Light micrograph of the tunica media of a human aorta.

Aortic-wall tissue (above) generates electricity if squeezed, an attribute previously observed only in hard materials such as bone. Credit: Jose Calvo/SPL

Biophysics

The body electric: soft tissue makes electricity under stress

Ultrasound pulses trigger an electrifying effect in samples of Achilles tendon, heart valve and more.

Achilles tendons and other soft bodily tissues can produce an electric voltage when squeezed, a finding that could aid the diagnosis of some medical problems.

Crystals, some semiconductors, dry biological tissues such as bone and other materials exhibit the piezoelectric effect, which is the ability to generate electricity when placed under mechanical stress. However, it was not clear whether soft tissues have the same property.

Kenji Ikushima and his colleagues at Tokyo University of Agriculture and Technology tested for the effect in samples of aortic walls and heart valves from pigs, and Achilles tendons from cows. The researchers induced mechanical stress in the tissues by blasting them with focused pulses of ultrasound waves. Using a tiny antenna, the team detected the resulting electromagnetic waves produced by the piezoelectric effect. The stronger the ultrasound waves and stresses, the stronger was the signal the antenna picked up.

Piezoelectric forces could one day be used to help detect fibrosis: scarred tissue that damages an organ’s ability to function.