Microbubble Size Research Articles

Microfluidic fabrication of monodisperse microcapsules with gas cores.

A facile strategy for efficient and continuous fabrication of monodisperse gas-core microcapsules with controllable sizes and excellent ultrasound-induced burst performances is developed based on droplet microfluidics and interfacial polymerization. Monodisperse gas-in-oil-in-water (G/O/W) double emulsion droplets with a gas core and monomer-contained oil layer are fabricated in the upstream of a microfluidic device as templates, and then water-soluble monomers are added into the aqueous continuous phase in the downstream to initiate rapid interfacial polymerization at the O/W interfaces to prepare monodisperse gas-in-oil-in-solid (G/O/S) microcapsules with gas cores. The sizes of both microbubbles and G/O/W droplet templates can be precisely controlled by adjusting the gas supply pressure and the fluid flow rates. Due to the very thin shells of G/O/S microcapsules fabricated via interfacial polymerization, the sizes of the resultant G/O/S microcapsules are almost the same as those of the G/O/W droplet templates, and the microcapsules exhibit excellent deformable properties and ultrasound-induced burst performances. The proposed strategy provides a facile and efficient route for controllably and continuously fabricating monodisperse microcapsules with gas cores, which are highly desired for biomedical applications.

Experimental and Computational Investigation of Microbubble Formation in a Single Capillary Embedded T-junction Microfluidic Device.

In recent years, there has been a notable increase in the interest toward microfluidic devices for microbubble synthesis. The upsurge can be primarily attributed to the exceptional control these devices offer in terms of both the size and the size distribution of microbubbles. Among various microfluidic devices available, capillary-embedded T-junction microfluidic (CETM) devices have been extensively used for the synthesis of microbubbles. One distinguishing feature of CETM devices from conventional T-junction devices is the existence of a wall at the right-most end, which causes a backflow of the continuous phase at the mixing zone during microbubble formation. The back flow at the mixing zone can have several implications during microbubble formation. It can possibly affect the local velocity and shearing force at the mixing zone, which in turn can affect the size and production rate of the microbubbles. Therefore, in this work, we experimentally and computationally understand the process of microbubble formation in CETM devices. The process is modeled using computational fluid dynamics (CFD) with the volume-of-fluid approach, which solves the Navier-Stokes equations for both the gas and liquid phases. Three scenarios with a constant liquid velocity of 0.053 m/s with varying gas velocity and three with a constant gas velocity of 0.049 m/s at different liquid velocities were explored. Increase in the liquid and gas velocity during microbubble formation was found to enhance production rates in both experiments and simulations. Additionally, the change in microbubble size with the change in liquid velocity was found to agree closely with the findings of the simulation with a coefficient of variation of 10%. When plotted against the time required for microbubble generation, the fluctuations in the pressure showed recurrent crests and troughs throughout the microbubble formation process. The understanding of microbubble formation in CETM devices in the presence of backflow will allow improvement in size reduction of microbubbles.

Controlled Tempering of Lipid Concentration and Microbubble Shrinkage as a Possible Mechanism for Fine-Tuning Microbubble Size and Shell Properties.

The acoustic response of microbubbles (MBs) depends on their resonance frequency, which is dependent on the MB size and shell properties. Monodisperse MBs with tunable shell properties are thus desirable for optimizing and controlling the MB behavior in acoustics applications. By utilizing a novel microfluidic method that uses lipid concentration to control MB shrinkage, we generated monodisperse MBs of four different initial diameters at three lipid concentrations (5.6, 10.0, and 16.0 mg/mL) in the aqueous phase. Following shrinkage, we measured the MB resonance frequency and determined its shell stiffness and viscosity. The study demonstrates that we can generate monodisperse MBs of specific sizes and tunable shell properties by controlling the MB initial diameter and aqueous phase lipid concentration. Our results indicate that the resonance frequency increases by 180-210% with increasing lipid concentration (from 5.6 to 16.0 mg/mL), while the bubble diameter is kept constant. Additionally, we find that the resonance frequency decreases by 260-300% with an increasing MB final diameter (from 5 to 12 μm), while the lipid concentration is held constant. For example, our results depict that the resonance frequency increases by ∼195% with increasing lipid concentration from 5.6 to 16.0 mg/mL, for ∼11 μm final diameter MBs. Additionally, we find that the resonance frequency decreases by ∼275% with increasing MB final diameter from 5 to 12 μm when we use a lipid concentration of 5.6 mg/mL. We also determine that MB shell viscosity and stiffness increase with increasing lipid concentration and MB final diameter, and the level of change depends on the degree of shrinkage experienced by the MB. Specifically, we find that by increasing the concentration of lipids from 5.6 to 16.0 mg/mL, the shell stiffness and viscosity of ∼11 μm final diameter MBs increase by ∼400 and ∼200%, respectively. This study demonstrates the feasibility of fine-tuning the MB acoustic response to ultrasound by tailoring the MB initial diameter and lipid concentration.

