Wednesday, February 15, 2012

The Flea: High Jump Champ and Energy Efficient

A creature exists that harnesses enough energy to propel itself at an acceleration fifty times that of the acceleration of a space shuttle.  This creature can also handle forces of 100 G's, where the average person will black out if exposed to any more than four or five G's.  This creature is a common little flea that could be found on a household pet, but also possesses extreme jumping abilities.

Since the 1960's, scientists have debated over how exactly the flea is able to jump as high and as fast as it is capable of.  Two main models exist describing the trajectory of the flea during take-off:  Bennet-Clark's lever model and Miriam Rothschild's model.  This debate has finally been settled thanks to the work of Malcolm Burrows and Gregory Sutton.  Using high speed cameras, Burrows was able to capture and analyze the movements of the fleas as they jump.  Burrows found that Bennet-Clark's model was able to predict the fleas' initial velocity of 1.35 m/s and its acceleration peak at 1500 m/s2.  The film also showed that the femora of the two hind legs move forward so they become almost vertical.  The fleas hold this position for about 100ms and then the hind femora and trochantera (knees) lower.  The tibiae (shins) extend, propelling the flea forward and upwards.  The fleas use the gripping claws on their tarsus (toe) to push off.  The process of how the flea became visible through the films; however the unobserved mystery is what enables them to produce enough energy to propel them to heights twenty-three times their body length.

Photo by Gregory Sutton
The key to the flea's efficient use of energy lies in the protein, resilin.  Resilin is able to stretch three times its length without breaking.  This material is very efficient in turning stored, elastic energy into mechanical energy.  In fact, in the locust tendon, resilin in 97% efficient, meaning that only 3% of stored energy is lost as thermal energy (heat).  This special insect "rubber" may be very useful for cardiac surgeries.

Ultimately tiny little fleas can teach us many things.  Dr. Sutton believes that the mechanics of flea jumps can be beneficial to engineers, especially in the construction of robots.  "Insect jumping in incredibly precise and incredible fast," said Dr. Sutton.  "If you could build a robot that could do that, it would be fantastic."  [New York Times].  Not only can the mechanics of flea jumping be beneficial, but the extremely elastic protein resilin can also be useful.  Scientist have already been able to manipulate E. coli to produce resilin.  Scientists believe that resilin can be used to repair damaged arteries, which are naturally made of elastin (the elastic protein that allows arteries to expand and contract).  Fleas are evidence that great discoveries may be hiding in the most unexpected places.

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