Acoustic Tweezers Research Articles

Wave number-spiral acoustic tweezers for dynamic and reconfigurable manipulation of particles and cells.

Acoustic tweezers have recently raised great interest across many fields including biology, chemistry, engineering, and medicine, as they can perform contactless, label-free, biocompatible, and precise manipulation of particles and cells. Here, we present wave number-spiral acoustic tweezers, which are capable of dynamically reshaping surface acoustic wave (SAW) wavefields to various pressure distributions to facilitate dynamic and programmable particle/cell manipulation. SAWs propagating in multiple directions can be simultaneously and independently controlled by simply modulating the multitone excitation signals. This allows for dynamic reshaping of SAW wavefields to desired distributions, thus achieving programmable particle/cell manipulation. We experimentally demonstrated the multiple functions of wave number-spiral acoustic tweezers, among which are multiconfiguration patterning; parallel merging; pattern translation, transformation, and rotation; and dynamic translation of single microparticles along complex paths. This wave number-spiral design has the potential to revolutionize future acoustic tweezers development and advance many applications, including microscale assembly, bioprinting, and cell-cell interaction research.

Axial acoustic radiation force on a spherical particle in a zero-order Mathieu beam.

In this paper, an expression for the acoustic radiation force on a sphere located on the axis of a zero-order Mathieu beam propagating in an ideal fluid is obtained. The simulation results of different kinds of spherical particles, including rigid spheres, fluid spheres, and elastic spheres, are presented to illustrate the theory. Curves of the acoustic radiation force function versus ka are obtained for different half-cone angles β and ellipticity parameters q of the Mathieu beam. The simulation results reveal that β and q have a direct effect on the acoustic radiation force exerted on a spherical object in an ideal fluid. The acoustic radiation force has negative values for a fluid sphere in a zero-order Mathieu beam when the half-cone angle is β≥60°. The value of the half-cone angle β also affects the direction of the acoustic radiation force for an elastic sphere. When the half-cone angle is set as a constant, the greater the ellipticity parameter is, the slower the decrease in the value of the acoustic radiation force function for a spherical particle. The conclusions of this work may be helpful for the design of acoustic tweezers and may also extend the potential applications of acoustic manipulation technology.

Two-Dimensional Mapping Separating the Acoustic Radiation Force and Streaming in Microfluidics

Field mapping of the acoustic radiation force and acoustic streaming is important for the design and calibration of acoustic tweezers, but we lack a method to disentangle and obtain accurate pictures of these fields. This study proposes a technique for multiradius microparticle image velocimetry, to solve this problem. The method requires no special assumptions about the driving acoustic field, and motorized scanning is unnecessary. This approach should impact various technologies for particle manipulation, including those exploiting acoustic, optical, dielectrophoretic, and magnetic forces.

Folding a focalized acoustical vortex on a flat holographic transducer: Miniaturized selective acoustical tweezers.

Acoustical tweezers based on focalized acoustical vortices hold the promise of precise contactless manipulation of millimeter down to submicrometer particles, microorganisms, and cells with unprecedented combined selectivity and trapping force. Yet, the widespread dissemination of this technology has been hindered by severe limitations of current systems in terms of performance and/or miniaturization and integrability. Here, we unleash the potential of focalized acoustical vortices by developing the first flat, compact, paired single electrode focalized acoustical tweezers. These tweezers rely on spiraling transducers obtained by folding a spherical acoustical vortex on a flat piezoelectric substrate. We demonstrate the ability of these tweezers to grab and displace micrometric objects in a standard microfluidic environment with unique selectivity. The simplicity of this system and its scalability to higher frequencies open tremendous perspectives in microbiology, microrobotics, and microscopy.

Theoretical study of acoustic radiation force and torque on a pair of polymer cylindrical particles in two Airy beams fields

In this work, we describe the acoustic radiation force (ARF) and torque acting on a pair of cylindrical particles induced by two Airy beams. The finite series expansion method and the addition theorem of the cylindrical Bessel function are used to analyze the acoustic scattered field by a pair of cylindrical particles in an effective incident acoustic field. The mathematical expressions for the ARF and the torque functions in multiple acoustic scattering by a pair of cylindrical particles are obtained. The influences of the phase difference, the beam distance, and the beam amplitude on the ARFs and torques are taken into consideration. The numerical examples illustrate that greater negative or positive forces on the two cylindrical particles emerge by adjusting the phase difference, the distance, or the amplitudes of the two Airy beams, which make it easier to separate the particles. The values of the torques will also increase or change between the positive and the negative, which increase the particles’ rotation velocity or change the particles’ rotation direction. This work will be conducive to the development of acoustic tweezers for polymer drugs separation (or cells separation) in medical domain.

