Effects Of Ultrasound Frequency Research Articles

A computational framework for the multiphysics simulation of microbubble-mediated sonothrombolysis using a forward-viewing intravascular transducer

Sonothrombolysis is a technique that utilises ultrasound waves to excite microbubbles surrounding a clot. Clot lysis is achieved through mechanical damage induced by acoustic cavitation and through local clot displacement induced by acoustic radiation force (ARF). Despite the potential of microbubble-mediated sonothrombolysis, the selection of the optimal ultrasound and microbubble parameters remains a challenge. Existing experimental studies are not able to provide a complete picture of how ultrasound and microbubble characteristics influence the outcome of sonothrombolysis. Likewise, computational studies have not been applied in detail in the context of sonothrombolysis. Hence, the effect of interaction between the bubble dynamics and acoustic propagation on the acoustic streaming and clot deformation remains unclear. In the present study, we report for the first time the computational framework that couples the bubble dynamic phenomena with the acoustic propagation in a bubbly medium to simulate microbubble-mediated sonothrombolysis using a forward-viewing transducer. The computational framework was used to investigate the effects of ultrasound properties (pressure and frequency) and microbubble characteristics (radius and concentration) on the outcome of sonothrombolysis. Four major findings were obtained from the simulation results: (i) ultrasound pressure plays the most dominant role over all the other parameters in affecting the bubble dynamics, acoustic attenuation, ARF, acoustic streaming, and clot displacement, (ii) smaller microbubbles could contribute to a more violent oscillation and improve the ARF simultaneously when they are stimulated at higher ultrasound pressure, (iii) higher microbubbles concentration increases the ARF, and (iv) the effect of ultrasound frequency on acoustic attenuation is dependent on the ultrasound pressure. These results may provide fundamental insight that is crucial in bringing sonothrombolysis closer to clinical implementation.

Ultrasound-enhanced coagulation for cyanobacterial removal: Effects of ultrasound frequency and energy density on coagulation performance, leakage of intracellular organic matters and toxicity

Ultrasound-enhanced coagulation is capable of effectively removing algal cells in algae-laden water. However, study differences in ultrasound settings, algal cell conditions and coagulant properties complicate the accurate evaluation of this technique for practical applications. No study has yet compared algae (and algal organic matters) removal among different frequencies of ultrasound in the ultrasound-coagulation process. In this study, the ultrasound at three typical frequencies, 29.4, 470 and 780 kHz, were applied for this purpose. The results showed that high-frequency ultrasound at 470 and 780 kHz had substantially greater improvement of coagulation than low-frequency ultrasound at 29.4 kHz (For example, the turbidity removal at 1 mg-Al/L of polymeric aluminum chloride increased by 204.2%, 571.9% and 563.2% under 29.4, 470 and 780 kHz ultrasound-coagulation, respectively, at 3.42 J/mL). Algal cells exhibited irreversible physical damage and the release of intracellular organic matters (such as odorous compounds) under low-frequency ultrasound with energy densities ≥ 3.42 J/mL, whereas high-frequency ultrasound was characterized by nonviolent impairment, including oxidative degradation and gas vacuole destruction (particularly reversible) resulting from ultrasound-induced radicals and cell resonance, respectively. Avoiding the severe destruction of algal cells is crucial for minimizing the toxicity and secondary pollution of the treated water. To achieve satisfactory removal, protected safety and better economy, the optimal energy density for each frequency was also determined. The findings from the analyses of the laboratory-cultured sample were confirmed via real eutrophic surface water. This study provides new insights and guidance for the ongoing study of harmful algal removal by ultrasound-enhanced coagulation.

