Mechanical Properties Of Silk Fibers Research Articles

Modifying the Mechanical Properties of Silk Fiber by Genetically Disrupting the Ionic Environment for Silk Formation.

Silks are widely used biomaterials, but there are still weaknesses in their mechanical properties. Here we report a method for improving the silk fiber mechanical properties by genetic disruption of the ionic environment for silk fiber formation. An anterior silk gland (ASG) specific promoter was identified and used for overexpressing ion-transporting protein in the ASG of silkworm. After isolation of the transgenic silkworms, we found that the metal ion content, conformation and mechanical properties of transgenic silk fibers changed accordingly. Notably, overexpressing endoplasmic reticulum Ca2+-ATPase in ASG decreased the calcium content of silks. As a consequence, silk fibers had more α-helix and β-sheet conformations, and their tenacity and extension increased significantly. These findings represent the in vivo demonstration of a correlation between metal ion content in the spinning duct and the mechanical properties of silk fibers, thus providing a novel method for modifying silk fiber properties.

Ca2+ and endoplasmic reticulum Ca2+-ATPase regulate the formation of silk fibers with favorable mechanical properties

Calcium ions (Ca2+) are crucial for the conformational transition of silk fibroin in vitro, and silk fibroin conformations correlate with the mechanical properties of silk fibers. To investigate the relationship between Ca2+ and mechanical properties of silk fibers, CaCl2 was injected into silkworms (Bombyx mori). Fourier-transform infrared spectroscopy (FTIR) analysis and mechanical testing revealed that injection of CaCl2 solution (7.5mg/g body weight) significantly increased the levels of α-helix and random coil structures of silk proteins. In addition, extension of silk fibers increased after CaCl2 injection. In mammals, sarcoplasmic reticulum Ca2+-ATPase in muscle and endoplasmic reticulum Ca2+-ATPase in other tissues (together denoted by SERCA) are responsible for calcium balance. Therefore, we analyzed the expression pattern of silkworm SERCA (BmSERCA) in silk glands and found that BmSERCA was abundant in the anterior silk gland (ASG). After injection of thapsigargin (TG) to block SERCA activity, silkworms showed a silk-spinning deficiency and their cocoons had higher calcium content compared to that of controls. Moreover, FTIR analysis revealed that the levels of α-helix and β-sheet structures increased in silk fibers from TG-injected silkworms compared to controls. The results provide evidence that BmSERCA has a key function in calcium transportation in ASG that is related to maintaining a suitable ionic environment. This ionic environment with a proper Ca2+ concentration is crucial for the formation of silk fibers with favorable mechanical performances.

Origin of the variability of the mechanical properties of silk fibers: 4. Order/crystallinity along silkworm and spider fibers

The poor crystallinity of proteic fibers has fuelled an ongoing debate over their exact organization. We present a full‐range Raman comparison of Nephila madagascariensis spider and Bombyx mori silkworm silks that sheds some new light on that matter. On the one hand, a large variability is observed along the fibers in the −200 to 200 cm−1 spectral window, which is sensitive to the long‐range order signature of polyamide chains. This questions the validity of previous literature data considering silk fiber as a homogeneous material. On the other hand, the ‘amide I’ band is almost independent of the targeted point, which sets a limit to this widely used structure probe. In‐line mapping of the fibers showed that the extension of the ordered zones ranges between 1 and 3 µm. The correlation between the macromechanical behavior (the stress–strain curves) and the nanomechanics (Raman low wavenumber signatures) under controlled tensile strain demonstrates a Prevorsek's type microstructure: the macromolecular chains belong to both ordered and amorphous ‘regions’. Copyright © 2014 John Wiley & Sons, Ltd.

