Converse piezoelectric effect detected in fresh cow femur bone

A piezoelectric effect has been reported to exist in biological tissues, in particular in dry bone. Since the precision and resolution now obtainable are much greater, we decided to verify the presence of the converse effect (dimensional change under the application of an electric field) in fresh bone samples, by using a very high sensitivity instrument. We took, in varying orientations, five fresh femur cylindrical bone specimens from a cow leg and placed them as a single piece, or as a stack of 10 thin interlayered slices from one specimen to improve sensitivity, in a special microwave double cavity differential dilatometer. The thickness of the specimen was approximately 10mm. The applied field strength for the nonstacked specimen was near 10 kV m-1. Thickness variation was measured along and across the electric field lines. We applied the electric field as a switched polarity square wave. This allows the thermal dilution of specimen warming and possible electrostriction effects, which are insensitive to the direction of the applied field, to be separated from an electromechanical effect which is sensitive to direction. Using coherent signal averaging over approximately 600 cycles to combat instrumental noise we observed nonthermal, nonelectrostrictional thickness variations in all samples. The amplitudes we observed were near 3 pm for the 1 cm nonstacked specimen, and the bone's responses to electric fields ranged from 26 to 38 fm V-1. With response magnitudes approximating those predicted theoretically for the converse piezoelectric effect in bone we conclude that the piezoelectric theory could not be falsified with our experiments.