Microbubble Formation Research Articles

Formation of composite material based on proteins, chitosan and nanotubes by nanosecond laser pulses

Aqueous dispersions with albumin, collagen, chitosan and single-walled carbon nanotubes (SWCNTs) in different combinations were studied. It was found, that an increase in the fluence above threshold leads to a significant increasing in the total absorption of radiation, moreover the main part of the energy was taken up by the SWCNTs. Thus, the thermal effect on proteins and chitosan decreased. This was confirmed by the nonlinear absorption coefficients, which were determined for the studied aqueous dispersions. Low threshold values of fluence for albumin 0.006 J/cm2 and collagen 0.009 J/cm2 are due to the onset of the denaturation process. This parameter increased up to ~0.05 J/cm2 after addition of SWCNTs that was caused by the formation of microbubbles due to the water evaporation from the heating of nanotubes. The reverse situation occurs in samples with chitosan (0.2 J/cm2) in which there was no denaturation. Adding SWCNTs leads to a decrease in the threshold fluence threshold to 0.15 J/cm2, which can be explained by the rapid heat transfer from nanotubes compared with chitosan. It was established, that optimal energy density range from 1 to 50 J/cm2 for the formation of a composite material using laser pulses with duration 16 ns.

Novel Preparation of Monodisperse Microbubbles by Integrating Oscillating Electric Fields with Microfluidics.

Microbubbles generated by microfluidic techniques have gained substantial interest in various industries such as cosmetics, food engineering, and the biomedical field. The microfluidic T-junction provides exquisite control over processing parameters, however, it relies on pressure driven flows only; therefore, bubble size variation is limited especially for viscous solutions. A novel set-up to superimpose an alternating current (AC) oscillation onto a direct current (DC) field is invented in this work, capitalising on the possibility to excite bubble resonance phenomenon and properties, and introducing relevant parameters such as frequency, AC voltage, and waveform to further control bubble size. A capillary embedded T-junction microfluidic device fitted with a stainless-steel capillary was utilised for microbubble formation. Furthermore, a numerical model of the T-junction was developed by integrating the volume of fluid (VOF) method with the electric module; simulation results were attained for the formation of the microbubbles with a particular focus on the flow fields along the detachment of the emerging bubble. Two main types of experiments were conducted in this framework: the first was to test the effect of applied AC voltage magnitude and the second was to vary the applied frequency. Experimental results indicated that higher frequencies have a pronounced effect on the bubble diameter within the 100 Hz and 2.2 kHz range, whereas elevated AC voltages tend to promote bubble elongation and growth. Computational results suggest there is a uniform velocity field distribution along the bubble upon application of a superimposed field and that microbubble detachment is facilitated by the recirculation of the dispersed phase. Furthermore, an ideal range of parameters exists to tailor monodisperse bubble size for specific applications.

Preparation and characterization of perfluorocarbon microbubbles using Shirasu Porous Glass (SPG) membranes

Microbubbles are increasingly used in several fields, such as medical imaging for enhanced contrast ultrasound imaging. Theses microbubbles usually consist of a gas core stabilized by surfactant molecules. In this study, a technique using Shirasu Porous Glass (SPG) membranes was used to produce perfluorocarbon microbubbles. The microbubbles obtained were characterized by their size, size distribution, and stability. The effect of several parameters on the microbubble's size was investigated related to the process (transmembrane pressure, ΔP, bubble point pressure, PBP, shear stress, τw), membrane pore size, Dp, and formulation (gas, surfactants in the aqueous phase). The transmembrane pressure nor the shear stress (τw) had influence on the microbubble's size or size distribution for ΔP/PBP <1.5. The decrease of the membrane pore size from 1.1, 0.5, to 0.2 μm led to lower microbubble size 13.3, 6.36, and 4.42 μm, respectively, which was associated with higher size distribution 16%, 24% and 31%, respectively due to the higher Laplace pressure exerted on smaller microbubbles leading to their destabilization. With the 1.1 μm pore size membrane, perfluorocarbon microbubbles were obtained with a diameter of 13.3 μm and coefficient of variation (CV) of 16% when stabilized by sodium dodecyl sulfate (SDS), 15.6 μm with CV% of 23% when stabilized by Tween20, and 16.5 μm with CV% of 26% when stabilized by Polyoxyethylene (40) stearate (PEG40S). These low CV were indication of monodispersity. Perfluorocarbon microbubbles had a smaller size than air microbubbles due to the lower surface tension that decreased the retention force, keeping the microbubbles at the pore opening. The stability study showed that the perfluorocarbon gas greatly increased the lifetime of the microbubbles with a slight increase in size of 1.3 after 90 s compared to 2.2 for air microbubbles. Overall, the membrane technique proved to be an effective, controlled and reproducible method to produce perfluorocarbon microbubbles at a high rate ∼0.6 − 1.5 × 10+10 microbubbles/min. The key factor that determines the microbubbles formation is the adsorption kinetics of the surfactant at the new gas–liquid interface at the pore opening.

