Acousto-microfluidics: Transporting microbubble and microparticle arrays in acoustic traps using surface acoustic waves

Abstract

We demonstrate that aqueous suspensions of microbubbles, formed into arrays using standing surface acoustic waves (SSAWs), can be transported by controlled modulation of the SSAW frequency. The array is repeatedly captured at a sequence of spatial positions along the acoustic beam path and long-range transportation is achieved by periodic cycling of the applied frequency across the transducer bandwidth. We also demonstrate that controllable alignment and transport can be achieved in a detachable microfluidic device, where the microfluidic channel, in which particle transport occurs, is separated from the piezoelectric substrate by an acoustic coupling gel. Proof-of-concept transport is first discussed using a test system of latex particles before the non-invasive manipulation technique is applied to arrays of microbubbles. We explore the role of acoustic radiation forces in the spatial control of particles by analysing the dynamics of particle manipulation by SSAWs. Our results highlight the exquisite control which we have over the position and transport of particles and we anticipate that this technique could find wide applications for the accurate and programmable, non-invasive ordering and transport of biological samples in microfluidic systems.

Flexible Printed Circuit Board as Novel Electrodes for Acoustofluidic Devices

“…1(a)) was applied to match the impedance between the power amplifier and the FPCB-SAW device. The use of the matching network is essential for the device as it minimizes the reflection of the RF power [19] to allow the power amplifier work safely and improve the conversion of SAWs. A vector network analyzer (VNA, E5061B ENA, Keysight, USA) was used to measure the reflection coefficient S11 of the device with and without the matching network.…”

Surface Acoustic Wave Microfluidics

“…This really only works if the reflection at the channel walls is weak, as the standing wave across the channel defined by the width of the fluid channel will interfere with the ability to perform phase shift manipulation. Such phase shifting was employed to alter the positions of the particle alignment (Meng et al 2011, Orloff et al 2011, which is useful for the downstream separation of particle species (see below) and marching single cells and bubbles in one and two dimensions (Meng et al 2011(Meng et al , 2012O'Rorke et al 2012). The ease of varying the phase using voltage control makes it particularly attractive in microfluidic systems for particle manipulation.…”

Slowness curve surface acoustic wave transducers for optimized acoustic streaming

“…Surface acoustic waves (SAWs) are widely used for non-contact micromanipulation of particles in microuidic systems as they can generate force gradients on length scales similar to the particles. [1][2][3][4][5][6][7][8][9][10] When placed beneath a microuidic channel, the displacement of a SAW generates a pressure wave in the liquid. The attenuation of this pressure wave in the liquid causes acoustic streaming that can act on suspended particles via a drag force, as well as acoustic radiation forces (ARFs) which direct suspended particles along time-averaged pressure gradients.…”