Microbubble Size Research Articles

Therapeutic Potential of Manuka Honey Microbubble Dressing in Wound Management

AbstractThis study investigates the antibacterial effects of Manuka honey (MH) microbubbles on Staphylococcus aureus (S. aureus) in wound dressings. MH solutions are passed through a microbubble generator with a high‐density stainless steel mesh nozzle to produce MH‐containing microbubbles, which are then injected into dressings in contact with S. aureus. The experiment examines variables including microbubble particle sizes, dressing types, MH microbubbles consumption, and antibacterial action durations. Statistical analyses are performed on colony survival rates under various conditions. Results indicate that MH microbubble characteristics, MH microbubbles consumption, and action duration indirectly enhance S. aureus elimination, with overall disinfection reaching 86% and some conditions achieving 100% efficacy. The study proposes using MH microbubble dressings for S. aureus elimination, environmental cleaning of affected areas, and shortening dermatitis treatment courses. This approach offers a promising method for enhancing wound care and bacterial control in medical settings.

Characterization of Microbubble Cavitation in Theranostic Ultrasound-mediated Blood-Brain Barrier Opening and Gene Delivery.

The characterization of microbubble activity has proven critical in assessing the safety and efficacy of ultrasound-mediated blood-brain barrier (BBB) opening and drug and gene delivery. In this study, we build upon our previous work on theranostic ultrasound (ThUS)-mediated BBB opening (ThUS-BBBO) and conduct for the first time a comprehensive characterization of the role of microbubble cavitation in ThUS-BBBO, as well as its impact on gene delivery with adeno-associated viruses (AAV). A repurposed imaging phased array was used throughout the study to generate focused transmits and record microbubble activity through high-resolution power cavitation imaging (PCI). The cavitation of microbubbles under ThUS pulses was first characterized in flow phantom using pulse lengths ranging from 1.5 to 20 cycles and under varying microbubble flow rates using a separate single-element transducer a passive cavitation detector (PCD). A comprehensive in vivo study in mice was then conducted to characterize the in vivo microbubble activity under ThUS and correlate the resulting cavitation with AAV-mediated transgene delivery and expression. The transcranial microbubble activity was first detected in two mice using a PCD, to confirm the findings of the flow phantom study. Next, three mouse studies were conducted to evaluate the relationship between cavitation and AAV delivery; one with three different microbubble size distributions using polydisperse and size-isolated microbubbles, one with variable burst length and burst repetition frequency, and one with different AAV serotypes and injection doses. Electronic beam steering was used to induce bilateral BBB opening with 1.5 cycle on the left and 10 cycles on the right hemisphere. Cavitation dose was correlated with BBB opening volume, AAV transgene expression was evaluated with immunofluorescence staining and histological safety was assessed with T2* imaging and Hematoxylin and Eosin staining. Frequency domain analysis in the phantoms revealed a broadband-cavitation dominance at the shorter pulse lengths, while harmonic cavitation components are significantly increased for longer pulses. The PCD was better at detecting higher frequency harmonics, while the signal received by the theranostic array was more broadband dominated. Analysis of signals in the time domain showed that the longer pulses induce higher microbubble collapse compared to short pulses. In the transcranial in vivo experiments, the PCD was able to detect increased harmonic cavitation for 10-cycle pulses. The microbubble study showed that 3-5 μm microbubbles resulted in the largest cavitation doses, BBBO volumes and AAV transgene expression compared to the smaller microbubble sizes. The burst sequence study revealed that the sequences with shorter bursts and faster burst repetition frequencies induce larger BBBO volumes and AAV transduction due to faster microbubble replenishment in the focal volume. Increased erythrocyte extravasation was observed on the hemisphere sonicated with 10-cycle pulses. Transgene expression was also increased with injection dose, without notable side effects during the three-week survival period. Finally, AAV9 was shown to be the serotype with the highest transduction efficiency compared to AAV2 and AAV5 at the same injected dose. This is the first comprehensive study into the microbubble cavitation under theranostic ultrasound. The phantom and in vivo studies show that the mechanism of ThUS-BBBO is mainly transient cavitation dominant, as microbubble collapse increases with pulse length despite the increased harmonic frequency response. Increased cavitation dose resulted in larger BBBO volumes and transgene expression in vivo . While ThUS induced microhemorrhage for most of the studied conditions, it did not have an impact on the survival and behavior of the mice.

