French company Ionitec, a subsidiary of Surfaces Synergie (Maîche, France), has developed an antimicrobial and self-cleaning titanium dioxide (TiO2) coating. The functional properties of the coating are triggered by exposure to a UV light source resulting in photocatalysis. The material and process have been tested to ISO 10678 (determination of the photocatalytic effect) and ISO 27447 (antimicrobial properties). The SaniUV coating is applied to the substrate through physical vapour deposition, the process parameters of which are the subject of a patent, according to Ionitec Business Manager Huu-Tuan Nguyen.
TiO2 is a semiconductor material. The electrons within the material can move from the valence band to the conduction band across an energy (or band) gap. This change in state generates what is called a hole, a deficit of electrons in the valence band (h+) coupled with excess electrons in the conduction layer (e-). The h+ holes react with water to form hydroxyl radicals (°OH), and the electrons react with oxygen to form superoxide (O2-). These powerful oxidants can destroy organic molecules such as bacteria, viruses, germs, odours, volatile organic compounds, mould, algae, fungi, pollen and dust mites.
By optimising the coating, a photocatalytic reaction can be produced using visible light, and the SaniUV coating is responsive to a range of lighting types including neon, compact fluorescent bulbs and LEDs. “However, the best results are achieved by exposing the surface to a light source with wavelengths under 388 nm, such as UV-A, UV-B and UV-C,” says Nguyen, “which can increase the antimicrobial effectiveness fourfold. The shorter the wavelength, the more immediate the reaction.”
It is also worth noting that the coating has a memory effect. In fact, following UV exposure, the coating remains active over a period of time and continues to combat contaminants.
The biocompatible coating is suited for use with a range of medical devices from simple surgical instruments to endoscopes, adds Nguyen.Norbert Sparrow