Reinforced and Ultraviolet Resistant Silks from Silkworms Fed with Titanium Dioxide Nanoparticles

As the perfect combination of strength and luster, silkworm silks have been widely used in many fields but still need improvements. This paper demonstrates an in vivo uptake of titanium dioxide (TiO2) nanoparticles by silkworms, leading to the direct production of intrinsically modified silk. The nanoparticles can be easily incorporated into the silk gland of silkworm by using this method due to the interactions between TiO2 and silk fibroin molecules. Infrared spectra indicate that TiO2 nanoparticles confine the conformation transition of silk fibroin from random coil/alpha-helix to beta-sheet. Results of synchrotron radiation wide-angle X-ray diffraction and small-angle X-ray scattering suggest that modified silks have lower crystallinity, higher mesophase content, and higher Herman's orientation functions of crystalline region and mesophase region than control group. The breaking strength and elongation at break of the modified silk can be improved up to 548 +/- 33 MPa and 16.7 +/- 0.8%, respectively, by adding 1% nanoanatase into the artificial diet. Moreover, the TiO2-1% modified silk shows well-improved ultraviolet resistant property as the breaking strength only decreased 15.9% after exposure to ultraviolet light for 3 h. The in vivo modification method for silkworm silk is a green, sustainable, and promising route for commercial production in the future.