Bioadhesives
Encyclopedia
Bioadhesives are natural polymer
ic materials that act as adhesives. The term is sometimes used more loosely to describe a glue formed synthetically
from biological monomers such as sugars, or to mean a synthetic material designed to adhere to biological tissue
.
Bioadhesives may consist of a variety of substances, but protein
s and carbohydrate
s feature prominently. Proteins such as gelatin
and carbohydrates such as starch
have been used as general-purpose glues by man for many years, but typically their performance shortcomings have seen them replaced by synthetic alternatives. Highly effective adhesives found in the natural world are currently under investigation but not yet in widespread commercial use. For example, bioadhesives secreted by microbes and by marine molluscs and crustaceans are being researched with a view to biomimicry
.
Bioadhesives are of commercial interest because they tend to be biocompatible, i.e. useful for biomedical
applications involving skin or other body tissue. Some work in wet environments and under water, while others can stick to low surface energy – non-polar
surfaces like plastics. In recent years, the synthetic adhesives industry has been impacted by environmental concerns
and health and safety issues relating to hazardous ingredients, volatile organic compound
emissions, and difficulties in recycling or remediating adhesives derived from petrochemical
feedstocks. Rising oil
prices may also stimulate commercial interest in biological alternatives to synthetic adhesives.
Some bioadhesives are very strong. For example, adult barnacles achieve pull-off forces as high as 2 MPa
(2 N/mm2).
Silk
dope can also be used as a glue by arachnids and insects.
-like slimes to create Stefan Adhesion, which makes pull-off much harder than lateral drag; this allows both attachment and mobility. Spores, embryos and juvenile forms may use temporary adhesives (often glycoproteins) to secure their initial attachment to surfaces favorable for colonization. Tacky and elastic secretions that act as pressure sensitive adhesive
s, forming immediate attachments on contact, are preferable in the context of self-defense and predation
. Molecular mechanisms include non-covalent interactions and polymer chain entanglement. Many biopolymers - proteins, carbohydrates, glycoprotein
s, and mucopolysaccharides - may be used to form hydrogels that contribute to temporary adhesion.
l foam of the mantis
) are generated by a "mix to activate" process that involves hardening via covalent cross-linking. On non-polar surfaces the adhesive mechanisms may include van der Waals force
s, whereas on polar
surfaces mechanisms such as hydrogen bonding and binding to (or forming bridges via) metal
cations may allow higher sticking forces to be achieved.
L-DOPA is a tyrosine
residue that bears an additional hydroxyl
group. The twin hydroxyl groups in each side-chain compete well with water for binding to surfaces, form polar attachments via hydrogen bonds, and chelate the metals in mineral
surfaces. The Fe(L-DOPA3) complex can itself account for much cross-linking and cohesion in mussel
plaque, but in addition the iron
catalyses oxidation
of the L-DOPA to reactive quinone
free radicals, which go on to form covalent bonds.
is an early example of a bioadhesive put to practical use. Additional examples now exist, with others in development:
Several commercial methods of production are being researched:
. Adhesion of a matter to this layer is hence called mucoadhesion. Mucoadhesive agents are usually polymers containing hydrogen bonding groups that can be used in wet formulations or in dry powders for drug delivery purposes. The mechanisms behind mucoadhesion have not yet been fully elucidated, but a generally accepted theory is that close contact must first be established between the mucoadhesive agent and the mucus, followed by interpenetration of the mucoadhesive polymer and the mucin and finishing with the formation of entanglements and chemical bonds between the macromolecules . In the case of a dry polymer powder, the initial adhesion is most likely achieved by water movement from the mucosa into the formulation, which has also been shown to lead to dehydration and strengthening of the mucus layer. The subsequent formation of van der Waals, hydrogen and, in the case of a positively charged polymer, electrostatic bonds between the mucins and the hydrated polymer promotes prolonged adhesion.
