Editing Spider silk (section)

==Properties==

===Structural===
[[File:Structure of spider silk thread Modified.svg|thumb|310x310px| Spider silk structure: crystalline beta-sheets separated by amorphous linkages]]

Silks have a hierarchical structure. The [[primary structure]] is the [[amino acid]] sequence of its proteins ([[spidroin]]), mainly consisting of highly repetitive [[glycine]] and [[alanine]] blocks,<ref name="Hinman 92">{{cite journal |author= Hinman, M. B.|author2= Lewis, R. V.|name-list-style= amp |date= 1992 |title= Isolation of a clone encoding a second dragline silk fibroin. Nephila clavipes dragline silk is a two-protein fiber |journal= J. Biol. Chem. |volume= 267 |pages= 19320–24 |pmid= 1527052 |issue= 27|doi= 10.1016/S0021-9258(18)41777-2|doi-access= free }}</ref><ref name="Simmons 96">{{cite journal |author= Simmons, A. H.|author2= Michal, C. A.|author3= Jelinski, L. W.|name-list-style= amp |date= 1996 |title= Molecular orientation and two-component nature of the crystalline fraction of spider dragline silk |journal= Science |volume= 271 |pages= 84–87 |doi= 10.1126/science.271.5245.84 |issue=5245 |pmid= 8539605|bibcode = 1996Sci...271...84S |s2cid= 40043335}}</ref> which is why silks are often referred to as a [[Copolymer|block co-polymer]]. On a secondary level, the short side-chained alanine is mainly found in the crystalline domains ([[beta sheet]]s) of the nanofibril. Glycine is mostly found in the so-called amorphous matrix consisting of helical and beta turn structures.<ref name="Simmons 96" /><ref name="van Beek 02">{{cite journal |author= van Beek, J. D.|author2= Hess, S.|author3= Vollrath, F.|author4= Meier, B. H.|name-list-style= amp |date= 2002 |title= The molecular structure of spider dragline silk: Folding and orientation of the protein backbone |journal= Proc. Natl. Acad. Sci. U.S.A. |volume= 99 |pages= 10266–71 |doi= 10.1073/pnas.152162299 |issue= 16 |pmid= 12149440 |pmc= 124902|bibcode = 2002PNAS...9910266V |doi-access= free}}</ref> The interplay between the hard crystalline segments and the strained elastic semi-amorphous regions gives spider silk its extraordinary properties.<ref>{{cite journal |author= Liu, Y.|author2= Sponner, A.|author3= Porter, D.|author4= Vollrath, F. |date= 2008 |title=Proline and Processing of Spider Silks |journal=[[Biomacromolecules]] |volume=9 |pages=116–21 |doi=10.1021/bm700877g |pmid= 18052126 |issue= 1}}</ref><ref>{{cite journal|author= Papadopoulos, P.|author2= Ene, R.|author3= Weidner, I.|author4= Kremer, F. |date= 2009 |title=Similarities in the Structural Organization of Major and Minor Ampullate Spider Silk |journal=[[Macromolecular Rapid Communications|Macromol. Rapid Commun.]] |volume=30 |pages=851–57 |doi=10.1002/marc.200900018|pmid= 21706668|issue= 9–10}}</ref> Various compounds other than protein are used to enhance the fibre's properties. [[Pyrrolidine]] has [[Hygroscopy|hygroscopic]] properties that keep the silk moist while warding off ant invasion. It occurs in high concentration in glue threads. [[Potassium hydrogen phosphate]] releases [[Hydron (chemistry)|hydrogen ions]] in aqueous solution, resulting in a [[pH]] of about 4, making the silk [[acid]]ic and thus protecting it from [[fungi]] and [[bacteria]] that would otherwise digest the protein. [[Potassium nitrate]] is believed to prevent the protein from denaturing in the acidic milieu.<ref name="Heimer">Heimer, S. (1988). Wunderbare Welt der Spinnen. ''Urania''. p. 12</ref>

