## 5 Discussion  
We investigated samples with different AgNP-Ti surface configurations as a result of different amounts of silver vaporized. Particle diameter, surface characteristics, cell viability, and hydrophilicity were compared. The nanoparticles created from 3 nm vaporized silver layers by heat treatment at 600 \({}^{\circ}\)C for 1 min had a good antibacterial effect, as we demonstrated in our former experiment [23] where the same 60 nm diameter silver nanoparticles were created and anchored to the titanium surface using electron cyclotron resonance (ECR) ion source. In this recent paper, we demonstrated that a surface with 60 nm silver particle diameter provided better viability for DPSCs than surfaces with a bigger particle diameter. Figure 8 shows that a layer with 100 nm or larger average nanoparticle size significantly decreased cell viability compared to 60 nm AgNF diameter. The success of biomaterial and cell interaction is determined by many factors, from the part of the substratum properties to cell-substratum interactions. A few works also revealed that cell behavior is determined by not only surface properties but also cell type [33; 34]. The influencing factors of surface properties such as surface hydrophilicity, roughness, texture, chemical composition of the substratum, charge, and others may be critical for the biocompatibility of the tested materials. [PERSON] et al. found that cell proliferation and substratum surface wettability are in direct relation (water contact angles were measured by the sessile drop method) [35]. [PERSON] et al. studied the phosphate buffer contact angle on modified glass surfaces at different pH by the sessile drop method, and they found that hydrophilic surfaces (the better wetting ability by water) significantly enhance cell attachment and spreading. Moreover, cell attachment is influenced by wettability and charging of the surface [36]; hydrophilic surface and moderate surface hydrophilicity promoted cell attachment. Surface wettability can be analyzed with contact angle measurements that give information about surface hydrophilicity. The contact angle data are strongly influenced by surface characteristics such as chemical composition of the sample surface, surface topography, presence of entrapped air bubbles in surface irregularities, and chemical interaction between the liquid and the surface. In this investigation, the tested sample surface could be chemically considered as a heterogeneous (mixed) surface, where the Ag/titanium ratio changed after heat treatment. Moreover, a surface roughness diversity appeared with the Ag formed clusters (discontinuities) on the titanium surface, which meant an additional macro roughness surface to the nanotopography of the polished titanium surface. The water CA was around 83\({}^{\circ}\) on polished titanium (data not shown), and that value decreased to 63.675\({}^{\circ}\) after 60 nm AgNPs were created on the surface (Figure 6). The water contact angle value increased up to 105\({}^{\circ}\) by increasing the size of AgNPs to 368 nm. That can be explained by the change of Ag/Ti ratio on the actual surface, where the water was connected to the surface. The smaller Ag particles meant the presence of more AgNPs on the same sized testing area, which contributed to CA decreasing (from 83 to 63.675\({}^{\circ}\)) compared to unmodified Ti. The CA shifted to higher values with the increased Ag particle size, whereas Ag/Ti ratio decreased (smaller amount of Ag on the same size test area). Based on our measurements, it was found that the Ag/Ti ratio on the surface could also be determined by the shape and the size of silver nanoparticles. [PERSON] et al. found a similar water contact angle on titanium surfaces, which was 89\({}^{\circ}\)[37]. In their study, the CA increased with silver deposition on the titanium surface, similar to our study findings.