Acoustic Radiation Force Research Articles

Three-dimensional FSI simulation of cell entrapment utilizing acoustic interparticle force in a standing acoustic field

Abstract In recent years, there has been significant development in microfluidic devices for cell separation and sorting using acoustic methods in biomedical applications. The acoustic interparticle force (AIF) arises from particle interactions with the scattered field of other particles, influencing particle motion at close ranges and facilitating optimal trapping and separation. This study analyzes a two-particle system consisting of a fixed particle and a white blood cell (WBC) within a standing acoustic field and creeping flow using fluid-structure interaction (FSI). To reduce computational costs by decoupling the acoustics and FSI, the acoustic pressure equation (AcPr) was solved on the frequency domain to calculate the total acoustic radiation force in each time step. Model accuracy was assessed by evaluating interparticle (AIF) and primary acoustic radiation forces (ARF) on a polystyrene particle and comparing simulation results to analytical and experimental data. Results demonstrate precise ARF performance, with discrepancies in acoustic interparticle force attributed to viscous losses near the particle surface. Moreover, the higher density of the fixed particle compared to WBCs induces significant acoustic interparticle attraction at close distances. Consequently, cell entrapment occurs through strong attraction and collision with fixed aluminum and silicon particles in creeping flow in all three Reynolds numbers 1.4E-3, 2.1E-3, and 3E-3. Increasing Reynolds numbers augment the likelihood of cell separation from the fixed particle. These findings contribute to optimizing cell isolation and entrapment strategies.

Acoustomotive diffuse correlation spectroscopy for sensing mechanical stiffness in tissue-mimicking phantoms.

Many diseases, such as inflammation, dropsy, or tumors, often cause alterations in the mechanical stiffness of human tissues. Ultrasound-based techniques are commonly adopted in clinics for stiffness assessment, whereas optical methodologies hold promise for sensing strain changes and providing optical information pertaining to the microcirculatory network, thereby facilitating comprehensive measurements of tissue physiopathology. Diffuse correlation spectroscopy (DCS), an emerging dynamic light scattering technique, has been used to capture the enhanced motion of light scatterers induced by acoustic radiation force (ARF). Theoretically, the amplitude of this enhanced scatterers motion is related to the medium stiffness. Based on this relationship, we report a light coherent technique that combines ARF and DCS to qualitatively evaluate changes in the stiffness of medium. We experimentally demonstrate the accuracy and feasibility of this technique for probing stiffness in homogeneous phantom by comparing it with independent ultrasound methods. Additionally, we explore a potential application of this technique in distinguishing between fluid filled lesion and homogeneous tissue through heterogeneous phantom experiments. This unique combination of ARF and DCS, namely, acoustomotive DCS (AM-DCS), would provide an alternative way to measure particle-motion related stiffness, thereby assisting in the diagnosis and treatment of diseases.

Acousto-dielectric tweezers enable independent manipulation of multiple particles.

Acoustic tweezers have gained substantial interest in biology, engineering, and materials science for their label-free, precise, contactless, and programmable manipulation of small objects. However, acoustic tweezers cannot independently manipulate multiple microparticles simultaneously. This study introduces acousto-dielectric tweezers capable of independently manipulating multiple microparticles and precise control over intercellular distances and cyclical cell pairing and separation for detailed cell-cell interaction analysis. Our acousto-dielectric tweezers leverage the competition between acoustic radiation forces, generated by standing surface acoustic waves (SAWs), and dielectrophoretic (DEP) forces, induced by gradient electric fields. Modulating these fields allows for the precise positioning of individual microparticles at points where acoustic radiation and DEP forces are in equilibrium. This mechanism enables the simultaneous movement of multiple microparticles along specified paths as well as cyclical cell pairing and separation. We anticipate our acousto-dielectric tweezers to have enormous potential in colloidal assembly, cell-cell interaction studies, disease diagnostics, and tissue engineering.

Acoustic radiation force impulse elastography in the evaluation of focal liver pathology: a prospective study

Acoustic radiation force impulse elastography in the evaluation of focal liver pathology: a prospective study

Liver stiffness measurement versus splenic stiffness measurement using ARFI (Acoustic radiation force impulse) in predicting esophageal varices as a marker of portal hypertension

Liver stiffness measurement versus splenic stiffness measurement using ARFI (Acoustic radiation force impulse) in predicting esophageal varices as a marker of portal hypertension

Lattice Boltzmann approach for acoustic manipulation.

