Piezoelectric effects in biological materials

Abstract

Abstract Strain-generated electrical signals detected in dry biological tissues (e.g., bone and tendon) are considered from the point of view of piezoelectricity. Although the magnitude and sign of the signals produced in bending experiments have been found to be inconsistent with expectations based on the classical theories of piezoelectricity and elasticity, a reconciliation has been shown to be possible if the piezoelectric moduli are taken to vary with location in the specimen. The complexity of the microstructure of the tissues and the finding of a spatially-varying spontaneous polarization justify the approach. The idea that a non-uniform polarization in the material leads to a large bending signal also finds applicability in the case of poled polymer films. The biological polymer collagen is, in fact, the electrically-active constituent in dry biological tissues. Although the piezoelectric effect is the electromechanical transduction mechanism in the case of dry tissues, physiologically-moist cartilage, tendon and bone also exhibit a streaming potential, which appears to dominate in mechanical measurements so far reported.