A novel numerical approach to elucidate experimental scatter in portal pressure measurement using ultrasound contrast agent.

The use of ultrasound contrast agents (UCAs) for estimating portal pressure has recently gained attention due to its clinical promise, yet variability in acoustic amplitude poses challenges. UCAs contain microbubbles (1-10 µm in diameter), and understanding their acoustic response is essential to address this variability. However, systematic exploration of factors influencing microbubble behavior remains limited in current literature. This paper introduces a novel finite element analysis-based framework for portal pressure estimation, bridging key gaps. Developed in two stages, the model first captures the subharmonic response of a single bubble to an acoustic excitation of 50 kPa at 4 MHz, highlighting the influence of bubble size on resonance frequency. In the second stage, single-bubble responses are extended to analyze how microbubble population, size, and spatial distribution affect portal pressure estimation. For the first time, this study elucidates the experimental scatter in pressure measurements through a comprehensive consideration of these variables, offering new directions for UCA-based clinical pressure estimation in applications such as portal and cardiac pressure assessment.

Experimental investigation on the effect of concentration on the resonance frequency of lipid coated ultrasonically excited microbubbles

This study presents an experimental investigation of the influence of MB concentration on the resonance frequency of lipid-coated microbubbles (MBs). Expanding on theoretical models and numerical simulations from previous research, this work experimentally investigates the effect of MB size on the rate of resonance frequency increase with concentration, a phenomenon observed across MBs with two different lipid compositions: propylene glycol (PG) and propylene glycol and glycerol (PGG). Employing a custom-designed ultrasound attenuation measurement setup, we measured the frequency-dependent attenuation of MBs, isolating MBs based on size to generate distinct monodisperse sub-populations for analysis. The resonance frequency of MBs was determined by identifying the attenuation peak in the broadband attenuation ultrasound attenuation measurements. Our experimental findings confirm that larger MBs (≈2.1μm) demonstrate a more significant shift in resonance frequency (≈ 5 MHz, ≈ 40%) as a function of MB concentration. In contrast, smaller MBs (≈1.3μm) show a minor shift in the resonant frequency (≈ 1.8MHz, ≈ 8%), underlining the importance of size in determining acoustic behavior compared to changes in the lipid shell properties. Additionally, we observed that resonance frequency increase with concentration reaching a saturation point at higher concentrations. This plateau occurs at higher concentrations for larger MBs (≈2.1μm), while smaller MBs (≈1.6μm and ≈1.3μm) reach this saturation point at lower concentrations. Furthermore, the study highlights the small effect of bubble-bubble interactions on the resonance frequency of MB populations, particularly at lower MB concentrations and for smaller MBs. This insight is important for applications utilizing MB clusters, such as contrast-enhanced ultrasound imaging and MB-mediated therapies. While both size and lipid shell composition influence resonance frequency, MB size has a more significant effect. In conclusion, our findings affirm the need to consider both MB size and concentration when utilizing MBs for clinical and industrial ultrasonic applications.

