Miniaturized therapeutic systems for ultrasound-modulated drug delivery to the central and peripheral nervous system

Ultrasound is a promising technology to address challenges in drug delivery, including limited drug penetration across physiological barriers and ineffective targeting. Here we provide an overview of the significant advances made in recent years in overcoming technical and pharmacological barriers using ultrasound-assisted drug delivery to the central and peripheral nervous system. We commence by exploring the fundamental principles of ultrasound physics and its interaction with tissue. The mechanisms of ultrasonic-enhanced drug delivery are examined, as well as the relevant tissue barriers. We highlight drug transport through such tissue barriers utilizing insonation alone, in combination with ultrasound contrast agents (e.g., microbubbles), and through innovative particulate drug delivery systems. Furthermore, we review advances in systems and devices for providing therapeutic ultrasound, as their practicality and accessibility are crucial for clinical application.

Enhanced cavitation dose and reactive oxygen species production in microbubble-mediated sonodynamic therapy for inhibition of Escherichia coli and biofilm

Sonodynamic therapy (SDT) is an emerging antibacterial therapy. This work selected hematoporphyrin monomethyl ether (HMME) as the sonosensitizer, and studied the enhanced inhibition effect of Escherichia coli and biofilm by microbubble-mediated cavitation in SDT. Firstly, the influence of microbubble-mediated cavitation effect on different concentrations of HMME (10 µg/ml, 30 µg/ml, 50 µg/ml) was studied. Using 1,3-diphenylisobenzofuran (DPBF) as an indicator, the effect of microbubble-mediated cavitation on the production of reactive oxygen species (ROS) was studied by absorption spectroscopy. Secondly, using agar medium, laser confocal microscopy and scanning electron microscopy, the effect of microbubble-mediated cavitation on the activity and morphology of bacteria was studied. Finally, the inhibitory effect of cavitation combined with SDT on biofilm was evaluated by laser confocal microscopy. The research results indicate that: (1) Microbubble-mediated ultrasound cavitation can significantly increase cavitation intensity and production of ROS. (2) Microbubble-mediated acoustic cavitation can alter the morphological structure of bacteria. (3) It can significantly enhance the inhibition of SDT on the activity of Escherichia coli and its biofilm. Compared with the control group, the addition of microbubbles resulted in an increase in the number of dead bacteria by 61.7 %, 71.6 %, and 76.2 %, respectively. The fluorescence intensity of the biofilm decreased by 27.1 %, 80.3 %, and 98.2 %, respectively. On the basis of adding microbubbles to ensure antibacterial and biofilm inhibition effects, this work studied the influence of cavitation effect in SDT on bacterial structure, providing a foundation for further revealing the intrinsic mechanism of SDT.

Silt erosion and cavitation impact on hydraulic turbines performance: An in-depth analysis and preventative strategies

The primary issues in the Himalayan Rivers are sediment and cavitation degradation of the hydroelectric power turbine components. During the monsoon season, heavy material is transported by streams in hilly areas like the Himalayas through regular rainfalls, glacial and sub-glacial hydrological activity, and other factors. The severe erosion of hydraulic turbines caused by silt abrasion in these areas requires hydropower facilities to be regularly shut down for maintenance, affecting the plant's overall efficiency. This article provides an in-depth examination of the challenges that can lead to cavitation, silt erosion, and a decrease in the efficiency of various hydroelectric turbines, and it demands attention on the design, manufacture, operation, and maintenance of the turbines. This study's main objective is to critically evaluate earlier theoretical, experimental, and numerical evaluation-based studies (on cavitation and silt erosion) that are provided and addressed throughout the study. As a part of this study, various strategies for mitigating the effects of these problems and elongating the time that turbine may be utilized before they must be replaced have been provided.

Cochlear aqueduct revisited: A histological study using human fetuses

BACKGROUND AND AIM

The cochlear aqueduct (CA) connects between the perilymphatic space of the cochlea and the subarachnoid space in the posterior cranial fossa. The study aimed to examine 1) whether cavitation of the CA occurs on the subarachnoid side or the cochlear side and 2) the growth and/or degeneration of the CA and its concomitant vein.

METHODS

We examined paraffin-embedded histological sections from human fetuses: 15 midterm fetuses (crown-rump length or CRL, 39-115 mm) and 12 near-term fetuses (CRL, 225-328 mm).

RESULTS

A linear mesenchymal condensation, i.e., a likely candidate of the CA anlage, was observed without the accompanying vein at 9-10 weeks. The vein appeared until 15 weeks, but it was sometimes distant from the CA. At 10-12 weeks, the subarachnoid space (or the epidural space) near the glossopharyngeal nerve rapidly protruded into the CA anlage and reached the scala tympani, in which cavitation was gradually on-going but without epithelial lining. However, CA cavitation did not to occur in the anlage. At the opening to the scala, the epithelial-like lining of the CA lost its meningeal structure. At near-term, the CA was often narrowed and obliterated.

CONCLUSION

The CA develops from meningeal tissues when the cavitation of the scala begins. The latter cavitation seemed to reduce tissue stiffness leading, to meningeal protrusion. The so-called anlage of CA might be a phylogenetic remnant of the glossopharyngeal nerve branch. A course of cochlear veins appears to be determined by a rule different from the CA development.

An 8 mm endoscopic histotripsy array with integrated high-resolution ultrasound imaging

An 8 mm diameter, image-guided, annular array histotripsy transducer was fabricated and characterized. The array was laser etched on a 5 MHz, 1-3 dice and fill, PZT-5H/epoxy composite with a 45 % volume fraction. Flexible PCBs were used to electrically connect to the array elements using wirebonds. The array was backed with a low acoustic impedance epoxy mixture. A 3.6 by 3.8 mm, 64-element, 30 MHz phased array imaging probe was positioned in the center hole, to co-align the imaging plane with the bubble cloud produced by the therapy array. A custom 16-channel high voltage pulse generator was used to test the annular array for focal lengths ranging from 3- to 8-mm. An aluminum lens-focussed transducer with a 7 mm focal length was fabricated using the same piezocomposite and backing material and tested along with the histotripsy array. Simulated results from COMSOL FEM models were compared to measured results for low voltage characterization of the array and lens-focussed transducer. The measured transmit sensitivity of the array ranged from 0.113 to 0.167 MPa/V, while the lens-focussed transducer was 0.192 MPa/V. Simulated values were 0.160 to 0.174 MPa/V and 0.169 MPa/V, respectively. The measured acoustic fields showed a significantly increased depth-of-field compared the lens-focussed transducer, while the beamwidths of the array focus were comparable to the lens. The measured cavitation voltage in water was between 254 V and 498 V depending on the focal length, and 336 V for the lens-focussed transducer. The array had a lower cavitation voltage than the lens-focussed transducer for a comparable operating depth. The histotripsy array was tested in a tissue phantom and an in vivo rat brain. It was used to produce an elongated lesion in the brain by electronically steering the focal length from 3- to 8-mm axially. Real time ultrasound imaging with a Doppler overlay was used to target the tissue and monitor ablation progress, and histology confirmed the targeted tissue was fully homogenized.

Advancements in transdermal drug delivery: A comprehensive review of physical penetration enhancement techniques

Transdermal drug administration has grown in popularity in the pharmaceutical research community due to its potential to improve drug bioavailability, compliance among patients, and therapeutic effectiveness. To overcome the substantial barrier posed by the stratum corneum (SC) and promote drug absorption within the skin, various physical penetration augmentation approaches have been devised. This review article delves into popular physical penetration augmentation techniques, which include sonophoresis, iontophoresis, magnetophoresis, thermophoresis, needle-free injection, and microneedles (MNs) Sonophoresis is a technique that uses low-frequency ultrasonic waves to break the skin's barrier characteristics, therefore improving drug transport and distribution. In contrast, iontophoresis uses an applied electric current to push charged molecules of drugs inside the skin, effectively enhancing medication absorption. Magnetophoresis uses magnetic fields to drive drug carriers into the dermis, a technology that has shown promise in aiding targeted medication delivery. Thermophoresis is the regulated heating of the skin in order to improve drug absorption, particularly with thermally sensitive drug carriers. Needle-free injection technologies, such as jet injectors (JIs) and microprojection arrays, offer another option by producing temporary small pore sizes in the skin, facilitating painless and effective drug delivery. MNs are a painless, minimally invasive method, easy to self-administration, as well as high drug bioavailability. This study focuses on the underlying processes, current breakthroughs, and limitations connected with all of these approaches, with an emphasis on their applicability in diverse therapeutic areas. Finally, a thorough knowledge of these physical enhancement approaches and their incorporation into pharmaceutical research has the potential to revolutionize drug delivery, providing more efficient and secure treatment choices for a wide range of health-related diseases.

