## 2 Materials and Methods  
A polished commercially pure titanium (CP Ti) with 25 \(\times\) 25 \(\times\) 4 mm dimension was subjected to laser processing. The nominal percentage chemical compositions of the elements on the polished sample as per the Energy-dispersive X-ray spectroscopy (EDX) were Ti = 99.1%, O = 0.7%, Fe = 0.1%, Al = 0.1%, and C = 0.1%. Before laser processing, the polished sample was ultrasonically cleaned in acetone and ethanol for 10 min each before drying using pressurized air. The laser structuring experiments were carried out using a picosecond laser system (Perla(r)100, Hilase, Dolni Brezany, Czech Republic) which has a picosecond pulsed laser (Yb-YAG thin disk medium), scanning head, beam expander, and XY translational stage. The schematic set-up of the laser system has been previously published [31]. The laser source produces laser pulses with a pulse width of 1 ps, a wavelength of 1030 nm, a repetition frequency of 60 kHz, and a maximum pulse energy of 1 mJ. The focusing lens (Linos, Qioptiq, Gottingen, Germany) on the scanning head (intelli_SCAN_ 14, Scanlab, Puchheim, Germany) ensured that the focussed spot diameter of the linearly polarised Gaussian laser beam during laser structuring experiments was \(\sim\)25 \(\upmu\)m.  
The sample was processed using a cross-hatching scanning strategy in a bidirectional manner to process a surface area of 4 \(\times\) 4 mm\({}^{2}\) by laser ablation to create cross-hatched patterns in ambient air according to selected laser parameters. The scanning patterning design was done by Direct Machining Control (DMC) 1.7.60 (64 bit) software (Direct Machining Control, UAB, Vilnius, Lithuania) and the laser processing scheme is shown in Figure 1. The detailed laser input parameters used in the laser structuring are found in Table 1. In this cross-hatching scanning strategy, the first scanning was done in a direction at an angle of 45\({}^{\circ}\) and the second scanning at an angle of 135\({}^{\circ}\) to create a cross-hatched grid pattern (SEM images showing the pattern are shown in Figure S1 (Supplementary Information)). The laser beam was moved on the surface at a specified hatching distance, H, and a scanning velocity, V, during the raster scanning of the sample and in bidirectional scan trajectories. From Table 1, the pulse overlap (PO) for regions 1, 2, 3, and 4 was 93, 90, 87, and 73% respectively, while the scanning line overlap (LO) was 80, 0, \(-\)60 and \(-\)100%, respectively [32]. After laser processing, the sample was cleaned using pressurized air only. The surface morphologies of the polished sample and the laser-processed regions were evaluated using a scanning electron microscope (SEM, MIRA, Tescan, Brno-Kohoutovice, Czech Republic) using secondary electrons. The sample was examined using a 5 kV accelerating voltage. Measurements of the periodicity and dimensions of micro/nanostructures on the sample surfaces were estimated from SEM images by the free image processing software ImageJ 1.54 g and the average of the measurement values are presented herein. The morphology was assessed also after immersion of the laser-structured sample in seawater from the Caspian Sea for 14 days to check if there were morphological changes after immersion. An energy-dispersive X-ray spectrometer (EDX, Oxford Instruments, Oxford, UK) attached to the MIRA SEM was used for elemental quantification of the CP Ti. The regions were examined using a 20 kV accelerating voltage and beam intensity (BI) index of 16.5 and both secondary electrons and backscattered electrons were collected. A surface profilometer (Dektak XT, Bruker, Billerica, MA, USA) was used to profile surface topography and determine surface-based roughness parameters of the laser-structured surfaces. The profiler has a vertical resolution of 1 A and the tip used has a radius of 2 \(\upmu\)m. The open-source Gwyddion 2.64 programme was used to evaluate the collected data. Optical observations were performed with a stereomicroscope (Stemi 508, Zeiss, Oberkochen, Germany) on the laser-ablated regions.