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57-480: Spider silk is classified as keratin, although production of the protein may have evolved independently of the process in vertebrates. Alpha-keratins (α-keratins) are found in all vertebrates. They form the hair (including wool ), the outer layer of skin , horns , nails , claws and hooves of mammals, and the slime threads of hagfish . The baleen plates of filter-feeding whales are also made of keratin. Keratin filaments are abundant in keratinocytes in

114-436: A glass transition . The glass-transition temperature depends on humidity, as water is a plasticiser for spider silk. When exposed to water, dragline silks undergo supercontraction, shrinking up to 50% in length and behaving like a weak rubber under tension. Many hypotheses have attempted to explain its use in nature, most popularly to re-tension webs built in the night using the morning dew. The toughest known spider silk

171-481: A golden tint made in Madagascar in 2009. Eighty-two people worked for four years to collect over one million golden orb spiders and extract silk from them. In 2012, spider silk fibres were used to create a set of violin strings. Peasants in the southern Carpathian Mountains used to cut up tubes built by Atypus and cover wounds with the inner lining. It reportedly facilitated healing, and connected with

228-470: A pH of about 4, making the silk acidic and thus protecting it from fungi and bacteria that would otherwise digest the protein. Potassium nitrate is believed to prevent the protein from denaturing in the acidic milieu. Termonia introduced this first basic model of silk in 1994. He suggested crystallites embedded in an amorphous matrix interlinked with hydrogen bonds . Refinements to this model include: semi-crystalline regions were found as well as

285-543: A basis for attempts to replicate necessary protein components. These proteins must then be extracted, purified, and then spun before their properties can be tested. Spider silks with comparatively simple molecular structure need complex ducts to be able to form an effective fibre. Approaches: Feedstock is forced through a hollow needle using a syringe. Although cheap and easy to produce, gland shape and conditions are loosely approximated. Fibres created using this method may need encouragement to solidify by removing water from

342-399: A fibrillar skin core model suggested for spider silk, later visualised by AFM and TEM . Sizes of the nanofibrillar structure and the crystalline and semi-crystalline regions were revealed by neutron scattering . The fibres' microstructural information and macroscopic mechanical properties are related. Ordered regions (i) mainly reorient by deformation for low-stretched fibres and (ii)

399-445: A genetic and structural level. The new term corneous beta protein (CBP) has been proposed to avoid confusion with α-keratins. Keratins (also described as cytokeratins ) are polymers of type I and type II intermediate filaments that have been found only in chordates ( vertebrates , amphioxi , urochordates ). Nematodes and many other non-chordate animals seem to have only type VI intermediate filaments , fibers that structure

456-489: A large amount of energy before breaking ( toughness , the area under a stress-strain curve). Strength and toughness are distinct quantities. Weight for weight, silk is stronger than steel, but not as strong as Kevlar . Spider silk is, however, tougher than both. The variability of spider silk fibre mechanical properties is related to their degree of molecular alignment. Mechanical properties also depend on ambient conditions, i.e. humidity and temperature. Young's modulus

513-496: A minimum of silk substrate. The pyriform threads polymerise under ambient conditions, become functional immediately, and are usable indefinitely, remaining biodegradable, versatile and compatible with other materials in the environment. The adhesive and durability properties of the attachment disc are controlled by functions within the spinnerets. Some adhesive properties of the silk resemble glue , consisting of microfibrils and lipid enclosures. All spiders produce silks, and

570-474: A sac with an opening at one end, to the complex, multiple-section ampullate glands of the golden silk orb-weavers . Behind each spinneret on the surface of the spider lies a gland, a generalised form of which is shown in the figure. Throughout the process the silk appears to have a nematic texture, in a manner similar to a liquid crystal , arising in part due to the high protein concentration of silk dope (around 30% in terms of weight per volume). This allows

