*2.1. Substrate*

Commercially pure titanium and porous titanium with 69.7% porosity were employed in this study.

Group A: Non-porous-Ti (Ti) (JIS Type-2, J. Morita Corp., Tokyo, Japan); spherical shape; specimen size was 14 mm in diameter and 2 mm in thickness.

Group B: Porous-Ti (powder sintering product with 69.7% porosity; Nagamine Manufacturing Company, Kagawa, Japan); specimen size was 14 mm2, 1 mm in thickness, and the pore size was <sup>287</sup> ± <sup>87</sup> <sup>μ</sup>m2.

The Ti disks were polished with silicon carbide abrasive papers (#240, then #600). The polished groups were named "Polished-Ti". "Porous-Ti" was used without polishing for the experiments.

Half of the polished-Ti and porous-Ti substrates were subjected to alkaline treatment prior to the solution plasma treatment (SPT). The disks were immersed in 5 M NaOH solution at 60 ◦C for 24 h [11]. The alkaline treatment formed a micrometric network layer of sodium titanate hydrogel on the titanium surface, which enhanced the apetite nucleation in mineralizing solution.

After alkaline treatment, the polished titanium (Ti) group was named "Ti-AT" and the porous titanium substrate (porous-Ti) group was named "Porous-Ti-AT".
