Scientists use ultra-fast lasers to create world’s first self-cleaning metals

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The researchers are using high-power laser cutting devices to create microscopic ‘spikes’ and ‘ridges’ in sheet metal, causing liquids to ‘bounce off’ the rough micro-topography. (Image: TresClean project)

A Horizon 2020 project has achieved a breakthrough using ultrafast high-power lasers that will enable the production of self-cleaning sheet metal on an industrial scale for the first time.

According to the European researchers of the ‘TresClean’ project (High Throughput Laser Texturing of Self-Cleaning and Antibacterial Surfaces), they have developed the first fluid-repellent, antibacterial, metal surface, which could enable products such as self-cleaning saucepans, toilets, and dishwashers.

Self-cleaning plastic components have been achieved previously, according to the researchers, however this is a first for self-cleaning metals.

Taking inspiration from nature, specifically from the from defence mechanisms of plants such as the lotus leaf, the researchers are using high-power laser cutting devices to create microscopic ‘spikes’ and ‘ridges’ in sheet metal, causing liquids to ‘bounce off’ the rough micro-topography – an effect observed on the surface of the lotus leaf. This roughened surface creates miniature pockets of air that minimises the contact area between the surface and a liquid, almost like standing on a bed of needles.

‘In the same way that Lotus leaves keep themselves clean, without the need for cleaning products or chemicals, their jagged, rough surfaces enable water to stay as spherical droplets by preventing “spreading”,’ explained professor Luca Romoli, project coordinator of TresClean. ‘Bacteria do not get a chance to stick because the contact with the metal surface and the liquid is reduced by over 80 per cent. We are looking at an anti-bacterial metal’.

The jagged, rough surfaces produced by the lasers will cause water to stay as spherical droplets by preventing 'spreading'. (Image: ALPhANOV)

The new technique will be used initially to create antibacterial surfaces for use in the food production industry – dramatically increasing productivity and reducing costs in factories which process biological food products such as milk, tomato sauce, and yoghurt.

Laser textured surfaces

The metal surfaces are textured using high-average power ultrashort-pulsed lasers and high-performance scanning heads that utilise an innovative beam delivery method to movements of up to 200m/s. This allows the researchers to achieve surface texturation quickly – cutting areas of 500cm2 in less than 30 minutes. This compares to the 1 square inch of metal that could be laser-etched in 1 hour back in 2015, making TresClean’s methods 156 times faster than previous methods.

Within the frame of the TresClean project, French research institute and project partner Alphanov acquired a new Tangor-350W laser from Amplitude Systemes towards the end of 2018. The laser runs at central wavelength of 1,030nm and can deliver up to 350W of average power at very high repetition rate (up to 13MHz) with pulse duration of 500 femtoseconds. The laser was connected to a polygonal scanner developed by Raylase, a manufacturer of beam delivery systems and also a partner of TresClean.

Battling bacteria

Initially aiming its product at machine parts for the food industry, TresClean hopes to make a significant impact on productivity: ‘Vats in milk factories need to be cleaned every 6-8 hours to avoid the exponential growth of bacteria. This hinders usage and therefore affects output,’ Romoli said.

‘By saving hours per day in cleaning, it will yield an efficiency improvement stemming from fewer sterilisation cycles and less cleaning time within production as a whole. This will also reduce energy consumption as a result of fewer cleaning phases making food production quicker, safer and more profitable’. 

Professor Romoli sees the long-term possibilities and implications for other sectors: ‘It is possible that any use of metal that needs to avoid the formation of bacteria will benefit from the TresClean product, such as medical cutting tools, sterile surfaces, dishwashers, or even saucepans.’

Coordinated by the Universitá Degli Studi Di Parma, the consortium includes members from Italy, France, Germany, Spain and the UK and has received a grant of €3,363,091.25 from the Photonics Public Private Partnership under the H2020 Industrial Leadership funding calls.

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