Removal of microplastics and refractory humic/fulvic – like components from landfill leachate using Coagulative Colloidal Gas Aphrons: Insights on dissolved organic matter fingerprints

Microplastics (<5 mm) are one of the most persistent and emerging pollutants found ubiquitously in the natural environment. Still, identifying the source of these pollutants is lacking. Landfill leachates are known to be a major pathway to transmit them in the environment. Yet, removing these microplastics from leachate is being another challenging task. This research work investigates the removal of microplastics, metal ions and refractory organic pollutants from landfill leachate using a unique technique known as coagulative colloidal gas aphrons (CCGA). The target microplastics chosen for this study are polyethylene terephthalate (PET), polystyrene (PST), polypropylene (PPL) and polyethylene (PEL) microplastics. The property of metastable with superior stability of CCGA was confined by various parameters such as surfactant solution, Fe (III) dosages, microplastic quantities, zeta potential, kinetics and size of microbubble. The excitation – emission matrix results help to understand the occurrence and removal of refractory humic, fulvic and tryptophan components. The removal efficiency of COD and DOC was found to be 86 and 84%, respectively. Here we show that the electrostatic attraction plays a significant role in removing microplastics and coagulation mechanism such as bridging, adsorption and sweeping performs a major role in treating ion concentration present in the leachate solution.

Dependence of sonoporation efficiency on microbubble size: An in vitro monodisperse microbubble study

Sonoporation is the process where intracellular drug delivery is facilitated by ultrasound-driven microbubble oscillations. Several mechanisms have been proposed to relate microbubble dynamics to sonoporation including shear and normal stress. The present work aims to gain insight into the role of microbubble size on sonoporation and thereby into the relevant mechanism(s) of sonoporation. To this end, we measured the sonoporation efficiency while varying microbubble size using monodisperse microbubble suspensions. Sonoporation experiments were performed in vitro on cell monolayers using a single ultrasound pulse with a fixed frequency of 1 MHz while the acoustic pressure amplitude and pulse length were varied at 250, 500, and 750 kPa, and 10, 100, and 1000 cycles, respectively. Sonoporation efficiency was quantified using flow cytometry by measuring the FITC-dextran (4 kDa and 2 MDa) fluorescence intensity in 10,000 cells per experiment to average out inherent variations in the bioresponse. Using ultra-high-speed imaging at 10 million frames per second, we demonstrate that the bubble oscillation amplitude is nearly independent of the equilibrium bubble radius at acoustic pressure amplitudes that induce sonoporation (≥ 500 kPa). However, we show that sonoporation efficiency is strongly dependent on the equilibrium bubble size and that under all explored driving conditions most efficiently induced by bubbles with a radius of 4.7 μm. Polydisperse microbubbles with a typical ultrasound contrast agent size distribution perform almost an order of magnitude lower in terms of sonoporation efficiency than the 4.7-μm bubbles. We elucidate that for our system shear stress is highly unlikely the mechanism of action. By contrast, we show that sonoporation efficiency correlates well with an estimate of the bubble-induced normal stress.

An investigation into the cytotoxic effects of microbubbles and their constituents on osteosarcoma and bone marrow stromal cells

