Study On Ememactin Benzoate PLA Microsphere And Its Controlled-release Property

Drugs dispersed into high polymer materials to form a kind of spherical entity, which wascalledmicrospheres. Microsphereswereuniform, which weredifferent from microcapsules. Considerableinterests had evolved in the use of polylactic acid(PLA) as drug carrier materials because of itsbiocompatibility and biodegradation. The development of controlled-release dosage forms has attractedmuch attention in recent years. Due to the similarity of pesticide formulation and pharmaceutical dosageforms, problems existing in pesticide formulation development can be solved using the new technologyin pharmaceutical dosage forms. This article wasto obtain the relatively optimum prescription andprocess conditions, and to investigate the stability, controlled-release property and the laboratorytoxicity of the emamectin benzoate PLA microspheres.In this study, using PLA as carrier materials and emamectin benzoate was prepared intomicrospheres by solvent-evaporation method. It was studied that how factors：such as concentration ofPLA, concentration of emulsifiers, mass ratio of emamectin benzoate to PLA, volume ratio of oil phaseto water phase, stirring ratio had an influence on the properties of emamectin benzoate PLAmicrospheres. The relatively optimum prescription and process conditions were as followed：concentration of PLA was60mg/mL, mass ratio of emamectin benzoate to PLA was1to4, volume ratioof oil phase and water phase was1to8, concentration of sodium dodecyl sulfate was0.5%(m/V),concentration of gelatin was2%(m/V), stirring ratio was1000r/min. Emamectin benzoate PLAmicrospheres prepared by these parameters had a good surface. D50was9.03μm, span was0.69,drug-loading rate was13.64%(W/W), entrapment rate was91.67%. The result of scanning electronmicroscope (SEM) showed that emamectin benzoate PLA microspheres had a relatively smooth surface.Fourier-transform infrared spectroscopy (FT-IR) and differential scanning calorimetry (DSC) showedthat emamectin benzoate had been encapsulated with PLA. Emamectin benzoate PLA microsphereswere stable being at(54±2)℃for14d and at (0±2)℃for7d. After10hours’ sunshine, photodegradationrate of emamectin benzoate technical material was82.22%, thatof microemulsion(ME) was80.04%,and that of emamectin benzoate PLA microspheres was31.74%.The controlled release effect of emamectin benzoate PLA microsphere wasnotable, the release ratewas more than60%after60days. The effects of diameters and dissolution medium on release rate andthe release characteristics of emamectin benzoate PLA microsphere wereinvestigated. The release ratereduced as the diameter of microspheres increased. And the release rate of emamectin benzoate inneutral and acid buffer solutions wasmore quick than that in alkaline buffer solutions. And the releasedata were fitted with three model equations: Higuchi Release Equation, First Order Release Equationand Zero Order Release Equation. The release of emamectin benzoate PLA microsphere in in neutraland acid buffer solutions better obeyed the First Order Release Equation comparing with Zero OrderEquation and Higuchi Equation. Theefficacy indoor of emamectin benzoate PLA microspheres and emamectin benzoate MEagainst2nd-instar larvae of Plutella xylostella was investigated. The result showed that the rapid effect ofemamectin benzoate PLA microsphere was less than ME. But after using30days, controlled releaseproperties of emamectin benzoate PLA microspheres took effect. After60days using emamectinbenzoate PLA microspheres, mortality of Plutella xylostella was49.99%, and that of emamectinbenzoate ME was11.33%.