Polymer
A polymer is a large molecule composed of repeating structural units. These subunits are typically connected by covalent chemical bonds...
ic materials that act as adhesives. The term is sometimes used more loosely to describe a glue formed synthetically
Chemical synthesis
In chemistry, chemical synthesis is purposeful execution of chemical reactions to get a product, or several products. This happens by physical and chemical manipulations usually involving one or more reactions...
from biological monomers such as sugars, or to mean a synthetic material designed to adhere to biological tissue
Tissue (biology)
Tissue is a cellular organizational level intermediate between cells and a complete organism. A tissue is an ensemble of cells, not necessarily identical, but from the same origin, that together carry out a specific function. These are called tissues because of their identical functioning...
.
Bioadhesives may consist of a variety of substances, but protein
Protein
Proteins are biochemical compounds consisting of one or more polypeptides typically folded into a globular or fibrous form, facilitating a biological function. A polypeptide is a single linear polymer chain of amino acids bonded together by peptide bonds between the carboxyl and amino groups of...
s and carbohydrate
Carbohydrate
A carbohydrate is an organic compound with the empirical formula ; that is, consists only of carbon, hydrogen, and oxygen, with a hydrogen:oxygen atom ratio of 2:1 . However, there are exceptions to this. One common example would be deoxyribose, a component of DNA, which has the empirical...
s feature prominently. Proteins such as 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...
and carbohydrates such as starch
Starch
Starch or amylum is a carbohydrate consisting of a large number of glucose units joined together by glycosidic bonds. This polysaccharide is produced by all green plants as an energy store...
have been used as general-purpose glues by man for many years, but typically their performance shortcomings have seen them replaced by synthetic alternatives. Highly effective adhesives found in the natural world are currently under investigation but not yet in widespread commercial use. For example, bioadhesives secreted by microbes and by marine molluscs and crustaceans are being researched with a view to biomimicry
Biomimicry
Biomimicry or biomimetics is the examination of nature, its models, systems, processes, and elements to emulate or take inspiration from in order to solve human problems. The term biomimicry and biomimetics come from the Greek words bios, meaning life, and mimesis, meaning to imitate...
.
Bioadhesives are of commercial interest because they tend to be biocompatible, i.e. useful for biomedical
Biomedical engineering
Biomedical Engineering is the application of engineering principles and design concepts to medicine and biology. This field seeks to close the gap between engineering and medicine: It combines the design and problem solving skills of engineering with medical and biological sciences to improve...
applications involving skin or other body tissue. Some work in wet environments and under water, while others can stick to low surface energy – non-polar
Chemical polarity
In chemistry, polarity refers to a separation of electric charge leading to a molecule or its chemical groups having an electric dipole or multipole moment. Polar molecules interact through dipole–dipole intermolecular forces and hydrogen bonds. Molecular polarity is dependent on the difference in...
surfaces like plastics. In recent years, the synthetic adhesives industry has been impacted by environmental concerns
Environmentalism
Environmentalism is a broad philosophy, ideology and social movement regarding concerns for environmental conservation and improvement of the health of the environment, particularly as the measure for this health seeks to incorporate the concerns of non-human elements...
and health and safety issues relating to hazardous ingredients, volatile organic compound
Volatile organic compound
Volatile organic compounds are organic chemicals that have a high vapor pressure at ordinary, room-temperature conditions. Their high vapor pressure results from a low boiling point, which causes large numbers of molecules to evaporate or sublimate from the liquid or solid form of the compound and...
emissions, and difficulties in recycling or remediating adhesives derived from petrochemical
Petrochemical
Petrochemicals are chemical products derived from petroleum. Some chemical compounds made from petroleum are also obtained from other fossil fuels, such as coal or natural gas, or renewable sources such as corn or sugar cane....
feedstocks. Rising oil
Petroleum
Petroleum or crude oil is a naturally occurring, flammable liquid consisting of a complex mixture of hydrocarbons of various molecular weights and other liquid organic compounds, that are found in geologic formations beneath the Earth's surface. Petroleum is recovered mostly through oil drilling...
prices may also stimulate commercial interest in biological alternatives to synthetic adhesives.