Sonochemical Catalyst Synthesis for HER and OER

Improvements on catalysts for electrochemical energy conversion is highly important if technologies such as fuel cells and electrolyzers are to become economically viable in the future. These improvements typically lie in the optimization of the catalyst’s particle size and available surface area, which means that nucleation and growth conditions during the synthesis must be controlled precisely. Common ways of producing such catalysts today involve chemical reduction methods were reducing agents like NaBH4 or ethylene glycol are used to reduce metal salts to their metallic state [1]. Even though such methods are fast and scalable, few ways are available for careful control over the nucleation and growth of the nanoparticles.To allow for better control over the nucleation and growth of nanoparticles, a sonochemical synthesis method can be employed instead [1]. In sonochemistry, high power ultrasound is applied to an aqueous metal precursor solution resulting in the formation of H-radicals and OH-radicals in the cavitation bubbles [1]. The highly reactive radicals will diffuse into the solution and reduce the metal ions to metallic nanoparticles. The nucleation and growth conditions can therefore simply be manipulated by controlling the rate of radical formation which is directly related to the ultrasound parameters. Several studies have found that the radical formation rate (or the metal reduction rate) is affected by the ultrasound frequency [2][3], ultrasound power [3], solution temperature [3], types of dissolved gasses [3], types of alcohols used [4], and types of surfactants used [5]. The ease of changing these parameters therefore ensures that nanoparticles of optimal sizes can be produced.In this project we have started to investigate exactly how ultrasound parameters influence the radical formation rate in aqueous systems. This information can therefore be used to synthesize electrocatalysts optimized for HER and OER. Initial investigations of how Ni- and Fe -precursors are affected by ultrasound have also been performed. Sonochemical assisted synthesis of NiFe nanoparticles with NaBH4 was also assessed as a potential hybrid solution.The results from the investigations of the ultrasound parameters suggested that the addition of ethanol effectively leads to a scavenging of the primary radicals in the solution. Consequently, more radicals become available for reducing metal ions, and the reduction rate increases. Higher ultrasonic power and lower ultrasonic frequency (580 kHz was the lowest frequency used in the experiment) increase the radical formation, which is supported by previous findings [2][3]. The effect of dissolved gasses showed that O2 saturation gave the highest radical yield. However, this can be traced to the sonolysis of O2 itself which lead to additional radical formation from the dissolved gas, and not just from the water vapor in the cavitation bubbles [3]. The ideal solution temperature was found to be dependent on the type of dissolved gas, with Ar exhibiting a higher ideal temperature than O2.The initial investigations of Ni- and Fe-precursors showed that the sonochemical reduction was not appreciable in the short time frame which was used (30 min). Longer sonication times will be attempted in future works.For the sonochemical assisted synthesis, NaBH4 was added as a reducing agent to aid the reduction, and an ultrasonic bath was used as the ultrasound source (42 kHz). Physical characterization of the resulting particles showed a significant decrease in the particle size due to the application of ultrasound. However, these changes were attributed to the mechanical effects most dominant at lower ultrasonic frequencies. Similar experiments will be attempted at higher frequencies to observe if the chemical effects of ultrasound act similarly.References Bruno G. Pollet. “The use of ultrasound for the fabrication of fuel cell materials”. International Journal of Hydrogen Energy 35.21 (2010). VIII symposium of the Mexican Hydrogen Society, pp. 11986–12004K Okitsu et al. “Sonochemical synthesis of gold nanoparticles: effects of ultrasound frequency”. The journal of physical chemistry. B109.44 (2005), p. 20673S Merouani et al. “Sensitivity of free radicals production in acoustically driven bubble to the ultrasonic frequency and nature of dissolved gases”. Ultrasonics – Sonochemistry 22.2 (2015), pp. 41–50Rachel A Caruso et al. “Sonochemical formation of colloidal platinum”. Colloids and Surfaces A: Physicochemical and Engineering Aspects 169.1-3 (2000), pp. 219–225K Okitsu et al. “Sonochemical preparation of ultrafine palladium particles”. Chemistry of Materials (USA) 8.2 (1996), pp. 315–317

In-situ ultrasound-assisted control of polymeric membrane fouling

Membrane separation processes have been more widely applied to industrial activities, especially in water and wastewater treatment. However, there are still challenges associated with the use of membranes. Concentration polarization and fouling can cause significant permeate flux decay during the filtration process, hindering its efficiency and increasing cost. Among many strategies, the combination of membrane filtration with ultrasound (US) application has shown promising results in reducing membrane fouling. The main goal of this research was to identify the effect of US frequency, US power intensity and feed solid concentration on permeate flux during ultrafiltration of simulated latex paint effluent. Maximum increase in permeate flux of 19.7% was obtained by applying 20 kHz and 0.29 W cm−2 to a feed solution containing 0.075 wt% of solid. Overall, the application of US improves permeate flux by reducing fouling of ultrafiltration polymeric membrane.

