## 3 Results and Discussion
### Composite Design by Combining 3D-Printed Pieces with Electrospinning PLA-Based Fibers  
3D-printing and electrospinning techniques were combined to produce 3D-printed/ electrospun composites, consisting of two 3D-printed pieces stacked on a central layer of PLA electrospun mat in a sandwich-like structure (Figure 6). Eight materials were obtained after combining the two pieces of the 3D-printed scaffold possessing square and ellipsoidal pores with the four different PLA electrospun mats. For the composite fabrication, a layer of PLA-based fibers was deposited by electrospinning, placing a 3D-printed PLA piece in the electrospinning collector, and then another 3D-printed PLA piece was stacked on top of them. While the 3D-printed scaffolds afford good mechanical properties to the composite, the PLA electrospun mats allow tuning of the material composition. Indeed, an electrospinning deposition of PLA 10 wt.% solution over the 3D-printed PLA pieces failed, whereas it succeeds using PLA/PEG and PLA/PEG/HA solutions (Figure 6). Dynamic mechanical analysis (DMA) was used to study the mechanical properties of 3D-printed pieces and composites at different temperatures. This technique performs a low deformation into the material, measuring the response of the material to a sinusoidal deformation. In DMA, the modulus is the parameter used to describe the overall resistance of materials to a deformation. The elastic modulus (or storage modulus, E\({}^{\prime}\)) measures the elasticity and the ability of the material to store energy; the viscous modulus (or loss modulus, E\({}^{\prime}\)) measures the ability of the material to dissipate energy, and the tan \(\delta\) (or damping factor) is calculated as the ratio of viscous to the elastic response. High values of tan \(\delta\) are indicative of a high potential of the material to dissipate energy by segmental motion. The damping factor reflects the energy dissipation potential of materials [46]. In Figure 7 is shown the evolution of E\({}^{\prime}\) and tan \(\delta\) of PLA 3D-printed pieces in a temperature scan from room temperature to 120 \({}^{\circ}\)C. During the thermal cycle applied, three clear zones are observed from both E\({}^{\prime}\) and tan \(\delta\), and are related to changes in molecular mobility of PLA chains in the material: glassy state, glass transition, and rubbery state, respectively. In the glassy state, the PLA molecules are forming a rigid structure, and only secondary  
Figure 5: Wettability of electrospun fibers. (A) PLA10, (B) PLA/PEG, (C) PLA/PEG/2.5 HA, and (D) PLA/PEG/5.0 HA. relaxations can occur (\(\gamma\) and \(\beta\)), thus a high E\({}^{\prime}\) value (\(>\)10\({}^{9}\) Pa) is observed in this zone, reflecting the glassy state of PLA at this temperature range. An increase in temperature produces an increase in polymer molecular mobility (\(\alpha\) relaxations), and is marked by a considerable drop in the E\({}^{\prime}\) observed in a narrow range of temperatures, also appearing at well-defined tan \(\delta\) peaks in this temperature range. In addition, tan \(\delta\) is frequently used to measure the glass transition (T\({}_{\rm g}\)) of polymers in DMA experiments [47; 48]. In our assays, the T\({}_{\rm g}\) of PLA used in 3D-printing is 67-68 \({}^{\circ}\)C, similar to reported values applying the same measurement conditions [49; 50]. In the rubbery state, all PLA macromolecules have enough mobility to form crystalline domains, then a small increase in the E\({}^{\prime}\) is observed over 90 \({}^{\circ}\)C, related to the cold-crystallization of PLA [51; 52]. Figure 6: (**I**) Images of 3D-printed/electrospun composites obtained after combining 3D-printed PLA pieces with ellipsoidal and square pores with PLA-based fibers. (**II**) SEM images of the fibrous layer of PLA-based electrospun composites deposited over the surface of 3D-printed pieces.