Spider silk, despite all its virtues is commercially futile. Can the transgenic silk worms fill the space?

In the movies one might have seen its casts tearing trough cobwebs, and doing adventurous tasks. But, the reality is quite contradictory. Spider silk, also known as Gossamer, has exceptional strength, abrasion resistance and elasticity.

In the world of natural fibres, spider silk has the reputation of being a wonder fibre. For many years spider silk had been the focus of research and development due to its incredible virtues, and potential applications in the textile segment. Spider silk has good tensile strength similar to high- grade steel, while its dense is only one fifth of the latter. It can stretch up to1.4 times than its relaxed length without breaking. It can also maintain temperature to a level of -40�C. It is three times tougher than aramid and other industrial fibres. The fineness of spider silk is around 4�m, limiting its mechanical properties into tensile mode.

Diameter of SpiderSilk and Other Reference Fibers

* In the case of B.mori silk, diameter shows means of bottom and height on the triangle shape.

Comparison with other fibres for balance of strength and toughness

The only constraint for the advancement of producing this fibre on a large scale is its lack of commercial viability. Spiders are not social, and are cannibalistic in nature making its cultivation impossible as is done with silkworms. Spider silk is superior to silkworm fibres. But cultivation of spider silk had been long given up. The drawback of spiders is that they are not capable to spin long fibres. Their capacity lies in making fibres up to a length of 130 meters from their silk glands, and 12 meters from their webs, whereas silk worms can produce longer fibres up to a length of 600 to 1200 meters long. Silk worms can be cultivated in a successful way, while spiders are territorial, and eat each other making its farming difficult. Attempts were earlier made to make spider silk through bacteria, yeast and insect cells, but were later given up being to be very expensive.

Monster silk an alternative to spider silk?

Scientists have combined spider silk proteins with silk worm proteins to make a new silk. The hybrid silk produced by transgenic silkworms, is on its way to commercialization. Certain spider silk proteins are combined with silkworm proteins to make a transgenic silkworm that produces a composite silk. Silkworms are injected with gene sequences for elasticity, and tensile strength of spider silk. Resultantly silkworms spin hybrid fibres containing 95% of silkworm, and 5% of spider proteins. Genetically engineered silk worms are used for creating hybrid silk, partly of the silk worm fibre, and partly of spider silk which is tougher than the natural fibre available from silkworms. Spider silk proteins are integrated into composite fibres with the beneficial impact on the mechanical properties of the fibres.

This comprises only 5% of spider silk protein, but exhibits much strength and elasticity comparatively over conventional silk. The presence of spider silk in the fibre acts like a rebar in a concrete and makes a reinforced fibre. This is named as Monster silk, and is affirmed, can be produced in commercially viable volumes. It foresees potential applications in apparel, and in medical field for making sutures, and artificial limbs.

Spider goats - an additional option:

Synthetic biology is in the evolution stage in its purest form, and in pursuit of applying engineering principles to life science. A fibre extracted from the milk of transgenic goats is used for making high strength fibres. Genes of the dragline silk spiders are put into goats and they make protein in their milk. These goats with the transplanted gene produce milk with special proteins which are extracted and spun into spider silk fibres.

Strength and toughness are the essential requirements of all textile fibres. Spider silk has immense textile applications. The customizable fibres obtained from transgenic silk worms include various mechanical and chemical properties, and is also expected to be commercially successful.

References:

1. Telegraphindia.com
2. Engineering properties of spider silk Frank K. Ko, Sueo Kawabata, Mari Inoue, Masako Niwa, Stephen Fossey and John W. Song, Web.mit.edu