Catalytic conversion of lignin to bio-oil over PTA/MCM-41 catalyst assisted by ultrasound acoustic cavitation

The ultrasound-assisted depolymerization of lignin was successfully conducted over a synthesized PTA/MCM-41 catalyst under different reaction conditions. Firstly, the structure of the prepared PTA/MCM-41 catalyst was characterized by various techniques, and its acidity was determined using Fourier-transform infrared spectroscopy (FT-IR) of pyridine adsorption and temperature-programmed desorption of ammonia (NH3-TPD). Then, the effects of ultrasound frequency, reaction temperature, and reaction time on the distribution and yield of the products of the ultrasound-assisted depolymerization of lignin were studied. The optimum reaction conditions were obtained at an ultrasound frequency of 30%, a reaction temperature of 300 °C, and a reaction time of 6 h. Under the optimum reaction conditions, the conversion of lignin depolymerization was equal to 94.79%, and the yield of phenolic monomers (PM) and lignin bio-oil was 8.37% and 90.58% respectively.

Effects of convective drying assisted by ultrasound and osmotic solution on polyphenol, antioxidant and microstructure of murtilla (Ugni molinae Turcz) fruit.

The effects of pretreatment with ultrasound and an osmotic solution combined with hot air convection drying on the total polyphenol content (TPC), antioxidant activity and microstructural of murtilla skin fruit were evaluated. The effects of ultrasound frequency (0 and 130kHz), osmotic solution concentration (0 and 70°Brix) and time (60 or 120min) on the TPC and the antioxidant activities as measured by 2,2-diphenyl-1-picrylhydrazyl (DPPH), ferric reducing antioxidant power (FRAP) and oxygen radical absorbance capacity (ORAC) assays were evaluated. The TPC and DPPH antioxidant activity decreased significantly (p < 0.05) when ultrasound was applied at 0°Brix for 60min. Higher FRAP activity was obtained upon treatment with ultrasound and an osmotic solution for 60min. The ORAC values did not significantly differ based on the pretreatment methods but decreased when an osmotic solution was applied for 120min without ultrasound. When ultrasound and the osmotic solution were applied, the skin cells of the dried murtilla fruit became more distorted, resulting in larger spaces between them and causing loss of shape. Although the application of pretreatment procedures before murtilla fruit drying did not positively affect the TPC, DPPH or ORAC individually, the application of a Global Standardized Response based on the followed by a mathematical model adjustment indicated that a 70°Brix osmotic solution applied for 60min was the best treatment for preparing murtilla fruit aiming a high antioxidant activity in dried product.

Effect of ultrasound on the flocculation-sedimentation and thickening of unclassified tailings.

In back-fill mining, how to rapidly increase the concentration of tailings is an important problem facing mining engineers. In this paper, the effects of ultrasound frequency (17-25kHz), power (50-100W), duration (5-20min) and start time (3-12min) on the final underflow concentration (FUC) of unclassified tailings (UTs) were investigated. The flocculation-sedimentation and thickening of tailings were compared with and without ultrasound application. The response surface method was applied to analyze the primary and secondary relationships and interactive relationships between the various ultrasound operating parameters and the FUC, and the optimal conditions were determined. In addition, Environmental Scanning Electron Microscope (E-SEM) was used to analyze the structural changes of underflow aggregates and clearly demonstrated a denser underflow after ultrasound treatment. The results indicated that ultrasound can significantly improve the underflow concentration of the UTs slurry. The frequency and power are the most important influencing factors. The best conditions for ultrasound application are a frequency of 20.4kHz, power of 90W, duration of 6.2min and start time at 15.0min. The FUC reached 71.75% after several minutes of sonication, which is 4.31% higher than the FUC of free flocculation. The results of E-SEM analysis showed significant differences among the microstructures of settled tailings (STs) after free flocculation and 17 and 20kHz ultrasound treatment. Ultrasound at a frequency of 20kHz has a more effective mechanical vibration and cavitation action and can therefore effectively break the polymer flocculant chains into shorter chains and promote the compaction of tailings and the release of water. The size distributions of the flocs before and after sonication also support this conclusion.