BackgroundUltrasound-responsive microbubbles offer a means of achieving minimally invasive, localised drug delivery in applications including regenerative medicine. To facilitate their use, however, it is important to determine any cytotoxic effects they or their constituents may have. The aim of this study was to test the hypothesis that phospholipid-shelled microbubbles are non-toxic to human bone-derived cells at biologically-relevant concentrations. MethodsMicrobubbles were fabricated using combinations of 1,2-distearoyl-sn-glycero-3-phosphocholine (DSPC), 1,2-dibehenoyl-sn-glycero-3-phosphocholine (DBPC), polyoxyethylene(40) stearate (PEG40S) and 1,2-distearoyl-sn-glycero-3-phosphoethanolamine-N-[methoxy(polyethylene-glycol)-2000] (DSPE-PEG2000). Microbubble size and concentration were measured as a function of time and temperature by optical microscopy. Effects on MG63 osteosarcoma and human bone marrow stromal cells (BMSCs) were measured for up to 72 h by assay for viability, metabolic activity and proliferation. ResultsDBPC:DSPE-PEG2000 microbubbles were significantly more stable than DSPC:PEG40S microbubbles under all conditions tested. Serum-containing medium had no detrimental effect on microbubble stability, but storage at 37 °C compared to at 4 °C reduced stability for both preparations, with almost complete dissolution of microbubbles at times ≥24 h. DSPC:PEG40S microbubbles had greater inhibitory effects on cell metabolism and growth than DBPC:DSPE-PEG2000 microbubbles, with PEG40S found to be the principle inhibitory component. These effects were only evident at high microbubble concentrations (≥20% (v/v)) or with prolonged culture (≥24 h). Increasing cell-microbubble contact by inversion culture in a custom-built device had no inhibitory effect on metabolism. ConclusionsThese data indicate that, over a broad range of concentrations and incubation times, DBPC:DSPE-PEG2000 and DSPC:PEG40S microbubbles have little effect on osteoblastic cell viability and growth, and that PEG40S is the principle inhibitory component in the formulations investigated.

Dependence of sonoporation efficiency on microbubble size: An in vitro monodisperse microbubble study

Sonoporation is the process where intracellular drug delivery is facilitated by ultrasound-driven microbubble oscillations. Several mechanisms have been proposed to relate microbubble dynamics to sonoporation including shear and normal stress. The present work aims to gain insight into the role of microbubble size on sonoporation by varying the microbubble size of monodisperse microbubble suspensions. Sonoporation experiments were performed in vitro on cell monolayers at an ultrasound frequency of 1 MHz at varying acoustic pressures (250–750 kPa) and pulse length (10, 100, 1000 cycles). Sonoporation efficiency was quantified using flow cytometry by measuring the FITC-dextran (4 kDa and 2 MDa) fluorescence intensity in 10,000 cells per experiment. We demonstrate that the bubble oscillation amplitude is nearly independent of the equilibrium bubble radius at acoustic pressure amplitudes that induce sonoporation (≥500 kPa). However, we show that sonoporation efficiency is strongly dependent on the equilibrium bubble size and most efficiently induced by off-resonance 4.7-μm radius bubbles. These 4.7-μm bubbles are an order of magnitude more efficient than the polydisperse bubbles. We discuss that for our system shear stress is highly unlikely the mechanism of action, while we show that sonoporation efficiency correlates well with an estimate of the bubble-induced normal stress.

Tracking adoptive natural killer cells via ultrasound imaging assisted with nanobubbles.

The recent years has witnessed an exponential growth in the field of natural killer (NK) cell-based immunotherapy for cancer treatment. As a prerequisite to precise evaluations and on-demand interventions, the noninvasive tracking of adoptive NK cells plays a crucial role not only in post-treatment monitoring, but also in offering opportunities for preclinical studies on therapy optimizations. Here, we describe an NK cell tracking strategy for cancer immunotherapy based on ultrasound imaging modality. Nanosized ultrasound contrast agents, gas vesicles (GVs), were surface-functionalized to label NK cells. Unlike traditional microbubble contrast agents, nanosized GVs with their unique thermodynamical stability enable the detection of labeled NK cells under nonlinear contrast-enhanced ultrasound (nCEUS), without a noticeable impact on cellular viability or migration. By such labeling, we were able to monitor the trafficking of systematically infused NK cells to a subcutaneous tumor model. Upon co-treatment with interleukin (IL)-2, we observed a rapid enhancement in NK cell trafficking at the tumor site as early as 3h post-infusion. Altogether, we show that the proposed ultrasound-based tracking strategy is able to capture the dynamical changes of cell trafficking in NK cell-based immunotherapy, providing referencing information for early-phase monotherapy evaluation, as well as understanding the effects of modulatory co-treatment. STATEMENT OF SIGNIFICANCE: In cellular immunotherapies, the post-infusion monitoring of the living therapeutics has been challenging. Several popular imaging modalities have been explored the monitoring of the adoptive immune cells, evaluating their trafficking and accumulation in the tumor. Here we demonstrated, for the first time, the ultrasound imaging-based immune cell tracking strategy. We showed that the acoustic labeling of adoptive immune cells was feasible with nanosized ultrasound contrast agents, overcoming the size and stability limitations of traditional microbubbles, enabling dynamical tracking of adoptive natural killer cells in both monotherapy and synergic treatment with cytokines. This article introduced the cost-effective and ubiquitous ultrasound imaging modality into the field of cellular immunotherapies, with broad prospectives in early assessment and on-demand image-guided interventions.

