**2.11 The piezoelectric effect**

The piezoelectric effect is a physiological characteristic of certain materials that generates an electric charge in response to a supported mechanical load. The suffix Piezo is derived from the Greek *piezein*, which means to press [7].

Bone has piezoelectric properties because of the highly oriented and patterned structure of collagen type I, and collagen's ability to respond to mechanical loads [7, 8]. When a shearing force is applied to collagen fibers, and the bundles glide past each other, an electric charge is generated. Collagen also has significantly lower elastic moduli than the bone's corresponding mineral component, which makes collagen microfibrils experience the greatest load when strained. Experiencing the greatest load under force deforms collagen fibbers, and this deformation leads to the piezoelectric effect [8]. The role of collagen's piezoelectricity in bone regeneration and remodeling is related to the formation of electric dipoles that stimulates the osteoblasts to promote mineral deposition in the extracellular matrix, increasing bone density. Clinically, when a fracture occurs, the collagen's piezoelectricity is potentiated with an additional mechanism for osteocytes to sense areas with more stress; the generated piezoelectric charge would be greater in stressed areas, which is produced when the bone suffers

deformation and negative charges are produced on the tension side and positive charge on traction side, generating bone growing by electric current [7].