Preliminary test of ultrasonically disinfection efficacy towards selected aquaculture pathogens

The disinfection potential of ultrasound was evaluated for fish production in aquaculture systems by investigating the sensitivity of a wide range of different model organisms representing different taxa of common fish pathogens such as bacteria or parasites and algae at a size range of a few micrometers to 1 mm. Therefore, dose-dependent inactivation rates depending on consumed energy (kJ/L) at low (20 kHz, LFUS) and high (850 kHz, HFUS) frequency ultrasound were determined in in-vitro tests using a laboratory-scaled set-up for three zooplankton and five algae species as well as for heterotrophic marine and fresh water bacteria separated from recirculating aquaculture system water. LFUS and HFUS were effective against most tested eukaryotic organisms even at low energy input and the dose-dependent inactivation could be well described by functions of an exponential decay. HFUS seemed to be more effective compared to LFUS regarding the inactivation of bigger-sized algae species (≥14 μm). Within the tested zooplankton species, no systematic correlation between the size of the organisms and the effect of ultrasound frequency on the inactivation efficiency became apparent, suggesting a strong species-dependency likely caused by additional relevant morphological and physiological factors. Our data also suggest ultrasound treatment alone to be insufficient for an efficient bacterial reduction as LFUS and HFUS did not significantly reduced total viable counts even at high energy inputs up to 144 kJ/L. Measurements of total residual oxidants (TRO) revealed a higher formation potential of sonochemically-produced oxidants for HFUS compared to LFUS as well as an increased TRO accumulation at saline waters most likely due to the formation of more persistent halogenated secondary oxidants. Hence, particularly when HFUS is applied in a marine process chain total residual oxidants should be monitored in order to avoid deleterious impacts on animal health.

Numerical simulation of heat and moisture transfer in fibrous porous media dehydration process with ultrasound assisted

In recent decades, the enhancement of ultrasound on heat and mass transfer in the processes of food processing, waste sludge dehydration and silica gel regeneration has been confirmed by experiments and simulations. The effect of ultrasound in the dehydration process of fibrous porous media has been experimentally studied, however, the theoretical simulation is still lacking, which will be presented in this paper. In the first place, the effects of ultrasound frequency and intensity on ultrasound propagation in fibrous porous media are investigated. For the pressure and deformation produced by ultrasound propagation in porous media, ultrasound intensity has an important influence on their magnitude, and their distribution trend is also affected by ultrasound frequency. Then, the fundamental heat and mass transfer process in fibrous porous media with ultrasound assisted dehydration is studied and the mathematical model is validated by experiments in terms of the drying curves under different ultrasound intensity. By numerical simulation, the distribution of liquid transmission velocity, temperature and dry basis moisture content are obtained which is useful to further analyse the mechanism of ultrasound enhancement in fibrous porous media dehydration.

Effect of Ultrasound Frequency and Treatment Duration on Antibiotic Elution from Polymethylmethacrylate Bone Cement

The objective of this study was to evaluate the effect of ultrasound frequency and treatment duration on antibiotic-impregnated polymethylmethacrylate (PMMA) antibiotic elution rates and mechanical strength. Two batches of PMMA were prepared: one with five grams of vancomycin powder and one without. Each batch was divided into two frequency groups: kHz and MHz. Each frequency group was divided into two duration groups: two minutes and ten minutes. Elution samples were measured daily using flow injection analysis. After one week of elution, ultrasound treatments were done daily until each group's average concentration fell below those of non-ultrasound control groups. After elution testing, compression testing determined mechanical properties. Paired t-tests were used to compare daily elution amounts to baseline values. Univariate ANOVAs were used to test for effects of both frequency and treatment duration on antibiotic elution amounts and on mechanical properties. All ultrasound treatments resulted in significant increases in antibiotic elution. Frequency and duration had significant effects of increasing antibiotic elution (p < 0.001). The kHz group produced significantly greater antibiotic elution than the MHz group (p < 0.001). The 10-minute duration produced significantly greater antibiotic elution than the two-minute duration (both p < 0.001). Frequency and duration did not have significant effects on yield stress (p = 0.841 and p = 0.179, respectively). Frequency had a significant effect (p = 0.024) on modulus, but duration did not (p = 0.136). Ultrasound frequency and treatment duration significantly affect antibiotic elution from PMMA which may be helpful for treatment of periprosthetic joint infections during revision arthroplasty.

