Exoskeleton

An exoskeleton (also called exoskeleton ) is a support structure for a body, which forms a stable outer shell around this.

Natural exoskeletons

In contrast to vertebrates, all arthropods ( Arthropoda ) including insects, pine pawl carrier and crustaceans possess an internal skeleton instead of a stabilizing exoskeleton. (Some, mostly tiny, aquatic crustaceans, it was abandoned in favor of a secondary hydraulic skeleton. )

Other animal phyla, such as the Mollusca and Bryozoa have exoskeletons.

The cuticle of arthropods, which acts functionally as an outer skeleton, is one of the outermost cell layer ( epidermis) to the outside shell deposited. Is a flexible high-performance composite of several components. A basic component, fibers of chitin, a nitrogen-containing carbohydrates having properties similar to cellulose. Each 19 chitin fibers are deposited anti- parallel to each other into a crystalline bundle of about 3 nanometers in thickness and 0.3 microns length ( a microfibril ) together. Chitin microfibrils are surrounded by structural proteins which have a specific binding site for chitin. (This protein component was earlier than you did not know its structure, called Arthropodin. This term is outdated, but found in older books yet). Created depending on the proportion and composition of the protein component, either a hard and firm cuticle, the cured plates ( sclerites ), limbs, hair, mouth parts and similar structures brings forth, or soft and flexible, for example, the flexible sheath of many insect larvae builds, or the hard sclerites keeps you moving through switched joint membranes. Flexible cuticle contains about twenty, cured may contain more than two hundred different proteins, which are divided into twelve each to the other like protein families. The process of hardening of the cuticle, called sclerotization based on two processes, the hormonally controlled complementary to one another run at the starting. On one hand, water is excreted, which assemble into the water-repellent (hydrophobic) components fixed. On the other hand, a part of the protein is tightly bound to a network structure. In the process of dopamine plays a key role. The synthesized from dopamine compounds N- acetyldopamine (NADA ) and N -beta- Alanyldopamin ( NBAD ) are released into the cuticle and oxidized enzymatically here to highly reactive quinones. These react with the proteins and form a stable, non -degradable more network of covalent bonds. It remains of NADA sclerotized cuticle colorless or straw-colored, while has a dark sclerotized of NBAD. Part of dopamine can also be converted to the dark pigment melanin, which is probably also involved in the networking and thereby strengthened the exoskeleton. The depending on the location and function so differently sclerotized chitin -protein complexes in turn form of fibers. These larger fibers join together to form plate-like associations. The finished cuticle consists of very many such layers in which the fibers are oriented more or less always parallel. The stacked plates then the direction of the fibers is always slightly offset each other so that the entire structure is composed of helically staggered fiberboard ( after its discoverer Bodigand structure called ). Thus, the strength is significantly increased, similar to the construction of plywood panels made from wooden slats, except that in the single plywood slats perpendicular to each other and not helically twisted lie.

Contrary to common belief, it is the cuticle of arthropods that is not predominantly of chitin, but from chitin and proteins and other components in approximately equal proportions. The Chitinanteil is typically between about 50% ( in flexible cuticle ) and 15 to 30 % ( in hardened cuticle of sclerites ) of dry matter.

In many crustaceans and centipedes, the hardness of the cuticle is increased by mineral deposits on ( very rare even in insects and arachnids ). This armor consists largely of calcium carbonate with certain proportions of phosphate and magnesium. The vast majority of this substance is present in amorphous and not crystalline, a smaller proportion, especially on the top, most highly stressed situation, crystalline than calcite. Since calcium carbonate would actually crystallize spontaneously, it is possible only by specially controlled deposition to keep it in an amorphous state. Here, the magnesium and the phosphate moiety play a role, but also special organic ligands that suppress crystallization. This also the phosphate moiety is unkristallin before ( the crystalline phase, apatite called, comes as Biomineral only in other groups of organisms before. Maybe passed the exoskeletons of some extinct arthropods thereof). The " lime " share of the carapace is resolved after molting in part, temporarily stored in the body and is reinstalled in the new tank. Only in recent years it is known that some arthropods strengthen with such a tank at these particularly high stress areas, such as on mouthparts, claws and spines, by retention of heavy metals such as zinc and manganese, and by halogens such as chloride and bromide on. It was demonstrated that the hardness can be increased by zinc storage to three times. In what form the storage takes place, has not yet been discovered.