627-424: A series of assembly steps beginning with dimerization; dimers assemble into tetramers and octamers and eventually, if the current hypothesis holds, into unit-length-filaments (ULF) capable of annealing end-to-end into long filaments. Cornification is the process of forming an epidermal barrier in stratified squamous epithelial tissue. At the cellular level, cornification is characterised by: Metabolism ceases, and

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684-432: A single spider can produce up to seven different types of silk for different uses. This is in contrast to insect silks, where an individual usually only produces a single type. Spiders use silks in many ways, in accord with the silk's properties. As spiders have evolved, so has their silks' complexity and uses, for example from primitive tube webs 300–400 million years ago to complex orb webs 110 million years ago. Meeting

741-482: A spider. Extrusion of protein fibres in an aqueous environment is known as "wet-spinning". This process has produced silk fibres of diameters ranging from 10 to 60 μm, compared to diameters of 2.5–4 μm for natural spider silk. Artificial spider silks have fewer and simpler proteins than natural dragline silk, and consequently offer half the diameter, strength, and flexibility of natural dragline silk. The earliest recorded attempt to weave fabric from spider silk

798-404: A variety of conditions including keratosis , hyperkeratosis and keratoderma . Mutations in keratin gene expression can lead to, among others: Several diseases, such as athlete's foot and ringworm , are caused by infectious fungi that feed on keratin. Keratin is highly resistant to digestive acids if ingested. Cats regularly ingest hair as part of their grooming behavior , leading to

855-439: A β-keratin, can have these two as 75–80% of the total, with 10–15% serine , with the rest having bulky side groups. The chains are antiparallel, with an alternating C → N orientation. A preponderance of amino acids with small, nonreactive side groups is characteristic of structural proteins, for which H-bonded close packing is more important than chemical specificity . In addition to intra- and intermolecular hydrogen bonds ,

912-467: Is a pultrusion , similar to extrusion, with the subtlety that the force is induced by pulling at the finished fibre rather than squeezing it out of a reservoir. The fibre is pulled through (possibly multiple) silk glands of multiple types. The gland's visible, or external, part is termed the spinneret . Depending on the complexity of the species, spiders have two to eight spinnerets, usually in pairs. Species have varying specialised glands, ranging from

969-624: Is a much less dense material, so that a given weight of spider silk is five times as strong as the same weight of steel.) The energy density of dragline spider silk is roughly 1.2 × 10  J/m . Silks are ductile , with some able to stretch up to five times their relaxed length without breaking. The combination of strength and ductility gives dragline silks a high toughness (or work to fracture), which "equals that of commercial polyaramid (aromatic nylon) filaments, which themselves are benchmarks of modern polymer fibre technology". According to Spider Silkome Database, Araneus ishisawai silk

1026-776: Is positioned below, and a difference in electrical potential is applied between the fluid and the substrate. The fluid is attracted to the substrate, and tiny fibres jump from their point of emission, the Taylor cone , to the substrate, drying as they travel. This method creates nano-scale fibres from silk dissected from organisms and regenerated silk fibroin. Silk can be formed into other shapes and sizes such as spherical capsules for drug delivery, cell scaffolds and wound healing, textiles, cosmetics, coatings, and many others. Spider silk proteins can self-assemble on superhydrophobic surfaces into nanowires, as well as micron-sized circular sheets. Recombinant spider silk proteins can self-assemble at

1083-406: Is produced by the species Darwin's bark spider ( Caerostris darwini ): "The toughness of forcibly silked fibers averages 350 MJ/m , with some samples reaching 520 MJ/m . Thus, C. darwini silk is more than twice as tough as any previously described silk and over 10 times tougher than Kevlar". Silk fibre is a two-compound pyriform secretion, spun into patterns (called "attachment discs") using

1140-439: Is pulled on demand from a precursor out of specialised glands, rather than continuously grown like plant cell walls. The spinning process occurs when a fibre is pulled away from the body of a spider, whether by the spider's legs, by the spider's falling under its own weight, or by any other method. The term "spinning" is misleading because no rotation occurs. It comes from analogy to the textile spinning wheels . Silk production

