stabilized by SF nanoparticles can endure heat and high ionic strength, while the emulsions stabilized by SF nanofibers show superior stability at high temperature, high salinity, and low pH due to the strong interfacial entangled nanofiber networks. In this review, the recent progress in research on SF-stabilized emulsions is summarized and generalized, including a systematic comparison of the stabilization mechanisms for different SF morphologies, and the influences of the emulsion fabrication technique, component type and proportions, and environmental conditions on the microstructures and properties of SF-stabilized emulsions. Understanding the stabilization mechanism and factors influencing the emulsion stability is of great significance for the design, preparation and application of SF-stabilized emulsions.