Acoustophoretic printing apparatus and method

Abstract

The present invention contains a printing apparatus and a method, e.g., for ejecting inks (i.e. pure liquids, mixtures, colloids, etc.) for a very broad range of physical properties (such as viscosity). Acoustic forces 3a may be generated by an emitter 1 and a reflector 2 to detach droplets 10 from a nozzle 6. The ink may be advanced through the nozzle 6 by a standard back pressure system 5. A reflectorless chamber 7 may enhance acoustic forces 8a and the droplets 10 may be ejected at a bottom 9 of said chamber 7, so that droplets 10 may be deposited on any substrate 11.

Claims

1. A printing apparatus comprising: an emitter arranged within a first fluid and configured to oscillate for generating an acoustic field in said first fluid; a nozzle with a nozzle tip placed at a predetermined position within said acoustic field; a second fluid within the nozzle, and a driving means configured to drive a predetermined volume of the second fluid out of the nozzle, wherein the emitter is configured to oscillate with a frequency of 1 Hz to 1 GHz.

2. The printing apparatus according to claim 1, characterized in that a reflector is arranged between the emitter and a printing substrate.

3. The printing apparatus according to claim 2, characterized in that a surface of the reflector is positioned at a distance (H) to the emitter, wherein the distance (H) is a multiple of /20.2, with being the wavelength of sound waves of a first acoustic field between the emitter and the reflector surface.

4. The printing apparatus according to claim 2, characterized in that the reflector has a reflectorless chamber which is arranged along a printing axis (A) between the nozzle tip and the printing substrate, wherein the reflectorless chamber is a through-hole in a body of the reflector.

5. The printing apparatus according to claim 4, characterized in that the predetermined position of the nozzle tip is within the reflectorless chamber in a region from an exit of the reflectorless chamber to Hh/3, with Hh being a height of the reflectorless chamber.

6. The printing apparatus according to claim 1, characterized in that the printing apparatus comprises a plurality of emitters, wherein the emitters are arranged such that emitted sound waves are focused on a predetermined point in space within the acoustic field, and the predetermined position of the nozzle tip is at said predetermined point in space or in the vicinity thereof.

7. The printing apparatus according to claim 1, characterized in that the acoustic field has a force gradient of acoustic forces, and the predetermined position of the nozzle tip is at a point or in the vicinity of a net force that pulls at the droplet pendant at the nozzle tip.

8. The printing apparatus according to claim 1, characterized in that a plurality of nozzles and/or reflectorless chambers are arrayed for forming a multi-nozzle print head.

9. The printing apparatus according to claim 1, characterized in that the nozzle has a heating means and/or a cooling means for heating/cooling the second fluid to a predetermined temperature.

10. The printing apparatus according to claim 1, characterized in that a print head, which can be the emitter or the reflector, comprises a plurality of reflectorless chambers.

11. The printing apparatus according to claim 1, characterized in that the nozzle and the drive means are connected via a tubing, wherein the tubing is introduced into the printing apparatus at a side surface thereof below the emitter or through a hole in the emitter.

12. The printing apparatus according to claim 1, characterized in that the predetermined volume ranges from nl to l.

13. The printing apparatus according to claim 1, characterized by further comprising a control means configured to control at least the oscillation of the emitter, the pressure application of the drive means and/or a driving of the printing apparatus to a printing position in relation to a printing substrate.

14. A printing apparatus comprising: an emitter arranged within a first fluid and configured to oscillate for generating an acoustic field in said first fluid; a nozzle with a nozzle tip placed at a predetermined position within said acoustic field; a second fluid within the nozzle; and a driving means configured to drive a predetermined volume of the second fluid out of the nozzle, wherein the acoustic field has a force gradient of acoustic forces, and the predetermined position of the nozzle tip is at a point or in the vicinity of a net force that pulls at a droplet pendant at the nozzle tip.

