Stabilized microbubbles have been used as ultrasound contrast agents for decades. A significant effort has been made in modeling the interaction of the ultrasound-driven bubble dynamics, including the detailed behavior of viscoelastic phospholipid shells and the effect of a surrounding viscoelastic medium. Yet, open questions remain with respect to the shell and medium viscoelastic behavior at high strain-rate, i.e., at the MHz frequencies used to drive the bubbles. Here, we investigate both effects in parallel. First, the response of single microbubbles in water is measured using an acoustical camera to characterize the high frequency stress–strain response of its viscoelastic shell. The measurements provide new insight into shell models, as well as an estimate of bubble-to-bubble variations. With this knowledge of viscoelastic shell properties, we proceed to model and measure the viscoelastic properties of the host medium, first analytically, and propose a new model that is both simple and general to describe bubble oscillations in viscoelastic media based on arbitrary relaxation functions. To the limit of a narrow bandwidth for bubble oscillations, we can use a simplified viscoelastic model and experimentally characterize the medium surrounding the bubble. These advances can play a significant role in using microbubble contrast agents as local sensors for the quantification of the mechanical properties of biological tissues.
Lajoinie et al. (Wed,) studied this question.