Spider silk
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223789350
2008-07-05T20:33:19Z
66.215.12.129
/* Artificial spider silk */
[[Image:Australian orb weaver spinning web.jpg|thumb|250px|An orb weaver producing silk from its spinnerets]]
'''Spider silk''', also known as [[gossamer]], is a [[fiber]] spun by [[spider]]s.
Spider [[silk]] is a remarkably strong material. Its [[tensile strength]] is comparable to that of high-grade [[steel]]<ref>{{cite journal
|author= Shao, Z. Vollrath, F.
|year=[[August 15]] [[2002]]
|title=Materials: Surprising strength of silkworm silk
|journal=[[Nature (journal)|Nature]]
|volume=418|pages=741
|doi=10.1038/418741a
}}</ref>, spider dragline silk has a tensile strength of roughly 1.3 [[Pascal (unit)|GPa]], while one source [http://www.geocities.com/pganio/materials.html] lists a tensile strength for one form of steel at 1.65 GPa. However, spider silk is much less dense than steel; its tensile strength to density ratio is roughly five times higher than that of [[steel]] (i.e. it is five times as strong as steel of the same density — as strong as [[Aramid]] filaments, such as [[Twaron]] or [[Kevlar]].) In fact, a strand of spider silk long enough to circle the earth would weigh less than 16 [[ounce]]s (450 [[gram|g]]).
==Usage==
[[Image:Argiopesilk.jpg|right|thumb|280px|A female specimen of [[Argiope appensa|''Argiope appensa'']] wraps her prey in silk.]] Spiders normally use their silk to make structures, either for protection for their offspring, or for predation on other creatures. They can also suspend themselves using their silk, normally for the same reasons. In some cases, spiders may even use silk as a source of [[food]].<ref>{{cite web |url=http://www.chm.bris.ac.uk/motm/spider/page2h.htm |title=Spider Silk |accessdate=2007-05-22 |format= |work= |publisher= School of Chemistry - Bristol University - UK}}</ref> <ref>{{cite journal |last=Miyashita |first=Tadashi |authorlink= |coauthors=Yasunori Maezono, Aya Shimazaki |year=2004 |month=March |title= Silk feeding as an alternative foraging tactic in a kleptoparasitic spider under seasonally changing environments |journal=Journal of Zoology |volume=262 |issue=03 |pages=225–229 |doi =10.1017/S0952836903004540 |id= |url=http://journals.cambridge.org/action/displayAbstract;jsessionid=E5F9929D3300E3C4E54DF68FB169AD62.tomcat1?fromPage=online&aid=204739 |accessdate=2007-05-22 |quote= }}</ref>
The [[trapdoor spider]] will burrow into the ground and weave a [[trapdoor]]-like structure with spindles around so it can tell when prey arrives and take it by surprise.
Many small spiders use silk threads for [[ballooning (spider)|ballooning]], the historical name by biologists for the dynamic kiting <ref>[http://books.google.com/books?id=Gvrt2eIVG7YC&pg=PT24&lpg=PT24&dq=spider+ballooning+is+really+kiting&source=web&ots=wHpCpxCy3r&sig=srQgV7Hf_SzOfhOSjrKvI9YKdwg&hl=en Spiders By Ann R. Heinrichs. Google Books. She observes that the so called ballooning is like a kite or balloon; she is mechanically correct about the kite part, as no true balloon is ever formed by the spider as told in the other references.]</ref> <ref>[http://www.snerdey.com/sky/index.html Flying Spiders over Texas! Coast to Coast. Chad B., Texas State University Undergrad: He correctly describes the mechanical kiting of spider "ballooning".]</ref> spiderlings (mostly) use for dispersal . They extrude several threads into the air and let themselves become carried away with upward winds. Although most rides will end a few meters later, it seems to be a common way for spiders to invade islands. Many sailors have reported that spiders have been caught in their ship's sails, even when far from land.