We employ a lattice Boltzmann method to compute the acoustic radiation force produced by standing waves on a compressible object for the density matched case. Instead of simulating the fluid mechanics equationsdirectly, the proposed method uses a lattice Boltzmann model that reproduces the wave equation, together with a kernel interpolation scheme, to compute the first-order perturbations of the pressure and velocity fields on the object's surface and, from them, the acoustic radiation force. The procedure reproduces with excellent accuracy the theoretical expressions by Gor'kov and Wei for the sphere as the 3D case and an infinitely long cylinder as the 2D case, respectively, even with a modest number of lattice Boltzmann cells. The proposed method shows to be a promising tool for simulating phenomena where the acoustic radiation force plays a relevant role, like acoustic tweezers or the acoustic manipulation of microswimmers, with applications in medicine and engineering.

Evaluating impedance boundary conditions to model interfacial dynamics in acoustofluidics

We present a numerical study to investigate the efficacy of impedance boundary conditions in capturing the interfacial dynamics of a particle subjected to an acoustic field and study the concomitant time-averaged acoustic streaming and radiation force fields. While impedance boundary conditions have been utilized to represent fluid–solid interface in acoustofluidics, such models assume the solid material to be locally reactive to the acoustic waves. However, there is a limited understanding of when this assumption holds true, raising concerns about the suitability of impedance boundary conditions. Here, we systematically investigate the applicability of impedance boundary conditions by comparing the predictions of an impedance boundary approach against a fully coupled fluid–solid model. We contrast the oscillation profiles of the fluid–solid interface predicted by the two models. We consider different scatterer materials to identify the extent to which the differences in interfacial dynamics impact the time-averaged fields and highlight the divergence within the predictions of the two models. Our findings indicate that, although impedance boundary conditions can yield qualitatively similar results to the full model in certain situations, the predictions from the two models generally differ both qualitatively and quantitatively. These results underscore the importance of exercising caution when applying these boundary conditions to model general acoustofluidic systems.

Analytical solution for acoustic radiation force and torque on a spheroid near a rigid or free planar boundary.

An analytical solution is developed for the acoustic radiation force and torque caused by an arbitrary sound field that is incident on a compressible spheroid of any size near a planar boundary that is either rigid or pressure release. The analysis is an extension of a recent solution for a compressible sphere near a planar boundary [Simon and Hamilton, J. Acoust. Soc. Am. 153, 627-642 (2023)]. Approximations that account for a boundary formed by a two-fluid interface may be incorporated as in the previous analysis for a sphere. The present solution is based on expansions of the total acoustic pressure field in spheroidal wave functions and the use of addition theorems. Verification of the solution is accomplished by comparison with a finite element model. Examples are presented for incident fields that are either plane or spherical waves. Effects resulting from the presence of the boundary are studied by comparing the full theory with a simplified model in which multiple scattering is neglected. Numerical implementation of the proposed solution is also discussed.

Removal of surface-attached micro- and nanobubbles by ultrasonic cavitation in microfluidics

Surface-attached micro- and nanobubbles are known for their resistance to external forces. This study experimentally and theoretically investigates their response to strong ultrasonic fields. Surface-attached micro- and nanobubbles with contact radii from 2 μm to 20 μm are generated in a microchannel and exposed to ultrasound through a vibrating glass substrate. At a driving frequency over 200 kHz up to 2 MHz tested, no significant response from the micro- and nanobubbles is observed. By contrast, at 100 kHz–200 kHz, ultrasonic cavitation bubbles appear in the microchannel and migrate toward the surface micro- and nanobubbles. Then the surface micro- and nanobubbles merge with the ultrasonic cavitation bubbles, detach from the substrate, and become free gaseous nuclei susceptible to further cavitation. Notably, the removal process leaves no observable residue. Theoretical analysis suggests that the directional migration of cavitation bubbles is driven by mutual acoustic radiation forces. This work demonstrates that ultrasonic fields can effectively remove surface micro- and nanobubbles, transforming them into free gaseous cavitation nuclei.

