Functional Silks From Silkworms Fed With Nanoparticles-containing Diet

Silkworm silks, made up with proteins, possess good mechanical properties, biocompatibility, degradation, and have widespread applications in textile, medicine and tissue engineering. However, despite the excellent integrated performance, silkworm silk is still not a patch on its counterpart, spider silk, in terms of tensile strength and toughness. Therefore, many researchers dedicate to the modification of silkworm silk in order to make it rival even exceed spider silk. Moreover, the limited anti-UV and anti-microbial properties of silkworm silk are not satisfactory and obstruct its further applications. Traditionally, silk is modified by using physical, chemical and blending methods, which are usually complex, costly and pollutional. Recently, a novel modification method to produce silk intrinsically through feeding silkworms with nanoparticles has been reported and proved workable.In this thesis, silkworms were fed by mulberry leaves which were coated with titanium dioxide(TiO2), graphene oxide(GO) and alumina(Al2O3) nanoparticles, to investigate the influence of the nanoparticles on silkworm silk. Results show that TiO2 and GO could improve the mechanical properties of silk. As the amount of nanoparticlas coated on limited mulberry leaves can not be controlled precisely, silkworms were further fed with artificial diet containing TiO2 and GO nanopariticals, respectively. The relationship between the additive amount of nanoparticles and the modification effect was investigated.This thesis demonstrates an in vivo uptake of 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 due to the interactions between TiO2 and silk fibroin molecules. Fourier Transform Infrared Spectroscopy(FTIR) and Raman spectra indicate that TiO2 nanoparticles confine the conformation transition of silk fibroin from random coil/α-helix to β-sheet. Results of synchrotron radiation wide-angle X-ray diffraction(WAXD) and small-angle X-ray scattering(SAXS) suggest that modified silks have lower crystallinity, higher mesophase content, and higher Herman’s orientation functions of 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 3h. However, when the additive amount of TiO2 exceeds 1%, the mechanical and ultraviolet resistant properties descend to some extent.Silkworms were then fed with GO to obtain intrinsically modified silk. Due to the outstanding mechanical properties of GO and the strong interaction between GO and silk fibroin, silk fibers were reinforced effectively. FTIR and Raman spectra indicate that TiO2 nanoparticles confine the conformation transition of silk fibroin from random coil/α-helix to β-sheet. Results of synchrotron radiation WAXD and SAXS suggest that modified silks have lower crystallinity, higher mesophase content, and lower Herman’s orientation of mesophase region than control group. The breaking strength of the GO modified silk was improved up to 508±23 MPa.Silks were greatly modi?ed by raising silkworms with a nanoparticles-containing diet. This simple feeding method is controllable and can maintain the natural merit of silk. Due to the low cost, green and sustainable process, the method has great potential of industrialization.