## 4 Conclusions  
In conclusion, 3D printed multifunctional PLA/PCL-based bioscaffolds that combine the bioactivity of HAp and the piezoelectricity of BT were fabricated using the FDM 3D printing technique. The filaments and the constructs were characterized in terms of morphology, structure, and thermal properties. Composite filaments were produced in a single screw extruder using flakes formed by the solvent casting method. The amount of fillers that was measured was in good agreement with the initially loaded amount. Additionally, it was found that the addition of PCL in the PLA matrix increases the elasticity of the filaments and influences their thermal properties by lowering the glass transition  
Figure 10: Real (**a**) and imaginary (**b**) parts of dielectric permittivity as a function of frequency at T = 37 \({}^{\circ}\)C for all studied systems.  
temperature of PLA. The used formulations produced 3D specimens with precise shape and structure. Morphological studies showed a good distribution of the fillers in the polymeric matrix. In this study, piezoelectric measurements were performed in the 3D constructs and the obtained values revealed that the composite scaffolds exhibited piezoelectric coefficient (d\({}_{33}\)) values close to the human bone. The incorporation of the HAp and BT nanoparticles significantly enhances the dielectric properties of the examined systems, while inducing their functional behavior. Dielectric permittivity increases with filler content and reduces rapidly with frequency. It is evident that all reinforced systems exhibit higher values of \(\epsilon^{\prime}\) in comparison with PLA/PCL. In addition, the sample with 20 HAp/20 BT content exhibit highest dielectric permittivity values. This study provides fundamental knowledge on the formation and characterization of multifunctional scaffolds based on bioactivity and piezoelectricity. Although the obtained results are very promising for possible applications as bone defect fillers in the skeletal system, more research is needed to evaluate their in vitro and in vivo behavior. For example, cell viability and proliferation experiments or deeper studies are needed to check their in vitro biocompatibility.  
The following are available online at [[https://www.mdpi.com/article/10.3390/app11094253/s1](https://www.mdpi.com/article/10.3390/app11094253/s1)]([https://www.mdpi.com/article/10.3390/app11094253/s1](https://www.mdpi.com/article/10.3390/app11094253/s1)), Figure S1: TGA and DTGA (insert) graphs of neat PLA and PCL pellets and PLA/PCL filaments, Figure S2: XRD graphs of raw polymers and pure polymeric filaments and 3D constructs.  
Conceptualization, N.B.; Investigation, E.M., A.C.P. and N.B.; Methodology, E.M., A.C.P. and N.B.; Validation, E.M., A.C.P. and N.B.; Writing--original draft, N.B.; Writing--review and editing, N.B., E.M. and A.C.P. All authors have read and agreed to the published version of the manuscript.  
This research is co-financed by Greece and the European Union (European Social Fund--ESF) through the Operational Programme \"Human Resources Development, Education and Lifelong Learning 2014-2020\" in the context of the project \"Development of smart bone implants using the 3D printing technique\" (5049388).  
Not applicable.  
The data presented in this study are available on request from the corresponding author.  
The authors gratefully acknowledge [PERSON] and the Laboratory of Electron Microscopy and Microanalysis, School of Natural Sciences, University of Patras for the TEM measurements.  
The authors declare no conflict of interest.