On efficient modelling of radical production in cavitation assisted reactors

Process intensification by cavitation is gaining widespread attention due to the benefits that the intense bubble collapse conditions can provide, yet, several knowledge gaps exist in the modelling of such systems. This work studies the numerical prediction of single bubble dynamics and the various approaches that can be employed to estimate the changes in the chemical composition of cavitating bubbles. Specific emphasis is placed on the prediction of the radical production rates during bubble collapse and the computational performance, with the aim of coupling the single bubble dynamics to flow models for reactor hydrodynamics. The results reveal that the choice of chemical reaction approach has virtually no effect on the bubble dynamics, whereas the predicted radical production rates can differ substantially. It is found that evaluating the radical production only on temperature peaks, an approach commonly followed in literature, may result in the most erroneous estimations (on average 12.8 times larger than those of the full kinetic model), while a simplified kinetic model yields more accurate predictions (2.3 times larger) at the expense of increased computational times. Continuous evaluation of the bubble content by assuming equilibrium when the bubble temperature is above a certain threshold (≈1500K) is shown to be capable of predicting total radical production values close to those estimated by solving the kinetics of a detailed reaction model (19.8% difference), as well as requiring only 22.2% more computational costs compared to simulations without chemical reaction modelling. Such an equilibrium approach is therefore recommended for future studies aiming to couple flow simulations with single bubble dynamics to accurately predict radical production rates in cavitation devices, involving numerous bubbles following different flow trajectories. Furthermore, an algebraic expression that successfully approximates the full kinetic simulation results is proposed as a function of the initial nucleus size and the time integral of the liquid pressure when it is under vapor pressure. Such a model can be applied in modelling efforts that do not require local instantaneous radical concentrations, and paves the way for efficient closure modelling of radical production in CFD simulations of hydrodynamic reactors.

Focused ultrasound-assisted delivery of immunomodulating agents in brain cancer

Focused ultrasound (FUS) combined with intravascularly circulating microbubbles can transiently increase the permeability of the blood-brain barrier (BBB) to enable targeted therapeutic delivery to the brain, the clinical testing of which is currently underway in both adult and pediatric patients. Aside from traditional cancer drugs, this technique is being extended to promote the delivery of immunomodulating therapeutics to the brain, including antibodies, immune cells, and cytokines. In this manner, FUS approaches are being explored as a tool to improve and amplify the effectiveness of immunotherapy for both primary and metastatic brain cancer, a particularly challenging solid tumor to treat. Here, we present an overview of the latest groundbreaking research in FUS-assisted delivery of immunomodulating agents to the brain in pre-clinical models of brain cancer, and place it within the context of the current immunotherapy approaches. We follow this up with a discussion on new developments and emerging strategies for this rapidly evolving approach.

Efficient ultrasound-mediated drug delivery to orthotopic liver tumors - Direct comparison of doxorubicin-loaded nanobubbles and microbubbles

Liver metastasis is a major obstacle in treating aggressive cancers, and current therapeutic options often prove insufficient. To overcome these challenges, there has been growing interest in ultrasound-mediated drug delivery using lipid-shelled microbubbles (MBs) and nanobubbles (NBs) as promising strategies for enhancing drug delivery to tumors. Our previous work demonstrated the potential of Doxorubicin-loaded C3F8 NBs (hDox-NB, 280 ± 123 nm) in improving cancer treatment in vitro using low-frequency unfocused therapeutic ultrasound (TUS). In this study, we investigated the pharmacokinetics and biodistribution of sonicated hDox-NBs in orthotopic rat liver tumors. We compared their delivery and therapeutic efficiency with size-isolated MBs (hDox-MB, 1104 ± 373 nm) made from identical shell material and core gas. Results showed a similar accumulation of hDox in tumors treated with hDox-MBs and unfocused therapeutic ultrasound (hDox-MB + TUS) and hDox-NB + TUS. However, significantly increased apoptotic cell death in the tumor and fewer off-target apoptotic cells in the normal liver were found upon the treatment with hDox-NB + TUS. The tumor-to-liver apoptotic ratio was elevated 9.4-fold following treatment with hDox-NB + TUS compared to hDox-MB + TUS, suggesting that the therapeutic efficacy and specificity are significantly increased when using hDox-NB + TUS. These findings highlight the potential of this approach as a viable treatment modality for liver tumors. By elucidating the behavior of drug-loaded bubbles in vivo, we aim to contribute to developing more effective liver cancer treatments that could ultimately improve patient outcomes and decrease off-target side effects.

Biofilm removal from Difficult-to-Reach places via secondary cavitation within a constrained geometry mimicking a Periodontal/Peri-Implant pocket

Biofilm removal from the apical region of the periodontal or peri-implant pocket, which is very difficult to achieve with mechanical instruments, is a major unresolved issue in dentistry. Here, we propose the use of photoacoustically induced streaming and secondary cavitation to achieve superior cleaning efficacy in the apical region of the periodontal and peri-implant pocket. We have used a prefabricated narrow wedge system that mimics the consistency of periodontal and peri-implant pockets of both healthy and severely inflamed tissue. We studied the effect of single-pulse modality Er:YAG on Pseudomonas aeruginosa biofilm removal. We used different laser energies, fiber-tip positions, and laser treatment durations. The cleaning process was monitored in real-time with a high-speed camera after each individual laser pulse application. The obtained results suggest that biofilm cleaning efficacy in a difficult-to-reach place in healthy model tissue is directly related to the onset of secondary cavitation bubble formation, which correlates with a significant improvement of biofilm removal from the apical region of the periodontal or peri-implant pocket. In comparison to the healthy tissue model, the laser energy in inflamed tissue model had to be increased to obtain comparable biofilm cleaning efficacy. The advantage of photoacoustic cavitation compared to other methods is that laser-induced cavitation can trigger secondary cavitation at large distances from the point of laser application, which in principle allows biofilm removal at distant locations not reachable with a laser fiber tip or other mechanical instruments.

Wave propagation

The dissolution of metals, influenced by mechanical and chemical factors, plays a crucial role in various applications. Ultrasonic irradiation has been explored for its ability to enhance dissolution rates and modify surface characteristics. In this study, we investigate the dissolution of magnesium (Mg) and magnesium alloys under high-intensity focused ultrasound (HIFU) conditions with frequency sweeping (wobbling). Our findings reveal distinct effects of cavitation and acoustic streaming on the dissolution process. For pure magnesium, ultrasonic treatment significantly increases dissolution rates compared to silent conditions. Negative frequency sweeps result in the highest dissolution rates, linked to increased cavitation activity, while positive sweeps reduce dissolution rates but maintain acoustic streaming effects. The removal of surface oxides is accelerated in all sonication conditions. Macro- and micro-roughness patterns on the surface correspond to the wobbling frequency range, with wavelengths matching the average ultrasonic frequency. However, dissolution is not uniform across the sample, and preferential attack occurs at the focal point during negative frequency sweeps. In contrast, magnesium alloys exhibit lower dissolution rates than pure Mg. The alloy's mechanical properties make it less susceptible to cavitation erosion but more sensitive to acoustic streaming-induced dissolution. Grain boundaries are preferentially attacked, revealing differences between ductile pure Mg and the harder, more cavitation-resistant, alloy. This study highlights the complex interplay between cavitation and acoustic streaming in the dissolution of magnesium and its alloys under HIFU conditions, shedding light on the limits and potential applications of this technique, particularly in microstructure analysis.

Numerical investigation of the effect of bubble properties on the linear resonance frequency shift due to inter-bubble interactions in ultrasonically excited lipid coated microbubbles

Ultrasonically excited microbubbles (MBs) have numerous applications in various fields, such as drug delivery, and imaging. Ultrasonically excited MBs are known to be nonlinear oscillators that generate secondary acoustic emissions in the media when excited by a primary ultrasound wave. The propagation of acoustic waves in the liquid is limited to the speed of sound, resulting in each MB receiving the primary and secondary waves at different times depending on their distance from the ultrasound source and the distance between MBs. These delays are referred to as primary and secondary delays, respectively. A previous study demonstrated that the inclusion of secondary delays in a model describing the interactions between MBs exposed to ultrasound results in an increase in the linear resonance frequency of MBs as they approach each other. This work investigates the impact of various MB properties on the change in linear resonance frequency resulting from changes in inter-bubble distances. The effects of shell properties, including the initial surface tension, surface dilatational viscosity of the shell monolayer, elastic compression modulus of the shell, and the initial radius of the MBs, are examined. MB size is a significant factor influencing the rate of linear resonance frequency increase with increasing concentration. Moreover, it is found that the shell properties of MBs play a negligible role in the rate of change in linear resonance frequency of MBs as the inter-bubble distances change.The findings of this study have implications for various applications of MBs in the biomedical field. By understanding the impact of inter-bubble distances and shell properties on the linear resonance frequency of MBs, the utilization of MBs in applications reliant on their resonant behavior can be optimized.

Towards portable MRI in the plant sciences

Plant physiology and structure are constantly changing according to internal and external factors. The study of plant water dynamics can give information on these changes, as they are linked to numerous plant functions. Currently, most of the methods used to study plant water dynamics are either invasive, destructive, or not easily accessible. Portable magnetic resonance imaging (MRI) is a field undergoing rapid expansion and which presents substantial advantages in the plant sciences. MRI permits the non-invasive study of plant water content, flow, structure, stress response, and other physiological processes, as a multitude of information can be obtained using the method, and portable devices make it possible to take these measurements in situ, in a plant's natural environment. In this work, we review the use of such devices applied to plants in climate chambers, greenhouses or in their natural environments. We also compare the use of portable MRI to other methods to obtain the same information and outline its advantages and disadvantages.

