MicroBubble

A microbubble is a gas-filled bubble dispersed in a liquid, typically measuring from about 1 to 1000 micrometers in diameter. In biomedical contexts, microbubbles are usually small enough to travel through the capillary network, with many formulations optimized for diameters of a few micrometers.

Most microbubbles consist of a gas core stabilized by a shell. The gas may be air, nitrogen, or heavier gases such as perfluorocarbons. The shell—composed of lipids, proteins (such as albumin), polymers, or surfactants—reduces gas loss to dissolution and controls circulation time and mechanical stability within the bloodstream.

Microbubbles are commonly produced by methods such as mechanical agitation, sonication, or microfluidic technologies, which can tailor bubble size distributions and shell composition. Some formulations are designed as intravascular ultrasound contrast agents and have regulatory approval for diagnostic imaging.

Under ultrasound, microbubbles respond to acoustic pressure by radial oscillations. This nonlinear response enhances echogenicity and enables contrast-enhanced imaging. At higher acoustic pressures, microbubbles may undergo inertial cavitation, a rapid collapse that can increase local permeability and promote delivery of therapeutic agents, a phenomenon explored for drug and gene delivery and sonoporation. They can also facilitate targeted disruption of biological barriers in experimental settings.

Applications extend beyond imaging to therapeutic uses, including localized drug or gene delivery, rehabilitation of damaged tissue, and research on blood-brain barrier modulation. In addition to medicine, microbubbles find use in industrial and research contexts for cleaning, sonochemistry, and material processing.

Safety and regulatory considerations focus on circulation time, clearance pathways, and potential risks from cavitation, with approved agents subject to clinical guidelines and monitoring.