Influences of Emulsifying Parameters on the Stability and Drug Encapsulation Efficiency of W/O/W Multiple Emulsions

The influences of emulsifying parameters of the first-step emulsifying procedure on the stability and insulin encapsulation efficiency (IEE) of the multiple emulsions (MEs) prepared by two-step emulsifying method were studied. The emulsion stability was characterized by the centrifugal creaming ratio of the emulsion,and its IEE was determined by HPLC (High-Performance Liquid Chromatograph). It was found that the emulsifying parameters of the first-step emulsifying procedure,such as emulsifying strength (stirring rate) and emulsifying time,have only little effect on the stability of the multiple emulsions,but remarkably affect the encapsulation efficiency of the MEs. The rheological properties and droplet size distribution of the primary emulsions prepared by the first-step emulsifying were investigated,and the data obtained indicate that there is an obvious direct relationship between the primary emulsion viscosity and the IEE of the MEs. Improving the emulsifying strength of the first-step emulsifying procedure will decrease the mean droplet size of the primary emulsion and increase its viscosity,which will increase the IEE of the multiple emulsions. However,improving the emulsifying strength of the first-step emulsifying procedure excessively will increase aggregation and coalesce of the primary emulsion droplets and decrease the viscosity of primary emulsion; hence the IEE of the MEs will decrease too. The optimal emulsifying parameters of the first-step emulsifying procedure with respect to IEE were found as follows: using Ultra-Turrax T25 emulsifying machine with stirring rate of 9500 r·min-1 and stirring time of 6 min.