Growth dynamics of microbubbles on microcavity arrays by solvent exchange: Experiments and numerical simulations

Solvent exchange is a flow process to induce a transient oversaturation for forming nanobubbles or nanodroplets on solid surfaces by displacing the solution of gases or droplet liquids with a controlled flow of a poor solvent. In this work, we experimentally and numerically investigate the effect of the flow rate and other control parameters on the formation of microbubbles on hydrophobic cavity arrays during the solvent exchange process. We find that the growth rate, location, and number density of microbubbles are closely related to flow rate, solvent concentration, cavity distance, and spatial arrangement. Higher growth rates and number densities of the bubbles were obtained for faster solvent exchange flow rates. The competition of neighbouring growing bubbles for dissolved gas is greatly alleviated when the inter-cavity distance is increased from 13 μm to 40 μm. The effects of the flow rate and the cavity spacing on the bubble growth are in agreement with the observations from our three-dimensional numerical simulations. The findings reported in this work provide important insight into the formation of multiple interacting surface microbubbles under various flow conditions. The understanding may be extended to a smaller scale for the growth of surface nanobubbles during solvent exchange, which is much harder to visualize in experiments.

Effects of junction angle and gas pressure on polymer nanosphere preparation from microbubbles bursted in a combined microfluidic device with thin capillaries

This study describes polymethylsilsesquioxane (PMSQ) nanospheres preparation from microbubble bursting in a 100 μm capillaries embedded combined microfluidic device based on effects of junction angle and flow rate of liquid solution. The effects of the junction angle (Ø = 0°–60°) between the liquid and gas channels and the gas pressure ratios (50–400 kPa) are considered. The digital microscope results indicate that the microbubble size during the bubble generation process generally decreases with the increase of junction angle at the same flow rate and gas pressure. In addition, the nanosphere size in the combined microfluidic junction device with 100 μm capillaries decreases as junction angle increases with the same flow and gas pressure conditions. When junction angle is about 60°, there always exists the smallest nanosphere formation in the device with thin capillaries used. The microbubble formation in the device used in this work depends significantly on the gas pressure, and the combined microfluidic junction device with thin capillaries becomes a microbubble generation when N2 gas pressure is greater than 50 kPa at the same junction angle and liquid flow rate. Furthermore, the resulting microbubble and polymer nanosphere size in the device used decreases with an increase of N2 gas pressure. To evaluate chemical structure of the polymers used before and after the microfluidic processing, PMSQ raw materials and the resultant Polymer nanospheres obtained were also characterised using an FTIR spectroscopy. The understanding of polymer nanosphere generation from microbubble bursting in the device with thin capillaries used could be very useful for many applications, such as cell transplantation in biomedical therapy, advanced therapeutic applications and food industry.

Foaming of blood in endovenous laser treatment.

