Kao and Riken say silicone polymer in topical formulations can stick to mosquito legs and reduce bites

08 Jul 2024 --- Kao and Riken researchers say the incorporation of low-viscosity polydimethylsiloxane (L-PDMS) in a topical silicone oil repels mosquitoes “significantly” and enhances effectiveness. They warn “mosquito-borne diseases are posing an increasing threat to humans worldwide.”

The study in Scientific Reports focused on L-PDMS’ impact on mosquito behavior and its potential to extend the effectiveness of traditional repellents. Researchers found that mixing L-PDMS in repellant improves its adhesive properties, helping it stick to mosquitoes’ legs longer and reducing the number of bites on human skin.

Furthermore, L-PDMS was shown to cause aversive learning to co-applied odors and hinder mosquitoes’ visual tracking abilities, providing an additional layer of defense.

Lead researcher Bianca Wiedemann at Kao explains: “Our goal is to develop repellent technologies that protect against mosquito-borne diseases, safeguarding future generations, particularly children.” This research is part of our ‘Guard Our Future’ project, which includes the launch of the ‘Bioré Guard Mos Block Serum’ in Thailand, Singapore, Taiwan, Hong Kong and Malaysia.

Attack on mosquito legs
The study highlights the use of citronella oil and DEET, commonly used in repellents. It finds certain mosquitoes can still detect them as they interact with their olfactory receptors, and some can mutate in response.

The researchers conducted three experiments to understand the mechanisms of L-PDMS.

Human participants in the “arm-in-cage” experiment inserted their arms into a cage containing female Aedes albopictus mosquitoes. According to the results, when L-PDMS and a mosquito repellent were applied to the arms, researchers noted a significantly lower number of mosquito bites than when the repellent was used alone.

“L-PDMS forms a low contact angle on hydrophobic surfaces including the scales of mosquitoes and efficiently wets mosquito legs upon contact. This wetting generates a capillary force, pulling the mosquito’s legs toward the liquid. As mosquitoes need to escape from this force, when applied on human skin, L-PDMS prevents the mosquitoes from frequently contacting and biting the skin,” suggests the paper.

Researchers found that L-PDMS enhances the adhesive properties of topical mosquito repellents, reducing bites on human skin (Image credit: Kao).In another experiment, they used a virtual flight arena to study mosquito behavior in response to visual and olfactory stimuli. An LED screen, a high-definition camera and microphones were installed in the arena to record any alterations in behavior. They noticed that after getting their legs wet with L-PDMS, mosquitoes were less able to track virtual objects.

Additionally, the group assessed the mosquitoes’ aversion to L-PDMS in combination with citronella oil. After pre-exposure to the mixture, mosquitoes developed a stronger aversion to citronella oil in the virtual arena, demonstrating that L-PDMS can train mosquitos to avoid certain odors.

“We found that the tarsal contact with L-PDMS is aversive enough for mosquitoes to form an associative olfactory memory. Mosquitoes learned to avoid the smell of citronella oil more strongly after a transient experience of having their legs covered by a mixture of citronella oil and L-PDMS,” details the study.

“The amount of citronellal transferred to the mosquito legs was increased almost six-fold by the addition of L-PDMS.”

Formulation possibilities
Compared to conventional repellents, researchers believe that repellents containing L-PDMS can offer longer-lasting mosquito protection. The capacity of silicone oil to reduce mosquito tracking and create a learned aversion to smells opens up new possibilities for the creation of repellent products that work even better.

“Since L-PDMS confers an aversive meaning to a simultaneously presented odor, the mere presence of this conditioned odor may be enough to protect the local environment from mosquitoes following learning,” notes Aya Kato-Namba of Human Health Care Products Research at Kao.

The study adds: “Adopting the skin-friendly cosmetic oil L-PDMS in conjunction with low concentrations of citronella oil into mosquito repellents will protect consumers and their local environment from mosquito bites while exhibiting hardly any odor.”

Kao and Riken believe the advancement could be key in combating mosquito-borne diseases.

By Venya Patel

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