Acoustic fluidic device and method for trapping particles in a fluid - Patents.com

Abstract

An acoustic fluidic device and method for trapping particles with positive acoustic contrast contained in a moving carrier fluid is disclosed. The device comprises a first channel 11 and a second channel 12 conducting a moving carrier fluid 14. The first channel 11 and a portion 121 of the second channel parallel to the first channel 11 are separated by a common separation wall 13. A drive circuit 31 for driving an acoustic transducer 30 is configured to drive the acoustic transducer 30 at a frequency that generates an acoustic radiation force 17 on a particle in the first channel 11 toward an antinode of the displacement of a natural vibration mode of the separation wall 13, while the moving carrier fluid 14 forms at least two counter-rotating flow vortices 18 which, in combination with the acoustic radiation force 17, form a particle trap 19 at the antinode of the displacement of the natural mode.

Description

[Technical field]

[0001] The present invention relates to an acoustic fluidic device and method for trapping particles with positive acoustic contrast contained in a moving carrier fluid. [Background technology]

[0002] Being able to manipulate small particles contained in a fluid is important in many situations. One prominent example is the need to transfer cells from a growth medium to a different fluid when preparing them for electroporation. Electroporation is the process of forming pores in the cell membrane during an electric shock. Once the pores are formed, genetic material can be delivered into the cell. This is an essential step in many workflows in genetic engineering. For successful electroporation, cells must be suspended in a low-conductivity medium to prevent the cells from being briefly exposed to a strong electric field, resulting in strong currents and subsequent Joule heating that affect cell viability. This requirement is in stark contrast to the growth medium, which provides a high conductivity due to the presence of dissolved salts and other charged molecules necessary for cell growth. Thus, medium exchange becomes an essential preparatory step for each form of transformation, and protocols for preparing competent cells usually include cumbersome and time-consuming centrifugation-based washing steps.

[0003] Several methods have been developed to continuously exchange media in microfluidic systems. These methods are based on particle trapping, particle entrainment through liquid interfaces, continuous buffer exchange, droplet merging, and fluid rearrangement. The forces utilized to achieve the exchange of media are diverse. The most commonly used forces are dielectric, magnetic, hydrodynamic, and acoustic.

[0004] Acoustophoresis, the non-contact manipulation of particles using acoustic forces, is one of the most used techniques for particle manipulation due to its non-invasiveness, label-free nature, design flexibility, and biocompatibility. Acoustophoresis is based on acoustic radiation force and drag force due to acoustic streaming. Acoustic radiation force is generated by scattering of ultrasound waves at the surface of the particle. The magnitude of the acoustic radiation force depends mainly on the particle size, the density and compressibility difference between the particle and its surrounding medium, and the amplitude of the sound pressure.

[0005] In bulk acoustic wave (BAW) devices, acoustic standing waves are generated in microfluidic channels by matching the elastic wavelength in the fluid to the channel dimensions. Particles with positive acoustic contrast, typical of biological samples, accumulate at the pressure nodes of the one-dimensional standing wave. This effect can be used, for example, to focus a stream of particles to the center of a microfluidic channel.

[0006] As an example, US Patent Publication 2007 / 0139964 discloses an acoustically driven rapid buffer exchange device that transfers cells from a sheath flow containing a highly conductive cell buffer to a low conductive electroporation buffer flowing through the center of a channel. An acoustic transducer is attached to the channel substrate and configured to generate an acoustic field that focuses the particle stream toward the center of the channel and thus into a flow region of the low conductive electroporation buffer fluid where the particles are collected through an outlet located on the centerline of the channel.

[0007] However, in some applications it may be advantageous to focus the particles towards one of the channel walls instead of the channel centre. In the prior art this is achieved by changing the acoustic properties of one of the channel walls. This is described in the following two examples.

[0008] US Patent No. 5,399,633 discloses a device for concentrating particles in a fluid. The device comprises a flow channel defined by a substantially acoustically transparent membrane, preferably the upper surface of a vibration generator. Alternatively, a configuration is disclosed in which the vibration generator is isolated from the fluid in the channel by an additional layer placed between the vibration generator and the fluid. The vibration generator allows for the generation of an acoustic field in the fluid, which generates at least one pressure minimum in the fluid. The membrane acts as a pressure release surface, i.e. the reflected wave is 180 degrees out of phase with the incident wave and the pressure wave is 90 degrees out of phase with the displacement wave, resulting in a pressure node located at the surface of the membrane. Particles with a positive acoustic contrast are then driven against this pressure node.

