Trapping of low sensitivity object by seed bubbles

Recently, many kinds of micro bubbles have been developed for ultrasonic wave contrast agents. Some bubbles have hard biopolymer shells in order to prevent internal gas diffusion. Another bubble is equipped with multiple shells to give some functions to the bubble. However, these developments usually harden the bubbles decreasing volumetric oscillation under ultrasonic wave radiation. The Bjerknes force, which is driving force in micro bubble trapping by ultrasonic wave, is proportional to the volumetric oscillation, the received force is often too small to manipulate the bubbles. In sonoporation, which is a sophisticated method in dose improvement, it is expected that the micro bubbles explode as a result of large volumetric oscillation. In this paper, a novel method of micro objects trapping by seed bubbles is proposed. The seed bubbles trap the target objects by spatially restricted Bjerknes force, which is generated by secondary ultrasonic waves radiated from the oscillating seed bubbles. The produced target objects-seed bubbles complex may play an important role in sonoporation, because the seed bubbles, which are easy to explode by high intensity ultrasonic wave, exist close to the payloads of the target objects.