1197-458: Is the amino acid sequence of its proteins ( spidroin ), mainly consisting of highly repetitive glycine and alanine blocks, which is why silks are often referred to as a block co-polymer . On a secondary level, the short side-chained alanine is mainly found in the crystalline domains ( beta sheets ) of the nanofibril. Glycine is mostly found in the so-called amorphous matrix consisting of helical and beta turn structures. The interplay between

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1254-610: Is the resistance to deformation elastically along the tensile force direction. Unlike steel or Kevlar which are stiff, spider silk is ductile and elastic, having lower Young's modulus. According to Spider Silkome Database, Ariadna lateralisl silk has the highest Young's modulus with 37 GPa, compared to 208 GPa for steel and 112 GPa for Kevlar. A dragline silk's tensile strength is comparable to that of high-grade alloy steel (450−2000 MPa), and about half as strong as aramid filaments, such as Twaron or Kevlar (3000 MPa). According to Spider Silkome Database, Clubiona vigil silk has

1311-449: Is the toughest. Elongation at break compares initial object length to final length at break. According to Spider Silkome Database, Caerostris darwini silk has the highest strain at break for any spider silk, breaking at 65% extension. While unlikely to be relevant in nature, dragline silks can hold their strength below -40 °C (-40 °F) and up to 220 °C (428 °F). As occurs in many materials, spider silk fibres undergo

1368-446: Is tied to courtship and mating . Silk produced by females provides a transmission channel for male vibratory courtship signals, while webs and draglines provide a substrate for female sex pheromones . Observations of male spiders producing silk during sexual interactions are common across widespread taxa. The function of male-produced silk in mating has received little study. Silks have a hierarchical structure. The primary structure

1425-468: The sauropsids , that is all living reptiles and birds . They are found in the nails, scales , and claws of reptiles , in some reptile shells ( Testudines , such as tortoise , turtle , terrapin ), and in the feathers , beaks , and claws of birds . These keratins are formed primarily in beta sheets . However, beta sheets are also found in α-keratins. Recent scholarship has shown that sauropsid β-keratins are fundamentally different from α-keratins at

1482-508: The spinnerets on spiders' tails, and the contributions of their interior glands , provide remarkable control of fast extrusion . Spider silk is typically about 1 to 2 micrometers (μm) thick, compared with about 60 μm for human hair, and more for some mammals. The biologically and commercially useful properties of silk fibers depend on the organization of multiple adjacent protein chains into hard, crystalline regions of varying size, alternating with flexible, amorphous regions where

1539-659: The Type I intermediate filaments (IFs) of the intracytoplasmatic cytoskeleton, which is present in all mammalian epithelial cells. Most of the type I keratins consist of acidic, low molecular weight proteins which in vivo are arranged in pairs of heterotypic Type I and Type II keratin chains, coexpressed during differentiation of simple and stratified epithelial tissues. Type I keratins are encoded on chromosome 17q and encompasses: K9, K10, K11, K12, K13, K14, K15, K16, K17, K18, K19 and K20. Their molecular weight ranges from 40 kDa (K19) to 64 kDa (K9). This protein -related article

1596-433: The basal membrane in tissue modeling. Microfluidics have the advantage of being controllable and able to test spin small volumes of unspun fibre, but setup and development costs are high. A patent has been granted and continuously spun fibres have achieved commercial use. Electrospinning is an old technique whereby a fluid is held in a container such that it flows out through capillary action. A conducting substrate

1653-480: The cells are almost completely filled by keratin. During the process of epithelial differentiation, cells become cornified as keratin protein is incorporated into longer keratin intermediate filaments. Eventually the nucleus and cytoplasmic organelles disappear, metabolism ceases and cells undergo a programmed death as they become fully keratinized. In many other cell types, such as cells of the dermis, keratin filaments and other intermediate filaments function as part of

