Antibacterial effects of nano-imprinted moth-eye film in practical settings.

BACKGROUND: Recent studies report that surfaces displaying micrometer- or nanometer-sized undulating structures exhibit antibacterial effects. In previous work, we described the use of an advanced nanofabrication technique to generate an artificial biomimetic Moth-eye film by coating a polyethylene terephthalate (PET) film with nanoscale moth-eye protrusions made from a hydrophilic resin. This moth-eye film exhibited enhanced antibacterial effects in in vitro experiments. The aim of the present study was to verify the antibacterial efficacy of the Moth-eye film in practical environments. MATERIALS AND METHODS: The antibacterial effects of three types of film (Moth-eye film, Flat film, and PET film) were compared. Sample films were pasted onto hand washing basins at the testing locations. After several hours, bacteria were collected from the surface of the sample films with one of three kinds of culture media stamper (to permit identification of bacterial species). The stampers were incubated for 48 hours at 35°C, and the numbers of colonies were counted. RESULTS AND DISCUSSION: The number of common bacteria including E. coli and S. aureus obtained from the Moth-eye film was significantly lower than those from the PET film (p<0.05) and Flat film at 1 hour (p<0.05). This study found that the Moth-eye film showed a long-term (6h) antibacterial effect and the Moth-eye structure (PET coated with nanoscale cone-shaped pillars) demonstrated a physical antibacterial effect from earlier time points. Therefore, the Moth-eye film appears to have potential general-purpose applications in practical environments.

Antibacterial effects of the artificial surface of nanoimprinted moth-eye film.

The antibacterial effect of a nanostructured film, known as "moth-eye film," was investigated. The moth-eye film has artificially formed nano-pillars, consisting of hydrophilic resin with urethane acrylate and polyethylene glycol (PEG) derivatives, all over its surface that replicates a moth's eye. Experiments were performed to compare the moth-eye film with a flat-surfaced film produced from the same materials. The JIS Z2801 film-covering method revealed that the two films produced a decrease in Staphylococcus aureus and Esherichia coli titers of over 5 and 3 logs, respectively. There was no marked difference in the antibacterial effects of the two surfaces. However, the antibacterial effects were reduced by immersion of the films in water. These results indicated that a soluble component(s) of the resin possessed the antibacterial activity, and this component was identified as PEG derivatives by time-of-flight secondary ion mass spectrometry (TOF-SIMS) and Fourier transform infrared spectroscopy (FT-IR). When a small volume of bacterial suspension was dropped on the films as an airborne droplet model, both films showed antibacterial effects, but that of the moth-eye film was more potent. It was considered that the moth-eye structure allowed the bacteria-loaded droplet to spread and allow greater contact between the bacteria and the film surface, resulting in strong adherence of the bacteria to the film and synergistically enhanced bactericidal activity with chemical components. The antibacterial effect of the moth-eye film has been thus confirmed under a bacterial droplet model, and it appears attractive due to its antibacterial ability, which is considered to result not only from its chemical make-up but also from physical adherence.