Sodium Dodecylbenzene Sulfonate-Mediated Self-Assembly of Silk Particles from Formic Acid Solutions into Robust Films

Silk proteins are versatile biopolymers well-suited to act as foundational components of a wide range of biomaterials. Rapidly gelling, self-assembling systems are especially valuable for drug delivery and biomedical applications. In this study, we present a way to induce the solid coaggregation of silk fibroin (SF) by adding the anionic surfactant sodium dodecylbenzene sulfonate (SDBS) into an SF solution prepared in formic acid (FA). SF films prepared by dissolving silk in CaCl₂-FA and subsequently rinsing in water to remove CaCl₂ were re-solubilized in FA with different content of SDBS. It was found that SF aggregation time is strongly modulated by the presence of SDBS. At increasing surfactant content, hydrophobic interactions between the SF chains and SDBS promote the formation of spherical coaggregates, whose size increases with surfactant concentration. FTIR analysis reveals that this process is accompanied by the formation of β-sheet structures, likely driven by hydrophobic interactions. This spontaneous liquid-to-solid phase transition promotes the formation of mechanically robust SF films with tunable electrical properties.