LES investigation of the wavy leading edge effect on cavitation noise

This paper investigates the noise reduction performance of biomimetic hydrofoils with wavy leading edge and the corresponding mechanisms. We employ Large Eddy Simulation (LES) approach and permeable Ffowcs Williams-Hawkings (PFW-H) method to predict cavitation noise around the baseline and biomimetic hydrofoils. The results show that the wavy leading edge can effectively reduce the high-frequency noise, but has little effect on the low-frequency noise. Further analyses and discussions deal with the noise reduction mechanisms. The main source for the low-frequency noise is the cavity volume acceleration, while the wavy leading edge has little effect on it. The high-frequency noise sources, related to the surface pressure fluctuations and the turbulence characteristics, are significantly suppressed by the wavy leading edge, thus decreasing the high-frequency noise intensity. Our investigation indicates that the wavy leading edge has great prospects for cavitation noise reduction technique.

Enhanced ultrasonic degradation of methylene blue using a catalyst-free dual-frequency treatment

Methylene blue is one of the most common pollutants found in wastewater, primarily due to its widespread use in the dye industry. Consequently, it is imperative to explore environmentally friendly and efficient methods for degrading this pollutant into non-toxic byproducts. While ultrasonic degradation methods in combination with additives or catalysts have proven effective, such additives or catalysts may inadvertently contribute to secondary pollution. Moreover, the preparation of these catalysts imposes an additional burden in terms of effort and cost. To address these issues, this paper introduces a catalyst-free dual-frequency ultrasound degradation approach for methylene blue. The sonochemical quality of the cavitation bubbles is improved using this technique because the bulk solution is populated with two types of bubbles, whose mean sizes are determined by the dual ultrasound frequencies. The findings demonstrate that, under identical acoustic power density conditions, dual-frequency ultrasound consistently outperforms single-frequency modes across all investigated parameters. Furthermore, the larger the difference between the dual frequencies used, the more effective the degradation of methylene blue. Finally, after just 20 min of sonication, a degradation efficiency of 91% was achieved with dual frequencies of 20 and 80 kHz at an acoustic power density of 209.63 ± 6.94 W/L. Consequently, this technique offers an environmentally friendly, catalyst-free, and highly effective method for degrading methylene blue.

A review on recent biodiesel intensification process through cavitation and microwave reactors: Yield, energy, and economic analysis

The use of biodiesel as a reliable and green energy source has grown over the past few years. Biodiesel is sustainable and biodegradable because it is only made from vegetable contents and waste cooking oil. Although biodiesel has many advantages over conventional fuels, there are still a lot of technological issues that need to be addressed during the production process. The yield of biodiesel produced using conventional methods is poor and the process is time-consuming. Process enhancements like cavitation and microwave have thus been developed to address this problem. Starting with a comparison to the conventional biodiesel process, this paper has reviewed the most recent developments in the increase of mixture and transfer of heat in these two reactors. This paper examined biodiesel improvement using microwave and cavitation reactors, including biodiesel yield, by meticulously reviewing and analyzing previous works. The production of biodiesel from various raw materials using a range of catalysts, energy requirements, as well as operating factors, activation energy, and constraints also have been discussed. Additionally, the economic analysis discusses the feasibility and cost-effectiveness of implementing these technologies on a commercial scale. Overall, this review provides valuable insights into the intensification of biodiesel production using cavitation and microwave reactors while considering both the technical and economic aspects.

Radiographic characteristics of rifampicin-resistant tuberculosis in the STREAM stage 1 trial and their influence on time to culture conversion in the short regimen

BACKGROUND

Stage 1 of the STREAM trial demonstrated that the 9 month (Short) regimen developed in Bangladesh was non-inferior to the 20 month (Long) 2011 World Health Organization recommended regimen. We assess the association between HIV infection and radiographic manifestations of tuberculosis and factors associated with time to culture conversion in Stage 1 of the STREAM trial.

METHODS

Reading of chest radiographs was undertaken independently by two clinicians, and films with discordant reading were read by a third reader. Recording of abnormal opacity of the lung parenchyma included location (right upper, right lower, left upper, and left lower) and extent of disease (minimal, moderately-advanced, and far advanced). Time to culture conversion was defined as the number of days from initiation of treatment to the first of two consecutive negative culture results, and compared using the log-rank test, stratified by country. Cox proportional hazards models, stratified by country and adjusted for HIV status, were used to identify factors associated with culture conversion.

RESULTS

Of the 364 participants, all but one had an abnormal chest X-ray: 347 (95%) had opacities over upper lung fields, 318 (87%) had opacities over lower lung fields, 124 (34%) had far advanced pulmonary involvement, and 281 (77%) had cavitation. There was no significant association between HIV and locations of lung parenchymal opacities, extent of opacities, the presence of cavitation, and location of cavitation. Participants infected with HIV were significantly less likely to have the highest positivity grade (3+) of sputum culture (p = 0.035) as compared to participants not infected with HIV. Cavitation was significantly associated with high smear positivity grades (p < 0.001) and high culture positivity grades (p = 0.004) among all participants. Co-infection with HIV was associated with a shorter time to culture conversion (hazard ratio 1.59, 95% CI 1.05-2.40).

CONCLUSIONS

Radiographic manifestations of tuberculosis among the HIV-infected in the era of anti-retroviral therapy may not differ from that among those who were not infected with HIV. Radiographic manifestations were not consistently associated with time to culture conversion, perhaps indicating that the Short regimen is sufficiently powerful in achieving sputum conversion across the spectrum of radiographic pulmonary involvements.

TRIAL REGISTRATION

ISRCTN ISRCTN78372190. Registered 14/10/2010. The date of first registration 10/02/2016.

Effects of the adsorbate-gas interface at the pore opening on the lower closure point in gaseous adsorption in porous solids

The limit to the lower closure point (LCP) observed experimentally in the desorption isotherm of gases in porous solids has been commonly attributed to the homogeneous cavitation of the condensate in cavities. It was proposed recently that the experimental limit to LCP could be described in simulations with the ink-bottle pore, provided that the length of the uniformly sized conduit connecting the closed cavity to the surrounding is shorter than 2 nm, and the evaporation is by way of pore blocking mechanism, rather than homogeneous cavitation. To substantiate this assertion, that deviates from the commonly belief of homogeneous cavitation, we further investigated in this paper with cavities having wedge-like pore opening, that better mimics real solids, and offer further explanation on the limit of the LCP to the pore blocking as the mechanism of evaporation with simulations of argon and nitrogen adsorption over a range of temperatures that are commonly used experimentally. It was found that simulation results correctly captured the experimental observations for carbon-based materials and silica-based materials in that the limit of LCP shifts to higher reduced pressures for weaker adsorbing silica, compared to stronger adsorbing carbon and for a given adsorbent it also shifts to higher reduced pressure for higher temperatures.

Degradation of Procion Brilliant Purple H-3R using ultrasound coupled with advanced oxidation processes

The complexity of wastewater matrix poses a challenge for conventional processes especially due to the presence of refractory compounds such as dyes. The present work focuses on utilizing ultrasound-induced cavitation in conjunction with different oxidants such as hydrogen peroxide, Fenton's reagent and potassium persulfate to treat Procion Brilliant Purple H-3R dye containing wastewater. The impact of various operating parameters as pH, frequency, and power on degradation levels has been studied with the aim of optimizing degradation. The optimal conditions for the degradation of Procion Brilliant Purple H-3R were determined as pH of 12, frequency of 22 kHz, and power of 250 W, resulting in a maximum degradation of 70.25%. Combination of a cavitation reactor with hydrogen peroxide, Fenton reagent, and KPS was then applied at optimized conditions, which confirmed a notable enhancement in degradation compared to the only ultrasound based process. Specifically, the degradation extent was 95.99% for combination with H2O2 at 0.5 g/L loading, 99.79% for combination with Fenton at H2O2/Fe2+ ratio of 50:1, and 99.05% for combination with KPS at loading of 0.75 g/L. The kinetic rate constant for the combined approach of US + Fenton was also maximum at 7.47 × 10-1 L mg-1 min-1. Toxicity analysis was conducted on two bacterial strains, Escherichia coli and Staphylococcus aureus, using the wastewater in native form and after treatment. The various processes were evaluated in terms of the cavitational yield and overall treatment cost and it was determined that US + Fenton process is the most efficient treatment method for fully degrading Procion Brilliant Purple H-3R, particularly at larger scales of operation and cost efficiently as demonstrated in the work.

Characterization of the acoustic cavitation in ionic liquids in a horn-type ultrasound reactor

Most ultrasound-based processes root in empirical approaches. Because nearly all advances have been conducted in aqueous systems, there exists a paucity of information on sonoprocessing in other solvents, particularly ionic liquids (ILs). In this work, we modelled an ultrasonic horn-type sonoreactor and investigated the effects of ultrasound power, sonotrode immersion depth, and solvent's thermodynamic properties on acoustic cavitation in nine imidazolium-based and three pyrrolidinium-based ILs. The model accounts for bubbles, acoustic impedance mismatch at interfaces, and treats the ILs as incompressible, Newtonian, and saturated with argon. Following a statistical analysis of the simulation results, we determined that viscosity and ultrasound input power are the most significant variables affecting the intensity of the acoustic pressure field (P), the volume of cavitation zones (V), and the magnitude of the maximum acoustic streaming surface velocity (u). V and u increase with the increase of ultrasound input power and the decrease in viscosity, whereas the magnitude of negative P decreases as ultrasound power and viscosity increase. Probe immersion depth positively correlates with V, but its impact on P and u is insignificant. 1-alkyl-3-methylimidazolium-based ILs yielded the largest V and the fastest acoustic jets - 0.77 cm3 and 24.4 m s-1 for 1-ethyl-3-methylimidazolium chloride at 60 W. 1-methyl-3-(3-sulfopropyl)-imidazolium-based ILs generated the smallest V and lowest u - 0.17 cm3 and 1.7 m s-1 for 1-methyl-3-(3-sulfopropyl)-imidazolium p-toluene sulfonate at 20 W. Sonochemiluminescence experiments validated the model.

