Artificial silk can't compete with the real thing

Challenge: a strong, multi-purpose, environmentally-friendly material

Natural solution: silkWomen wearing kimonos © Wdeon/ Dreamstime

 

 

 

Silk has been used by humans throughout history. The silkworm Bombyx mori has been farmed for 5000 years and is now completely domesticated. 1 Silkworm silk is used for a variety of purposes, from surgical sutures to clothing. 2  Globally, silk is a major industry: the total export value of silk across the world was 3.5 billion US dollars in 2008, with woven silk fabrics making up the majority of the trade (2.6 billion US dollars). 3 Silk is associated with traditional clothing in many parts of the world: kimonos in Japan, saris in India – but is also a modern fashion item: think Italian shirts or luxury interior furnishings. 4Dew on spider web © Constantin Giuhat, www.sxc.hu

 

 

 

 

 

 

 

 

Silkworms are not the only organisms that produce silk.  Spider webs have evolved over 400 million years to trap insects.  Spider silk must be strong enough that a large insect cannot break free, fine enough to be nearly invisible, and flexible enough to dissipate energy so that an insect flying into the web is not flung out by elastic recoil.  Many spiders, such as the garden spider Araneus diadematus, can produce different types of silk for different uses.  6  Their strongest silk has a higher tensile strength per unit weight than steel.  2 Other properties of spider silk continue to be discovered: for example its structure at a microscopic level enables it to collect water from the air. 5Spider cocooning insect © kevinp01, www.sxc.hu

 

 

 

 

 

The properties of spider silk would make it fantastically useful for humans, if it could be manufactured in sufficient quantities.  However, unlike silkworms, spiders cannot be farmed: they are highly territorial and can be cannibalistic. 2  Extensive research effort has therefore been directed at synthesising spider silk.  Silk offers  several distinct advantages over petroleum-based products: renewability, sustainability and biodegradability. 8  Spiders produce their silk at room temperature and pressure in a watery solution: an extremely energy-efficient and non-toxic process. 2  If humans could master synthesising artificial silk, different types of silk could be manufactured to meet specific needs. 6Surgeons operating © sean/ Dreamstime

 

 

 

 

Research has focused both on the silk itself and the spinning mechanism by which spiders produce it. 2  Silk is a highly organised structure of special proteins. 6  Scientists have successfully created films, fibres, sponges and non-woven mats from artificial silk proteins, 2 with numerous medical applications. 9 Genetic engineering has been used to produce silk from plants, 8 animal cells, 10 bacteria and even goats’ milk.  6  However, so far the methods tried have been low yield and high cost. 6  The mechanical properties of the man-made silk are inferior to spider silk because it is not yet possible to replicate the complex structure of natural silk. 2  The spider genes coding for silk are not well expressed in other organisms, meaning that only short lengths of silk are produced. 6 Research continues, and recently one team has managed to create threads of honeybee silk from genetically modified proteins. 11 However, so far human technology cannot match the techniques biodiversity has developed.

 

spider in web © Ellie Crane

 

There are approximately 50,000 known spider species in the world, and probably many yet to be discovered12  Different  species are found all across the world, each adapted to the particular environment in which they live. 13  Although spiders as a group are abundant, individual species with specialist habitat requirements, such as the UK’s fen raft spider, are now at risk of extinction from human activities. 14  Each spider species makes a different kind of silk, varying in elasticity, strength and stickiness.  Other creatures, including butterflies, pseudoscorpions, mayflies, lacewings, ants and beetles, make their own kinds of silk. 15  Biodiversity offers a huge and mostly untapped resource for the textiles industries of the future.

 

 

 

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References

  1. Kluge, J.A. et al (2008) Spider silks and their applications.  Trends in Biotechnology 26: 244-251
  2. Leng, B. et al (2009)   Inspiration from natural silks and their proteins.   In Advances in chemical engineering, volume 35, pp 119 - 148. Rudy Coopments (ed).  Academic Press, Amsterdam.
  3. International Trade Centre: trade map.  Accessed March 2010.
  4. International Trade Forum (1999)  Silk in world markets. Accessed March 2010.
  5. 5. Zheng, Y. et al (2010) Directional water collection on wetted spider silk. Nature 463:640-3
  6. Turner, J. et al (2003)  Advanced spider silk fibers by biomimicry.  In Natural fibers, plastics and composites, pp 11 - 26.  Frederick T. Wallenberger and Norman Weston (eds.).  Kluwer Academic Publishers, Massachusetts, USA.
  7. Hinman, M.B. et al (2000) Synthetic spider silk: a modular fibre.  Trends in Biotechnology 18: 374-379
  8. Moire, L. et al (2003) Synthesis of novel biomaterials in plants.  Journal of Plant Physiology 160: 831-839
  9. Vepari, C. et al (2007) Silk as a biomaterial.  Progress in Polymer Science 32, 991-1007
  10. Lazaris, A. et al (2002) Spider silk fibres spun from soluble recombinant silk produced in mammalian cells.  Science 18: 472 – 476
  11. Commonwealth Scientific and Industrial Research Organisation, February 2010.  Artificial bee silk a big step closer to reality. Accessed March 2010. 
  12. Encylopedia of Life: arachnida.  Accessed March 2010.
  13. Skerl, K. L. et al (1999) Spiders in conservation – tools, targets and other topics.  Journal of Insect Conservation, 3: 249 – 250. 
  14. Fen raft spider information site.  Accessed March 2010.
  15. Wild Solutions, Andrew Beattie and Paul R. Ehrlich (2001).  Yale University Press, USA.  Pp 185 – 190.

 

Further reading

The Gecko’s Foot, Peter Forbes (2005). Harper Perennial, London, UK.  Chapter 3, pp 55 – 78.