Supercritical Carbon Dioxide Impregnation of Gold Nanoparticles Demonstrates a New Route for the Fabrication of Hybrid Silk Materials

How many nanoparticles can we load in a fiber? How much will leak? Underlying is the relatively new question of the “space available” in fibers for nanoparticle loading. Here, using supercritical carbon dioxide (scCO2) as a carrier fluid, we explored the impregnation in four Indian silks (Mulberry, Eri, Muga, and Tasar) with five standard sizes of gold nanoparticles (5, 20, 50, 100 and 150 nm in diameter). All silks could be permanently impregnated with nanoparticles up to 150 nm in size under scCO2 impregnation. Accompanying structural changes indicated that the amorphous silk domains reorganized to accommodate the gold NPs. The mechanism was studied in detail in degummed Mulberry silk fibers (i.e., without the sericin coating) with the 5 nm nanoparticle. The combined effects of concentration, time of impregnation, scCO2 pressure, and temperature showed that only a narrow set of conditions allowed for permanent impregnation without deterioration of the properties of the silk fibers.

Spinning conditions affect structure and properties of Nephila spider silk

Raman spectroscopy is used to elucidate the effect of spinning conditions upon the structure and mechanical properties of silk spun by Nephila spiders from the major ampullate gland. Silk fibers produced under natural spinning conditions with spinning rates between 2 and 20 mm s−1 differed in microstructure and mechanical properties from fibers produced either more slowly or more rapidly. The data support the “uniform strain” hypothesis that the reinforcing units in spider silk fibers are subjected to the same strain as the fiber, to optimize the toughness. In contrast, in the case of synthetic high-performance polymer fibers, the both units and the fiber experience uniform stress, which maximizes stiffness. The comparison of Nephila major and minor ampullate silks opens an intriguing window into dragline silk evolution and the first evidence of significant differences between the two silks providing possibilities for further testing of hypotheses concerning the uniform strain versus uniform stress models. Impact statement It is well established that the microstructure and mechanical properties of engineering materials are controlled by the conditions employed to both synthesize and process them. Herein, we demonstrate that the situation is similar for a natural material, namely spider silk. We show that for a spider that normally produces silk at a reeling speed of between 2 and 20 mm s−1, silk produced at speeds outside this natural processing window has a different microstructure that leads to inferior tensile properties. Moreover, we also show that the silk has a generic microstructure that is optimized to respond mechanically to deformation such that the crystals in the fibers are deformed under conditions of uniform strain. This is different from high-performance synthetic polymer fibers where the microstructure is optimized such that crystals within the fibers are subjected to uniform stress. Graphic abstract

Vibrational Study on Structure and Bioactivity of Protein Fibers Grafted with Phosphorylated Methacrylates

In the last decades, silk fibroin and wool keratin have been considered functional materials for biomedical applications. In this study, fabrics containing silk fibers from Bombyx mori and Tussah silk fibers from Antheraea pernyi, as well as wool keratin fabrics, were grafted with phosmer CL and phosmer M (commercial names, i.e., methacrylate monomers containing phosphate groups in the molecular side chain) with different weight gains. Both phosmers were recently proposed as flame retarding agents, and their chemical composition suggested a possible application in bone tissue engineering. IR and Raman spectroscopy were used to disclose the possible structural changes induced by grafting and identify the most reactive amino acids towards the phosmers. The same techniques were used to investigate the nucleation of a calcium phosphate phase on the surface of the samples (i.e., bioactivity) after ageing in simulated body fluid (SBF). The phosmers were found to polymerize onto the biopolymers efficiently, and tyrosine and serine underwent phosphorylation (monitored through the strengthening of the Raman band at 1600 cm−1 and the weakening of the Raman band at 1400 cm−1, respectively). In grafted wool keratin, cysteic acid and other oxidation products of disulphide bridges were detected together with sulphated residues. Only slight conformational changes were observed upon grafting, generally towards an enrichment in ordered domains, suggesting that the amorphous regions were more prone to react (and, sometimes, degrade). All samples were shown to be bioactive, with a weight gain of up to 8%. The most bioactive samples contained the highest phosmers amounts, i.e., the highest amounts of phosphate nucleating sites. The sulphate/sulphonate groups present in grafted wool samples appeared to increase bioactivity, as shown by the five-fold increase of the IR phosphate band at 1040 cm−1.

The image of the modern teacher and its place in the culture of speech

There are aspects of dress that are related to a person's psyche, character, mood, upbringing, and taste. It is important to note that dress and customs did not arise spontaneously. There is no definitive conclusion as to when clothing appeared in human society. Man, who first learned to weave and sew fabrics from leather and wool, later gave comfort and beauty to clothes with the advent of cotton and silk fibers. Hence, the development of human thinking brought civilization to his dress as well .

Insights into detailed hierarchical puncture-resistance for Bombyx mori silkworm cocoons

Silkworm cocoons illustrate excellent puncture-resistance performance after an insight into their layers while a clear understanding of the correlation between the excellent puncture property and the silk secondary structure is still lacking. Herein, we peeled silkworm cocoon into eight layers, and a combination of examination techniques including scanning electron microscopy, tensile mechanical test, Fourier transform infrared spectroscopy, Raman spectroscopy, and X-ray diffraction were applied to figure out the morphologies (surface and cross-section view), mechanical properties, secondary structure, the content of β-sheet, and crystallinity of each layer's fibroin after degumming. The results indicated that the fifth layer offers a higher level of puncture-resistance than the other layers except for the eighth layer. Additionally, a high content level of β-sheet structure and high crystallinity gives rise to the high puncture strength as for hierarchical silk fibers. In general, the new finding holds great potential inspiration for the design of puncture-resistant composites.