Examples of bioadhesives in nature
Organisms may secrete bioadhesives for use in attachment, construction and obstruction, as well as in predation and defense. Examples include their use for- colonization of surfaces (e.g. bacteriaBacteriaBacteria are a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria have a wide range of shapes, ranging from spheres to rods and spirals...
, algaeAlgaeAlgae are a large and diverse group of simple, typically autotrophic organisms, ranging from unicellular to multicellular forms, such as the giant kelps that grow to 65 meters in length. They are photosynthetic like plants, and "simple" because their tissues are not organized into the many...
, fungiFungusA fungus is a member of a large group of eukaryotic organisms that includes microorganisms such as yeasts and molds , as well as the more familiar mushrooms. These organisms are classified as a kingdom, Fungi, which is separate from plants, animals, and bacteria...
, mussels, barnacles) - tube building by polychaetePolychaeteThe Polychaeta or polychaetes are a class of annelid worms, generally marine. Each body segment has a pair of fleshy protrusions called parapodia that bear many bristles, called chaetae, which are made of chitin. Indeed, polychaetes are sometimes referred to as bristle worms. More than 10,000...
worms, which live in underwater mounds - insectInsectInsects are a class of living creatures within the arthropods that have a chitinous exoskeleton, a three-part body , three pairs of jointed legs, compound eyes, and two antennae...
eggEgg (biology)An egg is an organic vessel in which an embryo first begins to develop. In most birds, reptiles, insects, molluscs, fish, and monotremes, an egg is the zygote, resulting from fertilization of the ovum, which is expelled from the body and permitted to develop outside the body until the developing...
, larvaLarvaA larva is a distinct juvenile form many animals undergo before metamorphosis into adults. Animals with indirect development such as insects, amphibians, or cnidarians typically have a larval phase of their life cycle...
l or pupaPupaA pupa is the life stage of some insects undergoing transformation. The pupal stage is found only in holometabolous insects, those that undergo a complete metamorphosis, going through four life stages; embryo, larva, pupa and imago...
l attachment to surfaces (vegetation, rocks), and insect mating plugs - hostHost (biology)In biology, a host is an organism that harbors a parasite, or a mutual or commensal symbiont, typically providing nourishment and shelter. In botany, a host plant is one that supplies food resources and substrate for certain insects or other fauna...
attachment by bloodBloodBlood is a specialized bodily fluid in animals that delivers necessary substances such as nutrients and oxygen to the cells and transports metabolic waste products away from those same cells....
-feeding ticks - nest-building by some insects, and also by some fishFishFish are a paraphyletic group of organisms that consist of all gill-bearing aquatic vertebrate animals that lack limbs with digits. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish, as well as various extinct related groups...
(e.g. the three-spined sticklebackThree-spined sticklebackThe three-spined stickleback, Gasterosteus aculeatus, is a fish native to much of northern Europe, northern Asia and North America. It has been introduced into parts of southern and central Europe.-Distribution and morphological variation:...
) - defense by NotadenNotadenNotaden is a genus of burrowing ground frogs native to central and northern Australia.- Description :Its body is very round in shape with a short neck. Its pupils are horizontal slits. It has long arms and short, stubby legs. Its fingers lack webbing and its toes may have slight to no webbing. ...
frogs and by sea cucumbers - prey capturePredationIn ecology, predation describes a biological interaction where a predator feeds on its prey . Predators may or may not kill their prey prior to feeding on them, but the act of predation always results in the death of its prey and the eventual absorption of the prey's tissue through consumption...
in spider webSpider webA spider web, spiderweb, spider's web or cobweb is a device built by a spider out of proteinaceous spider silk extruded from its spinnerets....
s and by velvet wormVelvet wormThe velvet worms are a minor ecdysozoan phylum. These obscurely segmented organisms have tiny eyes, antennae, multiple pairs of legs and slime glands. They have variously been compared to worms with legs, caterpillars and slugs...
s
Some bioadhesives are very strong. For example, adult barnacles achieve pull-off forces as high as 2 MPa
Pascal (unit)
The pascal is the SI derived unit of pressure, internal pressure, stress, Young's modulus and tensile strength, named after the French mathematician, physicist, inventor, writer, and philosopher Blaise Pascal. It is a measure of force per unit area, defined as one newton per square metre...
