## 4 Discussion of Results and Conclusions  
Ti6 Al4V alloy, after 316 LVM steel, is the most used biomaterial for implants in orthopedics. Amongst others, bone plates, stabilizing screws, and endoprostheses are made from this alloy. The development of additive manufacturing technologies makes it possible to implement modern design solutions and personalize implants, even with complex shapes. For this reason, performance tests were carried out for two groups of specimens prepared accordingly, with the aim of comparing the surface preparation and heat treatment applied. It was found that both the surface modification and the heat treatment influenced the properties of the samples produced by the incremental method in Ti6 Al4V alloy. Based on metallographic microscopic studies, a biphasic \(\alpha+\beta\) structure was found for all the samples studied. The post-treatment method influenced the surface roughness values. The highest value of the Sa parameter was determined for the surface of sandblasted samples in the initial state--13.41 \(\upmu\)m--while the heat treatment influenced the decrease in roughness in this group of samples--0.09 \(\pm\) 0.01 \(\upmu\)m. The lowest roughness was found for the surfaces after mechanical polishing, regardless of the temperature of the heat treatment applied. Additional surface analysis using a scanning electron microscope revealed unmelted titanium alloy powder, as well as sand grains after the sandblasting process, which was confirmed by qualitative analysis of the chemical composition using an EDS detector. Mechanical polishing removes the unmelted powder and sand residues after the sandblasting process. Hydrophilic properties were found for all the surfaces analyzed from 44.4\({}^{\circ}\) to 81.2\({}^{\circ}\). A material is assumed to have hydrophilic properties when the value of the contact angle is between 0\({}^{\circ}\) and 90\({}^{\circ}\). The hydrophilicity of the Ti6 Al4V alloy promotes cell adhesion to its surface, which is an important aspect in the context of implant applications, especially in orthopedics. The surface layer of the material should provide adequate adsorption properties for proteins and promote their functionality, including cell proliferation [40,41]. Heat treatment causes an increase in the contact angle and thus a decrease in wettability. Considering the tissue environment, the resistance of the implant to pitting corrosion is important. Of the sample groups analyzed, all the mechanically polished samples show the greatest resistance to this type of corrosion. This was also confirmed by macroscopic observations of the surface after testing. For this group, a smaller effect of heat treatment on the change in hardness was also found (from 382 HV5 to 390 HV5). In summary, an innovative approach described in the paper is the use of additive technologies, which replace traditional implant manufacturing methods with modern solutions with a higher degree of personalization. The original research aims to demonstrate how different heat treatment temperatures and surface treatments affect the physicochemical properties of printed Ti6 Al4V by using the DMLS method. It can be concluded that the selection of the type of surface and heat treatment will depend on the application of the implant in the tissue environment. Sandblasting is an important step after the 3D printing process to remove unbound powder particles from the sample surface. Skipping sandblasting could result in the presence of unintegrated Ti64 ELI alloy powder grains on the surface, which would significantly affect morphology evaluation. The use of mechanical polishing contributes to reducing surface roughness, which improves also resistance to pitting corrosion. A potential disadvantage of mechanical polishing is too smooth a surface, which can limit cell adhesion and hinder the process of osseointegration, which is crucial for connecting the implant with the surrounding bone.