SYNTHESIS, CHARACTERIZATION AND APPLICATION OF MICROBUBBLES: A REVIEW

Microbubbles are bubbles smaller than one millimeter in diameter, but larger than one micrometer. Microbubbles designate air or gas filled microspheres suspended in a liquid carrier phase which generally results from the introduction of air or gas. The liquid phase contains surfactants to control the surface properties as well as stability of the bubble. Microbubbles have an average size less than that of RBC’s i.e., they are capable of penetrating even into the smallest blood capillaries & releasing drugs or genes, incorporated on their surface, under the action of ultrasound. Microbubbles in general have a wide variety of applications. However in the biomedical field these are primarily used as diagnostic agents in combination with ultrasound for molecular imaging of various organs and even tumours. These are also proposed for drug and gene delivery to targeted regions in combination with various ligands. Most of the physicians today prefer imaging with ultrasound in combination with microbubbles compared to other diagnostic techniques for low cost and rapidity.  They are used in medical diagnostics as a contrast agent for ultrasound imaging. The gas-filled, e.g., air or perfluorocarbon, microbubbles oscillate and vibrate when a sonic energy field is applied and may reflect ultrasound waves. This distinguishes the microbubbles from surrounding tissues. The unique ability of microbubbles to respond to ultrasound makes them useful agents for contrast ultrasound imaging, molecular imaging, and targeted drug and gene delivery.  In practice, because gas bubbles in liquid lack stability and would therefore quickly dissolve; microbubbles must be encapsulated with a solid shell. The shell is made from either a lipid or a protein such as Optison-microbubbles which consist of perfluoropropane gas encapsulated by a serum albumin shell. Microbubbles may also be used for drug delivery and water/waste water treatment purposes.