Effects of ultrasound frequency and application time prior to deep-fat frying on quality aspects of fried potato strips

Abstract It is well known that edible oil consumption and saturated fat intake in high amount are individually associated with important health problems such as obesity, coronary heart disease, and cancer. In recent years, ultrasound application prior to deep-fat frying has been proposed as an innovative emerging technology to reduce oil uptake. The objective of this study was to investigate the influence of various ultrasound frequency-time combinations on quality characteristics of potato strips during deep-fat frying. Results indicated that the potato strips subjected to ultrasonic waves at the frequency of 40 kHz for 30 min, exhibited the highest moisture diffusivity, resulting in the highest reduction in oil uptake (23.18%) among all the samples. Additionally, the ultrasound combined frequencies of 28 kHz (for 20 min) and 40 kHz (for 10 min) showed the best performance in reducing the shrinkage of fried products. Moreover, ultrasound frequency of 40 kHz for 30 min and also combined frequencies of 28 kHz (for 15 min) and 40 kHz (for 15 min) increased the apparent density of samples. In summary, by considering proper ultrasound frequency-time combinations, ultrasound application before deep-fat frying can be a promising approach to decrease oil uptake and shrinkage of fried potato strips.

Modeling of sonochemistry in water in the presence of dissolved carbon dioxide

CO2 capture and utilization (CCU) is a process that captures CO2 emissions from sources such as fossil fuel power plants and reuses them so that they will not enter the atmosphere. Among the various ways of recycling CO2, reduction reactions are extensively studied at lab-scale. However, CO2 reduction by standard methods is difficult. Sonochemistry may be used in CO2 gas mixtures bubbled through water subjected to ultrasound waves. Indeed, the sonochemical reduction of CO2 in water has been already investigated by some authors, showing that fuel species (CO and H2) are obtained in the final products. The aim of this work is to model, for a single bubble, the close coupling of the mechanisms of bubble dynamics with the kinetics of gas phase reactions in the bubble that can lead to CO2 reduction. An estimation of time-scales is used to define the controlling steps and consequently to solve a reduced model. The calculation of the concentration of free radicals and gases formed in the bubble is undertaken over many cycles to look at the effects of ultrasound frequency, pressure amplitude, initial bubble radius and bubble composition in CO2. The strong effect of bubble composition on the CO2 reduction rate is confirmed in accordance with experimental data from the literature. When the initial fraction of CO2 in the bubble is low, bubble growth and collapse are slightly modified with respect to simulation without CO2, and chemical reactions leading to CO2 reduction are promoted. However, the peak collapse temperature depends on the thermal properties of the CO2 and greatly decreases as the CO2 increases in the bubble. The model shows that initial bubble radius, ultrasound frequency and pressure amplitude play a critical role in CO2 reduction. Hence, in the case of a bubble with an initial radius of around 5 μm, CO2 reduction appears to be more favorable at a frequency around 300 kHz than at a low frequency of around 20 kHz. Finally, the industrial application of ultrasound to CO2 reduction in water would be largely dependent on sonochemical efficiency. Under the conditions tested, this process does not seem to be sufficiently efficient.

Effect of ultrasound frequency on the Nakagami statistics of human liver tissues.

The analysis of the backscattered statistics using the Nakagami parameter is an emerging ultrasound technique for assessing hepatic steatosis and fibrosis. Previous studies indicated that the echo amplitude distribution of a normal liver follows the Rayleigh distribution (the Nakagami parameter m is close to 1). However, using different frequencies may change the backscattered statistics of normal livers. This study explored the frequency dependence of the backscattered statistics in human livers and then discussed the sources of ultrasound scattering in the liver. A total of 30 healthy participants were enrolled to undergo a standard care ultrasound examination on the liver, which is a natural model containing diffuse and coherent scatterers. The liver of each volunteer was scanned from the right intercostal view to obtain image raw data at different central frequencies ranging from 2 to 3.5 MHz. Phantoms with diffuse scatterers only were also made to perform ultrasound scanning using the same protocol for comparisons with clinical data. The Nakagami parameter–frequency correlation was evaluated using Pearson correlation analysis. The median and interquartile range of the Nakagami parameter obtained from livers was 1.00 (0.98–1.05) for 2 MHz, 0.93 (0.89–0.98) for 2.3 MHz, 0.87 (0.84–0.92) for 2.5 MHz, 0.82 (0.77–0.88) for 3.3 MHz, and 0.81 (0.76–0.88) for 3.5 MHz. The Nakagami parameter decreased with the increasing central frequency (r = −0.67, p < 0.0001). However, the effect of ultrasound frequency on the statistical distribution of the backscattered envelopes was not found in the phantom results (r = −0.147, p = 0.0727). The current results demonstrated that the backscattered statistics of normal livers is frequency-dependent. Moreover, the coherent scatterers may be the primary factor to dominate the frequency dependence of the backscattered statistics in a liver.