This work is dedicated to a challenging issue of modern phlebology-establishment of a physical mechanism of the endovenous laser treatment (EVLT) against great saphenous vein incompetence (protuberant varicosities). Using optical and acoustical methods, we have studied the laser-induced formation of microbubbles in an aqueous solution of surface-active substances, serum, and blood directly in patients while conducting EVLT of the great saphenous vein in a clinical setting. We have used lasers with wavelengths 0.97 and 1.47μm. Their radiation was transmitted through a quartz-quartz polymer fiber 600μm in diameter. It has been found that in all cases, the laser beam with moderate power (1-10W) supplied through an optical fiber leads to the formation of micro-bubbled foam. It has been shown that laser exposure during EVLT induces blood boiling, which results in heating of the venous walls (thermal destruction of the intima) and provides effective foam occlusion of the blood vessels (hemostasis). Necessary and sufficient conditions for a successful EVLT are associated with the thermal destruction of intima and laser-induced foam hemostasis.

Microbubble-Triggered Spontaneous Separation of Transparent Thin Films from Substrates Using Evaporable Core-Shell Nanocapsules.

The spontaneous separation of a polymer thin film from a substrate is an innovative technology that will enable material recycling and reduce manufacturing cost in the film industry, and this can be applied in a wide range of applications, from optical films to wearable devices. Here, we present an unprecedented spontaneous strategy for separating transparent polymer films from substrates on the basis of microbubble generation using nanocapsules containing an evaporable material. The core-shell nanocapsules are prepared from poly(methyl methacrylate)-polyethyleneimine nanoparticles via the encapsulation of methylcyclohexane (MCH). A spherical nanostructure with a vaporizable core is obtained, with the heat-triggered gas release ability leading to the formation of microbubbles. Our separation method applied to transparent polymer films doped with a small amount of the nanocapsules encapsulating evaporable MCH enables spontaneous detachment of thin films from substrates via vacuum-assisted rapid vaporization of MCH over a short separation time, and clear detachment of the film is achieved with no deterioration of the inherent optical transparency and adhesive property compared to a pristine film.

On the mechanism of pulsed laser ablation of phthalocyanine nanoparticles in an aqueous medium

Laser ablation of phthalocyanine nanoparticles has potential for cancer treatment. The ablation is accompanied by the formation of microbubbles and the sublimation of nanoparticles. This was investigated in a liquid medium simulating tissue using optical-acoustic and spectral-luminescent methods. The thresholds for the appearance of microbubbles have been determined as a function of nanoparticle size. For the minimal size particles (80 nm) this threshold is equal to about 20–25 mJ cm−2 and for the maximal size particles (230 nm) this threshold is equal to about 7 mJ cm−2. It was estimated that the particle temperature at which bubbles arise is near 145 °С.

Ultrasound Cavitation/Microbubble Detection and Medical Applications

Over the past decades, different techniques have been investigated for detecting microbubbles. The purpose of this work is to review the state-of-the-art of medical microbubble detection along with therapeutic, monitoring, and diagnostic applications. The presence of microbubbles in the human body can be induced either through cavitation or exogenous introduction of bubbles. One of the effects of ultrasound is cavitation, or microbubble formation and collapse. Cavitation produces high pressures and temperatures, and microbubble expansion and then collapse close to cells can lead to cellular damage or hemorrhage in biological tissues. Cavitation is, in most cases, an undesired event in clinical diagnostic imaging. Considering that cavitation microbubble formation is largely unpredictable, ultrasound imaging may present a rare or yet unknown risk, particularly to fetuses and embryos. Although most therapeutic ultrasound modalities work based on physical and thermal effects of cavitation, the safety of treatment strongly depends on accurate knowledge of the location of the cavitation inception point. Cavitation detection is an important factor with respect to improving the safety of ultrasound imaging and therapy. It is essential to recognize the existence and location of cavitation inception points. In addition, the use of encapsulated microbubbles as contrast agents for diagnostic imaging, as vehicles for local drug or gene delivery, and as tools for microbubble and ultrasound therapy in thrombolysis has increased the demand for an accurate deep tissue microbubble detection technique. There have been many attempts to detect cavitation bubbles, but each contains its own limitations. There is no doubt that continuous discoveries and developments in microbubble detection modalities will lead to safer and more efficient therapeutic and diagnostic equipment.

