Bio-cellulose nanocrystal gel act as “chemical camouflage” against mosquitos, find researchers

13 Apr 2023 --- Researchers at the Hebrew University of Jerusalem have found that biomaterial cellulose nanocrystal (CNC) has “excellent potential” for active repellents against Aedes Aegytpi (mosquitos) and is also produced safely and sustainably.

“Mosquitoes are the deadliest of all combined insects and animals, affecting millions and killing hundreds or thousands of people each year,” highlight the author.

“Existing protection methods, however, are limited and include volatile compounds that actively repel mosquitoes such as N, N-Diethyl-meta-toluamide (DEET) or different essential oils such as geraniol and citronella. However, these materials have a limited effective distance and time range.”

The researchers aimed to find a solution that did not chemically interact with body odors but formed a barrier to block mosquitos and reduce biting. 

CNC was most effective when combined with glycerol and indole (Image Credit: Study).CNCs’ effectiveness
In the study, CNC caused a reduction in the blood-feeding of Ae. aegypti when tested on the author’s hand and an artificial feeding system. Through the system, researchers also fed the mosquitos with CNC and found that mosquitos fed on CNC had a “significant” reduction in laid eggs.

Only female mosquitos feed on blood as it functions as a source of nutrition to lay eggs.

“CNC’s chemical barrier effect was shown in a headspace experiment where ammonium hydroxide, a known mosquito attractant, was blocked by the CNC–glycerol coating,” detail the authors. “This work saw a significant 80% decrease in feeding on human skin when a thin CNC coat was applied.”

“The biocompatibility of the CNCs, their ubiquity, as well as the self-assembly characteristic together with the ability for cost-effective mass production makes CNC ideal for developing a new generation of mosquito personal protective equipment.”

Blood-feeding was reduced by 80% when CNC and glycerol was applied (Image Credit: Study).Cosmetic potential
The researchers found that CNC, in combination with glycerol, a popular moisturizer in cosmetics, and indole, an organic compound often used in fragrances, led to a “dramatic” decrease in laid eggs – “with 99.4% fewer eggs as compared to control.”

CNC in water did not dry ideally on the skin’s surface and cracks formed due to its brittleness. This is why CNC was combined with glycerol and indole as a gel to create a better texture.

“Very few mosquitos landed on the hand, suggesting the CNC offers a chemical barrier. Moreover, the few females that did land on CNC-coated hands systematically blood-fed, suggesting that the physical barrier hypothesis was not confirmed. This may be due to uneven spread of the CNC–glycerol which could be improved with cosmetic formulation,” note the authors. 

“Another option is that CNC–glycerol does not fully dry on the skin and the complex probing of the mosquitos’ proboscis allows it to penetrate through by agitating the molecules and creating a path through to the skin.”

The researchers sourced CNC from cellulose – described as the “most abundant polymer on earth and the strength building block of the plant world.” 

It can be directly sourced from the wood industry but is also available in food and paper waste, which is an “excellent incentive” for using cellulose. “CNCs are challengers to fossil-derived materials in a wide range of industries from packaging to cosmetics,” share the authors. 

In related developments, Kao introduced Bioré Guard Mos Block Serum mosquito repellent in Thailand. The natural citronella oil-formulated “Mos Protection Skin Shield” serum acts as a skin shield against mosquitos and can be used daily.

By Venya Patel