[0009] US Patent No. 5,399,633 discloses a microfluidic particle separator comprising an acoustic extension structure located adjacent to a channel carrying a particle-containing fluid, the acoustic extension structure being used to position at least one pressure node eccentrically within the particle-fluid channel, and consisting of a second fluid channel located substantially parallel to the particle-fluid channel such that the wall between the two channels is thin enough to be "acoustically transparent", or consisting of a gel located adjacent to the particle-fluid channel.

[0010] One major drawback of acoustophoresis is its limitation on particle size. Manipulation of particles below a critical particle radius is hindered by drag forces caused by acoustic streaming. Acoustic streaming is a time-averaged nonlinear viscous effect resulting from harmonic pumping of a fluid. The acoustic radiation force is expressed as r 3 (r is the particle radius), whereas the Stokes drag force due to boundary-driven streaming scales proportionally with r. Thus, the smaller the particle radius, the stronger the competition between the drag force and the acoustic radiation force.

[0011] None of the above mentioned examples of microfluidic devices address the problem of trapping small particles where drag forces cannot be ignored.

[0012] To enable efficient focusing of small particles in BAW devices, US Pat. No. 6,399,433 discloses a method that uses burst-mode acoustic excitation to suppress the acoustic streaming field.

[0013] Another approach to focusing small particles in a moving fluid is to generate an acoustic streaming field that exhibits a particular shape. For example, an acoustic streaming field exhibiting a single vortex toward the center of a square channel has been shown by et al., "Acoustic Streaming Fields with a Single Vortex toward the Center of a Square Channel," Journal of Experimental Fluid Dynamics, Vol. 1, No. 1, pp. 111-115, 2002, and is disclosed in U.S. Patent No. 5,333,311.

[0014] Alternatively, the acoustic streaming field can be shaped by adjusting the acoustic impedance gradient, as shown by [3].

[0015] These methods of modulating the acoustic streaming field disclosed above allow for focusing of particles but not trapping, ie, particles collect at the center of the channel but continue to move along with the moving carrier fluid.

[0016] To trap submicron particles, a technique based on preloading larger seed particles in an acoustic trap and enhancing trapping through particle-particle interactions is disclosed by et al., Phys. 1999, 144:1311-1322. [Prior art documents] [Patent documents]

[0017] [Patent Document 1] International Publication No. 2020 / 047504 [Patent Document 2] US Patent Application Publication No. 2008 / 0245745 [Patent Document 3] US Patent Application Publication No. 2013 / 0043170 [Patent Document 4] U.S. Patent No. 5,831,166 [Patent Document 5] International Publication No. 2014 / 178782

Non-Patent Literature

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Summary of the Invention

[0019] In a first aspect, the object of the present invention is to provide an acoustofluidic device for trapping particles with positive acoustic contrast contained in a moving fluid. In particular, the acoustofluidic device of the present invention makes it possible to trap small particles, such as cells, for which the effect of drag forces caused by acoustic streaming is not negligible.

[0020] This object is achieved by an acoustic fluidic device according to claim 1. Further embodiments of the invention are defined in the dependent claims.

[0021] An acoustofluidic device is disclosed for trapping particles, particularly cells, having positive acoustic contrast contained in a moving carrier fluid. a first channel for conducting a moving carrier fluid containing the particles; a second channel having a portion parallel to the first channel, the parallel portions of the first channel and the second channel being separated by a common separation wall; an acoustic transducer for exciting an ultrasonic field in the first channel, the ultrasonic field generating an acoustic radiation force on the particles and causing the separation wall to vibrate; A drive circuit unit that drives the transducer; Equipped with.

[0022] In the acoustic fluid device of the present invention, the driving circuitry is configured to drive the acoustic transducer at a frequency at which the separation wall vibrates in a natural vibration mode and at which the acoustic radiation force experienced by the particles with positive acoustic contrast in the first channel is directed toward a displacement antinode of said natural mode, the term "displacement antinode" being understood as relating to the part of the separation wall where the displacement amplitude has a local maximum value.

[0023] In addition, the drive circuitry is configured to drive the acoustic transducer by providing a drive signal having an amplitude and / or frequency correspondingly set to cause at least two counter-rotating flow vortices to be formed by the moving carrier fluid which in combination with the acoustic radiation force forms a particle trap at the antinode of the displacement of the eigenmode.

