Chitosan
Encyclopedia
Chitosan is a linear polysaccharide
composed of randomly distributed β-(1-4)-linked D-glucosamine (deacetylated unit) and N-acetyl-D-glucosamine
(acetylated unit). It has a number of commercial and possible biomedical uses.
Chitosan is produced commercially by deacetylation
of chitin
, which is the structural element in the exoskeleton
of crustaceans (such as crabs and shrimp) and cell walls of fungi. The degree of deacetylation (%DD) can be determined by NMR spectroscopy
, and the %DD in commercial chitosans ranges from 60 to 100%. On average, the molecular weight of commercially produced chitosan is between 3800 and 20,000 Daltons
. A common method for the synthesis of chitosan is the deacetylation of chitin using sodium hydroxide in excess as a reagent and water as a solvent. This reaction pathway, when allowed to go to completion (complete deacetylation) yields up to 98% product.
The amino group in chitosan has a pKa value of ~6.5, which leads to a protonation in acidic to neutral solution with a charge density dependent on pH and the %DA-value. This makes chitosan water soluble and a bioadhesive which readily binds to negatively charged surfaces such as mucosal membranes. Chitosan enhances the transport of polar drugs
across epithelial surfaces, and is biocompatible
and biodegradable. Purified quantities of chitosans are available for biomedical applications.
Chitosan and its derivatives, such as trimethylchitosan (where the amino group has been trimethylated), have been used in nonviral gene delivery. Trimethylchitosan, or quaternised chitosan, has been shown to transfect
breast cancer cells, with increased degree of trimethylation increasing the cytotoxicity; at approximately 50% trimethylation, the derivative is the most efficient at gene delivery. Oligomeric derivatives (3-6 kDa) are relatively nontoxic and have good gene delivery properties.
, chitosan is used primarily as a natural seed treatment and plant growth enhancer, and as an ecologically friendly biopesticide
substance that boosts the innate ability of plants to defend themselves against fungal infections. The natural biocontrol
active ingredients, chitin/chitosan, are found in the shells of crustaceans, such as lobster
s, crab
s, and shrimp
, and many other organisms, including insects and fungi. It is one of the most abundant biodegradable materials in the world. Degraded molecules of chitin/chitosan exist in soil and water. Chitosan applications for plants and crops are regulated by the EPA, and the USDA National Organic Program
regulates its use on organic certified farms and crops. EPA-approved, biodegradable chitosan products are allowed for use outdoors and indoors on plants and crops grown commercially and by consumers. The natural biocontrol ability of chitosan should not be confused with the effects of fertilizers or pesticides upon plants or the environment. Chitosan active biopesticides represent a new tier of cost-effective biological control of crops for agriculture and horticulture. The biocontrol mode of action of chitosan elicits natural innate defense responses within plant to resist insects, pathogens, and soil-borne diseases when applied to foliage or the soil. Chitosan increases photosynthesis, promotes and enhances plant growth, stimulates nutrient uptake, increases germination and sprouting, and boosts plant vigor. When used as seed treatment or seed coating on cotton, corn, seed potatoes, soybeans, sugar beets, tomatoes, wheat and many other seeds, it elicits an innate immunity response in developing roots which destroys parasitic cyst nematodes without harming beneficial nematodes and organisms. Agricultural applications of chitosan can reduce environmental stress due to drought and soil deficiencies, strengthen seed vitality, improve stand quality, increase yields, and reduce fruit decay of vegetables, fruits and citrus crops (see photo right). Horticultural applications of chitosan increases blooms and extends the life of cut flowers and Christmas trees. The US Forest Service has conducted research on chitosan to control pathogens in pine trees. and chitosan's ability to increase pine tree resin pitch outflow by 40% to resist pine beetle infestation.
