## 3 Results and Discussion
### Dielectric Properties  
In this study, the combination of the bioactive properties of HAp with a piezoelectric and high permittivity ferroelectric material, such as BT, was attempted. Figure 10 depicts the variation of the real and imaginary parts of dielectric permittivity with frequency at 37 \({}^{\circ}\)C, for all the types of the examined systems. The influence of the reinforcing phase becomes evident via the enhancement of (\(\epsilon^{\prime}\)) with filler content. The real part of dielectric permittivity increases with frequency diminishing for constant temperatures. This is expected since epsilon prime reflects the level of the achieved polarization. When the frequency is low, permanent and induced dipoles acquire sufficient time to align themselves parallel to the applied field. Figure 10 denotes that the effect of BT inclusions is more pronounced with respect to the effect of HAp.  
In general, it is normally observed that the dielectric constant decreases as the frequency increase until a constant plateau value; this maximum value depends on the fact that beyond a certain frequency of the electric field, the dipoles are not affected by the alterations on the field. In the case of ionic crystals (e.g., hydroxyapatite crystal structure), the total polarization is electronic and ionic in nature. The hydroxyapatite crystal structure consists of vertically aligned OH\({}^{-}\) ions along the c-axis and Ca\({}^{2+}\) and PO\({}_{4}\)\({}^{3-}\) ions. This dipole moment of the hydroxyl ions is mainly responsible for the dielectric nature of hydroxyapatite. As in most cases, at low frequencies, polarization is fairly affected by the alterations of the field but at high frequencies, the heavy charge of positive and negative ions cannot follow the field variations; the dipole moment of the hydroxyl ions is unaffected by alterations on the field and therefore polarization decreases, resulting in the decrease of \(\epsilon^{\prime}\).  
Figure 9: Piezoelectric coefficient (d\({}_{33}\)) as a function of HAp/BT composition.  
The values of \(\varepsilon^{\prime}\) of the reinforced with HAp composites are attributed to the dipole moment of hydroxyl ions in HAp [68, 69]. Concerning a binary system of two components varying significantly in permittivity values, one should expect that the permittivity of the whole system should increase monotonically with the concentration of the high permittivity constituent. Since dielectric permittivity of BT is much higher than that of PLA/PCL and HAp, the recorded behavior for the filler concentration up to 20 HAp/20 BT, in Figure 10 is quite understandable.  
Specimens with the highest BT content exhibit relatively high values of losses (\(\varepsilon^{\prime}\)), although the losses of the specimens with lower BT concentration can be considered as low. It could suggest that the employed fabrication procedure via 3D printing appears to be beneficial upon the reduction of dielectric losses.  
[PERSON] et al. measured the dielectric properties of bones containing different amounts of water in a frequency range from \(10^{5}\) to \(10^{3}\) Hz. The dielectric constant of the human cortical bone has been found to a very sensitive function of water content. The dielectric constant of dry human cortical bone is around 10. The measured dielectric constant of dry bone values is on average 5.7-6.5 [70]. Furthermore, composite scaffolds with potential applications in bone tissue engineering composed of chitosan and HAp prepared by coprecipitation from aqueous solutions. Dielectric permittivity measurements at 1 MHz, 1000 kHz, and 10 kHz are in the same range with values reported in the present study [71]. Finally, since polarization is proportional to the real part of dielectric permittivity (\(\varepsilon^{\prime}\)) high values of \(\varepsilon^{\prime}\) results higher polarization in bioscaffolds and therefore can help bone regeneration.