Uncertainty quantification for the drag reduction of microbubble-laden fluid flow in a horizontal channel

Over three decades, much research has proven the bubble drag reduction (BDR) technique. Recently, the improvement of computing performance has enabled the simulation of multi-phase flows. The present work simulated the microbubble-laden turbulent horizontal channel flow by Nek5000 code, which is based on the spectral element method. To resolve the microbubble dynamics, the 2-way coupling Euler–Lagrange approach was combined with Nek5000 code. Furthermore, for high accuracy, high-order Lagrange interpolation was adopted to track the microbubble's location and velocity in this code. All microbubbles were assumed as non-deformable, spherical, and immiscible. For the investigation of the drag reduction effect of microbubble size and the number of microbubbles, the uncertainty quantification (UQ) method was adopted with the non-intrusive polynomial chaos method. The Latin hypercube sampling method was used to obtain precision with lesser number of samples than the Monte Carlo method. The distribution of random variables was assumed to be Gaussian and generalized polynomial chaos expansion (gPC) was applied to build the surrogate model. The mean value (μ) of random variables was 110 µm, 6,345 each, while the standard deviation (σ) was ± 0.33 μ. As a result, the uncertainty propagation of velocity, second-order turbulence statistics, and drag reduction were achieved.

Aphron properties and application of surfactant drilling fluids in depleted reservoirs

Aphron drilling fluids (ADFs) are finding increasing application in science engineering fields because of their distinctive characteristic. As the interest in the application of aprons-based fluids continues to grow, there is a decisive need to advance a deeper understanding of the factors affecting their behavior and properties, especially for successful petroleum industries, such as drilling depleted reservoirs and production. This study delves into investigating the density, rheological behavior and properties, filtration properties, bubble size, and their distribution of Aphrons-drilling fluids utilizing two ionic surfactants. Sodium Dodecyl Benzene Sulfate (SDBS) as an anionic surfactant, Cetyl Trimethyl Ammonium Bromide (CTAB) as a cationic surfactant, described as environmentally friendly, in Iraqi depleted reservoirs drilling. With an emphasis on the concentrations balance between Aphron generator (SDBS) and Aphron stabilizer (CTAB), the study analyzes the behavior and characteristics of Aphron drilling fluid. The investigation demonstrates that adding SDBS and CTAB reduces system density by 28%, owing to microbubbles production which is utilized with near-balance drilling. Rheological testing reveals that shear-thinning behavior in all Aphron samples improved, and the presence of SDBS affects the fluid's internal friction, gel strength, and short-term gel structure. Filtering control characteristic study demonstrates that the presence of microbubbles significantly minimizes fluid loss by 33% with 0.20% SDBS during filtering. Bubble size and dispersion studies demonstrate that 0.20% SDBS concentration, along with 0.30% CTAB, gives the best microbubble size and distribution. These findings suggest that Aphron fluids will be a promising innovation in petroleum industries, during actual drilling operations in Iraqi depleted oilfields.

Ultrasound-triggered drug release and cytotoxicity of microbubbles with diverse drug attributes

Ultrasound (US)-triggered cavitation of drug-loaded microbubbles (MBs) represents a promising approach for targeted drug delivery, with substantial benefits attainable through precise control over drug release dosage and form. This study investigates Camptothecin-loaded MBs (CPT-MBs) and Doxorubicin-loaded MBs (DOX-MBs), focusing on how properties such as hydrophilicity, hydrophobicity, and charged functional groups affect their interaction with the lipid surfaces of MBs, thereby influencing the fundamental characteristics and acoustic properties of the drug-loaded MBs. In comparison to DOX-MBs, CPT-MBs showed larger MB size (2.2 ± 0.3 and 1.4 ± 0.1 μm, respectively), a 2-fold increase in drug loading, and an 18 % reduction in leakage after 2 h at 37℃. Under 1 MHz US with a 100 ms pulse repetition interval (PRI), 1000 cycles, 5-minute duration, and 550 kPa acoustic pressure, CPT-MBs undergo inertial cavitation, while DOX-MBs undergo stable cavitation. Drug particles released from these MBs under US-induced cavitation were analyzed using dynamic light scattering, NanoSight, cryo-electron microscopy, and density gradient ultracentrifugation. Results showed that CPT-MBs mainly release free CPT, while DOX-MBs release multilayered DOX-lipid aggregates. The cytotoxicity to C6 cells induced by US-triggered cavitation of these two types of MBs also differed. DOX-lipid aggregates delayed initial uptake, leading to less pronounced short-term (2 h) effects compared to the rapid release of free CPT from CPT-MBs. These findings underscore the need to optimize drug delivery strategies by fine-tuning MB composition and US parameters to control drug release kinetics and achieve the best tumoricidal outcomes.

