Encapsulation of Neem oil from Azadirachta indica into Poly (lactic-co-glycolic acid) as a novel sprayable miticide system with long-term storage stability and controlled release kinetic

In this study, Neem oil (NO) was extracted from the seeds of Azadirachta indica as a natural miticide agent. To prolong the insecticidal activity and control the sustainable release, various concentrations of NO were encapsulated in poly(D, L-lactic-co-glycolic) acid (PLGA) copolymers and high and low molecular weight (Mw) polyvinyl alcohol (PVAH and PVAL) microparticles (MPs) using the single and double emulsion solvent evaporation method. The effects of different parameters, such as the molecular weight of the stabilizing agent (PVA), stirring time, and polymer concentrations, on the size, stability, morphology, encapsulation efficiency, and release kinetics of the MPs were investigated. The presence of NO in PLGA/PVA MPs was confirmed by a shift in the glass transition temperature (T_g) to lower temperatures in the DSC thermograph, the appearance of peaks at 2854 cm⁻¹ in the FTIR spectrum, a peak at 205 nm in the UV–vis spectrum and a rough surface in SEM. Moreover, the release kinetics of the MPs demonstrated sustained release of NO over 48 h. In terms of MPs storage, temperature affected short-term stability, while long-term stability after one year in a dark environment at room temperature was confirmed by the particles' strength. The miticide assay on dust mites Dermatophagoides pteronyssinus revealed that MPs with the highest NO concentration (PLGA/PVAL/NO 65%) exhibited the most effective miticidal activity, achieving a 100% kill rate after 24 h. Finally, the colloidal dispersion and stability of the MPs over time were assessed using rheology, and the results confirmed the particles' spray ability for miticide application.