15. A printing apparatus comprising: an emitter arranged within a first fluid and configured to oscillate for generating an acoustic field in said first fluid; a nozzle with a nozzle tip placed at a predetermined position within said acoustic field; a second fluid within the nozzle; a driving means configured to drive a predetermined volume of the second fluid out of the nozzle; and a control means configured to control at least an oscillation of the emitter, a pressure application of the drive means, and/or a driving of the printing apparatus to a printing position in relation to a printing substrate.

Description

(1) In the following, examples are set forth with reference to the attached schematic drawings:

(2) FIG. 1 An acoustophoretic ejection system/acoustophoretic printing apparatus. A reflectorless chamber is halved only for illustration purposes. The close ups show ejected glycerol and water droplets (scale bar=500 m).

(3) FIG. 2a) Acoustic levitation in a conventional (state-of-the art) standing wave levitator and acoustic force distribution. In this case, one acoustic node is present (H/2);

(4) b) When a pendant drop is placed within the conventional standing wave levitator, it experiences both body forces (gravitational, F.sub.g) and surface forces (acoustics, F.sub.a, and capillary, F.sub.c).

(5) FIG. 3 Acoustophoretic printing size control capabilities. More than three orders of magnitude of volume for DOD ejection can be controlled with the here-described acoustophoretic printing apparatus/method.

(6) FIG. 4 Two preferred alternative configurations of an acoustophoretic printing apparatus:

(7) Configuration A) A nozzle is introduced from a side of a chamber (with a main/first standing wave) and reaches a reflectorless chamber where a secondary acoustic standing wave is present.

(8) Configuration B) A nozzle enters from a hole on a top of the emitter/reflector and ends in a reflectorless chamber.

(9) FIG. 5 Multiple nozzle configuration of an acoustophoretic printing apparatus. By replicating a configuration as depicted in FIGS. 4a, 4b, multiple droplets (also of different inks) can be simultaneously ejected. The ejection angle allows for a fine printing resolution at the substrate/target surface.

(10) FIG. 6 Two emitters are used to achieve a standing wave without a reflector.

(11) FIG. 7 Multiple emitters can be used to enhance the acoustic radiation pressure at a single focal point or to create a vortex beam.

(12) FIG. 8 An emitter can be designed so that it can simultaneously act as a reflector. Both sides oscillate from opposite direction, creating a standing wave.

(13) FIG. 9 An acoustophoretic printing apparatus used as a sample dispenser for biological solutions in the nl-l range volume for standard 96, 384 and 1536 well plates.

(14) FIG. 10 An exemplary numerical simulation of the acoustic pressure (in Pascal) within a preferred configuration of an acoustophoretic printing apparatus. In this particular case, the maximum acoustic pressure in the primary chamber is 3300 Pa, while in a reflectorless chamber the pressure is 15000 Pa. Since the acoustic forces are proportional to the square of the acoustic pressure, an enhancement of 25 times is expected.

(15) References in the specification to a given example indicate that the example described may include a particular feature, structure, or characteristic, but every example may not necessarily include the particular feature, structure, or characteristic. It should be noted that the description and drawings/figures merely illustrate the principles of the proposed apparatus and method. It will thus be appreciated that those skilled in the art will be able to devise various combinations and the like that are not explicitly described or shown herein. Furthermore, all examples recited herein are principally intended expressly to be only for pedagogical purposes to aid the reader in understanding the principles of the proposed method and apparatus and the concepts contributed by the inventors to furthering the art, and are to be construed as being without limitation to such specifically recited examples and conditions. Moreover, all statements herein reciting principles, aspects, and embodiments, as well as specific examples thereof, are intended to encompass equivalents thereof.

(16) FIGS. 2a and 2b show conventional configurations of a standing wave levitator, which are used for trapping particles or fluids at a location of an acoustic node between an emitter 1 and a reflector 2. The emitter 1 generates an acoustic field 3 of sound waves, which apply an acoustic force 3a (radiation pressure) on objects, which are positioned within the acoustic field 3. In the typical configuration of a standing wave levitator, as depicted in FIGS. 2a and 2b, a (detached) droplet 10 is trapped at the location of the acoustic node (see FIG. 2a). An ejection of the trapped droplet 10 with the conventional standing wave levitator is very difficult.

