PhD defence: Movement of a buckling ultrasound contrast agent under low-frequency ultrasound excitation - Andréa Feasson (MC2, LIPhy)

Microrobots have held the interest of the scientific community for some decades now. Their versatility of application, especially in medicine, can explain the enthusiasm for this field of research.

The present work focuses on the navigation of phospholipidic microshells called ultrasound contrast agents (UCAs) via a buckling instability triggered by pressure. A potential application of this phenomenon would be to navigate UCAs in the bloodstream for targeted drug delivery purposes.

We studied experimentally the swimming motion of these ultrasound contrast agents under a standing wave field of ultrasound around 26.5 kHz for a pressure amplitude ranging from 0 to 30 kPa. This thesis aimed to determine if buckling can induce motion under ultrasound. Indeed, in an acoustic field, there are two main known mechanisms to cause movement on a UCA: radiation forces and streaming. We developed an experimental setup allowing us to study the swimming motion separately from the radiation forces. Using this setup, we could indirectly link the swimming motion to buckling.

In the optics of further application where the radiation forces will be present, we studied the coupling between the swimming and the radiation forces. We analysed the coupling at the same frequency in standing waves in the same ultrasound pressure interval as previously.