## 3 Results and Discussion
### Roughness Measurement  
The Ra and Rz roughness values obtained through the measurements are presented in Table 4.  
The results showed that the DF1-F(\(-\)) condition (phosphorus and fluorine under negative polarity) produced the highest roughness values among all samples. The arithmetic mean roughness (Ra) reached 17.37 \(\pm\) 2.94 \(\upmu\)m, while the mean roughness depth (Rz) reached 89.43 \(\pm\) 12.12 \(\upmu\)m. High surface roughness is beneficial for biomedical applications, as it promotes cell adhesion and osseointegration in metallic implants [14; 16].  
The DF2-Ca(\(-\)) condition (calcium under negative polarity) exhibited the second highest values (Ra \(\approx\) 15.44 \(\pm\) 3.64 \(\upmu\)m; Rz \(\approx\) 71.65 \(\pm\) 16.44 \(\upmu\)m), followed by the DF2-Ca(\(+\)) condition (calcium under positive polarity), which resulted in intermediate measurements (Ra \(\approx\) 12.09 \(\pm\) 1.47 \(\upmu\)m; Rz \(\approx\) 58.69 \(\pm\) 9.07 \(\upmu\)m). These results suggest that negative polarity enhances surface roughness, likely due to the greater intensity of electrical discharge erosion and the formation of irregular recast layers during the electrical discharge machining (EDM) process [49; 50].  
In contrast, the DF1-F(\(+\)) condition (phosphorus and fluorine under positive polarity) resulted in significantly lower values (Ra \(\approx\) 5.86 \(\pm\) 1.37 \(\upmu\)m; Rz \(\approx\) 36.16 \(\pm\) 8.72 \(\upmu\)m). This reduction may be attributed to more homogeneous material deposition, leading to a smoother finish.  
The reference sample (not machined by EDM) exhibited the lowest roughness values (Ra \(\approx\) 4.06 \(\pm\) 0.48 \(\upmu\)m; Rz \(\approx\) 22.10 \(\pm\) 3.63 \(\upmu\)m), confirming that the EDM process significantly modifies the surface topography. Smoother surfaces, such as the reference sample and the DF1-F(\(+\)) condition, exhibited lower roughness values, which may limit their ability to promote cell adhesion. Rougher surfaces, on the other hand, tend to increase the contact area and improve cell-surface interactions, favoring attachment and proliferation, factors that are crucial for effective osseointegration [69].  
Overall, DF1-F(\(-\)) proved to be the most effective condition for increasing surface roughness, reinforcing the role of phosphorus and fluorine under negative polarity in modifying surface topography. These findings highlight the potential of this condition for biomedical applications, particularly those requiring enhanced cell adhesion to improve implant integration and tissue compatibility [70; 71; 72; 73; 74].  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Roughness** & **DF1-F(\(+\))** & **DF1-F(\(-\))** & **DF2-Ca(\(+\))** & **DF2-Ca(\(-\))** & **Reference Sample** \\ \hline Ra (\(\upmu\)m) & 5.86 \(\pm\) 1.37 & 17.37 \(\pm\) 2.94 & 12.09 \(\pm\) 1.47 & 15.44 \(\pm\) 3.64 & 4.30 \(\pm\) 0.48 \\ Rz (\(\upmu\)m) & 36.16 \(\pm\) 8.72 & 89.43 \(\pm\) 12.12 & 58.69 \(\pm\) 9.07 & 71.65 \(\pm\) 16.44 & 22.10 \(\pm\) 3.63 \\ \hline \hline \end{tabular}
\end{table}
Table 4: Roughness and standard deviation of the machined samples with the fluids and polarities used.