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[[Image:Lyristes plebejus.jpg|thumb|right|A [[cicada]] emerges from its nymphal exoskeleton; the shed exoskeleton is mostly modified chitin ([[sclerotin]]) but the wings and much of the adult body are still unsclerotized chitin at this stage]]
[[Image:Lyristes plebejus.jpg|thumb|right|A [[cicada]] emerges from its nymphal exoskeleton; the shed exoskeleton is mostly modified chitin ([[sclerotin]]) but the wings and much of the adult body are still unsclerotized chitin at this stage]]


'''Chitin''' ([[carbon|C]]<sub>8</sub>[[hydrogen|H]]<sub>13</sub>[[oxygen|O]]<sub>5</sub>[[nitrogen|N]])<sub>n</sub> ({{IPAc-en|ˈ|k|aɪ|t|ᵻ|n}} {{respell|KY|tin}}) is a long-chain [[polymer]] of [[N-Acetylglucosamine|''N''-acetylglucosamine]], an [[amide]] derivative of [[glucose]]. Chitin is the second most abundant [[polysaccharide]] in nature (behind only [[cellulose]]); an estimated 1 billion tons of chitin are produced each year in the [[biosphere]].<ref>{{Cite book |last=Nelson, D.L., Cox, M.M. |title=Lehninger Principles of Biochemistry |publisher=McMillan Learning |year=2017 |isbn=978-1-4641-2611-6 |edition=7th}}</ref> It is a primary component of [[cell wall]]s in [[fungi]] (especially filamentous and mushroom-forming fungi), the [[exoskeleton]]s of [[arthropod]]s such as crustaceans and insects, the [[radula]]e, [[cephalopod beak]]s and [[Gladius (cephalopod)|gladii]] of [[mollusc]]s and in some nematodes and diatoms.<ref name=":0">{{Cite journal |last1=Sanjanwala |first1=Dhruv |last2=Londhe |first2=Vaishali |last3=Trivedi |first3=Rashmi |last4=Bonde |first4=Smita |last5=Sawarkar |first5=Sujata |last6=Kale |first6=Vinita |last7=Patravale |first7=Vandana |date=2022-12-02 |title=Polysaccharide-based hydrogels for drug delivery and wound management: a review |url=https://www.tandfonline.com/doi/full/10.1080/17425247.2022.2152791 |journal=Expert Opinion on Drug Delivery |language=en |volume=19 |issue=12 |pages=1664–1695 |doi=10.1080/17425247.2022.2152791 |pmid=36440488 |s2cid=254041961 |issn=1742-5247|url-access=subscription }}</ref><ref name=":1">{{Cite journal |last1=Sanjanwala |first1=Dhruv |last2=Londhe |first2=Vaishali |last3=Trivedi |first3=Rashmi |last4=Bonde |first4=Smita |last5=Sawarkar |first5=Sujata |last6=Kale |first6=Vinita |last7=Patravale |first7=Vandana |date=2024-01-01 |title=Polysaccharide-based hydrogels for medical devices, implants and tissue engineering: A review |url=https://www.sciencedirect.com/science/article/pii/S0141813023053874 |journal=International Journal of Biological Macromolecules |volume=256 |issue=Pt 2 |pages=128488 |doi=10.1016/j.ijbiomac.2023.128488 |pmid=38043653 |issn=0141-8130|url-access=subscription }}</ref>
'''Chitin''' ([[carbon|C]]<sub>8</sub>[[hydrogen|H]]<sub>13</sub>[[oxygen|O]]<sub>5</sub>[[nitrogen|N]])<sub>n</sub> ({{IPAc-en|ˈ|k|aɪ|t|ᵻ|n}} {{respell|KY|tin}}) is a long-chain [[polymer]] of [[N-Acetylglucosamine|''N''-acetylglucosamine]], an [[amide]] derivative of [[glucose]]. Chitin is the second most abundant [[polysaccharide]] in nature (behind only [[cellulose]]); an estimated 1 billion tons of chitin are produced each year in the [[biosphere]].<ref>{{Cite book |last=Nelson, D.L., Cox, M.M. |title=Lehninger Principles of Biochemistry |publisher=McMillan Learning |year=2017 |isbn=978-1-4641-2611-6 |edition=7th}}</ref> It is a primary component of [[cell wall]]s in [[fungi]] (especially filamentous and mushroom-forming fungi), the [[exoskeleton]]s of [[arthropod]]s such as crustaceans and insects, the [[radula]]e, [[cephalopod beak]]s and [[Gladius (cephalopod)|gladii]] of [[mollusc]]s and in some nematodes and diatoms.<ref name=":0">{{Cite journal |last1=Sanjanwala |first1=Dhruv |last2=Londhe |first2=Vaishali |last3=Trivedi |first3=Rashmi |last4=Bonde |first4=Smita |last5=Sawarkar |first5=Sujata |last6=Kale |first6=Vinita |last7=Patravale |first7=Vandana |date=2022-12-02 |title=Polysaccharide-based hydrogels for drug delivery and wound management: a review |url=https://www.tandfonline.com/doi/full/10.1080/17425247.2022.2152791 |journal=Expert Opinion on Drug Delivery |language=en |volume=19 |issue=12 |pages=1664–1695 |doi=10.1080/17425247.2022.2152791 |pmid=36440488 |s2cid=254041961 |issn=1742-5247|url-access=subscription }}</ref><ref name=":1">{{Cite journal |last1=Sanjanwala |first1=Dhruv |last2=Londhe |first2=Vaishali |last3=Trivedi |first3=Rashmi |last4=Bonde |first4=Smita |last5=Sawarkar |first5=Sujata |last6=Kale |first6=Vinita |last7=Patravale |first7=Vandana |date=2024-01-01 |title=Polysaccharide-based hydrogels for medical devices, implants and tissue engineering: A review |url=https://www.sciencedirect.com/science/article/pii/S0141813023053874 |journal=International Journal of Biological Macromolecules |volume=256 |issue=Pt 2 |article-number=128488 |doi=10.1016/j.ijbiomac.2023.128488 |pmid=38043653 |issn=0141-8130|url-access=subscription }}</ref>
It is also synthesised by at least some fish and [[lissamphibia]]ns.<ref>{{cite journal | pmid = 25772447 | doi=10.1016/j.cub.2015.01.058 | volume=25 | issue=7 | title=Chitin is endogenously produced in vertebrates | pmc=4382437 | journal=Curr Biol | pages=897–900 | last1 = Tang | first1 = WJ | last2 = Fernandez | first2 = JG | last3 = Sohn | first3 = JJ | last4 = Amemiya | first4 = CT | year=2015| bibcode=2015CBio...25..897T }}</ref> Commercially, chitin is extracted from the shells of crabs, shrimps, shellfish and lobsters, which are major by-products of the seafood industry.<ref name=":0" /><ref name=":1" /> The structure of chitin is comparable to cellulose, forming crystalline nanofibrils or whiskers. It is functionally comparable to the protein [[keratin]]. Chitin has proved useful for several medicinal, industrial and biotechnological purposes.<ref name=":1" /><ref>{{Cite journal |last1=Morin-Crini |first1=Nadia |last2=Lichtfouse |first2=Eric |last3=Torri |first3=Giangiacomo |last4=Crini |first4=Grégorio |date=2019-12-01 |title=Applications of chitosan in food, pharmaceuticals, medicine, cosmetics, agriculture, textiles, pulp and paper, biotechnology, and environmental chemistry |url=https://doi.org/10.1007/s10311-019-00904-x |journal=Environmental Chemistry Letters |language=en |volume=17 |issue=4 |pages=1667–1692 |doi=10.1007/s10311-019-00904-x |bibcode=2019EnvCL..17.1667M |issn=1610-3661}}</ref>
It is also synthesised by at least some fish and [[lissamphibia]]ns.<ref>{{cite journal | pmid = 25772447 | doi=10.1016/j.cub.2015.01.058 | volume=25 | issue=7 | title=Chitin is endogenously produced in vertebrates | pmc=4382437 | journal=Curr Biol | pages=897–900 | last1 = Tang | first1 = WJ | last2 = Fernandez | first2 = JG | last3 = Sohn | first3 = JJ | last4 = Amemiya | first4 = CT | year=2015| bibcode=2015CBio...25..897T }}</ref> Commercially, chitin is extracted from the shells of crabs, shrimps, shellfish and lobsters, which are major by-products of the seafood industry.<ref name=":0" /><ref name=":1" /> The structure of chitin is comparable to cellulose, forming crystalline nanofibrils or whiskers. It is functionally comparable to the protein [[keratin]]. Chitin has proved useful for several medicinal, industrial and biotechnological purposes.<ref name=":1" /><ref>{{Cite journal |last1=Morin-Crini |first1=Nadia |last2=Lichtfouse |first2=Eric |last3=Torri |first3=Giangiacomo |last4=Crini |first4=Grégorio |date=2019-12-01 |title=Applications of chitosan in food, pharmaceuticals, medicine, cosmetics, agriculture, textiles, pulp and paper, biotechnology, and environmental chemistry |journal=Environmental Chemistry Letters |language=en |volume=17 |issue=4 |pages=1667–1692 |doi=10.1007/s10311-019-00904-x |bibcode=2019EnvCL..17.1667M |issn=1610-3661}}</ref>