(17) The here-described printing apparatus and the printing method make use of the same physical principle as the conventional standing wave levitator, however, different to the standing wave levitator, allow ejecting droplets, in particular, from a nozzle.

(18) The physical principle of levitating objects by acoustic forces will be briefly described: sound waves apply forces on objects. The acoustic forces 3a, 8a, which are used in connection with the here described printing apparatus and printing method, in particular, arise from radiation pressure. Radiation pressure is a nonlinear effect of the acoustic field 3 (E. H. Brandt, Nature 413 (2001)). Based on wave scattering, acoustic forces are practically material independent, in particular when handling samples in air (D. Foresti, and D. Poulikakos, Physical Review Letters (2014)). Albeit radiation pressure is usually relatively weak, it can levitate, e.g. in open air, objects as heavy as steel marbles. The levitation can be achieved, e.g., when properly focusing the radiation pressure (N. Bjelobrk et al., Appl Phys Lett 97 (2010); D. Foresti et al., Sci Rep-UK 3 (2013)). To describe modulation of such acoustic forces 3a, 8a in time and space that can facilitate transport of matter, the term acoustophoresis is used (D. Foresti et al., P Natl Acad Sci USA 110 (2013)).

(19) The enhancement of such forces 3a, 8a is typically, but not necessarily, achieved by generating an acoustic standing wave, established between an emitter 1 and a reflector 2 (see FIG. 2a; and D. Foresti, M. Nabavi, and D. Poulikakos, Journal of Fluid Mechanics 709 (2012)). The resonant condition suggests the distance H between an oscillating source and a reflective surface to be about a multiple of half of the wavelength . When H/2, a pressure node is generated in the middle of the levitator. Below the node the acoustic forces 3a, 8a oppose the gravitational force, and vice versa above the node (FIG. 2a). Acoustic levitation is indeed intrinsically stable.

(20) When a drop 10 of radius R.sub.s is introduced in the system, as it is exemplarily shown in FIG. 2b, wherein the drop 10 is pendant from a nozzle 6 of diameter d, the drop 10 experiences a force that is the sum of the capillary force F.sub.c=d, the gravitational force F.sub.g and the acoustic force F.sub.a (FIG. 2b).

(21) If F.sub.c>F.sub.g+F.sub.a, the droplet 10 stays attached to the nozzle 6, otherwise the droplet 10 will detach. The acoustic force F.sub.a scales with the volume of the drop/droplet 10 (being attached to the nozzle 6), hence F.sub.a R.sub.s.sup.3. Since the same scaling applies for the gravity force, an acoustic acceleration g.sub.a can be introduced, which is similar to the gravitational acceleration g, and the following relationship is obtained:

(22) $F_c=d=F_g+F_a=\frac{4}{3}{R}_s^3\left(g+g_a\right)R_s=\sqrt[3]{\frac{3d}{4\left(g+g_a\right)}}$

(23) The above relationship tells that the droplet size at detachment is controllable by controlling the acoustic acceleration g.sub.a, i.e., the acoustic forces F.sub.a.

(24) Hence, differently from conventional inkjet printing, the acoustphoretically detached droplet 10 is pulled out of the nozzle 6 by/from the external acoustic field 3 (specifically, the acoustic forces 3a, 8a resulting therefrom) instead of being pushed by an internal pressure wave. The external acoustic field 3 is tunable. The fluid dynamics within the nozzle 6 do not limit the printing. The above relationship shows the independence of the printing method from the viscosity of the fluid (for Newtonian fluids).

(25) A preferred example of the here-introduced acoustophoretic printing apparatus may be called a reflectorless standing wave levitator. A schematic representation of is shown, e.g., in FIG. 1.

