Scientists have developed several reliable ways to keep insects away, but most of the time, these come in the form of a spray or lotion, which can have an unpleasant smell, and needs to be applied regularly. So a team of researchers from Martin Luther University Halle-Wittenberg (MLU) wanted a different solution: something you can wear.

The team worked with IR3535, an insect repellent developed by Merck. They chose this one because it’s been in use successfully for many years and because it’s gentle on the skin. The repellent is typically applied as a spray or lotion and protects against insects for several hours. But the MLU team wanted to deploy it in a different form and make it last longer.

So they developed a custom 3D printing technique that inserts the repellant into a biodegradable polymer that releases it gradually over time. They embedded the system into a ring.

“The basic idea is that the insect repellent continuously evaporates and forms a barrier for insects,” explains the lead author of the study, Fanfan Du, a doctoral candidate at the MLU.

The rate at which the repellent is released depends on several factors, both depending on the structure of the polymer (which can be tweaked) and by outside temperature. The team estimates that it would take around a week or a bit more for the entire repellant to be released.

“For all samples, regardless of the initial repellent concentration, the repellent-release rate increases with temperature, and at ambient temperature, the release-time constant is in the order of 10 days,” the study reads.

However, this is still an incipient study. While researchers have shown that it is possible to release the repellant this way, they haven’t really tested it to see how well it works in realistic conditions. They also emphasize that there are also several encapsulation tweaks that can be used to further improve the material, but efficacy tests are required to see how well this method repels insects compared to conventional methods.

Nevertheless, researchers are confident in their newly-created device and say it should work in a practical situation.

“The study successfully proved the applicability of the technology of extrusion-based 3D-printing for the preparation of polymer parts with a specific shape/design containing mosquito-repellent at a concentration which raises the expectation to be used as a repellent delivery-device.”

Journal Reference: Fanfan Du et al, 3D-printing of the polymer/insect-repellent system poly(l-lactic acid)/ethyl butylacetylaminopropionate (PLLA/IR3535), International Journal of Pharmaceutics (2022). DOI: 10.1016/j.ijpharm.2022.122023