==Etymology==
==Etymology==
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== Chemistry, physical properties and biological function ==
== Chemistry, physical properties and biological function ==


[[File:Chitin glucose and cellulose.svg|200px|thumb|right|Chemical configurations of the different monosaccharides (glucose and N-acetylglucosamine) and polysaccharides (chitin and cellulose) presented in [[Haworth projection]]]]
[[File:Chitin glucose and cellulose.svg|400px|thumb|right|Chemical configurations of the different monosaccharides (glucose and N-acetylglucosamine) and polysaccharides (chitin and cellulose) presented in [[Haworth projection]]]]


The structure of chitin was determined by [[Albert Hofmann]] in 1929. Hofmann hydrolyzed chitin using a crude preparation of the enzyme chitinase, which he obtained from the snail ''Helix pomatia''.<ref>{{cite thesis| first= A. |last= Hofmann | year=1929| title= Über den enzymatischen Abbau des Chitins und Chitosans| trans-title= On the enzymatic degradation of chitin and chitosan| publisher= University of Zurich |place= Zurich, Switzerland}}</ref><ref>{{cite journal| first1= P.| last1= Karrer |first2= A. |last2= Hofmann | year= 1929| title= Polysaccharide XXXIX. Über den enzymatischen Abbau von Chitin and Chitosan I| journal= Helvetica Chimica Acta| language= de| volume= 12| number= 1| pages= 616–637 | doi= 10.1002/hlca.19290120167}}</ref><ref>{{cite journal| first1= Nathaniel S.| last1= Finney| first2= Jay S.| last2= Siegel| year= 2008| title= In Memoriam: Albert Hofmann (1906-2008)| journal= CHIMIA| volume= 62| number= 5| pages= 444–447| url= http://www.zora.uzh.ch/9154/2/Siege_Finney_Hoffmann_2008V.pdf| publisher= University of Zurich| doi= 10.2533/chimia.2008.444| access-date= 2013-04-14| archive-date= 2013-06-16| archive-url= https://web.archive.org/web/20130616034406/http://www.zora.uzh.ch/9154/2/Siege_Finney_Hoffmann_2008V.pdf| url-status= dead}}</ref>
The structure of chitin was determined by [[Albert Hofmann]] in 1929. Hofmann hydrolyzed chitin using a crude preparation of the enzyme chitinase, which he obtained from the snail ''Helix pomatia''.<ref>{{cite thesis| first= A. |last= Hofmann | year=1929| title= Über den enzymatischen Abbau des Chitins und Chitosans| trans-title= On the enzymatic degradation of chitin and chitosan| publisher= University of Zurich |place= Zurich, Switzerland}}</ref><ref>{{cite journal| first1= P.| last1= Karrer |first2= A. |last2= Hofmann | year= 1929| title= Polysaccharide XXXIX. Über den enzymatischen Abbau von Chitin and Chitosan I| journal= Helvetica Chimica Acta| language= de| volume= 12| number= 1| pages= 616–637 | doi= 10.1002/hlca.19290120167}}</ref><ref>{{cite journal| first1= Nathaniel S.| last1= Finney| first2= Jay S.| last2= Siegel| year= 2008| title= In Memoriam: Albert Hofmann (1906-2008)| journal= CHIMIA| volume= 62| number= 5| pages= 444–447| url= http://www.zora.uzh.ch/9154/2/Siege_Finney_Hoffmann_2008V.pdf| publisher= University of Zurich| doi= 10.2533/chimia.2008.444| access-date= 2013-04-14| archive-date= 2013-06-16| archive-url= https://web.archive.org/web/20130616034406/http://www.zora.uzh.ch/9154/2/Siege_Finney_Hoffmann_2008V.pdf}}</ref>


Chitin is a modified [[polysaccharide]] that contains nitrogen; it is [[biosynthesis|synthesized]] from units of [[N-acetylglucosamine|''N''-acetyl-<small>D</small>-glucosamine]] (to be precise, 2-(acetylamino)-2-deoxy-<small>D</small>-glucose). These units form covalent β-(1→4)-linkages (like the linkages between [[glucose]] units forming [[cellulose]]). Therefore, chitin may be described as [[cellulose]] with one [[hydroxyl]] group on each [[monomer]] replaced with an [[acetyl]] [[amine]] group. This allows for increased [[hydrogen bonding]] between adjacent [[polymers]], giving the chitin-polymer matrix increased strength.
Chitin is a modified [[polysaccharide]] that contains nitrogen; it is [[biosynthesis|synthesized]] from units of [[N-acetylglucosamine|''N''-acetyl-<small>D</small>-glucosamine]] (to be precise, 2-(acetylamino)-2-deoxy-<small>D</small>-glucose). These units form covalent β-(1→4)-linkages (like the linkages between [[glucose]] units forming [[cellulose]]). Therefore, chitin may be described as [[cellulose]] with one [[hydroxyl]] group on each [[monomer]] replaced with an [[acetyl]] [[amine]] group. This allows for increased [[hydrogen bonding]] between adjacent [[polymers]], giving the chitin-polymer matrix increased strength.


