“…When subjected to mechanical loading, bone generates an electric charge (direct piezoelectric effect), and conversely, when an electrical charge is applied, strains/stresses can appear in bone (converse piezoelectric effect) ( Fernández et al, 2012a ; Fernández et al, 2012c ) (see Figure 1B ). Similar to other studies ( Fotiadis et al, 1999 ; Qin and Ye, 2004 ; Fernández et al, 2012a , Fernández et al, 2012c ; Duarte et al, 2018 ), the bone was assumed to behave like a crystal with hexagonal symmetry, i.e., the third-order piezoelectric stress tensor ℰ is defined by four values and the electric permittivity tensor (dielectric tensor) is a diagonal matrix with two constants. These tensors can be written in the following matrix form: where the third principal direction represents the longitudinal direction of the tibia bone ( Fernández et al, 2012c ).…”