Microbubble Intensification of Bioprocessing

Microbubbles are famed for their large surface area-to-volume ratio, with the promise of intensification of interfacial phenomena, highlighted by more rapid gas exchange. However, for bioprocessing, it has been recognised for many decades that surfactant-rich fermentation media hinders mass transfer and possibly other interfacial processes due to surfactant loading on the interface. This article focuses on the roles of microbubble size and bubble bank, dispersed microbubbles that are sufficiently small to be non-buoyant, in mediating other modes of interfacial transfer via collisions with microorganisms and self-assembled clusters of microorganisms and microbubbles. These provide a more direct route of mass transfer for product gases that can be released directly to the microbubble with ~104 faster diffusion rates than liquid mediated gas exchange. Furthermore, secreted external metabolites with amphoteric character are absorbed along the microbubble interface, providing a faster route for liquid solute transport than diffusion through the boundary layer. These mechanisms can be exploited by the emerging fields of symbiotic or microbiome engineering to design self-assembled artificial lichen dispersed structures that can serve as a scaffold for the selected constituents. Additionally, such designed scaffolds can be tuned, along with the controllable parameters of microbubble mediated flotation separations or hot microbubble stripping for simultaneous or in situ product removal. Staging the product removal thus has benefits of decreasing the inhibitory effect of secreted external metabolites on the microorganism that produced them. Evidence supporting these hypotheses are produced from reviewing the literature. In particular, recent work in co-cultures of yeast and microalgae in the presence of a dispersed bubble bank, as well as anaerobic digestion (AD) intensification with dispersed, seeded microbubbles, is presented to support these proposed artificial lichen clusters.

Disturbing bubbles in drop-on-demand piezo-acoustic inkjet printing

Drop-on-demand piezo-acoustic inkjet printing is the method of choice for high-frequency and high-precision droplet deposition. Microbubbles entrained in a piezo-driven silicon MEMS printhead disturb the acoustics of the microfluidic ink channel and, thereby, the jetting behavior. The strong deformations of the air-liquid interface at the nozzle exit may lead to an inward directed air jet with bubble pinch-off and the subsequent entrainment of an air bubble. Here, we use ultrafast x-ray phase-contrast imaging and direct numerical simulations to study the mechanisms underlying the bubble entrainment, where we demonstrate good agreement between experiments and numerics. The entrained bubbles were also visualized in the ink channel of the silicon printhead in a highly sensitive shortwave infrared (SWIR) imaging setup exploiting the optical window at 1550 nm. The infrared recordings show the rich phenomena of acoustically driven bubble dynamics inside the printhead. We also study the resonance behavior of the ink channel as a function of the microbubble size and number of bubbles through theoretical modeling and experiments. The system is modeled as a set of two coupled harmonic oscillators, one for the compliant ink channel and one for the microbubble and where we find excellent agreement between the predicted and measured eigenfrequencies.

Interactions of NaCl with frother surfactants in producing microbubbles through modifying air/water interfacial energy and interfacial charge

The interactions of NaCl with flotation frothers (i.e., weak surfactants) were investigated in the production of microbubbles at low frother concentrations far below their critical micelle concentrations. Two widely used flotation frothers, methyl isobutyl carbinol (MIBC) which is an alcohol-based frother and Dowfroth 250 (DF250) which is a polyglycol ether-based frother were studied. While in-situ measurements of microbubble number and size distribution were carried out to indicate the production of microbubbles, interfacial energy and interfacial charge were determined to understand the generation and stabilization of microbubbles. It was found that a synergy occurred between NaCl and the tested frothers in producing microbubbles. However, the significant synergistic effect was only observed at a low frother concentration. In the case of MIBC, the synergistic effect was weakened at the tested high MIBC concentrations of 16 and 40 mg/L. In the case of DF250, the synergy turned antagonistic as the addition of NaCl slightly enlarged the bubble size and significantly reduced the number of microbubbles at the tested high DF250 concentrations of 16 and 40 mg/L. The effects were explained through possible interactions of NaCl with interfacial water molecules and with the tested frothers as well as through the NaCl’s effect of compressing the electrical double layers of air bubbles.

