## 3 Results and Discussion
### Wettability Analysis on the Laser-Treated Surfaces  
When a metal is subjected to laser ablation, its wetting properties are significantly modified. To understand the influence of laser processing on the wettability of pure titanium, contact angle (CA) measurements were determined two months after laser processing, before immersion, immediately after immersion, and 10 days after immersion. The CA of the polished CP Ti was measured to be about 66\({}^{\circ}\)\(\pm\) 5\({}^{\circ}\) (and a sample image of the water droplet captured is shown in Figure 7a) and this exhibits the hydrophilic nature of the CP Ti [11; 17; 53]. Theoretically, immediately after laser structuring, Ti has hydrophilic behaviour, hence the need to wait for two months to obtain steady-state conditions for measurements of the CAs [33]. Sample images of water droplets on the laser-structured surfaces at the C3 region are shown in Figure 7. This illustrates how the contact angle for water droplets on laser-treated surfaces changes when exposed to different storage environments over time. The observations show that at the C3 region, the surface was in a hydrophobic, highly hydrophilic, and almost hydrophobic state two months after laser processing before immersion, immediately after immersion, and 10 days after immersion, respectively. The average CA measurements of the surfaces of the laser-processed CP Ti regions two months before immersion, immediately after immersion, and 10 days after immersion are plotted as shown in column green (CA 1), column red (CA 2), and column blue (CA 3), respectively, in Figure 8. Before immersion in seawater, as shown in the green column  
Figure 7: Water contact angle measurements on the (**a**) polished surface and the laser-structured surface at the C3 region, (**b**) two months before immersion, (**c**) immediately after immersion, and (**d**) 10 days after immersion. (CA 1) in Figure 8, it can be noted that the CA measurements after laser processing have significantly increased as compared to the polished CP Ti surface. Except for the A4 region, which had a CA of roughly 87\({}^{\circ}\), all regions processed by laser had CAs of \(\geq\)91\({}^{\circ}\). This suggests that following laser processing the majority of the regions' surfaces were hydrophobic. Particularly in the regions of A1, B1, C1, D1, and E1, strong hydrophobicity was observed after processing at 100 mm/s, 5 \(\upmu\)m hatching distance, and one scanning pass. Through comparison of the CAs of regions A1, B1, C1, D1, and E1 before immersion, as seen in Figure 8, it can be noticed that the CA increased as the laser fluence increased. However, CA in the A1 region was much lower in comparison to the other four regions. These variations of CAs point to different surface structures existing on the laser-structured surface. These surface structures exhibited various morphologies and topographies as shown in Figures 2 and 4, respectively. A1 is made up of entirely HSFL and has a CA of 119\({}^{\circ}\), while B1, C1, D1, and E1 regions made up of NC-LIPSS have Cas of 139\({}^{\circ}\), 139\({}^{\circ}\), 141\({}^{\circ}\), and 143\({}^{\circ}\), respectively. Consequently, these surface structures have different roughness (Table 2), and this roughness influences the wettability. It is evident from looking at the CAs in the C1, C2, C3, and C4 regions (Figure 8) that the CAs decrease with increasing scanning velocity and/or hatching distance. The CA values of the C1, C2, C3, and C4 regions, which were processed at a hatching distance of 5 \(\upmu\)m, 25 \(\upmu\)m, 40 \(\upmu\)m, and 50 \(\upmu\)m, were 139\({}^{\circ}\), 137\({}^{\circ}\), 134\({}^{\circ}\), and 127\({}^{\circ}\), respectively. Based on Figure S1, the morphologies of these regions vary. That means that the wettability will also vary depending on the surface structures present in each region. This signifies that regions subjected to short hatching distances will be more hydrophobic due to their rougher texture, and vice versa [28].