Termonia introduced this first basic model of silk in 1994.<ref name="Termonia 94">{{cite journal |author= Termonia, Y. |date= 1994 |title= Molecular Modeling of Spider Silk Elasticity |journal= Macromolecules |volume= 27 |pages= 7378–81 |doi=10.1021/ma00103a018 |issue= 25 |bibcode = 1994MaMol..27.7378T }}</ref> He suggested [[Crystallite|crystallites]] embedded in an amorphous matrix interlinked with [[Hydrogen bond|hydrogen bonds]]. Refinements to this model include: semi-crystalline regions were found<ref name="Simmons 96" /> as well as a fibrillar skin core model suggested for spider silk,<ref>{{cite journal |author= Vollrath, F.|author2= Holtet, T.|author3= Thogersen, H. C.|author4= Frische, S.|name-list-style= amp |date= 1996 |title= Structural organization of spider silk |journal= [[Proceedings of the Royal Society B]] |volume= 263 |pages= 147–51 |doi=10.1098/rspb.1996.0023 |issue= 1367 |bibcode= 1996RSPSB.263..147V|s2cid= 136879037}}</ref> later visualised by [[Atomic Force Microscopy|AFM]] and [[Transmission Electron Microscopy|TEM]].<ref>{{cite journal |author= Sponner, A.|date= 2007 |title= Composition and hierarchical organization of a spider silk |journal= PLOS ONE|volume=2 |pages= e998 |doi= 10.1371/journal.pone.0000998 |issue= 10 |pmid= 17912375 |pmc= 1994588 |bibcode = 2007PLoSO...2..998S |editor1-last= Scheibel |editor1-first= Thomas |first2= Wolfram |first3= Shamci |first4= Eberhard |first5= Frank |first6= Klaus |last2= Vater, Wolfram |last3= Monajembashi, Shamci |last4= Unger, Eberhard |last5= Grosse, Frank |last6= Weisshart, Klaus |doi-access= free }} {{open access}}</ref> Sizes of the nanofibrillar structure and the crystalline and semi-crystalline regions were revealed by [[neutron scattering]].<ref>{{cite journal |author= Sapede, D.|date= 2005 |title= Nanofibrillar structure and molecular mobility in spider dragline silk |journal=  Macromolecules|volume= 34 |page= 623 |doi=10.1021/ma0507995 |bibcode = 2005MaMol..38.8447S |first2= T. |last3= Forsyth |first3= V. T. |last4= Koza |first4= M. M. |last5= Schweins |first5= R. |last6= Vollrath |first6= F. |last7= Riekel |first7= C. |issue= 20 |last2= Seydel }}</ref>

The fibres' microstructural information and macroscopic mechanical properties are related.<ref name="plaza 12">{{cite journal |author= Plaza, G.R.|author2= Pérez-Rigueiro, J.|author3= Riekel, C.|author4= Perea, G.B.|author5= Agulló-Rueda, F.|author6= Burghammer, M.|author7=  Guinea, G.V.|author8= Elices, M.|date= 2012 |title= Relationship between microstructure and mechanical properties in spider silk fibers: identification of two regimes in the microstructural changes |journal= Soft Matter |volume=8 |pages= 6015–26 |doi= 10.1039/C2SM25446H |issue= 22|bibcode= 2012SMat....8.6015P|url= https://zenodo.org/record/897750}}</ref> Ordered regions (i) mainly reorient by deformation for low-stretched fibres and (ii) the fraction of ordered regions increases progressively for higher fibre stretching.<br /><gallery widths="900" heights="400">
File:0.Figure.png|Schematic of the spider's orb web, structural modules, and spider silk structure.<ref>{{Cite journal|last1=Zhao|first1=Yue|last2=Hien|first2=Khuat Thi Thu|last3=Mizutani|first3=Goro|last4=Rutt|first4=Harvey N.|date=June 2017|title=Second-order nonlinear optical microscopy of spider silk|journal=Applied Physics B|volume=123|issue=6|pages=188|arxiv=1706.03186|doi=10.1007/s00340-017-6766-z|bibcode=2017ApPhB.123..188Z|s2cid=51684427}}</ref> On the left is shown a schematic drawing of an orb web. The red lines represent the dragline, radial line, and frame lines. The blue lines represent the spiral line, and the centre of the orb web is called the "hub". Sticky balls drawn in blue are made at equal intervals on the spiral line with viscous material secreted from the aggregate gland. Attachment cement secreted from the piriform gland is used to connect and fix different lines. Microscopically, the spider silk secondary structure is formed of spidroin with the structure shown on the right side. In the dragline and radial line, a crystalline β-sheet and an amorphous helical structure are interwoven. The large amount of β-spiral structure gives elastic properties to the capture part of the orb web. In the structural modules diagram, a microscopic structure of dragline and radial lines is shown, composed mainly of two proteins of MaSp1 and MaSp2, as shown in the upper central part. The spiral line has no crystalline β-sheet region.
</gallery>

===Mechanical===
Each spider and each type of silk has a set of mechanical properties optimised for their biological function.

