## 3 Results and Discussion
### PLA-Based Composites as Scaffolds  
#### 3.4.1 SFB Assay  
The potential of the 3D-printed/electrospun composites to induce apatite formation in their surface when immersed in an acellular ionic solution and the simulated body fluid assay (SBF) were used as an in-vitro bioactivity test to study the bone-bonding ability of designed materials [54]. For the obtained composites, we studied the mechanical properties, molecular weight, and calcium derivative depositions after 30 days of immersion of the composites in SBF media. DMA was used to measure the E\({}^{\prime}\) of the composites at body temperature, 37 \({}^{\circ}\)C, being PLA in their glassy state, and compared before (t\({}_{0}\)) and after immersion in SBF media for 30 days (t\({}_{30}\)) (Figure 9). A control sample was fabricated using two 3D-printed pieces bonded in the absence of a layer of electrospun fibers. The control samples having an ellipsoidal and square pore shape present a E\({}^{\prime}\) at 37 \({}^{\circ}\)C of 1610 \(\pm\) 315 MPa and 707 \(\pm\) 37 MPa, respectively, as can be seen in the Figure 9. The E\({}^{\prime}\) of 3D-printed/electrospun composites did not vary significantly as compared with control samples. In t\({}_{30}\) samples is observed an increase in E\({}^{\prime}\) compared with samples at t\({}_{0}\), which is more pronounced in composites possessing square pores, and is less pronounced in the ellipsoidal. The increase in E\({}^{\prime}\) is related to the formation of a layer of calcium derivatives on the surface of the materials [12; 55].  
Figure 8: Comparison of E\({}^{\prime}\) for ellipsoidal **(I)** and square **(II)** pore shape 3D-printed materials at 25 \({}^{\circ}\)C for single 3D-printed pieces (single 3D), two 3D-printed pieces bonded (composite), and 3D-printed/electrospun composites (PLA10, PLA/PEG/, PLA/PEG/2.5 HA, and PLA/PEG/5.0 HA).  
Molecular weight of 3D-printed/electrospun composites immersed in SBF at t\({}_{0}\) and t\({}_{30}\) was studied by GPC, estimating the molecular weight by using narrow PMMA standards. Considering that the mass of the composite is mainly the 3D-printed structure, the results shown in Figure 10 are related to the molecular weight of the PLA used in the fabrication of 3D-printed structures. 3D-printed/electrospun composites at t\({}_{0}\) present a M\({}_{\text{w}}\) of 1.0-1.6 \(\times\) 10\({}^{5}\) Da, with PDI ranging from 1.69 to 1.75. No significant differences in M\({}_{\text{w}}\) are observed at t\({}_{30}\); thus, no evidence of PLA degradation after 30 days was observed.  
The deposition of calcium derivatives over the composites during SBF assay was studied by SEM-EDS (see Table S2 in Supplementary Materials). The analysis was done qualitatively in some punctual zones due to the composites here studied did not present a flat surface, required parameter for quantitative SEM-EDS analysis [56]. EDS measurements in 3D-printed/electrospun composites formulated with PLA/PEG/2.5 HA and PLA/PEG/5.0 HA revealed the presence of Ca and P, with ratios exceeding the expected value for HA, i.e., 5.9-8.9 vs. 2.2 (wt.% ratio), respectively. This might indicate of the formation of calcium derivatives over the surface of composites as expected from the SBF assay. The Ca exceeding the amount might be related to the presence of calcium salts used in the SBF assay.