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Going Ballistic: Soft Structures Could Spell The End For Slow Shrimps

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10.04.2002

Many animals are able to rapidly extend their tongues to catch prey. In fact, the chameleon extends its tongue at an acceleration rate of 500 metres per second square - generating 5 times the G force experienced by an F-16 fighter during its most demanding maneouvre! New research presented at the Society for Experimental Biology conference in Swansea today has shed light on exactly how these remarkable feats are achieved.

Dr Johan van Leeuwen of Wageningen University, the Netherlands, suggests that these `ballistic movements` are possible due to nature`s remarkable `soft body mechanics`. In research which has studied the bullet-like extension of squid tentacles and snake and chameleon tongues, it has become clear that such movements are possible due to the interaction of muscle fibres and fluid pockets associated with them - the principle constituents of the tongue. Muscle fibres are arranged in a criss-cross pattern, extending up and down and side to side. Co-contraction of these fibres - squeezing the tongue to make it thinner and narrower - pressurises the fluid pockets of the tongue, forcing them to expand rapidly forwards extending the tongue or tentacle. Using high speed filming and mathematical techniques Dr Leeuwen has developed a computer model which effectively predicts the projected pathway of tongues and tentacles.

The actual construction of these muscle fibres are very different from our own. At a molecular level, the human tongue musculature consists of a series of actin and myosin filaments which slide over one another to shorten their overall length and thus contract the muscle. In humans, these fibres are long which enables a great number of bonds to form between the actin and myosin filaments - this results in a very strong system. In creatures capable of ballistic tongue movements, the fibres are shorter. Thus there are more `sliding possibilities` and less bonds between the two filament types. As a result, strength is reduced but speed is greatly increased. These propertries allow the squid`s prey catching tentacles to increase in length by around 80% in just 20-30 milliseconds - bad news if you`re a shrimp!

These `soft body mechanics` are in direct contrast to our own robotic designs. Man-made machines are created using rigid limbs and joints whilst many natural systems rely on pressurised fluid alone for support. Dr van Leeuwen suggests that this property allows the tongue to be "controllable, lightweight and flexible."

"Nature has found solutions to produce intricate `robotic` arms which are made only of soft tissue. The perpendicular arrangement of fibres in the tongue is a clever system. When the tongue muscles contract, you get an enormous extension, allowing predators to capture fast moving prey. "

Jenny Gimpel | Source: alphagalileo

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