[0024] Without wishing to be bound by theory, the following explanation is offered to better understand the rationale behind the present invention. A detailed derivation of the various equations can be found in H. Bruus, "Acoustofluidics 7: The acoustic radiation force on small particles", Lab on a Chip 12, 1014-1021 (2012), DOI: 10.1039 / C2LC21068A, M. Settnes et al., "Forces acting on a small particle in an acoustical field in a viscous fluid", Phys. Rev. E 85, 016327 (2012), DOI: 10.1103 / PhysRevE.85.016327, and T. Laurell et al., "Microscale Acoustofluidics", Royal Society of Chemistry (2014), ISBN: 978-1-84973-671-8, chapter 4.

[0025] For a particle in an inviscid fluid, the acoustic radiation force F rad is given by the negative gradient of the Gor'kov potential, i.e.

number

number

[0026] By "particles with positive acoustic contrast" is understood particles for which the acoustic contrast coefficient is positive, ie φ>0.

[0027] The angle brackets indicate time averaging, i.e.

number

[0028] Another force that must be considered in the acoustic fluidic devices of the present invention is the drag force caused by acoustic streaming.

number

[0029] For particles experiencing acoustic radiation and drag forces of similar magnitude, traps can form in regions of the fluid where the acoustic radiation and drag forces are spatially directed in opposite directions.

[0030] On the one hand, the driving circuitry in the microfluidic device of the invention is configured to drive the acoustic transducer at a frequency at which the Gorkov potential exhibits a minimum at the antinode of the displacement of the natural vibration mode of the separation wall. In other words, particles with a positive acoustic contrast are pushed towards said antinode of the displacement of the natural vibration mode of the separation wall. On the other hand, the driving circuitry is configured to drive the acoustic transducer such that in addition to said Gorkov potential minimum, there are at least two counter-rotating vortices in the moving carrier fluid. Without loss of generality, the flow direction of the fluid in the first channel can be referred to as the x-direction in the Cartesian coordinate system, the direction perpendicular to the separation wall can be referred to as the transverse or y-direction, and the direction perpendicular to both the flow direction x and the transverse direction y can be referred to as the height or z-direction. The direction of rotation of each vortex is such that the flow velocity vector observed in the yz-plane at the height (relative to the z-direction) of the antinode of the displacement of the natural vibration mode of the vibrating separation wall points away from the separation wall.

[0031] This arrangement of forces and flow fields creates particle traps at the antinodes of the displacements of the natural vibration modes of the separating wall.

[0032] In an advantageous embodiment, the first and second channels may be formed in a common substrate for ease of device manufacture and handling, and the separation wall is integrally formed with the substrate and extends perpendicular to the substrate plane, i.e. if the substrate plane is the xy plane, then the separation wall extends in the xz plane.

[0033] The first and second channels can be formed by removing material of the substrate, in particular by etching or micromachining, so that the separating walls present free-standing ends extending parallel to the plane of the substrate along the flow direction (x).

[0034] Alternatively, the first and second channels can be formed by shaping the material of the substrate such that the separating walls present free-standing ends extending parallel to the plane of the substrate along the flow direction (x).

[0035] The acoustic fluid device may include a cover plate that secures a free-standing end of the separation wall to facilitate excitation of a fundamental natural vibration mode that characterizes a displacement antinode at half the height of the separation wall.

[0036] In an advantageous embodiment, the natural vibration mode of the separation wall can exhibit exactly one displacement antinode in the z direction, preferably at half the height of the separation wall, i.e. the natural vibration mode corresponds to a fundamental mode in the z direction, resulting in exactly two counter-rotating vortices in the yz plane and generating only one trapped area in the z direction.

[0037] To enable simple and efficient acoustic excitation, the separation wall can be formed on a first side of the substrate relative to the substrate plane, and the acoustic transducer can be located on a second side of the substrate opposite the first side relative to the substrate plane.

[0038] In order to obtain a preferred vibration pattern of the separation wall, the second channel can have at least one open end, preferably two open ends, allowing pressure compensation of the fluid in the second channel relative to the surrounding environment.

[0039] In an advantageous embodiment, the second channel can contain a gas, in particular can be filled with a gas.

[0040] The first channel may include two or more inlets for directing fluids into the first channel, in an advantageous embodiment, a first inlet may be used to direct a carrier fluid into the first channel and a second inlet may be used to direct a displacement fluid into the first channel.

