© 1999 Robert A. Freitas Jr. All Rights Reserved.

Robert A. Freitas Jr., Nanomedicine, Volume I: Basic Capabilities, Landes Bioscience, Georgetown, TX, 1999

4.9.3.3 Piezoelectric Stress Macrosensing

The piezoelectric effect (Sections 6.3.2 and 6.3.5) is "the production of electrical polarization in a material by the application of mechanical stress".³⁰⁸⁹ Many materials in the human body are piezoelectric, including tendon and elastin, dentin and bone.^{1939-1942,3089-3095} This polarization, or surface charge, varies as the physical stress imposed on the material changes over time. Thus, measurement of the piezoelectric effect in bone or tendon can provide information on the physical loads that are being carried by these materials. For example, a shear stress applied along the long axis of a bone alters the polarization voltage that appears on a surface at right angles to the axis.³⁰⁸⁹ In another experiment,³⁰⁹³ piezoelectric surface charges on a loaded human femur were measured to range from -131 to +207 picocoulombs/cm² (-8 to +13 charges/micron²) from one end of the bone to the other end, depending upon position along the shaft. Real-time monitoring of this data would permit specific inferences as to the amount of load the bone was carrying and from what direction, including bending, shearing, and twisting forces, from which whole-body activity states could subsequently be inferred. Knowledge of these surface charge variations might also be exploited in osteographic (Section 8.2.4) or functional (Section 8.4) navigation.

Last updated on 17 February 2003