Chitosan has a rich history of being researched for applications in agriculture and horticulture dating back to the 1980s. By 1989, Bentech Labs patented chitosan salt solutions applied to crops for improved freeze protection or to crop seed for seed priming. Shortly thereafter, Bentech's chitosan salt received the first ever biopesticide
label from the EPA. Numerous other chitosan patents for plants soon followed. Chitosan applications to protect plants have been used in space, as well. NASA first flew a chitosan experiment to protect adzuki beans grown aboard the space shuttle and Mir space station in 1997 (see photo left). NASA results revealed chitosan induces increased growth (biomass) and pathogen resistance due to elevated levels of beta 1-3 glucanase enzymes within plant cells. NASA confirmed chitosan elicits the same effect in plants on earth. Over 20 years of research and development by DuPont/ConAgra Ventures (DCV) and AgriHouse, Inc have gone into developing nontoxic, low molecular weight chitosan polymer solutions safe enough for broad-spectrum agricultural and horticultural use. In 2008, AgriHouse, Inc, Denver (Berthoud), Colorado, was granted EPA natural broad-spectrum elicitor status for YEA! Yield Enhancing Agent, a liquid solution containing an ultralow molecular active ingredient of 0.25% chitosan. YEA! is a next-generation, natural chitosan elicitor solution for agriculture and horticultural uses, and was granted an amended label for foliar and irrigation applications by the EPA in June, 2009. A milliliter of YEA! contains over 14.4 X 10¹³ bioactive, low molecular weight chitosan molecules, and it is 600 times more effective than common chitosan. Given its low potential for toxicity and its abundance in the natural environment, chitosan does not harm people, pets, wildlife, or the environment when used according to label directions. Agricultural chitosan facts are located on USDA and EPA web sites.
The US Forest Service tested chitosan as an ecofriendly biopesticide, to prearm pine trees to defend themselves against mountain pine beetle
s.
Chitosan is an important additive in the filtration process. Sand filtration apparently can remove up to 50% of the turbidity
alone, while the chitosan with sand filtration removes up to 99% turbidity
. Chitosan has been used to precipitate caseins from bovine milk and cheese making. http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6T7C-478GXJ6-5&_user=10&_rdoc=1&_fmt=&_orig=search&_sort=d&view=c&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=8596d416c811c30e6151b28c78d6474ehttp://jds.fass.org/cgi/content/abstract/84/2/361
Chitosan is also useful in other filtration situations, where one may need to remove suspended particles from a liquid. In combination with bentonite
, gelatin
, silica gel
, isinglass
, or other fining agents, it is used to clarify wine
, mead
, and beer
. Added late in the brewing process, chitosan improves flocculation
, and removes yeast cells, fruit particles, and other detritus that cause hazy wine. Chitosan combined with colloid
al silica is becoming a popular fining agent for white wines, because chitosan does not require acidic tannin
s (found primarily in red wines) with which to flocculate.
coating that heals its own scratches when exposed to sunlight, offering the promise of scratch-free cars and other products. The self-healing coating uses chitosan incorporated into traditional polymer materials, such as those used in coatings on cars, to protect paint. When a scratch damages the chemical structure, the chitosan responds to ultraviolet light by forming chemical chains that begin bonding with other materials in the substance, eventually smoothing the scratch. The process can take less than an hour.
Marek W. Urban, a scientist working on this project, said the polymer can only repair itself in the same spot once, and would not work after repeated scratches. Whether this technology can be applied to industrial materials, however, depends on a number of factors (long-term persistence of "healability", stiffness and heat resistance of coating, knowledge of the exact mechanism of healing, etc.) not present initial studies; further investigation into these factors can potentially take decades to rectify.
to quickly stop bleeding and to reduce blood loss, and result in 100% survival of otherwise lethal arterial wounds in swine. Chitosan hemostatic products reduce blood loss in comparison to gauze dressings and increase patient survival. Chitosan hemostatic products have been sold to the U.S. Army
and are currently used by the UK military. Both the US and UK have already used the bandages on the battlefields of Iraq
and Afghanistan
. Chitosan is hypoallergenic and has natural antibacterial properties, which further support its use in field bandages.