Most silks, in particular dragline silk, have exceptional mechanical properties. They exhibit a unique combination of high [[tensile strength]] and extensibility ([[ductility]]). This enables a silk fibre to absorb a large amount of energy before breaking ([[toughness]], the [[Integral|area under]] a stress-strain curve).

[[File:Mechanical Properties of Spider Silk.svg|right|thumb|280px| An illustration of the differences between toughness, stiffness and strength]]
Strength and toughness are distinct quantities. Weight for weight, silk is stronger than steel, but not as strong as [[Kevlar]]. Spider silk is, however, tougher than both.

The variability of spider silk fibre mechanical properties is related to their degree of molecular alignment.<ref name="guinea 05">{{cite journal |author= Guinea, G.V.|author2= Elices, M.|author3= Pérez-Rigueiro, J.|author4= Plaza, G.R.|name-list-style= amp |date= 2005 |title= Stretching of supercontracted fibers: a link between spinning and the variability of spider silk |journal= [[Journal of Experimental Biology]] |volume= 208 |pages= 25–30 |doi=10.1242/jeb.01344 |pmid= 15601874|issue= 1 |doi-access=  |s2cid= 6964043}}</ref> Mechanical properties also depend on ambient conditions, i.e. humidity and temperature.<ref name="plaza 06">{{cite journal |bibcode=2006JPoSB..44..994P |title=Thermo-hygro-mechanical behavior of spider dragline silk: Glassy and rubbery states |last1=Plaza |first1=Gustavo R. |last4=Elices |volume=44 |date=2006 |pages=994–99 |journal=Journal of Polymer Science Part B: Polymer Physics |doi=10.1002/polb.20751 |first2=Gustavo V. |first3=José |first4=Manuel |issue=6 |last2=Guinea |last3=Pérez-Rigueiro}}</ref>

==== Young's modulus ====
[[Young's modulus]] is the resistance to deformation elastically along the tensile force direction. Unlike steel or Kevlar which are stiff, spider silk is ductile and elastic, having lower Young's modulus. According to Spider Silkome Database, ''Ariadna lateralis'' silk has the highest Young's modulus with 37 GPa,<ref name=":1">{{Cite journal |last1=Arakawa |first1=Kazuharu |last2=Kono |first2=Nobuaki |last3=Malay |first3=Ali D. |last4=Tateishi |first4=Ayaka |last5=Ifuku |first5=Nao |last6=Masunaga |first6=Hiroyasu |last7=Sato |first7=Ryota |last8=Tsuchiya |first8=Kousuke |last9=Ohtoshi |first9=Rintaro |last10=Pedrazzoli |first10=Daniel |last11=Shinohara |first11=Asaka |last12=Ito |first12=Yusuke |last13=Nakamura |first13=Hiroyuki |last14=Tanikawa |first14=Akio |last15=Suzuki |first15=Yuya |date=2022-10-14 |title=1000 spider silkomes: Linking sequences to silk physical properties |journal=Science Advances |language=en |volume=8 |issue=41 |pages=eabo6043 |doi=10.1126/sciadv.abo6043 |issn=2375-2548 |pmc=9555773 |pmid=36223455|bibcode=2022SciA....8O6043A }}</ref> compared to 208 GPa for steel<ref>{{Cite journal |last1=Chen |first1=Zhong |last2=Gandhi |first2=Umesh |last3=Lee |first3=Jinwoo |last4=Wagoner |first4=R. H. |date=2016-01-01 |title=Variation and consistency of Young's modulus in steel |url=https://www.sciencedirect.com/science/article/pii/S0924013615301011 |journal=Journal of Materials Processing Technology |volume=227 |pages=227–243 |doi=10.1016/j.jmatprotec.2015.08.024 |issn=0924-0136}}</ref> and 112 GPa for Kevlar.<ref>{{Cite journal |last1=Nair |first1=Anand Narayanan |last2=Sundharesan |first2=Santhosh |last3=Al Tubi |first3=Issa Saif Mohammed |date=2020-11-01 |title=Kevlar-based Composite Material and its Applications in Body Armour: A Short Literature Review |journal=IOP Conference Series: Materials Science and Engineering |volume=987 |issue=1 |pages=012003 |doi=10.1088/1757-899X/987/1/012003 |issn=1757-8981|doi-access=free |bibcode=2020MS&E..987a2003N }}</ref>