Subharmonic resonance of phospholipid coated ultrasound contrast agent microbubbles

Phospholipid encapsulated ultrasound contrast agents have proven to be a powerful addition in diagnostic imaging and show emerging applications in targeted therapy due to their resonant and nonlinear scattering. Microbubble response is affected by their intrinsic (e.g. bubble size, encapsulation physics) and extrinsic (e.g. boundaries) factors. One of the major intrinsic factors at play affecting microbubble vibration dynamics is the initial phospholipid packing of the lipid encapsulation. Here, we examine how the initial phospholipid packing affects the subharmonic response of either individual or a system of two closely-placed microbubbles. We employ a finite element model to investigate the change in subharmonic resonance under 'small' and 'large' radial excursions. For microbubbles ranging between 1.5 and 2.5 µm in diameter and in its elastic state (σ0 = 0.01 N/m), we demonstrate up to a 10 % shift towards lower frequencies in the peak subharmonic response as the radial excursion increases. However, for a bubble initially in its buckled state (σ0 = 0 N/m), we observe a maximum shift of 8 % towards higher frequencies as the radial excursion increases over the same range of bubble sizes - the opposite trend. We studied the same scenario for a system of two individual microbubbles for which we saw similar results. For microbubbles that are initially in their elastic state, in both cases of a) two identically sized bubbles and b) a bubble in proximity to a smaller bubble, we observed a 6 % and 9 % shift towards lower frequencies respectively; while in the case of a neighboring larger bubble no change in subharmonic resonance frequency was observed. Microbubbles that are initially in a buckled state exert no change, 5 % and 19 % shift towards higher frequencies, in two-bubble systems consisting of a) same-size, b) smaller, and c) larger neighboring bubble respectively. Furthermore, we examined the effect of two adjacent bubbles with non-equal initial phospholipid states. The results presented here have important implications in ultrasound contrast agent applications.

Influence of Atherosclerotic Risk Factors on the Effectiveness of Therapeutic Ultrasound Cavitation for Flow Augmentation

BACKGROUND

Shear created by inertial cavitation of microbubbles by ultrasound augments limb and myocardial perfusion and can reverse tissue ischemia. Our aim was to determine whether this therapeutic bioeffect is attenuated by atherosclerotic risk factors that are known to impair shear-mediated vasodilation and adversely affect microvascular reactivity.

METHODS

In mice, lipid-stabilized decafluorobutane microbubbles (2 × 108) were administered intravenously while exposing a proximal hind limb to ultrasound (1.3 MHz, 1.3 mechanical index, pulsing interval 5 seconds) for 10 minutes. Murine strains included wild-type mice and severely hyperlipidemic mice at 15, 35, or 52 weeks of age as a model of aging and elevated cholesterol, and obese db/db mice (≈15 weeks) with severe insulin resistance. Quantitative contrast-enhanced ultrasound perfusion imaging was performed to assess microvascular perfusion in the control and ultrasound-exposed limb. An in situ electrochemical probe and in vivo biophotonic imaging were used to assess limb nitric oxide (NO) and adenosine triphosphosphate concentrations, respectively.

RESULTS

Microvascular perfusion was significantly increased by several fold in the cavitation-exposed limb versus control limb for all murine strains and ages (P < .001). In wild-type and hyperlipidemic mice, hyperemia from cavitation was attenuated in the 2 older age groups (P < .01). In young mice (15 weeks), perfusion in cavitation-exposed muscle was less in both the hyperlipidemic mice and the obese db/db mice compared with corresponding wild-type mice. Using young hyperlipidemic mice as a model for flow impairment, limb NO production after cavitation was reduced but adenosine triphosphosphate production was unaltered when compared with age-matched wild-type mice.

CONCLUSIONS

In mice, ultrasound cavitation of microbubbles increases limb perfusion by several fold even in the presence of traditional atherosclerotic risk factors. However, older age, hyperlipidemia, and insulin resistance modestly attenuate the degree of flow augmentation, which could impact the degree of flow response in current clinical trials in patients with critical limb ischemia.

Frequency dependence of ultrasonic effects on the kinetics of hen egg white lysozyme fibrillation

Our study aimed to investigate the effects of ultrasound on the fibrillation kinetics of HEWL (hen egg white lysozyme) and its physicochemical properties. Ultrasound, a mechanical wave, can induce conformational changes in proteins. To achieve this, we developed an ultrasound exposure system and used various biophysical techniques, including ThT fluorescence spectroscopy, ATR-FTIR, Far-UV CD spectrophotometry, Fluorescence microscopy, UV-spectroscopy, and seeding experiments. Our results revealed that higher frequencies significantly accelerated the fibrillation of lysozyme by unfolding the native protein and promoting the fibrillation process, thereby reducing the lag time. We observed a change in the secondary structure of the sonicated protein change to the β-structure, but there was no difference in the Tm of native and sonicated proteins. Furthermore, we found that higher ultrasound frequencies had a greater seeding effect. We propose that the effect of frequency can be explained by the impact of the Reynolds number, and for the Megahertz frequency range, we are almost at the transition regime of turbulence. Our results suggest that laminar flows may not induce any significant change in the fibrillation kinetics, while turbulent flows may affect the process.

Investigation of the ultrasound-induced collapse of air bubbles near soft materials

A numerical investigation into the ultrasound-induced collapse of air bubbles near soft materials, utilizing a novel multi-material diffuse interface method (DIM) model with block-structured adaptive mesh refinement is presented. The present work expands from a previous five-equation DIM by incorporating Eulerian hyperelasticity. The model is applicable to any arbitrary number of interacting fluid and solid material. A single conservation law for the elastic stretch tensor enables tracking the deformations for all the solid materials. A series of benchmark cases are conducted, and the solution is found to be in excellent agreement against theoretical data. Subsequently, the ultrasound-induced bubble-tissue flow interactions are examined. The bubble radius was found to play a crucial role in dictating the stresses experienced by the tissue, underscoring its significance in medical applications. The results reveal that soft tissues primarily experience tensile forces during these interactions, suggesting potential tensile-driven injuries that may occur in relevant treatments. Moreover, regions of maximal tensile forces align with tissue elongation areas. It is documented that while early bubble dynamics remain relatively unaffected by changes in shear modulus, at later stages of the penetration processes and the deformation shapes, exhibit notable variations. Lastly, it is demonstrated that decreasing standoff distances enhances the interaction between bubbles and tissue, thereby increasing the stress levels in the tissue, although the behavior of the bubble dynamics remains largely unchanged.

Cavitation cloud formation and surface damage of a model stone in a high-intensity focused ultrasound field

This work investigates the fundamental role of cavitation bubble clouds in stone comminution by focused ultrasound. The fragmentation of stones by ultrasound has applications in medical lithotripsy for the comminution of kidney stones or gall stones, where their fragmentation is believed to result from the high acoustic wave energy as well as the formation of cavitation. Cavitation is known to contribute to erosion and to cause damage away from the target, yet the exact contribution and mechanisms of cavitation remain currently unclear. Based on in situ experimental observations, post-exposure microtomography and acoustic simulations, the present work sheds light on the fundamental role of cavitation bubbles in the stone surface fragmentation by correlating the detected damage to the observed bubble activity. Our results show that not all clouds erode the stone, but only those located in preferential nucleation sites whose locations are herein examined. Furthermore, quantitative characterizations of the bubble clouds and their trajectories within the ultrasonic field are discussed. These include experiments with and without the presence of a model stone in the acoustic path length. Finally, the optimal stone-to-source distance maximizing the cavitation-induced surface damage area has been determined. Assuming the pressure magnitude within the focal region to exceed the cavitation pressure threshold, this location does not correspond to the acoustic focus, where the pressure is maximal, but rather to the region where the acoustic beam and thereby the acoustic cavitation activity near the stone surface is the widest.

Efficient sonochemical catalytic degradation of tetracycline using TiO2 fractured nanoshells

Overexposure to antibiotics originating in wastewater has profound environmental and health implications. Conventional treatment methods are not fully effective in removing certain antibiotics, such as the commonly used antibiotic, tetracycline, leading to its accumulation in water catchments. Alternative antibiotic removal strategies are garnering attention, including sonocatalytic oxidative processes. In this work, we investigated the degradation of tetracycline using a combination of TiO2 fractured nanoshells (TFNs) and an advanced sonochemical reactor design. The study encompassed an examination of multiple process parameters to understand their effects on the degradation of tetracycline. These included tetracycline adsorption on TFNs, reaction time, initial tetracycline concentration, solvent pH, acoustic pressure amplitude, number of acoustic cycles, catalyst dosage, TFNs' reusability, and the impact of adjuvants such as light and H2O2. Though TFNs adsorbed tetracycline, the addition of ultrasound was able to degrade tetracycline completely (with 100% degradation) within six minutes. Under the optimal operating conditions, the proposed sonocatalytic system consumed 80% less energy compared to the values reported in recently published sonocatalytic research. It also had the lowest CO2 footprint when compared to the other sono-/photo-based technologies. This study suggests that optimizing the reaction system and operating the reaction under low power and at a lower duty cycle are effective in achieving efficient cavitation for sonocatalytic reactions.