Chitosan's properties also allow it to be used in transdermal drug delivery; it is mucoadhesive in nature, reactive (so it can be produced in many different forms), and most importantly, its positive charge under acidic conditions. This positive charge comes from protonation of its free amino groups. Lack of a positive charge means chitosan is insoluble in neutral and basic environments. However, in acidic environments, protonation of the amino groups leads to an increase in solubility. The implications of this are very important to biomedical applications. This molecule will maintain its structure in a neutral environment, but will solubilize and degrade in an acidic environment. This means chitosan can be used to transport a drug to an acidic environment, where the chitosan packaging will then degrade, releasing the drug to the desired environment. One example of this drug delivery has been the transport of insulin.
s to two companies who made inappropriate claims, according to the regulator. Although detractors claim using chitosan may have the deleterious effect of rendering ineffective certain minerals found in foodstuffs, several animal studies contradicted this statement by showing no or little effect. In mice, dietary ingestion of chitosan did not depress the level of iron, zinc or copper. Moreover, there is no proof of any adverse events, in particular regarding nutrient absorption, in humans.
(the second-most-common dietary fiber, after cellulose). Studies have shown chitosan has the following properties:
Polysaccharide
Polysaccharides are long carbohydrate molecules, of repeated monomer units joined together by glycosidic bonds. They range in structure from linear to highly branched. Polysaccharides are often quite heterogeneous, containing slight modifications of the repeating unit. Depending on the structure,...
composed of randomly distributed β-(1-4)-linked D-glucosamine (deacetylated unit) and N-acetyl-D-glucosamine
N-Acetylglucosamine
N-Acetylglucosamine is a monosaccharide derivative of glucose. It is an amide between glucosamine and acetic acid...
(acetylated unit). It has a number of commercial and possible biomedical uses.
Manufacture and properties
Acetylation
Acetylation describes a reaction that introduces an acetyl functional group into a chemical compound...
of chitin
Chitin
Chitin n is a long-chain polymer of a N-acetylglucosamine, a derivative of glucose, and is found in many places throughout the natural world...
, which is the structural element in the exoskeleton
Exoskeleton
An exoskeleton is the external skeleton that supports and protects an animal's body, in contrast to the internal skeleton of, for example, a human. In popular usage, some of the larger kinds of exoskeletons are known as "shells". Examples of exoskeleton animals include insects such as grasshoppers...
of crustaceans (such as crabs and shrimp) and cell walls of fungi. The degree of deacetylation (%DD) can be determined by NMR spectroscopy
Spectroscopy
Spectroscopy is the study of the interaction between matter and radiated energy. Historically, spectroscopy originated through the study of visible light dispersed according to its wavelength, e.g., by a prism. Later the concept was expanded greatly to comprise any interaction with radiative...
, and the %DD in commercial chitosans ranges from 60 to 100%. On average, the molecular weight of commercially produced chitosan is between 3800 and 20,000 Daltons
Atomic mass unit
The unified atomic mass unit or dalton is a unit that is used for indicating mass on an atomic or molecular scale. It is defined as one twelfth of the rest mass of an unbound neutral atom of carbon-12 in its nuclear and electronic ground state, and has a value of...
. A common method for the synthesis of chitosan is the deacetylation of chitin using sodium hydroxide in excess as a reagent and water as a solvent. This reaction pathway, when allowed to go to completion (complete deacetylation) yields up to 98% product.
The amino group in chitosan has a pKa value of ~6.5, which leads to a protonation in acidic to neutral solution with a charge density dependent on pH and the %DA-value. This makes chitosan water soluble and a bioadhesive which readily binds to negatively charged surfaces such as mucosal membranes. Chitosan enhances the transport of polar drugs
Medication
A pharmaceutical drug, also referred to as medicine, medication or medicament, can be loosely defined as any chemical substance intended for use in the medical diagnosis, cure, treatment, or prevention of disease.- Classification :...
across epithelial surfaces, and is biocompatible
Biocompatibility
Biocompatibility is related to the behavior of biomaterials in various contexts. The term may refer to specific properties of a material without specifying where or how the material is used , or to more empirical clinical success of a whole device in...
and biodegradable. Purified quantities of chitosans are available for biomedical applications.
Chitosan and its derivatives, such as trimethylchitosan (where the amino group has been trimethylated), have been used in nonviral gene delivery. Trimethylchitosan, or quaternised chitosan, has been shown to transfect
Transfection
Transfection is the process of deliberately introducing nucleic acids into cells. The term is used notably for non-viral methods in eukaryotic cells...
breast cancer cells, with increased degree of trimethylation increasing the cytotoxicity; at approximately 50% trimethylation, the derivative is the most efficient at gene delivery. Oligomeric derivatives (3-6 kDa) are relatively nontoxic and have good gene delivery properties.
