Piezoelectricity of natural biomaterials

Abstract

Shear piezoelectricity is observed in uniaxially oriented system of optically active biopolymers such as polysaccharides, polypeptides and polynucleotides. The magnitude of the piezoelectric constant is proportional to the degree of crystallinity, the degree of orientation and the piezoelectric constants in single crystal, as illustrated for wood. The superposition of instantaneous and relaxational polarizations may account for the sign reversal of the piezoelectric constant for oriented amylose film when temperature increases from - 150°C to 50°C. The piezoelectric constant for oriented polyhydroxybutyrate film is shown to be the sum of contributions from crystalline phase and oriented noncrystalline phase with opposite sign. The increase of the latter with increasing temperature may explain the relaxation of the piezoelectric constant at the glass transition around 20°C. When a d.c. field is biased, isotropic polymer systems such as gelatin may show apparent induced piezoelectricity through the stress-induced change of capacitance and conductivity. Application of a piezoelectric polymer film in vivo enhances the metabolic activity of bone cell and promotes osteogenesis.