(2 N/mm2).
Silk
Silk
Silk is a natural protein fiber, some forms of which can be woven into textiles. The best-known type of silk is obtained from the cocoons of the larvae of the mulberry silkworm Bombyx mori reared in captivity...
dope can also be used as a glue by arachnids and insects.
Temporary adhesion
Organisms such as limpets and sea stars use suction and mucusMucus
In vertebrates, mucus is a slippery secretion produced by, and covering, mucous membranes. Mucous fluid is typically produced from mucous cells found in mucous glands. Mucous cells secrete products that are rich in glycoproteins and water. Mucous fluid may also originate from mixed glands, which...
-like slimes to create Stefan Adhesion, which makes pull-off much harder than lateral drag; this allows both attachment and mobility. Spores, embryos and juvenile forms may use temporary adhesives (often glycoproteins) to secure their initial attachment to surfaces favorable for colonization. Tacky and elastic secretions that act as pressure sensitive adhesive
Pressure sensitive adhesive
Pressure sensitive adhesive is adhesive which forms a bond when pressure is applied to marry the adhesive with the adherend...
s, forming immediate attachments on contact, are preferable in the context of self-defense and predation
Predation
In ecology, predation describes a biological interaction where a predator feeds on its prey . Predators may or may not kill their prey prior to feeding on them, but the act of predation always results in the death of its prey and the eventual absorption of the prey's tissue through consumption...
. Molecular mechanisms include non-covalent interactions and polymer chain entanglement. Many biopolymers - proteins, carbohydrates, glycoprotein
Glycoprotein
Glycoproteins are proteins that contain oligosaccharide chains covalently attached to polypeptide side-chains. The carbohydrate is attached to the protein in a cotranslational or posttranslational modification. This process is known as glycosylation. In proteins that have segments extending...
s, and mucopolysaccharides - may be used to form hydrogels that contribute to temporary adhesion.
Permanent adhesion
Many permanent bioadhesives (e.g., the oothecaOotheca
An ootheca is a type of egg mass made by any member of a variety of species .The word is a latinized combination of oo-, meaning "egg", from the Greek word ōon , and theca, meaning a "cover" or "container", from the Greek theke...
l foam of the mantis
Mantis
Mantis is the common name of any insect in the order Mantodea, also commonly known as praying mantises. The word itself means "prophet" in Latin and Greek...
) are generated by a "mix to activate" process that involves hardening via covalent cross-linking. On non-polar surfaces the adhesive mechanisms may include van der Waals force
Van der Waals force
In physical chemistry, the van der Waals force , named after Dutch scientist Johannes Diderik van der Waals, is the sum of the attractive or repulsive forces between molecules other than those due to covalent bonds or to the electrostatic interaction of ions with one another or with neutral...
s, whereas on polar
Chemical polarity
In chemistry, polarity refers to a separation of electric charge leading to a molecule or its chemical groups having an electric dipole or multipole moment. Polar molecules interact through dipole–dipole intermolecular forces and hydrogen bonds. Molecular polarity is dependent on the difference in...
surfaces mechanisms such as hydrogen bonding and binding to (or forming bridges via) metal
Metal
A metal , is an element, compound, or alloy that is a good conductor of both electricity and heat. Metals are usually malleable and shiny, that is they reflect most of incident light...
cations may allow higher sticking forces to be achieved.
