## 1 Introduction  
Among metallic materials, titanium alloys and specifically Ti-6 Al-4V are widely employed as implants for the biomedical industry owing to the favorable properties such as biocompatibility, resistance to corrosion in the body fluids [1, 2, 3, 4], a high strength/density ratio [5, 6, 7], excellent mechanical strength, including tensile and fatigue resistance, as well as a Young's modulus comparable to or closer to that of the natural human bone [8, 9, 10]. These titanium-based metals are bioinert and do not form chemical bonds with bone tissue after implantation. Osseointegration results from both physical and chemical interactions between the implant surface and bone tissue. However, in the case of titaniumand its alloys, this process is primarily governed by mechanical interlocking, without the occurrence of chemical bonding, which may prolong healing time [11]. Thus, surface modifications have been necessary for materials used in implants, as they contribute significantly to the improvement of osseointegration [12; 13]. Apart from surface topography and roughness, surface properties such as chemical composition or surface energy have been reported to influence interfacial reactions of biomedical devices [14; 15; 16; 17; 18]. According to the ASME B46.1 standard [19], surface topography refers to the overall morphology of the surface, encompassing all its geometrical features at different scales. Roughness, in turn, refers to the random small-scale irregularities, which can be quantified by parameters such as Ra and Rz. Thus, roughness is a quantitative aspect within the broader context of surface topography [20]. Several techniques have been developed and applied to Ti-6 Al-4V to enhance the properties required for biomedical application [21; 22; 23]. More recent studies have reinforced the role of EDM in biomedical applications, particularly in improving surface roughness, wettability, and biofunctionality [24; 25; 26; 27; 28]. Moreover, titanium and its alloys are difficult to machine due to several inherent properties of the material. Titanium is chemically very reactive with almost all cutting tool materials and its low thermal conductivity and elastic modulus range also impair machinability. Therefore, traditional machining techniques are often unable to machine this alloy economically [29]. Electrical discharge machining (EDM) presents a potential solution for the direct fabrication of complex shapes commonly observed in surgical implants [30]. It is a technique traditionally used to remove material from metal workpieces and form cavities by applying electrical discharge [31]. However, beyond its conventional applications, EDM can also be used to deposit materials onto the surface of the machined sample by using dielectric fluids containing conductive powders or chemical elements of interest [32]. This approach can enhance the properties of the workpiece through doping [33; 34; 35]. Powder-mixed EDM, in particular, has demonstrated promising results in enhancing surface properties through the incorporation of bioactive particles such as hydroxyapatite [36]. Typically, the tool electrode is set to a positive polarity (anodic), while the workpiece is set to a negative polarity (cathodic) [37]. In addition to polarity, the electrode material also significantly influences the surface characteristics resulting from EDM. Copper electrodes can lead to the deposition of metallic residues, such as copper ions, on the machined surface. It has been shown that even low concentrations of these ions can induce cytotoxic effects, depending on the location of the cells and the exposure time [38]. Graphite electrodes, on the other hand, tend to generate surface layers composed of carbon. Although this aspect is not widely discussed in the EDM literature, some studies indicate that carbon-containing surfaces do not impair cell adhesion or proliferation, making graphite a promising alternative for biomedical applications [39; 40].