Cavitation bubbles in tissue simulants

Cavitation formation and dynamics in the human body, when subjected to rapid mechanical load, is being considered as a possible injury mechanism. We consider cavitation in a tissue simulant utilizing four different gel types: gelatin A/B, agar, and agarose. The gels are prepared at different gel concentrations (c) in pure water for each gel type so that the effect of gel’s properties on cavitation can be experimentally characterized. A well-controlled mechanical impact is applied to each sample to simulate typical brain injury scenarios. For gelatin A/B, the critical acceleration (a_cr) that triggers the onset of inertial cavitation monotonically rises with increasing gel stiffness and spherical bubbles are observed regardless of c. In contrast, the a_cr for agar and agarose monotonically increases, but followed by plateau. In addition, bubble shape transitions from sphere to saucer with increasing c. We hypothesize that hydrophobic molecular bundles in agar and agarose cause these unique responses. Our theoretical analysis using both Rayleigh-Plesset and fracture-based models confirms that our proposed mechanisms offer reasonable explanations for the observed cavitation behavior in soft tissue simulants.