Acceleration mechanism of abrasive particle in ultrasonic polishing under synergistic physical vibration and cavitation: Numerical study

Ultrasonic technology is widely applied in the engineering ceramic polishing processes without the limitation of material properties and ideally integrated into computer numerical control system. Ultrasonic-induced cavitation and mechanical vibration effect could accelerate the motion of solid abrasives. The individual behaviors of microjet/shockwave of ultrasonic cavitation in gases and liquids, and micro-abrasives with simple harmonic vibrations in solids and liquids has been extensively studied. To conduct a systematic and integrated study of abrasives behavior in the polishing contact region involving abrasive, surround-workpiece wall, ultrasonic physical vibration, and ultrasonic cavitation impact, a novel model integrating the free abrasive motion velocity and fixed abrasive indentation depth under multi-scale contact was proposed according to Hertzian contact theory, Greenwood-Williamson model, indentation deformation theory, the basic equations of cavitation bubble dynamics, cavitation impact control equations, and Newton's law of motion equation. The effects of ultrasonic amplitude, ultrasonic frequency, preloading force and particle size on the proposed model were investigated by theoretical analysis and numerical simulations. Ultrasonic physical vibration mainly influences the dynamic gap and further influence the number of different abrasives. Furthermore, the indentation depth of fixed abrasive depends mainly on the abrasive geometry. As the contact gap and abrasive size decrease, the indentation depth gradually decreases. Under the synergistic effect of cavitation-induced shock wave and microjet, the velocity of free abrasive in this paper is generally 0-150 m/s, and the kinetic energy of free abrasive increases roughly linearly with increasing frequency and approximately as a quadratic function with increasing particle size. Increasing the preloading force leads to a reduction in the abrasive kinetic energy. Besides, the kinetic energy induced by the shock wave has a cliff-like increment at an amplitude of 0.7-0.8 μm. It is revealed that the abrasive kinetic energy is suppressed by the cavitation bubble expansion and collapse at smaller ultrasonic pressure amplitude and surround-wall distance. This research provides a theoretical reference for the modeling of potential defects and material removal on the workpiece surface caused by abrasive motion during polishing, and reduces the trial cost for parameter optimization in actual polishing processing.

Dynamics of oil-water interface at the beginning of the ultrasonic emulsification process

A lot of effort has been dedicated in recent years towards understanding the basics of cavitation induced emulsification, mainly in the form of single cavitation bubbles. Regarding bulk acoustic emulsification, a lot less research has been done. In our here presented work we utilize advanced high-speed observation techniques in visible light and X-Rays to build upon that knowledge and advance the understanding of bulk emulsion preparation. During research we discovered that emulsion formation has an acute impact on the behavior of the interface and more importantly on its position relative to the horn, hence their interdependence must be carefully studied. We did this by observing bulk emulsification with 2 cameras simultaneously and corroborating these measurements with observation under X-Rays. Since the ultrasonic horns location also influences interface behavior, we shifted its initial position to different locations nearer to and further away from the oil-water interface in both phases. We found that a few millimeters distance between the horn and interface is not enough for fine emulsion formation, but that they must be completely adjacent to each other, with the horn being located inside the oil-water interface. We also observed some previously undiscovered phenomena, such as the splitting of the interface to preserve continuous emulsion formation, climbing of the interface up the horn and circular interface protrusions towards the horn forming vertical emulsion streams. Interestingly, no visible W/O emulsion was ever formed during our experiments, only O/W regardless of initial horn position.

Probability of Cavitation in a Custom Iron-Based Coupling Medium for Transcranial Magnetic Resonance-Guided Focused Ultrasound Procedures

OBJECTIVE

A coupling bath of circulating, chilled, degassed water is essential to safe and precise acoustic transmittance during transcranial magnetic resonance-guided focused ultrasound (tMRgFUS) procedures, but the circulating water impairs the critical real-time magnetic resonance imaging (MRI). An iron-based coupling medium (IBCM) using iron oxide nanoparticles previously developed by our group increased the relaxivity of the coupling bath such that it appears to be invisible on MRI compared with degassed water. However, the nanoparticles also reduced the pressure threshold for cavitation. To address this concern for prefocal cavitation, our group recently developed an IBCM of electrosterically stabilized and aggregation-resistant poly(methacrylic acid)-coated iron oxide nanoparticles (PMAA-FeOX) with a similar capability to reduce the MR signal of degassed water. This study examines the effect of the PMAA-FeOX IBCM on the cavitation threshold.

METHODS

Increasing concentrations of PMAA-FeOX nanoparticles in degassed, deionized water were placed at the focus of two different transducers to assess low and high duty-cycle pulsing parameters which are representative of two modes of focused ultrasound being investigated for tMRgFUS. Passive cavitation detection and high-speed optical imaging were used to measure cavitation threshold pressures.

RESULTS

The mean cavitation threshold was determined in both cases to be indistinguishable from the degassed water control, between 6-8 MPa for high duty-cycle pulsing (CW) and between 25.5-26.5 MPa for very low duty-cycle pulsing.

CONCLUSION

The findings of this study indicate that an IBCM of PMAA-FeOX nanoparticles is a possible solution to reducing MRI interference from the coupling bath without increasing the risk of prefocal cavitation.

Degradation studies of bisphenol S by ultrasound activated persulfate in aqueous medium

The degradation of recalcitrant organic pollutants by sulphate radical (SO4•-) represents one of the most recent developments in oxidation-based water treatment. In most cases, persulfate (PS) acts as a precursor of sulphate radicals. This study employed ultrasound-activated PS to generate reactive species, facilitating the degradation of bisphenol S (BPS), a well-known contaminant of emerging concern (CECs). An ultrasound with a frequency of 620 kHz and 80 W power was utilised for the degradation studies. The applied oxidation system successfully resulted in the complete degradation of BPS in both pure and real environmental water samples. Additionally, the Chemical oxygen demand (COD) was reduced to an acceptable limit in both matrices, with a reduction of 85 % in pure water and 73 % in river water. The degradation was monitored by varying chemical parameters such as pH, inorganic ions, and organics concentration. The results indicate that under specific pH conditions, the degradation efficiency followed the order of pH 3 > 4 > 7 > 11. The presence of coexisting matrices suppressed the efficiency by scavenging the reactive species. Utilizing high-resolution mass spectrometry (HRMS) analysis, this study identified seven intermediate products during identified during the degradation of BPS. Furthermore, a comprehensive mechanism has been deduced for the transformation and degradation process. All the results presented in this study underscore the applicability of the US/PS system in the removal of CECs.

Sonophotocatalytic water splitting by BaTiO3@SrTiO3 core shell nanowires

Sonophotocatalysis has garnered significant attention due to its potential to enhance advanced oxidation processes, particularly water splitting, by employing materials with combined sonocatalytic and photocatalytic properties. In this study, we synthesized and investigated core-shell BaTiO3@SrTiO3 nanowires (BST NWs) with varying Sr/Ba molar ratios (2.5:7.5, 5.0:5.0, 7.5:2.5 mM, denoted as BST-1, BST-2, and BST-3, respectively) as catalysts for hydrogen production through water splitting. The piezoelectric nanowires demonstrated hydrogen evolution via both sonocatalysis and photocatalysis. In the sonophotocatalysis process, the ultrasonic vibration induced mechanical forces on the BST nanowires, thereby establishing a built-in electric field. This built-in electric field facilitated the effective separation of photo-generated charge carriers and prolonged their lifetimes, leading to a synergistic enhancement of hydrogen evolution. The pristine BaTiO3 and SrTiO3 nanowires exhibited relatively low hydrogen evolution rates (HER) of 7.0 and 6.0 µmol·g-1min-1, respectively. In contrast, the core-shell nanowires exhibited a substantial improvement in the hydrogen evolution rate. The HER increased with the addition of Sr, and BST-1, BST-2, and BST-3 achieved HERs of 12.0, 13.5, and 18.0 µmol·g-1min-1, respectively. The superior performance of BST-3 nanowires can be attributed to their highest piezoelectric potential and largest surface area. Additionally, BST-3 nanowires demonstrated remarkable stability over multiple cycles, validating their practical applicability as efficient photocatalysts.

Mechanistic study of ultrasound-assisted chromatography using plastic and stainless steel columns

Based on the previous ultrasound-assisted chromatography (UAC) studies on plastic and stainless steel (SS) columns, this study explores the UAC mechanism by comparatively analyzing ultrasound effects on plastic and SS columns with C18 stationary phase when separating a mixture of polycyclic aromatic hydrocarbons (PAHs) under various ultrasound intensities. The results showed a substantial difference in H values between the PEEK and SS columns under the influence of ultrasound agitation. Specifically, for the pyrene peak, as the ultrasonic intensity increased from 0% to 100% of 900 W, the H values of the SS column slightly rose from 8.82 μm to 9.86 μm. Conversely, the corresponding values for the PEEK column exhibited a significant 12-fold increase from 11.5 μm to 134 μm. The findings demonstrated poor penetration of ultrasound energy through the SS column, and the temperature rise of the medium induced by the ultrasound was the primary contributing factor to PAH separation. However, ultrasound easily penetrated through the plastic column, resulting in acoustic cavitation within the C18 polyether ether ketone (PEEK) column. Cavitation induced heat generation and contributed to a decrease in retention time and the magnitude of peak broadening or distortion, depending on the specific ultrasonic energy. Based on the estimated change in inlet temperature of the PEEK column due to an acoustic effect, the comparison with temperature effects under non-sonic conditions consistently demonstrated a stronger acoustic effect in reducing the retention time, by 2-9%, depending on specific peaks and pairs. We revisited the previously described separation mechanism of ultrasound-assisted ion chromatography and conjoined with our findings to infer and establish a thorough explanation for the previously unexplained separation mechanism of chiral separation and size exclusion chromatography by UAC using SS columns.