Microbubble-enhanced HIFU therapy for vascularized tumors using Levovist contrast agent

High-intensity focused ultrasound (HIFU) has enormous potential in the treatment of cancers; however, there is still plenty of challenges associated with using acoustic energy to treat vascularized tumors. Among them, the blood flow cooling reduces the treatment efficiency significantly and results in a long treatment period. Various studies have shown that the HIFU improves cancer treatment by targeting the cancer tissue. Unfortunately, the issues related to vascularization have remained unsolved. In the present study, through a novel approach, a promising strategy is proposed by injecting Levovist contrast agent solution in the vascularized tumor. The complicated interaction between the Levovist microbubble (MB) and the ultrasonic waves is innovatively modeled by considering the coupled effect of HIFU wave propagation, fluid flow, MB oscillations, and transient heat transfer for a multi-layered porous model of liver tumor. The proposed strategy is evaluated in terms of the extent of irreversible TD and treatment duration. The results reflect the role of MB oscillation on the temperature rise, as injection of a 2 μm-MB during 15 s of HIFU sonication increases the temperature by 9.61% compared to no-MB condition. Meanwhile, the MB oscillation advances the irreversible damage, and tumor cells undergo thermal ablation by 48.94% earlier than the case with no-MB agent. Additionally, it is found that the MB size has a substantial effect on the amount of heat deposition. At an operating condition of 1.25 MHz and 10 W, the viscous power deposition for a 2 μm-MB is3.81 mW, while for a 50 μm-MB, it is reduced to 0.96 mW. On the contrary, the heat source due to the secondary acoustic power deposition is proportional to the MB size, as it increases from 60.5 mW for a 2 μm-MB to 180 mW for a 50 μm-MB, demonstrating a 2.97-fold increase. Eventually, an assessment of the extent of the necrotic area shows an increase at all frequencies by injecting an MB into the tumor area. At an operating condition of 1.5 MHz, oscillation of 2 μm-MB expands the necrotic area by 4.01% compared to the no-MB condition. Based on the obtained results, the injection of Levovist contrast agent solution in the vascularized tumor can be regarded as an effective method for reducing the treatment time and avoiding several sonication.

Delivery of sPD1 gene by anti-CD133 antibody conjugated microbubbles combined with ultrasound for the treatment of cervical cancer in mice

To explore new therapeutic options for cervical cancer, the inhibitory effect on cervical cancer of targeted CD133-loaded sPD1 gene microbubbles (MBs) combined with low-frequency ultrasound was studied and its mechanism was explored. We prepared microbubbles conjugated with anti-CD133 antibody to deliver the sPD1 gene and determined concentration, particle size, and potentials of MBs. In addition, we verified that CD133 targeted-MBs could specifically bind to U14 cervical cancer cells in vitro. A mouse model of subcutaneous xenograft cervical cancer was established and mice were divided into a control group, an non-targeted microbubble group, a CD133-MBs group, an sPD1-MBs group and a CD133/sPD1-MBs group. Compared with the control group, tumor growth was inhibited in each group, with the CD133/sPD1 group showing the strongest inhibitory effect after treatment. The tumor volume and weight inhibition rates in the CD133/sPD1-MBs group were 78.01% and 72.25% respectively, which were statistically different from the other groups (P < 0.05), and HE staining and TUNEL immunofluorescence showed necrosis and apoptosis in tumor tissue. Flow cytometry, lactate dehydrogenase, and indirect immunofluorescence experiments showed that T lymphocytes were activated and a large number of CD8-positive T cells infiltrated the tumor tissue after treatment, with the CD133/sPD1-MBs group showing the most prominent effects (P < 0.05). The combination of ultrasound with anti- CD133 antibody-conjugated microbubbles loaded with the sPD1 gene can inhibit the growth of cervical cancer, suggesting that the immunosuppressive microenvironment of the tumor is improved after treatment.