Natural biocontrol and elicitor
In agricultureAgriculture
Agriculture is the cultivation of animals, plants, fungi and other life forms for food, fiber, and other products used to sustain life. Agriculture was the key implement in the rise of sedentary human civilization, whereby farming of domesticated species created food surpluses that nurtured the...
, chitosan is used primarily as a natural seed treatment and plant growth enhancer, and as an ecologically friendly biopesticide
Biopesticide
Biopesticides include "naturally occurring substances that control pests , microorganisms that control pests , and pesticidal substances produced by plants containing added genetic material or PIPs."Biopesticides are biochemical pesticides that are naturally occurring substances that control pests...
substance that boosts the innate ability of plants to defend themselves against fungal infections. The natural biocontrol
BioControl
BioControl is a peer-reviewed scientific journal published by Springer Science+Business Media covering all aspects of basic and applied research in biological control of invertebrate, vertebrate, and weed pests, and plant diseases. The journal was established in 1956 as Entomophaga and published by...
active ingredients, chitin/chitosan, are found in the shells of crustaceans, such as lobster
Lobster
Clawed lobsters comprise a family of large marine crustaceans. Highly prized as seafood, lobsters are economically important, and are often one of the most profitable commodities in coastal areas they populate.Though several groups of crustaceans are known as lobsters, the clawed lobsters are most...
s, crab
Crab
True crabs are decapod crustaceans of the infraorder Brachyura, which typically have a very short projecting "tail" , or where the reduced abdomen is entirely hidden under the thorax...
s, and shrimp
Shrimp
Shrimp are swimming, decapod crustaceans classified in the infraorder Caridea, found widely around the world in both fresh and salt water. Adult shrimp are filter feeding benthic animals living close to the bottom. They can live in schools and can swim rapidly backwards. Shrimp are an important...
, and many other organisms, including insects and fungi. It is one of the most abundant biodegradable materials in the world. Degraded molecules of chitin/chitosan exist in soil and water. Chitosan applications for plants and crops are regulated by the EPA, and the USDA National Organic Program
National Organic Program
In the United States, the National Organic Program is the federal regulatory framework governing organic food. It is also the name of the organization in the Department of Agriculture responsible for administering and enforcing the regulatory framework. The Organic Food Production Act of 1990 In...
regulates its use on organic certified farms and crops. EPA-approved, biodegradable chitosan products are allowed for use outdoors and indoors on plants and crops grown commercially and by consumers. The natural biocontrol ability of chitosan should not be confused with the effects of fertilizers or pesticides upon plants or the environment. Chitosan active biopesticides represent a new tier of cost-effective biological control of crops for agriculture and horticulture. The biocontrol mode of action of chitosan elicits natural innate defense responses within plant to resist insects, pathogens, and soil-borne diseases when applied to foliage or the soil. Chitosan increases photosynthesis, promotes and enhances plant growth, stimulates nutrient uptake, increases germination and sprouting, and boosts plant vigor. When used as seed treatment or seed coating on cotton, corn, seed potatoes, soybeans, sugar beets, tomatoes, wheat and many other seeds, it elicits an innate immunity response in developing roots which destroys parasitic cyst nematodes without harming beneficial nematodes and organisms. Agricultural applications of chitosan can reduce environmental stress due to drought and soil deficiencies, strengthen seed vitality, improve stand quality, increase yields, and reduce fruit decay of vegetables, fruits and citrus crops (see photo right). Horticultural applications of chitosan increases blooms and extends the life of cut flowers and Christmas trees. The US Forest Service has conducted research on chitosan to control pathogens in pine trees. and chitosan's ability to increase pine tree resin pitch outflow by 40% to resist pine beetle infestation.