In its pure, unmodified form, chitin is translucent, pliable, resilient, and quite tough. In most [[arthropod]]s, however, it is often modified, occurring largely as a component of [[composite material]]s, such as in [[sclerotin]], a tanned [[protein]]aceous matrix, which forms much of the [[exoskeleton]] of [[insect]]s. Combined with [[calcium carbonate]], as in the shells of [[crustacean]]s and [[mollusc]]s, chitin produces a much stronger composite. This composite material is much harder and stiffer than pure chitin, and is tougher and less brittle than pure [[calcium carbonate]].<ref name="Campbell">Campbell, N. A. (1996) ''Biology'' (4th edition) Benjamin Cummings, New Work. p.69 {{ISBN|0-8053-1957-3}}</ref> Another difference between pure and composite forms can be seen by comparing the flexible body wall of a [[caterpillar]] (mainly chitin) to the stiff, light [[elytron]] of a [[beetle]] (containing a large proportion of [[sclerotin]]).<ref>{{cite book | author = Gilbert, Lawrence I. | title = Insect development : morphogenesis, molting and metamorphosis | publisher = Elsevier/Academic Press | location = Amsterdam Boston | year = 2009 | isbn = 978-0-12-375136-2 }}</ref>
In its pure, unmodified form, chitin is translucent, pliable, resilient, and quite tough. In most [[arthropod]]s, however, it is often modified, occurring largely as a component of [[composite material]]s, such as in [[sclerotin]], a tanned [[protein]]aceous matrix, which forms much of the [[exoskeleton]] of [[insect]]s. Combined with [[calcium carbonate]], as in the shells of [[crustacean]]s and [[mollusc]]s, chitin produces a much stronger composite. This composite material is much harder and stiffer than pure chitin, and is tougher and less brittle than pure [[calcium carbonate]].<ref name="Campbell">Campbell, N. A. (1996) ''Biology'' (4th edition) Benjamin Cummings, New Work. p.69 {{ISBN|0-8053-1957-3}}</ref> Another difference between pure and composite forms can be seen by comparing the flexible body wall of a [[caterpillar]] (mainly chitin) to the stiff, light [[elytron]] of a [[beetle]] (containing a large proportion of [[sclerotin]]).<ref>{{cite book | author = Gilbert, Lawrence I. | title = Insect development: morphogenesis, molting and metamorphosis | publisher = Elsevier/Academic Press | location = Amsterdam Boston | year = 2009 | isbn = 978-0-12-375136-2 }}</ref>


In butterfly wing scales, chitin is organized into stacks of [[gyroid]]s constructed of chitin [[photonic crystal]]s that produce various [[iridescent]] colors serving [[phenotype|phenotypic]] signaling and communication for mating and foraging.<ref name="wings">{{cite journal|journal=Proc Natl Acad Sci U S A|year=2010|volume=107|issue=26|pages=11676–81|doi=10.1073/pnas.0909616107|title=Structure, function, and self-assembly of single network gyroid (I4132) photonic crystals in butterfly wing scales|vauthors=Saranathan V, Osuji CO, Mochrie SG, Noh H, Narayanan S, Sandy A, Dufresne ER, Prum RO|pmid=20547870|pmc=2900708|bibcode=2010PNAS..10711676S|doi-access=free}}</ref> The elaborate chitin gyroid construction in butterfly wings creates a model of optical devices having potential for innovations in [[biomimicry]].<ref name="wings" /> [[Scarab beetle]]s in the genus ''[[Cyphochilus]]'' also utilize chitin to form extremely thin [[Scale (anatomy)|scales]] (five to fifteen [[micrometre]]s thick) that diffusely reflect white light. These scales are networks of randomly ordered filaments of chitin with diameters on the scale of hundreds of [[nanometre]]s, which serve to scatter light. The [[Scattering#Single and multiple scattering|multiple scattering]] of light is thought to play a role in the unusual whiteness of the scales.<ref>{{cite web|url=https://www.bbc.co.uk/news/science-environment-28811232|date=16 August 2014|title=Beetles' whiteness understood|author=Dasi Espuig M|publisher=BBC News: Science and Environment|access-date=15 November 2014}}</ref><ref name="Burresi">{{cite journal |first1 = Matteo |last1 = Burresi |first2 = Lorenzo |last2 = Cortese| first3 = Lorenzo |last3 = Pattelli | first4 = Mathias | last4 = Kolle | first5 = Peter | last5 = Vukusic | first6 = Diederik S. | last6 = Wiersma | first7 =  Ullrich | last7 = Steiner |first8 = Silvia | last8 = Vignolini |title=Bright-white beetle scales optimise multiple scattering of light |journal=Scientific Reports |volume = 4 |pages = 6075 |year = 2014 |doi = 10.1038/srep06075 | pmid=25123449 | pmc=4133710|bibcode = 2014NatSR...4E6075B }}</ref> In addition, some social wasps, such as ''[[Protopolybia chartergoides]]'', orally secrete material containing predominantly chitin to reinforce the outer nest envelopes, composed of paper.<ref>{{Cite journal |last1=Kudô |first1=K. |last2=Yamane |first2=Sô. |last3=Mateus |first3=S. |last4=Tsuchida |first4=K. |last5=Itô |first5=Y. |last6=Miyano |first6=S. |last7=Yamamoto |first7=H. |last8=Zucchi |first8=R. |date=2001-10-01 |title=Nest materials and some chemical characteristics of nests of a New World swarm-founding polistine wasp, Polybia paulista (Hymenoptera Vespidae) |url=https://doi.org/10.1080/08927014.2001.9522766 |journal=Ethology Ecology & Evolution |volume=13 |issue=4 |pages=351–360 |doi=10.1080/08927014.2001.9522766 |bibcode=2001EtEcE..13..351K |s2cid=86452110 |issn=0394-9370|url-access=subscription }}</ref>
In butterfly wing scales, chitin is organized into stacks of [[gyroid]]s constructed of chitin [[photonic crystal]]s that produce various [[iridescent]] colors serving [[phenotype|phenotypic]] signaling and communication for mating and foraging.<ref name="wings">{{cite journal|journal=Proc Natl Acad Sci U S A|year=2010|volume=107|issue=26|pages=11676–81|doi=10.1073/pnas.0909616107|title=Structure, function, and self-assembly of single network gyroid (I4132) photonic crystals in butterfly wing scales|vauthors=Saranathan V, Osuji CO, Mochrie SG, Noh H, Narayanan S, Sandy A, Dufresne ER, Prum RO|pmid=20547870|pmc=2900708|bibcode=2010PNAS..10711676S|doi-access=free}}</ref> The elaborate chitin gyroid construction in butterfly wings creates a model of optical devices having potential for innovations in [[biomimicry]].<ref name="wings" /> [[Scarab beetle]]s in the genus ''[[Cyphochilus]]'' also utilize chitin to form extremely thin [[Scale (anatomy)|scales]] (five to fifteen [[micrometre]]s thick) that diffusely reflect white light. These scales are networks of randomly ordered filaments of chitin with diameters on the scale of hundreds of [[nanometre]]s, which serve to scatter light. The [[Scattering#Single and multiple scattering|multiple scattering]] of light is thought to play a role in the unusual whiteness of the scales.<ref>{{cite web|url=https://www.bbc.co.uk/news/science-environment-28811232|date=16 August 2014|title=Beetles' whiteness understood|author=Dasi Espuig M|publisher=BBC News: Science and Environment|access-date=15 November 2014}}</ref><ref name="Burresi">{{cite journal |first1 = Matteo |last1 = Burresi |first2 = Lorenzo |last2 = Cortese| first3 = Lorenzo |last3 = Pattelli | first4 = Mathias | last4 = Kolle | first5 = Peter | last5 = Vukusic | first6 = Diederik S. | last6 = Wiersma | first7 =  Ullrich | last7 = Steiner |first8 = Silvia | last8 = Vignolini |title=Bright-white beetle scales optimise multiple scattering of light |journal=Scientific Reports |volume = 4 |page = 6075 |year = 2014 |doi = 10.1038/srep06075 | pmid=25123449 | pmc=4133710|bibcode = 2014NatSR...4E6075B }}</ref> In addition, some social wasps, such as ''[[Protopolybia chartergoides]]'', orally secrete material containing predominantly chitin to reinforce the outer nest envelopes, composed of paper.<ref>{{Cite journal |last1=Kudô |first1=K. |last2=Yamane |first2=Sô. |last3=Mateus |first3=S. |last4=Tsuchida |first4=K. |last5=Itô |first5=Y. |last6=Miyano |first6=S. |last7=Yamamoto |first7=H. |last8=Zucchi |first8=R. |date=2001-10-01 |title=Nest materials and some chemical characteristics of nests of a New World swarm-founding polistine wasp, Polybia paulista (Hymenoptera Vespidae) |journal=Ethology Ecology & Evolution |volume=13 |issue=4 |pages=351–360 |doi=10.1080/08927014.2001.9522766 |bibcode=2001EtEcE..13..351K |s2cid=86452110 |issn=0394-9370}}</ref>