Active microswimmers in a finite two dimensional trap: The role of hydrodynamic interaction.

We investigate the dynamics of two identical artificial active particles suspended in a free-standing fluid film with a trap of finite radius in an acoustic tweezer. In the two dimensional Oseen approximation, their hydrodynamic coupling is long ranged, which naturally raises the question as under what conditions they can simultaneously reside in the trap. We determine a critical value of the hydrodynamic coupling below which that happens and study the ensuing active pair dynamics inside the trap. For larger couplings, only one particle sits in the trap, while the other diffuses freely until it eventually replaces the particle in the trap. Such a mechanism repeats itself with a characteristic noise-dependent mean residence-retrapping time.

17th annual Anglo-French Physical Acoustics Conference (AFPAC)

Proceedings of the Anglo-French Physical Acoustics Conference (AFPAC)PrefaceThe 17th annual Anglo-French Physical Acoustics Conference (AFPAC) was held at the Selsdon Park Hotel is Surrey UK from 17th to 19th of January 2018. Over the years AFPAC has established a unique character where a most diverse range of topics covering the many application of acoustics and ultrasonics are discussed in a friendly environment with almost a residential workshop feel. The scientific standards are always high and PhD students make up a large proportion of the presentations. This 17th annual meeting was no exception. There were 42 presentations including 4 from invited speakers. These invited speakers included Andrea Colombi from Imperial College who talked about seismic waves and metamaterials. James Windmill of Strathclyde University presented work on how the study of insects is being used to develop new sensors. Emmanuel Moulin from Université de Valenciennes talked about coda waves in Structural Health monitoring (SHM) and Régis Marchiano from Université Pierre et Marie Curie in Paris presented work from a project on inverse problems using data collected by large arrays of microphones. Other subjects covered included acoustofluidics, acoustic tweezers and particle manipulation, biomedical ultrasound applications such as histotripsy, lithotripsy and HIFU, NDE and SHM for plate-like structures, corrosion and polycrystalline materials. There were also presentations on acoustically driven bubbles. A truly eclectic mix for those who are fascinated by all things acoustic!These proceedings contain a collections of papers submitted by the participants at the 2018 AFPAC. Submission of manuscripts has always been done on a voluntary basis and we have continued to maintain a high standard of reviewing for those who choose to have their work published here.Nader SaffariAlain Lhemery

Extraordinary manipulations of particles by acoustic radiation forces and torques

Particle manipulations using radiation forces and torques produced by acoustic waves have been found valuable applications in biomedical and material engineering. Recent work suggests extraordinary manipulations of particles associated with direction reversals of forces and torques by some specific sound beams. When considering the three-dimensional acoustic radiation force, the momentum view enlightens into the superposition and coupling of manipulations by multiple beams and the force dependence on scattering functions [L. Zhang, JASA 144 (1), 443–447 (2018)]. It is efficient to apply the superposition to consider forces and torques on particles moved away from the equilibrium trapping position [L. Zhang, JASA 143(5), 2796–2800 (2018)]. The superposition reveals how the radiation torque associated with energy absorption can spin an object around its center of mass in a direction reversed with respect to the wave vortex’s handedness [L. Zhang, Phys. Rev. Appl. 10(3), 034039 (2018)]. These insights into extraordinary manipulations are of interest for advancing the flexibility of particle manipulations by acoustic tweezers and to the field of acoustofluidics.

Elastic Phased Diffraction Gratings for Manipulation of Ultrasonic Guided Waves in Solids

Lamb waves and surface acoustic waves (SAWs) are of great interest for frontier technologies, including structural health monitoring, energy harvesting, sensors, and acoustic tweezers. This work presents elastic phased diffraction gratings, passive structures for controlling guided ultrasonic waves in solids. Such a grating adopts an array of interchangeable superstrates to modulate wave dispersion, and thus the diffraction wave field. Experiments demonstrate the ability to modulate antisymmetric and symmetric Lamb waves at 100 kHz, and Rayleigh SAWs at 100 MHz. These gratings are comparatively easy to fabricate, interchangeable, and theoretically feasible for all Rayleigh-Lamb modes.

Programmable Acoustic Metasurfaces.

Metasurfaces open up unprecedented potential for wave engineering using subwavelength sheets. However, a severe limitation of current acoustic metasurfaces is their poor reconfigurability to achieve distinct functions on demand. Here a programmable acoustic metasurface that contains an array of tunable subwavelength unit cells to break the limitation and realize versatile two-dimensional wave manipulation functions is reported. Each unit cell of the metasurface is composed of a straight channel and five shunted Helmholtz resonators, whose effective mass can be tuned by a robust fluidic system. The phase and amplitude of acoustic waves transmitting through each unit cell can be modulated dynamically and continuously. Based on such mechanism, the metasurface is able to achieve versatile wave manipulation functions, by engineering the phase and amplitude of transmission waves in the subwavelength scale. Through acoustic field scanning experiments, multiple wave manipulation functions, including steering acoustic waves, engineering acoustic beams, and switching on/off acoustic energy flow by using one design of metasurface are visually demonstrated. This work extends the metasurface research and holds great potential for a wide range of applications including acoustic imaging, communication, levitation, and tweezers.