Cerebral microembolism in the critically ill with acute kidney injury (COMET-AKI trial): study protocol for a randomized controlled clinical trial

BackgroundMicroembolism is a frequent pathological event during extracorporeal renal replacement therapy (RRT). Some previous data indicate that microemboli are generated in patients who are undergoing RRT and that these may contribute to increased cerebrovascular and neurocognitive morbidity in patients with end-stage renal disease. The current trial aims to quantify the microembolic load and respective qualitative composition that effectively reaches the intracerebral circulation in critically ill patients treated with different RRT modalities for acute kidney injury (AKI).Methods/designThe COMET-AKI trial is a prospective, randomized controlled clinical trial with a 2-day clinical assessment period and follow-up visits at 6 and 12 months. Consecutive critically ill patients with AKI on continuous renal replacement therapy (CRRT) scheduled for a switch to intermittent renal replacement therapy (IRRT) will be randomized to either switch to IRRT within the next 24 h or continued CRRT for an additional 24 h. Cerebral microembolic load will be determined at baseline, i.e., before switch (on CRRT for both groups) and on IRRT versus CRRT, whichever group they were randomized to. The primary endpoint is defined as the difference in mean total cerebral microemboli count during the measurement period on CRRT versus IRRT following randomization. Microemboli will be assessed within the RRT circuit by a 1.5-MHz ultrasound detector attached to the venous RRT tubing and cerebral microemboli will be measured in the middle cerebral artery using a 1.6-MHz robotic transcranial Doppler system with automatic classification of Doppler signals as solid or gaseous. In addition to Doppler measurements, patients will be examined by magnetic resonance imaging and neurocognitive tests to gain better understanding into the potential morphological and clinical consequences of embolization.DiscussionThe results of COMET-AKI may help to gain a better insight into RRT modality-associated differences regarding microbubble generation and the cerebral microembolic burden endured by RRT recipients. Furthermore, identification of covariates of microbubble formation and distribution may help to encourage the evolution of next-generation RRT circuits including machinery and/or filters.Trial registrationClinicalTrials.gov, ID: NCT02621749. Registered on 3 December 2015.

Regimes of Micro-bubble Formation Using Gas Injection into Ladle Shroud

Gas injection into a ladle shroud is a practical approach to produce micro-bubbles in tundishes, to promote inclusion removal from liquid steel. A semi-empirical model was established to characterize the bubble formation considering the effect of shearing action combined with the non-fully bubble break-up by turbulence. The model shows a good accuracy in predicting the size of bubbles formed in complex flow within the ladle shroud.

Fundamental Limits of Optical Tweezer Nanoparticle Manipulation Speeds.

Optical tweezers are a noncontact method of 3D positioning applicable to the fields of micro- and nanomanipulation and assembly, among others. In these applications, the ability to manipulate particles over relatively long distances at high speed is essential in determining overall process efficiency and throughput. In order to maximize manipulation speeds, it is necessary to increase the trapping laser power, which is often accompanied by undesirable heating effects due to material absorption. As such, the majority of previous studies focus primarily on trapping large dielectric microspheres using slow movement speeds at low laser powers, over relatively short translation distances. In contrast, we push nanoparticle manipulation beyond the region in which maximum lateral movement speed is linearly proportional to laser power, and investigate the fundamental limits imposed by material absorption, thus quantifying maximum possible speeds attainable with optical tweezers. We find that gold and silver nanospheres of diameter 100 nm are limited to manipulation speeds of ∼0.15 mm/s, while polystyrene spheres of diameter 160 nm can reach speeds up to ∼0.17 mm/s, over distances ranging from 0.1 to 1 mm. When the laser power is increased beyond the values used for these maximum manipulation speeds, the nanoparticles are no longer stably trapped in 3D due to weak confinement as a result of material absorption, heating, microbubble formation, and enhanced Brownian motion. We compared this result to our theoretical model, incorporating optical forces in the Rayleigh regime, Stokes' drag, and absorption effects, and found good agreement. These results show that optical tweezers can be fast enough to compete with other common, serial rapid prototyping and nanofabrication approaches.