In vitro investigation of stone ablation efficiency, char formation, spark generation, and damage mechanism produced by thulium fiber laser

To investigate stone ablation characteristics of thulium fiber laser (TFL), BegoStone phantoms were spot-treated in water at various fiber tip-to-stone standoff distances (SDs, 0.5 ~ 2 mm) over a broad range of pulse energy (Ep, 0.2 ~ 2 J), frequency (F, 5 ~ 150 Hz), and power (P, 10 ~ 30 W) settings. In general, the ablation speed (mm3/s) in BegoStone decreased with SD and increased with Ep, reaching a peak around 0.8 ~ 1.0 J. Additional experiments with calcium phosphate (CaP), uric acid (UA), and calcium oxalate monohydrate (COM) stones were conducted under two distinctly different settings: 0.2 J/100 Hz and 0.8 J/12 Hz. The concomitant bubble dynamics, spark generation and pressure transients were analyzed. Higher ablation speeds were consistently produced at 0.8 J/12 Hz than at 0.2 J/100 Hz, with CaP stones most difficult yet COM and UA stones easier to ablate. Charring was mostly observed in CaP stones at 0.2 J/100 Hz, accompanied by strong spark-generation, explosive combustion, and diminished pressure transients, but not at 0.8 J/12 Hz. By treating stones in parallel fiber orientation and leveraging the proximity effect of a ureteroscope, the contribution of bubble collapse to stone ablation was found to be substantial (16% ~ 59%) at 0.8 J/12 Hz, but not at 0.2 J/100 Hz. Overall, TFL ablation efficiency is significantly better at high Ep/low F setting, attributable to increased cavitation damage with less char formation.

Impact of sonication power on the degradation of paracetamol under single- and dual-frequency ultrasound

The effects of sonication power on the ultrasonic cavitation and sonochemistry as well as the degradation of paracetamol were studied and compared for single- and dual-frequency sonoreactors. For the single-frequency sonication, a 500 kHz plate transducer was employed, with three different calorimetric powers of 8.4, 16.7 and 27.9±3.9 W. For the dual-frequency sonication, the plate transducer was perpendicularly coupled with a low-frequency 20 kHz ultrasonic horn, and three calorimetric powers of 27.9, 33.4, 44.6±3.9 W were studied. At all the studied powers, dual-frequency sonication led to a synergistic effect in the degradation of paracetamol, though varying the power of the horn did not affect the degradation rate. A comparison of the degradation data versus the yield of oxidants as well as the overall intensities of sonoluminescence and sonochemiluminescence suggested the degradation is by the action of oxidants near the surface of the bubbles as the major reaction mechanism. Despite the enhancement observed for the degradation, dual-frequency sonication had no significant effect on the yield of either of the oxidants, regardless of the applied power to the horn. In contrast, dual-frequency sonication decreased the overall sonoluminescence and sonochemiluminescence intensities at all powers studied, suggesting that the application of dual-frequency sonication reduces the size of cavitation bubbles. Normal distribution function analysis confirmed dual-frequency sonication resulted in smaller sonoluminescing bubbles, hence the reduction in the sonoluminescence intensity. The increase in degradation rate under DFUS is attributed to the increase in the transfer of paracetamol from the bulk towards the bubbles. As a result, the availability of the pollutant molecules in the vicinity of the bubbles to react with HO• would increase and consequently, the degradation rate would enhance under DFUS.

Enhancement of sonochemical production of hydroxyl radicals from pulsed cylindrically converging ultrasound waves

Sonochemistry is the use of ultrasound to generate highly reactive radical species through the inertial collapse of a gas/vapour cavity and is a green alternative for hydrogen production, wastewater treatment, and chemical synthesis and modifications. Yet, current sonochemical reactors often are limited by their design, resulting in low efficacy and yields with slow reaction kinetics. Here, we constructed a novel sonochemical reactor design that creates cylindrically converging ultrasound waves to create an intense localised region of high acoustic pressure amplitudes (15 MPaPKPK) capable of spontaneously nucleating cavitation. Using a novel dosimetry technique, we determined the effect of acoustic parameters on the yield of hydroxyl radicals (HO), HO production rate, and ultimately the sonochemical efficiency (SE) of our reactor. Our reactor design had a significantly higher HO production rate and SE compared to other conventional reactors and across literature.

Is cavitation a truly sensible choice for intensifying photocatalytic oxidation processes? - Implications on phenol degradation using ZnO photocatalysts

Phenols are recalcitrant compounds that constitute the majority of organic contaminants in industrial wastewaters. Their removal at large scales require a combination of various processes to reach the desired discharge quality. An extensive body of work has already been published in the area of phenol removal from wastewater, however none of them have focussed on a truly 'sensible' approach for coupling advanced oxidation processes (AOPs). Rather, a higher removal efficiency was targeted by unduly complicating the process by combining multiple AOPs. The most influential AOP as the primary method typically driven by the nature of the pollutant should form the basis for a hybrid AOP followed by a complementary AOP to intensify the oxidation process. This strategy is lacking in current literature. We address this knowledge gap directly by systematically identifying the best hybrid process for ZnO mediated photocatalysis of phenol. Either a cavitation mediated pre-treatment of ZnO or cavitation-photocatalysis-peroxide based hybrid AOP was investigated. While the pre-treatment approach led to >25% increase in phenol oxidation compared to bare ZnO photocatalysis, the hydrodynamic cavitation-photocatalysis-peroxide based system was found to have a cavitational yield 5 times higher than its acoustic cavitation counterpart. A new phenomenon known as the 'pseudo staggered effect' was also observed and established in hydrodynamic cavitation mediated photocatalysis-peroxide hybrid process for the first time. While we demonstrated that cavitation is a truly 'sensible' choice to enhance photocatalysis, the nature of the pollutant under investigation must always be the key driver when designing such hybrid AOPs.

A review of electro-Fenton and ultrasound processes: towards a novel integrated technology for wastewater treatment

Nowadays, the presence of persistent dissolved pollutants in water has received increasing attention due to their toxic effects on living organisms. Considering the limitations of conventional wastewater treatment processes for the degradation of these compounds, advanced oxidation processes such as electro-Fenton and sono-chemical process, as well as their combination, appear as potentially effective options for the treatment of wastewater contaminated with bio-recalcitrant pollutants. In view of the importance of the development of processes using real effluents, this review aims to provide a comprehensive perspective of sono-electro-Fenton-related processes applied for real wastewater treatment. In the first section, the fundamentals and effectiveness of both homogeneous and heterogeneous electro-Fenton approaches for the treatment of real wastewater are presented. While the second part of this work describes the fundamentals of ultrasound-based processes, the last section focuses on the coupling of the two methods for real wastewater treatment and on the effect of the main operational parameters of the process. On the basis of the information presented, it is suggested that sono-electro-Fenton processes substantially increase the efficiency of the treatment as well as the biodegradability of the treated wastewater. The combined effect results from mass transfer improvement, electrode cleaning and activation, water electrolysis, and the electro-Fenton-induced production of hydroxyl radicals. The information presented in this work is expected to be useful for closing the gap between laboratory-scale assays and the development of novel wastewater technologies.

Release of liposomally formulated near-infrared fluorescent probes included in giant cluster vesicles by ultrasound irradiation

Detection of tumors and regional lymph nodes during surgery has been proposed in the diagnosis of lymphatic metastasis and the surgical treatment of malignant diseases. Giant cluster vesicles (GCVs), including liposomally formulated indocyanine green (LP-ICG) derivatives, are a possible candidate for agents to realize the two contradictory properties, i.e., retention in tissue for lesion-marking and trace for sentinel lymph nodes (SLNs) identification. We attempted to release the LP-ICG derivatives from GCVs using ultrasound contrast agents (UCAs) under ultrasound irradiation. An absorption spectrophotometer quantitatively evaluated the amounts of released LP-ICG derivatives. As a result, we demonstrated that it depended on conditions for sound pressure, burst length, and number density of UCAs, and had a sound pressure threshold independent of burst length and number density of UCAs. The results will aid to determine appropriate conditions to maximize the released amount of LP-ICG derivatives while keeping safety.