Acoustic levitation and manipulation by a high-frequency focused ring ultrasonic transducer

Recently, acoustic levitation for non-contact micro-particle manipulation has been attracting great interest in physical, biological, and medical applications. Among the state-of-the-art manipulation technologies, single beam acoustic tweezing exhibits advantages of providing stronger trapping force and deeper penetration depth in tissues, inducing less tissue damage, and a simple configuration involving only one device. However, particle trapping by the single beam acoustic tweezer could only be operated on a smooth two-dimensional substrate, which limits the potential for real applications. Here, we report an initial attempt to acoustically levitate an individual micro-particle stably in water and manipulate the levitated micro-particle arbitrarily two-dimensionally by simply employing a 60-MHz focused ring ultrasonic transducer. The proposed working mechanism agrees well with the phenomenon. This approach could not only acoustically levitate and manipulate a micro-particle on a culture dish and on a mylar film, but could also work properly in levitating and manipulating a micro-particle placed inside the polyimide tube. This simple and low-cost approach is extremely useful for effective non-contact micro-particle manipulation without having critical concerns on the substrate properties.

Trapping Force of Acoustical Bessel Beams on a Sphere and Stable Tractor Beams

In noncontact particle manipulation by acoustic or optical beams, which is important for applications in the biological sciences and materials engineering, a $t\phantom{\rule{0}{0ex}}r\phantom{\rule{0}{0ex}}a\phantom{\rule{0}{0ex}}c\phantom{\rule{0}{0ex}}t\phantom{\rule{0}{0ex}}o\phantom{\rule{0}{0ex}}r$ $b\phantom{\rule{0}{0ex}}e\phantom{\rule{0}{0ex}}a\phantom{\rule{0}{0ex}}m$ can pull particles toward the beam's source, but long-range pulling is impossible without simultaneous trapping in the transverse direction. This study uses theory to gain insight into the parameters and conditions for simultaneous trapping and pulling of a spherical particle by an acoustic Bessel beam. Trapping at the pressure maximum of an axisymmetric Bessel beam in the Rayleigh regime is more flexible than the trapping by focused beams currently used for acoustic tweezers.

Holographic acoustic tweezers

Acoustic tweezers use sound radiation forces to manipulate matter without contact. They provide unique characteristics compared with the more established optical tweezers, such as higher trapping forces per unit input power and the ability to manipulate objects from the micrometer to the centimeter scale. They also enable the trapping of a wide range of sample materials in various media. A dramatic advancement in optical tweezers was the development of holographic optical tweezers (HOT) which enabled the independent manipulation of multiple particles leading to applications such as the assembly of 3D microstructures and the probing of soft matter. Now, 20 years after the development of HOT, we present the realization of holographic acoustic tweezers (HAT). We experimentally demonstrate a 40-kHz airborne HAT system implemented using two 256-emitter phased arrays and manipulate individually up to 25 millimetric particles simultaneously. We show that the maximum trapping forces are achieved once the emitting array satisfies Nyquist sampling and an emission phase discretization below π/8 radians. When considered on the scale of a wavelength, HAT provides similar manipulation capabilities as HOT while retaining its unique characteristics. The examples shown here suggest the future use of HAT for novel forms of displays in which the objects are made of physical levitating voxels, assembly processes in the micrometer and millimetric scale, as well as positioning and orientation of multiple objects which could lead to biomedical applications.

Acoustic tweezers for the life sciences.

Acoustic tweezers are a versatile set of tools that use sound waves to manipulate bioparticles ranging from nanometer-sized extracellular vesicles to millimeter-sized multicellular organisms. Over the past several decades, the capabilities of acoustic tweezers have expanded from simplistic particle trapping to precise rotation and translation of cells and organisms in three dimensions. Recent advances have led to reconfigured acoustic tweezers that are capable of separating, enriching, and patterning bioparticles in complex solutions. Here, we review the history and fundamentals of acoustic-tweezer technology and summarize recent breakthroughs.

Biomechanical Characterization at the Cell Scale: Present and Prospects.

The rapidly growing field of mechanobiology demands for robust and reproducible characterization of cell mechanical properties. Recent achievements in understanding the mechanical regulation of cell fate largely rely on technological platforms capable of probing the mechanical response of living cells and their physico–chemical interaction with the microenvironment. Besides the established family of atomic force microscopy (AFM) based methods, other approaches include optical, magnetic, and acoustic tweezers, as well as sensing substrates that take advantage of biomaterials chemistry and microfabrication techniques. In this review, we introduce the available methods with an emphasis on the most recent advances, and we discuss the challenges associated with their implementation.