Micro-bubble Formation under Non-wetting Conditions in a Full-scale Water Model of a Ladle Shroud/Tundish System

Micro-bubble Formation under Non-wetting Conditions in a Full-scale Water Model of a Ladle Shroud/Tundish System

Nanobubbles generation in a high-rate hydrodynamic cavitation tube

Gas dispersion parameters (air holdup-ɛg, superficial air velocity-Jg and bubble surface area flux-Sb) and especially the concentration of formed nanobubbles in a hydrodynamic cavitation tube were measured. Best results were obtained at 30% air/liquid volume ratio; 49 mN m−1 air/liquid interfacial tension resulting in an air holdup of 16%, a Jg of 0.87 cm s−1, a Sb of 85 s−1 and a nanobubbles (230–280 nm) concentration of 6.4 × 108 NBs mL−1. The lower the air/liquid interfacial tension, the higher the air holdup; this proceed by assisting cavitation and formation of micro and nano-sized bubbles. Data obtained are discussed in terms of solution, hydrodynamics and interfacial phenomena. Main mechanisms involving the role of the nanobubbles and their interactions with solids and bigger bubbles were envisaged. It is believed that these findings are important because of the need for techniques and devices producing nanobubbles at low cost and high rate. This work shows that the cavitation tube studied has a high potential, due to the wide size of bubbles formed, high bubble surface flux obtained and especially the generation of a high concentration of nanobubbles. These bubbles are very important in modern flotation of mineral fines and in pollutant separation in wastewater treatment and some examples are shown and discussed.

Investigation of morphological, structural, and mechanical characteristics of Zircaloy-4 irradiated with 3.5 MeV hydrogen ions beam

Zircaloy-4 specimens were irradiated with 3.5 MeV hydrogen ions (dose range: 1 × 1013 H+1 cm−2 to 1 × 1015 H+1 cm−2) using a Pelletron accelerator. FESEM studies reveal formation of hydrogen micro-bubbles, bubbles induced blisters of irregular shapes, and development of cracks on the specimen surface, as in the case of pure zirconium. However, for the highest irradiation dose of 1 × 1015 H+1 cm−2, agglomeration of flower-shape blisters is observed. XRD analysis shows that the most preferentially oriented crystallographic plane is (0 0 4) with texture coefficient values 1.832–2.308 depending on the ions dose. Its diffraction peak intensity first decreases with the increase in ions dose up to 5 × 1013 H+1 cm−2 and later increases up to 1 × 1015 H+1 cm−2. Opposite is found in case of diffraction peak width. Crystallite size and lattice strain determined by Williamson–Hall analysis display a linear relationship between the two with positive slope. Mechanical strength, namely yield stress (YS), ultimate tensile strength (UTS), and fracture stress (FS), increases sharply with ions dose up to 5 × 1013 H+1 cm−2. For 1 × 1014 H+1 cm−2 dose there is a sudden drop of stress to a lowest value and then a slow steady increase in stress up to the highest dose 1 × 1015 H+1 cm−2. Same pattern is followed by uniform elongation and total elongation. All three stress parameters YS, UTS, and FS follow Inverse Hall–Petch relation.

On-chip microfluidic generation of monodisperse bubbles for liquid interfacial tension measurement

A novel microfluidic method for measuring liquid interfacial tension using monodisperse microbubbles generated in situ has been proposed. Instead of bulky gas supply used in traditional microfluidic devices, microbubbles are efficiently generated via water electrolysis in the devices. Since the bubble formation frequency is related to the interfacial tension of liquids used, thus, precisely measuring the interfacial tension of liquids in microfluidics can be achieved. In addition, it is found that during the microbubble formation, the electrochemical potential fluctuates regularly at controlled electrolysis current, and the fluctuating period depends on the microbubble generation rate. Therefore, the change in electrochemical potential can be directly used to monitor the bubble formation process, which avoids the use of an external optical detection system. As demonstration, the interfacial tension of isopentanol solutions with different concentrations was measured, and the results show good agreement with the ones obtained using the maximum bubble pressure method, confirming the accuracy of the present method. The proposed strategy offers a simple, low cost and accurate solution to measure the liquid interfacial tension confined in microfluidic channels. The present platform is easily constructed and facilely manipulated in common laboratories, which is expected to be widely used in microfluidic-based research and application fields.

