Controlled generation of single microbubbles

The size of a microbubble, which dictates its surface to volume ratio, plays an important role in how it interacts with fluids, surfaces, and (electric or acoustic) fields. Therefore, many biomedical and scientific applications require accurate bubble size control. To address this need, a new method of controlled generation of single microbubbles was developed in this study, which uses timed gas injection and liquid co-flow. In this device, a pressure pulse generated by a system of multiple solenoid valves is used to inject a small, controlled burst of air through a micropipette to generate individual microbubbles. As an added degree of freedom, an external co-flow of water was used to control the drag force which can influence when the bubble detaches from the micropipette. By limiting the air flow through a micropipette with an automatically actuated pressure pulse and by adjusting the co-flow rate, the present method was able to generate single microbubbles in the range of 62.6–150.8 µm in diameter (without the use of surfactants and buoyancy). Compared to other reported gas injection techniques which generate sub-millimetric single bubbles, the 62.6 µm bubbles generated in this study represent a 37% reduction in measured diameter.