Stability and size dependence of protein microspheres prepared by ultrasonication

Protein microspheres have been prepared by sonicating oil in an aqueous protein solution. Such prepared microspheres can be used in magnetic resonance imaging (MRI), micro-encapsulation, and drug delivery systems. When they are used in the blood circulation, their size and stability become most important. In this paper, the factors affecting the size and size distribution of these microspheres are discussed and a way to control the size of the microspheres is put forward. Small microspheres with size less than 1 mm were selected by gravitational sedimentation. The selected microspheres have a narrow size distribution and can be used in the blood circulation safely. The loading of dye into these microspheres was easily achieved by dissolution of drugs in the oil phase before sonication. The protein microspheres showed excellent protection for the loaded dye, which can be stably carried for several weeks.