Biopesticide
Biopesticides include "naturally occurring substances that control pests , microorganisms that control pests , and pesticidal substances produced by plants containing added genetic material or PIPs."Biopesticides are biochemical pesticides that are naturally occurring substances that control pests...
label from the EPA. Numerous other chitosan patents for plants soon followed. Chitosan applications to protect plants have been used in space, as well. NASA first flew a chitosan experiment to protect adzuki beans grown aboard the space shuttle and Mir space station in 1997 (see photo left). NASA results revealed chitosan induces increased growth (biomass) and pathogen resistance due to elevated levels of beta 1-3 glucanase enzymes within plant cells. NASA confirmed chitosan elicits the same effect in plants on earth. Over 20 years of research and development by DuPont/ConAgra Ventures (DCV) and AgriHouse, Inc have gone into developing nontoxic, low molecular weight chitosan polymer solutions safe enough for broad-spectrum agricultural and horticultural use. In 2008, AgriHouse, Inc, Denver (Berthoud), Colorado, was granted EPA natural broad-spectrum elicitor status for YEA! Yield Enhancing Agent, a liquid solution containing an ultralow molecular active ingredient of 0.25% chitosan. YEA! is a next-generation, natural chitosan elicitor solution for agriculture and horticultural uses, and was granted an amended label for foliar and irrigation applications by the EPA in June, 2009. A milliliter of YEA! contains over 14.4 X 10¹³ bioactive, low molecular weight chitosan molecules, and it is 600 times more effective than common chitosan. Given its low potential for toxicity and its abundance in the natural environment, chitosan does not harm people, pets, wildlife, or the environment when used according to label directions. Agricultural chitosan facts are located on USDA and EPA web sites.
The US Forest Service tested chitosan as an ecofriendly biopesticide, to prearm pine trees to defend themselves against mountain pine beetle
Mountain pine beetle
The mountain pine beetle Dendroctonus ponderosae, is a species of bark beetle native to the forests of western North America from Mexico to central British Columbia. It has a hard black exoskeleton, and measures about 5 millimeters, about the size of a grain of rice.Mountain pine beetles inhabit...
s.
Water filtration
Chitosan can also be used in water processing engineering as a part of a filtration process. Chitosan causes the fine sediment particles to bind together, and is subsequently removed with the sediment during sand filtration. It also removes phosphorus, heavy minerals, and oils from the water.Chitosan is an important additive in the filtration process. Sand filtration apparently can remove up to 50% of the turbidity
Turbidity
Turbidity is the cloudiness or haziness of a fluid caused by individual particles that are generally invisible to the naked eye, similar to smoke in air. The measurement of turbidity is a key test of water quality....
alone, while the chitosan with sand filtration removes up to 99% turbidity
Turbidity
Turbidity is the cloudiness or haziness of a fluid caused by individual particles that are generally invisible to the naked eye, similar to smoke in air. The measurement of turbidity is a key test of water quality....
. Chitosan has been used to precipitate caseins from bovine milk and cheese making. http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6T7C-478GXJ6-5&_user=10&_rdoc=1&_fmt=&_orig=search&_sort=d&view=c&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=8596d416c811c30e6151b28c78d6474ehttp://jds.fass.org/cgi/content/abstract/84/2/361
Chitosan is also useful in other filtration situations, where one may need to remove suspended particles from a liquid. In combination with bentonite
Bentonite
Bentonite is an absorbent aluminium phyllosilicate, essentially impure clay consisting mostly of montmorillonite. There are different types of bentonite, each named after the respective dominant element, such as potassium , sodium , calcium , and aluminum . Experts debate a number of nomenclatorial...
, gelatin
Gelatin
Gelatin is a translucent, colorless, brittle , flavorless solid substance, derived from the collagen inside animals' skin and bones. It is commonly used as a gelling agent in food, pharmaceuticals, photography, and cosmetic manufacturing. Substances containing gelatin or functioning in a similar...
, silica gel
Silica gel
Silica gel is a granular, vitreous, porous form of silica made synthetically from sodium silicate. Despite its name, silica gel is a solid. It is a naturally occurring mineral that is purified and processed into either granular or beaded form...
, isinglass
Isinglass
Isinglass is a substance obtained from the dried swim bladders of fish. It is a form of collagen used mainly for the clarification of wine and beer. It can also be cooked into a paste for specialized gluing purposes....
