This study demonstrates a simple and effective approach – a combination of surface nanocrystallization and thermal oxidation treatment – for reduced biofilm adherence to stainless steel with the aim of suppressing the formation of biofilms on medical implants (suitable for not only stainless steel but also other passive metallic implant materials).

It is known that the passive film or a thermally formed oxide film on a material can reduce its reactivity. Such a function could be significantly enhanced when the substrate is nanocrystalline, because the associated high-density grain boundaries can considerably promote element diffusion (e.g. chromium diffusion along grain boundaries), increase the oxide nucleation rate and enhance the oxide adherence to the substrate. All of these could generate a stronger, more protective and stable oxide film. The expected advantages motivated the authors to conduct the present study.

The new findings are: 1) this feasible surface modification process combining nanocrystallization and thermal oxidation results in markedly reduced adhesive force for biofilms; 2) the binding assays for assessing the ability of Pseudomonas aeruginosa to bind to nanocrystalline and microcrystalline stainless steel surfaces have provided direct evidence to confirm the original expectation; and 3) the correlation between adhesion and electron behavior has been demonstrated.

This surface modification has the potential not only for suppressing bacterial biofilms on medical implant materials but also for modifying materials used in food processing and storage as well as for biocorrosion control. It is possible to add additional elements into the nanocrystalline surface layer to further improve implant surfaces and others with anti-bacteria capability. The follow-up research is being planned and conducted.