[0041] The first channel and / or the second channel may preferably have an essentially rectangular cross-section. In this context, "essentially rectangular" means that the angles between the channel walls aim for a 90° angle, but may deviate from 90° by normal, unavoidable amounts caused by the manufacturing process, e.g., etching.

[0042] In a second aspect, it is an object of the present invention to provide a method for trapping particles having positive acoustic contrast contained in a moving carrier fluid, the method comprising: Providing a carrier fluid containing particles; - establishing a flow of a carrier fluid through a first channel of an acoustic fluid device, preferably an acoustic fluid device according to the first aspect of the present invention, the acoustic fluid device comprising a second channel having a portion parallel to the first channel, the parallel portions of the first and second channels being separated by a common separation wall; driving an acoustic transducer to excite an ultrasonic field in the first channel, the ultrasonic field generating an acoustic radiation force on the particles and causing the separation wall to vibrate; Including, the acoustic transducer is driven at a frequency such that the separation wall vibrates in a natural vibration mode and such that the acoustic radiation force experienced by the particles having positive acoustic contrast in the first channel is directed toward an antinode of the displacement of the natural vibration mode; The acoustic transducer includes a moving carrier fluid that is actuated to form at least two counter-rotating flow vortices that combine with an acoustic radiation force to form a particle trap at a displacement antinode of the eigenmode.

[0043] The method of trapping particles can further include disrupting a flow of the carrier fluid containing the particles and then establishing a flow of a replacement fluid through the first channel.

[0044] The displacement fluid may be supplied to the first channel through the same inlet as the carrier fluid containing the particles and / or through a different inlet.

[0045] The method can further include switching off the acoustic transducer and releasing the particles while maintaining a flow of the replacement fluid through the first channel.

[0046] Preferred embodiments of the invention will now be described with reference to the drawings, which are intended to illustrate preferred embodiments of the invention and are not intended to limit the invention. [Brief description of the drawings]

[0047] [Figure 1] FIG. 1 is a schematic plan view of a microfluidic device according to a preferred embodiment. [Diagram 2] FIG. 2 is a schematic cross-sectional view of the microfluidic device of FIG. [Figure 3a] FIG. 3a is a schematic enlarged cross-sectional view of the microfluidic device of FIG. [Figure 3b] FIG. 3b is a schematic enlarged cross-sectional view of the microfluidic device of FIG. [Figure 4] FIG. 4 is a schematic side view of a preferred method of using a microfluidic device according to the present invention. [Figure 5a] FIG. 5a is a schematic enlarged plan view of a preferred method of using a microfluidic device according to the present invention. [Figure 5b] FIG. 5b is a schematic enlarged plan view of a preferred method of using a microfluidic device according to the present invention. [Figure 5c] FIG. 5c is a schematic enlarged plan view of a preferred method of using a microfluidic device according to the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0048] <Definition> In the present disclosure, a "carrier fluid" can be any type of fluid capable of carrying particles. In particular, the carrier fluid can be the growth medium in which the cells were grown.

[0049] The "replacement fluid" can be any type of fluid into which the particles are transferred. In particular, the replacement fluid can be an aqueous solution having a lower conductivity than the carrier fluid. In particular, the replacement fluid can be a solution having a conductivity low enough to allow electroporation of cells in said solution without affecting the viability of the cells.

[0050] The "acoustic transducer" may be any type of transducer capable of inducing ultrasonic waves in the first channel and vibrating the separating wall. In particular, the acoustic transducer may be a piezoelectric transducer.

[0051] The term "drive circuitry" should be understood to relate to any device or configuration of devices capable of driving a particular acoustic transducer such that the transducer induces ultrasound waves in the first channel and vibrates the separation wall. In particular, the drive circuitry may comprise a function generator that generates a periodic voltage signal having an adjustable frequency, and may also comprise a voltage amplifier.

[0052] Preferred Embodiments Figures 1 to 5 show an acoustic fluidic device according to a preferred embodiment of the present invention. It should be understood that the acoustic fluidic device is shown very diagrammatically and the drawings are not to scale. The cross-sectional plane of the cross-sectional views of Figures 2, 3a and 3b is shown as plane AA in Figure 1.

