Trains can cross the Oder Bridge at speeds of up to 120 km/h making use of carbon hangers for the first time worldwide. Image: Deutsche Bahn AG / Oliver Lang

According to the jury of the German Bridge Construction Prize, the Küstrin Oder Bridge is not only considered an engineering masterpiece but is also pioneering in terms of economy and sustainability. The 88 carbon hangers significantly reduce the weight compared to conventional flat steel hangers. This is because CFRP offers higher tensile strength and better fatigue resistance than steel – while also being significantly lighter. This opens up new design freedoms, as the airy, transparent appearance of the Oder Bridge impressively demonstrates. In addition, the material savings reduce construction costs and maintenance requirements in the long term.

Overall, the use of CFRP hangers saved around 500 tons of steel and 1,350 tons of reinforced concrete in the bridge's overall structure. A sustainability study by Urs Meier, CFRP pioneer and former member of Empa's Directorate, shows that the carbon version saves around 20 percent of CO₂ emissions compared to a steel structure.

Hangers made of carbon fiber reinforced polymer tested at Empa provide strength and sustainability. Image: Empa

The railway bridge over the Oder is a double-track network arch bridge in composite construction, equipped with prestressed CFRP hangers. Although such carbon cables have already been used on another bridge, this is the first time they have been used worldwide for heavy rail freight traffic. Trains can now pass over the structure at speeds of up to 120 kilometers per hour – which required extensive testing and complex approval procedures.

According to Lorenz Haspel, the project manager responsible at the engineering firm schlaich bergermann partner, this carbon bridge would not have been possible without Empa. The innovative CFRP hangers come from the Empa spin-off Carbo-Link in Fehraltorf – founded by Andreas Winistörfer, CEO and former Empa doctoral student – and have now been used for the second time in a network arch bridge. “We used such carbon cables for the first time as highly stressed tension members in a network arch on the city railway bridge in Stuttgart,” says Haspel.

The fatigue tests for the Oder bridge were largely carried out by a team from Empa's Structural Engineering lab led by Robert Widmann and Dimitri Ott in Empa's construction hall – confirming the necessary fatigue strength of the innovative CFRP material. Giovanni Terrasi, head of Empa's Mechanical Systems Engineering lab, also worked with Christian Affolter to prepare the technical report for the now award-winning bridge. “We have thus laid the foundation for a new generation of filigree network arch bridges with carbon hangers as load-bearing elements,” Terrasi is convinced.

Antibiotic-resistant bacteria and emerging viruses are a rapidly increasing threat to the global healthcare system. Around 5 million deaths each year are linked to antibiotic-resistant germs, and more than 20 million people died during the COVID-19 virus pandemic. Empa researchers are therefore working on new, urgently needed strategies to combat such pathogens. One of the goals is to prevent the spread of resistant pathogens and novel viruses with smart materials and technologies.

Surfaces that come into constant contact with infectious agents, such as door handles in hospitals or equipment and infrastructure in operating theaters, are a particularly suitable area of application for such materials. An interdisciplinary team from three Empa laboratories, together with the Czech Palacký University in Olomouc, has now developed an environmentally friendly and biocompatible metal-free surface coating that reliably kills germs. The highlight: The effect can be reactivated again and again by exposing it to light.

Biocompatible: Stable and safely embedded in a compatible polymer, graphenic acid is deadly for germs. Image: Empa

“The new material is designed to kill microorganisms locally and quickly,” explains Giacomo Reina from Empa's Nanomaterials in Health Laboratory in St. Gallen. A basic matrix of polyvinyl alcohol, a biocompatible plastic that is also used in the food industry, was used for this purpose. Embedded in this matrix is specially synthesized graphenic acid, which is ideally suited as an antimicrobial coating due to its chemical properties. Its full potential can be exploited by using near-infrared light. As soon as the composite material is irradiated, it unfolds its dual strategy: Firstly, it absorbs the energy of the infrared light and converts it into germicidal heat. It also stimulates the formation of oxygen radicals, which cause additional damage to the pathogens.

