## 3 Results and Discussion  
### Oxide Surface Characterization  
#### 3.1.1 Oxide Crystallinity Analyses  
Representative XRD spectra collected over a 20\({}^{\circ}\) to 60\({}^{\circ}\) two-theta range for each oxide group are provided in Figure 1. The XRD analyses confirmed the formation of calcium phosphate-based crystalline phases, including \(\alpha\)-tricalcium phosphate and hydroxyapatite, in both the NOJ CP and NOJ MP anodized oxides. The tri-calcium phosphate and hydroxyapatite dual-phase compounds are known as biphasic calcium phosphates and are also widely used in orthopedic grafts and bone cement due to their beneficial bioresorbability, biocompatibility, and mechanical integration [31]. Tricalcium phosphates are the second most abundant calcium phosphate phases found in human bones and are commonly knownas bioactive, osteeconductive ceramic material [31]. \(\alpha\)-tricalcium phosphate has been shown to enhance the initial biological response by promoting the recruitment, adhesion, and differentiation of bone cells, leading to dynamic bone remodeling [31]. Hydroxyapatite has been extensively used as a coating material over titanium implants due to its similarity to the chemistry and crystallinity of natural bone [32; 33]. Coatings of hydroxyapatite on titanium are known to significantly enhance osteoblast viability, differentiation, and matrix mineralization in vitro [33]. In vivo hydroxyapatite coated implant studies in rat and rabbit femur models have shown improved bone-to-implant contact (BIC) compared to uncoated titanium [34; 35]. Compared to hydroxyapatite, tricalcium phosphates are more resorbable and lead to a controlled resorption rate, allowing the compound to be gradually replaced by newly formed bone [31]. The promising citrus-fruit-based anodization processes in the present study revealed the co-deposition of \(\alpha\)-tricalcium phosphate and hydroxyapatite on the anodized titanium surfaces.  
Calcium titanate phase peaks were also shown in Figure 1 XRD spectra for both the NOJ CP and NOJ MP oxides. Previously, nanostructured calcium titanate coatings fabricated on porous Ti-6 Al-4V scaffolds via hydrothermal treatment have demonstrated significant osteogenic benefits. In vitro studies revealed that titanate coatings significantly enhanced the osteogenic differentiation of pre-osteoblasts, as indicated by elevated alkaline phosphatase (ALP) activity and increased mineral deposition. In vivo, calcium titanate-coated scaffolds have shown improved osseointegration, as well as neurovascular integration when compared to uncoated titanium controls. A prior sol-gel study demonstrated that the presence of calcium titanate as an interlayer between the hydroxyapatite coating and titanium substrate improved the adhesion strength [36]. Thus, the formation of calcium titanate in our anodization processes will also likely improve the stability and long-term mechanical integrity of the oxide coatings.  
Figure 1: Representative X-ray diffraction spectra from each oxide. 20\({}^{\circ}\) to 60\({}^{\circ}\) two-theta scans containing characteristic peaks for calcium titanate, \(\alpha\)-tricalcium phosphate, and hydroxyapatite phases are shown.