When people talk about the world’s deadliest animal, many think of sharks, alligators, or lions. But in reality, it is a small, unassuming – yet all the more annoying – insect: the mosquito. Worldwide, more than 700,000 people die each year from diseases transmitted by mosquito bites. The shark, by contrast, is responsible for only ten human deaths per year.
Malaria (see info box) is the most common mosquito-borne disease. According to the World Health Organization (WHO), more than 280 million people in 80 countries contracted malaria in 2024. Of these, 610,000 died as a result of the disease. Malaria is therefore a global problem – and it is becoming increasingly serious. This is because more and more mosquitoes are developing resistance to the commonly used pyrethroid-based insecticides that are employed to protect against bites. Although preventive medications and a vaccine against malaria exist, their effectiveness is also waning, and for most people in the affected countries, they are unaffordable anyway. Insect repellents and mosquito nets are therefore the primary means of protection against mosquitoes.

Liquid-core fibers with carefully balanced parameters
Nets treated with insecticides are particularly effective. Until now, such nets were either impregnated with pyrethroid insecticides or manufactured using synthetic yarns consisting of a mixture of polymers and insecticides. These synthetic yarns are produced through a process known as melt spinning: Molten polymers are pressed through fine nozzles at high temperatures. The only problem is that many non-pyrethroid-based insecticides evaporate as soon as they are heated.
To solve this problem, a research team at Empa led by Edith Perret from the Advanced Fibers laboratory in St. Gallen launched the Innosuisse project MalCoFil to develop a new method for producing durable insecticidal polymer fibers. The results are promising: After a three-year development and testing phase, the Empa team has come up with a liquid-core fiber consisting of a sheath made of polymers and a liquid core containing the insecticide. “The liquid-core fiber makes it possible to incorporate novel insecticides into the fiber that could not be used with the previous approach – for example, those that would evaporate at high temperatures,” explains Perret. “In addition, this fiber can be loaded with larger amounts of insecticide.” The insecticide gradually diffuses through the fiber’s polymer sheath to the fiber surface, ensuring that the net continuously releases insecticide. Edith Perret estimates that this effect lasts for about three years, meaning the net remains effective for years and can even withstand multiple wash cycles. However, this still needs to be confirmed through large-scale testing.
It has already been shown that the mechanical properties of the fibers are preserved even with the new technology. “The yarn must be suitable for weaving, it must have high tensile strength, and the fiber must not become brittle,” explains Edith Perret. Her team therefore spent a long time fine-tuning the process to find the optimal parameters and carefully balance them: a permeable – but not overly permeable – polymer for the coating, and a suitable carrier fluid for the core, to which various insecticides can be added.

Valuable collaboration with industry
In the project, the Empa team benefited from its collaboration with two Swiss industry partners: While Vestergaard Sárl specializes in the development and production of insecticide-treated mosquito nets, Monosuisse AG possesses expert knowledge in the manufacture of so-called high-performance filaments – that is, yarns made from various materials. Conversely, both companies benefit from Empa’s expertise in the design of polymer fibers and their processing technologies.
The Empa researchers were also able to count on the support of their industry partners during testing of the liquid-core fibers they developed: Vestergaard has already conducted various tests, examining the mechanical properties of the new yarns during knitting as well as their effectiveness in killing mosquitoes – including resistant species. Monosuisse, in turn, has collaborated with the Empa team to develop a new spinning nozzle that can be scaled up for the industrial production of the fibers.
It remains to be seen whether the new fibers can be successfully transferred to industrial production and distributed on a larger scale. In any case, a potential solution to the increasingly urgent problem of pyrethroid-resistant, malaria-transmitting mosquitoes is now at hand. The WHO’s goal of eradicating malaria by 2030 is thus one step closer to being achieved.