Shear wave excitation in tissue phantom through non-spherical bubble collapse

Tissue exposed to a rapid acceleration, for example from traumatic impact, form voids that expand and collapse. The collapse of these cavitation bubbles has been made responsible for the damage to nearby cells through shear and strain. Bubbles collapsing non-spherically are known to launch shear waves. We present detailed measurements of how these shear waves are emitted from a well-controlled single laser-induced cavitation bubble. The bubbles are generated in a transparent tissue-mimicking hydrogel embedded with tracer particles. High-speed imaging of the tracer particles and the bubble shape allow quantifying the shear wave and relate it to the bubble dynamics. It is found that different stages of the bubble dynamics contribute to the shear wave generation and the mechanism of shear wave emission, its direction and the efficiency of energy converted into the shear wave depend crucially on the bubble to wall stand-off distance. These shear waves may travel far from the site of generation and could thus transport energy from the impact site, damaging remote delicate cellular structures.