[0053] The acoustic fluidic device comprises a channel arrangement 10. The channel arrangement 10 comprises a first channel 11 and a second channel 12. The second channel 12 has a parallel portion 121 to the first channel 11. The parallel portions 121 of the first channel 11 and the second channel 12 are separated by a common separation wall 13. The parallel portions 121 of the first channel 11 and the second channel 12 are arranged side-by-side in a common plane. The common plane is referred to below as the substrate plane or the xy plane. The directions are defined as follows: the x direction extends along the parallel portion 121 of the second channel; the y direction is transverse to the substrate plane, perpendicular to the x direction; and the z direction is perpendicular to both the x and y directions. Figure 1 shows a plan view (xy plane) of a preferred channel arrangement 10.

[0054] The first channel has a first inlet 111 and a second inlet 112. The second channel 12 is open at both ends. The channels 11 and 12 are embedded in a substrate 20, which in particular may be a silicon wafer.

[0055] FIG. 2 shows a cross-sectional view of the acoustic fluidic device in the plane AA of FIG. 1. The center of the first channel 11 can be offset in the y direction by a distance d with respect to the center of the substrate 20. The separation wall 13 is formed integrally with the substrate 20 and extends along the z direction in the xz plane, i.e. perpendicular to the substrate plane. The separation wall 13 is formed on a first side of the substrate 20 and the acoustic transducer 30 is arranged on a second side of the substrate 20 opposite the first side. The acoustic transducer 30 can be connected to the substrate 20 using a layer of adhesive 32. The acoustic fluidic device further comprises a cover plate 40 that mechanically clamps the free-standing end of the separation wall 13. The cover plate 40 can be a glass wafer that is anodically bonded to the substrate 20. The first channel 11 conducts a carrier fluid 14 containing particles 15. The second channel 12 contains a gas 16, which in particular can be air.

[0056] The acoustic transducer 30 is driven by a driving circuitry 31. The acoustic transducer 30 excites an ultrasonic field in the first channel 11, vibrating the separation wall 13. The ultrasonic field generates an acoustic radiation force 17 on the particle 15. The driving circuitry 31 drives the acoustic transducer 30 at a frequency at which the separation wall 13 vibrates in a natural vibration mode that exhibits a displacement antinode. The natural vibration mode can exhibit multiple displacement antinodes in the x-direction, but preferably exhibits exactly one displacement antinode in the z-direction. The displacement antinode is preferably located at half the height of the separation wall 13 (along the z-direction), as shown diagrammatically in Figures 3a and 3b. The acoustic radiation force 17 experienced by the particle 15 with positive acoustic contrast in the first channel 11 is directed towards the displacement antinode of the natural mode when the transducer 30 is driven at the frequency. The magnitude and direction of the acoustic radiation force 17 are diagrammatically indicated by the length and direction, respectively, of the arrow in Figure 3a.

[0057] In addition, drive circuitry 31 drives acoustic transducer 30 such that at least two counter-rotating flow vortices 18 are formed by the moving carrier fluid 11 which combine with the acoustic radiation force 17 to form particle traps 19 at the displacement antinodes of the eigenmode. The magnitude and direction of the flow velocities are indicated by the length and direction, respectively, of the arrows in Figure 3b.

[0058] 4 and 5 show diagrammatically a preferred method of exchanging fluid around a particle 15 using the acoustic fluid device 1. FIG.

[0059] As can be seen in Fig. 4, the carrier fluid 14 containing the particles 15 is provided in the reservoir 51 and the replacement fluid 70 is provided in the reservoir 52. The fluid supply mechanism 60 connects the reservoirs 51 and 52 to the channel mechanism 10. The supply mechanism 60 may comprise glass capillaries inserted into the inlets 111 and 112 and fixed by a two-component adhesive. The fluid supply mechanism 60 may further comprise a junction and / or a valve. Flow generation devices 81 and 82 are provided to establish the flow of the carrier fluid 14 and the replacement fluid 70, respectively. The flow generation devices 81 and 82 may be pumps that exert mechanical pressure on the fluids, for example syringe pumps or peristaltic pumps, or pneumatic sources that provide air pressure in a gas in contact with the fluids. The flow generation device 81 may be based on a different operating principle than the flow generation device 82.

[0060] In a first step of the preferred method, a flow of carrier fluid 14 containing particles 15 is established through the first channel 11 using a flow generating device 81. The carrier fluid 14 preferably enters the first channel 11 through a first inlet 111. The acoustic transducer 30 is driven using drive circuitry 31 at a frequency at which the separation wall 13 vibrates in a natural vibration mode and at a frequency at which the acoustic radiation force 17 experienced by the particles 15 in the first channel 11 is directed towards one or more displacement antinodes of said natural mode. Furthermore, the acoustic transducer is driven such that the moving carrier fluid 14 creates at least two counter-rotating flow vortices 18 adjacent each displacement antinode which in combination with the acoustic radiation force 17 form particle traps 19 at the displacement antinodes of the natural mode.