Graphene-Loaded Aphron Microbubbles for Enhanced Drilling Fluid Performance and Carbon Capture and Storage.

Maintaining the stability of microbubbles is essential for enhancing the longevity of aphronic water-based drilling fluid usage in drilling depleted reservoirs and other under-pressured zones. Here, we introduce the integration of partially reduced graphene oxide (PrGO) nanosheets into the shell of aphron microbubbles (AMBS) to enhance the stability and size distribution, particularly for drilling fluid applications and carbon geological storage. The amphiphilic characteristic of PrGO nanosheets, due to meticulous control of the reduction process of graphene oxide, facilitates their spontaneous adsorption at interfaces, thereby reducing the interfacial energy as a two-dimensional surfactant. The loading of PrGO nanosheets in the polymeric shell of AMBs enhances mechanical strength, stability, and resistance to gas diffusion, prolonging the half-life of the microbubbles to over 120%. According to the results, a more uniform size distribution and reduction of microbubble size up to 60% have been achieved at a concentration of 0.30 wt % PrGO. Rheological studies using various models indicate the optimal PrGO concentration for improved stability in aphronic fluids. Filtration tests indicate the loaded PrGO can reduce filtration loss by up to 45% at 0.50 wt % by forming a cohesive and compressible cake, improving filtration control. Changes in the Fourier-transform infrared spectra and contact angle measurements suggest increased surface hydrophobicity with higher graphene concentrations in aphronic fluid cakes. Moreover, the study elucidates that the stability of microbubbles is influenced by the type of core gas, with N2 gas yielding the highest stability and CO2 the lowest. Ultimately, these results highlight the beneficial effect of incorporation of PrGO nanosheets in aphron microbubbles to boost the drilling fluid performance and efficiency, which will pave the way toward ultralightweight fluids that can even be used as carrier and injection fluids in carbon capture and leak-free geological storage technologies.

Effect of Microbubble Size, Composition, and Multiple Sonication Points on Sterile Inflammatory Response in Focused Ultrasound-Mediated Blood-Brain Barrier Opening.

Blood-brain barrier opening (BBBO) using focused ultrasound (FUS) and microbubbles (MBs) has emerged as a promising technique for delivering therapeutics to the brain. However, the influence of various FUS and MB parameters on BBBO and subsequent sterile inflammatory response (SIR) remains unclear. In this study, we investigated the effects of MB size and composition, as well as the number of FUS sonication points, on BBBO and SIR in an immunocompetent mouse model. Using MRI-guided MB + FUS, we targeted the striatum and assessed extravasation of an MRI contrast agent to assess BBBO and RNaseq to assess SIR. Our results revealed distinct effects of these parameters on BBBO and SIR. Specifically, at a matched microbubble volume dose (MVD), MB size did not affect the extent of BBBO, but smaller (1 μm diameter) MBs exhibited a lower classification of SIR than larger (3 or 5 μm diameter) MBs. Lipid-shelled microbubbles exhibited greater BBBO and a more pronounced SIR compared to albumin-shelled microbubbles, likely owing to the latter's poor in vivo stability. As expected, increasing the number of sonication points resulted in greater BBBO and SIR. Furthermore, correlation analysis revealed strong associations between passive cavitation detection measurements of harmonic and inertial MB echoes, BBBO, and the expression of SIR gene sets. Our findings highlight the critical role of MB and FUS parameters in modulating BBBO and subsequent SIR in the brain. These insights inform the development of targeted drug delivery strategies and the mitigation of adverse inflammatory reactions in neurological disorders.

