Novel bioadhesive polycarbophil-based liquid crystal systems containing Melaleuca alternifolia oil as potential repellents against Aedes aegypti

Dengue, chikungunya, zika, and urban yellow fever are diseases which etiologic agents are transmitted by the bite of Aedes aegypti female mosquitoes, being responsible for serious public health problems. Essential oils, such as tea tree (Melaleuca alternifolia) possess great potential as repellents; however, the high volatility often represents an important technical limitation to overcome, leading to a lower repellent efficiency. Thus, the development and research must be conducted to achieve innovative formulations that are effective in fixing aromatic compounds on the skin and increase the duration of repellent activity. Nanostructured systems such as liquid-crystalline systems (LCS) can be interesting in the sense of improve the repellent efficiency. The addition of a polymer such as polycarbophil may improve the bioadhesion of these systems, increasing the residence time of the repellent active. The aim of this work was evaluate the potential of a novel bioadhesive LCS loaded with tea tree oil (M. alternifolia) as potential repellent against Ae. aegypti. LCS was prepared with polycarbophil dispersion as the aqueous phase, Procetyl AWS as the surfactant and tea tree essential oil as the oily phase. Polarized light microscopy was used to characterize the LCS as well texture profile analysis, in vitro bioadhesion, and rheology measurements. The in vivo repellent potential LCS against A. aegypti was evaluated in healthy humans up to 120 min. The results showed the presence of regions of cubic mesophases (B, C, and D) and microemulsions (A), fixing the concentration of the surfactant at 30% and varying the proportion of water and oil. All formulations presented pseudoplastic behavior. Analysis of TPA showed that the formulation D presented the highest compressibility, hardness, and adhesion, indicating greater organization of this system, as well it presented the greatest ability to bioadhesion and in vivo repellency. Formulations with more cohesive internal structures, like cubic mesophases, possess better bioadhesive properties than those less cohesive formulations, as microemulsions. The results showed the repellent activity of nanostructured systems based on tea tree essential oil and opens up new perspectives for the development of repellent formulations to replace DEET.