Programmable Assembly and Steering of Microbubble Droplets using Ultrasound

Gas-filled microbubbles have been extensively used as contrast agents for ultrasound therapies and have recently been explored as microrobots. When exposed to an intense acoustic wave, microbubbles oscillate and scatter the sound field, leading to assembly and manipulation behaviors. Although traditional microbubbles demonstrated promising potential for manipulation in physiological environments, we recognized the need for improved assembly selectivity and acoustically directed propulsion. For this, we developed a new microbubble design using microfluidics. We engineered microbubbles with an outer oil droplet encapsulating a gas core, allowing the gas to move freely within the oil. When the gas reaches the droplet’s periphery, the oil attenuates the scattered wave, ensuring that scattering or acoustic amplification is concentrated near the droplet’s edge. This approach enabled us to control the organized assembly of microbubbles and direct their acoustic navigation. We believe this approach will open new possibilities for using gas-filled microbubbles as safer drug carriers or for micro-interventions in biomedical settings.