Sonopermeation With Size-sorted Microbubbles Synergistically Increases Survival and Enhances Tumor Apoptosis With L-DOX by Increasing Vascular Permeability and Perfusion in Neuroblastoma Xenografts

ObjectiveDespite aggressive therapy, approximately 50% of patients with neuroblastoma (NB) fail to respond, and survivors endure lifelong toxicities. Sonopermeation increases drug uptake via cell bilayer disruption through focused ultrasound and microbubbles (MBs)—gas-filled, sound sensitive lipid spheres. MB response to a given ultrasound pulse (cavitation) varies according to MB size. We asked whether size-sorted MBs (SSMB) 4 to 5 µm in diameter will more consistently and predictably enhance doxorubicin uptake, compared with polydisperse MBs (PMB, 0.5–10 µm in diameter), thereby increasing drug delivery to NB xenografts. MethodsHuman NB cells were implanted into the left kidney of nude mice and grown for 5 to 6 wk. Mice received sonopermeation alongside either PMB or SSMB at low (0.6 MPa) or high (2 MPa) negative pressures. Some mice also received different chemotherapy agents (doxorubicin, etoposide or cyclophosphamide). Circulating tumor cells were assessed by flow cytometry 1 h after treatment. Survival was assessed for up to 21 d, a subset of mice was euthanized 24 h after treatment for histological assessment of apoptosis, vascular lumen size and tight junctions. ResultsTumors treated with SSMB and high pressure showed synergy with liposomal doxorubicin (L-DOX) owing to increased vascular lumen and disruption of tight junctions, resulting in drug uptake, apoptosis, lack of tumor growth and increased survival. We found no difference in the numbers of circulating tumor cells. ConclusionSonopermeation with SSMB at 2 MPa synergizes with L-DOX delivery, increasing apoptosis, perfusion and vascular permeability, suggesting that SSMB sonopermeation at high pressure is promising for NB-targeted treatment, especially in combination with L-DOX.

Control of photothermal liquid jets through microbubble Regulation: Fundamental mechanisms and Developing Strategies

Plasmon-induced photoacoustic streaming, considered as a potential application for micro-pumps in microfluidics, currently encounters ongoing debates concerning its fundamental mechanisms. In this study, we investigate the crucial role played by microbubbles in generation of jets in an ethanol aqueous solution. The power density threshold for bubble generation and its dependency on jet initiation are confirmed and the microbubble behavior is well regulated by manipulating the laser and liquid properties. Through simulations coupling fluidic and thermal fields, the significant role of Marangoni effect is validated in jet formation. Specifically, the temperature gradient of microbubbles is determined to be a pivotal factor in the generation of collimated jets. Additionally, factors influencing jetting, such as microbubble size and temperature gradients are studied, and noticeably, a stabilized jet lasting over 4 h is achieved based upon.

Application of microbubble air flotation to harvest Microcystis sp. from agriculture wastewater: The regulation and mechanisms.

The harvesting of microalgae is the main bottleneck of its large-scale biomass production, and seeking an efficient, green, and low-cost microalgae harvesting technology is one of the urgent problems to be solved. Microbubble air flotation has been proven to be an effective measure, but the mechanisms of microbubbles-algal cell attachment are still unclear. In this study, microbubble air flotation was used as a harvesting method for Microcystis cultured in agricultural wastewater. The process mechanism of microbubble air flotation harvesting microalgae in wastewater was fully revealed from three aspects (the design of bubble formation, the adhesion law, and the recovery rate of microalgae under different working conditions). The results show that the length of the release pipe is the main factor affecting the proportion of microbubbles with a particle size of less than 50 μm. In the process of adhesion, when the particle size of microbubbles is 0.6-1.7 times the size of Microcystis, the adhesion efficiency of microbubbles to Microcystis is the highest. Under the conditions of pressure 0.45 MPa, gas-liquid ratio 5%, and release pipe length 100 cm, the harvesting performance of Microcystis was the best. Microbubble air flotation has better harvesting performance (63.5%, collection rate) of Microcystis with higher density. By understanding the mechanism of microbubble flotation, the technical parameters of microbubble flotation for harvesting energy microalgae are optimized to provide support for the development of efficient and low-cost devices and equipment for collecting microalgae.

