Application of overall desirability in optimization of preparation process of microspheres containing spinosad and emamectin benzoate

Polylactic acid microspheres containing spinosad and emamectin benzoate w ere prepared by solvent evaporation method using central composite design. Influence of content of polylactic acid in oil phase( X 1),theoretical pesticide loading( X 2) and stirring speed( X 3) in the preparation process w as investigated. Integrated effect of dependent variables including pesticide loading,entrapment rate,mean diameter,span and release percentage in 5 days w as transformed into overall desirability by mathematical method. Data of overall desirabilities w ere fitted to a second-order polynomial equation,through w hich three dimensional response surface graphs w ere described. Optimum experimental conditions w ere calculated by Design-expert V 8. 06. The results indicated that overall desirability increased w hen content of polylactic acid and stirring speed decreased or w hen theoretical pesticide loading increased. The highest overall desirability( 0. 681 1) could be obtained w hen content of polylactic acid,theoretical pesticide loading and stirring speed w ere 77. 79 mg/mL, 51. 06% and 560. 91 r/min, respectively. M icrospheres prepared according to the optimum experimental conditions resulted in an overall desirability of 0. 630 5 w hile entrapment rate,mean diameter, span, release percentage in 5 days w ere 84. 49%, 7. 19 μm, 1. 134, 52. 95% respectively. The difference betw een observed and predicted values of the overall desirability of the optimum formulation w as- 5. 03%. The microspheres w ere smooth,and the results of DSC show ed that pesticides had combined w ith polylactic acid skeleton properly, w hich indicated that the mathematical model established in this study could be used to predict the optimized formulation of microspheres containing spinosad and emamectin benzoate.