[[Argiope argentata]] has five different types of silk, each for a different purpose:<ref>Cunningham, A. (2007), Taken for a Spin. ''Science News'' vol. 171, pp. 231-233</ref><ref>Blackledge, T.A., and Hayashi, C.Y. (2006). Silken toolkits: Biomechanics of silk fibers spun by the orb web spider Argiope argentata. ''Journal of Experimental Biology'' 209(July 1), pp. 2452-2461 ([http://www.sciencenews.org/articles/20070414/bob8.asp references])</ref>
* '''dragline silk''': Used for the web's outer rim and spokes, as well as for the [[lifeline]]. As strong as steel, but much tougher.
* '''capture-spiral silk''': Used for the capturing lines of the web. Sticky, extremely stretchy and tough.
* '''tubiliform silk''': Used for protective egg sacs. Stiffest silk.
* '''aciniform silk''': Used to wrap and secure freshly captured prey. Two to three times as tough as the other silks, including dragline.
* '''minor-ampullate silk''': Used for temporary scaffolding during web construction
== Properties==
[[Image:Araneus diadematus underside 2.jpg|thumb|left|280px| A [[European garden spider|garden spider]] spinning its web.]]
[[Image:Spider silk microscopic structure.png|thumb|right|280px| Structure of spider silk. Inside a typical fiber, one finds crystalline regions separated by amorphous linkages. The crystals are beta-sheets that have assembled together.]]
Spider silk is also especially [[ductile]], able to stretch up to 40% of its length without breaking. This gives it a very high [[toughness]] (or work to fracture), which "equals that of commercial [[aramid|polyaramid]] ([[aromaticity|aromatic]] [[nylon]]) filaments, which themselves are benchmarks of modern polymer fiber technology."<ref>{{cite journal
|author= Vollrath, F. Knight, D.P.
|year= 2001
|title=Liquid crystalline spinning of spider silk
|journal=[[Nature (journal)|Nature]]
|volume=410|pages=541
|doi=10.1038/35069000
}}</ref>
The notion that spider silk is stronger than any industrial fiber is a common misconception as whilst some may be stronger, none are tougher (total energy to break). Numerous artificial fibers are similar or stronger, notably [[aramid]]s like [[Kevlar]] and [[carbon fibre]] materials (see [[tensile strength]] for common comparisons). Nonetheless, there is much interest in duplicating the silk process artificially, since spiders use renewable materials as input and operate at room temperature, low pressures and using water as a solvent. There have been difficulties though in finding any commercially viable process to mass produce spider silk. Low production yields makes domesticating spiders for silk production infeasible, and, as of yet, no other organisms have been able to produce the silk through the introduction of [[recombinant DNA]]. [http://www.sciencedirect.com.libproxy.lib.unc.edu/science?_ob=ArticleURL&_udi=B6TCW-4S4J6G0-3&_user=130907&_coverDate=05%2F31%2F2008&_rdoc=5&_fmt=high&_orig=browse&_srch=doc-info(%23toc%235181%232008%23999739994%23686677%23FLA%23display%23Volume)&_cdi=5181&_sort=d&_docanchor=&_ct=9&_acct=C000004198&_version=1&_urlVersion=0&_userid=130907&md5=4e943bf9f8b13ee1aca065ebce361f56]
Spider silk is composed of complex [[protein]] [[molecule]]s. This, coupled with the isolation stemming from the spider's [[predator]]y nature, has made the study and replication of the substance quite challenging. Because of the repetitive nature of the [[DNA]] encoding the silk protein, it is difficult to determine its [[sequencing|sequence]] and to date, silk-producing sequences have only been decoded for fourteen [[species]] of spider. In 2005, independent researchers in the [[University of Wyoming]] (Tian and Lewis), [[University of the Pacific (United States)|University of the Pacific]] (Hu and Vierra), the [[University of California, Riverside|University of California at Riverside]] (Garb and Hayashi) and [[Shinshu University]] (Zhao and Nakagaki) have uncovered the molecular structure of the gene for the protein that various female spider species use to make their silken egg cases.
Although different species of spider, and different types of silk, have different protein sequences, a general trend in spider silk structure is a sequence of amino acids (usually alternating [[glycine]] and [[alanine]], or alanine alone) that [[Molecular self-assembly|self-assemble]] into a [[beta sheet]] conformation. These "Ala rich" blocks are separated by segments of amino acids with bulky side-groups. The beta sheets stack to form [[crystals]], whereas the other segments form [[amorphous]] domains. It is the interplay between the hard crystalline segments, and the elastic semi amorphous regions, that gives spider silk its extraordinary properties.