Empirical Mode Decomposition of Ultrasound Imagingfor Gain-Independent Measurement on Tissue Echogenicity: A Feasibility Study

Empirical mode decomposition (EMD) is an adaptive method for decomposing a signal into intrinsic mode functions (IMFs).This study explored using EMD of ultrasound imaging for gain-independent measurements on tissue echogenicity. The IMF-based echogenicity ratio (IER) was proposed using the first (C1) and second IMFs (C2) of ultrasound radiofrequency data. Experiments on lipid phantoms were conducted to investigate the practical performance of IER. Phantoms with lipid concentrations 0%–30% (n = 36) were scanned using a clinical ultrasound scanner to acquire the radiofrequency data under different gains (12–33 dB) for EMD and IER calculations. Experiments on a tissue-mimicking phantom were further performed using the same ultrasound system and data acquisition procedure to investigate the effect of ultrasound frequency on the IER at5–8 MHz.Experimental results showed that the IER measured under 33-dB gain decreased from 6.65 ± 0.23 to 3.97 ± 0.10 when the lipid concentrations were increased from 0% to 30%. When 12-dB gain was used, the IER decreased from 6.21 ± 0.29 to 3.39 ± 0.07. However, whenincreasing the frequency, the IER had a mean decreasing rate of −8.67% per MHz, which was lower than those of the C1 and C2 intensities.The proposed IER may allow gain-independent measurement on tissue echogenicity.

Effects of ultrasound pretreatment on enzymolysis of sodium caseinate protein: Kinetic study, angiotensin-converting enzyme inhibitory activity, and the structural characteristics of the hydrolysates

Effects of ultrasound frequency and power density on enzymolysis of sodium caseinate (NaCas) and on the structure of the protein hydrolysate were studied. Enzymolysis kinetics, angiotensin-I converting enzyme (ACE) inhibitory activity, atomic force microscopy (AFM), scanning electron microscopy (SEM), intrinsic fluorescence and the circular dichroism (CD) were determined. Ultrasound significantly (p < .05) increased the degree of hydrolysis (DH), conversion rates of protein, ACE inhibitory activity and the apparent breakdown rate (kA) but decreased the apparent constant (kM). AFM revealed that sonication increased the protein particles diameters, and Rq and Ra values. Fluorescence spectra and SEM images show increases in surface areas of NaCas. CD spectra revealed increases in β-sheet, β-turn and random coil by 20, 5.33 and 5.91%, respectively, and decreased α-helix by 8.82%. Overall, ultrasound successfully improved enzymolysis of NaCas and release more ACE inhibitory activity due to the increases in specific surface area of protein molecule. Practical applications NaCas is a functional ingredient widely used in foods industry, that is, it has beneficial effects on lowering blood pressure by producing ACE inhibitory peptides. Effects of ultrasound frequency and power density were performed to improve the enzymolysis of NaCas and the release of ACE inhibitory peptides. The mechanism of ultrasound on releasing of ACE inhibitory peptides was studied by monitoring the changes in protein structure. Generally, sonication remarkably provided a good reference about the enzymolysis of NaCas and the ACE inhibitory activity in polypeptides industries.

