Shock-induced collapse of surface nanobubbles

Ultrasound-mediated drug-free theranostics for treatment of prostate cancer

Lipid-shelled nanobubbles (NBs) can be visualized and activated using noninvasive ultrasound (US) stimulation, leading to significant bioeffects. Prior work demonstrates that active targeting of NBs to prostate-specific membrane antigen (PSMA) overexpressed in prostate cancer (PCa) results in enhanced cellular internalization and prolongs NB retention with persistent, cancer-cell specific acoustic activity. In this work, we hypothesized that tumor-accumulated PSMA-NBs combined with low frequency unfocused therapeutic US (TUS) will lead to selective damage and induce a specific therapeutic effect in PSMA-expressing tumors compared to PSMA-negative tumors. We observed that the internalized NBs and cellular compartments were disrupted after the PSMA-NB + TUS (targeted NB therapy or TNT) application, yet treated cells remained intact and viable. In vivo, PSMA-expressing tumors in mice receiving TNT treatment demonstrated a significantly greater extent of apoptosis (78.4 ± 9.3 %, p < 0.01) compared to controls. TNT treatment significantly inhibited the PSMA expressing tumor growth and increased median survival time by 103 %, p < 0.001). A significant reduction in tumor progression compared to untreated control was also seen in an orthotopic rabbit PCa model. Results demonstrate that cavitation of PSMA-NBs internalized via receptor-mediated endocytosis into target PCa cells using unfocused ultrasound results in significant, tumor-specific bioeffects. The effects, while not lethal to PSMA-expressing cancer cells in vitro, result in significant in vivo reduction in tumor progression in two models of PCa. While the mechanism of action of these effects is yet unclear, it is likely related to a locally-induced immune response, opening the door to future investigations in this area.

Characterization of the Dynamic Behavior of Multinanobubble System under Shock Wave Influence

Shockwave-induced changes in nanobubbles cause cavitation erosion and membrane damage but can also be applied to biocarrier transport. Currently, research focuses on single nanobubbles; however, in reality, nanobubbles usually appear as a multibubble system. Therefore, this study proposes a method based on cutting and replicating to construct a multibubble model. This method can be widely applied to molecular dynamics (MD) models and enhance the customization capabilities of MD models. The dynamic behavior of a multinanobubble system with different numbers and arrangements of nanobubbles is investigated with the MD method under the influence of shock waves in a liquid argon system. The study also explores the range of influence between nanobubbles. The results show that in the case of two nanobubbles, when the distance between the bubbles is constant, the smaller the angle between the direction of the shock wave and the line connecting the bubbles, the greater is the influence between nanobubbles, and the moment of collapse of the nanobubbles farther away from the shock wave is slower. When three nanobubbles are arranged with a right offset, after the first bubble collapses, the effect on the other two bubbles is similar to the changes in bubbles when the angle of arrangement is 30° or 60°. Under a different arrangement, the change of shock wave velocity on the nanobubble size only affects its collapse time and contraction collapse rate. When the shock wave with a radian of about 2.87 or greater than 2.87 touches the bubbles, the collapse of the second nanobubble will not be affected.

The impact of low-velocity shock waves on the dynamic behaviour characteristics of nanobubbles

Low-velocity shock wave-induced contraction and expansion of nanobubbles can be applied to biocarriers and microfluidic systems. Although experiments have been conducted to study the application effects, the dynamic behavior characteristics of nanobubbles remain unexplored. In this work, we utilize molecular dynamics (MD) simulations to investigate the dynamic behavior characteristics of nanobubbles influenced by low-velocity shock waves in a liquid argon system. The DBSCAN (Density-Based Spatial Clustering of Applications with Noise) machine learning method is used to calculate the equivalent radius of nanobubbles. Two statistical methods are then utilized to predict the time series changes in the equivalent radius of nanobubbles without rebound shock waves. The piston velocity is analyzed using the bisection method to obtain the critical impact states of the nanobubble. The results show that at the low velocity shock wave (piston velocity of 0.1 km s-1), the shock wave pressure is small, the non-vacuum nanobubbles contract and expand in a circular shape, and the gas particles inside the bubble are not dispersed. In contrast, the vacuum nanobubbles collapse directly. As the shock wave rebounds upon impact, it triggers periodic contraction and expansion of the nanobubbles. The predictions indicate that the equivalent radius will vary within a small range according to the pre-predicted values in the absence of the rebound shock wave. Nanobubbles are present in four critical impact states: dispersed gaps, multiple smaller bubbles, two split bubbles, and a concave bubble.