== Synthesis ==
The unspun silk dope is pulled through silk [[glands]], resulting in a transition from stored gel to final solid fiber. Many [[species]] of [[spider]] have different [[spinneret|glands]] for different jobs, such as [[house|housing]] and [[spider web|web]] construction, defense, capturing and detaining [[prey]], or mobility Thus, different specialized silks have evolved with material properties optimized for their intended use.
The gland's visible, or external, part is termed the [[spinneret]]. Depending on the [[species]], spiders will have anything from two to eight spinnerets, usually in pairs. The beginning of the gland is rich in [[thiol]] and [[tyrosine]] groups. After this beginning process, the [[ampulla]] acts as a storage sac for the newly created fibers. From there, the spinning [[duct]] effectively removes [[water]] from the fiber and through fine channels also assists in its formation. [[Lipid]] secretions take place just at the end of the distal limb of the duct, and proceeds to the [[valve]]. The valve is believed to assist in rejoining broken fibers, acting much in the way of a [[helical pump]].
Various compounds other than protein are used to enhance the fiber's properties. [[Pyrrolidine]] has [[hygroscopic]] properties and helps to keep the thread moist. It occurs in especially high concentration in glue threads. [[Potassium]] [[hydrogen phosphate]] releases [[proton]]s in aqueous solution, resulting in a [[pH]] of about 4, making the silk [[acid]]ic and thus protecting it from [[fungus]] and [[bacteria]] that would otherwise digest the protein. [[Potassium nitrate]] is believed to prevent the protein from denaturating in the acidic milieu.<ref name=Heimer>Heimer, S. (1988). Wunderbare Welt der Spinnen. ''Urania''. p.12</ref>
The spinneret apparatus of a ''[[Araneus diadematus]]'' consists of the following glands:
* 500 [[Glandulae piriformes]] for attachment points
* 4 [[Glandulae ampullaceae]] for the web frame
* about 300 [[Glandulae aciniformes]] for the outer lining of egg sacs, and for ensnaring prey
* 4 [[Glandulae tubuliformes]] for egg sac silk
* 4 [[Glandulae aggregatae]] for glue
* 2 [[Glandulae coronatae]] for the thread of glue lines<ref name="Heimer" />
==Human use==
Peasants in the southern [[Carpathian Mountains]] used to cut up tubes built by ''[[Atypus]]'' and cover wounds with the inner lining. It reportedly facilitated healing, and even connected with the skin. This is believed to be due to antiseptic properties of spider silk (which is made of protein)<ref name=Heimer>Heimer, S. (1988). Wunderbare Welt der Spinnen. ''Urania''. p.14</ref>
Some fishermen in the indo-pacific ocean use the web of ''[[Nephila]]'' to catch small fish.<ref name="Heimer" />
The silk of ''[[Nephila clavipes]]'' has recently been used to help in [[mammal]]ian [[neuron]]al regeneration. <ref>Allmeling, C., Jokuszies, A., Reimers, K., Kall, S., Vogt, P.M. (2006): Use of spider silk fibres as an innovative material in a biocompatible artificial nerve conduit. ''J. Cell. Mol. Med.'' 10(3):770-777 [http://www.jcmm.ro/download/jcmm010.003.18.pdf PDF] - {{DOI|10.2755/jcmm010.003.18}}</ref>
At one time, it was common to use spider silk as a thread for [[crosshair]]s in telescopes, microscopes and similar optical instruments.<ref>Berenbaum, May R., ''Field Notes - Spin Control'', The Sciences, The New York Academy Of Sciences, September/October 1995</ref>
== Artificial spider silk ==
Spider silk's properties have made it the target of industrial research efforts. It is not generally considered possible to use spiders themselves to produce industrially useful quantities of spider silk, due to the difficulties of managing large quantities of small spiders (although it was tried with ''[[Nephila]]'' silk<ref name="Heimer" />). Compared with [[silkworms]], spiders are aggressive and will eat one another, making it inadvisable to keep many spiders together in the same space. Other efforts have involved extracting the spider silk [[gene]] and using other organisms to produce the required amount