[0061] Figures 5a-c show an excerpt of the channel arrangement 10 seen from above. As shown diagrammatically in Figure 5a, particles accumulate in traps 19 located at the antinodes of the displacement of the natural vibration mode of the separation wall 13.

[0062] In a second step of the preferred method, shown in Figure 5b, the flow of carrier fluid 14 containing particles 15 is interrupted. Using a flow generating device 82, a flow of displacement fluid 70 is established through the first channel 11. The displacement fluid 70 preferably enters the first channel 11 through the second inlet 112. The carrier fluid 14 still present in the first channel 11 after interrupting the flow of the carrier fluid is replaced by the displacement fluid 70 while the particles 15 remain in the trap 19.

[0063] In a third step of the preferred method, which is preferably performed as soon as the carrier fluid 14 has been completely expelled from the first channel 11, the acoustic transducer 30 is switched off and the particles 15 are released while maintaining the flow of replacement fluid 70 through the first channel 11.

[0064] The replacement fluid 70 containing the particles 15 can then be collected using an outlet mechanism 90, which can include a glass capillary tube inserted into the downstream end of the first channel 11 and secured by a two-component adhesive.

[0065] <Determination of excitation frequency> In acoustohydrodynamics, it is customary to use acoustic energy density as a benchmark for device performance. Average Acoustic Energy Density

number

number

[0066] The average acoustic energy density integrated over the cross section of the first channel 11 and divided by its area can be evaluated as a function of the frequency f at which the transducer 30 is excited. Furthermore, a two-dimensional numerical model can be used to predict the amplitudes of the natural vibration modes of the separation wall 13 as a function of frequency f. Maxima of the amplitudes of the natural vibration modes of the average acoustic energy density and the separation wall displacement, which coincide with respect to the position on the frequency axis, indicate the resonances of the device. At these resonant frequencies, the acoustic radiation force derived from the Gorkov potential and the flow velocity field can be evaluated numerically to verify: 1. The acoustic radiation force is directed toward the antinode of the displacement of the eigenmode of the separation wall (schematically shown in FIG. 3a); and 2. Two counter-rotating vortices are generated, and the direction of rotation of each vortex is such that the flow velocity vector at the antinode height (z direction) of the displacement of the eigenmode of the vibrating separating wall is directed towards the centre of the first channel 11 (schematically shown in Figure 3b).

[0067] The excitation frequency selected according to these two criteria results in the formation of particle traps at the antinodes of the displacement of the eigenmodes of the separation wall. To account for the mismatch between the idealized material parameters used as input for the simulation and the real material parameters, the drive circuitry 31 can be configured to sweep the excitation frequency around a numerically determined frequency that satisfies the above-mentioned criteria. Furthermore, the drive circuitry 31 can be configured to adjust the amplitude of the drive signal used to drive the acoustic transducer to account for the fact that the acoustic transducer may have an impedance that depends on the excitation frequency. Sweeping the frequency and / or adjusting the amplitude of the drive signal to optimize particle trapping can be done experimentally while observing the particle trapping process. The efficiency of the particle trapping process can be evaluated in real time by imaging the trapping area using a microscope or by determining the particle concentration in the carrier fluid downstream of the first channel 11 and comparing it to the particle concentration in the carrier fluid upstream of the first channel 11.

[0068] Dimensional considerations, material considerations, and device fabrication In a particular embodiment of the present invention, the substrate 20 may be made of silicon and has a width w s = 4mm and height h s = 500 μm. Both the first channel 11 and the parallel portion 121 of the second channel have an essentially rectangular cross section. Both the first channel 11 and the parallel portion 121 of the second channel have a height h c The center of the first channel 11 may be offset in the y direction by a distance d=200 μm relative to the center of the substrate 20. The first channel 11 may have a width w c1 = 154 μm, while the parallel portion 121 of the second channel can have a width w c2 = 150 μm. The cover plate 40 may be made of glass and have a thickness t g = 700 μm.