Experimental measurement of the size distribution of microbubbles prepared by reciprocating syringe technique

Microbubbles have captured the attention of scholars due to their exceptional physical and chemical properties that exhibit practical applications. Transcranial Doppler ultrasound is a diagnostic tool used in clinical medicine to identify patent foramen ovale (PFO) heart disease caused by incomplete fusion of primary and secondary septum after birth, using microbubbles. The volume of gas and size of the bubbles determine the consequences of air entering the bloodstream. Therefore, it is imperative to investigate stable and efficient microbubble generation technology. The team designed and developed a new type of bubble generator and performed basic research on the flow and mixing rules in the gas-liquid two-phase system in the syringe. The shadow imaging method was used to explore the influence of the equipment operation parameters on the experimental system's microbubble flow process. After analyzing multiple sets of experimental data, it was found that the diameter of bubbles decreases as the frequency increases. After ten times of high-frequency reciprocating movement of the equipment, the microbubble size distribution is mainly between 10–100 μm, the mean diameter is between 23–26 μm, and the relative standard deviation is less than 4.5 %. Compared to manual methods, the device exhibits good accuracy and repeatability.

Numerical simulation study on opening blood–brain barrier by ultrasonic cavitation

Experimental studies have shown that ultrasonic cavitation can reversibly open the blood–brain barrier (BBB) to assist drug delivery. Nevertheless, the majority of the present study focused on experimental aspects of BBB opening. In this study, we developed a three-bubble-liquid-solid model to investigate the dynamic behavior of multiple bubbles within the blood vessels, and elucidate the physical mechanism of drug molecules through endothelial cells under ultrasonic cavitation excitation. The results showed that the large bubbles have a significant inhibitory effect on the movement of small bubbles, and the vibration morphology of intravascular microbubbles was affected by the acoustic parameters, microbubble size, and the distance between the microbubbles. The ultrasonic cavitation can significantly enhance the unidirectional flux of drug molecules, and the unidirectional flux growth rate of the wall can reach more than 5 %. Microjets and shock waves emitted from microbubbles generate different stress distribution patterns on the vascular wall, which in turn affects the pore size of the vessel wall and the permeability of drug molecules. The vibration morphology of microbubbles is related to the concentration, arrangement and scale of microbubbles, and the drug permeation impact can be enhanced by optimizing bubble size and acoustic parameters. The results offer an extensive depiction of the factors influencing the blood–brain barrier opening through ultrasonic cavitation, and the model may provide a potential technique to actively regulate the penetration capacity of drugs through endothelial layer of the neurovascular system by regulating BBB opening.

The role of microbubble dose in combined microflotation of fine particles

Flotation of small particles is one of the global challenges facing the mineral raw materials processing industry. Large amounts of non-ferrous and rare metals are lost in the flotation tailings in the form of mineral particles below 15 µm in size as a result of the low effectiveness of their capture by coarse bubbles generated in conventional flotation machines. The method of combined microflotation, developed in recent years, uses conventional coarse bubbles (CB) and microbubbles (MB) produced in the stand-alone generator of air-in-water microdispersion, which serves as the flotation carriers. Depending on the MB dose, the effect of their application may be positive or negative. The theoretical analysis of various mechanisms of particle transfer onto the surface of coarse bubbles and further into the froth layer allowed to obtain the formula for the optimal MB dose f=d<sub>d</sub>/2d<sub>p</sub>r<sub>p</sub>, where d<sub>d</sub> is MB size; d<sub>p</sub> and r<sub>p</sub> respectively are the size and the density of particles. Experiments performed on the copper ore flotation tailings at the Atalaya Mining (Spain) and Chaarat Kapan (Armenia) concentrators showed that, besides the optimal MB dose in the range of 1-3 ml/g, there is another optimal MB dose in the range of 10-20 ml/g, where the copper recovery increases by several percent compared to the reference test (f = 0). The deep minimum in copper recovery is observed in the area between the optimal MB doses, which is by several percent lower than the value in the reference test.

