Fig. 1

Preparation and characterization of Cur@SF NPs. A Preparation process of silk fibroin-loaded curcumin (Cur@SF NPs). B Scanning electron microscopy (SEM) image of Cur@SF NPs at two magnifications (scale bars: 200 nm and 100 nm). C Hydrodynamic size distribution of Cur@SF NPs. D Ultraviolet and visible spectrophotometry (UV–Vis) spectra showing the characteristic absorption of curcumin in Cur@SF NPs. E Fourier transform infrared spectroscopy (FTIR) of SF, curcumin and Cur@SF NPs. The spectral peaks at 1010 cm⁻¹ and 1046 cm⁻¹ were assigned to the -C–O–C- vibration of curcumin. The anti-symmetric stretching of the C–O–C from curcumin is at approximately 1150 cm⁻¹. The characteristic absorption peak of SF was observed at 3300 cm⁻¹, which represented the stretching vibration of the peptide bond (-CONH-) of SF. Specific peaks were also observed at 1600 cm⁻¹ (amide I, C-O) and 1550 cm⁻¹ (amide II, N–H), which represented β-sheets of SF. The carbonyl peak of curcumin and the amide peak of SF may partially overlap, which are all attributed to the strong absorption at approximately 1500 cm⁻¹. F Determination of the release of curcumin from Cur@SF NPs in type XIV collagenase solution by detecting curcumin content within 120 h