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Spider Silk: A Thread So Fine
Spider silk can actually stop a train!

A group of physics students at United Kingdom's University of Leicester declare. According to their calculations, a single strand of silk from Darwin's bark spider (Caerostris darwini) proved to have the strength required to stop a moving train.

But that doesn’t surprise the scientist much. Assessed to be tougher than steel, even Kevlar (a synthetic material which is used to produce bullet proof vests), spider silk has long since attracted the attention of the scientists.

The combination of the unique strength, extensibility and tensile properties of spider silk makes it incomparable to any other substance, natural or man-made. Adding to those qualities, spider silk is naturally waterproof, biocompatible, and biodegradable. Most importantly, a recent study reported that bioengineered spider silks generate no toxicity or immunogenicity in humans, thus enabling it being used for biomedical applications.

Due to their exclusive properties, spider silk has received the attention of many industrialists. An amazing assortment of industrial products such as textiles, protective clothing, parachute cords, and airplane parts etc. can be produced with this material.
Spider silk also holds the promise for many biomedical applications including Band-Aids, wound sutures, drug carriers, artificial ligaments and tendons and organ implants. Another interesting use of spider silk will be in the cosmetic industry, enhancing the softness, toughness and brightness of products such as shampoo, soaps, nail varnish etc.

Can we harvest spider silk directly from spiders?

Unfortunately, we can’t. Since the spiders can’t be reared in farms due to their highly territorial and cannibalistic characteristics, researches are being conducted on transgenic production of spider silk. This involves genetically engineering other organisms to express the spider silk proteins, followed by the purification of the proteins and finally spinning those into silk strands.

But altering the genome of another organism to express the spider silk proteins is not as easy as it sounds, scientists declare. The complex nature of the genes encoding spider silk proteins poses the major obstruction in expressing natural-like transgenic spider silk in other organisms. Those genes contain large repetitive sequences with high GC contents making it hard to clone the respective genes using PCR.

Over the years, several efforts to produce recombinant spider silk proteins have been made with various hosts such as bacteria, yeast, mammalian cells, insects and transgenic plants. Each of these hosts expressed spider silk proteins but each endeavour presented their own complications.

Silk ‘Spinning’ Bacteria

The expression of the spider silk genes by bacterial hosts is not feasible due to the nature of these genes. It was found that bacteria, being prokaryotic, have difficulties decoding the gene codons of spiders. Furthermore, the gene expression in bacteria is size-limited. Therefore the bacteria, unable to express the lengthy repetitive gene sequences coding for the spider silk proteins, tend to remove those sequences by a mechanism of homologous recombination. This results in gene products with a lower molecular weight yielding silk fibres of inferior quality.

Since the codon usage of eukaryotic organisms is compatible with that of the spiders, and the gene expression in them is not size-limited, the scientists have made efforts using the eukaryotic cells as hosts in order to overcome this problem.

Silk ‘Milking’ Goats

One such experiment, carried out by the Nexia Biotechnologies, Canada, engineered the spider silk gene into the DNA of mammary epithelial cells of goats, thus producing transgenic goats that secreted the milk protein in their milk. This ‘milk silk’ was then purified and spun into and spun in to yarns of silk, dubbed ‘Biosteel’ by the company. However, these products did not adequately imitate the native spider silk fibres and the yields were not sufficient for industrial production.

Studies were also performed using other mammalian cells such as Baby Hamster Kidney cells, yeasts, plant cells and insect cells. Each of these effort yielded silk. But there were problems with the purification of the proteins and the yields were not sufficient for industrial applications. Furthermore, producing these organisms at large scale was difficult and uneconomical.

A Man Made Gene

A synthetic spider silk gene manufactured by the scientists has proved to overcome many of these hurdles. This artificial gene, having an adjusted codon usage can be used with any host including bacteria.

Bacteria Again

A study published in the journal Proceedings of the National Academy of Sciences in 2010 reports incorporation of the synthetic gene into E. coli which was then metabolically engineered by elevating its glycyl tRNA pools. This resulted in higher yields of recombinant silk protein with a molecular weight similar to that of authentic dragline silk protein of the spider Nephila clavipes. These proteins were then spun into silk fibres with mechanical properties comparable to those of the native silk.

Chimeric Silk Proteins

Another article published in the same journal in 2012 records the attempt to create transgenic silkworms using piggyBac vectors. These engineered silkworms could produce silk fibres composed of silk proteins containing both spider and silkworm characteristics. The article states that these fibres were tougher than the parental silkworm silk fibres and as tough as native dragline spider silk fibres. Since the silkworms were naturally capable of assembling the silk proteins into silk threads, this process has an added advantage.

However, a viable and economical technique of producing transgenic spider silk at industrial-scales is yet to be achieved.


1. Dams-Kozlowska, H., Majer, A., Tomasiewicz, P., Lozinska, J., Kaplan, D. L. and Mackiewicz, A. (2013), Purification and cytotoxicity of tag-free bioengineered spider silk proteins . J. Biomed. Mater. Res., 101A: 456–464. doi: 10.1002/jbm.a.34353

2. Teulé, F., Miao, Y. G., Sohn, B. H., Kim, Y. S., Hull, J. J., Fraser, M. J., ... & Jarvis, D. L. (2012). Silkworms transformed with chimeric silkworm/spider silk genes spin composite silk fibers with improved mechanical properties. Proceedings of the National Academy of Sciences, 109(3), 923-928.

3. Vendrely, C., & Scheibel, T. (2007). Biotechnological Production of Spider‐Silk Proteins Enables New Applications. Macromolecular bioscience, 7(4), 401-409.

4. Xia, X. X., Qian, Z. G., Ki, C. S., Park, Y. H., Kaplan, D. L., & Lee, S. Y. (2010). Native-sized recombinant spider silk protein produced in metabolically engineered Escherichia coli results in a strong fiber. Proceedings of the National Academy of Sciences, 107(32), 14059-14063.
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Obstacles and Limitations

Interesting topic! There are several more difficulties when it comes to the artificial development of spider silk. First, the spiders have seven glands that produce the components of this fascinating material, and different genes are expressed in the cells of different glands. It would be a problem to identify and transfer all the genes in another organism and make them functional, but once it is done, this material could really bring a revolution in many fields of industry.

The use of spider silk would be limited to some cases where strong and biodegradable material is needed, but not for long–term purposes. Namely, the dust and exposure to air, damage this material very quickly and it becomes fragile. Spider silk has about 50% protein content and it is insoluble in water. These properties are going to be the target of future studies in order to modify them and make this material more appropriate for wide use.

Light Conductivity

Microchips and sensors have already entered serious studies with the aim to be used to improve human vision, hearing, movement, and other functions, but now, we have the opportunity to use the product of a living creature to develop new microchips. An interesting property of spider silk to conduct light was recently discovered. Scientists believe that the implementation of this material into the microchip could bring great benefit as spider silk can not only conduct light, but also redirect and divert light to different parts of the chip. These chips would be less expensive than the standard chips with glass microfibers, and could be used for the detection of presence of some molecules in blood samples.

The Competitor

In the world of biomaterials, the greatest competitor of spider silk is Hagfish protein. Namely, Hagfish produce a protein which has similar mechanical characteristics as spider silk. Scientists at Shoals Marine Lab claim that this material has simpler chemical structure than spider silk, and that it could be less expensive for mass production.
Sasa Milosevic
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