Effect of Shock-Wave-Mediated Collapse on Nanobubble Characteristics

To enhance the comprehension of the cavitation mechanism and explore its practical use in industrial production, this study developed models involving oxygen, varying bubble radii, and bubble quantities. This study uses molecular dynamics simulations coupled with the momentum mirror method to examine the collapse characteristics of bubbles during ultrasonic cavitation. The investigation uncovers patterns in the fluctuation of the maximum local density of water molecules, released pressure, and temperature. The findings demonstrate that, when oxygen-containing bubbles collapse at identical radii, the local density is notably higher and diminishes more rapidly. Moreover, the changes in the shape exhibit greater regularity. During the bubble collapse, a depression forms on the bubble's surface, coinciding with a notable surge in local density around the depression. As bubble radii and quantities increase, so does the local density along with a concurrent rise in the maximum pressure. Intriguingly, the model demonstrates the lowest pressure at Z = 35 Å accompanied by the emergence of a small crescent-shaped region with a reduced density. Throughout the pressure ascension phase, the rate of the maximum pressure change escalates with an increase in the number of bubbles. Conversely, during the pressure descent phase, the rate of the maximum pressure change diminishes with a growing number of bubbles. However, it is important to note that the maximum pressure does not exhibit a direct correlation with the number of bubbles. Ultimately, this study provides valuable technical guidance and a theoretical foundation for the integration of ultrasonic cavitation in industrial production processes.

Thermal Oscillations of Nanobubbles

Nanobubble cavitation is advancing technologies in enhanced wastewater treatment, cancer therapy and diagnosis, and microfluidic cleaning. Current macroscale models predict that nanobubble oscillations should be isothermal, yet recent studies suggest that they are adiabatic with an associated increase in natural frequency, which becomes challenging when characterizing nanobubble sizes using ultrasound in experiments. We derive a new theoretical model that considers the nonideal nature of the nanobubble's internal gas phase and nonequilibrium effects, by employing the van der Waals (vdW) equation of state and implementing a temperature jump term at the liquid-gas interface, respectively, finding excellent agreement with molecular dynamics (MD) simulations. Our results reveal how adiabatic behavior could be erroneously interpreted when analyzing the thermal response of the gas using the commonly employed polytropic process and explain instead how nanobubble oscillations are physically closer to their isothermal limit.

Ultrasound-mediated drug-free theranostics for treatment of prostate cancer

Rationale

Lipid-shelled nanobubbles (NBs) can be visualized and activated using noninvasive ultrasound (US) stimulation, leading to significant bioeffects. We have previously shown that active targeting of NBs to prostate-specific membrane antigen (PSMA) overexpressed in prostate cancer (PCa) enhances the cellular internalization and prolongs retention of NBs with persistent acoustic activity (~hrs.). In this work, we hypothesized that tumor-accumulated PSMA-NBs combined with low frequency therapeutic US (TUS) will lead to selective damage and induce a therapeutic effect in PSMA-expressing tumors compared to PSMA-negative tumors.

Methods

PSMA-targeted NBs were formulated by following our previously established protocol. Cellular internalization of fluorescent PSMA-NBs was evaluated by confocal imaging using late endosome/lysosome staining pre- and post-TUS application. Two animal models were used to assess the technique. Mice with dual tumors (PSMA expressing and PSMA negative) received PSMA-NB injection via the tail vein followed by TUS 1 hr. post injection (termed, targeted NB therapy or TNT). Twenty-four hours after treatment mice were euthanized and tumor cell apoptosis evaluated via TUNEL staining. Mice with single tumors (either PSMA + or -) were used for survival studies. Tumor size was measured for 80 days after four consecutive TNT treatments (every 3 days). To test the approach in a larger model, immunosuppressed rabbits with orthotopic human PSMA expressing tumors received PSMA-NB injection via the tail vein followed by TUS 30 min after injection. Tumor progression was assessed via US imaging and at the end point apoptosis was measured via TUNEL staining.