Another advantage here is that this strategy is completely different from the mode of action of conventional antibiotics. The material thus offers continuous protection against a broad spectrum of microorganisms without contributing to the development of resistance. “Our laboratory experiments have clearly confirmed the effectiveness of the antimicrobial material against various bacteria and viruses,” says the Empa researcher.

Antibiotic resistance: One of the most dreaded germs in the oral cavity is the bacterium Pophyromonas gingivalis, a pathogen that causes severe periodontitis with increasing antibiotic resistance. Image: Adobe Stock.

An initial application for the antimicrobial coating is currently being developed for dentistry. To this end, Empa researchers are working together with the Center for Dental Medicine at the University of Zurich on a dental splint that kills microorganisms in the oral cavity.

The microbial flora in the mouth is a particularly unpleasant opponent in the fight against infectious agents: Complex communities of bacteria cavort in inaccessible niches, embedded in a self-produced mucous matrix. Antibiotics and disinfectants barely penetrate these resistant biofilms. This allows the germs to ruin teeth unhindered or even lead to extensive infections in the body. The interdisciplinary team led by Giacomo Reina is therefore working on a plastic splint into which nanomaterials such as graphenic acid can be stably integrated. As near-infrared light can penetrate the tissue several centimeters deep, the splint can be placed in the oral cavity and activated from the outside by a light source, over and over again.

The project can be started thanks to generous donations from the Eduard Aeberhardt Foundation and another foundation. Clinic Director Ronald Jung from the Center for Dental Medicine at the University of Zurich appreciates this interdisciplinary approach to materials science and clinical research. “Such new and innovative solutions will offer great added value for patients,” says Jung.

The new cement-reduced concrete significantly lowers emissions in building material production – while maintaining consistent mechanical performance. Photo: Empa

"Omya is a globally leading Swiss producer of industrial minerals and supplies a wide range of industries — from construction to pharmaceuticals. Collaborating to develop sustainable building materials and testing them directly under real-life conditions at NEST accelerates the transfer of innovation into climate-friendly construction," emphasizes Empa Director Tanja Zimmermann.
Further information about the new NEST unit: Beyond.Zero 

First, the two researchers focused on additive manufacturing, i.e. the 3D printing of metals using lasers. This process, known as powder bed fusion (PBF), works slightly differently to conventional 3D printing. Thin layers of metal powder are melted by the laser in exactly the right spots so that the final component is gradually “welded” out of them.

PBF allows the creation of complex geometries that are hardly possible with other processes. Before production can begin, however, a complex series of preliminary tests is almost always required. This is because there are basically two modes for laser processing of metal, including PBF: In conduction mode, the metal is simply melted. In keyhole mode, it is even vaporized in some instances. The slower conduction mode is ideal for thin and very precise components. Keyhole mode is slightly less precise, but much faster and suitable for thicker workpieces.

Where exactly the boundary between these two modes lies depends on a variety of parameters. The right settings are needed for the best quality of the final product – and these vary greatly depending on the material being processed. “Even a new batch of the same starting powder can require completely different settings,” says Masinelli.

PBF is not the only laser process that can be optimized using machine learning. In another project, Rajani and Masinelli focused on laser welding – but went one step further. They not only optimized the preliminary experiments, but also the welding process itself. Even with the ideal settings, laser welding can be unpredictable, for example if the laser beam hits tiny defects on the surface of the metal.

“It is currently not possible to influence the welding process in real time,” says Chang Rajani. “This is beyond the capabilities of human experts.” The speed at which the data have to be evaluated and decisions to be made is a challenge even for computers. This is why Rajani and Masinelli used a special type of computer chip for this task, a so-called field-programmable gate array (FPGA). “With FPGAs, we know exactly when they will execute a command and how long the execution will take – which is not the case with a conventional PC,” explains Masinelli.