81 research outputs found
Ultrasound-enhanced mass transfer during single-bubble diffusive growth
Ultrasound is known to enhance surface bubble growth and removal in catalytic
and microfluidic applications, yet the contributions of rectified diffusion and
microstreaming phenomena towards mass transfer remain unclear. We quantify the
effect of ultrasound on the diffusive growth of a single spherical CO
bubble growing on a substrate in supersaturated water. The time dependent
bubble size, shape, oscillation amplitude and microstreaming flow field are
resolved. We show and explain how ultrasound can enhance the diffusive growth
of surface bubbles by up to two orders of magnitude during volumetric
resonance. The proximity of the wall forces the bubble to oscillate
non-spherically, thereby generating vigorous streaming during resonance that
results in convection-dominated growth.Comment: Accepted in Phys. Rev. Fluid
Plasmonic Bubbles in n-Alkanes
In this paper we study the formation of microbubbles upon the irradiation of
an array of plasmonic Au nanoparticles with a laser in n-alkanes
(, with n = 5-10). Two different phases in the evolution of the
bubbles can be distinguished. In the first phase, which occurs after a delay
time {\tau}d of about 100 {\mu}s, an explosive microbubble, reaching a diameter
in the range from 10 {\mu}m to 100 {\mu}m, is formed. The exact size of this
explosive microbubble barely depends on the carbon chain length of the alkane,
but only on the laser power . With increasing laser power, the delay time
prior to bubble nucleation as well as the size of the microbubble both
decrease. In the second phase, which sets in right after the collapse of the
explosive microbubble, a new bubble forms and starts growing due to the
vaporization of the surrounding liquid, which is highly gas rich. The final
bubble size in this second phase strongly depends on the alkane chain length,
namely it increases with decreasing number of carbon atoms. Our results have
important implications for using plasmonic heating to control chemical
reactions in organic solvents
The role of ultrasound-driven microbubble dynamics in drug delivery : from microbubble fundamentals to clinical translation
In the last couple of decades, ultrasound-driven microbubbles have proven excellent candidates for local drug delivery applications. Besides being useful drug carriers, microbubbles have demonstrated the ability to enhance cell and tissue permeability and, as a consequence, drug uptake herein. Notwithstanding the large amount of evidence for their therapeutic efficacy, open issues remain. Because of the vast number of ultrasound- and microbubble-related parameters that can be altered and the variability in different models, the translation from basic research to (pre)clinical studies has been hindered. This review aims at connecting the knowledge gained from fundamental microbubble studies to the therapeutic efficacy seen in in vitro and in vivo studies, with an emphasis on a better understanding of the response of a microbubble upon exposure to ultrasound and its interaction with cells and tissues. More specifically, we address the acoustic settings and microbubble-related parameters (i.e., bubble size and physicochemistry of the bubble shell) that play a key role in microbubble cell interactions and in the associated therapeutic outcome. Additionally, new techniques that may provide additional control over the treatment, such as monodisperse microbubble formulations, tunable ultrasound scanners, and cavitation detection techniques, are discussed. An in-depth understanding of the aspects presented in this work could eventually lead the way to more efficient and tailored microbubble-assisted ultrasound therapy in the future
Insights into acoustically induced piezoluminescence : the visualization of ultrasonic beam patterns
Ultrasonic transducers are used in many fields of application, including medical imaging/treatment, non-destructive testing and material characterization. To assure the quality of the ultrasonic investigation transducers require regular checks for possible deterioration and accurate calibration. Current methods rely on point-by-point scanning of the ultrasound field with a needle hydrophone, which is expensive and time consuming. Recently, we have developed a new concept, in which a fast full-field visualization of the radiation field is achieved through Acoustically induced PiezoLuminescence (APL). Here, we report on an improved ultrasonic beam visualization and provide further insights into the mechanism underlying APL and mechanoluminescence
Time-resolved velocity and pressure field quantification in a flow-focusing device for ultrafast microbubble production
Flow-focusing devices have gained great interest in the past decade, due to
their capability to produce monodisperse microbubbles for diagnostic and
therapeutic medical ultrasound applications. However, up-scaling production to
industrial scale requires a paradigm shift from single chip operation to highly
parallelized systems. Parallelization gives rise to fluidic interactions
between nozzles that, in turn, may lead to a decreased monodispersity. Here, we
study the velocity and pressure field fluctuations in a single flow-focusing
nozzle during bubble production. We experimentally quantify the velocity field
inside the nozzle at 100 ns time resolution, and a numerical model provides
insight into both the oscillatory velocity and pressure fields. Our results
demonstrate that, at the length scale of the flow focusing channel, the
velocity oscillations propagate at fluid dynamical time scale (order of
microseconds) whereas the dominant pressure oscillations are linked to the
bubble pinch-off and propagate at a much faster time scale (order of
nanoseconds).Comment: 30 pages, 7 figure
Inverse Leidenfrost drop manipulation using menisci
Drops deposited on an evaporating liquid bath can be maintained in an inverse
Leidenfrost state by the vapor emanating from the bath, making them levitate
and hover almost without friction. These perfectly non-wetting droplets create
a depression in the liquid interface that sustains their weight, which
generates repellent forces when they approach a meniscus rising against a wall.