Bubble Cloud Characteristics and Ablation Efficiency in Dual-Frequency Intrinsic Threshold Histotripsy

Histotripsy is a non-thermal focused ultrasound ablation method that destroys tissue through the generation and activity of acoustic cavitation bubble clouds. Intrinsic threshold histotripsy uses single-cycle pulses to generate bubble clouds when the dominant negative pressure phase exceeds an intrinsic threshold of ~25-30 MPa. The ablation efficiency is dependent upon the size and density of bubbles within the bubble cloud. This work investigates the effects of dual-frequency pulsing schemes on the bubble cloud behavior and ablation efficiency in intrinsic threshold histotripsy. A modular 500 kHz:3 MHz histotripsy transducer treated agarose phantoms using dual-frequency histotripsy pulses with a 1:1 pressure ratio from 500 kHz and 3 MHz frequency elements and varying arrival times for the 3 MHz pulse relative to the arrival of the 500 kHz pulse (-100 ns, 0 ns, and +100 ns). High-speed optical imaging captured cavitation effects to characterize bubble cloud and individual bubble dynamics. The effects of dual-frequency pulsing on lesion formation and ablation efficiency were also investigated in red blood cell (RBC) phantoms. Results showed that the single bubble and bubble cloud size for dual-frequency cases were intermediate to published results for the component single frequencies of 500 kHz and 3 MHz. Additionally, bubble cloud size and dynamics were shown to be altered by the arrival time of the 3 MHz pulse with respect to the 500 kHz pulse, with more uniform cloud expansion and collapse observed for early (-100 ns) arrival. Finally, RBC phantom experiments showed that dual-frequency exposures were capable of generating precise lesions with smaller areas and higher ablation efficiencies than previously published results for 500 kHz or 3 MHz. Overall, results demonstrate dual-frequency histotripsy's ability to modulate bubble cloud size and dynamics can be leveraged to produce precise lesions at higher ablation efficiencies than previously observed for single-frequency pulsing.

Chronic effects of pulsed high intensity focused ultrasound aided delivery of gemcitabine in a mouse model of pancreatic cancer

Pulsed high intensity focused ultrasound (pHIFU) is a non-invasive method that allows to permeabilize pancreatic tumors through inertial cavitation and thereby increase the concentration of systemically administered drug. In this study the tolerability of weekly pHIFU-aided administrations of gemcitabine (gem) and their influence on tumor progression and immune microenvironment were investigated in genetically engineered KrasLSL.G12D/þ; p53R172H/þ; PdxCretg/þ (KPC) mouse model of spontaneously occurring pancreatic tumors. KPC mice were enrolled in the study when the tumor size reached 4-6 mm and treated once a week with either ultrasound-guided pHIFU (1.5 MHz transducer, 1 ms pulses, 1% duty cycle, peak negative pressure 16.5 MPa) followed by administration of gem (n = 9), gem only (n = 5) or no treatment (n = 8). Tumor progression was followed by ultrasound imaging until the study endpoint (tumor size reaching 1 cm), whereupon the excised tumors were analyzed by histology, immunohistochemistry (IHC) and gene expression profiling (Nanostring PanCancer Immune Profiling panel). The pHIFU + gem treatments were well tolerated; the pHIFU-treated region of the tumor turned hypoechoic immediately following treatment in all mice, and this effect persisted throughout the observation period (2-5 weeks) and corresponded to areas of cell death, according to histology and IHC. Enhanced labeling by Granzyme-B was observed within and adjacent to the pHIFU treated area, but not in the non-treated tumor tissue; no difference in CD8 + staining was observed between the treatment groups. Gene expression analysis showed that the pHIFU + gem combination treatment lead to significant downregulation of 162 genes related to immunosuppression, tumorigenesis, and chemoresistance vs gem only treatment.

Acoustic droplet vaporization for on-demand modulation of microporosity in smart hydrogels

Microporosity in hydrogels is critical for directing tissue formation and function. We have developed a fibrin-based smart hydrogel, termed an acoustically responsive scaffold (ARS), which responds to focused ultrasound in a spatiotemporally controlled, user-defined manner. ARSs are highly flexible platforms due to the inclusion of phase-shift droplets and their tunable response to ultrasound through a mechanism termed acoustic droplet vaporization (ADV). Here, we demonstrated that ADV enabled consistent generation of micropores in ARSs, throughout the entire thickness (∼5.5 mm), utilizing perfluorooctane phase-shift droplets. Size characteristics of the generated micropores were quantified in response to critical parameters including acoustic properties, droplet size, and shear elastic modulus of fibrin using confocal microscopy. The findings showed that the length of the generated micropores correlated directly with excitation frequency, peak rarefactional pressure, pulse duration, droplet size, and indirectly with the shear elastic modulus of the fibrin matrix. The ADV-generated micropores in ARSs were further compared with cavitation-mediated micropores in fibrin gels without droplets. Additionally, the Keller-Miksis equation was used to predict an upper bound for micropore formation in ARSs at varying driving frequencies and droplet sizes. Finally, our in vivo studies showed that host cell migration following ADV-induced micropore formation was frequency-dependent, with up to 2.6 times higher cell migration at lower frequencies. Overall, these findings demonstrate a new potential application of ADV in hydrogels. STATEMENT OF SIGNIFICANCE: Interconnected micropores within a hydrogel can facilitate many cell-mediated processes. Most techniques for generating micropores are typically not biocompatible or do not enable controlled, in situ micropore formation. We used an ultrasound-based technique, termed acoustic droplet vaporization, to generate microporosity in smart hydrogels termed acoustically responsive scaffolds (ARSs). ARSs contain a fibrin matrix doped with a phase-shift droplet. We demonstrate that unique acoustic properties of phase-shift droplets can be tailored to yield spatiotemporally controlled, on-demand micropore formation. Additionally, the size characteristics of the ultrasound-generated micropores can be modulated by tuning ultrasound parameters, droplet properties, and bulk elastic properties of fibrin. Finally, we demonstrate significant, frequency-dependent host cell migration in subcutaneously implanted ARSs in mice following ultrasound-induced micropore formation in situ.

Piezo/sono-catalytic activity of ZnO micro/nanoparticles for ROS generation as function of ultrasound frequencies and dissolved gases

We report an accurate study on sonocatalytic properties of different ZnO micro and nanoparticles to enhance OH radical production activated by cavitation. In order to investigate some of the still unsolved aspects related to the piezocatalytic effect, the degradation of Methylene Blue and quantification of radicals production have been evaluated as function of different ultrasonic frequencies (20 kHz and 858 kHz) and dissolved gases (Ar, N₂ and air). The results shown that at low frequency the catalytic effect of ZnO particles is well evident and influenced by particle dimension while at high frequency a reduction of the degradation efficiency have been observed using larger particles. An increase of radical production have been observed for all ZnO particles tested while the different saturating gases have poor influence. In both ultrasonic set-up the ZnO nanoparticles resulted the most efficient on MB degradation revealing that the enhanced radical production may arise more from bubbles collapse on particles surface than the discharge mechanism activate by mechanical stress on piezoelectric particles. An interpretation of these effects and a possible mechanism which rules the sonocatalytic activity of ZnO will be proposed and discussed.

Water treatment by cavitation: Understanding it at a single bubble - bacterial cell level

Cavitation is a potentially useful phenomenon accompanied by extreme conditions, which is one of the reasons for its increased use in a variety of applications, such as surface cleaning, enhanced chemistry, and water treatment. Yet, we are still not able to answer many fundamental questions related to efficacy and effectiveness of cavitation treatment, such as: "Can single bubbles destroy contaminants?" and "What precisely is the mechanism behind bubble's cleaning power?". For these reasons, the present paper addresses cavitation as a tool for eradication and removal of wall-bound bacteria at a fundamental level of a single microbubble and a bacterial cell. We present a method to study bubble-bacteria interaction on a nano- to microscale resolution in both space and time. The method allows for accurate and fast positioning of a single microbubble above the individual wall-bound bacterial cell with optical tweezers and triggering of a violent microscale cavitation event, which either results in mechanical removal or destruction of the bacterial cell. Results on E. coli bacteria show that only cells in the immediate vicinity of the microbubble are affected, and that a very high likelihood of cell detachment and cell death exists for cells located directly under the center of a bubble. Further details behind near-wall microbubble dynamics are revealed by numerical simulations, which demonstrate that a water jet resulting from a near-wall bubble implosion is the primary mechanism of wall-bound cell damage. The results suggest that peak hydrodynamic forces as high as 0.8 μN and 1.2 μN are required to achieve consistent E. coli bacterial cell detachment or death with high frequency mechanical perturbations on a nano- to microsecond time scale. Understanding of the cavitation phenomenon at a fundamental level of a single bubble will enable further optimization of novel water treatment and surface cleaning technologies to provide more efficient and chemical-free processes.

High-Speed Imaging of Microsphere Transport by Cavitation Activity in a Tissue-Mimicking Phantom

OBJECTIVE

Ultrasound-mediated cavitation has been harnessed to improve the delivery of various therapeutics, including the extravasation of small molecule drugs and nanoparticles (<1 µm) into soft tissue. This study investigated whether cavitation could also enhance the extravasation of larger (>10 µm) therapeutic particles, representative of radio- or chemo-embolic particles, in a tissue-mimicking phantom.

METHODS

High-speed (10³-10⁶ frames/s) optical imaging was used to observe the motion of glass microspheres with diameters of 15-32 or 105-107 µm in an agar phantom under exposure to high-intensity focused ultrasound (0.5 MHz) at a range of peak negative pressures (1.9-2.8 MPa) in the presence of SonoVue microbubbles.

