Controlled rotation of micro-objects using acoustically driven microbubbles

Micromanipulation has significantly advanced both biomedical and industrial fields. However, there is still an urgent demand for controlled rotational manipulation at the microscale. Here, we report a noncontact rotational micromanipulation method using the acoustically driven microbubble contained in a micropipette. Acoustic vibration of the microbubble close to its resonant frequency was used to generate radiation force and microstreaming in the aqueous medium, allowing for trapping and rotating the micro-object. Simulation and particle visualization of the flow field clearly showed the microstreaming pattern induced by the oscillating microbubble. Experiments with different microbeads demonstrated the highly stable immobilization and rotation that related to the size and density of the microbead. By adjusting the frequency and voltage of the sinusoidal wave applied to the piezoelectric transducer, we demonstrated that the rotation frequency could be controlled over a broad range.