Microbubbles are bubbles smaller than one hundredth of a millimetre in diameter, but larger than one micrometre. They have widespread application in industry, medicine,[1] life science,[2] and food technology.[3] The composition of the bubble shell and filling material determine important design features such as buoyancy, crush strength, thermal conductivity, and acoustic properties.
They are used in medical diagnostics as a contrast agent for ultrasound imaging.[4]
The gas-filled microbubbles, typically air or perfluorocarbon, oscillate, and vibrate if a sonic energy field is applied and may reflect ultrasound waves. This distinguishes the microbubbles from surrounding tissues. Because gas bubbles in liquid lack stability and would therefore quickly dissolve, microbubbles are typically encapsulated by shells. The shell is made from elastic, viscoelastic, or viscous material. Common shell materials are lipid, albumin, and protein.
Materials having a hydrophilic outer layer to interact with the bloodstream and a hydrophobic inner layer to house the gas molecules are thermodynamically stable. Air, sulfur hexafluoride, and perfluorocarbon gases all can serve as the composition of the microbubble interior. Microbubbles with one or more incompressible liquid or solid cores surrounded by gas are referred to as microscopic or endoskeletal antibubbles. For increased stability and persistence in the bloodstream, gases with high molecular weight as well as low solubility in the blood are attractive candidates for microbubble gas cores.[5]
Microbubbles may be used for drug delivery,[6]biofilm removal,[7] membrane cleaning[8][9] /biofilm control and water/waste water treatment purposes.[10] They are also produced by the movement of a ship’s hull through water, creating a bubble layer; this may interfere with the use of sonar because of the tendency of the layer to absorb or reflect sound waves.[11]