Other areas of the exoskeleton are not optimized for hardness, but on extensibility or flexibility. Special features gives a family of rubber -like proteins, called resilin, by their elasticity, for example, contribute significantly to the jumping ability of fleas.

As always with biological constructions, the exoskeleton is optimized by fine tuning of material properties and shape of the components on. Racked sclerites carry in rib-like reinforcements, which are partly outside by lines ( sutures called ) betrayed. The attachment points of the muscles are often ( here called Apodeme ) by depressions especially reinforced. Further, the cuticle carries a plurality of scales, hair, and excesses, including sensory hairs of komplexestem internal structure.

The strength of the exoskeleton is very different depending on the structure in different batches. Stronger sclerotized areas can reach the strength of hardwood or aluminum, single edges can reach that of steel. On average, the more sclerotized outer tank also quite small arthropods are harder than the human skin, but do not reach the values ​​of bone.

Since in this particular case a complete body cladding was cured, the passive no longer can grow, the exoskeleton during growth must be completely thrown off and again renewed (molting ). Recently there is evidence that not only Arthropods, but also to other häutende invertebrates whose cuticle is, however, usually remained relatively non- hardened, an evolutionary lineage Community form ( molting animals ).

The cuticle of arthropods is in the form shown almost no protection against water loss and dehydration, it is permeable to water vapor. Above all insects have this as the outermost wrapping an extremely thin layer of wax-like substances (eg, long-chain hydrocarbons ), Epikutikula called. This is eliminated by the pores of the cuticle by the formation. Millipedes, crustaceans and most jaw jaw carriers have no such Epikutikula. Country living forms shun therefore generally direct sunlight. Mainly nocturnal and benthic forms of these groups but in extremely dry, arid areas such as Deserts occur if they are daytime hiding places available.

Artificial exoskeletons

External support structures ( orthotics ) are sometimes used in medicine until the natural skeleton is healed again.

As well as various types of armor exoskeleton be described that support and amplify by joints are driven by servo motors on the exoskeleton, the movements of the wearer. These types of exoskeletons are currently developed in the USA and Japan. However, there are still no reports of sophisticated military models. About civilian models are currently no reports of widespread use, there are several concept studies in various stages of maturity. In the field of rehabilitation robotics for rehabilitation clinical trials using exoskeletons for paralysis are carried out, such as with Ekso 's eLEGS, Cyberdyne 's HAL and Argo 's ReWalk. The American company They Shall walk the founder Monty K. Reed in Seattle developed the Lifesuit for movement in the paralyzed people.

Also for applications in industry, for example for lifting heavy loads, exoskeletons are developed, such as Panasonic 's Power Loader or Percro 's Body Extender.

Probably the first attempt to build an exoskeleton was the Hardiman, an unsuccessful experimental prototype of General Electric from 1965.

Modern civilian exoskeleton Hybrid Assistive Limb ( HAL) (prototype)

Modern exoskeleton for the Future Force Warrior ( model)

Exoskeleton of the DARPA

Fictional exoskeletons

Fictional exoskeletons are found repeatedly in entertainment media, such as comics, manga / anime, science fiction movies and video games. They support the protagonists here both in ordinary work tasks such as futuristic forklift in Aliens - The Return as well as in the form of armed during the fight, such as in the movie- Iron Man (Powered exoskeleton ), matrix ( Armored Personnel Unit or APU) or Avatar - Pandora ( Amplified Mobility Platform or AMP suit ). Previously they found in the novel series Lensmen and several years later in the novel Starship Troopers mention.