Development, characterization and modeling of mosquito repellent release from microporous devices

Abstract

Nanocomposite strands with mosquito repellent DEET or Icaridin incorporated in a poly(ethylene-co-vinyl acetate) (EVA) matrix, with either pyrogenic silica or an organoclay as a nanofiller, were prepared by a twin-screw extrusion compounding technique. The nature and levels of the repellent and nanofiller that was used affected the material phase morphology. The repellent release was followed as a function of aging time in convection ovens set at 30 and 50 C. The experimental release data of the mosquito repellent from the microporous polymer swellable matrix strands was mathematically modeled and fitted using a range of semi-empirical models. In the majority of case, the Korsmeyer-Peppas power law model provided the best data fit. As expected, the wide range of internal morphologies also resulted in quite different release profiles. These models were found to be valuable as they provided insights into the mechanism of repellent release from EVA swellable matrices. It was possible to differentiate between diffusion and relaxation mechanisms. Surprisingly, strands containing nominally more than 30 wt% Icaridin showed accelerating mass loss during the initial phase, consistent with Super Case II transport. Diffusional exponents as high as 1.81 were found. Furthermore, the internal microporous region of the extruded EVA strands was covered by a surface membrane that acted a diffusion barrier that, in effect, controlled the release rate of the mosquito repellents. Some of the investigated samples exhibited release profiles that suggest that longer lasting effective release of repellents is possible than currently achieved by available commercially products. K E Y W O R D S controlled release, microporous system, modeling, repellent 1 | INTRODUCTION Collectively, the mosquito-borne diseases of malaria, Dengue, Yellow fever, O'nyong-nyong fever, Zika and lymphatic filariasis (elephantiasis) are the single biggest cause of morbidity and mortality in humans. These mosquito-transmitted infections occur at the global scale and involve a wide range of viral and other pathogenic

Mosquito‐repellent controlled‐release formulations for fighting infectious diseases

“…4 , it can be represented as: where M t / M ∞ is a fraction of core material released as the function of time t, k corresponds to the release rate constant and n is the diffusional exponent for active release. The diffusion mechanisms are represented as n = 0.5 indicating Fickian diffusion (Case I), n = 1.0 indicates relaxational transport (Case II), 0.5 < n < 1.0 corresponds non-Fickian diffusion (anomalous diffusion), and n > 1 corresponds Super Case II [ 169 , 170 ]. The release rate of encapsulated repellent N,N-diethyl-3-methylbenzamide (DEET) is shown in Fig.…”

Properties of Mosquito Repellent-Plasticized Poly(lactic acid) Strands

“…The first relates to repellents that dissolve and cause significant swelling of a polymer matrix that exists well above its glass transition temperature. That was the case for the EVA polymer studied by Sitoe et al [26]. These strands shrank over time in step with the release of the repellents resulting in a significant decrease in both length and diameter.…”

“…Long strands with a circular cross-section, containing a fugitive repellent, can be modelled as infinite cylinders of diameter d . Several different cases were dealt with previously [ 4 , 26 , 27 ]. The first relates to repellents that dissolve and cause significant swelling of a polymer matrix that exists well above its glass transition temperature.…”

Slow-DEET-Release Mosquito-Repellent System Based on Poly(butylene succinate)

“…Although the differences may be considered marginal, a comparison of images taken at the skin and the core of the thin sections suggests a slightly finer morphology in skin-near regions, which, again, likely is caused by faster cooling of the latter, and crystallization of PBS at a lower temperature. In the context of using such strands for repellent release, such skin-core morphology may affect the release rate as proposed in the literature. , …”

“…A specific approach to protect against outdoor mosquito bites is the development of drug-delivery devices, which release mosquito repellents. , While commercial solutions are available, to be effective over short time periods, , long-lasting protection devices are hardly present. A possible route is the generation of a polymer scaffold hosting a sufficient amount of repellent in its open pores, being effective by evaporation over a long time. , The formation of microporous polymeric scaffolds typically is achieved by thermally induced phase separation (TIPS) on cooling solutions, either by crystallization-caused solid–liquid (S–L) phase separation or by liquid–liquid (L–L) phase separation, followed by polymer crystallization. − …”