Automated droplet manipulation enabled by a machine-vision-assisted acoustic tweezer

Automated droplet manipulation holds great significance for various biochemical applications, including but limited to heavy metal ions detection. Despite notable progress, contactless-acoustic-tweezer-based automated droplet manipulation on superhydrophobic surfaces is rarely reported. In this work, we introduce a machine-vision-assisted acoustic tweezer (MVAAT) for automated and contactless manipulation of droplets on a superhydrophobic surface. The MVAAT generates ultrasound standing waves between an ultrasonic transducer (UST) and a superhydrophobic surface, inducing acoustic radiation force to facilitate contactless droplet manipulation on the superhydrophobic surface. An industrial-camera-based machine vision system is employed for real-time detection and tracking of droplets, providing precise droplet positions for automated droplet transportation and merging via a UST equipped on a Cartesian robot. Experimental results demonstrate that the proposed MVAAT can transport droplets of various volumes on a superhydrophobic surface along planned paths at considerably high velocities exceeding one centimeter per second. Furthermore, with the vision feedback, the MVAAT can reliably and precisely transport a droplet to a target position, even if the droplet fails to follow the UST during its movement. Moreover, automated merging and patterning of multiple droplets are achieved, showcasing the versatility of the MVAAT. Last, the MVAAT is applied for fluorescence-based Cu2+ detection to showcase its potential for practical biochemical analyses. The proposed MVAAT significantly expands the capability of ultrasound for droplet manipulation on superhydrophobic surfaces, promising numerous practical applications in biology and chemistry.

Ultrasonic aperture-tunable gel lens

Conventional camera modules require mechanical moving parts to move their lenses and to adjust their focal points. This paper examines optically tunable lenses with a focal length and lens aperture that can be controlled using ultrasound vibration and a transparent gel. The lens uses the acoustic radiation force, which induces changes in the lens profile; varifocal convex and concave lenses can be fabricated by adjusting the input signals. The optical characteristics of the lenses were evaluated using ray tracing simulations. The aperture can be controlled with the driving frequency, with higher frequencies leading to a wider range of focal length changes with a lower input voltage.

Volumetric Measurement Of The Acoustically Induced Fluid Flow In A Micro Chamber With A Two-Dimensional Standing Surface Acoustic Wave Field

The non-invasive, contactless and label-free trapping and patterning of individual cells with acoustic tweezers is a key technology to reliably analyze single cells and cell-cell interactions in biological applications. By using two-dimensional standing surface acoustic waves (2DsSAW), the precise manipulation of the cells in a micro chamber is primarily governed by the acoustic radiation force, which acts directly on the cells due to scattering effects of the acoustic waves. However, a fluid flow of three-dimensional nature is concurrently induced acoustically, which additionally influences the cell pattern by Stokes' drag. In this study, we shed light on the complex acoustically induced fluid flow forming in an acoustic tweezer by 3D3C velocity measurements using the astigmatism particle tracking velocimetry (APTV). Vortex structures above the antinodes of the 2DsSAW field were revealed. The fluid flow converge and diverge in the vicinity of the chamber bottom and ceiling, respectively. Hence, the fluid flow influences the stable trapping locations of cells or particles in different ways depending on their height position, which might explain the recently reported formation of various particle patterns at different height levels. Moreover, the experimental findings are used to validate a three-dimensional numerical model. The numerical model provides deep insights into the underlying acoustic fields responsible for the formation of the fluid flow and acoustic radiation force. By combining the experimental and numerical results, a profound understanding of the physical mechanisms for cell or particle trapping and patterning is established.

Ultrasonic liquid crystal tunable light diffuser

Conventional light diffusers have periodic surface profiles, periodic refractive index distributions, or light scattering layers containing colloids. In all such structures the optical directivity of the light diffuser is cannot typically be controlled. Here we propose an electrically tunable light diffuser based on the application of ultrasound to a nematic liquid crystal (LC) material. The ultrasonic LC diffuser consists of an LC layer sandwiched by two glass discs and an ultrasonic transducer. The electrodes of the transducer are divided in a circumferential direction so that a resonant non-coaxial flexural vibration mode can be generated on the diffuser by controlling the electrical input signals. A continuous reversed-phase sinusoidal electric signal to the transducer generates the non-coaxial resonant flexural vibration mode on the glass disc, inducing an acoustic radiation force acting on the boundary between the LC layer and glass discs. This effect changes the molecular orientation of the LC and the transmitted light distribution. The diffusion angle of the transmitted light depends on the input voltage amplitude, and the diffusion angle was maximized at 16.0 V. The vibrational distribution and the diffusion directivity could be rotated by adjusting the input voltages to different electrodes, meaning that an ultrasonic LC diffuser with a thin structure and no moving mechanical parts provided a tunable light-diffusing functionality with rotatable directivity.

