E. coli Inactivation by High-Power Impulse Magnetron Sputtered (HIPIMS) Cu Surfaces

This study reports HIPIMS-sputtered samples of Cu-particulate films with currents at 6 and 60 amps leading to E. coli inactivation. The Cu coverage and nanoparticle structure of the fibers is reported by TEM. Evidence is presented of redox processes in the Cu taking place during E. coli inactivation and the buildup of intermediate species resulting from the bacterial oxidation. Cu is deposited on the polyester in the form of Cu2O and CuO as observed by XPS. During the bacterial oxidation, the CuO on the polyester after 30 min decreases from 84 to 70%. After longer bacterial inactivation times, the CuO oxidizes again increases its presence to 94% when the bacterial inactivation has been completed within 90 min. The broadening of the O-C=O signal during E. coli inactivation suggests direct interaction of Cu with carboxylic groups. The surface atomic concentration of 0, Cu, and C was determined within the E. coli inactivation time. The E. coli inactivation occurred within 90 min on Cu-nanoparticulate films sputtered for 61 s at 60 amps being 28 nm thick. This Cu-layer thickness is equivalent to 140 layers with a content of 1.4 x 10(17) atoms Cu/cm(2), and the sputtering proceeded with deposition rate of 2.3 x 10(15) atoms/cm(2)s. The values found for the rugosity indicate that the texture of the Cu-nanoparticulate film is smooth. R-q values and the R-a were similar before and after the E. coli inactivation, providing further evidence of the stability of the Cu-nanoparticulate films during the bacterial inactivation process. The Cu-loading percentage required in the Cu-nanoparticulate films sputtered by HIPIMS to inactivate E. coli completely was about three times lower compared with DCMS-sputtered Cu-nanoparticulate films. This indicates a substantial Cu-metal savings within the preparation of antibacterial films.