Encapsulating aspirin into a surfactant-free ethyl cellulose microsphere using non-toxic solvents by emulsion solvent-evaporation technique

Microencapsulation of aspirin in ethylcellulose was studied in a surfactant-free, water-in-oil type of emulsification/solvent evaporation process using non-toxic solvents. Ethanol was used as the dispersed phase and soybean oil as the continuous phase. The recovered weight, particle size distribution, aspirin loading efficiency, and the aspirin release rate of microspheres were analysed. The addition of a small amount of non-solvent (water) prior to the emulsification was found to have a significant impact on the microencapsulation process. Adding non-solvent increases the recovered weight and the size of the microspheres. The addition of non-solvent also markedly changes the microsphere characteristics, resulting in a coarser surface and an increased release rate. Increasing the emulsification evaporation temperature increases the size of the microsphere, but reduces the recovered weight and loading efficiency. The release rate follows a first-order kinetics and Higuchi matrix kinetics at low concentrations of non-solvent, suggesting a monolithic system with aspirin uniformly distributed in the microsphere.