- MicroorganismMicroorganismA microorganism or microbe is a microscopic organism that comprises either a single cell , cell clusters, or no cell at all...
s use acidic polysaccharidePolysaccharidePolysaccharides 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,...
s (molecular massMolecular massThe molecular mass of a substance is the mass of one molecule of that substance, in unified atomic mass unit u...
around 100 000 DaAtomic mass unitThe 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...
) - Marine bacteria use carbohydrate exopolymers to achieve bond strengths to glass of up to 500 000 N/m2
- Marine inverterbrates commonly employ protein-based glues for irreversible attachment. Some mussels achieve 800 000 N/m2 on polar surfaces and 30 000 N/m2 on non-polar surfaces
- Some algae and marine invertebrates use polyphenolic proteinPolyphenolic proteinPolyphenolic proteins are proteins produced by some algae and marine invertebrates like the blue mussel, Mytilus edulis or the polychaete Phragmatopoma californica that are used as bioadhesives. These proteins contain a high level of L-DOPA and cystine....
s containing L-DOPALevodopaL-DOPA is a chemical that is made and used as part of the normal biology of some animals and plants. Some animals including humans make it via biosynthesis from the amino acid L-tyrosine. L-DOPA is the precursor to the neurotransmitters dopamine, norepinephrine , and epinephrine collectively... - Proteins in the oothecal foam of the mantis are cross-linked covalently by small molecules related to L-DOPA via a tanningTanningTanning is the making of leather from the skins of animals which does not easily decompose. Traditionally, tanning used tannin, an acidic chemical compound from which the tanning process draws its name . Coloring may occur during tanning...
reaction that is catalysedCatalysisCatalysis is the change in rate of a chemical reaction due to the participation of a substance called a catalyst. Unlike other reagents that participate in the chemical reaction, a catalyst is not consumed by the reaction itself. A catalyst may participate in multiple chemical transformations....
by catechol oxidaseCatechol oxidaseCatechol oxidase is an enzyme that catalyses the oxidation of phenols such as catechol. Catechol oxidase is a copper-containing enzyme whose activity is similar to that of tyrosinase, a related class of copper oxidases....
or polyphenol oxidasePolyphenol oxidasePolyphenol oxidase is a tetramer which contains four atoms of copper per molecule, and binding sites for two aromatic compounds and oxygen...
enzymes.
L-DOPA is a tyrosine
Tyrosine
Tyrosine or 4-hydroxyphenylalanine, is one of the 22 amino acids that are used by cells to synthesize proteins. Its codons are UAC and UAU. It is a non-essential amino acid with a polar side group...
residue that bears an additional hydroxyl
Hydroxyl
A hydroxyl is a chemical group containing an oxygen atom covalently bonded with a hydrogen atom. In inorganic chemistry, the hydroxyl group is known as the hydroxide ion, and scientists and reference works generally use these different terms though they refer to the same chemical structure in...
group. The twin hydroxyl groups in each side-chain compete well with water for binding to surfaces, form polar attachments via hydrogen bonds, and chelate the metals in mineral
Mineral
A mineral is a naturally occurring solid chemical substance formed through biogeochemical processes, having characteristic chemical composition, highly ordered atomic structure, and specific physical properties. By comparison, a rock is an aggregate of minerals and/or mineraloids and does not...
surfaces. The Fe(L-DOPA3) complex can itself account for much cross-linking and cohesion in mussel
Mussel
The common name mussel is used for members of several families of clams or bivalvia mollusca, from saltwater and freshwater habitats. These groups have in common a shell whose outline is elongated and asymmetrical compared with other edible clams, which are often more or less rounded or oval.The...
plaque, but in addition the iron
Iron
Iron is a chemical element with the symbol Fe and atomic number 26. It is a metal in the first transition series. It is the most common element forming the planet Earth as a whole, forming much of Earth's outer and inner core. It is the fourth most common element in the Earth's crust...
catalyses oxidation
Redox
Redox reactions describe all chemical reactions in which atoms have their oxidation state changed....
of the L-DOPA to reactive quinone
Quinone
A quinone is a class of organic compounds that are formally "derived from aromatic compounds [such as benzene or naphthalene] by conversion of an even number of –CH= groups into –C– groups with any necessary rearrangement of double bonds," resulting in "a fully conjugated cyclic dione structure."...
free radicals, which go on to form covalent bonds.
