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Silk products are often sought after by consumers, however; do many of us know the process or source by which this silk is obtained?
Additionally, if there was a way that manufacturers could improve the strength of silk for expanding its applications, what would that entail? A recent group of Researchers supported by the European Union Graphene Flagship have looked at combining the remarkable graphene material and spiders to do just this.
One of the earliest attempts to obtain spider silk is cited in 1709, when French Naturalist René-Antoine Ferchault de Réaumur collected numerous spider egg sacs to make clothing material such as stockings and gloves.
While raising silkworms, which are the primary source of commercial silks, is not a difficult task. Ferchault de Réaumur was the first of many to discover the difficulties in raising spiders in a group setting for such production purposes1.
Spider silk is used in nature for a variety of purposes including as a trap for their prey that is created by their elaborate webs, a method of return transportation back to their nest and a protection shield for their eggs.
Over the last several years, Researchers have spent a considerable amount of time and resources to fully investigate the extraordinary strength of spider silk. As a structure that consists primarily of proteins, spider silk is a semi-crystalline, biocompatible material that exhibits an impressive tensile strength measuring to approximately 1.5 GPa and a toughness of 150 Jg-1.
The biopolymer applications of spider silk have looked to potential applications of this material as a linear thread, creating a variety of useful products including wear-resistant lightweight clothing, bullet-proof clothing, ropes, nets, seat belts, bandages, surgical thread, artificial ligaments or tendons, biodegradable bottles and food wraps, and much more.
Despite its potential, the challenges associated with raising spiders, as well as developing an adequate way to spin the fibers limit this material for mass production of such commercial items.
The Graphene Flagship research endeavor involved exposing three different species of spiders to aqueous dispersions containing either CoMoCAT single-wall nanotubes or graphite flakes.
Dragline silk was then collected 2-12 days following the treatment. However, during this time 29% of the spiders died before the first silk collection as a result of starvation during this treatment process, and a further 24% died after 12 days for the same reason.
To obtain silk samples from the treated spiders, a ‘C’ shaped cardboard was placed within the cage, which allowed the spiders to wrap their silk around this structure for collection purposes. Analysis of the silk fibers involved diameter measurements through field emission scanning electron microscopy. Mechanical properties, such as tensile strength and toughness, were determined by Raman spectroscopy.
The spider silk obtained from the treated spiders in this study exhibited a strength of 5.4 GPa, which is almost a 4-fold increase as compared to natural silk obtained from spiders, and a toughness modulus of approximately 1567 Jg-1, which is almost a 10-fold increase as compared to natural spider silk2.
Despite the spider deaths that occurred due to the purely graphite and carbon nanotube diet, the results of this study are promising for future manufacturing of spider silk products. Future studies investigating the properties of spider silk, especially those that involve graphite or other treatments for the potential property enhancement of this material, must consider all challenges that Researchers have faced in the past in order to ensure that their final product is adequate for their specific production needs.
These challenges include limiting the amount of spiders kept in close quarters to smaller numbers so as to limit the amount of interaction and subsequent killing between spiders, as well as maintaining their natural diets so as to avoid death by starvation.
Sources and Further Reading
- “Spider silk reinforced by graphene or carbon nanotubes” E. Lepore, F. Bosia, et al.
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