, or other fining agents, it is used to clarify wine
Wine
Wine is an alcoholic beverage, made of fermented fruit juice, usually from grapes. The natural chemical balance of grapes lets them ferment without the addition of sugars, acids, enzymes, or other nutrients. Grape wine is produced by fermenting crushed grapes using various types of yeast. Yeast...
, mead
Mead
Mead , also called honey wine, is an alcoholic beverage that is produced by fermenting a solution of honey and water. It may also be produced by fermenting a solution of water and honey with grain mash, which is strained immediately after fermentation...
, and beer
Beer
Beer is the world's most widely consumed andprobably oldest alcoholic beverage; it is the third most popular drink overall, after water and tea. It is produced by the brewing and fermentation of sugars, mainly derived from malted cereal grains, most commonly malted barley and malted wheat...
. Added late in the brewing process, chitosan improves flocculation
Flocculation
Flocculation, in the field of chemistry, is a process wherein colloids come out of suspension in the form of floc or flakes by the addition of a clarifying agent. The action differs from precipitation in that, prior to flocculation, colloids are merely suspended in a liquid and not actually...
, and removes yeast cells, fruit particles, and other detritus that cause hazy wine. Chitosan combined with colloid
Colloid
A colloid is a substance microscopically dispersed evenly throughout another substance.A colloidal system consists of two separate phases: a dispersed phase and a continuous phase . A colloidal system may be solid, liquid, or gaseous.Many familiar substances are colloids, as shown in the chart below...
al silica is becoming a popular fining agent for white wines, because chitosan does not require acidic tannin
Tannin
A tannin is an astringent, bitter plant polyphenolic compound that binds to and precipitates proteins and various other organic compounds including amino acids and alkaloids.The term tannin refers to the use of...
s (found primarily in red wines) with which to flocculate.
Potential industrial use
Scientists have recently developed a polyurethanePolyurethane
A polyurethane is any polymer composed of a chain of organic units joined by carbamate links. Polyurethane polymers are formed through step-growth polymerization, by reacting a monomer with another monomer in the presence of a catalyst.Polyurethanes are...
coating that heals its own scratches when exposed to sunlight, offering the promise of scratch-free cars and other products. The self-healing coating uses chitosan incorporated into traditional polymer materials, such as those used in coatings on cars, to protect paint. When a scratch damages the chemical structure, the chitosan responds to ultraviolet light by forming chemical chains that begin bonding with other materials in the substance, eventually smoothing the scratch. The process can take less than an hour.
Marek W. Urban, a scientist working on this project, said the polymer can only repair itself in the same spot once, and would not work after repeated scratches. Whether this technology can be applied to industrial materials, however, depends on a number of factors (long-term persistence of "healability", stiffness and heat resistance of coating, knowledge of the exact mechanism of healing, etc.) not present initial studies; further investigation into these factors can potentially take decades to rectify.
Biomedical uses
Chitosan's properties allow it to rapidly clot blood, and has recently gained approval in the United States and Europe for use in bandages and other hemostatic agents. Chitosan hemostatic products have been shown in testing by the U.S. Marine CorpsUnited States Marine Corps
The United States Marine Corps is a branch of the United States Armed Forces responsible for providing power projection from the sea, using the mobility of the United States Navy to deliver combined-arms task forces rapidly. It is one of seven uniformed services of the United States...
to quickly stop bleeding and to reduce blood loss, and result in 100% survival of otherwise lethal arterial wounds in swine. Chitosan hemostatic products reduce blood loss in comparison to gauze dressings and increase patient survival. Chitosan hemostatic products have been sold to the U.S. Army
United States Army
The United States Army is the main branch of the United States Armed Forces responsible for land-based military operations. It is the largest and oldest established branch of the U.S. military, and is one of seven U.S. uniformed services...
and are currently used by the UK military. Both the US and UK have already used the bandages on the battlefields of Iraq
Iraq
Iraq ; officially the Republic of Iraq is a country in Western Asia spanning most of the northwestern end of the Zagros mountain range, the eastern part of the Syrian Desert and the northern part of the Arabian Desert....
and Afghanistan
Afghanistan
Afghanistan , officially the Islamic Republic of Afghanistan, is a landlocked country located in the centre of Asia, forming South Asia, Central Asia and the Middle East. With a population of about 29 million, it has an area of , making it the 42nd most populous and 41st largest nation in the world...