Here, we study this reflection in detail, and show that frictionless
Leidenfrost drops are a simple and efficient tool to probe the shape of an
unknown interface. We then use the menisci to control the motion of the
otherwise elusive drops. We create waveguides to direct and accelerate them and
use parabolic walls to reflect and focus them. This could be particularly
beneficial in the scale up of droplet cryopreservation processes: capillary
interactions can be used to transport, gather and collect vitrified biological
samples in absence of contact and contamination
Transverse flow under oscillating stimulation in helical square ducts with cochlea-like geometrical curvature and torsion
The cochlea is our fluid-filled organ of hearing with a unique spiral shape.
The physiological role of this shape remains unclear. Previous research has
paid only little attention to the occurrence of transverse flow in the cochlea,
in particular in relation to the cochlea's shape. To better understand its
influence on fluid dynamics, this study aims to characterize transverse flow
due to harmonically oscillating axial flow in square ducts with curvature and
torsion, similar to the shape of human cochleae. Four geometries were
investigated to study curvature and torsion effects on axial and transverse
fluid flow components. Twelve frequencies from 0.125 Hz to 256 Hz were studied,
covering infrasound and low-frequency hearing, with mean inlet velocity
amplitudes representing levels expected for normal conversations or louder
situations. Our simulations show that torsion contributes significantly to
transverse flow in unsteady conditions, and that its contribution increases
with increasing oscillation frequencies. Curvature has a small effect on
transverse flow, which decreases rapidly for increasing frequencies.
Strikingly, the combined effect of curvature and torsion on transverse flow is
greater than expected from a simple superposition of the two effects,
especially when the relative contribution of curvature alone becomes
negligible. These findings could be relevant to understand physiological
processes in the cochlea, including metabolite transport and wall shear
stresses. Further studies are needed to investigate possible implications on
cochlear mechanics.Comment: 26 pages, 7 figure
Monodisperse versus polydisperse ultrasound contrast agents: nonlinear response, sensitivity, and deep tissue imaging potential
Monodisperse microbubble ultrasound contrast agents have been proposed to
further increase the signal-to-noise-ratio of contrast enhanced ultrasound
imaging. Here, the sensitivity of a polydisperse preclinical agent was compared
experimentally to that of its size- and acoustically-sorted derivatives by
using narrowband pressure- and frequency-dependent scattering and attenuation
measurements. The sorted monodisperse agents showed up to a two orders of
magnitude increase in sensitivity, i.e. in the average scattering cross-section
per bubble. Moreover, we demonstrate here, for the first time, that the highly
nonlinear response of acoustically sorted microbubbles can be exploited to
confine scattering and attenuation to the focal region of ultrasound fields
used in clinical imaging. This property is a result of minimal prefocal
scattering and attenuation and can be used to minimize shadowing effects in
deep tissue imaging. Moreover, it potentially allows for more localized therapy
using microbubbles through the spatial control of resonant microbubble
oscillations
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