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1. Modulation of energy thresholds for laser-induced cavitation using gold nanoparticles

   https://doi.org/10.1117/12.3081310  

   Baker, Jacob C; Shrestha, Binita; Wang, Sicong; Rajan, Abhishek; Yadav, Aditya; Porter, Tyrone; Yang, Jin (March 2026, SPIE)

   Bixler, Joel N; Linz, Norbert; Walsh, Alex J (Ed.)

   The precise control of laser-induced cavitation (LIC) at the micro and nanoscale holds significant promise for biomedical applications ranging from targeted drug delivery and microsurgery to materials processing and microfluidics. Gold nanoparticles (AuNPs) are known to act as potent enhancers for LIC by reducing cavitation energy thresholds. However, a quantitative understanding of how AuNP properties regulate cavitation events remains limited, which is crucial for optimizing the aforementioned applications. In this study, we systematically investigate AuNP-mediated modulation of LIC energy thresholds using nanosecond laser pulses and ultra-high-speed imaging. While LIC in deionized (DI) water typically exhibits a sharp transition from no cavitation to large bubble formation (maximum bubble radius Rmax >100 μm) once a critical energy threshold is exceeded. In contrast, the introduction of AuNPs reveals four distinct cavitation regimes: (i) no observable bubbles, (ii) single small bubbles (Rmax ∼ 1-20 μm), (iii) multiple small bubbles forming bubble clouds, and (iv) single large bubbles (Rmax ∼ 100-1000 μm). Each AuNP system exhibits a characteristic energy threshold at which large cavitation emerges. We attribute these differences to a shift in the dominant cavitation nucleation mechanisms. These results demonstrate that AuNP optical properties play a critical role in governing LIC mechanisms, cavitation regimes, and energy thresholds. By enabling tunable and predictable cavitation behavior, this work provides a framework for the rational design of nanoparticle-assisted cavitation in advanced biomedical and engineering applications. 

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2. Investigation of the Primary Mechanisms of Cavitation-Induced Damages

   Zhao, Ben; Cao, Shunxiang; Wang, Kevin; Coutier-Delgosha, Olivier (July 2018, Cav2018)

   Erosion of solid surfaces due to cavitation has been studied for decades. However, it has been a long debate that which mechanism, namely shockwaves, microjets towards the surface, or both, during the cavitation bubble collapse is the primary factor responsible for that erosion. In this project we investigate the small-scale mechanisms of material erosion induced by the collapse of a single cavitation bubble close to a wall. More specifically, our experimental setup includes modification of the initial nucleus size, the maximum bubble radius, the stand-off distance to the wall, the material softness, and the initial flow temperature. We record the evolution of the bubble using high speed cameras as well as the local impacts on the materials. With the help of specifically designed cold-wires, we also measure the temperature in the liquid and in the bubble. Two different methods are used to generate the bubble: (i) an acoustic shockwave of variable intensity, (ii) a YAG laser, which may introduce a high temperature at the start. We also combine the two methods in which the laser initially creates a nucleus, then the shockwave triggers the expansion of the bubble. The objectives of the project are included in this paper, while some first results will be presented at the CAV2018 conference. 

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3. Energy transfer of two spherical oscillating bubbles in a free field

   https://doi.org/10.1063/5.0300783  

   Kim, M; Lee, J J; Rodriguez, M (February 2026, Physics of Fluids)

   Cavitation bubbles often appear as populations in a wide range of naval and biomedical applications. While the oscillations of an isolated spherical bubble are relatively well understood, the dynamics of multiple bubbles remain less characterized due to the large number of parameters associated with bubble size and spatial configuration. In the present study, we develop an energy budget framework for quantifying energy transfer and pressure work during the oscillations of spherical bubbles while conserving the total energy of the system. We focus on a two-bubble system in the dilute limit, in which bubbles interact weakly and largely maintain spherical symmetry. The energy budget framework uses the outputs of the coupled Keller–Miksis equations to evaluate individual energy components and their temporal evolution. Three key parameters—bubble size ratio, bubble–bubble distance, and driving pressure ratio—are observed to nonlinearly alter collapse time, energy concentration, and radiated acoustic energy. We show that stronger interactions, caused by larger size ratios or smaller separation distances, lead to reduced compression and less violent and delayed collapse, thereby lowering the energy concentrated in the bubble. We further determine scaling relationships for bubble dynamics and energy components at the instant of collapse based on the initial problem parameters. We identify the initial driving pressure conditions where the dominant energy reduction mechanism shifts from bubble–bubble interactions at low driving pressures to liquid compressibility at high pressures. The proposed framework and scaling relations provide a robust basis for incorporating bubble–bubble interactions and energy redistribution mechanisms into bubble cloud models, in the dilute limit. 