Evaluation of Mechanical Properties of Silk Fiber Reinforced Biodegradable Plastic Composites (Part 2, Analytical Prediction for Stress-Strain Relationships of Silk/PBS Laminates)

In the recent years, natural fiber reinforced composites are expected as alternative materials for traditional fiber reinforced composites. Though many experimental studies on mechanical properties of biodegradable composites have been presented in literature, analytical investigations are rarely reported. In this regard, mechanical properties of silk fiber reinforced poly(butylene succinate) (PBS) biodegradable composite (SF/PBS) laminates are investigated in the present study. In order to investigate the effects of surface treatment of the silk fiber on the mechanical properties of the SF/PBS laminates, four types of surface treatment has been applied to the silk fiber. Tensile tests are conducted on cross-ply laminates and angle-ply laminates. When the silk fibers without sericin are used, tensile strengths and Young's modulus are the highest in all laminate configurations. Stress-strain relations of both cross-ply and angle-ply laminates are predicted by combining the three-parameter plasticity model and the classical laminated plate theory. In the analysis, the properties in unidirectional composite from the generalized method of cells (GMC) micromechanics or experimental results are used. It has been found that it is possible to predict the stress-strain relations for both laminates when the experimentally-obtained properties of unidirectional laminates are used. This implies that nonlinearity caused by damages such as debondings in the unidirectional laminates under off-axis loading should be incorporated in the analysis. It has been also found that it is necessary to consider changes in fiber orientation angle due to deformation of the plates in predicting the stress-strain relation for the angle-ply laminates.

Evaluation of Mechanical Properties of Silk Fiber Reinforced Biodegradable Plastic Composites (Part 1, Effect of Fiber Surface Treatment on Mechanical Properties of Unidirectional Composites)

Researches on the natural fiber reinforced “green” composites have been increasing in recent years due to concern over exhaustible petroleum resources and environmental destruction, and demands for energy saving and carbon dioxide reduction. Green composites are also expected as alternative materials for traditional fiber reinforced composites. Although green composites comprised of plant-derived natural fibers have been investigated by many researchers, use of animal-based natural fibers such as silk fiber (SF) in green composites has been rarely reported. In this regard, the mechanical properties and stress-strain relationships of silk fiber reinforced poly(butylene succinate) (PBS) biodegradable composites (SF/PBS) are evaluated in the present study. In order to investigate the effects of surface treatment of the silk fiber on the mechanical properties of SF/PBS, four types of surface treatment has been applied to the silk fiber. Tensile tests are conducted on the single silk fiber and unidirectional SF/PBS laminates. From the experimental results it has been found that removal of sericin in the silk fiber by the surface treatment improves Young's modulus but decreases fracture strain of the silk fiber. Predictions by generalized method of cells (GMC) micromechanics have shown good agreement with experimental results of the stress-strain relationship of 0° unidirectional laminates. However, nonlinear behavior in high stress region of 45° and 90° unidirectional laminates have not been predicted precisely due to internal damages such as interfacial debonding in the plates.

Mechanical properties of silk fibers in a wet state obtained by preirradiation grafting of Methacryl amide

Mechanical properties of silk fibers in a wet state obtained by preirradiation grafting of Methacryl amide

Effect of temperature on the mechanical properties of silk fiber in water

Effect of temperature on the mechanical properties of silk fiber in water

Effects of Fiber Surface Treatment on Mechanical Properties of Silk Fiber Reinforced Polybutylenesuccinate(PBS)Composites

Effects of Fiber Surface Treatment on Mechanical Properties of Silk Fiber Reinforced Polybutylenesuccinate(PBS)Composites

Properties and performance of polypyrrole (PPy)-coated silk fibers

Different silk substrates in form of spun silk tops, nonwoven web, yarn, and fabric were coated with electrically conducting doped polypyrrole (PPy) by in situ oxidative polymerization from an aqueous solution of pyrrole (Py) at room temperature using FeCl3 as catalyst. PPy-coated silk materials were characterized by optical (OM) and scanning electron (SEM) microscopy, FT-IR spectroscopy, and thermal analysis (DSC, TG). OM and SEM showed that PPy completely coated the surface of individual silk fibers and that the polymerization process occurred only at the fiber surface and not in the bulk. Dendrite-like aggregates of PPy adhered to the fiber surface, with the exception of the sample first polymerized in the form of tops and then spun into yarn using conventional industrial machines. FT-IR (ATR mode) showed a mixed spectral pattern with bands typical of silk and PPy overlapping over the entire wavenumbers range. DSC and TG showed that PPy-coated silk fibers attained a significantly higher thermal stability owing to the protective effect of the PPy layer against thermal degradation. The mechanical properties of silk fibers remained unchanged upon polymerization of Py. The different PPy-coated silk materials displayed excellent electrical properties. After exposition to atmospheric oxygen for two years a residual conductivity of 10–20 % was recorded. The conductivity decreased sharply under the conditions of domestic washing with water, while it remained essentially unchanged upon dry cleaning. Abrasion tests caused a limited increase of resistance. PPy-coated silk tops were successfully spun into yarn either pure or in blend with untreated silk fibers. The resulting yarns maintained good electrical properties.

