Bio-based Polymer Assemblies for Insecticide Delivery

Abstract

Vector-borne diseases (VBDs) such as malaria present a significant global health concern, leading to chronic health complications and mortality, particularly among children and pregnant women. Fortunately, there are several different intervention techniques which have mitigated the spread and severity of the outbreaks amongst at-risk communities including the most popular method called insecticide treated nets or long-lasting insecticide nets. These are bednets which are either coated or infused with insecticidal compounds to maintain insecticidal capability for extended periods. A critical concern with these products is their reliance on petroleum-based polymers, such as polyethylene and polyester, which hinder their recyclability and contribute to a dependance on non-renewable resources. The function and longevity of these products have also come into question after studies reveal that they are only effective for mosquitoes after around 2 to 3 years of use. Because of these major drawbacks, it is necessary to develop a sustainable and durable alternative. Cellulose, the most abundant polymer on Earth, can be utilized as an alternative due to its history in textile manufacturing and surface tunability. Tuning the release of various active ingredients is possible by modifying the surface of cellulose or dissolving it directly in cellulose solvents before fiber formation. In this dissertation, we aim to evaluate the potential of sustainable biomass, in combination with environmentally friendly chemistry and processing techniques, to improve insecticide-treated net (ITN) technology. This research aims to develop bio-based insecticidal fibers with enhanced durability, efficacy, and controlled release of active ingredients while minimizing environmental impact. To this end, a comprehensive analysis of the methods and materials currently available to manufacture these products was conducted (Chapter 3), revealing that polyethylene and polyester are the main materials which are melt spun with pyrethroids to make the base fibers for ITNs. This information was then used to introduce common insecticides, permethrin and PBO into regenerated cellulose fibers using ionic liquid and dry jet wet spinning. It was found that permethrin was retained 70% and PBO 30% upon processing, which was comparable to the results of traditional nets upon washing, likely due to the hydrophilicity of PBO. This work is described in Chapter 4. To improve on this retention, we then focused on clickable cellulose nanofibrils as a substrate for regeneration into fibers by using a silane coupling agent with a thiol functional group to modify cellulose (Chapter 5). The introduction of this active ingredient negatively impacted the stability of the spinning and the strength of the composite fiber, and the silanes were desorbed from the cellulose by the solvent. As a result, we then aimed to try an alternative insecticide, abamectin, to the traditional pyrethroids while also scaling up the process of fiber spinning as a response to the scientific interest in novel insecticides which do not display the reduced efficacy observed in pyrethroids based on mosquito resistance. The abamectin was also reacted with the modified CNF with no success, but it was able to be spun with cellulose into high strength fibers and maintain a 63.5% abamectin retention. The final chapter of this work focused on implementing the silane coupler to click eugenol to the CNF as a potential insecticidal or insect repellent coating. This was studied using surface instruments to analyze the mechanism by which the eugenol was attaching to the surface, and the reaction was successful, giving preliminary results for the engineering of a new surface coating for insect repellent textiles. Interactions with cellulose were an important consideration in this work for the release of insecticides from the cellulosic substrate, and it was demonstrated that it is possible to develop an engineered biobased insecticidal net and coating, however additional efforts should be completed to push this work further into commercialization. Overall, these advancements aim to improve performance and longer-lasting protection, while also helping to lessen the environmental impact caused by unsustainable materials and waste from ITNs.