[[Chitosan]] is produced commercially by [[deacetylation]] of chitin by treatment with [[sodium hydroxide]]. Chitosan has a wide range of biomedical applications including wound healing, drug delivery and tissue engineering.<ref name=":0" /><ref name=":1" /> Due to its specific intermolecular hydrogen bonding network, dissolving chitin in water is very difficult.<ref name=Bedian2017rev>{{cite journal|last1=Bedian|first1=L|last2=Villalba-Rodríguez|first2=AM|last3=Hernández-Vargas|first3=G|last4=Parra-Saldivar|first4=R|last5=Iqbal|first5=HM|title=Bio-based materials with novel characteristics for tissue engineering applications - A review.|journal=International Journal of Biological Macromolecules|date=May 2017|volume=98|pages=837–846|doi=10.1016/j.ijbiomac.2017.02.048|pmid=28223133}}</ref> Chitosan (with a degree of deacetylation of more than ~28%), on the other hand, can be dissolved in dilute acidic aqueous solutions below a pH of 6.0 such as acetic, formic and lactic acids. Chitosan with a degree of deacetylation greater than ~49% is soluble in water<ref>{{Cite journal |last1=Cho |first1=Yong-Woo |last2=Jang |first2=Jinho |last3=Park |first3=Chong Rae |last4=Ko |first4=Sohk-Won |date=2000-12-01 |title=Preparation and Solubility in Acid and Water of Partially Deacetylated Chitins |url=https://pubs.acs.org/doi/10.1021/bm000036j |journal=Biomacromolecules |language=en |volume=1 |issue=4 |pages=609–614 |doi=10.1021/bm000036j |pmid=11710189 |issn=1525-7797|url-access=subscription }}</ref><ref>{{Citation |last1=Rouhani Shirvan |first1=Anahita |title=5 - Recent advances in application of chitosan and its derivatives in functional finishing of textiles |date=2019-01-01 |url=https://www.sciencedirect.com/science/article/pii/B9780081024911000058 |work=The Impact and Prospects of Green Chemistry for Textile Technology |pages=107–133 |editor-last=Shahid-ul-Islam |access-date=2023-12-18 |series=The Textile Institute Book Series |publisher=Woodhead Publishing |isbn=978-0-08-102491-1 |last2=Shakeri |first2=Mina |last3=Bashari |first3=Azadeh |editor2-last=Butola |editor2-first=B. S.}}</ref>
[[Chitosan]] is produced commercially by [[deacetylation]] of chitin by treatment with [[sodium hydroxide]]. Chitosan has a wide range of biomedical applications including wound healing, drug delivery and tissue engineering.<ref name=":0" /><ref name=":1" /> Due to its specific intermolecular hydrogen bonding network, dissolving chitin in water is very difficult.<ref name=Bedian2017rev>{{cite journal|last1=Bedian|first1=L|last2=Villalba-Rodríguez|first2=AM|last3=Hernández-Vargas|first3=G|last4=Parra-Saldivar|first4=R|last5=Iqbal|first5=HM|title=Bio-based materials with novel characteristics for tissue engineering applications - A review.|journal=International Journal of Biological Macromolecules|date=May 2017|volume=98|pages=837–846|doi=10.1016/j.ijbiomac.2017.02.048|pmid=28223133}}</ref> Chitosan (with a degree of deacetylation of more than ~28%), on the other hand, can be dissolved in dilute acidic aqueous solutions below a pH of 6.0 such as acetic, formic and lactic acids. Chitosan with a degree of deacetylation greater than ~49% is soluble in water.<ref>{{Cite journal |last1=Cho |first1=Yong-Woo |last2=Jang |first2=Jinho |last3=Park |first3=Chong Rae |last4=Ko |first4=Sohk-Won |date=2000-12-01 |title=Preparation and Solubility in Acid and Water of Partially Deacetylated Chitins |url=https://pubs.acs.org/doi/10.1021/bm000036j |journal=Biomacromolecules |language=en |volume=1 |issue=4 |pages=609–614 |doi=10.1021/bm000036j |pmid=11710189 |issn=1525-7797|url-access=subscription }}</ref><ref>{{Citation |last1=Rouhani Shirvan |first1=Anahita |title=5 - Recent advances in application of chitosan and its derivatives in functional finishing of textiles |date=2019-01-01 |url=https://www.sciencedirect.com/science/article/pii/B9780081024911000058 |work=The Impact and Prospects of Green Chemistry for Textile Technology |pages=107–133 |editor-last=Shahid-ul-Islam |access-date=2023-12-18 |series=The Textile Institute Book Series |publisher=Woodhead Publishing |isbn=978-0-08-102491-1 |last2=Shakeri |first2=Mina |last3=Bashari |first3=Azadeh |editor2-last=Butola |editor2-first=B. S.}}</ref>


