Clean production and characterization of nanobubbles using laser energy deposition

Enhancing ultrasound applications through shell-less nanobubbles: A study on acoustic and optical properties

Histotripsy employs acoustic inertial cavitation to mechanically destroy tissue, producing acellular debris. While introducing bubbles can lower the cavitation threshold and enhance treatment efficiency, micrometer-scale bubbles struggle to penetrate tissues effectively. Shell-less nanobubbles, with their high internal pressure, stability, negatively charged surfaces, and unique lifetimes ranging from weeks to months, offer a promising alternative. However, their interactions with ultrasound remain unexplored. This study used a claw-type pump nanobubble generator to produce nanobubbles and employed acoustic and optical methods to observe their behavior under high-intensity ultrasound exposure. The results demonstrated that the device generated nanobubble solutions with an average particle size of 107 nm, a concentration of 1.94 × 109 particles/mL, a lifetime exceeding one week, and a zeta potential of -21.2 mV. Acoustic and optical observations further revealed that nanobubble solutions reduced the inertial cavitation threshold of the liquid from 26.5 MPa to 10.3 MPa. These findings suggest a potential strategy to enhance the efficiency of ultrasound histotripsy treatments.

Nanobubble nucleation by pulsed laser illumination of colloidal gold nanoparticles

This study expands upon a technique our team previously developed for generating nanobubbles on demand with a collimated pulsed laser beam. This work highlights how the controlled addition of gold nanoparticles enhances nanobubble generation efficiency in water, even at laser intensities well below the threshold for multiphoton ionization. Specifically, we investigated the influence of nanoparticles of three distinct sizes on the laser fluence threshold for bubble nucleation and the lifetime of the resultant nanobubbles. Our findings confirm that nanoparticles with a diameter of 60 nm exhibit the greatest nucleation efficiency, achieving nearly 45 % at a fluence threshold of around [Formula: see text]. Interestingly, nanoparticle size did not impact the nanobubble lifetime.

Chitosan-functionalized nanobubbles for precision oncology: advances in targeted cancer therapeutics

The convergence of nanotechnology and cancer therapeutics has opened new frontiers in the development of advanced drug delivery systems. Among the various nanocarriers, nanobubbles offer significant potential due to their unique properties, such as high payload capacity, responsiveness to external stimuli like ultrasound, and enhanced permeability and retention (EPR) effects. Functionalizing these nanobubbles with chitosan, a naturally derived biopolymer known for its biocompatibility, biodegradability, and ability to enhance cellular uptake, further improves their therapeutic efficacy. This review provides a comprehensive analysis of the synthesis, functionalization, and application of chitosan-functionalized nanobubbles in cancer therapy. We discuss their mechanism of action, including targeted drug delivery, ultrasound-mediated release, and immune modulation, alongside recent advancements and challenges in their clinical translation. This review also explores future directions in this rapidly evolving field, aiming to offer insights into the development of next-generation cancer therapeutics.

High-speed ultrasound imaging of bubbly flows and shear waves in soft matter

In this methods paper, we explore the capabilities of high-speed ultrasound imaging (USI) to study fast varying and complex multi-phase structures in liquids and soft materials. Specifically, we assess the advantages and the limitations of this imaging technique through three distinct experiments involving rapid dynamics: the underwater flow induced by an external jet, the dissolution of sub-micron bubbles in water, and the propagation of shear waves in a soft elastic material. The phenomena were simultaneously characterized using optical microscopy and USI. In water, we use compounded USI for tracking a multi-phase flow produced by a jetting bubble diving into a liquid pool at speeds around 20 m s-1. These types of jets are produced by focusing a single laser pulse below the liquid surface. Upon breakup, they create a bubbly flow that exhibits high reflectivity to the ultrasound signal, enabling the visualization of the subsequent turbulent flow. In a second experiment, we demonstrate the potential of USI for recording the diffusive shrinkage of micro- and nanobubbles in water that could not be optically resolved. Puncturing an elastic material with a liquid jet creates shear waves that can be utilized for elastography measurements. We analysed the shape and speed of shear waves produced by different types of jetting bubbles in industrial gelatin. The wave characteristics were simultaneously determined by implementing particle velocimetry in optical and ultrasound measurements. For the latter, we employed a novel method to create homogeneously distributed micro- and nanobubbles in gelatin by illuminating it with a collimated laser beam.

Evidence of laser-induced nanobubble formation mechanism in water

Principles of laser-induced nanobubble formation in water are studied and presented. Nanobubbles were generated by laser light at intensities below threshold for laser-induced breakdown and subsequently expanded by a rarefaction wave to facilitate their observation and analysis. Different methods were used to study nanobubble formation and characteristics. Firstly, probability of nanobubble formation as a function of water sample purity was examined. Secondly, relation between laser fluence at different wavelengths and the number of generated nanobubbles was investigated. Thirdly, measurements of nanobubble lifetime were conducted indicating a contradiction to the Epstein-Plesset equation-based prediction of free bubble dissociation. Accumulated evidence suggests that the presence of physical impurities is a prerequisite for nanobubble formation. Consequently, a lack of impurities results in the absence of nanobubbles in contrast to assumptions by existing studies. The findings presented in this paper provide new insights into the fundamental properties of laser-induced nanobubbles in water.

Memory-friendly fixed-point iteration method for nonlinear surface mode oscillations of acoustically driven bubbles: from the perspective of high-performance GPU programming

A fixed-point iteration technique is presented to handle the implicit nature of the governing equations of nonlinear surface mode oscillations of acoustically excited microbubbles. The model is adopted from the theoretical work of Shaw [1], where the dynamics of the mean bubble radius and the surface modes are bi-directionally coupled via nonlinear terms. The model comprises a set of second-order ordinary differential equations. It extends the classic Keller-Miksis equation and the linearized dynamical equations for each surface mode. Only the implicit parts (containing the second derivatives) are reevaluated during the iteration process. The performance of the technique is tested at various parameter combinations. The majority of the test cases needs only a single reevaluation to achieve 10-9 error. Although the arithmetic operation count is higher than the Gauss elimination, due to its memory-friendly matrix-free nature, it is a viable alternative for high-performance GPU computations of massive parameter studies.