Cellular response of Staphylococcus aureus to nanostructured metallic biomedical devices: surface binding and mechanism of disruption of colonization

Metallic materials with nanometre-sized grains provide surfaces that are different from conventional polycrystalline materials because of large proportion of grain boundaries. We describe here, the combination of materials science and engineering involving nanocrystallization and alloying with copper and cellular biology to develop our understanding of inhibition of bacterial colonization and biofilm formation on nanostructured surfaces that are significantly different from conventional coarse-grained (CG) structures. A novel process referred as phase reversion was used to induce nanostructuring in the conventional CG metallic material. Quantitative and qualitative studies of bacterial colonization indicated that the combined effect of nanostructuring and alloying with copper effectively influenced the degree of bacterial colonization, a behaviour related to passive film on the surface. The high density of grain boundaries in nanocrystalline materials provided increased diffusion path for Cr and Cu atoms to reach the surface to form a stable passive film with a high copper concentration. It is envisaged that the stable passive film on the nanostructured surface develops inward-growing oxide pegs at high fraction grain boundaries that lead to strong interfacial bonds between the substrate and exterior passive film. The passive film minimized free energy of the system and surface electron activity, which effectively hindered interaction between the material surface and the micro-organism.