Retention of Antibacterial Activity in Geranium Plasma Polymer Thin Films

Abstract

Bacterial colonisation of biomedical devices demands novel antibacterial coatings. Plasma-enabled treatment is an established technique for selective modification of physicochemical characteristics of the surface and deposition of polymer thin films. We investigated the retention of inherent antibacterial activity in geranium based plasma polymer thin films. Attachment and biofilm formation by Staphylococcus aureus, Pseudomonas aeruginosa, and Escherichia coli was significantly reduced on the surfaces of samples fabricated at 10 W radio frequency (RF) power, compared to that of control or films fabricated at higher input power. This was attributed to lower contact angle and retention of original chemical functionality in the polymer films fabricated under low input power conditions. The topography of all surfaces was uniform and smooth, with surface roughness of 0.18 and 0.69 nm for films fabricated at 10 W and 100 W, respectively. Hardness and elastic modules of films increased with input power. Independent of input power, films were optically transparent within the visible wavelength range, with the main absorption at ~290 nm and optical band gap of ~3.6 eV. These results suggest that geranium extract-derived polymers may potentially be used as antibacterial coatings for contact lenses.

Keywords: antibacterial coatings; essential oils; geranium oil-derived polymer; plasma polymerisation.

Figure 1

Schematic of the nano-indentation test for hardness and the modulus measurement.

Figure 2

FTIR spectra of geranium essential oil (precursor) and geranium oil-based polymer fabricated at 10 W and 100W.

Figure 3

Optical constants of geranium oil-derived polymer films fabricated at various deposition powers; (a) Refractive index; (b) Extinction coefficient.

Figure 4

(a) UV–vis absorption spectrum of geranium oil-derived films; (b) The optical energy gap of geranium oil-derived films fabricated at various radio frequency (RF) powers.

Figure 5

Typical three-dimensional atomic force microscope images of 3 µm × 3 µm scanning area of geranium oil-derived film surfaces fabricated at various RF power.

Figure 6

(a) Load displacement versus time curve of geranium oil-derived film fabricated at 10 W and 100 W. (b) Pile up and sink in phenomena in the film. (c) AFM image of plastic impressions left behind in geranium oil-derived thin polymer fabricated at 50 W after indentations. (d) Profile plane of the investigated surface.

Figure 7

Evolution of contact angle with contact time: (A) water, (B) DIM, and (C) glycerol.

Figure 8

Representative P. aeruginosa, S. aureus, and E. coli attachment patterns on the surfaces of the control glass, and geranium oil-derived polymer film samples fabricated at 10 W and 50 W after 18 h incubation. SEM images represent an overview of the attachment pattern.