Nanobubbles (NBs), consisting of a lipid shell surrounding a gas core, have gained significant interest as contrast agents for ultrasound molecular imaging. Their acoustic response is strongly influenced by size and shell properties, yet most prior work has focused on microbubble characterization. Building on insights from microbubble studies, this work investigates the viscoelastic properties of in-house synthesized phospholipid-coated submicron NBs (average diameters of 650–720 nm) using ultrasound bulk attenuation measurements. Three NB formulations with distinct shell compositions were examined. The results highlight the critical role of shell properties in determining NB resonance frequencies. Furthermore, pressure-dependent shifts in resonance revealed strong nonlinear behavior at higher acoustic driving pressures (up to 280 kPa). Comparison with microbubbles of identical shell types showed that shell stiffness and friction are size-dependent, likely due to shell properties and the shear-thinning behavior of phospholipids. These findings provide new insights into NB dynamics with potential implications for both diagnostic and therapeutic ultrasound applications.
Yaali et al. (Fri,) studied this question.