Commercial applications
ShellacShellac
Shellac is a resin secreted by the female lac bug, on trees in the forests of India and Thailand. It is processed and sold as dry flakes , which are dissolved in ethyl alcohol to make liquid shellac, which is used as a brush-on colorant, food glaze and wood finish...
is an early example of a bioadhesive put to practical use. Additional examples now exist, with others in development:
- Commodity woodWoodWood is a hard, fibrous tissue found in many trees. It has been used for hundreds of thousands of years for both fuel and as a construction material. It is an organic material, a natural composite of cellulose fibers embedded in a matrix of lignin which resists compression...
adhesiveAdhesiveAn adhesive, or glue, is a mixture in a liquid or semi-liquid state that adheres or bonds items together. Adhesives may come from either natural or synthetic sources. The types of materials that can be bonded are vast but they are especially useful for bonding thin materials...
based on a bacterial exopolysaccharide - USB PRF/Soy 2000, a commodity wood adhesive that is 50% soy hydrolysate and excels at finger-jointing green lumberLumberLumber or timber is wood in any of its stages from felling through readiness for use as structural material for construction, or wood pulp for paper production....
- MusselMusselThe common name mussel is used for members of several families of clams or bivalvia mollusca, from saltwater and freshwater habitats. These groups have in common a shell whose outline is elongated and asymmetrical compared with other edible clams, which are often more or less rounded or oval.The...
adhesive proteins can assist in attaching cellCell (biology)The cell is the basic structural and functional unit of all known living organisms. It is the smallest unit of life that is classified as a living thing, and is often called the building block of life. The Alberts text discusses how the "cellular building blocks" move to shape developing embryos....
s to plasticPlasticA plastic material is any of a wide range of synthetic or semi-synthetic organic solids used in the manufacture of industrial products. Plastics are typically polymers of high molecular mass, and may contain other substances to improve performance and/or reduce production costs...
surfaces in laboratory cell and tissue cultureTissue cultureTissue culture is the growth of tissues or cells separate from the organism. This is typically facilitated via use of a liquid, semi-solid, or solid growth medium, such as broth or agar...
experiments (see External Links) - The Notaden frog glue is under development for biomedicalBiomedical engineeringBiomedical Engineering is the application of engineering principles and design concepts to medicine and biology. This field seeks to close the gap between engineering and medicine: It combines the design and problem solving skills of engineering with medical and biological sciences to improve...
uses, e.g. as a surgicalSurgerySurgery is an ancient medical specialty that uses operative manual and instrumental techniques on a patient to investigate and/or treat a pathological condition such as disease or injury, or to help improve bodily function or appearance.An act of performing surgery may be called a surgical...
glue for orthopedic applications or as a hemostatHemostatA hemostat , is a vital surgical tool used in almost any surgical procedure, usually to control bleeding. Therefore, it is not uncommon to see the initial incision lined with hemostats closing blood vessels awaiting ligation during the initial phases of surgery... - Mucosal drug deliveryDrug deliveryDrug delivery is the method or process of administering a pharmaceutical compound to achieve a therapeutic effect in humans or animals. Drug delivery technologies modify drug release profile, absorption, distribution and elimination for the benefit of improving product efficacy and safety, as well...
applications. For example, films of mussel adhesive protein give comparable mucoadhesion to polycarbophilPolycarbophilPolycarbophil calcium is a drug used as a stool stabilizer. Chemically, it is a synthetic polymer the calcium salt of polyacrylic acid cross-linked with divinyl glycol.-Clinical uses:...
