Uniformity of Laser-Induced Periodic Surface Structures and Their Effect on the Antibacterial Performance of Stainless Steel

To evaluate the antibacterial performance of laser-induced periodic surface structures (LIPSS) formed on SUS430 stainless steel (equivalent to AISI 430, ferritic stainless steel), surface patterns were fabricated using femtosecond laser pulses (wavelength: 1030 nm; pulse duration: 150 fs) with controlled fluence.Two types of LIPSS were produced with average ridge and valley widths of approximately 410-nm and 380-nm/750-nm mixed structure, respectively.Antibacterial performance was assessed against Escherichia coli using the film-attachment method in accordance with the JIS Z 2801:2021 standard.Compared with the untreated SUS430 surface, the 410-nm LIPSS surface exhibited a reduction of approximately 83% in bacterial colony count, while the 380-nm/750-nm mixed structure showed a reduction of only about 31%.Fast Fourier transform analysis of scanning electron microscopy images revealed that the 410-nm structures had finer ridge and valley widths and higher structural uniformity.These findings suggest that the geometric characteristics of LIPSS, particularly ridge and valley width and uniformity, play a crucial role in enhancing antibacterial performance.This study demonstrates the potential of femtosecond laser processing as a novel approach to impart antibacterial functionality to material surfaces without the use of chemical agents.