RESULTS

In contrast to the microstreaming reported to be responsible for nanoparticle transport, the formation and translation of bubble clouds were found to be primarily responsible for the motion of glass microspheres. The bubble clouds were seen both to create channels in the phantom and to travel along them under the action of primary acoustic radiation force, either propelling or entraining microspheres with them. Collisions between microspheres were also seen to promote cloud formation and cavitation activity.

CONCLUSION

Ultrasound-mediated cavitation can promote the transport of solid microparticles in tissue-mimicking material. Further work is needed to understand the influence of tissue mechanical properties and ultrasound exposure parameters on the extent and uniformity of particle distribution that can be achieved.

Effect of dissolved gases on sonochemical oxidation in a 20 kHz probe system: Continuous monitoring of dissolved oxygen concentration and sonochemical oxidation activity

Dissolved gases have a substantial influence on acoustic cavitation and sonochemical oxidation reactions. Little research on the changes in dissolved gases and the resultant changes in sonochemical oxidation has been reported, and most studies have focused only on the initial dissolved gas conditions. In this study, the dissolved oxygen (DO) concentration was measured continuously during ultrasonic irradiation using an optical sensor in different gas modes (saturation/open, saturation/closed, and sparging/closed modes). Simultaneously, the resulting changes in sonochemical oxidation were quantified using KI dosimetry. In the saturation/open mode using five gas conditions of Ar and O₂, the DO concentration decreased rapidly when O₂ was present because of active gas exchange with the atmosphere, and the DO concentration increased when 100% Ar was used. As a result, the order of the zero-order reaction constant for the first 10 min (k_0-10) decreased in the order Ar:O₂ (75:25) > 100% Ar ≈ Ar:O₂ (50:50) > Ar:O₂ (25:75) > 100% O₂, whereas that during the last 10 min (k_20-30) when the DO concentration was relatively stable, decreased in the order 100% Ar > Ar:O₂ (75:25) > Ar:O₂ (50:50) ≈ Ar:O₂ (20:75) > 100% O₂. In the saturation/closed mode, the DO concentration decreased to approximately 70-80% of the initial level because of ultrasonic degassing, and there was no influence of gases other than Ar and O₂. Consequently, k_0-10 and k_20-30 decreased in the order Ar:O₂ (75:25) > Ar:O₂ (50:50) > Ar:O₂ (25:75) > 100% Ar > 100% O₂. In the sparging/closed mode, the DO concentration was maintained at approximately 90% of the initial level because of the more active gas adsorption induced by gas sparging, and the values of k_0-10 and k_20-30 were almost the same as those in the saturation/closed mode. In the saturation/open and sparging/closed modes, the Ar:O₂ (75:25) condition was most favorable for enhancing sonochemical oxidation. However, a comparison of k_0-10 and k_20-30 indicated that there would be an optimal dissolved gas condition that was different from the initial gas condition. In addition, the mass-transfer and ultrasonic-degassing coefficients were calculated using changes in the DO concentration in the three modes.

Investigation of cavitation noise using Eulerian-Lagrangian multiscale modeling

We have employed the large eddy simulation (LES) approach to investigate the cavitation noise characteristics of an unsteady cavitating flow around a NACA66 (National Advisory Committee for Aeronautics) hydrofoil by employing an Eulerian-Lagrangian based multiscale cavitation model. A volume of fluid (VOF) method simulates the large cavity, whereas a Lagrangian discrete bubble model (DBM) tracks the small bubbles. Meanwhile, noise is determined using the Ffowcs Williams-Hawkings equation (FW-H). Eulerian-Lagrangian analysis has shown that, in comparison to VOF, it is more effective in revealing microscopic characteristics of unsteady cavitating flows, including microscale bubbles, that are unresolvable around the cloud cavity, and their impact on the flow field. It is also evident that its evolution of cavitation features on the hydrofoil is more consistent with the experimental observations. The frequency of the maximum sound pressure level corresponds to the frequency of the main cavity shedding for the noise characteristics. Using the Eulerian-Lagrangian method to predict the noise signal, results show that the cavitation noise, generated by discrete bubbles due to their collapse, is mainly composed of high-frequency signals. In addition, the frequency of cavitation noise induced by discrete microbubbles is around 10 kHz. A typical characteristic of cavitation noise, including two intense pulses during the collapsing of the cloud cavity, is described, as well as the mechanisms that underlie these phenomena. The findings of this work provide for a fundamental understanding of cavitation and serve as a valuable reference for the design and intensification of hydrodynamic cavitation reactors.

Mechanistic and synergistic aspects of ultrasonics and hydrodynamic cavitation for food processing

Compared with traditional methods, cavitation-based processing technology has received extensive attention for its low energy consumption and high processing efficiency. The cavitation phenomenon releases high energy due to the generation and collapse of bubbles, which improves the efficiency of various food processing. This review details the cavitation mechanism of ultrasonic cavitation (UC) and hydrodynamic cavitation (HC), factors affecting cavitation, the application of cavitation technology in food processing, and the application of cavitation technology in the extraction of various natural ingredients. The safety and nutrition of food processed by cavitation technology and future research directions are also discussed. The mechanism of UC refers to longitudinal displacement of the particles of the medium induced by ultrasonic waves causing a series of alternating compression and rarefaction of particles, whereas HC occurs when liquid enters a narrow section and undergoes large pressure differentials, both of which can trigger the generation, growth, and collapse of microbubbles. Cavitation could be applied in microbial inactivation, and drying and freezing processing. In addition, cavitation bubbles can have mechanical and thermal effects on plant cells. In general, cavitation technology is a new sustainable, green, and innovative technology with broad application prospects and capabilities.

Baseline characteristics and analysis of predictors of the Outcome of septic pulmonary embolism in children: a retrospective observational study

BACKGROUND

Septic pulmonary embolism is a rare disease in children. We aimed to assess the clinical, microbiological, and radiological characteristics and outcomes of pediatric septic pulmonary embolism (SPE) and to identify any predictive factors for in-hospital mortality in patients with this unusual disease to enhance prognosis and treatment.

METHODS

A retrospective study to search the electronic medical records of children admitted to the pediatric pulmonology unit, Tanta University hospital with the diagnosis of SPE between January 2015 and June 2022.

RESULTS

Seventeen pediatric patients were identified; ten males and seven females with a mean age of 9.4 ± 5.2 years. The most common presenting complaints were fever and shortness of breath (n = 17) followed by chest pain (n = 9), pallor (n = 5), limb swelling (n = 4), and back pain (n = 1). Methicillin-resistant Staphylococcus aureus (MRSA) was the most common causative pathogen in nine patients. The most common extra-pulmonary septic foci were septic arthritis in five patients (29.4%), septic thrombophlebitis in four patients (23.5%), and infective endocarditis in two patients (11.8%). All patients exhibited wedge-shaped peripheral lesions and feeding vessel sign in CT chest, whereas bilateral diffuse lesions, nodular lesions, and cavitation were present in 94.1% of patients, pleural effusion was identified in 58.8% of patients, and pneumothorax was detected in 41.2% of patients. Fifteen patients improved and survived (88.2%), while two patients died (11.8%).

CONCLUSION

Early diagnosis of SPE with vigorous early therapy is critical for a better outcome, including appropriate antibiotics and timely surgical interference to eradicate extra-pulmonary septic foci.

Fluid flow influences ultrasound-assisted endothelial membrane permeabilization and calcium flux

The local fluid dynamics experienced by circulating microbubbles vary across different anatomical sites, which can influence ultrasound-mediated therapeutic delivery efficacy. This study aimed to elucidate the effect of fluid flow rate in combination with repeated short-pulse ultrasound on microbubble-mediated endothelial cell permeabilization. Here, a seeded monolayer of human umbilical (HUVEC) or brain endothelial cells (HBEC-5i) was co-perfused with a solution of microbubbles and propidium iodide (PI) at either a flow rate of 5 or 30 ml/min. Using an acoustically coupled inverted microscope, cells were exposed to 1 MHz ultrasound with 20-cycle bursts, 1 ms PRI, and 2 s duration at a peak negative pressure of 305 kPa to assess the role of flow rate on ultrasound-stimulated endothelial cell permeability, as well as Ca²⁺ modulation. In addition, the effect of inter-pulse delays (∆t = 1s) on the resulting endothelial permeability was investigated. Our results demonstrate that under an identical acoustic stimulus, fast-flowing microbubbles resulted in a statistically significant increase in cell membrane permeability, at least by 2.3-fold, for both endothelial cells. Likewise, there was a substantial difference in intracellular Ca²⁺ levels between the two examined flow rates. In addition, multiple short pulses rather than a single pulse ultrasound, with an equal number of bursts, significantly elevated endothelial cell permeabilization, at least by 1.4-fold, in response to ultrasound-stimulated microbubbles. This study provides insights into the design of optimal, application-dependent pulsing schemes to improve the effectiveness of ultrasound-mediated local therapeutic delivery.

Sonochemistry of molten gallium

This review article summarizes the comprehensive work that was done in our laboratory in recent years, as-well-as other reports, on the various aspects of sonochemistry of molten gallium. The low mp (29.8 °C) of gallium enables its melting in warm water, aqueous solutions and organic liquids. This opened a new research direction that focused on the chemical and physical properties of gallium particles that were formed in such media. It includes their interactions with water and with organic and inorganic solutes in aqueous solutions and with carbon nanoparticles. Formation of nanoparticles of liquid gallium alloys was also reported.