Initial surface roughness influence on the generation of LIPSS on titanium and stainless steel and their effect on cell/bacteria viability

In this work, the influence of initial surface roughness on laser-induced periodic surface structures (LIPSS) formation is explored for titanium and stainless steel samples polished with grain sizes of 18.3µm, 8.4µm, 5µm, and 0.5µm, and lasered maintaining the same irradiation conditions. The resulting structures were studied by scanning electron microscopy (SEM), atomic force microscopy (AFM), Raman spectroscopy, and contact angle (CA) measurements, in order to characterize LIPSS periodicity and orientation, as well as surface chemistry and wettability. After characterization, representative structures were chosen to further explore their potential for bone implant treatment by inducing cells (MG63) and bacteria (E.coli and S.aureus) and testing for viability by resazurin assays, alkaline phosphatase activity, and SEM imaging. Results show that initial surface roughness (Ra) plays a different role on LIPSS generation for both materials, with stainless steel showing a higher dependence on Ra than titanium, however, both materials show a reduction on bacterial viability, while cell proliferation between polished and lasered samples also show an enhanced osteogenic effect.