===Humans and other mammals===
===Humans and other mammals===
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Plants also have receptors that can cause a response to chitin, namely chitin elicitor receptor kinase 1 and chitin elicitor-binding protein.<ref name=Komi2017rev/>  The first chitin receptor was cloned in 2006.<ref name=Sanchez2015rev>{{cite journal|last1=Sánchez-Vallet|first1=A|last2=Mesters|first2=JR|last3=Thomma|first3=BP|title=The battle for chitin recognition in plant-microbe interactions.|journal=FEMS Microbiology Reviews|date=March 2015|volume=39|issue=2|pages=171–83|doi=10.1093/femsre/fuu003|pmid=25725011|issn=0168-6445|doi-access=free|hdl=20.500.11850/97275|hdl-access=free}}</ref>  When the receptors are activated by chitin, genes related to plant defense are expressed, and [[jasmonate]] hormones are activated, which in turn activate systemic defenses.<ref name=Sharp2013rev/>  [[Commensalism|Commensal]] fungi have ways to interact with the host immune response that, {{as of|2016|lc=y}}, were not well understood.<ref name=Sanchez2015rev/>
Plants also have receptors that can cause a response to chitin, namely chitin elicitor receptor kinase 1 and chitin elicitor-binding protein.<ref name=Komi2017rev/>  The first chitin receptor was cloned in 2006.<ref name=Sanchez2015rev>{{cite journal|last1=Sánchez-Vallet|first1=A|last2=Mesters|first2=JR|last3=Thomma|first3=BP|title=The battle for chitin recognition in plant-microbe interactions.|journal=FEMS Microbiology Reviews|date=March 2015|volume=39|issue=2|pages=171–83|doi=10.1093/femsre/fuu003|pmid=25725011|issn=0168-6445|doi-access=free|hdl=20.500.11850/97275|hdl-access=free}}</ref>  When the receptors are activated by chitin, genes related to plant defense are expressed, and [[jasmonate]] hormones are activated, which in turn activate systemic defenses.<ref name=Sharp2013rev/>  [[Commensalism|Commensal]] fungi have ways to interact with the host immune response that, {{as of|2016|lc=y}}, were not well understood.<ref name=Sanchez2015rev/>


Some pathogens produce chitin-binding proteins that mask the chitin they shed from these receptors.<ref name=Sharp2013rev>{{cite journal|last1=Sharp|first1=Russell G.|title=A Review of the Applications of Chitin and Its Derivatives in Agriculture to Modify Plant-Microbial Interactions and Improve Crop Yields|journal=Agronomy|date=21 November 2013|volume=3|issue=4|pages=757–793|doi=10.3390/agronomy3040757|language=en|doi-access=free}}</ref><ref>{{cite journal|last1=Rovenich|first1=H|last2=Zuccaro|first2=A|last3=Thomma|first3=BP|title=Convergent evolution of filamentous microbes towards evasion of glycan-triggered immunity.|journal=The New Phytologist|date=December 2016|volume=212|issue=4|pages=896–901|doi=10.1111/nph.14064|pmid=27329426|doi-access=free}}</ref> ''[[Zymoseptoria tritici]]'' is an example of a fungal pathogen that has such blocking proteins; it is a major pest in [[wheat]] crops.<ref name=Kettles2016rev/>
Some pathogens produce chitin-binding proteins that mask the chitin they shed from these receptors.<ref name=Sharp2013rev>{{cite journal|last1=Sharp|first1=Russell G.|title=A Review of the Applications of Chitin and Its Derivatives in Agriculture to Modify Plant-Microbial Interactions and Improve Crop Yields|journal=Agronomy|date=21 November 2013|volume=3|issue=4|pages=757–793|doi=10.3390/agronomy3040757|language=en|doi-access=free}}</ref><ref>{{cite journal|last1=Rovenich|first1=H|last2=Zuccaro|first2=A|last3=Thomma|first3=BP|title=Convergent evolution of filamentous microbes towards evasion of glycan-triggered immunity.|journal=The New Phytologist|date=December 2016|volume=212|issue=4|pages=896–901|doi=10.1111/nph.14064|pmid=27329426|doi-access=free}}</ref>


==Fossil record==
==Fossil record==
Line 59: Line 59:


=== Industrial ===
=== Industrial ===
Chitin is used in many industrial processes. Examples of the potential uses of chemically modified chitin in [[food processing]] include the formation of edible films and as an additive to thicken and stabilize foods and food emulsions.<ref>{{Cite journal|last1=Tzoumaki|first1=Maria V.|last2=Moschakis|first2=Thomas|last3=Kiosseoglou|first3=Vassilios|last4=Biliaderis|first4=Costas G.|date=August 2011|title=Oil-in-water emulsions stabilized by chitin nanocrystal particles|journal=Food Hydrocolloids|volume=25|issue=6|pages=1521–1529|doi=10.1016/j.foodhyd.2011.02.008|issn=0268-005X}}</ref><ref name=Shahidi>{{cite journal | last1 = Shahidi | first1 = F. | last2 = Arachchi | first2 = J.K.V. | last3 = Jeon | first3 = Y.-J. | year = 1999 | title = Food applications of chitin and chitosans | journal = Trends in Food Science & Technology | volume = 10 | issue = 2| pages = 37–51 | doi=10.1016/s0924-2244(99)00017-5}}</ref> Processes to [[Sizing|size]] and strengthen [[paper]] employ chitin and chitosan.<ref>{{Cite journal |last1=Hosokawa |first1=Jun |last2=Nishiyama |first2=Masashi |last3=Yoshihara |first3=Kazutoshi |last4=Kubo |first4=Takamasa |date=May 1990 |title=Biodegradable film derived from chitosan and homogenized cellulose |url=https://pubs.acs.org/doi/abs/10.1021/ie00101a015 |journal=Industrial & Engineering Chemistry Research |language=en |volume=29 |issue=5 |pages=800–805 |doi=10.1021/ie00101a015 |issn=0888-5885|url-access=subscription }}</ref><ref>{{Cite journal |last1=Gällstedt |first1=Mikael |last2=Brottman |first2=Angela |last3=Hedenqvist |first3=Mikael S. |date=July 2005 |title=Packaging-related properties of protein- and chitosan-coated paper |url=https://onlinelibrary.wiley.com/doi/10.1002/pts.685 |journal=Packaging Technology and Science |language=en |volume=18 |issue=4 |pages=161–170 |doi=10.1002/pts.685 |s2cid=96578009 |issn=0894-3214|url-access=subscription }}</ref>
Chitin is used in many industrial processes. Examples of the potential uses of chemically modified chitin in [[food processing]] include the formation of edible films and as an additive to thicken and stabilize foods and food emulsions.<ref>{{Cite journal|last1=Tzoumaki|first1=Maria V.|last2=Moschakis|first2=Thomas|last3=Kiosseoglou|first3=Vassilios|last4=Biliaderis|first4=Costas G.|date=August 2011|title=Oil-in-water emulsions stabilized by chitin nanocrystal particles|journal=Food Hydrocolloids|volume=25|issue=6|pages=1521–1529|doi=10.1016/j.foodhyd.2011.02.008|issn=0268-005X}}</ref><ref name=Shahidi>{{cite journal | last1 = Shahidi | first1 = F. | last2 = Arachchi | first2 = J.K.V. | last3 = Jeon | first3 = Y.-J. | year = 1999 | title = Food applications of chitin and chitosans | journal = Trends in Food Science & Technology | volume = 10 | issue = 2| pages = 37–51 | doi=10.1016/s0924-2244(99)00017-5}}</ref> Processes to [[Sizing|size]] and strengthen [[paper]] employ chitin and [[chitosan]].<ref>{{Cite journal |last1=Hosokawa |first1=Jun |last2=Nishiyama |first2=Masashi |last3=Yoshihara |first3=Kazutoshi |last4=Kubo |first4=Takamasa |date=May 1990 |title=Biodegradable film derived from chitosan and homogenized cellulose |url=https://pubs.acs.org/doi/abs/10.1021/ie00101a015 |journal=Industrial & Engineering Chemistry Research |language=en |volume=29 |issue=5 |pages=800–805 |doi=10.1021/ie00101a015 |issn=0888-5885|url-access=subscription }}</ref><ref>{{Cite journal |last1=Gällstedt |first1=Mikael |last2=Brottman |first2=Angela |last3=Hedenqvist |first3=Mikael S. |date=July 2005 |title=Packaging-related properties of protein- and chitosan-coated paper |url=https://onlinelibrary.wiley.com/doi/10.1002/pts.685 |journal=Packaging Technology and Science |language=en |volume=18 |issue=4 |pages=161–170 |doi=10.1002/pts.685 |s2cid=96578009 |issn=0894-3214|url-access=subscription }}</ref>