Sonofragmentation: Effect of Ultrasound Frequency and Power on Particle Breakage

This paper investigates, for the first time, the breaking mechanism of particles exposed to implosions of stable and transient cavitation bubbles via Kapur function analysis. The effect of ultrasonic frequencies of 30–1140 kHz and powers of 4–200 W on particle breakage of paracetamol crystals was studied. The dominant cavitation bubble type was defined via sonoluminescence measurements. The breakage rate of seed crystals with a median size of 75 μm was found to be independent of the applied power when ultrasonically generated stable cavitation bubbles were generated. Furthermore, a particle size threshold of ca. 35 μm was observed. The particle size could not be reduced below this size regardless of the applied power or frequency. For transient bubbles, in contrast, higher powers lead to considerably smaller particles, with no threshold size within the investigated power range. The Kapur function analysis suggests that stable bubbles are more efficient than transient bubbles to break coarse particles with...

Optimisation of ultrasound exposure parameters for extravasation and drug delivery using submicron cavitation nuclei

Sub-micron cavitation nuclei with the ability to passively extravasate through the leaky tumor vasculature have been shown to enhance both extravasation and penetration of pharmaceuticals in tumors. The aim of the present work is to optimize the acoustic parameters and maximize drug delivery mediated by cavitational microstreaming. Either lipid-shell microbubbles, or gas-stabilizing polymeric submicron cups of mean diameter 480 nm are co-administered with a model drug through a flow channel formed in agarose gel. The effect of ultrasound frequency, pressure amplitude, pulse duration, duty cycle, and pulse repetition frequency on the delivery of the drug is first evaluated, using both a single-layer and a dual-layer flow phantom that better represents the leaky tumor vasculature and dense extracellular matrix. The optimal parameters at 0.5 MHz and 1.6 MHz are then selected and used to deliver an oncolytic virus, genetically modified to express the RFP reporter gene, thus allowing the quantification of the ...

Characterization of delaminations in composite laminates by laser ultrasonics

Abstract The influence of delaminations in the anisotropic carbon fiber reinforced plastics (CFRP) on laser- generated ultrasound is investigated. A 3D-finite element method is used to simulate the propagation of ultrasonic waves in CFRP with delaminations. The asymmetric properties and distortions as well as the wave reflection and attenuation at delamination interfaces are clearly shown. Measurements on CFRP specimens with circular delaminations above 2 mm in diameter are imaged by C-scans and correlated to the modeling results. The effects of ultrasound frequency, defect size and depth location are discussed. The results show that it is possible to decrease the influence of anisotropy in CFRP composites by choosing appropriate ultrasonic frequencies and controlling the laser parameters.

The role of ultrasound in pharmaceutical production: sonocrystallization.

The main aim of this review was to develop a critical discussion of the key role ultrasound (US) can play on the production of active pharmaceutical ingredients (APIs) by discussing the versatile effect this type of energy produces. The different crystallization techniques that can be assisted and improved by US are discussed in the light of the available US devices and the effect pursued by application of US energy. Simple and complex analytical methods to monitor API changes are also discussed. The countless achievements of API US-assisted production are summarized in a table, and outstanding effects such as narrower particle size distribution; decreased particle size, induction time, metastable zone and supersaturation levels; or a solubility increase are critically discussed. The indisputable advantages of sonocrystallization over other ways of API production have been supported on multiple examples, and pending goals in this field (clarify the effect of US frequency on crystallization, know the mechanism of sonocrystallization, determine potential degradation owing to US energy, avoid calculation of the process yield by determining the concentration of the target drug remaining in the solution, etc.) should be achieved.

Investigation of the Effect of Ultrasound Parameters on Continuous Sonocrystallization in a Millifluidic Device

Continuous-flow crystallization of adipic acid in a millichannel chip equipped with a piezoelectric element is presented and investigated experimentally and numerically. A single, straight channel chip (cross section: 2 mm × 5 mm, length: 76 mm) made of glass, which is ultrasonically transparent, was designed and fabricated. The piezoelectric element allows studying the effect of different ultrasound frequencies in the kHz to MHz range. Ultrasound was applied in burst mode to reduce heating; this allowed operating at higher levels of input power. To accurately control the temperature of the fluid, Peltier elements were used to cool the bottom and top surfaces of the chip. Crystallization was performed in isothermal conditions, ensuring that the temperature and in turn the supersaturation were kept uniform along the channel. The effect of ultrasound frequency and sonication time was studied. Crystal size distributions at different operating conditions were obtained by laser diffraction. The distributions w...