Bubble Characteristics Required for the Complete Removal of Alumina Inclusions from Steel Melts

Gas bubbling can be an effective means to float out alumina inclusions from liquid steel in a ladle. However, large spherical cap bubbles are formed when using porous plugs, as the liquid steel is nonwetting to the porous refractory. These bubbles rise rapidly through the liquid steel, forming a fast‐moving bubble plume, restricting contact times. Sized microbubbles, by contrast, have now been generated in liquid metals by shearing methods, involving linear crossflows to an entering flow of gas, or alternatively by rotational shearing. Combined with these convective shearing forces, local kinetic energy of turbulence can also play an important part in determining final microbubble size distributions. As microbubbles have much smaller rise velocities and present a far greater inclusion capture surface area than those of a single large bubble of the same gross volume, this will allow us to remove sub‐50 μm inclusions from liquid steel. It is expected that this goal will require a redesign of current ladle shrouds.

High-Speed Optical Characterization of Protein-and-Nanoparticle–Stabilized Microbubbles for Ultrasound-Triggered Drug Release

BackgroundUltrasound-triggered bubble-mediated local drug delivery has shown potential to increase therapeutic efficacy and reduce systemic side effects, by loading drugs into the microbubble shell and triggering delivery of the payload on demand using ultrasound. Understanding the behavior of the microbubbles in response to ultrasound is crucial for efficient and controlled release. MethodsIn this work, we characterize the response of microbubbles with a coating consisting of poly(2-ethyl-butyl cyanoacrylate) (PEBCA) nanoparticles and denatured casein. High-speed recordings are taken of single microbubbles, both in bright-field and fluorescence. ResultsThe nanoparticle-loaded microbubbles show resonance behavior, but with a large variation in response, demonstrating a substantial inter-bubble variation in mechanical shell properties. The probability of shell rupture and the probability of nanoparticle release were found to strongly depend on the microbubble size, and the most effective size was inversely proportional to the driving frequency. Both the rupture and release probabilities increased with increasing driving pressure amplitude. Rupture of the microbubble shell occurred after fewer cycles of ultrasound as the driving pressure amplitude or driving frequency was increased. ConclusionsThe results highlight the importance of careful selection of the driving frequency, driving pressure amplitude, and duration of the ultrasound to achieve the most efficient ultrasound-triggered shell rupture and nanoparticle release of protein-and-nanoparticle-stabilized microbubbles.

Eulerian–Lagrangian multiscale numerical analysis of multimodal partial shedding dynamics