Acoustic radiation force on a cylindrical composite particle with an elastic thin shell and an internal eccentric liquid column in a plane ultrasonic wave field

Abstract A model with three-layer structure is introduced to explore the acoustic radiation force (ARF) on composite particles with an elastic thin shell. Combing acoustic scattering of cylinder and the thin-shell theorem, the ARF expression was derived, and the longitudinal and transverse components of the force and axial torque for an eccentric liquid-filled composite particle was obtained. It was found that many factors, such as medium properties, acoustic parameters, eccentricity, and radius ratio of the inner liquid column, affect the acoustic scattering field of the particle, which in turn changes the forces and torque. The acoustic response varies with the particle structures, so the resonance peaks of the force function and torque shift with the eccentricity and radii ratio of particle. The acoustic response of the particle is enhanced and exhibits higher force values due to the presence of the elastic thin shell and the coupling effect with the eccentricity of the internal liquid column. The decrease of the inner liquid density may suppress the high-order resonance peaks, and internal fluid column has less effects on the change in force on composite particle at ka > 3, while limited differences exist at ka < 3. The axial torque on particles due to geometric asymmetry is closely related to ka and the eccentricity. The distribution of positive and negative force and torque along the axis ka exhibits that composite particle can be manipulated or separated by ultrasound. Our theoretical analysis can provide support for the acoustic manipulation, sorting, and targeting of inhomogeneous particles.

Ultrasonic Healing of Plastrons.

Superhydrophobic surfaces (SHS) exhibit a pronounced ability to resist wetting. When immersed in water, water does not penetrate between the microstructures of the SHS. Instead, a thin layer of trapped gas remains, i.e., plastron. This fractional wetting is also known as the Cassie-Baxter state (CB). Impairment of superhydrophobicity occurs when water penetrates the plastron and, when complete wetting is achieved, a Wenzel state (W) results. Subsequent recovery back to CB state is one of the main challenges in the field of SHS wetting. Current methods for plastron recovery require complex mechanical or chemical integration, are time-consuming or lack spatial control. Here an on-demand, contact-less approach for performing facile transitions between these wetting states at micrometer length scales is proposed. This is achieved by the use of acoustic radiation force (ARF) produced by high-intensity focused ultrasound (HIFU). Switching from CB to W state takes <100 µs, while the local recovery back to CB state takes <45 s. To the best of authors knowledge, this is the first demonstration of ARF-induced manipulation of the plastron enabling facile two-way controlled switching of wettingstates.

Quantitative Viscoelastic Response (QVisR): Direct Estimation of Viscoelasticity With Neural Networks.

We present a machine learning method to directly estimate viscoelastic moduli from displacement time-series profiles generated by viscoelastic response (VisR) ultrasound excitations. VisR uses two colocalized acoustic radiation force (ARF) pushes to approximate tissue viscoelastic creep response and tracks displacements on-axis to measure the material relaxation. A fully connected neural network is trained to learn a nonlinear mapping from VisR displacements, the push focal depth, and the measurement axial depth to the material elastic and viscous moduli. In this work, we assess the validity of quantitative VisR (QVisR) in simulated materials, propose a method of domain adaption to phantom VisR displacements, and show in vivo estimates from a clinically acquired dataset.

Acoustic radiation force-induced longitudinal shear wave for ultrasound-based viscoelastic evaluation

Acoustic radiation force (ARF) is widely used to induce shear waves for evaluating the mechanical properties of biological tissues. Two shear waves can be generated when exciting with ARF: a transverse shear wave, also simply called shear wave (SW), and a longitudinal shear wave (LSW). Shear waves (SWs) have been broadly used to assess the mechanical properties. Some articles have reported that the LSW can be used to evaluate mechanical properties locally. However, existing LSW studies are mainly focused on the group velocity evaluation using optical coherence tomography (OCT). Here, we report that a LSW generated with ARF can be used to probe viscoelastic properties, including shear modulus and viscosity, using ultrasound. We took advantage of the surface boundary effect to reflect the LSW, named RLSW, to address the energy deficiency of LSW induced by ARF. We systematically evaluated the experiments with tissue-mimicking viscoelastic phantoms and validated by numerical simulations. Phase velocity and dispersion comparison between the results induced by a RLSW and a SW exhibit good agreement in both the numerical simulations and experimental results. The Kelvin-Voigt (KV) model was used to determine the shear modulus and viscosity. RLSW shows great potential to evaluate localized viscoelastic properties, which could benefit various biomedical applications such as evaluating the viscoelasticity of heterogeneous materials or microscopic lesions of tissues.