====Tensile strength====
A dragline silk's [[tensile strength]] is comparable to that of high-grade alloy [[steel]] (450−2000 MPa),<ref>{{cite journal |doi=10.1007/BF00551703 |title=The strength of spider silk |date=1980 |last1=Griffiths |first1=J. R. |last2=Salanitri |first2=V. R. |journal=Journal of Materials Science |volume=15 |issue=2 |pages=491–96 |bibcode=1980JMatS..15..491G|s2cid=135628690 }}</ref><ref>{{cite web |url=http://www.matweb.com/search/datasheettext.aspx?matguid=210fcd12132049d0a3e0cabe7d091eef |title=Overview of materials for AISI 4000 Series Steel |publisher=matweb.com |access-date=18 August 2010}}</ref> and about half as strong as [[aramid]] filaments, such as [[Twaron]] or Kevlar (3000 MPa).<ref>{{cite web |url=http://www.matweb.com/search/datasheettext.aspx?matguid=77b5205f0dcc43bb8cbe6fee7d36cbb5 |title=DuPont Kevlar 49 Aramid Fiber |publisher=matweb.com |access-date=18 August 2010}}</ref> According to Spider Silkome Database, ''Clubiona vigil'' silk has the highest tensile strength.<ref name=":1" />

====Density====
Consisting of mainly protein, silks are about a sixth of the density of steel (1.3&nbsp;g/cm<sup>3</sup>). As a result, a strand long enough to circle the Earth would weigh about {{convert|2|kg}}. (Spider dragline silk has a tensile strength of roughly 1.3&nbsp;[[Pascal (unit)|GPa]]. The tensile strength listed for steel might be slightly higher{{snd}}e.g. 1.65&nbsp;GPa,<ref>{{cite web |url=http://www.geocities.com/pganio/materials.html |title=Material Tensile Strength Comparison |last1=Ganio Mego |first1=Paolo |archive-url=https://web.archive.org/web/20091026041350/http://geocities.com/pganio/materials.html|archive-date=26 October 2009 |date=c. 2002|access-date=3 January 2012}}</ref><ref>{{cite journal |bibcode=2002Natur.418..741S |title=Materials: Surprising strength of silkworm silk |last1=Shao |first1=Zhengzhong |last2=Vollrath |volume=418 |date=2002 |pages=741 |journal=Nature |doi=10.1038/418741a |pmid=12181556 |first2=F |issue=6899|s2cid=4304912 |doi-access=free }}</ref> but spider silk is a much less dense material, so that a given weight of spider silk is five times as strong as the same weight of steel.)

====Energy density====
The [[energy density]] of dragline spider silk is roughly {{val|1.2|e=8|u=J/m3}}.<ref name="Vollrath 01">{{cite journal |bibcode=2005EPJE...16..199P |title=Predicting the mechanical properties of spider silk as a model nanostructured polymer |last1=Porter |first1=D. |last3=Shao |volume=16 |date=2005 |pages=199–206 |journal=European Physical Journal E |doi=10.1140/epje/e2005-00021-2 |pmid=15729511 |first2=F. |first3=Z. |issue=2 |last2=Vollrath|s2cid=32385814 }}</ref>

====Ductility====
Silks are [[ductile]], with some able to stretch up to five times their relaxed length without breaking.