(26) The acoustophoretic printing apparatus of FIG. 1 has an emitter 1 which (periodically) oscillates so that sound waves are emitted that form an acoustic field 3 within a first fluid (not explicitly shown). The first fluid is preferably air. In a possibly simplest configuration, the emitter 1 is a planar or curved member with a circular, elliptic, quadratic, rectangular or the like cross-section, which oscillates. The emitter 1 may be connected to an oscillator (not shown) which excites/moves the emitter 1.

(27) Further, the acoustophoretic printing apparatus according to the example of FIG. 1 has a nozzle 6 being placed inside a reflectorless chamber or conduit 7. The reflectorless chamber 7 is formed as a through-hole, which extends from an upper surface 2a of a reflector 2 to a lower surface 2b of the reflector 2. FIG. 1 shows a preferred example of an annular-shaped reflector 2. The axis of symmetry of the reflector 2 is arranged on a printing axis A (see FIG. 4), along which droplets 10 of second fluid are ejected. The surfaces 2a, 2b are shown as planar surfaces. Said chamber 7 traps a (second or secondary) acoustic standing wave 8.

(28) The reflector 2 of said preferred configuration of an acoustophoretic printing apparatus may have one or more of the following three characteristics: (1) There is no reflector on top or bottom of the nozzle axis; hence, the name reflectorless. In other words, the reflectorless chamber 7 connects two openings being arranged within the upper and lower surface 2a, 2b of the reflector 2. (2) The acoustic force 3a, 8a (inside the chamber 7) is enhanced up to 1-100, e.g. 30 times, compared to the above-described typical conventional levitator configuration as shown in FIG. 2a. (3) A force gradient of the acoustic forces 3a, 8a, in particular with a top force stronger than a bottom force (directions according to FIG. 1), is present. A net force is, i.a., present because of the optimal design of the reflectorless chamber 7, e.g. the (relatively small) diameter of the reflectorless chamber 7 compared to the wavelength of the acoustic field. This particular distribution enables the droplet 10 to be detached, accelerated and ejected out of the reflectorless levitator/acoustophoretic printing apparatus and to be printed on any object/(printing) substrate 11.

(29) Further, a drive means 5, e.g. a syringe pump as shown in FIG. 1, is used to feed the nozzle 6, via a tubing 4, with droplets on-demand so that a highly-precisely controlled droplet ejection is possible. The tubing 4 may be flexible, and, for instance, the tubing 4 may be made from flexible plastics.

(30) Proof of principle experiments with water and glycerol confirmed the droplet ejection (FIG. 3). For the experiments, a reflectorless chamber 7 diameter of 2 mm and with a length of 5 mm was used. The emitter diameter was set to 17 mm (circular), the height of the reflector emitter (shaped as shown in FIG. 1) was 7 mm, the nozzle tip 6a was placed at Hh=0.7 (i.e. in the lower part of the reflectorless chamber diameter 7). The distance H between the upper surface 2a of the reflector 2 and the lower surface 1a of the emitter 1 was 0.52. A drive means 5, a syringe pump, imposed a flow rate through the nozzle 6, while the acoustic forces 3a, 8a can control the droplet size detachment up to 3 orders of magnitude with a single 50 m diameter nozzle (75 m<Rs<650 m). The ultrasonic frequency, which was used in this example experiment, was set to 25 kHz. With the interplay of flow rate and acoustic force 3a, 8a, ejection frequency can go as high as 2 kHz in the DOD mode or several kHz in continuous jetting mode. Additionally, the extrusion mode can also be potentially used, since the ink flows through a nozzle 6.

(31) Further, in addition to the experimental results, a numerical simulation was carried out. FIG. 10 presents results of an exemplary numerical simulation of the acoustic pressure (in Pascal) within a preferred configuration of an acoustophoretic printing apparatus. In this particular example case, the maximum acoustic pressure in the (primary) chamber (between the emitter 1 and the reflector 2) is 3300 Pa, while in the reflectorless chamber 7 the pressure is 15000 Pa. Since the acoustic forces 3a, 8a are proportional to the square of the acoustic pressure, an enhancement of 25 times is expected.

