Acoustic droplet vaporization (ADV) enables on-demand bubble generation through ultrasound-induced phase transition, offering a unique approach for characterizing tissue mechanics. Although ADV has been investigated in various biomedical applications, its potential in tissue characterization remains unexplored. In this study, we investigated how stiffness and microstructure of surrounding media influence ADV bubble dynamics as well as acoustic emissions. Using advanced imaging techniques, we captured both ultra-high-speed expansion and quasi-static diffusion behavior of perfluoropentane droplets (diameter: ∼12 µm) embedded in tissue-mimicking hydrogels with elastic moduli ranging from 0.2 to 30 kPa. Under identical ultrasound exposure conditions, perfluoropentane droplets expanded ∼5.5-fold in a soft (0.2 kPa) hydrogel but only ∼1.2-fold in a stiff (30 kPa) one. In addition, for hydrogels with comparable elastic moduli, differences in microstructure led to distinct post-ADV behaviors. Specifically, stable bubbles persisted in fibrin and gelatin hydrogels, whereas recondensation occurred in polyacrylamide and PEG-based matrices. Acoustic backscatter analysis revealed that a ∼6-kPa increase in stiffness reduced both linear and nonlinear responses by up to 10 dB. These observations highlight the promising potential of ADV as an effective method for probing the mechanical and structural properties of soft tissues.
Mitra Aliabouzar (Wed,) studied this question.