Dynamic formation and scaling law of hollow droplet with gas/oil/water system in dual‐coaxial microfluidic devices

Based on the one‐step microfluidic method of producing hollow droplet with thin film, this article studies the effect of water and oil flow rate, gas pressure, and viscosity of aqueous phase on the dynamic formation and size of hollow droplet by analyzing large amounts of data acquired automatically. The results show that the filling stage of hollow droplet is similar to that of microbubble formation, while the necking stage is similar to that of droplet formation process. Furthermore, based on the data and mathematical model describing droplet formation mechanism, a filling stage model including Capillary number of continuous phase is developed. Considering the dynamic interface breakup and displacement of droplet in necking stage, a necking stage model is developed. The results show that the model results considering filling and necking stage fit well with the experimental data, and the relative error is less than 5%. Finally, the same model with parameters is used to predict the size of hollow droplet with other systems and devices, and the model is proved to be relative precise in our experimental conditions. The results presented in this work provide a more in‐depth understanding of the dynamic formation and scaling law of hollow droplet with G/L/L systems in microfluidic devices. © 2017 American Institute of Chemical Engineers AIChE J, 64: 730–739, 2018

Ultrasound-to-plastic optical fiber coupling as an acoustic source probe.

An integrated ultrasonic detection system that consists of emission and detection has been proposed and demonstrated experimentally. The proposed emission source is based on plastic optical fiber (POF). In order to promote the coupling of ultrasound-to-POF, and the end of the POF is heated to form a circular pedestal. A homemade fiber Fabry-Perot interferometer is employed to evaluate the coupling efficiency of ultrasound-to-POF. The sensing head is spliced with a short section of hollow-core fiber and single-mode fiber, resulting in an air microbubble formation by discharging. The experimental results show that ultrasound can be transmitted effectively in a narrow space using the coupling method, and the compact sensor also presents a considered sensitivity for ultrasonic detection. This all-fiber ultrasonic interrogation can be integrated as a system for the application in the bioimaging field, especially the organism body.

Formation Characteristics of microbubble in a co-flowing liquid in microfluidic chip

Microbubble formation under the surroundings of co-flowing liquid (CFL) in a specially designed microfluidic chip was investigated. A new microfluidic chip utilizing several capillary tubes was fabricated to provide the co-axial flowing conditions. An experiment platform based on high-speed microscopic camera system (HSMCS) was designed and set up. The influences of nitrogen pressure and liquid flow rate on detachment distance and volume variation of target microbubble were studied experimentally. Experimental data and analysis results indicated that the detachment distance of target microbubble decreases substantially as the rate of CFL increases while it is almost independent of nitrogen pressure. Additionally, the volume growth rate of target microbubble almost keeps constant under fixed nitrogen pressure. The present study provides empirical references for studies in microbubble formation in microfluidic chips which contributes to realize the accurate controllability in diameter and size distribution of microbubble.

Sequential and selective localized optical heating in water via on-chip dielectric nanopatterning.

We study the use of nanopatterned silicon membranes to obtain optically-induced heating in water. We show that by varying the detuning between an absorptive optical resonance of the patterned membrane and an illumination laser, both the magnitude and response time of the temperature rise can be controlled. This allows for either sequential or selective heating of different patterned areas on chip. We obtain a steady-state temperature of approximately 100 °C for a 805.5nm CW laser power density of 66 µW/μm2 and observe microbubble formation. The ability to spatially and temporally control temperature on the microscale should enable the study of heat-induced effects in a variety of chemical and biological lab-on-chip applications.