Photocatalytic coatings for medical applications

Abstract

Medical equipment and environmental surfaces can provide a source of infection if not disinfected properly and contribute to the transmission of healthcare associated infection (HCAI). To help combat the problem of HCAI photocatalytically active titanium dioxide (TiO2) coatings could be used. The coatings have a self-cleaning effect and when activated by light of appropriate wavelength generate reactive oxygen species that can inactivate pathogenic micro-organisms. More recent work in photocatalytic disinfection has centred on the use of doped-TiO2 coatings which could be activated by ambient indoor light without the need for UV sources.

In this work a range of metal and non-metal doped TiO2 coatings were characterised and assessed for their anti-bacterial ability for use as potential coatings for environmental surfaces. All films showed the presence of anatase, the most photocatalytically active form of TiO2, however some of the films did not show the presence of the dopant, possibly due to concentration being below XPS detection limit. In disinfection testing, most of the films did not exhibit visible light activated photocatalytic disinfection towards E. coli. Aside from the Ag-TiO2 film which, after 6 h visible light irradiation, did show slightly better inactivation of bacteria when compared to the light control. The only film to reduce bacteria considerably was S-TiO2 after 1.5 h irradiation; however this film also inactivated bacteria in the dark therefore the activity of S-TiO2 was likely due to sulphur radicals and probably not a photocatalytic affect however further investigation into inactivation mechanism is needed. These findings suggest that doped-TiO2 films activated by visible light lacked a photocatalytic affect and would not be beneficial as self-disinfecting surfaces. TiO2 films were then created via sputter deposition. To gain anatase phase a range of power settings and gas settings were varied until finally increasing the gas pressure resulted in anatase formation instead of rutile. The films were tested for their bactericidal ability but showed no enhanced killing when compared to the UVA light. It was thought the planar surface of the sputtered coatings had a low surface area therefore reducing their photocatalytic disinfecting ability. However the films produced did show potential photocatalytic activity due to an increase in hydrophilicity of the surface after UVA irradiation. Finally anatase TiO2 was sputtered onto Poly methyl methacrylate (PMMA) and assessed for UVC protection, increased hardness and disinfection properties under UVC irradiation. The coating prevented the degradation of the polymer under UVC irradiation and therefore would allow for rapid UVC disinfection of PMMA medical devices to prevent transmission of infection. UVC disinfection studies on the TiO2 coated PMMA showed complete inactivation of E. coli after 10 s and complete inactivation of Fusarium solani spores in 5 min. Hardness and Young’s modulus testing showed that both parameters were slightly enhanced with the addition of the TiO2 coating which may increase wear resistance. Therefore, TiO2 coatings could be used as a protective coating for polymers used in medical devices and allow UVC disinfection of these devices to reduce the risk of infection.

Date of Award	Oct 2014
Original language	English
Sponsors	Department for Employment and Learning (DEL)
Supervisor	John Byrne (Supervisor), Jim McLaughlin (Supervisor) & Patrick Dunlop (Supervisor)