Airborne Acoustic Vortex End Effector‐Based Contactless, Multi‐Mode, Programmable Control of Object Surfing

AbstractTweezers based on optical, electric, magnetic, and acoustic fields have shown great potential for contactless object manipulation. However, current tweezers designed for manipulating millimeter‐sized objects such as droplets, particles, and small animals exhibit limitations in translation resolution, range, and path complexity. Here, a novel acoustic vortex tweezers system is introduced, which leverages a unique airborne acoustic vortex end effector integrated with a three‐degree‐of‐freedom (DoF) linear motion stage, for enabling contactless, multi‐mode, programmable manipulation of millimeter‐sized objects. The acoustic vortex end effector utilizes a cascaded circular acoustic array, which is portable and battery‐powered, to generate an acoustic vortex with a ring‐shaped energy pattern. The vortex applies acoustic radiation forces to trap and spin an object at its center, simultaneously protecting this object by repelling other materials away with its high‐energy ring. Moreover, The vortex tweezers system facilitates contactless, multi‐mode, programmable object surfing, as demonstrated in experiments involving trapping, repelling, and spinning particles, translating particles along complex paths, guiding particles around barriers, translating and rotating droplets containing zebrafish larvae, and merging droplets. With these capabilities, It is anticipated that the tweezers system will become a valuable tool for the automated, contactless handling of droplets, particles, and bio‐samples in biomedical and biochemical research.

Protein Gas Vesicles of Bacillus megaterium as Enhancers of Ultrasound-Induced Transcriptional Regulation.

Gas vesicles (GVs) are large cylindrical gas-filled protein assemblies found in diverse aquatic bacteria that enable their adaptation of buoyancy. GVs have already been used as ultrasound contrasting agents. Here, we investigate GVs derived from Bacillus megaterium, aiming to minimize the number of accessory Gvps within the GV gene cluster and demonstrate the use of GVs as enhancers of acoustic radiation force administered by ultrasound. Three (GvpR, GvpT, and GvpU) out of 11 genes in the cluster were found to be dispensable for functional GV formation, and their omission resulted in narrower GVs. Two essential proteins GvpJ and GvpN were absent from recently determined GV structures, but GvpJ was nevertheless found to be tightly bound to the cylindrical part of GVs in this study. Additionally, the N-terminus of GvpN was observed to play an important role in the formation of mature GVs. The binding of engineered GvpC fromAnabaena flos-aquae to HEK293 cells via integrins enhanced the acoustic force delivered by ultrasound and resulted in an increased Ca2+ influx into cells. Coupling with a synthetic Ca2+-dependent signaling pathway GVs efficiently enhanced cell stimulation by ultrasound, which expands the potentials of noninvasive sonogenetics cell stimulation.

Acoustofluidic separation of bacteria from platelets using tilted-angle standing surface acoustic wave

Separation of microscale objects, such as cells and bacteria, is an essential sample preparation step in various microfluidic applications in microbiology, chemistry, biology, and biomedicine. Microfluidic separation of bacteria from blood cells is highly in demand to prevent or investigate bacterial infectious diseases. Unlike red and white blood cells, platelets have a similar size distribution to that of bacteria, which makes bacteria separation from platelets technically challenging. Most previous techniques for microfluidic separation rely on size as a separation marker. These size-based separation methods are not applicable to separation of the same or similar-sized samples. Here, we propose an acoustofluidic method using tilted-angle standing surface acoustic wave (taSSAW) for label-free separation of the microscale objects of the same or similar size based on compressibility. From the experimental investigation with polymethylmethacrylate, polystyrene, and polycaprolactone microparticles of the same size, we found that less compressible objects migrated further when exposed to the taSSAW field formed within a microchannel. Based on the findings, we demonstrated that Escherichia coli (E. coli) can be separated from platelets because the taSSAW-induced acoustic radiation force acting on comparatively less compressible E. coli was greater than that applied to the platelets. Fluorescence microscopy, scanning electron microscope, hemocytometry, sodium dodecyl sulfate polyacrylamide gel electrophoresis, and polymerase chain reaction were conducted to confirm the successful positive separation of bacteria from platelets with high purity of exceeding 96 % and recovery rate of exceeding 81 %.