1710-504: The chains are randomly coiled . A somewhat analogous situation occurs with synthetic polymers such as nylon , developed as a silk substitute. Silk from the hornet cocoon contains doublets about 10 μm across, with cores and coating, and may be arranged in up to 10 layers, also in plaques of variable shape. Adult hornets also use silk as a glue , as do spiders. Glues made from partially-hydrolysed keratin include hoof glue and horn glue . Abnormal growth of keratin can occur in

1767-443: The coiled-coil structure is hydrophobic interactions between apolar residues along the keratins helical segments. Limited interior space is the reason why the triple helix of the (unrelated) structural protein collagen , found in skin , cartilage and bone , likewise has a high percentage of glycine . The connective tissue protein elastin also has a high percentage of both glycine and alanine . Silk fibroin , considered

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1824-467: The crystal structure of a helical domain of keratins. The human genome has 54 functional annotated Keratin genes, 28 are in the Keratin type 1 family, and 26 are in the Keratin type 2 family. Fibrous keratin molecules supercoil to form a very stable, left-handed superhelical motif to multimerise, forming filaments consisting of multiple copies of the keratin monomer . The major force that keeps

1881-449: The cytoskeleton to mechanically stabilize the cell against physical stress. It does this through connections to desmosomes, cell–cell junctional plaques, and hemidesmosomes, cell-basement membrane adhesive structures. Cells in the epidermis contain a structural matrix of keratin, which makes this outermost layer of the skin almost waterproof, and along with collagen and elastin gives skin its strength. Rubbing and pressure cause thickening of

1938-434: The distinguishing feature of keratins is the presence of large amounts of the sulfur -containing amino acid cysteine , required for the disulfide bridges that confer additional strength and rigidity by permanent, thermally stable crosslinking —in much the same way that non-protein sulfur bridges stabilize vulcanized rubber . Human hair is approximately 14% cysteine. The pungent smells of burning hair and skin are due to

1995-415: The feedstock (the unspun silk dope in spiders), and synthesis of the production conditions (the funnel, valve, tapering duct, and spigot). Few strategies have produced silk that can efficiently be synthesised into fibres. The molecular structure of unspun silk is both complex and long. Though this endows the fibres with desirable properties, it also complicates replication. Various organisms have been used as

2052-447: The fibre with chemicals such as (environmentally undesirable) methanol or acetone , and also may require later stretching of the fibre to achieve desirable properties. Placing a solution of spider silk on a superhydrophobic surface can generate sheets, particles, and nanowires of spider silk. Self-assembly of silk at standing liquid-gas interphases of a solution tough and strong sheets. These sheets are now explored for mimicking

2109-411: The fraction of ordered regions increases progressively for higher fibre stretching. Each spider and each type of silk has a set of mechanical properties optimised for their biological function. Most silks, in particular dragline silk, have exceptional mechanical properties. They exhibit a unique combination of high tensile strength and extensibility ( ductility ). This enables a silk fibre to absorb

2166-405: The gradual formation of hairballs that may be expelled orally or excreted. In humans, trichophagia may lead to Rapunzel syndrome , an extremely rare but potentially fatal intestinal condition. Keratin expression is helpful in determining epithelial origin in anaplastic cancers. Tumors that express keratin include carcinomas , thymomas , sarcomas and trophoblastic neoplasms . Furthermore,

2223-447: The hard crystalline segments and the strained elastic semi-amorphous regions gives spider silk its extraordinary properties. Various compounds other than protein are used to enhance the fibre's properties. Pyrrolidine has hygroscopic properties that keep the silk moist while warding off ant invasion. It occurs in high concentration in glue threads. Potassium hydrogen phosphate releases hydrogen ions in aqueous solution, resulting in

2280-469: The highest tensile strength. Consisting of mainly protein, silks are about a sixth of the density of steel (1.3 g/cm ). As a result, a strand long enough to circle the Earth would weigh about 2 kilograms (4.4 lb). (Spider dragline silk has a tensile strength of roughly 1.3  GPa . The tensile strength listed for steel might be slightly higher – e.g. 1.65 GPa, but spider silk