[0069] The separation wall, in this particular embodiment, may have a thickness of 4 μm where the separation wall 13 connects to the substrate 20 and a thickness of 5 μm where the separation wall 13 contacts the cover plate 40. The transducer has a length l p = 10mm, height h p = 0.9 mm, and width w p = 2 mm and can be a piezoelectric element (piezo) that can be driven by a high frequency amplified AC signal from a waveform generator at a frequency f = 1.8 MHz. In a particular method of using this particular device to capture E. coli cells, the flow rate of the carrier fluid 14 can be set to 10 μL / min in a first step of the process, and in a second step of the process, the flow rate of the carrier fluid can be set to zero and the flow rate of the displacement fluid 70 can be set to 10 μL / min with the piezo still driven. In a third step of the process, the waveform generator driving the piezo is switched off and the flow rate of the displacement fluid 70 can be set to 20 μL / min.

[0070] In a preferred embodiment, the substrate 20 may be made of silicon and the channel feature 10 may be obtained as follows: First, using photolithography (resist: S1813, Shipley, 4000 rpm; exposure dose: 230 mJ / cm 2 A chrome mask is then placed in an inductively coupled plasma deep reactive ion etching (ICP-DRIE) machine (Estrellas, Oxford instruments) to transfer the design from the chrome mask onto a silicon wafer. Using a fast process modified as described by MS Gerlt et al., "Reduced etch lag and high aspect ratios by deep reactive ion etching (DRIE)", https: / / arxiv.org / abs / 2104.02763, (2021), straight channel walls are achieved with a selectivity (ratio of the etch rate of photoresist to silicon) of about 350 and an angle α of about 89.7°, where α is defined as the angle in the yz plane between the substrate plane and the separation wall when the separation wall is not vibrating (see Figures 3a and 3b).

[0071] In further embodiments, the substrate 20 can be comprised of, but is not limited to, an oxide (e.g., glass), a metal (e.g., steel, tungsten, titanium), an elastomer (e.g., PDMS), a thermoplastic (e.g., PET, PS, COC), or a thermoset polymer.

[0072] Instead of being formed by etching, the channels can be formed by mechanical or optical micromachining, or by shaping the material of the substrate.

[0073] The material of the cover plate 40 is not limited to glass, but can be any other suitable material or combination of materials.

[0074] Further embodiments of the present invention may exhibit different channel dimensions than the exemplary embodiment described above. The width and height of the first channel may vary, but preferably the first channel has a channel cross-sectional area of ​​30000 μm 2 ~40,000μm 2 The height of the second channel (i.e. along the z-direction) is preferably the same as the height of the first channel. The separation walls can have different thicknesses and different wall angles. 2 ~40,000μm 2 In this case, the average thickness of the separation walls is preferably less than 15 μm, the wall angle α is preferably between 87° and 90°, and the length of the separation walls (in x-direction) is preferably between 1 mm and 8 mm. Microfluidic devices according to further embodiments can operate over a wide range of excitation frequencies, typically between 1 kHz and 3 MHz. The optimal excitation frequency depends on the combination of geometric dimensions and material selection, but can always be found using a combination of the numerical and experimental steps described above.

[0075] <Other modifications> Many variations of the microfluidic device described above are possible. For example, the inlets 111 and 112 may be located outside the substrate 20 instead of being embedded therein, for example formed by a capillary arrangement with one or more junctions. The number of inlets and outlets is also not limited, and the inlets and outlets can be located in all directions in three-dimensional space. Fluids can also be directed towards and / or out of the first channel 11 through a cover plate. [Explanation of symbols]

[0076] 10 Channel facility 11 First Channel 12 Second Channel 13 Separation wall 14 Carrier Fluid 15 particles 16 Gas 17 Acoustic radiation force 18 Flow Vortex 19 Particle Trap 20 Substrate 30 Acoustic Transducer 31 Drive circuit section 32 Glue Layer 40 Cover Plate 51 Reservoir 52 Reservoir 60 Supply mechanism 70 Displacement fluid 81 Flow Generation Device 82 Flow Generation Device 111 Entrance 112 Entrance 121 Parallel section of the second channel α angle