==Research==
==Research==
How chitin interacts with the [[immune system]] of plants and animals has been an active area of research, including the identity of key [[Receptor (biochemistry)|receptors]] with which chitin interacts, whether the size of chitin particles is relevant to the kind of immune response triggered, and mechanisms by which immune systems respond.<ref name="Gomez-Casado2016rev">{{Cite journal |last1=Gómez-Casado |first1=Cristina |last2=Díaz-Perales |first2=Araceli |last3=Hedenqvist |first3=Mikael S. |date=2016-10-01 |title=Allergen-Associated Immunomodulators: Modifying Allergy Outcome |url=https://doi.org/10.1007/s00005-016-0401-2 |journal=Archivum Immunologiae et Therapiae Experimentalis |language=en |volume=64 |issue=5 |pages=339–347 |doi=10.1007/s00005-016-0401-2 |issn=1661-4917 |pmid=27178664 |s2cid=15221318|url-access=subscription }}</ref><ref name=Kettles2016rev>{{cite journal|last1=Kettles|first1=GJ|last2=Kanyuka|first2=K|title=Dissecting the Molecular Interactions between Wheat and the Fungal Pathogen Zymoseptoria tritici|journal=Frontiers in Plant Science|date=15 April 2016|volume=7|pages=508|pmid=27148331|pmc=4832604|doi=10.3389/fpls.2016.00508|doi-access=free}}</ref> Chitin is deacetylated  chemically or enzymatically to produce [[chitosan]], a highly [[Biocompatibility|biocompatible]] polymer which has found a wide range of applications in the biomedical industry.<ref name=":0" /><ref>{{Cite journal |last1=Kapadnis |first1=Gaurav |last2=Dey |first2=Anomitra |last3=Dandekar |first3=Prajakta |last4=Jain |first4=Ratnesh |date=June 2019 |title=Effect of degree of deacetylation on solubility of low-molecular-weight chitosan produced via enzymatic breakdown of chitosan |url=https://onlinelibrary.wiley.com/doi/10.1002/pi.5795 |journal=Polymer International |language=en |volume=68 |issue=6 |pages=1054–1063 |doi=10.1002/pi.5795 |s2cid=104427459 |issn=0959-8103|url-access=subscription }}</ref><ref>{{Citation |last1=Desai |first1=Ranjeet |title=Review of the Structure of Chitosan in the Context of Other Sugar-Based Polymers |date=2021 |url=https://link.springer.com/10.1007/12_2021_89 |work=Chitosan for Biomaterials III |volume=287 |pages=23–74 |editor-last=Jayakumar |editor-first=R. |place=Cham |publisher=Springer International Publishing |language=en |doi=10.1007/12_2021_89 |isbn=978-3-030-83806-5 |access-date=2022-12-19 |last2=Pachpore |first2=Radhika |last3=Patil |first3=Ashwini |last4=Jain |first4=Ratnesh |last5=Dandekar |first5=Prajakta |s2cid=244341955 |editor2-last=Prabaharan |editor2-first=M.|url-access=subscription }}</ref> Chitin and chitosan have been explored as a [[vaccine adjuvant]] due to its ability to stimulate an immune response.<ref name=":0" /><ref name=Komi2017rev/>
Chitin is deacetylated  chemically or enzymatically to produce [[chitosan]], a highly [[Biocompatibility|biocompatible]] polymer which has found a wide range of applications in the biomedical industry.<ref name=":0" /><ref>{{Cite journal |last1=Kapadnis |first1=Gaurav |last2=Dey |first2=Anomitra |last3=Dandekar |first3=Prajakta |last4=Jain |first4=Ratnesh |date=June 2019 |title=Effect of degree of deacetylation on solubility of low-molecular-weight chitosan produced via enzymatic breakdown of chitosan |url=https://onlinelibrary.wiley.com/doi/10.1002/pi.5795 |journal=Polymer International |language=en |volume=68 |issue=6 |pages=1054–1063 |doi=10.1002/pi.5795 |s2cid=104427459 |issn=0959-8103|url-access=subscription }}</ref><ref>{{Citation |last1=Desai |first1=Ranjeet |title=Review of the Structure of Chitosan in the Context of Other Sugar-Based Polymers |date=2021 |url=https://link.springer.com/10.1007/12_2021_89 |work=Chitosan for Biomaterials III |volume=287 |pages=23–74 |editor-last=Jayakumar |editor-first=R. |place=Cham |publisher=Springer International Publishing |language=en |doi=10.1007/12_2021_89 |isbn=978-3-030-83806-5 |access-date=2022-12-19 |last2=Pachpore |first2=Radhika |last3=Patil |first3=Ashwini |last4=Jain |first4=Ratnesh |last5=Dandekar |first5=Prajakta |s2cid=244341955 |editor2-last=Prabaharan |editor2-first=M.|url-access=subscription }}</ref> Chitin and chitosan have been explored as a [[vaccine adjuvant]] due to its ability to stimulate an immune response.<ref name=":0" /><ref name=Komi2017rev/>