2337-465: The hornified layer of the epidermis ; these are proteins which have undergone keratinization . They are also present in epithelial cells in general. For example, mouse thymic epithelial cells react with antibodies for keratin 5, keratin 8, and keratin 14. These antibodies are used as fluorescent markers to distinguish subsets of mouse thymic epithelial cells in genetic studies of the thymus . The harder beta-keratins (β-keratins) are found only in

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2394-572: The inside of the human body. Silk has been used to suspend inertial confinement fusion targets during laser ignition, as it remains considerably elastic and has a high energy to break at temperatures as low as 10–20 K. In addition, it is made from "light" atomic number elements that emit no x-rays during irradiation that could preheat the target, limiting the pressure differential required for fusion. Type I keratin Type I keratins (or Type I cytokeratins ) are cytokeratins that constitute

2451-674: The liquid-air interface of a standing solution to form protein-permeable, strong and flexible nanomembranes that support cell proliferation. Potential applications include skin transplants, and supportive membranes in organ-on-a-chip. These nanomembranes have been used to create a static in-vitro model of a blood vessel. Replicating the complex conditions required to produce comparable fibres has challenged research and early-stage manufacturing. Through genetic engineering , E. coli bacteria, yeasts, plants, silkworms, and animals other than silkworms have been used to produce spider silk-like proteins, which have different characteristics than those from

2508-408: The manufacturing of military, medical, and consumer goods, such as ballistic armour , athletic footwear, personal care products, breast implant and catheter coatings, mechanical insulin pumps, fashion clothing, and outerwear . However, due to the difficulties in extracting and processing, the largest known piece of cloth made of spider silk is an 11-by-4-foot (3.4 by 1.2 m) textile with

2565-878: The nucleus . The human genome encodes 54 functional keratin genes , located in two clusters on chromosomes 12 and 17. This suggests that they originated from a series of gene duplications on these chromosomes. The keratins include the following proteins of which KRT23 , KRT24 , KRT25 , KRT26 , KRT27 , KRT28 , KRT31 , KRT32 , KRT33A , KRT33B , KRT34 , KRT35 , KRT36 , KRT37 , KRT38 , KRT39 , KRT40 , KRT71 , KRT72 , KRT73 , KRT74 , KRT75 , KRT76 , KRT77 , KRT78 , KRT79 , KRT8 , KRT80 , KRT81 , KRT82 , KRT83 , KRT84 , KRT85 and KRT86 have been used to describe keratins past 20. The first sequences of keratins were determined by Israel Hanukoglu and Elaine Fuchs (1982, 1983). These sequences revealed that there are two distinct but homologous keratin families, which were named type I and type II keratins. By analysis of

2622-710: The outer, cornified layer of the epidermis and form protective calluses, which are useful for athletes and on the fingertips of musicians who play stringed instruments. Keratinized epidermal cells are constantly shed and replaced. These hard, integumentary structures are formed by intercellular cementing of fibers formed from the dead, cornified cells generated by specialized beds deep within the skin. Hair grows continuously and feathers molt and regenerate. The constituent proteins may be phylogenetically homologous but differ somewhat in chemical structure and supermolecular organization. The evolutionary relationships are complex and only partially known. Multiple genes have been identified for

2679-669: The precise expression-pattern of keratin subtypes allows prediction of the origin of the primary tumor when assessing metastases . For example, hepatocellular carcinomas typically express CK8 and CK18, and cholangiocarcinomas express CK7, CK8 and CK18, while metastases of colorectal carcinomas express CK20, but not CK7. Spider silk Spider silk is a protein fibre or silk spun by spiders . Spiders use silk to make webs or other structures that function as adhesive traps to catch prey, to entangle and restrain prey before biting, to transmit tactile information, or as nests or cocoons to protect their offspring. They can use

2736-403: The primary structures of these keratins and other intermediate filament proteins, Hanukoglu and Fuchs suggested a model in which keratins and intermediate filament proteins contain a central ~310 residue domain with four segments in α-helical conformation that are separated by three short linker segments predicted to be in beta-turn conformation. This model has been confirmed by the determination of