Experimental measurements on the microbubble characteristics and dissolved oxygen (DO) in water using single and twin-Venturi type microbubble generators

The aim of this paper is to develop low cost and low power consumption microbubble generator to improve the mass transfer of gas to liquid. Microbubble aeration used in aquaculture to improve dissolve oxygen level, water recycling through dissolved air flotation (DAF), oil refinement and reduction of skin friction on ship Hull. A single Venturi and 3 twin-Venturis microbubble generators are manufactured and tested in this study. Experimental data on microbubbles diameters distribution and dissolved oxygen are presented. The main conclusions are: i) the mean microbubbles diameters produced by twin-Venturi are smaller by 10 µm than single Venturi generator; ii) the dissolved oxygen concentration was higher for twin-Venturi microbubble generator; iii) the microbubbles size distribution from twin-Venturis have a narrower distribution which reduces the probability of bubbles coalesce as they have very close values of velocities; iv) the bubbles diameters and velocities increase with the height in the water tank.

Tuning microbubble-mediated endothelial drug delivery outcome with monodisperse microbubbles of different sizes

Microbubble-mediated drug delivery using polydisperse microbubbles has shown differences in drug delivery outcome due to the microbubble’s differences in size and, thus, acoustic response. The aim of this study was to investigate whether monodisperse microbubbles can achieve controllable sonoporation and tunnel formation. Using the Horizon microfluidics platform, monodisperse phospholipid-coated microbubbles were produced with radii of 1.25–3.5 μm. Single microbubble-endothelial cell interactions (n = 82) upon insonification at 2 MHz (200 kPa PNP, 10 cycles) were investigated in vitro using confocal microscopy and ultra-high-speed imaging (10Mfps). No cellular response was observed for the 3.5 μm microbubbles having excursion amplitudes (Rmax-R0) ranging from 0.3 to 0.6 μm. PI uptake and resealing pores were observed more often for the 1.5 μm microbubbles (50%) with excursion amplitudes ranging from 0.5 to 0.9 μm than for the other microbubble sizes. PI uptake and tunnel formation was most observed for the 1.25 μm microbubbles (46.6%; 0.4–0.6 μm excursion amplitudes) and least for the 3 μm microbubbles (4.2%; 1.0 μm excursion amplitude). No other cellular responses were observed for the 3 μm microbubbles. The excursion ratio (Rmax-Rmin/R0) better separated the tunnel formation events (&amp;gt;0.6) from other cellular responses (0.1–0.6). This study shows the importance of monodisperse microbubbles for tuning drug delivery.

Bubble formation by shearing-to-squeezing transition in a T-junction

A shearing-to-squeezing transition process for bubble formation in a T-junction was reported using microscopy and digital image technology. The investigations were conducted in a polydimethylsiloxane (PDMS) T-junction. According to the aspect ratio of air slug and bubble generation frequency, the bubbles generated in the microchannel were identified to three types, namely dispersed bubble, short-slug bubble and long-slug bubble. The corresponding modes of bubble formation were identified as shearing, transition and squeezing modes, respectively. Additionally, the microbubble size and generation frequency with various gas pressures and velocity of liquid flows in each mode were investigated. The relevant dimensional arguments were performed to characterize the microbubble formation process in the T-junction. A new scaling law, based on the formation mechanisms, was proposed to predict the size of the microbubbles and showed a good agreement with the experimental results.

Removal of ultrafine colloidal particles from shale gas fracturing flowback fluid by microbubble-intensified flocculation: Effect of microbubble size

Shale gas fracturing flowback fluid (FFF) is characterized as the hazardous wastewater with high viscosity, large displacement, and complex components, which is difficult to deal with. Flocculation has been proven to be the most extensively applied treatment process considering its effortless operation, low energy consumption, and comparatively high efficiency. However, efficient removal of ultrafine colloidal particles (<10 μm) from FFF still remains a big challenge since their extremely stable properties. Herein, microbubbles (MBs) were introduced into the flocculation reaction to enhance the flocculation performance. When the median particle diameter (d50) of MBs reached 0.97 μm (which matched the size of selected colloidal particles), the turbidity removal rate was as high as 91.93 % at 0.70 g/L flocculant dosage, which was superior to traditional stir flocculation without MBs (66.67 %). Under this condition, the mean floc size reached the maximum value of 64.77 μm at 30 s after adding the flocculant. Meanwhile, the floc fractal dimension was significantly improved and the flocs held more resilient, which was beneficial for solid-liquid separation. The MBs worked by the trapping and bridging functions. Consequently, microbubble-intensified flocculation provided an advantageous way for the effective removal of ultrafine colloidal particles in FFF by controlling the bubble size appropriately.

Venous chambers in clinical use for hemodialysis have limited capacity to eliminate microbubbles from entering the return bloodline: An in vitro study.