(32) Further, two preferred alternative configurations of the acoustophoretic printing apparatus are depicted by FIG. 4.

(33) Configuration A) of FIG. 4 shows that the nozzle 6 is introduced from a side (wall) of a chamber or open space between the emitter 1 and the reflector 2. The open space or chamber includes the first/main standing wave. The tubing 4 is bent so that the nozzle 6 can reach the conduit or reflectorless chamber 7, where a secondary acoustic standing wave or, at least, a second acoustic field 8 is present.

(34) Configuration B) of FIG. 4 shows that the nozzle 6 or the tubing 4 enters from a hole 14 on a top of the emitter 1 and ends in the reflectorless chamber 7.

(35) Furthermore, it is noted that different combinations are possible: emitter 1 and reflector 2 (as seen in FIG. 1), or emitter 1 and emitter 1 (see e.g. FIG. 6). The emitter 1 and reflector 2 can be placed either up or down as indicated in FIG. 4 by the use of the combined reference signs 1/2 at the positions of the emitter 1 and the reflector 2.

(36) The fluids (first and second fluid) can be any fluid at any temperature that preferably does not spontaneously change their thermodynamic state (liquid and gas). Typically, the acoustophoretic printing system would work in air and would eject liquids. The air can be at high or low temperature. In principle, the same system can be designed to perform controlled ejection of liquids in immiscible liquids (the acoustic medium can be oil, for instance). The acoustic impedance of material may be carefully determined.

(37) The geometry of reflector 2 and emitter 1 can be axi-symmetric, two-dimensional (extrusion in the plane) or other geometries that allow for the formation of the standing wave. Typically, an emitter 1 with circular, squared, hexagonal or rectangular (cross-)section would be used and a reflector 2 with a characteristic dimension of its (cross-)section of the same order of magnitude.

(38) The distance H (FIG. 4) between emitter 1 and reflector 2, more specifically between the relevant surfaces of the emitter 1 and the reflector 2 can be a multiple of /20.2, such as 0.50.2, 1.00.2, 1.50.2, etc. In such a way, an acoustic standing wave is imposed between the emitter 1 and reflector 2. Typically, a distance H/2 offers the strongest acoustic standing wave. The relevant surfaces of the emitter 1 and the reflector 2 in the configuration of FIG. 1 are the lower surface 1a of the emitter 1 and the upper surface 2a of the reflector 2.

(39) The emitter(s) 1 oscillate(s) periodically with any wave form (typically a sinusoidal shape in ultrasonic range). The oscillation frequency can be in the range from 10 Hz to 100 MHz. The wavelength is in the range 1 m to several meters. Typically, frequencies above 16 kHz (close to the ultrasound range=not audible by human earing) and below 1 MHz offer the best compromise between acoustophoretic printing feature size, strength of acoustic forces, component manufacturing. The oscillation velocity amplitude can range from 1 m/s to 100 m/s. The emitters 1 can include or be a piezoelectric transducer, a magnetostrictive transducer or other systems that can provide the needed wave excitation.

(40) A characteristic dimension T of the reflectorless chamber/conduit 7 (i.e. the diameter if it is a circular geometry, or the side length if it is square geometry, etc.) can be in the range of 0.01 to . The reflectorless chamber 7 typically has a constant characteristic dimension T along an ejection line/printing axis A: preferably, the reflectorless chamber 7 is a cylindrical section with a constant radius (as shown in FIG. 4). The reflectorless chamber 7 may also be conical, increasing the T-value while exiting the reflectorless chamber 7. In general, a larger T at the exit or bottom 9 of the reflectorless chamber 7 allows for a more stable droplet ejection. A height Hh (FIG. 4) of the reflectorless chamber 7 can be in the range from 0.01 to 100 . Typically, a preferred height Hh range for reliable and stable ejection may be up to 10.

