Many materials of biological origin such as wood, 1,2 bone 3 and tendon 4 as well as bioinspired peptide nanotubes 5 exhibit piezoelectricity. Piezoelectricity is a property of crystals and chiral molecules that originates from the absence of a center of symmetry in their structures. When such materials are stressed, their electrical neutrality is perturbed and a net polarization results at the surface of the material. The Curie brothers first demonstrated this property, known as the direct piezoelectric effect, in 1880. 6 There also exists an opposite effect known as the converse piezoelectric effect; in this case, an electrical field applied across a piezoelectric material causes a mechanical strain to develop. Of the 32 crystallographic point groups, 21 do not possess a center of symmetry and 20 of these classed as piezoelectric. 7
The direct piezoelectric effect in the globular protein lysozyme
ABSTRACT
Here, we present experimental evidence of the direct piezoelectric effect in the globular protein, lysozyme. Piezoelectric materials are employed in many actuating and sensing applications because they can convert mechanical energy into electrical energy and vice versa. Although originally studied in inorganic materials, several biological materials including amino acids and bone, also exhibit piezoelectricity. The exact mechanisms supporting biological piezoelectricity are not known, nor is it known whether biological piezoelectricity conforms strictly to the criteria of classical piezoelectricity. The observation of piezoelectricity in protein crystals presented here links biological piezoelectricity with the classical theory of piezoelectricity. We quantify the direct piezoelectric effect in monoclinic and tetragonal aggregate films of lysozyme using conventional techniques based on the Berlincourt Method. The largest piezoelectric effect measured in a crystalline aggregate film of lysozyme was approximately 6.5 pC N −1 . These findings raise fundamental questions as to the possible physiological significance of piezoelectricity in lysozyme and the potential for technical applications.
http://aip.scitation.org/doi/10.1063/1.4997446
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Matti, you come up with some interesting articles.
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