Two-dimensional spatial manipulation of microparticles in continuous flows in acoustofluidic systems

Abstract

We report a modeling and experimental study of techniques to acoustically focus particles flowing through a microfluidic channel. Our theoretical model differs from prior works in that we solve an approximate 2-D wave transmission model that accounts for wave propagation in both the solid and fluid phases. Our simulations indicate that particles can be effectively focused at driving frequencies as high as 10% off of the resonant condition. This conclusion is supported by experiments on the acoustic focusing of particles in nearly square microchannels, which are studied for different flow rates, driving frequencies and placements of the lead zirconate titanate transducer, either underneath the microchannel or underneath a parallel trough. The relative acoustic potential energy and the resultant velocity fields for particles with positive acoustic contrast coefficients are estimated in the 2-D limit. Confocal microscopy was used to observe the spatial distribution of the flowing microparticles in three dimensions. Through these studies, we show that a single driving frequency from a single piezoelectric actuator can induce the 2-D concentration of particles in a microchannel with a nearly square cross section, and we correlate these behaviors with theoretical predictions. We also show that it is possible to control the extent of focusing of the microparticles, and that it is possible to decouple the focusing of microparticles in the vertical direction from the lateral direction in rectangular channels with anisotropic cross sections. This study provides guidelines to design and operate microchip-based acoustofluidic devices for precise control over the spatial arrangement of microparticles for applications such as flow cytometry and cellular sorting. V C 2015 AIP Publishing LLC. [http://dx

Fabrication and Operation of Acoustofluidic Devices Supporting Bulk Acoustic Standing Waves for Sheathless Focusing of Particles

“…We found that these particles, which have a positive acoustic contrast factor, focused along the pressure node as expected. 6 We also injected red fluorescent particles with a negative acoustic contrast factor (i.e., ɸ ≈ −0.88, synthesized from a process described previously) 8 to verify that our device could induce their concentration along the pressure antinodes ( Figure 2C). …”

“…Turn on the function generator and power amplifier to begin actuating the PZT transducer. 6 1. To estimate the resonant frequency of the device, follow the equation c = λ * ƒ, where c is the speed of sound of the medium (i.e., water), λ is the acoustic wavelength and ƒ is the frequency of the PZT transducer.…”

Translating microfluidics: Cell separation technologies and their barriers to commercialization

“…The third class of active cell sorters uses acoustic forces to sort cells via: (i) bulk acoustic standing waves (), (ii) standing surface acoustic waves (SSAWs) () or (iii) bulk acoustic travelling waves . Petersson et al first demonstrated the utility of bulk acoustic standing waves by separating lipids from blood cells .…”

“…Leveraging existing frameworks, such as the monolithic techniques from the semiconductor industry, as well as emerging techniques (e.g., 3D printing) may help to overcome these challenges (99)(100)(101); however, the ideal material for industrial-scale productions of microfluidic devices ultimately depends on the separation technique at hand. For example, microfluidic devices supporting bulk acoustic standing waves must be made from rigid materials, such as silicon, glass, or polymethyl methacrylate (PMMA) (76,102), whereas optoelectronic devices are typically made, at least in part, from transparent, electrically conductive materials, such as indium tin oxide (ITO) (88).…”

Modeling and Analysis of the Two-Dimensional Axisymmetric Acoustofluidic Fields in the Probe-Type and Substrate-Type Ultrasonic Micro/Nano Manipulation Systems

“…For SAW-based devices, diverse manipulation functions, such as trapping [26,27], patterning [28,29], separation [30,31], concentration [32,33], mixing [34,35], and rotation [36,37] have been implemented by various groups. For BAW-based devices, manipulation functions such as levitation [38,39], assembly [40,41], focusing [42,43] and sorting [44] have also been realized by many researchers.…”