Silk is made from the strands of a protein called fibroin which are then wound to make a strong, flexible fibre unlike any material humans have been able to produce.
While it is produced by a range of invertebrate animals, the most commonly known producers are moth caterpillars and spiders, those being the producers of commercial silk and the strongest silk, respectively.
Silkworms are the larva, or caterpillar, of the Bombyx silkmoth and are utilised for silk textile production as they are easily farmed in great numbers.
The silkworm pupates in a protective cocoon which it spins from silk secreted from its salivary glands. The cocoon's silk is colourless and it is easily cleared of minerals, making them an ideal material for winding into a thread.
Although silkworm silk has been historically the most useful, spider silk may be the material of the future! At up to five times as strong as the equivalent steel thread and almost three times stronger than Kevlar, spider silk's strength is unrivalled in nature.
Spiders secrete liquid silk proteins out of structures called spigots located on the spinnerets at the rear of the abdomen. On touching the air the liquid proteins solidify into long strands which are partly coiled, giving its elasticity. The spinnerets then wind these strands around each other, like threads in a cord, to create a strong silk fibre.
Spiders use this super silk in a variety of ways, such as in webs, as a net or lasso, and as a safety line. Tarantulas are even able to secrete silk from their feet, walking like spiderman up smooth surfaces.
As an incredibly strong, elastic material, spider silk has the potential for a variety of applications, such as a biodegradable replacement for plastics or even rip-resistant paper. Spider silk could be utilised by the military to create body armour that replaces Kevlar, or for medical use as the scaffolding for artificial skin or sutures for wounds. Its potential antimicrobial properties may even help to prevent infection!
However, spider silk has proved hard to mass produce.
Spiders only contain a small amount of silk and as predators they will often cannibalise other spiders making farming in great numbers problematic, while harvesting from individual spiders is too labour intensive.
Genetics To The Rescue!
The limitations on spider farming hasn't dissuaded some researchers who have found several methods of spider silk replication through genetic modification.
Other research has shown that silkworms given spider silk genes will excrete tougher and more flexible silk which is both twice as strong and elastic as standard silkworm silk. Meanwhile a group of Korean researchers have produced silk from genetically modified E. coli bacteria.
However, replicating spider spinnerets in winding silk proteins into an equivalently strong thread is one hurdle we are yet to overcome before products made of spider's super silk become commonplace.