Antibacterial Metallic Touch Surfaces

Abstract

Our aim is to present a comprehensive review of the development of modern antibacterial metallic materials as touch surfaces in healthcare settings. Initially we compare Japanese, European and US standards for the assessment of antimicrobial activity. The variations in methodologies defined in these standards are highlighted. Our review will also cover the most relevant factors that define the antimicrobial performance of metals, namely, the effect of humidity, material geometry, chemistry, physical properties and oxidation of the material. The state of the art in contact-killing materials will be described. Finally, the effect of cleaning products, including disinfectants, on the antimicrobial performance, either by direct contact or by altering the touch surface chemistry on which the microbes attach, will be discussed. We offer our outlook, identifying research areas that require further development and an overview of potential future directions of this exciting field.

Keywords: antimicrobial; copper; disinfection; touch surfaces.

Figure 1

Representation of the contributing antimicrobial mechanisms of Cu ions released by a Cu bearing Zr-based bulk metallic glass [11].

Figure 2

Survival of E. faecalis deposited as a bacterial aerosol on stainless steel AISI 304, stainless steel AISI 211 + 3Cu and copper) at 25 °C and (a) relative humidity of 100% and (b) relative humidity of 0% [30].

Figure 3

Growth of E. coli on exposure to Ti-6Al-4V, Zr₅₅Al₁₀Ni₅Cu₃₀ BMG, (Zr₅₅Al₁₀Ni₅Cu₃₀ BMG)₉₉Y₁ and pure copper after 4 h [11].

Figure 4

Kinetics of bacterial killing on thin copper films. A suspension of Staphylococcus aureus was deposited on a thin copper film supported by a stainless steel support under ambient conditions (22 °C). Samples were taken periodically and survivors were quantified by culturing serial decimal dilutions on LB agar plates (unpublished results from the authors).

Figure 5

(a) Plot showing oxide growth versus oxidation time in PBS and in Tris; (b) Plot survival of E. hirae exposed to glass, Cu, CuO and Cu₂O at different times [57].

Figure 6

Killing of E. coli exposed to a-TiO₂, Ag/a-TiO₂ and Ag-TiO₂/Ag/a-TiO₂ photocatalyst thin films as compared to blank (control) sample, in dark (■) or irradiated with visible light ($▲$) or solar light ($●$) [52].