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4. Experimental Characterization of High-Strain-Rate Viscoelastic and Damage Behavior in Anisotropic Soft Materials Using Laser-Induced Inertial Cavitation

   https://doi.org/10.1007/s11340-026-01315-0  

   Wang, S; Bao, J; Chen, J; Santacruz, S R; Estrada, JB; Fan, D Emma; Yang, J (May 2026, Experimental Mechanics)

   Abstract BackgroundCharacterizing soft materials at ultra-high strain rates ($$>10^{3}\ \mathrm {s^{-1}}$$ $>{10}^3{s}^{-1}$ ) remains a significant challenge due to their nonlinear, large-deformation, and rate-dependent mechanical behavior. Despite these challenges, understanding material response in this regime is essential for a wide range of engineering and biomedical applications, including laser eye surgery, lithotripsy, and high-rate energy deposition in soft tissues. Laser-induced cavitation (LIC) has recently emerged as a powerful experimental approach for subjecting soft materials to extreme, localized loading rates on the microscale, regimes that are difficult to access using conventional mechanical testing methods. However, most biological tissues are anisotropic, optically opaque, and prone to damage at high strain rates, and their orientation-dependent ultra-high-rate mechanical behavior remains poorly understood. ObjectiveThe objective of this study is to develop and validate an experimental method that is based on laser-induced inertial cavitation and enables quantitative measurement of anisotropic soft materials and biological tissues at ultra-high strain rates, while explicitly accounting for fiber-directional mechanics and damage evolution. MethodsLIC experiments were performed in synthetic anisotropic polyvinyl alcohol (PVA) hydrogels and fresh chicken breast tissue using nanosecond-duration pulsed lasers to generate ultra-high-rate deformation. Simultaneously, cavitation bubble dynamics were captured using ultra-high-speed videography at 1-2 million frames per second. Two nonlinear hyper-viscoelastic constitutive models (a Poynting-Thomson model and a generalized Maxwell model) were developed and integrated with the measured bubble dynamics to quantify fiber-directional material response and investigate rate-dependent damage mechanisms. In addition, complementary quasistatic and oscillatory shear rheometry tests were conducted to provide low-rate mechanical benchmarks and investigate the rate dependency of soft materials’ mechanical behavior. ResultsLIC experiments revealed pronounced anisotropic bubble dynamics, with preferential elongation along fiber directions in both PVA hydrogels and chicken breast tissue. Model-based fitting of major-axis bubble radius-time histories enabled the extraction of effective ultra-high-rate directional moduli and critical stretch thresholds for damage initiation. ConclusionsIn summary, this study introduces a new experimental methodology for characterizing anisotropic soft materials at ultra-high strain rates. The experimental data and analysis approaches obtained from this introduction of experimental and computational methods will benefit future studies on high-strain-rate material damage and tissue injury, laser and ultrasound-related medical procedures, and anisotropic tissue constitutive modeling. 

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5. Shock-induced bubble collapse near solid materials: effect of acoustic impedance

   https://doi.org/10.1017/jfm.2020.810  

   Cao, S.; Wang, G.; Coutier-Delgosha, O.; Wang, K. (January 2021, Journal of Fluid Mechanics)

   null (Ed.)

   The fluid dynamics of a bubble collapsing near an elastic or viscoelastic material is coupled with the mechanical response of the material. We apply a multiphase fluid–solid coupled computational model to simulate the collapse of an air bubble in water induced by an ultrasound shock wave, near different types of materials including metals (e.g. aluminium), polymers (e.g. polyurea), minerals (e.g. gypsum), glass and foams. We characterize the two-way fluid–material interaction by examining the fluid pressure and velocity fields, the time history of bubble shape and volume and the maximum tensile and shear stresses produced in the material. We show that the ratio of the longitudinal acoustic impedance of the material compared to that of the ambient fluid, $$Z/Z_0$$ , plays a significant role. When $$Z/Z_0<1$$ , the material reflects the compressive front of the incident shock into a tensile wave. The reflected tensile wave impinges on the bubble and decelerates its collapse. As a result, the collapse produces a liquid jet, but not necessarily a shock wave. When $$Z/Z_0>1$$ , the reflected wave is compressive and accelerates the bubble's collapse, leading to the emission of a shock wave whose amplitude increases linearly with $$\log (Z/Z_0)$$ , and can be much higher than the amplitude of the incident shock. The reflection of this emitted shock wave impinges on the bubble during its rebound. It reduces the speed of the bubble's rebound and the velocity of the liquid jet. Furthermore, we show that, for a set of materials with $$Z/Z_0\in [0.04, 10.8]$$ , the effect of acoustic impedance on the bubble's collapse time and minimum volume can be captured using phenomenological models constructed based on the solution of Rayleigh–Plesset equation. 

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