Mechanical Properties of Silk Fiber Reinforced Polymer Composites with Carbon Nanotubes

Biodegradable composites consisting of poly(butylene succinate) (PBS) and carbon nanotube (CNT)-coated silk (Bombxy mori) fibers were prepared by melt compression molding. The results show that even with addition of a small amount of reinforcements (about 3 wt%), the tensile strength and modulus of the composites improved dramatically by about 195% and 121%, respectively, compared with PBS. The improvement is attributed to stronger interfacial shear strength between the PBS matrix and the CNT-coated surface of silk fiber, which was obtained by the microbond droplet test between PBS matrix and fibers. Furthermore, scanning electron microscopy images indicated that the interfacial adhesion between PBS matrix and CNT-coated fiber improved in the composites.

Spider Silk Proteins – Mechanical Property and Gene Sequence

Spiders spin up to seven different types of silk and each type possesses different mechanical properties. The reports on base sequences of spider silk protein genes have gained importance as the mechanical properties of silk fibers have been revealed. This review aims to link recent molecular data, often translated into amino acid sequences and predicted three dimensional structural motifs, to known mechanical properties.

Finding inspiration in argiope trifasciata spider silk fibers

The outstanding mechanical properties of silk fibers from the spider Argiope trifasciata are reviewed in this article, particularly the tensile behavior under controlled humidity and temperature. Samples obtained by forced silking showed a remarkable reproducibility. A novel procedure, wet stretching, developed by the authors, promises to shed light on the spinning of artificial silk fibers.

Mechanical properties of silk fibers treated with methacrylamide

Tussah silk fibers were treated with methacrylamide (MAA). The polymerization of MAA onto tussah silk fibers and the mechanical properties of the MAA-treated tussah silk fibers were investigated. The tanning agent contained in tussah silk fibers acted as an inhibitor to the radical polymerization of MAA. The alkali treatment enhanced the swelling of noncrystalline regions of the tussah silk fibers and promoted the polymerization of MAA onto the tussah silk fibers. The cross-sectional area of the MAA-treated tussah silk fiber was given by the sum of the cross-sectional area of the original silk fiber and that of the MAA polymer. Breaking load of the fibers was almost unchanged by the MAA treatment, while rigidity was markedly increased. Young's modulus of the MAA-treated tussah silk fibers decreased with decreasing volume fractions of the fiber in the MAA-treated tussah silk fibers. Young's modulus of the MAA polymer in the MAA-treated tussah silk fibers was estimated by extrapolating the relation between Young's moduli and the volume fractions of the fiber to zero volume fraction. Young's modulus of the MAA polymer in the MAA-treated tussah silk fibers was significantly larger than the modulus of a MAA polymer plate.

Mechanical properties of silk fibers treated with methacrylamide

Mechanical properties of silk fibers treated with methacrylamide

Modification of silk fiber by freeze drying.

The modification of silk fiber by freezing-drying after immersion of silk fiber in water is a process of bulkiness modification, in which the volume expansion of water due to freezing was utilized.In this paper we intended to elucidate the conditions for swelling and freeze-drying and to clarify the relation between the structure and the mechanical properties of silk fiber. The rapid freezing of silk fiber was required for the prevention of fiber degradation. From the morphological observation, silk fibers were expanded by freezing of water in the viods and crackes. Therefore, the bulkiness, softness and hygroscopic property of silk fiber were improved by the freeze-drying. The crystallinity was unchanged by the freeze-drying, however, the changes of microstructure related to the mechanical properties of silk fiber.