. Chitosan is hypoallergenic and has natural antibacterial properties, which further support its use in field bandages.
Chitosan's properties also allow it to be used in transdermal drug delivery; it is mucoadhesive in nature, reactive (so it can be produced in many different forms), and most importantly, its positive charge under acidic conditions. This positive charge comes from protonation of its free amino groups. Lack of a positive charge means chitosan is insoluble in neutral and basic environments. However, in acidic environments, protonation of the amino groups leads to an increase in solubility. The implications of this are very important to biomedical applications. This molecule will maintain its structure in a neutral environment, but will solubilize and degrade in an acidic environment. This means chitosan can be used to transport a drug to an acidic environment, where the chitosan packaging will then degrade, releasing the drug to the desired environment. One example of this drug delivery has been the transport of insulin.
Possible health benefits
Chitosan is frequently sold as tablet form at health stores as a "fat binder": It is supposed to have the capability to interact with lipids (fat) from the digestive system and limit their absorption in the body. Therefore, chitosan can be an effective complement to help lose weight during diet period or to stabilise one's weight. In the 2007 Cochrane meta-analysis, which evaluated all available clinical trials performed with chitosan on the subject of weight loss, body weight and all parameters related to cholesterol changed in favor of chitosan compared to placebo. The mean difference in body weight was −1.7 kg (range: −2.1 to −1.3) in favor of chitosan, which was statistically significant. There was no difference between chitosan and placebo concerning side effects. The various qualities (in terms of duration, sample size, doses, subject characteristics, type of diet, chitosan quality and characteristics, etc.) of the clinical trials performed to evaluate the effect of chitosan on body weight might account for some of the disparities observed in clinical trial results, and the subsequent critics regarding the real efficacy of chitosan. In an experimental model of the stomach and duodenum tract, chitosan has shown to interact with oil, which inhibited duodenal absorption and enhanced lipid excretion. However, the mechanism of interaction between chitosan and fat is not very well understood and has not been proved clinically yet. Because of this, the FDA has issued in 2004 Warning LetterFDA Warning Letter
The United States Food and Drug Adminstration defines a Warning Letter as "...a correspondence that notifies regulated industry about violations that FDA has documented during its inspections or investigations...
s to two companies who made inappropriate claims, according to the regulator. Although detractors claim using chitosan may have the deleterious effect of rendering ineffective certain minerals found in foodstuffs, several animal studies contradicted this statement by showing no or little effect. In mice, dietary ingestion of chitosan did not depress the level of iron, zinc or copper. Moreover, there is no proof of any adverse events, in particular regarding nutrient absorption, in humans.
Medical research
Chitosan is currently the focus of much medical research, as it is a polyglucosamineGlucosamine
Glucosamine is an amino sugar and a prominent precursor in the biochemical synthesis of glycosylated proteins and lipids. Glucosamine is part of the structure of the polysaccharides chitosan and chitin, which compose the exoskeletons of crustaceans and other arthropods, cell walls in fungi and...
(the second-most-common dietary fiber, after cellulose). Studies have shown chitosan has the following properties:
- As a soluble dietary fiberDietary fiberDietary fiber, dietary fibre, or sometimes roughage is the indigestible portion of plant foods having two main components:* soluble fiber that is readily fermented in the colon into gases and physiologically active byproducts, and* insoluble fiber that is metabolically inert, absorbing water as it...
