Jetting Behaviour of Ultrasound-driven Microbubbles in Contact with a Soft Substrate

The use of ultrasound-driven microbubbles presents a promising avenue for facilitating the localised delivery of therapeutics by inducing controlled nanodamage on capillary walls. Despite the tangible clinical evidence of the success of this approach, the underlying physical mechanism leading to nanodamage remains under debate. In this study, time-resolved side-view visualisations elucidate the interplay between soft substrates and microbubbles under clinically relevant ultrasound regimes. Our findings reveal the existence of four distinct regimes of bubble behaviour dependent on the bubble's size and the role of shape deformations as governing mechanism for the bubble behaviour. Among these regimes, three result in the formation of periodic microjets. The remarkable speed of these microjets indicates their significant contribution in causing surface nanodamage.