Localized Tissue Surrogate Deformation due to Controlled Single Bubble Cavitation

Cavitation-induced shock wave, as might occur in the head during exposure to blast waves, was investigated as a possible damage mechanism for soft brain tissues. A novel experimental technique was developed to visualize and control single bubble cavitation and its collapse, and the influence of this process on a nearby tissue surrogate was investigated. The experiment utilized a Hopkinson pressure bar system which transmits a simulated blast pressure wave (with over-pressure and under-pressure components) to a fluid-filled test chamber implanted with a seed gas bubble. Growth and collapse of this bubble was recorded during passage of the blast wave with a high speed camera. To investigate the potential for cavitation damage to a tissue surrogate, local changes in strain were measured in hydrogel slices placed in various configurations next to the bubble. The strain measurements were made using digital image correlation (DIC) technique by monitoring the motion of material points on the tissue surrogate. In one configuration, bubble contact dynamics resulted in compression contact (>60 μs) followed by inertially-driven tension (>140 μs). In another configuration, the influence of local shock waves emanating from collapsed bubbles was captured. Large compressive strains (0.25 to 0.5) that were highly localized (0.18 mm²) were measured over a short time period (<24 μs) after bubble collapse. High bubble collapse pressures 29 to 125 times that of peak blast overpressure are predicted to be the source of these large strains. Consistent with theoretical predictions, these cavitation-based strains are far larger than the strains imposed by passage of the simulated blast wave alone. Finally, the value of this experimental platform to investigate the single bubble cavitation-induced damage in a biological tissue is illustrated with an example test on rat brain slices.