, it increases gastrointestinal lumenLumen (anatomy)A lumen in biology is the inside space of a tubular structure, such as an artery or intestine...
viscosity and slows down the emptying of the stomach. - It alters bile acidBile acidBile acids are steroid acids found predominantly in the bile of mammals. Bile salts are bile acids compounded with a cation, usually sodium. In humans, the salts of taurocholic acid and glycocholic acid represent approximately eighty percent of all bile salts. The two major bile acids are cholic...
composition, increasing the excretionExcretionExcretion is the process by which waste products of metabolism and other non-useful materials are eliminated from an organism. This is primarily carried out by the lungs, kidneys and skin. This is in contrast with secretion, where the substance may have specific tasks after leaving the cell...
of sterolSterolSterols, also known as steroid alcohols, are a subgroup of the steroids and an important class of organic molecules. They occur naturally in plants, animals, and fungi, with the most familiar type of animal sterol being cholesterol...
s and reducing the digestibility of ilealIleumThe ileum is the final section of the small intestine in most higher vertebrates, including mammals, reptiles, and birds. In fish, the divisions of the small intestine are not as clear and the terms posterior intestine or distal intestine may be used instead of ileum.The ileum follows the duodenum...
fats. It is unclear how chitosan does this, but the currently favored hypotheses involve the increase of intestinal viscosity or bileBileBile or gall is a bitter-tasting, dark green to yellowish brown fluid, produced by the liver of most vertebrates, that aids the process of digestion of lipids in the small intestine. In many species, bile is stored in the gallbladder and upon eating is discharged into the duodenum...
acid-binding capacity.- Chitosan is relatively insoluble in water, but can be dissolved by dilute acids, which would make it a highly-viscous dietary fiber. Such fibers might inhibit the uptake of dietary lipids by increasing the thickness of the boundary layer of the intestinal lumenLumen (anatomy)A lumen in biology is the inside space of a tubular structure, such as an artery or intestine...
, which has been observed in animal experiments. - Having very few acetyl groups, chitosan contains cationic groups. This may cause chitosan to have bile acid-binding capacity, which causes mixed micelleMicelleA micelle is an aggregate of surfactant molecules dispersed in a liquid colloid. A typical micelle in aqueous solution forms an aggregate with the hydrophilic "head" regions in contact with surrounding solvent, sequestering the hydrophobic single tail regions in the micelle centre. This phase is...
s to be entrapped or disintegrated in the duodenumDuodenumThe duodenum is the first section of the small intestine in most higher vertebrates, including mammals, reptiles, and birds. In fish, the divisions of the small intestine are not as clear and the terms anterior intestine or proximal intestine may be used instead of duodenum...
and ileumIleumThe ileum is the final section of the small intestine in most higher vertebrates, including mammals, reptiles, and birds. In fish, the divisions of the small intestine are not as clear and the terms posterior intestine or distal intestine may be used instead of ileum.The ileum follows the duodenum...
. This would interrupt bile acid circulation, causing reduced lipid absorption and increased sterol excretion, which has also been observed in animal experiments.
- Chitosan is relatively insoluble in water, but can be dissolved by dilute acids, which would make it a highly-viscous dietary fiber. Such fibers might inhibit the uptake of dietary lipids by increasing the thickness of the boundary layer of the intestinal lumen
External links
- Crab chemical could give cars a self-healing "shell" — Video of self-healing action
- Information about chitosan properties and research and development projects (Heppe Medical Chitosan)
- Chitosan: Revolutionizing Weight Loss? — Jamie Fritch's opinion of chitosan
- The Chitosanase Web Page — dedicated to the enzymatic hydrolysisHydrolysisHydrolysis is a chemical reaction during which molecules of water are split into hydrogen cations and hydroxide anions in the process of a chemical mechanism. It is the type of reaction that is used to break down certain polymers, especially those made by condensation polymerization...
of chitosan. - Battlefield Band-Aids — "But now, scientists have created a bandage that is actually able to clot a bullet wound in less than a minute. The bandages are laced with a mixture of ground shrimp shells and vinegar, a concoction that has been found to clot blood instantly. The key ingredient in the shrimp shells is called chitosan."
- Is Chitosan a "Fat Magnet"? — A critical look on the claims how chitosan can be used for weight management
- Crab Glue (08/05/2008) — Catalyst (an ABC-TV Program) looked at chitosan's potential as a surgical adhesive in theatre.
- Chitosan for emergency bleeding — more information on emergency bleeding products made with Chitosan.
- Absorbitol - an alternative name for Chitosan — Research led information on Absorbitol and its uses as a nutritional supplement