As kids, we would have watched the amazing comic hero Spiderman hanging upside down, swinging and shooting his spider silk all across the city. Little would have we thought, if such fragile looking fibres would be able to pull or handle such heavy weight. The flabbergasting fact behind these fibres is that its elasticity enables the fibre to be stretched from five to twenty times of its normal length, and has the resistance of steel that it can also be used as a rip proof fabric.
'Spider silk' is one of the most sought after biomaterial. Also known as 'gossamer', this is a protein fiber spun by spiders. Due to its demand, and unavailability, it has even acquired the nickname, 'Holy Grail". This silk comes from the glands of the spider and is both flexible and lightweight. For a spider, this fibre is used for catching its prey, serves as a life line while jumping, and a place to nest its egg. As far as the human side is concerned, the silk is used in making bullet proof clothing, rust-free panels on motor vehicles, surgical thread etc.
These fibres are flexible, waterproof, and one of the toughest materials in the world. They are extremely weightless that a fibre long enough to cover the world would only weigh less than 170 grams. The fibres are flexible enough to be stretched upto 40% of its original length, without any breakage problems, which give high ductility to the strands. Despite the fact that they are identical to that of the silkworm, spider silk lacks commercial value. Fabrics from spider silk lacks luster. Due to the difficulty in encoding the silk protein, it is a tedious task to identify the sequence, and till today, only 14 species of silk producing spiders are decoded.
Types of Spider Silk:
Different spiders have different glands for producing different kinds of silk, and for different reasons, like web construction, capturing prey, defense, or mobility. Each fibre gives a different kind of silk.
Tubiliform silk: This fibre is used for protecting egg sacs. Its nature is very stiff.
Capture-spiral silk: This fibre is extremely sticky, and stretchy by nature, and is used for the capturing lines of the web.
Minor-Ampullate silk: This fibre is used for web construction purposes.
Aciniform silk: This fibre is used to wrap the captured prey. This is three times tougher than the dragline silk.
Possible Applications of Spider Silk:
Spider silk applications have been in vogue for more than thousands of years. The Greeks used them to stop bleeding from wounds. On devices such as telescopes, and guns, it is used as crosshairs. Some people use it as fishing nets. In the present day, this fibre has the following potential applications.
Used for making artificial tendons and ligaments for supporting weak blood vessels.
For making rust-free panels on motor vehicles or boats.
Making bandages and surgical threads.
Manufacturing rip-proof, and light weight clothing.
Making biodegradable bottles.
Can be used in ropes, seat belts, and parachutes due to its tensile strength.
Artificial Spider Silk:
It is a tedious process to manufacture large quantity of spider silk from spiders. Though high in demand, mass production of spider silk is impossible as it is difficult to maintain spiders. Extraction of silk from spider webs is not a cost-effective process. Hence, attempts were made to manufacture spider silk in an artificial way. A Canadian company undertook researches to produce spider silk from goats. Goats have spider silk protein gene, and their milk also contained a sizable amount of protein. But, efforts undertaken to spin the protein into a fibre equivalent to the natural spider silk proved futile. This silk is composed of complex protein molecules. Combined with the isolation stemming from the predatory nature of the spider, manufacturing the same; artificially, becomes difficult.
Spider silk is a material that has held human fascination for many years. Main interest is due to the presence of mechanical properties, and non-polluting nature of the fibre. Its production is environmentally friendly, and is biodegradable. It posses many desirable properties, and can be used in a wide variety of fields including medical, military and other industries. Due to its complex nature, mass production of this fibre is not possible, and this remains a challenge to scientists and researchers all across the globe to understand the spiders' inherent skills, and manufacture the silk thread.