(41) A nozzle tip 6a or its opening 6b can have a diameter ranging from 0.01 m to several centimeters. The tubing 4 connected to the nozzle 6 can have a diameter ranging from 0.1 m to several centimeters. Typically, nozzle tips/openings 6a, 6b with diameters in the range of 1 m to 250 m offer the best compromise between the minimum acoustophoretic printed feature size and pressure drops within the nozzle 6.

(42) The nozzle tip 6a can be positioned in any place within the reflectorless chamber 7, in particular, where a net force of the acoustic force 8a is present. However, if Hh is the height of the reflectorless chamber 7, one of the preferred regions to place the nozzle tip 6a for a reliable ejection is between the exit 9 of the reflectorless chamber 7 and Hh/3. The nozzle tip 6a can be of any material. Typically, it can be a tapered glass capillary, a Teflon capillary or a microfabricated tube. If a glass capillary is used, it is usually useful to carry out a hydrophobic treatment, depending on the ink that is printed. For water-based inks (e.g. most of the biological solutions), the wetting of the nozzle tips by the inks is reduced by using hydrophobic treatment. This also advantageously reduces the capillary force Fc.

(43) To advance the ink through the nozzle 6, a drive means 5, such as a back pressure system would suffice. Typically, it can be a syringe-pump or pressure controlled (second fluid) reservoir.

(44) Steps of the printing method for ejecting the second fluid from the nozzle (6) include the forming of the droplet 10 at the nozzle tip 6a. Preferably, the droplet 10 is formed by applying a pressure on the second fluid. An acoustic field 3, 8 with a force gradient, which points from the nozzle tip 6a to the printing substrate 11, is generated/activated by an oscillating emitter 1. The actual detaching of the droplet 10 may be actuated by activating the emitter oscillations or by modulating the oscillations to build up sufficient acoustic forces 3a, 8a. After the detachment, it is possible to deactivate the oscillations again or to modulate the oscillations such that the acoustic force 3a, 8a cannot detach a droplet 10 from the nozzle 6. Further, the detaching may also be caused by the droplet reaching a size at which the net force of the acoustic field 3, 8 overcomes the capillary forces, i.e. without modulating/activating the acoustic field 3, 8.

(45) FIG. 5 shows a further preferred configuration of an acoustophoretic printing apparatus. Specifically, FIG. 5 shows a multiple nozzle configuration. By replicating a configuration, such as depicted in FIGS. 1 and 4, multiple droplets 10 (also of different inks) may be simultaneously and/or serially ejected. The reflectorless chambers/conduits 7 may be comprised in a single reflector-member or print head, as shown in FIG. 5, and, alternatively, a plurality of reflectors 2 may abut on each other so that the print head as shown in FIG. 5 is formed. The reflectorless chambers 7 and the printing axes A may be vertically arranged, as shown in FIG. 4. Alternatively, as FIG. 5 depicts, may be arranged with an angle of up to 90 with regard to the vertical axis. More specifically, FIG. 5 shows that the printing axes A of the plurality of reflectorless chambers 7 are varied such that the printed droplets 10 may be deposited on a single position on the substrate 11. The ejection angle allows for a fine printing resolution at the substrate/target surface.

(46) In other words, FIG. 5 shows that the acoustophoretic printing apparatus is amenable to parallelization through a multiple nozzle system. This allows increasing the output capability. This renders feasible up-scaling and multiple-materials can be used in acoustophoretic 3D-printing. The print head features a nozzle array with independently controllable droplet size and the pitch between printed droplets.