2793-483: The silk from a particular gland can be linked to its use. Many species have different glands to produce silk with different properties for different purposes, including housing, web construction, defence, capturing and detaining prey , egg protection, and mobility (fine "gossamer" thread for ballooning , or for a strand allowing the spider to drop down as silk is extruded). Silk production differs in an important aspect from that of most other fibrous biomaterials. It

2850-416: The silk to flow through the duct as a liquid while maintaining molecular order. As an example of a complex spinning field, the spinneret apparatus of an adult Araneus diadematus (garden cross spider) consists of many glands shown below. A similar gland architecture appears in the black widow spider. To artificially synthesise spider silk into fibres, two broad tasks are required. These are synthesis of

2907-500: The silk to suspend themselves from height, to float through the air , or to glide away from predators. Most spiders vary the thickness and adhesiveness of their silk according to its use. In some cases, spiders may use silk as a food source. While methods have been developed to collect silk from a spider by force, gathering silk from many spiders is more difficult than from silk-spinning organisms such as silkworms . All spiders produce silk, although some spiders do not make webs. Silk

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2964-648: The skin. This is believed to be due to the silk's antiseptic properties, and because silk is rich in vitamin K , which can aid in clotting blood. N. clavipes silk was used in research concerning mammalian neuronal regeneration. Spider silk has been used as a thread for crosshairs in optical instruments such as telescopes, microscopes, and telescopic rifle sights . In 2011, silk fibres were used to generate fine diffraction patterns over N-slit interferometric signals used in optical communications. Silk has been used to create biolenses that could be used in conjunction with lasers to create high-resolution images of

3021-432: The specification for all these ecological uses requires different types of silk presenting different properties, as either a fibre, a structure of fibres, or a globule. These types include glues and fibres. Some types of fibres are used for structural support, others for protective structures. Some can absorb energy effectively, whereas others transmit vibration efficiently. These silk types are produced in different glands; so

3078-405: The surface of many cell types. It has been proposed that keratins can be divided into 'hard' and 'soft' forms, or ' cytokeratins ' and 'other keratins'. That model is now understood to be correct. A new nuclear addition in 2006 to describe keratins takes this into account. Keratin filaments are intermediate filaments . Like all intermediate filaments, keratin proteins form filamentous polymers in

3135-1079: The volatile sulfur compounds formed. Extensive disulfide bonding contributes to the insolubility of keratins, except in a small number of solvents such as dissociating or reducing agents. The more flexible and elastic keratins of hair have fewer interchain disulfide bridges than the keratins in mammalian fingernails , hooves and claws (homologous structures), which are harder and more like their analogs in other vertebrate classes. Hair and other α-keratins consist of α-helically coiled single protein strands (with regular intra-chain H-bonding ), which are then further twisted into superhelical ropes that may be further coiled. The β-keratins of reptiles and birds have β-pleated sheets twisted together, then stabilized and hardened by disulfide bridges. Thiolated polymers (= thiomers ) can form disulfide bridges with cysteine substructures of keratins getting covalently attached to these proteins. Thiomers exhibit therefore high binding properties to keratins found in hair, on skin and on

3192-452: The β-keratins in feathers, and this is probably characteristic of all keratins. The silk fibroins produced by insects and spiders are often classified as keratins, though it is unclear whether they are phylogenetically related to vertebrate keratins. Silk found in insect pupae , and in spider webs and egg casings, also has twisted β-pleated sheets incorporated into fibers wound into larger supermolecular aggregates. The structure of

3249-504: Was in 1709 by François Xavier Bon who, using a process similar to creating silkworm silk, wove silk derived spider's egg cocoons into stockings and gloves. Fifty years later Jesuit missionary Ramón M. Termeyer  [ pl ] invented a reeling device for harvesting spider silk directly from spiders, allowing it to be spun into threads. Neither Bon nor Termeyer were successful in producing commercially viable quantities. The development of methods to mass-produce spider silk led to

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