Biodegradable polymeric microcapsules can be produced through different methods of which emulsion solvent-evaporation/extraction is frequently used. In this technique, the polymer (often polylactide) is dissolved in a good solvent and is emulsified together with a poor solvent into a nonsolvent phase. The solvent is then removed through the nonsolvent phase by evaporation. This results in solidification of the polymer around an internal droplet of the poor solvent. The poor solvent may be removed later when hollow capsules are required. This paper discusses the fundamental aspects of the formation process of hollow polylactide microcapsules and its effects on the physical and chemical properties of the capsules, with emphasis on the solidification process of the polymer and the resulting properties of the shell. The scope for improvement and adaptation of the current process, including new emulsification techniques, is also discussed. The main message of this paper is that the properties of the capsules can be optimized through the solidification process of the polymer which can be highly influenced by the proper choice of the nonsolvent and oil. Since this field is hardly investigated in literature, there is room for improvement, especially if the capsules can be produced with the newest emulsification technologies that are becoming available.
- membrane emulsification technique
- hollow polylactide microcapsules
- ultrasound contrast agents
- poly(lactic acid)
- poly(l-lactic acid)
- size distribution