, a synthetic hydrogel used to achieve effective drug delivery at low drug doses. An increased residence time through adhesion to the mucosal surface, such as in the eye or the noseNasal administrationNasal administration can be used to deliver drugs for either local or systemic effect. Locally acting drugs are for example decongestants and allergy treatments...
can lead to an improved absorption of the drug .
Several commercial methods of production are being researched:
- direct chemical synthesis, e.g. incorporation of L-DOPA groups in synthetic polymers
- fermentationFermentation (biochemistry)Fermentation is the process of extracting energy from the oxidation of organic compounds, such as carbohydrates, using an endogenous electron acceptor, which is usually an organic compound. In contrast, respiration is where electrons are donated to an exogenous electron acceptor, such as oxygen,...
of transgenic bacteria or yeasts that express bioadhesive protein genesGênesGênes is the name of a département of the First French Empire in present Italy, named after the city of Genoa. It was formed in 1805, when Napoleon Bonaparte occupied the Republic of Genoa. Its capital was Genoa, and it was divided in the arrondissements of Genoa, Bobbio, Novi Ligure, Tortona and... - farming of natural organisms (small and large) that secrete bioadhesive materials
Mucoadhesion
A more specific term than bioadhesion is mucoadhesion. Most mucosal surfaces such as in the gut or nose are covered by a layer of mucusMucus
In vertebrates, mucus is a slippery secretion produced by, and covering, mucous membranes. Mucous fluid is typically produced from mucous cells found in mucous glands. Mucous cells secrete products that are rich in glycoproteins and water. Mucous fluid may also originate from mixed glands, which...
. Adhesion of a matter to this layer is hence called mucoadhesion. Mucoadhesive agents are usually polymers containing hydrogen bonding groups that can be used in wet formulations or in dry powders for drug delivery purposes. The mechanisms behind mucoadhesion have not yet been fully elucidated, but a generally accepted theory is that close contact must first be established between the mucoadhesive agent and the mucus, followed by interpenetration of the mucoadhesive polymer and the mucin and finishing with the formation of entanglements and chemical bonds between the macromolecules . In the case of a dry polymer powder, the initial adhesion is most likely achieved by water movement from the mucosa into the formulation, which has also been shown to lead to dehydration and strengthening of the mucus layer. The subsequent formation of van der Waals, hydrogen and, in the case of a positively charged polymer, electrostatic bonds between the mucins and the hydrated polymer promotes prolonged adhesion.
External links
- Cell-Tak, a mussel adhesive protein preparation sold for use in cell and tissue culture.
- "Mussels inspire new surgical glue possibilities". ScienceDaily article, Dec 2007.
- Frog glue story on ABC TVABC TelevisionABC Television is a service of the Australian Broadcasting Corporation launched in 1956. As a public broadcasting broadcaster, the ABC provides four non-commercial channels within Australia, and a partially advertising-funded satellite channel overseas....
science program Catalyst. - "Marine algae hold key to better biomedical adhesives", [ftp://ftp.cordis.europa.eu/pub/nmp/docs/biomaterials_web.pdf Biomaterials for healthcare: a decade of EU-funded research], p. 23
- New adhesives including ones from cornstarchCornstarchCorn starch, cornstarch, cornflour or maize starch is the starch of the corn grain obtained from the endosperm of the corn kernel.-History:...
and a sugarSugarSugar is a class of edible crystalline carbohydrates, mainly sucrose, lactose, and fructose, characterized by a sweet flavor.Sucrose in its refined form primarily comes from sugar cane and sugar beet...
-based Pressure sensitive adhesivePressure sensitive adhesivePressure sensitive adhesive is adhesive which forms a bond when pressure is applied to marry the adhesive with the adherend...
. - Review of bioadhesives from 2005.
- Thesis on mucoadhesive gels
- Thesis on mucoadhesive microparticles for nasal drug delivery