Chitin and chitosan are under development as [[Tissue engineering#Scaffolds|scaffolds]] in studies of how tissue grows and how [[Wound healing|wounds heal]], and in efforts to invent better [[bandages]], [[surgical suture|surgical thread]], and materials for [[allotransplantation]].<ref name=":0" /><ref name=Bedian2017rev/><ref>{{cite journal|pmc=4557018|year=2015|last1=Cheung|first1=R. C.|title=Chitosan: An Update on Potential Biomedical and Pharmaceutical Applications|journal=Marine Drugs|volume=13|issue=8|pages=5156–5186|last2=Ng|first2=T. B.|last3=Wong|first3=J. H.|last4=Chan|first4=W. Y.|doi=10.3390/md13085156|pmid=26287217|doi-access=free}}</ref> [[Surgical suture|Sutures]] made of chitin have been experimentally developed, but their lack of elasticity and problems making thread have prevented commercial success so far.<ref>{{cite book|editor1-last=Ducheyne|editor1-first=Paul|editor2-last=Healy|editor2-first=Kevin|editor3-last=Hutmacher|editor3-first=Dietmar E.|editor4-last=Grainger|editor4-first=David W.|editor5-last=Kirkpatrick|editor5-first=C. James|title=Comprehensive biomaterials|date=2011|publisher=Elsevier|location=Amsterdam|isbn=9780080552941|page=230|url=https://books.google.com/books?id=oa8YpRsD1kkC&pg=RA1-PA230}}</ref>
Chitin and chitosan are under development as [[Tissue engineering#Scaffolds|scaffolds]] in studies of how tissue grows and how [[Wound healing|wounds heal]], and in efforts to invent better [[bandages]], [[surgical suture|surgical thread]], and materials for [[allotransplantation]].<ref name=":0" /><ref name=Bedian2017rev/><ref>{{cite journal|pmc=4557018|year=2015|last1=Cheung|first1=R. C.|title=Chitosan: An Update on Potential Biomedical and Pharmaceutical Applications|journal=Marine Drugs|volume=13|issue=8|pages=5156–5186|last2=Ng|first2=T. B.|last3=Wong|first3=J. H.|last4=Chan|first4=W. Y.|doi=10.3390/md13085156|pmid=26287217|doi-access=free}}</ref> [[Surgical suture|Sutures]] made of chitin have been experimentally developed, but their lack of elasticity and problems making thread have prevented commercial success so far.<ref>{{cite book|editor1-last=Ducheyne|editor1-first=Paul|editor2-last=Healy|editor2-first=Kevin|editor3-last=Hutmacher|editor3-first=Dietmar E.|editor4-last=Grainger|editor4-first=David W.|editor5-last=Kirkpatrick|editor5-first=C. James|title=Comprehensive biomaterials|date=2011|publisher=Elsevier|location=Amsterdam|isbn=978-0-08-055294-1|page=230|url=https://books.google.com/books?id=oa8YpRsD1kkC&pg=RA1-PA230}}</ref>


[[Chitosan]] has been demonstrated and proposed to make a reproducible form of [[biodegradable]] plastic.<ref>{{cite web | title =Team creates bioplastic made from shrimp shells|url=https://phys.org/news/2014-05-team-bioplastic-shrimp-shells.html|date=6 May 2014|access-date=14 October 2024}}</ref> Chitin [[nanofiber]]s are extracted from crustacean waste and mushrooms for possible development of products in [[tissue engineering]], drug delivery and medicine.<ref name=":0" /><ref>{{cite journal|doi=10.3390/molecules191118367|pmid=25393598|pmc=6271128|title=Chitin and Chitosan Nanofibers: Preparation and Chemical Modifications|journal=Molecules|volume=19|issue=11|pages=18367–80|year=2014|last1=Ifuku|first1=Shinsuke|doi-access=free}}</ref>
[[Chitosan]] has been demonstrated and proposed to make a reproducible form of [[biodegradable]] plastic.<ref>{{cite web | title =Team creates bioplastic made from shrimp shells|url=https://phys.org/news/2014-05-team-bioplastic-shrimp-shells.html|date=6 May 2014|access-date=14 October 2024}}</ref> Chitin [[nanofiber]]s are extracted from crustacean waste and mushrooms for possible development of products in [[tissue engineering]], drug delivery and medicine.<ref name=":0" /><ref>{{cite journal|doi=10.3390/molecules191118367|pmid=25393598|pmc=6271128|title=Chitin and Chitosan Nanofibers: Preparation and Chemical Modifications|journal=Molecules|volume=19|issue=11|pages=18367–80|year=2014|last1=Ifuku|first1=Shinsuke|doi-access=free}}</ref>
Chitin has been proposed for use in building structures, tools, and other solid objects from a [[composite material]], combining chitin with [[Martian soil|Martian regolith]].<ref>{{Cite journal|last1=Shiwei|first1=Ng|last2=Dritsas|first2=Stylianos|last3=Fernandez|first3=Javier G.|date=September 16, 2020|title=Martian biolith: A bioinspired regolith composite for closed-loop extraterrestrial manufacturing|journal=PLOS ONE|volume=15|issue=9|pages=e0238606|doi=10.1371/journal.pone.0238606|pmid=32936806|pmc=7494075|bibcode=2020PLoSO..1538606S|doi-access=free}}</ref> To build this, the [[biopolymers]] in the chitin are suggested as the [[Binder (material)|binder]] for the regolith [[Aggregate (composite)|aggregate]] to form a [[concrete]]-like [[composite material]]. The authors believe that waste materials from food production (e.g. scales from fish, exoskeletons from crustaceans and insects, etc.) could be put to use as feedstock for manufacturing processes.


==See also==
==See also==

Latest revision as of 04:44, 1 November 2025

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File:Chitin.svg
Structure of the chitin molecule, showing two of the N-acetylglucosamine units that repeat to form long chains in β-(1→4)-linkage.
File:Haworth projection of chitin.svg
Haworth projection of the chitin molecule.
File:Glanzkaefer.jpg
A close-up of the wing of a leafhopper; the wing is composed of chitin.
File:Lyristes plebejus.jpg
A cicada emerges from its nymphal exoskeleton; the shed exoskeleton is mostly modified chitin (sclerotin) but the wings and much of the adult body are still unsclerotized chitin at this stage

Chitin (C8H13O5N)n (Template:IPAc-en Script error: No such module "Respell".) is a long-chain polymer of N-acetylglucosamine, an amide derivative of glucose. Chitin is the second most abundant polysaccharide in nature (behind only cellulose); an estimated 1 billion tons of chitin are produced each year in the biosphere.[1] It is a primary component of cell walls in fungi (especially filamentous and mushroom-forming fungi), the exoskeletons of arthropods such as crustaceans and insects, the radulae, cephalopod beaks and gladii of molluscs and in some nematodes and diatoms.[2][3] It is also synthesised by at least some fish and lissamphibians.[4] Commercially, chitin is extracted from the shells of crabs, shrimps, shellfish and lobsters, which are major by-products of the seafood industry.[2][3] The structure of chitin is comparable to cellulose, forming crystalline nanofibrils or whiskers. It is functionally comparable to the protein keratin. Chitin has proved useful for several medicinal, industrial and biotechnological purposes.[3][5]

Etymology

The English word "chitin" comes from the French word chitine, which was derived in 1821 from the Greek word χιτών (khitōn) meaning covering.[6]

A similar word, "chiton", refers to a marine animal with a protective shell.

