From Academic Kids
An exoskeleton, in contrast to an endoskeleton, is an external anatomical feature that supports and protects an animal's body. Many invertebrate animals such as insects, crustaceans and shellfish have exoskeletons. Lobsters, for example, have tough outer shell systems which provide rigidity and shape to their bodies.
Humans have long used armour as an artificial exoskeleton for protection, especially in combat. Exoskeletal items are also used for medical and industrial purposes. Human exoskeletons are a feature of science fiction writing.
Types of exoskeletonsChitin
An exoskeleton may interfere with an animal's growth. To overcome this, arthropods go through a process called moulting in which they shed their exoskeleton and replace it with a new, larger one.
Excellent as a principle of defence, exoskeletons may nevertheless cause problems where entities carry an excessive weight to surface-area ratio; or whenever organism growth requires an enlarged exoskeleton.
Artificial human exoskeletons
Exoskeletons in history
Medieval armour (in the case of mounted knights) is not load-bearing, but furnishes the appearance of an artificial human exoskeleton. Modern motorists use automobiles as temporary protective exoskeletons in harsh traffic environments.
Exoskeletons in medicine
An "orthosis" (plural orthoses) is a device which attaches to a limb, or the torso, to support the function or correct the shape of that limb or the spine. "Orthotics" is the term for the field dealing with orthoses, their use and manufacturing. An "Orthotist" is the name given to a person who designs and fits an orthosis.
A limb "prosthesis" (plural prostheses) is a device that substitutes for a missing part of the limb. If the prosthesis is a hollow shell and self-carrying, it is exoskeletal. If internal tubes are used in the device and the cover (cosmesis) to create the outside shape is made of a soft, non-carrying material, it is endoskeletal. "Prosthetics" is the term for the field dealing with prostheses, their use and manufacturing. A "Prosthetist" is the name given to a person who designs and fits a prosthesis.
Exoskeletons in modern and near-future technology
In the early 2000s a number of companies and research centres developed the first practical models of human exoskeletons. One of the main uses is enabling a soldier to carry heavy weights (50–100 kg) while running or climbing stairs. Most models use a hydraulic system controlled by an on-board computer. They can be powered by an internal combustion engine, batteries or, potentially, fuel cells. Another area of application is medical care, nursing in particular. Faced with the impending shortage of medical professionals and the increasing number of people in elderly care, several teams of Japanese engineers have developed exoskeletons designed to help nurses lift and carry patients.
Commercially-available exoskeletons are expected by the end of 2005  (http://www.newscientist.com/article.ns?id=mg18624945.800).
In the future exoskeletons are expected to become widely used by the military and police in the form of nanotechnological combat clothes. Civilian uses will no doubt be found later. However they will have to compete for adoption with another approach — surgically and genetically enhancing the human body itself by use of artificial bones and muscles.