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Poly(L-lactide) (PLLA) microcapsules containing acetaminophen (APAP) were prepared by three emulsion solvent-evaporation methods including an O/W-emulsion method, an O/W-emulsion co-solvent method and a W/O/W-multiple-emulsion method. The average size and morphology of the microcapsules varied substantially among these three preparation methods. Various alcohol and alkane co-solvents were found to exert significant impact on the O/W-emulsion co-solvent method and a more lipophilic co-solvent such as heptane appeared to enhance drug encapsulation with an efficiency nearly double of the O/W-emulsion method. When a small amount of water was added as the internal aqueous phase in the W/O/W-multiple-emulsion method, the encapsulation efficiency was found nearly triple of that for the O/W-emulsion method. While having a higher encapsulation efficiency, the microcapsules prepared by the W/O/W-multiple-emulsion method had as good controlled release behaviour as those prepared by the O/W-emulsion method. The release kinetics of microcapsules prepared by the O/W-emulsion method and the O/W-emulsion co-solvent (alcohol) method fitted the Higuchi model well in corroboration with the uniform distribution of APAP in PLLA matrix, i.e. the monolithic type microcapsules. However, the release kinetics of microcapsules prepared by the O/W-emulsion co-solvent (alkane) method and the W/O/W-multiple-emulsion method fitted the first-order model better, indicating the reservoir type microcapsules.

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Microencapsulation of acetaminophen in poly(L-lactide) was studied using the oil-in-water emulsification solvent-evaporation technique. Methylene chloride was used as the dispersed medium and water as the dispersing medium. The thermogravimetric analysis and differential scanning calorimetry data indicated that the acetaminophen was encapsulated and uniformly distributed in the poly(L-lactide) microcapsules. The addition of either gelatin or polyvinyl alcohol as the protective colloid to the emulsion was found to have a significant impact on the resulting microcapsules. Increasing the concentration of either protective colloid in the dispersing medium increased the recovery and the release rate of acetaminophen, but reduced the particle size and loading efficiency of the microcapsules. Scanning electron micrographs manifested that all the microcapsules attained a nearly round shape. While gelatin imparted a smooth topography to the surface of the microcapsules, PVA made the surface of the microcapsules bumpy and humped.