Fig. 4: Assembly and fibril formation of SF coacervates with acidification and shear force.

a Optical and (b) fluorescence images of silk fibroin (SF) coacervates at different pH values. c Optical and (d) fluorescence images of SF coacervates at different pH values after direct stretching with a syringe needle. The blue arrows in (c) indicate shear-induced fibril formation of coacervates. The white arrows in (b, d) indicate bead-on-a-string structure (c: scale bar=100 µm; a, b, d: scale bar=50 µm). e Panoramic image of a fiber stretched from a droplet of LLPS solution (pH 3.5, [Ca²⁺]=37.5 mM). f Diffusion coefficient calculated from FRAP measurements of SF coacervates at different pH values ([Ca²⁺]=37.5 mM). Data are presented as mean ± SD for n = 3 independent experiments. The statistical significance (P < 0.05) of the differences was checked using one-way analysis of variance (ANOVA) with Tukey’s test. A significant difference was found between pH 4.0 and pH 3.0 (P = 0.01651), while no significant differences were observed between pH 3.5 and pH 3.0 (P = 0.06183) or between pH 4.0 and pH 3.5 (P = 0.54017). The corresponding data points of the bar graphs in (f) are indicated as triangels.