of spider silk. In [[2000]], [http://www.nexiabiotech.com/en/00_home/index.php Nexia], a [[Canadian]] [[biotechnology]] company, was successful in producing spider silk [[protein]] in [[transgenic]] [[goat]]s. These goats carried the gene for spider silk protein, and the milk produced by the goats contained significant quantities of the protein (1-2 grams of silk proteins / liter of milk). Attempts to spin the protein into a fiber similar to natural spider silk (what would be the [[biosteel]]) resulted in fibers with tenacities of 2-3 grams/denierr. The spider's highly sophisticated spinneret is instrumental in
organizing the silk proteins into strong domains. Specifically, the spinneret creates a gradient of protein [[concentration]], [[pH]], and [[pressure]], which drive the protein solution through [[liquid crystal]]line [[phase transitions]], ultimately generating the required silk structure (which is a mixture of [[crystal]]line and [[amorphous]] [[biopolymer]] regions). Replicating these complex conditions in lab environment has proved difficult. Nexia used wet spinning methodologies which implied "squeezing" the recombinant silk-protein solution (BIOSTEEL) through small extrusion holes in order to simulate the behavior of the spinneret, but this was insufficient to replicate the exact properties of the native spider silk. Ultimately, Nexia currently continues research and product development with BIOSTEEL by collaborating with academic labs and companies that are willing to work with BIOSTEEL. Extrusion of protein fibers in an aqueous environment is known as 'wet-spinning'. This process has so far produced silk fibers of diameters ranging from 10-60 μm, compared to diameters of 2.5-4 μm seen in natural spider silk.<ref>Scheibel, T. (2004): Spider silks: recombinant synthesis, assembly, spinning, and engineering of synthetic proteins. "Microb Cell Fact" 3:14 [http://www.microbialcellfactories.com/content/3/1/14]</ref>
==See also==
*[[Hagfish]] - produces similar fiber.
*[[Silk]] - natural fibre produced by silkworms, the larvae of the moth [[Bombyx mori]].
==References==
{{reflist}}
{{refbegin}}
*Forbes, Peter (4th Estate, London 2005). "''The Gecko's Foot - Bio Inspiration: Engineered from Nature''", ISBN 0-00-717990-1 in H/B
*Graciela C. Candelas, José Cintron. "''A spider fibroin and its synthesis''", Journal of Experimental Zoology (1981), Department of Biology, University of Puerto Rico, Río Piedras, Puerto Rico 00931
{{refend}}
== External links ==
{{wikinews|Spiders' egg case silk gene found}}
*[http://hubcap.clemson.edu/~ellisom/biomimeticmaterials/files/spiderbiology.htm The Silk Gland] - A very nice breakdown of the [[spinneret|silk gland]], its parts and uses with images and drawings.
*[http://lsda.jsc.nasa.gov/scripts/experiment/exper.cfm?exp_index=428 Spiders in Space] - [[NASA]] article and [[database]] information on the research of [[spider]]s in [[outer space|space]].
*[http://www.isracast.com/tech_news/271204_tech.htm Israeli and German scientists created artificial silk using genetically engineered spider proteins] - Article on IsraCast
*[http://jeb.biologists.org/cgi/reprint/202/23/3295.pdf The mechanical design of spider silks: from fibroin sequence to mechanical function] - Article on The Journal of Experimental Biology
*[http://www.livescience.com/technology/041129_spider_man.html The Real Spider-Man] - Article on forming Spider Silk Fibers from Caterpillars
*[http://www.newscientisttech.com/article.ns?id=dn9316&feedId=online-news_rss20 Genetic tweak boosts stiffness of spider silk]
*[http://www.arachnology.be/pages/Silk.html Silk & Webs - The Arachnology Home Page]
*[http://www.oxfordsilkgroup.com Silk Research Group at Oxford University]
*[http://www.tms.org/pubs/journals/JOM/0502/Elices-0502.html Finding Inspiration in Spider Silk Fibers]
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[[Category:Spider anatomy]]
[[Category:Materials science]]
[[Category:Natural materials]]
[[Category:Polyamides]]
[[Category:Silk]]
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