(47) FIG. 6 shows two emitters 1 (the use of more than two emitters is possible) that are used to focus the acoustic fields 3 at a focus point/predetermined point in space. This allows generating a net force which is large enough to detach and accelerate the pendant droplet 10. However, more preferably, the emitters 1 are arranged such as to form a standing wave without a reflector 2. To form a standing wave, in fact, at least two travelling waves travelling in a substantially opposite direction are needed, and, e.g., they should to have a predetermined phase difference to create a standing wave. Similarly, for instance, in the emitter-reflector configuration the reflector acts as an emitter with a specific phase. The reflected wave will have a phase depending on the physical distance from the emitter 1.

(48) FIG. 7 shows using even more (multiple) emitters 1 to enhance the acoustic radiation pressure/acoustic force in a single focal point/predetermined point in space; a standing wave is not necessarily created. The emitters 1 are driven by (electric drive) signals with different phases and amplitudes. Alternatively, the emitters 1 can be used to produces one/multiple vortex beam(s) acting on the pendant droplet 10, generating a net force on it.

(49) FIG. 8 shows a further configuration according to which an emitter 1 can be designed so that it can act as a (integrated) reflector 2. The emitter 1 has a cavity 15, into which the nozzle tip 6a with the pendant droplet 10 is inserted. The cavity is formed by the two side walls 16 of the emitter 1, which both oscillate from opposite directions, creating a standing wave.

(50) FIG. 9 shows, as one example, the use of the acoustophoretic printing apparatus as a sample dispenser for biological solutions in the nl-l range volume for standard 96, 384 and 1536 well plates 12. Configurations of the printing apparatus as shown in FIGS. 1, 4 and 5 may be used. The droplets 10 are ejected into in the wells/grooves 13 of the well plate 12, e.g., for further inspection/treatment.

(51) Furthermore, the herein-described the acoustophoretic printing method/apparatus may be used in any field of printing. In particular, the advantage of the Z-number freedom offered by the acoustophoretic printing drastically broadens the material choice. Example fields of application are:

(52) 1) Application of the acoustophoretic printing to high-Z inks (from 1 to 10.sup.4). A sample dispenser of biological solutions in the nL-L range volume for standard 96, 384 and 1536 well plates 12 (FIG. 6).

(53) 2) Application of the acoustophoretic printing to low-Z inks (from 10.sup.4 to 1). The capability of ejecting DOD highly viscous fluid allows the use of conducting colloids with the purity of the inkjet inks but with the conductivity and metal concentration of contact printing technology. The application can be extended to the nontoxic, conductive, low melting point alloys as the eutectic gallium-indium, material of growing interest for soft electromechanical system.

(54) 3) 3D-printing using Newtonian fluids: 3D-structures by DOD acoustophoretic printing of fused deposition modeling (FDM) materials. This system would require a heated nozzle for melting commercially available FDM thermoplastics in filament form.

(55) 4) 3D-printing using non-Newtonian fluids: 3D-structures by DOD acoustophoretic printing of thixotropic fluids. Ceramic, polymeric and metallic inks, now printed only in filament forms due to their shear-thinning behavior, would be DOD dispensed, paving the way for new functional printing.

(56) 5) 3D-printing of tissue engineering: hydrogel bioinks are the key materials for engineering complex human tissues. Bioinks engineered for extrusion printing can be printed with the acoustophoretic DOD printing technology.

(57) 6) Microparticle production: compared to microfluidics, in which an immiscible oil phase is necessary for droplet (particle) creation, the acoustophoretic ejection employs surface forces in air. The use of a gas as external medium (first fluid) allows the production of complex microparticles. Additionally, by using a nozzle characterized by a coaxial flow, Janus and hollow microparticles can be acoustophoretically produced.

(58) 7) Biochemical analytical measurements: precise and rapid metering of chemicals and assays for rapid chemical, biochemical and biological reactors.

(59) Summarizing, the described acoustophoretic printing allows a controlled ejection of predetermined volumes by use of acoustophoretic forces, at controlled frequency of droplet ejection. This can be used in diverse applications such as a biological dispenser, as a two dimensional or three-dimensional (3D) printer and for the production of microparticles. The printing process is not dependent from the material properties of the second fluid.