Characterizing Deformability of Drug Resistant Patient-Derived Acute Lymphoblastic Leukemia (ALL) Cells Using Acoustic Tweezers

The role of cell mechanics in cancer cells is a novel research area that has resulted in the identification of new mechanisms of therapy resistance. Single beam acoustic (SBA) tweezers are a promising technology for the quantification of the mechanical phenotype of cells. Our previous study showed that SBA tweezers can be used to quantify the deformability of adherent breast cancer cell lines. The physical properties of patient-derived (primary) pre-B acute lymphoblastic leukemia (ALL) cells involved in chemotherapeutic resistance have not been widely investigated. Here, we demonstrate the feasibility of analyzing primary pre-B ALL cells from four cases using SBA tweezers. ALL cells showed increased deformability with increasing acoustic pressure of the SBA tweezers. Moreover, ALL cells that are resistant to chemotherapeutic drugs were more deformable than were untreated ALL cells. We demonstrated that SBA tweezers can quantify the deformability of nonadherent leukemia cells and discriminate this mechanical phenotype in chemotherapy-resistant leukemia cells in a contact- and label-free manner.

Reversals of Orbital Angular Momentum Transfer and Radiation Torque

The transfer of orbital angular momentum (OAM) from a vortex wave field to an object is interesting for developing vortex-based acoustic or optical tweezers, particularly for biomedical applications. When the object is not aligned with the vortex's core, it is unclear how OAM transfer relates to energy transfer. The author finds that here the ratio of torque to absorbed power is not given by---and can even be opposite to---the ratio of vortex topological charge to angular frequency. This suggest a negative radiation torque, associated with energy absorption, that spins an off-core axisymmetric object around its center of mass, in the direction opposite to the wave vortex's handedness.

Acoustic tweezer and its biomedical applications

Acoustic tweezer, the counterpart of optical tweezer in acoustics, was developed more than 10 years later than optical tweezer. It has been found to be capable of performing many tasks similar to optical tweezer but substantial differences also exist. Because of its larger wavelength, acoustic tweezer manipulates larger particles and yields larger forces in the nanonewton range. A number of biomedical applications have been studied including measuring intercellular forces and cellular mechanical properties. These results along with its physical principles will reviewed in this paper.

The development of dynamic holographic acoustic tweezers

Radiation forces due to sound waves can be used to create acoustic tweezers that can trap and manipulate matter without contact. They provide unique advantages when compared to the more established optical tweezers, such as higher trapping forces per unit input power and the ability to trap a wide range of sample materials. This paper describes the development of dynamically reconfigurable holographic acoustic tweezers that can independently manipulate multiple millimetre-scale particles. We present hardware and algorithms that create converging acoustic radiation forces at multiple locations in space with an array of phase controlled emitters. We experimentally demonstrate a 40 kHz airborne ultrasonic system and manipulate up to 25 particles simultaneously. As the acoustic field is dynamically up-dated in real-time and manipulation speeds of up 40 mm/s are shown. When considered on the scale of a wavelength, this system has similar manipulation capabilities to optical tweezers. We show experimental results that demonstrate potential applications, e.g., for assembly processes both in the micro-metre and millimetric scale, as well as positioning and orientation of multiple object which could led to biomedical applications.

Compact selective tweezers based on focalized acoustical vortices and spiraling interdigitated transducers

With the emergence of regenerative medicine, cell printers, and labs on chips, the contactless selective manipulation of microscopic objects such as particles, cells, or drops has become a key feature. To complete this task, acoustic tweezers appear as a tremendous alternative to their magnetic and optical counterpart. Indeed, they do not require pre-tagging of the manipulated object and they enable particles trapping with forces several orders of magnitude larger than optical tweezers at same input power. Recently, Baresh et al. [Phys. Rev. Lett., 116, 024301 (2016)] demonstrated the selective 3D manipulation of particles with a specific class of waves called acoustical vortices. Nevertheless, such manipulation was achieved with a complex transducer array coupled with a high end programmable electronics. This system is cumbersome, not compatible with microscopes and hardly miniaturizable. To overcome these difficulties, our team developed new tweezers [Riaud et al., Phys. Rev. Appl. 7, 024007 (2017)] based on spiraling interdigitated transducers (IDTs), some electrodes sputtered at the surface of piezoelectric substrates patterned by photolithography. The shape of the electrodes encodes the phase of the field like a hologram. For applications, these tweezers have many attractive features: they are selective, flat, easily integrable, and compatible with disposable substrates.