Figure 2. Scanning electron microscopy images of the central and marginal areas after He-APPJ treatment. The control group (no treatment) showed heavy bacterial accumulation on the discs. In the He gas–only treatment group, remaining bacterial biofilm was observed in both the central and marginal areas in the 3-minute treatment group, while bacterial rods had been eliminated from the central area of the 5-minute treatment group, but not in the marginal area. However, the He-APPJ group showed a clear titanium surface without a bacterial biofilm in both the 3-minute and 5-minute treatment groups.

He-APPJ: helium atmospheric-pressure plasma jet.