# Anodic Oxidation of 3D Printed Ti6 Al4V Scaffold Surfaces: In Vitro Studies
## 3 Results and Discussion  
### Surface Characterization  
The presence of powder particles, originating from the PBF-EB manufacturing process, can be observed on both the surface and internal walls of the scaffold's as-built structure, as shown in Figure 4a. These particles are more visible at higher magnification (indicated by the red arrow). The results of chemical polishing are shown in Figure 4b, where it can be observed that the surfaces of the struts are more uniform. This demonstrates the successful removal of fused powder particles from the inner wall of the sample. Minimizing defects in the lattice structure, as defined by the unit cells, is crucial for preserving its properties, especially its mechanical properties. These defects can have a significant impact on the performance of the structure. Several defects that should be minimized include high surface roughness, the presence of unmelted powder particles, and porosity [21; 22]. The use of anodic oxidation after chemical polishing did not compromise the obtained geometry, as can be seen in the images in Figure 3. This is an important parameter to consider. Figure 5 presents SEM images that provide a detailed view of the scaffolds after anodic oxidation. The top-view images reveal a nanoporous structure characterized by irregular cavities that are randomly distributed on the surface. Figure 4: (**a**) Scaffold Ti\({}_{6}\)Al\({}_{4}\)V as-built structure: details of the internal walls of the scaffold with unmelted particles from the PBF-EB process (indicated by red arrows) in a magnified strut surface image. (**b**) Scaffold Ti\({}_{6}\)Al\({}_{4}\)V after chemical polishing, shown in a magnified strut surface image. (**c**) Scaffold Ti\({}_{6}\)Al\({}_{4}\)V after anodic oxidation, shown in a magnified strut surface image. To analyze the crystal structure of the scaffolds after anodization, we utilized the X-ray diffractometry (XRD) technique (Figure 6). In the Ti6 Al4V sample, only peaks corresponding to the phases present in the substrate were observed, mainly the \(\alpha/\alpha^{\prime}\) phases. This observation is consistent with the literature [3; 18; 23; 24]. Although the PBF-EB technique involves high temperatures for melting the metallic powder, it is performed under controlled conditions, such as a vacuum atmosphere. This prevents the formation of significant quantities of oxides that could be detected via XRD. The diffractogram obtained after anodizing the scaffolds shows new peaks, indicating the formation of an oxide layer. The anodization process produces an amorphous layer, but the layer becomes biphasic with peaks identified as the rutile and anatase phases after the growth of nanotubes. Similar behavior was observed in studies conducted by  
Figure 5: FEG-SEM image of the anodized surface of the Ti\({}_{6}\)Al\({}_{4}\)V scaffold (top view) fabricated using PBF-EB, revealing the presence of a nanoporous layer. Figure 6: XRD patterns of the porous scaffolds produced via the PBF-EB process after anodization (ao), compared to the control group (as built). [PERSON] et al. [3] on the surface modification of the Ti6 Al4V scaffolds produced through PBF-EB using electrochemical techniques. Studies have shown that crystalline anatase phases exhibit better bioactivity than the amorphous phase [22]. X-ray photoelectron spectroscopy (XPS) was used to measure the elements, chemical states, and their interactions. The complete range of Ti6 Al4V alloy samples, both before and after the growth of a nanotube layer, is shown in Figure 7a. The results of the deconvolution can be found in Table 1. The main elements observed in both cases were titanium (Ti), oxygen (O), and carbon (C), with trace amounts of nitrogen (N), silicon (Si), and copper (Cu) also detected. These lower levels are likely related to surface contamination that occurred during sample processing and preparation. Two peaks indexed to Ti6 Al4V were identified (Figure 7d,e): Ti 2p 1/2 and Ti 2p 3/2.