## 3 Results and Discussion
### Oxide Cross-Section Evaluation
#### 3.2.2 Oxide Cross-Sectional Compositional Analyses  
The representative cross-sectional EDS line scans for each oxide group are illustrated in Figure 7. Given the high number of dopant elements incorporated into these oxides, the element distributions across the cross-sectional thicknesses were divided into two sub-groups for clarity. The Ti, O, and substrate alloying element distributions are shown in the leftmost column, while the distributions of elements incorporated from the anodization electrolyte (Ca, P, and Mg) are shown in the rightmost column. Within each of the images in Figure 7, the substrate material-oxide interface is shown on the left side, followed by the inner layer oxide, and then the outer layer oxide corresponding with the oxide thickness descriptions provided in Figure 6. The cross-sectional EDS line scans clarified  
Figure 5: Representative FTIR spectrum for each oxide group. Each oxide surface shows a strong PO\({}_{4}\)\({}^{3-}\) absorption peak at 1050 cm\({}^{-1}\), indicative of hydroxyapatite and \(\alpha\)-tricalcium phosphate formation. Additionally, weak O-H bands between 3000 and 3600 cm\({}^{-1}\) represent the bending mode of adsorbed water, with a poorly defined characteristic hydroxyapatite OH\({}^{-}\) peak at 3570 cm\({}^{-1}\). High-intensity CO\({}_{3}\)\({}^{2-}\) substitution peaks at 875, 1450, and 1570 cm\({}^{-1}\) confirmed the presence of bone-like carbonated apatite on all oxide surfaces. the presence of bi-layered structures for each oxide. The inner oxide layers were found to be titanium dioxide-rich, and the outer oxide layers contained calcium compounds and magnesium dopant uptake levels, which explain the hydroxyapatite and tricalcium phosphate formation shown in the XRD analyses in Figure 1. Furthermore, the inner layer oxides in each group revealed the incorporation of some of the substrate alloying elements. For the two TiMo oxides, the substrate oxide interfaces clearly show a drop in the Mo levels as it is incorporated as a dopant into at least the inner oxide layer. This finding explains the formation of the omega phase on the substrate surfaces as the beta-stabilizing Mo levels are no longer sufficient to stabilize the beta-phase titanium. The concentration of Ti within the oxide cross-sections continued to decrease, moving away from the substrate, and it was almost completely absent in the outer oxide layer for most of the oxides. Another interesting note is that the wider inner oxide layer regions in the TiMo alloys, based on the inner layer's thickness measurements, revealed substantial Ca and P uptake profiles on the outer or rightmost sides of these inner layer oxides. However, given the formation of the embrittling omega phase at the alloy substrate-oxide interfaces, the use of these anodization processes on TiMo would not be recommended. Figure 6: Representative cross-sectional oxide thickness values: (**A**) inner oxide layer and (**B**) outer oxide layer. TiMo \(\beta\) and TiMo \(\alpha+\beta\) oxides exhibit significantly thicker inner oxide layers compared to CPTi and TAV (\(p<0.0001\)). Conversely, CPTi shows significantly lower outer oxide thickness than other alloys (\(p<0.0001\)), resulting in the lowest total oxide thickness. The * symbol denotes a statistical significance of \(p<0.05\) and the ****symbols denote a statistical significance of \(p<0.0001\). Figure 7: _Cont._  
The Ca, P, and Mg dopant uptake was found to be predominately in the outer layers of each oxide formed through our anodization processes. The representative EDS Ca, P, and Mg dopant uptake levels within the outermost two microns of the outer oxide layers and the corresponding Ca/P ratios are illustrated in Figure 8A,B. The chemistries in these outermost two microns are particularly relevant as they would approximate the chemistries in contact with most of the bodily fluids and tissues. The TiO \(\beta\), TiO \(\alpha+\beta\), and TAV oxide groups exhibited slightly higher Ca, P, and Mg dopant uptake compared to the CPTi oxides.