mori are predicted to produce heterogeneous structures, whereas the strictly modular repeats of the saturniid sequences are hypothesized to produce structures that respond in a concerted manner.Within saturniid fibroins, thermal stability was found to correlate with the abundance of poly-alanine residues, whereas differences in fibre extensibility can be related to varying ratios of GGX motifs versus bulky hydrophobic residues in the amorphous phase., and humans have utilized silk for millennia to produce textiles of great value and beauty.
Further investigations are clearly needed to resolve this issue.We used native silk fibres unravelled directly from the cocoons, rather than degummed fibres that have been subjected to harsh chemical treatments, to minimize changes in properties that result from such methods The morphological features of the silks investigated in this study are presented in Fig. Variations in cocoon appearance, fibre packing density, degree of bonding, and cross-sectional shape were observed. mori cocoons exhibited a high degree of porosity and relatively loose bonding with sericin gum, which correlates with the relative ease of unraveling the fibres from the cocoons. fugax, fibres were densely packed and almost uninterruptedly coated with sericin. jonasii featured a lattice-like morphology with large apertures ((a) First row, representative photographs of cocoons (not to scale); second row, representative photomicrographs showing cross-sections of silk fibres embedded in cyanoacrylate glue (scale bar = 20 μm); third row, representative SEM images of fibre surfaces (scale bar = 10 μm).Antheraea cocoons featured thicker fibres that were densely packed, whereas S. The phylogenetic assignment is based on Sima et al.. (c) Cross-sectional photomicrograph showing the common occurrence of silk fibres stuck together with gum material in S. (d) SEM image showing an example of abrupt changes in the morphology and fibre diameter in A. Light microscopy of cross-sections and SEM surface visualization showed details of the fibre dimensions and morphology (Fig. In all cases, the native fibres (baves) consisted of two filaments or brins surrounded by an outer layer of sericin. mori silk samples typically displayed triangular cross-sections, with considerable variations in surface areas. pryeri, with crystal dimensions of 0.5–2 μm on a side), corresponding to the secretion of calcium oxalate by the larvae during cocoon construction. aliena fibres showed the greatest structural heterogeneity, with frequent splitting and drastic changes in fibre diameter and morphology (Fig.Branch lengths are arbitrary, and the position of R. (b) SEM image showing the presence of calcium oxalate crystals on the surface of S. SEM images revealed a mostly intact sericin layer surrounding the fibres, occasionally with thin cracks or locally abraded regions (not shown). fugax, the silk fibres had flattened or wing-shaped cross-sections, although variations were also common (e.g., as shown for A. Under SEM, cubic crystals were frequently observed on the surface of the saturniid silks (shown in Fig. 1c), which may help account for their poor mechanical properties (see below). jonasii, the fibres were especially rounded and thick (typically 20 μm in diameter) and were typically encountered in bundles that were firmly bonded together (Fig. The results of tensile deformation tests, which measured the ultimate tensile strength, extensibility (elongation to break), Young’s modulus, and toughness (energy to break) of individual silk fibres are summarized in Table S1; representative stress-strain curves of each of the samples are shown in Fig. The overall results fall within the range of expected values, although with a large data spread and a generally low level of reproducibility even between fibres from the same cocoon, as previously noted. the higher initial elastic modulus observed for Indian B.mori silk (with a mean value of 8.6 GPa) compared to the other B. jonasii displayed less defined peaks compared to the other saturniid samples, possibly reflecting a reduction in concerted molecular motions during heating. jonasii, which produced weakly diffracting patterns. Bragg peaks corresponding to the (020), (210), (100), and (300)/(400) reflections were identified in most cases. 5, which shows average values for (020) and (210) of 2.6 nm and 4.5 nm, respectively, for the B.