## 3 Results and Discussion
### Contact Angle  
The water contact angle of each sample was measured, as shown in Figure 6. The untreated sample exhibited the highest contact angle (30.2\({}^{\circ}\)\(\pm\) 1), indicating low surface wettability. Samples machined with DF1-F presented contact angles of 5.5\({}^{\circ}\)\(\pm\) 1 and 17.8\({}^{\circ}\)\(\pm\) 1 under negative and positive polarities, respectively. In contrast, the surfaces treated with DF2-Ca showed significantly enhanced wettability under both conditions, to the extent that contact angle measurements could not be obtained using a goniometer due to complete droplet spreading. Accordingly, all surfaces can be classified as hydrophilic, with the exception of those treated with DF2-Ca, which demonstrated superhydrophilic behavior.  
A number of studies have shown that modifying titanium alloy surfaces to obtain oxides as rutile or a mixture of rutile and anatase, is crucial to increased proliferation and differentiation of cells such as osteoblasts. These oxides are chemically stable and have greater hydrophilicity, which promotes cell attachment to the surface. Therefore, it is known that the most desirable contact angle value for hard tissue regeneration ranges from 35 to 80 degrees [79].  
Otherwise, hydrophilic surfaces coated with calcium phosphate, such as those machined with DF2-Ca, exhibit a low water contact angle, indicating high wettability. This property may enhance cell coverage, improve osseointegration, and is essential for biomedical applications [80, 81]. Although the DF2-Ca samples did not exhibit the highest surface roughness, their superhydrophilic behavior may significantly favor protein adsorption during the early stages of osseointegration. Recent studies have demonstrated that the synergistic effect of combining microroughness with superhydrophilicity leads to enhanced biological response and faster integration of implants with bone tissue [80, 81]. Therefore, EDM-treated surfaces like those obtained with DF2-Ca may offer promising biological performance even when roughness is not maximized.  
The superhydrophilicity observed in the DF2-Ca samples can be attributed to the combined effect of the porous surface morphology and the incorporation of calcium and phosphate species derived from the dielectric fluid. These elements are known to increase surface energy and enhance water affinity by promoting the formation of polar groups on the material surface [82]. This mechanism leads to the complete spreading of the water droplet, as observed in the wettability test.  
Figure 6: Water droplets on different surfaces: Ti-6 Al-4V control, (**A**) negative and (**B**) positive polarity using DF1-F, and (**C,D**) machined with DF2-Ca in the negative and positive polarities, respectively.  
Studies indicate that superhydrophilic surfaces favor the adsorption of fibrinogen, a protein that plays an important role in bone healing [83]. In addition, such surfaces can promote osteoblast adhesion, proliferation, and differentiation [84]. These findings suggest that the surface characteristics obtained through the EDM process with DF2-Ca may provide a biologically favorable environment for enhanced cellular response.