====Toughness====
The combination of strength and ductility gives dragline silks a high [[toughness]] (or work to fracture), which "equals that of commercial [[polyaramid]] (aromatic nylon) filaments, which themselves are benchmarks of modern polymer fibre technology".<ref name="Vollrath 410" /><ref>{{cite web |url=http://www.chm.bris.ac.uk/motm/spider/page2.htm |title=Spider Silk |publisher=chm.bris.ac.uk |access-date=18 August 2010}}</ref> According to Spider Silkome Database, ''Araneus ishisawai'' silk is the toughest.<ref name=":1" />

==== Elongation at break ====
Elongation at break compares initial object length to final length at break. According to Spider Silkome Database, ''Caerostris darwini'' silk has the highest strain at break for any spider silk, breaking at 65% extension.<ref name=":1" />

====Temperature====
While unlikely to be relevant in nature, dragline silks can hold their strength below -40&nbsp;°C (-40&nbsp;°F) and up to 220&nbsp;°C (428&nbsp;°F).<ref>{{cite journal |doi=10.1002/adma.200400344 |title=Toughness of Spider Silk at High and Low Temperatures |date=2005 |last1=Yang |first1=Y. |last2=Chen |first2=X. |last3=Shao |first3=Z. |last4=Zhou |first4=P. |last5=Porter |first5=D. |last6=Knight |first6=D. P. |last7=Vollrath |first7=F. |journal=Advanced Materials |volume=17 |issue=1 |pages=84–88|bibcode=2005AdM....17...84Y |s2cid=136693986 }}</ref> As occurs in many materials, spider silk fibres undergo a [[glass transition]]. The glass-transition temperature depends on humidity, as water is a [[plasticiser]] for spider silk.<ref name="plaza 06" />

====Supercontraction====
When exposed to water, dragline silks undergo supercontraction, shrinking up to 50% in length and behaving like a weak rubber under tension.<ref name="plaza 06" /> Many hypotheses have attempted to explain its use in nature, most popularly to re-tension webs built in the night using the morning dew.{{Citation needed|date=May 2013}}

====Highest-performance====
The toughest known spider silk is produced by the species [[Darwin's bark spider]] (''Caerostris darwini''): "The toughness of forcibly silked fibers averages 350 [[Toughness#Unit of toughness|MJ/m<sup>3</sup>]], with some samples reaching 520 MJ/m<sup>3</sup>. Thus, ''C. darwini'' silk is more than twice as tough as any previously described silk and over 10 times tougher than Kevlar".<ref name="Agnarsson 10">{{cite journal |bibcode=2010PLoSO...511234A |title=Bioprospecting Finds the Toughest Biological Material: Extraordinary Silk from a Giant Riverine Orb Spider |last1=Agnarsson |first1=Ingi |last2=Kuntner |last3=Blackledge |volume=5 |date=2010 |page=11234 |journal=PLOS ONE|doi=10.1371/journal.pone.0011234 |editor1-last=Lalueza-Fox |editor1-first=Carles |first2=Matjaž |first3=Todd A. |issue=9 |pmid=20856804 |pmc=2939878|doi-access=free }} {{open access}}</ref>

===Adhesive===
Silk fibre is a two-compound [[wikt:pyriform|pyriform]] secretion, spun into patterns (called "attachment discs") using a minimum of silk substrate.<ref name="wolff">{{cite journal|pmid=25672841|year=2015|last1=Wolff|first1=J. O.|title=Spider's super-glue: Thread anchors are composite adhesives with synergistic hierarchical organization|journal=Soft Matter|volume=11|issue=12|pages=2394–403|last2=Grawe|first2=I|last3=Wirth|first3=M|last4=Karstedt|first4=A|last5=Gorb|first5=S. N.|doi=10.1039/c4sm02130d|bibcode=2015SMat...11.2394W|doi-access=free}}</ref> The pyriform threads [[polymer]]ise under ambient conditions, become functional immediately, and are usable indefinitely, remaining biodegradable, versatile and compatible with other materials in the environment.<ref name="wolff" /> The adhesive and durability properties of the attachment disc are controlled by functions within the spinnerets.<ref>{{cite journal|pmid=23033082|year=2012|last1=Sahni|first1=V|title=Cobweb-weaving spiders produce different attachment discs for locomotion and prey capture|journal=Nature Communications|volume=3|pages=1106|last2=Harris|first2=J|last3=Blackledge|first3=T. A.|last4=Dhinojwala|first4=A|doi=10.1038/ncomms2099|bibcode=2012NatCo...3.1106S|doi-access=free}}</ref> Some adhesive properties of the silk resemble [[glue]], consisting of [[microfibrils]] and [[lipid]] enclosures.<ref name="wolff" />