Results

In vitro TNT studies using confocal microscopy showed that the internalized NBs and cellular compartments were disrupted after the TUS application, yet treated cells remained intact and viable. In vivo, PSMA-expressing tumors in mice receiving TNT treatment demonstrated a significantly greater extent of apoptosis (78.45 ± 9.3%, p < 0.01) compared to the other groups. TNT treatment significantly inhibited the PSMA (+) tumor growth and overall survival significantly improved (median survival time increase by 103%, p < 0.001). A significant reduction in tumor progression compared to untreated control was also seen in the rabbit model in intraprostatic (90%) and in extraprostatic lesions (94%) (p = 0.069 and 0.003, respectively).

Conclusion

We demonstrate for the first time the effect of PSMA-targeted nanobubble intracellular cavitation on cancer cell viability and tumor progression in two animal models. Data demonstrate that the targeted nanobubble therapy (TNT) approach relies primarily on mechanical disruption of intracellular vesicles and the resulting bioeffects appear to be more specific to target cancer cells expressing the PSMA receptor. The effect, while not lethal in vitro, resulted in significant tumor apoptosis in vivo in both a mouse and a rabbit model of PCa. While the mechanism of action of these effects is yet unclear, it is likely related to a locally-induced immune response, opening the door to future investigations in this area.

Molecular dynamics of the spontaneous generation mechanism of natural gas hydrates during methane nanobubble rupture

Natural gas hydrates have garnered significant attention as a potential new source of alternative energy, and understanding their formation mechanism is of paramount importance for efficient utilization and pipeline transportation. However, there is no consensus among academics on the formation mechanism of natural gas hydrates. In this paper, we propose a method for promoting the rapid formation of natural gas hydrates based on the rupture of methane nanobubbles, which creates local high temperature and pressure to facilitate the mixing of methane and water. The rapid decrease in system temperature and pressure during the process further enhances the formation of gas hydrates. Using molecular dynamics simulations, we theoretically verify the formation of natural gas hydrates. Our results indicate that the instantaneous rupture of methane nanobubbles induced by shock waves leads to a dramatic increase in the local molecular motion velocity around the bubbles. This results in extreme local high temperature and high pressure, leading to complete mixing of methane and water and rapid formation of gas hydrates during the cooling and pressure drop of the mixture. We confirm our findings by analyzing F3-order parameters, F4-order parameters, and water cage statistics.

Degradation Mechanism of Micro-Nanobubble Technology for Organic Pollutants in Aqueous Solutions

Micro-nanobubbles (MNBs) technology has emerged as an effective means of sewage treatment, while the molecular mechanism for its pollutant degradation is still unknown. In this paper, the reactive molecular dynamics simulation technique is used to study the degradation mechanism of pollutants caused by shock-induced nanobubble collapse. We first demonstrate that the propagating shock wave can induce nanobubble collapse, and the collapsing nanobubble has the ability to focus mechanical energy via the converging motion of liquid in the interior of the bubble, leading to the formation of a high-speed jet with a much higher energy density. We also unveil the mechanical nature of long-chain pollutant degradation and the mechanism of free radical generation. Due to the impacting jet, the high-gradient flow has the ability to stretch the long-chain molecule and cause mechanical scission of the molecule in a homolytic manner. Finally, our simulation results reveal that adding ozone molecules to the collapsing bubble would introduce an additional dehydrogenation mechanism.

Cavitation Erosion Characteristics for Different Metal Surface and Influencing Factors in Water Flowing System

The impact of cavitation erosion behavior on different metals in a water flowing system was investigated experimentally. A flowing system of water was built and a transparent observation window is designed to capture the cavitation flow. Erosion tests were carried out on red copper, brass, pure aluminum, and an aluminum alloy. The cavitation behaviors are presented by the weight loss and cavitation erosion rate, and related changes in the topography of the metal surface are also discussed. The variation in the cavitation erosion on metallic specimens with increasing time could be divided into three stages: rising stage, stable stage, and attenuation stage. The pure aluminum material had the lowest yield strength, and suffered the most severe cavitation erosion while brass had the highest yield strength and good mechanical properties, which suffered the least cavitation erosion. Furthermore, the roughness of the material surface was also one of the important factors affecting the cavitation erosion rate. The weight loss of milling specimens with higher surface roughness was slightly lower than that of grinding. The high roughness of the metallic surface increased the pressure loss along the flow path and the suppressed cavitation strength. This work provides an experimental reference for the anti-cavitation ability improvement in metal materials and promotes an understanding of the related mechanism.