## 3 Results and Discussion
120-gri zirconia sand at a 45\({}^{\circ}\) angle, followed by etching with 3 M HF solution (Figure 5a), exhibited irregular protrusions and depressions with multi-scale features. This composite treatment method preserves the macroscopic roughness produced by sandblasting while further enhancing surface complexity at the microscopic scale through acid etching. Such a structure may be conducive to cell adhesion and the osseointegration process. Figure 5b-d display surface morphologies after shot peening with different parameters, followed by etching with 3 M HF solution. A clear trend in surface structure changes is observed as the shot peening pressure decreases. Treatment at 2 kg/cm\({}^{2}\) (Figure 5b) produced larger plastic deformations and irregular structures, while treatment at 0.5 kg/cm\({}^{2}\) (Figure 5d) resulted in a more uniform and refined surface morphology. This trend indicates that precise control over the initial surface morphology can be achieved by modulating shot peening parameters, subsequently influencing the corrosion behavior during the acid etching process. Comparing all treatment methods, it is evident that they all generated complex three-dimensional structures on the Ti-64 surface, albeit with different specific morphological features. Sandblasting followed by acid etching (Figure 5a) created deeper etch pits with sharp edges, while shot peening followed by acid etching (Figure 5b-d) formed more rounded protrusions and depressions. These differences may arise from the varying effects of initial mechanical treatment methods on surface stress states and microstructures. Notably, all treated surfaces exhibited multi-scale roughness features, ranging from micron-scale major protrusions to nano-scale fine structures. This multi-scale structure may have complex effects on subsequent biological performance, potentially promoting the attachment and proliferation of certain cell types while also influencing the material's fatigue properties and corrosion behavior. The diverse range of complex structures created on the Ti-64 surface by combining mechanical treatments and chemical corrosion provides a broad design space for optimizing the surface characteristics of implant materials. Future research should focus on quantifying the relationship between treatment parameters and resulting surface characteristics, including roughness, porosity, and chemical composition. Figure 5: SEM images of Ti-6 Al-4V surfaces after various treatments followed by 3 M HF etching. (**a**) Sandblasted with 120-gri zirconia sand at 45\({}^{\circ}\); (**b**) shot-peened with zirconia beads at 2 kg/cm\({}^{2}\) for 5 s; (**c**) shot-peened at 1 kg/cm\({}^{2}\) for 5 s; (**d**) shot-peened at 0.5 kg/cm\({}^{2}\) for 5 s. All images demonstrate complex surface structures resulting from combined mechanical and chemical treatments, with varying degrees of roughness and feature sizes. Comprehensive in vitro studies are necessary to assess the biological response of various cell types to these modified surfaces, while in vivo experiments would evaluate the osseointegration performance of implants with these surface modifications. Additionally, investigating the long-term stability of these surface structures under physiological conditions and assessing the impact of surface treatments on the bulk mechanical properties and corrosion resistance of the material are crucial for ensuring the overall performance and safety of the implants. Table 1 summarizes the surface roughness parameters (Ra and Rq) and surface hardness (HR15N) of the Ti-64 alloy under various surface treatment conditions. These data reveal the significant impact of different surface treatment methods on the surface characteristics of Ti-64. The original polished Ti-64 surface exhibited extremely low roughness (Ra = 0.09 \(\pm\) 0.01 \(\upmu\)m), consistent with the smooth surface expected after mechanical polishing. However, surface roughness increased significantly with immersion corrosion treatment alone.