During hemodialysis (HD), blood passes through an extracorporeal circuit (ECC). To prevent air administration to the patient, a venous chamber (chamber) is located before the blood return. Microbubbles (MBs) may pass through the chamber and end up as microemboli in organs such as the brain and heart. This in vitro study investigated the efficacy of various chambers in MB removal. The in vitro recirculated setting of an ECC included an FX10 dialyzer, a dextran-albumin solution to mimic blood viscosity and chambers with different flow characteristics in clinical use (Baxter: AK98 and Artis, Fresenius: 5008 and 6008) and preclinical test (Embody: Emboless®). A Gampt BCC200 device measured the presence and size of MBs (20-500 μm). Percentage change of MBs was calculated: ΔMB%=100*(outlet-inlet)/inlet for each size of MB. Blood pump speed (Qb) was 200 (Qb200) or 300 (Qb300) ml/minute. Wilcoxon paired test determined differences. With Qb200 median ΔMB% reduction was: Emboless -58%, AK98 -24%, Fresenius 5008 -23%, Artis -8%, and Fresenius 6008 ± 0%. With Qb300 ΔMB% was: Emboless -36%, AK98 ± 0%, Fresenius 5008 ± 0%, Artis +25%, and Fresenius 6008 + 21%. The Emboless was superior to all other chambers with Qb200 and Qb300 (p < 0.001). Further, the Emboless with Qb300 still eliminated more MBs than all other chambers with Qb200 (p ≤ 0.003). The results from the present study indicate that flow characteristics of the chamber and the Qb are important factors to limiting exposure of MB to the return bloodline. The Emboless chamber reduced MBs more effective than those chambers in clinical use investigated.

Fiber Optic Ice Sensor for Measuring Ice Thickness, Type and the Freezing Fraction on Aircraft Wings

Ice accretion on an aircraft affects the aerodynamic performance of the wings by disrupting the airflow, increasing drag, and altering its flight characteristics, leading to a main or tail wing-stall and altimetry to aircraft loss. The current generation of ice-detection systems relies on environmental parameters to determine icing conditions, with the sensors usually located on the nose of the aircraft, giving no information on the ice accreted on the wings. This work focuses on modeling and developing a fiber-optic-array ice sensor, which illuminates and detects the reflected and scattered light directly from the ice surface and volume, and measures the accretion rate and type of ice on the wings. The ice morphology is influenced by the rate of freezing of the super-cooled droplets impacting the wings, and partially or totally trapping the dissolved gasses. This leads to the formation of rugged surfaces and ice shapes, which can be transparent or opaque, a process which is dependent on the local Freezing Fraction (FF) of the impinging super cooled water. The detection method relies on the optical characteristics of ice, affected by density and the size of micro-cracks and micro-bubbles formed during freezing. By using high Numerical Aperture (NA) fibers, it was possible to accurately measure the ice thickness, and to investigate a proof-of-concept experiment, correlating the optical diffusion to the FF of the ice on a wing.

Evaluation of a hydrodynamic cavitation-type bubble generator in a prototype bench-scale flotation unit for poultry processing wastewater treatment

ABSTRACT Dissolved Air Flotation (DAF) systems are designed to remove oil and grease (O&G) and total suspended solids (TSS) in wastewater treatment. These systems require saturation tanks, water pumps, and high-pressure compressors to control the pressure, hydraulic retention time, and airflow parameters. DAF process efficiency depends on complex operational controls associated with these components, and the most critical aspect of an effectively operating DAF unit is a generated bubble size. This work presents the design and operational test of a flotation unit prototype that replaces the saturation tank and high-pressure compressors present in DAF with the CARMIN microbubble injector, the evaluation of the proposed system's TSS and O&G removal efficiency was carried out considering different initial configurations of the injector to change the generated microbubble size, four synthetic wastewater solutions, and poly aluminum chloride as a flocculant to establish the potential of this system for the poultry processing wastewater treatment. Mean microbubble size results were obtained from 47.41 µm to 116.17 µm. The average removal efficiency of TSS exceeded 65% under a high concentration of suspended particles (1,560 mg/l) and 80% under a lower TSS concentration (795 mg/l). Meanwhile, 70% and 90% of O&G were removed from high (400 mg/l) and low (100 mg/l) initial O&G concentrations, respectively. These removal levels are similar to those reported in the literature for DAF for poultry processing wastewater, albeit with a simple configuration and better controllability and scalability.