Claims

1. 1. An acoustofluidic device for trapping particles, particularly cells, having positive acoustic contrast, contained in a moving carrier fluid, comprising: a first channel (11) for conducting the moving carrier fluid (14) containing the particles (15); a second channel (12) having a portion (121) parallel to the first channel, the first channel (11) and the parallel portion (121) of the second channel being separated by a common separation wall (13); an acoustic transducer (30) for exciting an ultrasonic field in the first channel (11), the ultrasonic field generating an acoustic radiation force (17) on the particles (15) and causing the separation wall (13) to vibrate; a drive circuitry (31) for driving the transducer (30), the drive circuitry (31) being configured to drive the acoustic transducer (30) at a frequency at which the separation wall (13) vibrates in a natural vibration mode and at which the acoustic radiation force (17) experienced by the particles (15) having a positive acoustic contrast in the first channel (11) is directed toward an antinode of the displacement of the natural mode; Equipped with 1. The acoustic fluid device, wherein the drive circuitry (31) is configured to drive the acoustic transducer (30) such that at least two counter-rotating flow vortices (18) are formed by the moving carrier fluid (14) which, in combination with the acoustic radiation force (17), form a particle trap (19) at the displacement antinode of the eigenmode.

2. The acoustic fluidic device of claim 1, wherein the first channel (11) and the second channel (12) are formed in a common substrate (20) defining a substrate plane, the first channel and the second channel are arranged side-by-side with respect to the substrate plane, and the separation wall (13) is formed integrally with the substrate (20) and extends perpendicular to the substrate plane.

3. the first channel (11) and the second channel (12) are formed by removing material of the substrate (20), in particular by etching or micromachining, such that the separating wall (13) presents a free-standing end parallel to the substrate plane, or the first channel (11) and the second channel (12) are formed by shaping the material of the substrate (20) such that the separation wall (13) presents a free-standing edge parallel to the substrate plane; 3. The acoustic fluid device of claim 2.

4. 4. The acoustic fluid device of claim 3, further comprising a cover plate (40) that secures the free-standing end of the separation wall (13).

5. 5. An acoustic fluidic device according to claim 4, wherein the natural vibration mode of the separation wall (13) exhibits exactly one displacement antinode in a direction perpendicular to the substrate plane.

6. The acoustic fluid device of any one of claims 2 to 5, wherein the separation wall (13) is formed on a first side of the substrate (20) relative to the substrate plane, and the acoustic transducer (30) is arranged on a second side of the substrate (20) opposite the first side relative to the substrate plane.

7. An acoustic fluidic device according to any one of the preceding claims, wherein the second channel (12) has at least one open end, preferably two open ends.

8. The acoustic fluidic device according to any one of the preceding claims, wherein the first channel comprises two or more inlets (111, 112) for directing fluid into the first channel (11).

9. An acoustic fluidic device according to any one of the preceding claims, wherein the first channel (11) and / or the second channel (12) have an essentially rectangular cross section.

10. The acoustic fluid device of any one of claims 1 to 5, wherein the second channel (12) contains a gas (16).

11. A method for trapping particles, particularly cells, with positive acoustic contrast contained in a moving carrier fluid (14), comprising the steps of: Providing a carrier fluid (14) containing particles (15); - establishing a flow of said carrier fluid (14) through a first channel (11) of an acoustic fluid device, preferably an acoustic fluid device according to any one of claims 1 to 5, said acoustic fluid device comprising a second channel (12) having a portion (121) parallel to said first channel, said parallel portions (121) of said first channel (11) and said second channel being separated by a common separating wall (13); driving an acoustic transducer (30) to excite an ultrasonic field in the first channel (11), the ultrasonic field generating an acoustic radiation force (17) on the particles (15) and vibrating the separation wall (13); Including, the acoustic transducer (30) is driven at a frequency at which the separation wall (13) vibrates in a natural vibration mode and at a frequency at which the acoustic radiation force (17) experienced by the particles (15) having a positive acoustic contrast in the first channel is directed toward an antinode of the displacement of the natural mode; the acoustic transducer (30) is driven such that at least two counter-rotating flow vortices (18) are formed by the moving carrier fluid (14) which in combination with the acoustic radiation force (17) form a particle trap (19) at the displacement antinode of the eigenmode.

12. disrupting a flow of the carrier fluid (14) containing the particles (15); thereafter, establishing a flow of a displacement fluid (70) through said first channel (11); The method of claim 11 further comprising:

13. 13. The method of claim 12, further comprising supplying the replacement fluid (70) to the first channel (11) through the same inlet (111) as the carrier fluid (14) containing the particles (15) and / or through a different inlet (112).

14. 13. The method of claim 12, further comprising switching off the acoustic transducer (30) and releasing the particle (15) while maintaining a flow of the displacement fluid (70) through the first channel (11).

15. 13. The method of claim 12, wherein the displacement fluid (70) is a low-conductivity fluid suitable for electroporation.

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