arXiv subjects

Jonathan R. Sukovich

Publications and source records attributed to Jonathan R. Sukovich.

3 recordsLinked to original sources

arXiv2026

Microbubble surface instabilities in a strain stiffening viscoelastic material

Understanding the dynamics of instabilities along fluid-solid interfaces is critical for the efficacy of focused ultrasound therapy tools (e.g., histotripsy) and microcavitation rheometry techniques. Non-uniform pressure fields generated by either ultrasound or a focused laser can cause non-spherical microcavitation bubbles. Previous perturbation amplitude evolution models in viscoelastic materials either assume pure radial deformation or have inconsistent kinematic fields between the fluid and solid contributions. We derive a kinematically-consistent theoretical model for the evolution of surface perturbations. The model captures the non-linear kinematics of a strain-stiffening viscoelastic material surrounding a non-spherical bubble. The model is validated for (i) small, approximately linear radial oscillations and (ii) large inertial oscillations using laser-induced microcavitation experiments in a soft hydrogel. For the former, the bubble is allowed to reach mechanical equilibrium, and then surface perturbations are excited using ultrasound forcing. For the latter, the microbubble forms small bubble surface perturbations at its maximum radius that grow during collapse. The model's dominant surface perturbation mode scales linearly with equilibrium radius and matches experiments. Similarly, the model's perturbation amplitude evolution sufficiently constrains the rheometry problem and is experimentally validated.

physics.flu-dyn↗

arXiv2021

Growth and Collapse of an Isolated Bubble Driven by a Single Negative Histotripsy Cycle in Agarose Gel: Stress, Strain, and Strain Rate Fields

Histotripsy relies on cavitation to mechanically homogenize soft tissue. There is strong evidence that the high stresses, strains, and strain rates developed as bubbles grow and collapse contribute to this tissue homogenization. While such stresses and strains have been examined computationally in model systems with assumed constitutive models (e.g., finite-deformation Neo-Hookean model) and viscoelastic properties determined under quasi-static conditions, recent studies proposed that the Quadratic Law Kelvin-Voigt (QLKV) constitutive model, which additionally accounts for strain stiffening, more accurately represents the viscoelastic response of soft materials subjected to cavitation; this model has also been used to infer viscoelastic properties at high rates. In this work, we use the QLKV model and these properties to calculate the time-dependent stress, strain, and strain rate fields produced during the growth and collapse of individual bubbles subjected to a histotripsy-relevant pressure waveform in agarose gels of 0.3~\% and 1.0~\% concentration and corresponding to actual (past) experiments. We find that, as the gel concentration is increased, strain stiffening manifests in larger elastic stresses and compressive stresses extending into the collapse phase, particularly for the 1.0~\% concentration gel. As a result, the duration of the collapse phase also increases. In comparison with the conventional Neo-Hookean model, the compressive stress has a larger magnitude, extends farther into the surrounding medium, and shows an increased departure from growth/collapse symmetry close to the bubble; all of these effects are magnified in the stiffer gel.

cond-mat.soft↗

arXiv2020

Acoustic Cavitation Rheometry

Characterization of soft materials is challenging due to their high compliance and the strain-rate dependence of their mechanical properties. The inertial microcavitation-based high strain-rate rheometry (IMR) method [Estrada et al., J. Mech. Phys. Solids, 2018, 112, 291-317] combines laser-induced cavitation measurements with a model for the bubble dynamics to measure local properties of polyacrylamide hydrogel under high strain-rates from $10^3$ to $10^8$ s$^{-1}$. While promising, laser-induced cavitation involves plasma formation and optical breakdown during nucleation, a process that could alter local material properties before measurements are obtained. In the present study, we extend the IMR method to another means to generate cavitation, namely high-amplitude focused ultrasound, and apply the resulting acoustic-cavitation-based IMR to characterize the mechanical properties of agarose hydrogels. Material properties including viscosity, elastic constants, and a stress-free bubble radius are inferred from bubble radius histories in $0.3\%$ and $1\%$ agarose gels. An ensemble-based data assimilation is used to further help interpret the obtained estimates. The resulting parameter distributions are consistent with available measurements of agarose gel properties and with expected trends related to gel concentration and high strain-rate loading. Our findings demonstrate the utility of applying IMR and data assimilation methods with single-bubble acoustic cavitation data for measurement of viscoelastic properties.

cond-mat.soft↗