An exoskeleton (from Greek έξω, éxō “outer” and σκελετός, skeletós “skeleton”), in zoology, is an external structure, more or less rigid, which acts as protection to the body of the animal and possibly as support to the organs. It is a term used in opposition to that of endoskeleton, which refers to the internal skeleton with which they are equipped, for example, humans. It is also often referred to by other designations, i.e. armor, carapace, or other. Exoskeletons, due to their extraordinary preservation, play a key role in paleontology.

Exoskeleton animals

Examples of animates equipped with exoskeletons are insects such as coelifers (grasshoppers or locusts) and blattoids (cockroaches or roaches) and crustaceans such as crabs and Nephropidae (lobster, mantis shrimp, crab). The so-called shells of various mollusks such as snails, clams, scaphopods, chitons, and nautilus are also exoskeletons. Some animals, such as testudinids, have both endoskeletons and exoskeletons.

Exoskeletons contain chitin and the addition of calcium carbonate makes them further rigid and strong, fulfilling a number of functional roles, including protection, excretion, support, and acting as a barrier against desiccation. Exoskeletons also play a role in defending against parasites or predators, providing support, and providing an attacking framework for musculature. In the latter case, the important elements for connecting to muscles are apodemes, structures about six times stronger and stiffer than vertebrate tendons.

In bioengineering, an exoskeleton is an experimental anthropomorphic machine, similar in appearance to the robot, but which presents, compared to the latter, substantial differences both in concept and application. In fact, the exoskeleton is not remotely controlled, but houses the operator inside it and achieves an integration with him such that when the operator makes a movement the exoskeleton repeats it exactly.

Naturally, each mechanical limb is endowed with strength, speed and resistance markedly superior to natural human ones. The basic requirement of the exoskeleton is that the mechanical limbs perform exactly the same operations as the natural limbs: for this purpose, the exoskeleton is equipped with a system of feedback signals which allows the operator to “feel” through the mechanical appendages the force and displacement signals and allows him to use these mechanical appendages as if they were his natural limbs, without having to divert his attention from his work to devote it to operating the machine.

This integration between the machine and the human nervous system, called “cybernetic control”, is possible thanks to a chain of electronic components that “extends” the operator’s nervous system to the machine. The operator’s command is then amplified by hydropneumatic systems to obtain mechanical limb movements with the desired characteristics.

The power required to operate the exoskeleton is provided by electric motors powered by electric or nuclear batteries according to the desired use and autonomy. The exoskeletons can be used in the civil field for rescue operations on difficult terrain (swamps, snow, etc..); in toxic atmospheres; in fire zones; for work to be performed in conditions not tolerable for humans (on the sea floor or on other planets) and also for a whole series of more traditional operations, such as lifting and transporting objects of all kinds, now entrusted to cranes, carts, etc..