Laser-induced in-plane curving of ripples on biomedical stainless steel and their relationship to biological functions

Laser-induced periodic surface structures (LIPSS) on biomedical stainless steel in air and water were systematically studied. The LIPSS exhibit in-plane curves near the ripple centres in the individual tracks of laser scan and the curving was opposite to the laser scan direction. The collective in-plane curving of LIPSS, a hitherto unknown feature for single train pulsed laser processing, is attributed to the accumulative effect of laser ablation and redeposition, which modifies the interference between the surface scattered wave and the incident laser beam. Combinations of media, scan-speed, and laser fluence, showed that the roughness can be increased by slowing the scan-speed. Ripples fabricated in the flowing water with slow scan-speed and high laser power are helpful for the hydrophilicity of biomaterials. A contact angle as low as 47.00 +/- 9.35 degrees is obtained towards high surface hydrophilicity. The results provide new insights on LIPSS about their formation and biomedical applications.