Designing thermoreversible gels for extended release of mosquito repellent†

Mosquito-borne diseases are responsible for 700 000 deaths annually. Current outdoor protective strategies primarily focus on direct skin application of commercial repellents (i.e., aerosol sprays or topical lotions) which are typically limited to efficacy times of ≤10 hours due to rapid evaporation and dermal absorption. Consequently, frequent reapplication for continuous protection can increase associated health hazards and cause noncompliance. This study utilizes Hansen solubility parameter modeling to design physical gels composed of insect-repelling N,N-diethyl-meta-toluamide (DEET) and modacrylic copolymer poly(acrylonitrile-co-vinyl chloride) (P(AN–VC)). The P(AN–VC)/DEET composites exhibit tunable and reversible sol–gel transition temperatures that can meet the thermomechanical stability demands of the intended application and permit facile transition to commercial melt processing techniques such as injection molding, filament spinning, or film casting. P(AN–VC)/DEET gel films demonstrate mosquito repellency for more than half a year—performing longer than any other known material to date—due to the high reservoir of repellent and its desorption hindrance from the polymer matrix. Therefore, P(AN–VC)/DEET gels hold significant potential for extended protection against mosquitos and other biting arthropods.