Acoustofluidic platforms for particle manipulation

Abstract

There is an increasing interest in acoustics for microfluidic applications. This field, commonly known as acoustofluidics involves the interaction of ultrasonic standing waves with fluids and dispersed microparticles. The combination of microfluidics and the so-called acoustic standing waves (ASWs) led to the development of integrated systems for contactless on-chip cell and particle manipulation where it is possible to move and spatially localize these particles based on the different acoustophysical properties. While it was initially suggested that the acoustic forces could be harmful to the cells and could impact cell viability, proliferation, or function via phenotypic or even genotypic changes, further studies disproved such claims. This review is summarizing some interesting applications of acoustofluidics in the manipulations of biomaterials, such as cells or subcellular vesicles, in works published mainly within the last 5 years.

Integrated Microfluidics for Single‐Cell Separation and On‐Chip Analysis: Novel Applications and Recent Advances

“…• Micro-patterning of magnetic microsources to establish localized, high magnetic fields [54][55][56][57] • Magnetic microtweezers for single cell manipulation [57] • Negative selection of non-targeted cells [60] • Magnetomicrofluidic circuits for spatial single cell control [254,255] • Use of alternating magnetic fields for advanced particle movement [62] Acoustophoresis • Label-free, contact-free separation [63] • Large operation/penetration distances [21] • Large volume and high-throughput processing [63] • Application independent of properties like pH, ionic strength, or charge [64] • Bulk piezoelectric transducers pose geometric limitations to integration [68] • Less sensitive sample discrimination than on dielectric polarizability [21] • Cell manipulation efficiency influenced by the properties of the medium and the microfluidic channel geometry [65,66] • Requires the use materials with high specific acoustic impedances relative to the fluid [70] • Most effective for the manipulation of spherical cells [75] • Applications of acoustophoretic principles in polymer-based platforms. [66,[70][71][72] • Size-independent cell separation via isoacoustic focusing [75] • Generation of 2D acoustic standing waves in microchannels to focus non-spherical cells [76] • Acoustic cell washing [77,78] • Use of secondary acoustic radiation forces or acoustic streaming to manipulate single-cell motion [81,82,84] Optical Tweezers • Label-free, contact-free separation [86,95,256] • High force resolution [86] • Application possible both in flow and static conditions…”

“…[63] When sound waves resonating inside microfluidic devices are reflected at the channel walls, they establish standing waves, which generate strong pressure gradients steering cells/particles toward specific positions in the channel. [64] This separation relies on intrinsic cell/particle properties, such as density, compressibility, and size, as well as the material properties of the acoustophoretic chip and the geometry of the microchannel. [65,66] As most cells and microparticles are denser or less compressible than their surrounding medium, they have a positive acoustic contrast factor (ϕ > 0 see Table S1, Supporting Information) and are therefore steered toward pressure nodes, i.e., regions of lowest pressure amplitude.…”

Two-photon microscopy of acoustofluidic trapping for highly sensitive cell analysis

“…The visual sample analysis is generally performed using bright-field or confocal microscopy. 10,[15][16][17] Furthermore, Santos et al 18 presented an acoustofluidic device in combination with Raman spectroscopy. However, the Raman method worked only well for particles with a diameter larger than 15 μm in their case because smaller particles were liable to microstreaming effects.…”

Acoustic Trapping: An Emerging Tool for Microfabrication Technology

“…As an emerging tool in microscale manipulation, a wide range of acoustofluidic platforms for particle separation and sorting has been developed [11,12,16,[43][44][45][46][47][48][49] as well as acoustic tweezers that allow the precise manipulation of various biological samples. [50] However, the potential applications of the acoustic technology for high-throughput deposition of microscale objects have not been the subject of a dedicated review.…”