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Abstract: Silkworms have been developed over thousands years to optimize folding and crystallization of fibroin under highly controlled conditions which have resulted in their efficient fiber formation. In this paper, we reconstructed the three-dimensional architecture of the spinneret of a wild silkworm Samia cynthia ricini from approximately 1000 optical micrographs of the semi-thin cross sections. The chitin plates and muscles were observed in the silk press part together with large change in the diameter of the spinneret lumen at the press part by large shear stress. This is similar to the case of the spinneret of Bombyx mori silkworm, indicating that the structural change in the silk fibroin of S.c. ricini silkworm occurs exclusively at the silk press part due to large shear stresses. Molecular dynamics (MD) calculations were then performed to study the structural change that occurs in the crystalline region of S.c. ricini silk fibroin under shear stress. Namely, using the peptide AGGAGG(A)12GGAGAG as a model of the crystalline part of the silk fibroin under different shear stresses in the presence of water molecules and followed by molecular mechanics (MM) calculation after removal of water molecules. The simulation indicates that the Ala residues in the model peptides adopt a predominantly β-sheet structure under shear stresses of above 1.0GPa. [Copyright &y& Elsevier]

The properties of polyglycolide (PGA) fibers used as surgical sutures depend on their aggregated state structure. The study investigated the relationship between the structural evolution and macroscopic properties of PGA fibers with low-crystallinity under coupled stress-temperature fields by conducting in-situ WAXD/SAXS, DSC and SEM measurements. The WAXD and SAXS results indicated that the structural evolution during the low-temperature stretching stage primarily relied on stress-induced amorphous molecular chain orientation and the formation of small crystals. The DSC results confirmed that uniaxial stretching enhanced the orientation of amorphous molecular chains, leading to cold crystallization of PGA fibers at lower temperatures. During the heating stretching stage at temperatures of 60–90 °C, numerous crystals were generated through a lamellar insertion mechanism and underwent lateral growth. This is reflected by the crystallinity, crystal orientation, and crystallite sizes increased significantly, while the long period decreased rapidly. The high-temperature stretching stage resulted in fragmentation and recrystallization of lamellar crystals, forming fibrous crystals. Stretching at 110 °C exhibited higher Iq 2 /Iq 1 values than other temperatures, which means that 110 °C is more favorable for the formation of fibrous crystals. Additionally, PGA fibers stretched at 150 °C exhibited the highest crystallinity and crystal orientation, which led to a 440 % increase in tensile strength. Its resistance to degradation has also been significantly improved compared to the original fibers. [Display omitted] • Low-crystallinity PGA fibers were stretched during variable temperature. • The stress and temperature fields dominated the structural evolution in different stretching stages. • Hot stretching improved the mechanical properties and resistance to degradation of PGA fibers. [ABSTRACT FROM AUTHOR]