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High ThRoughput lasEr texturing of Self-CLEANing and antibacterial surfaces

Periodic Reporting for period 2 - TresClean (High ThRoughput lasEr texturing of Self-CLEANing and antibacterial surfaces)

Reporting period: 2017-10-01 to 2020-09-30

The aim of TresClean was to demonstrate high-throughput laser-based manufacturing applied to the production of plastic and metal components in consumer white goods and liquid filling machines through the development and novel implementation of high-average power ultrashort pulsed lasers in combination with high-performance optical devices and beam delivery systems. Using ultrashort pulsed laser irradiation under highly controlled conditions the project aimed to produce hierarchical micro and nanoscale surface features, leading to superhydrophobic behaviour and a reduction in bacterial adhesion responsible for biofouling.

The motivation for the project was to go far beyond the state of the art in laser surface texturing and demonstrate industrial relevance by applying laser surface texturing techniques over large areas of machine parts and tools. Therefore, bridging the gap between the lab-tested feasibility of these laser-treated surfaces and the production for real applications. Among the array of industrial applications that could exploit functionalised surfaces, the project focused on producing self-cleaning and fluid-repellent machine parts for the food industry and home appliances with the objective of enabling easier maintenance and longer service life.

Through a period of very intense research, TresClean demonstrated that laser texturing, characterised by surface features only a few hundred nanometres in size, can be achieved over areas larger than one square meter to induce unique functionalities such as antibacterial and self-cleaning behaviour. The scanning system, specifically conceived within TresClean, achieved speeds of several hundred meters per second, which translates to processing times that are of real industrial interest. Furthermore, an antibacterial effect for surfaces textured with the TresClean technologies, was demonstrated under laboratory conditions, showing the potential of texturing for enhancing the service life of components for agri-food machinery and home appliances. Overall, the project has taken a significant step towards bringing laser texturing out of the lab and demonstrated the value of tailored photonics solutions in a very innovative field.
TresClean delivered a programme of work that was guided by an end-user requirement for high throughput manufacturing technologies that are tailored to meet the needs of industry. In the first phase of the project the research and innovation activities focussed on defining the physical and technical requirements for the industrial prototypes that were to be tested during the project (WP1). Using these requirements key performance indicators for evaluating the antibacterial performance of surfaces textured with ultrashort-pulsed lasers were defined (WP2) and the features necessary to achieve fluid repellent behaviour and minimise bacterial contact area were identified (WP3).

Technology development during this period focused on the design of the laser amplifier required to achieve the 1kW of output power for high-through put processing (WP4) and the design of a new scan head to support high speed large area structuring with high power lasers (WP5). Tests to assess the application of these technologies for the texturing process found that upscaling to high throughout production using the TresClean techniques was feasible, as the same geometry and wettability properties could be achieved when structuring at high and low speed (WP6).

In the second phase of the project, activities focussed on refining the surface structuring techniques to optimise fluid repellent and antibacterial properties (WP3), production of the laser amplifier (WP4) and scanning head (WP5) and integration (WP6) and demonstration (WP7) of these technologies in laser processing platforms designed for high-throughput texturing of large surface areas. The integrated systems were tested in terms of their ability to texture industrially relevant prototypes with the TresClean nanostructures. Sample metal pipes and injection moulds for dish washer tanks were successfully laser structured using the TresClean technologies (WP6). The performance of the resulting pipes and dish washer tanks was then evaluated in terms of bacterial attachment and cleanability under laboratory and operational conditions (WP7).

The main achievements of TresClean are:

1. Identification of ultrashort pulsed laser texturing as a suitable technique for producing antibacterial surfaces.
2. Application of laser texturing to generate different topographies, characterized by feature size ranging from a few hundreds of nm to tens of µm
3.Identification of suitable surface topographies to reach super-hydrophobic and antibacterial effects.
4. Development of a high-power laser delivering 1kW of output power and >3mJ of pulse energy, including the demonstration of high-power visible (green) and UV radiations with more than 600W and 200W power respectively.
5. Development of a scanning system with processing speeds of up to several hundred m/s, improved resolution and enough accuracy to support laser power up to 1kW.
6. Upscaling of the TresClean laser texturing technique to produce structures with a laser repetition rate of 10 MHz, at a scanning speed of 200 m/s in a field size of 200x200 mm.
7. Transfer of nanoscale topographies on polymers by injection moulding.
8. Generation of functionalised surfaces on free-form components such as metal pipes

In addition to the research activities TresClean also actively disseminate and communicate the project concepts and results. Project videos and promotional materials were produced to promote both the activities of the individual partners and the emerging results which have broad applications in the emerging laser surface texturing markets. Further information on use of the results is available on the TresClean website, www.tresclean.eu.
TresClean aimed to transform laser surface texturing from a low productivity process, limited by a lack of power and restricted beam manipulation, to a high-throughput process harnessing ultrashort pulsed high-power lasers and high-speed scanners. The project worked with early adopter customers to establish a platform meeting the needs of key end users in their respective sectors, and production operations. As a result of this collaboration TresClean has successfully taken laser texturing out of the lab and contributed to promoting tailored photonics solutions in a very innovative field. The project demonstrated the industrial relevance of ultrashort pulsed laser-based processing and the applicability of different laser processing strategies, facilitated by high average powers and fast scanning capability, for the structuring of fluid repellent surfaces. These findings have opened the possibility of applying the TresClean techniques for a range of applications beyond the food and home appliance markets.

In addition to commercial benefits TresClean may also have a significant societal impact in the longer term. There is growing concern over the transfer of pathogens on the surface of products and the ability to produce self-cleaning and potentially antibacterial surfaces would be a considerable breakthrough in breaking the chain of transmission. Whilst further research is required to deliver on this vision, TresClean has taken the first steps towards producing self-cleaning and antimicrobial surfaces without the need for chemical coatings.
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