Synergetic Enhancement of Mechanical Properties for Silk Fibers by a Green Feeding Approach with Nano-hydroxyapatite/collagen Composite Additive

In the current study, a novel intrinsic functionalization approach based on composite feeding additive for silkworms to produce silk fibers (SFs) with enhanced mechanical properties has been successfully developed. Effect of single feeding additive by either nano hydroxyapatite (Nano-HA) or collagen, and composite feeding by both additives on the silkworm larvae growth and cocooning, crystalline structure, molecular conformationas as well as mechanical properties of SFs have been systematically investigated. Experimental results demonstrated that feeding additive strategy could greatly facilitate the growth and cocooning of the silkworms. Surface and cross-section morphology observation suggested the additive has been absorbed into silkworm body and eventually embedded in SFs. Meanwhile, the basic structure of SFs still kept integrity after feeding additive from X-ray diffraction (XRD) analysis. Furthermore, fourier transform infrared (FTIR) spectrum demonstrated that random coil/α-helix and β-sheet content of SFs by feeding additive presented an increase and decrease change than natural SFs. More importantly, mechanical properties of SFs exhibited an obvious enhancement by composite additive than single additive feeding due to the nanoconfined crystallite toughening and polymer physical blending mechanism. Inspired by this approach, the composite additive feeding may open a novel and green strategy to fabricate SFs with enhanced mechanical properties.