The objective of this paper is to investigate the multimodal partial shedding dynamics from a multiscale perspective of cloud cavitating flows under two distinct cavity shedding mechanisms, namely the re-entrant jet mechanism and the shock wave propagation mechanism. A two-way Eulerian–Lagrangian coupling algorithm is applied to capture the multiscale vapor topologies from microbubble to large-scale cavities. The large-scale cavity evolution is solved through large eddy simulations (LES) with the volume of fraction (VOF) method in Eulerian frame. The sub-grid microbubbles are tracked in Lagrangian frame based on the discrete bubble model (DBM) method. The predictions agree well with experimental observation of the periodical cavity evolution and microbubble dynamics under both the re-entrant jet mechanism and shock wave mechanism around a NACA66 hydrofoil. The numerical simulation provides detailed analysis of the cavitating turbulent flow on the microbubble behavior with emphasis on the spatial-temporal distribution characteristics of microbubbles. The results show that the number and mean size of microbubbles in the cavitation region increase gradually with the growth of attached sheet cavity, development of re-entrant jet and collapse of largescale cavity for both cavitation patterns. Meanwhile, microbubbles are mainly distributed on the largescale interfaces where have high value of vorticity and turbulent kinetic energy under the effect of re-entrant jet and vortex structures. And the probability density functions (PDFs) of microbubble exhibit gamma distributions with a dominant peak at approximately 50 μm for both shedding mechanisms. However, the shock wave formation and propagation process only occurs in the final stage of cavitating flow under shock wave mechanism causing the condensation of vapor and the decrease of the number and mean size of microbubbles. Moreover, the microbubbles are uniformly distributed along the streamwise and vertical directions behind shock wave front.

Effect of microbubbles on immersion freezing of grape tomato

Microbubbles (MBs) were incorporated into calcium chloride solution as a novel freezing medium for immersion freezing of grape tomato. The effects of MB size (39, 43, 48 μm mean diameter), entrapped gas (air, N2, CO2) and freezing temperature (−10, −15, −20 °C) on the freezing behavior and quality attributes of tomato were investigated. MBs increased the nucleation temperature from −7.4 to −3.5 °C and reduced the onset time of nucleation from 5.8 to 2.9 min at freezing temperature of −20 °C, which facilitated the formation of small ice crystals within tomato. MB-assisted freezing reduced the drip loss by 13.7–17.0% and improved the firmness of tomato, particularly when MB size and freezing temperature decreased. Freezing tomato with air-MBs did not compromise its nutritional quality, using N2- and CO2-MBs even increased its lycopene content, by 31% and 23%, respectively. The results proved the preservation effect of MBs on fruit during immersion freezing. This study can benefit the fruit and vegetable industry by providing an efficient freezing technology for producing frozen products with high sensory and nutritional quality.

Understanding the effects of microbubble concentration on localization accuracy in super-resolution ultrasound imaging.

Super-resolution ultrasound (SRUS) through localising and tracking of microbubbles (MBs) can achieve sub-wavelength resolution for imaging microvascular structure and flow dynamics in deep tissuein vivo. The technique assumes that signals from individual MBs can be isolated and localised accurately, but this assumption starts to break down when the MB concentration increases and the signals from neighbouring MBs start to interfere. The aim of this study is to gain understanding of the effect of MB-MB distance on ultrasound images and their localisation. Ultrasound images of two MBs approaching each other were synthesised by simulating both ultrasound field propagation and nonlinear MB dynamics. Besides the distance between MBs, a range of other influencing factors including MB size, ultrasound frequency, transmit pulse sequence, pulse amplitude and localisation methods were studied. The results show that as two MBs approach each other, the interference fringes can lead to significant and oscillating localisation errors, which are affected by both the MB and imaging parameters. When modelling a clinical linear array probe operating at 6 MHz, localisation errors between 20 and 30μm (∼1/10 wavelength) can be generated when MBs are ∼500μm (2 wavelengths or ∼1.7 times the point spread function (PSF)) away from each other. When modelling a cardiac probe operating at 1.5 MHz, the localisation errors were as high as 200μm (∼1/5 wavelength) even when the MBs were more than 10 wavelengths apart (2.9 times the PSF). For both frequencies, at smaller separation distances, the two MBs were misinterpreted as one MB located in between the two true positions. Cross-correlation or Gaussian fitting methods were found to generate slightly smaller localisation errors than centroiding. In conclusion, caution should be taken when generating and interpreting SRUS images obtained using high agent concentration with MBs separated by less than 1.7 to 3 times the PSF, as significant localisation errors can be generated due to interference between neighbouring MBs.