Material characterization and bacterial interaction of titanium discs produced by selective laser melting

The aim of this work was to characterize at nano-, micro-, and chemical level the surface topography of two new surfaces produced in Ti6Al4V by selective laser melting (SLM) and then subjected to the electrochemical polishing (EL) and organic acids-etching (OAE). Moreover, the capability of Streptococcus oralis to form biofilm on these surfaces was also studied. In addition, the microbiological results were compared with the topographical characteristics of the surfaces. The nano-pattering of the samples was investigated with the Atomic Force Microscopy (AFM); the micro-features, before and after the bacterial growth, were evaluated by the SEM observation and the Energy Dispersive X-ray Spectrometry (EDS) analyzed the chemical composition of the upper layers. The wetting properties of the discs were also evaluated. The colony-forming units (CFUs), the bacterial biomass, and the percentage of viable and dead cells were measured after 24 h of S. oralis biofilm formation on the different discs. Organic acids-etching samples were characterized by a ripple texture, higher nano-roughness, and wettability, respecting the machined and EL ones. The SEM observations showed that EL and OAE samples had an irregular surface with respect to the machined ones. The EDS found no significant differences for the Oxygen content of the upper layers of the samples. The microbiological analysis showed a significantly lower bacterial count and biofilm biomass formation on OAE in respect to the EL and the machined samples. In particular, the S. oralis biofilm formation was inversely correlated with the nano-roughness of the samples. The process of production of the discs, turning or SLM, significantly affected the micro-roughness of the samples. On the contrary, the treatment with OAE and EL modified the nano-topography of the samples and influencing the bacterial biofilm growth.