Chemistry, physical properties and biological function

File:Chitin glucose and cellulose.svg
Chemical configurations of the different monosaccharides (glucose and N-acetylglucosamine) and polysaccharides (chitin and cellulose) presented in Haworth projection

The structure of chitin was determined by Albert Hofmann in 1929. Hofmann hydrolyzed chitin using a crude preparation of the enzyme chitinase, which he obtained from the snail Helix pomatia.[7][8][9]

Chitin is a modified polysaccharide that contains nitrogen; it is synthesized from units of N-acetyl-D-glucosamine (to be precise, 2-(acetylamino)-2-deoxy-D-glucose). These units form covalent β-(1→4)-linkages (like the linkages between glucose units forming cellulose). Therefore, chitin may be described as cellulose with one hydroxyl group on each monomer replaced with an acetyl amine group. This allows for increased hydrogen bonding between adjacent polymers, giving the chitin-polymer matrix increased strength.

In its pure, unmodified form, chitin is translucent, pliable, resilient, and quite tough. In most arthropods, however, it is often modified, occurring largely as a component of composite materials, such as in sclerotin, a tanned proteinaceous matrix, which forms much of the exoskeleton of insects. Combined with calcium carbonate, as in the shells of crustaceans and molluscs, chitin produces a much stronger composite. This composite material is much harder and stiffer than pure chitin, and is tougher and less brittle than pure calcium carbonate.[10] Another difference between pure and composite forms can be seen by comparing the flexible body wall of a caterpillar (mainly chitin) to the stiff, light elytron of a beetle (containing a large proportion of sclerotin).[11]

In butterfly wing scales, chitin is organized into stacks of gyroids constructed of chitin photonic crystals that produce various iridescent colors serving phenotypic signaling and communication for mating and foraging.[12] The elaborate chitin gyroid construction in butterfly wings creates a model of optical devices having potential for innovations in biomimicry.[12] Scarab beetles in the genus Cyphochilus also utilize chitin to form extremely thin scales (five to fifteen micrometres thick) that diffusely reflect white light. These scales are networks of randomly ordered filaments of chitin with diameters on the scale of hundreds of nanometres, which serve to scatter light. The multiple scattering of light is thought to play a role in the unusual whiteness of the scales.[13][14] In addition, some social wasps, such as Protopolybia chartergoides, orally secrete material containing predominantly chitin to reinforce the outer nest envelopes, composed of paper.[15]

Chitosan is produced commercially by deacetylation of chitin by treatment with sodium hydroxide. Chitosan has a wide range of biomedical applications including wound healing, drug delivery and tissue engineering.[2][3] Due to its specific intermolecular hydrogen bonding network, dissolving chitin in water is very difficult.[16] Chitosan (with a degree of deacetylation of more than ~28%), on the other hand, can be dissolved in dilute acidic aqueous solutions below a pH of 6.0 such as acetic, formic and lactic acids. Chitosan with a degree of deacetylation greater than ~49% is soluble in water.[17][18]

Humans and other mammals

Humans and other mammals have chitinase and chitinase-like proteins that can degrade chitin; they also possess several immune receptors that can recognize chitin and its degradation products, initiating an immune response.[19]

Chitin is sensed mostly in the lungs or gastrointestinal tract where it can activate the innate immune system through eosinophils or macrophages, as well as an adaptive immune response through T helper cells.[19] Keratinocytes in skin can also react to chitin or chitin fragments.[19]

Plants

Plants also have receptors that can cause a response to chitin, namely chitin elicitor receptor kinase 1 and chitin elicitor-binding protein.[19] The first chitin receptor was cloned in 2006.[20] When the receptors are activated by chitin, genes related to plant defense are expressed, and jasmonate hormones are activated, which in turn activate systemic defenses.[21] Commensal fungi have ways to interact with the host immune response that, since 2016Template:Dated maintenance category (articles)Script error: No such module "Check for unknown parameters"., were not well understood.[20]

Some pathogens produce chitin-binding proteins that mask the chitin they shed from these receptors.[21][22]

Fossil record

Script error: No such module "For". Chitin was probably present in the exoskeletons of Cambrian arthropods such as trilobites. The oldest preserved (intact) chitin samples thus far reported are dated to the Oligocene, about 25 million years ago, from specimens encased in amber where the chitin has not completely degraded.[23]

Uses

Agriculture

Chitin is a good inducer of plant defense mechanisms for controlling diseases.[24] It has potential for use as a soil fertilizer or conditioner to improve fertility and plant resilience that may enhance crop yields.[25][26]

Industrial

Chitin is used in many industrial processes. Examples of the potential uses of chemically modified chitin in food processing include the formation of edible films and as an additive to thicken and stabilize foods and food emulsions.[27][28] Processes to size and strengthen paper employ chitin and chitosan.[29][30]

Research

Chitin is deacetylated chemically or enzymatically to produce chitosan, a highly biocompatible polymer which has found a wide range of applications in the biomedical industry.[2][31][32] Chitin and chitosan have been explored as a vaccine adjuvant due to its ability to stimulate an immune response.[2][19]

Chitin and chitosan are under development as scaffolds in studies of how tissue grows and how wounds heal, and in efforts to invent better bandages, surgical thread, and materials for allotransplantation.[2][16][33] Sutures made of chitin have been experimentally developed, but their lack of elasticity and problems making thread have prevented commercial success so far.[34]

Chitosan has been demonstrated and proposed to make a reproducible form of biodegradable plastic.[35] Chitin nanofibers are extracted from crustacean waste and mushrooms for possible development of products in tissue engineering, drug delivery and medicine.[2][36]

See also

References

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  1. ↑ Script error: No such module "citation/CS1".
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  5. ↑ Script error: No such module "Citation/CS1".
  6. ↑ Script error: No such module "Citation/CS1".
  7. ↑ Template:Cite thesis
  8. ↑ Script error: No such module "Citation/CS1".
  9. ↑ Script error: No such module "Citation/CS1".
  10. ↑ Campbell, N. A. (1996) Biology (4th edition) Benjamin Cummings, New Work. p.69 Template:ISBN
  11. ↑ Script error: No such module "citation/CS1".
  12. ↑ a b Script error: No such module "Citation/CS1".
  13. ↑ Script error: No such module "citation/CS1".
  14. ↑ Script error: No such module "Citation/CS1".
  15. ↑ Script error: No such module "Citation/CS1".
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  17. ↑ Script error: No such module "Citation/CS1".
  18. ↑ Script error: No such module "citation/CS1".
  19. ↑ a b c d e Script error: No such module "Citation/CS1".
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  26. ↑ Script error: No such module "Citation/CS1".
  27. ↑ Script error: No such module "Citation/CS1".
  28. ↑ Script error: No such module "Citation/CS1".
  29. ↑ Script error: No such module "Citation/CS1".
  30. ↑ Script error: No such module "Citation/CS1".
  31. ↑ Script error: No such module "Citation/CS1".
  32. ↑ Script error: No such module "citation/CS1".
  33. ↑ Script error: No such module "Citation/CS1".
  34. ↑ Script error: No such module "citation/CS1".
  35. ↑ Script error: No such module "citation/CS1".
  36. ↑ Script error: No such module "Citation/CS1".

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External links

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