Acoustofluidics and Whole-Blood Manipulation in Surface Acoustic Wave Counterflow Devices

Abstract

On-chip functional blocks for sample preprocessing are necessary elements for the implementation of fully portable micrototal analysis systems (μTAS). We demonstrate and characterize the microparticle and whole-blood manipulation capabilities of surface acoustic wave (SAW) driven counterflow micropumps. The motion of suspended cells in this system is governed by the two dominant acoustic forces associated with the scattered SAW (of wavelength λf): acoustic-radiation force and acoustic-streaming Stokesian drag force. We show that by reducing the microchannel height (h) beyond a threshold value the balance of these forces is shifted toward the acoustic-radiation force and that this yields control of two different regimes of microparticle dynamics. In the regime dominated by the acoustic radiation force (h ≲ λf), microparticles are collected in the seminodes of the partial standing sound-wave arising from reflections off microchannel walls. This enables the complete separation of plasma and corpuscular components of whole blood in periodical predetermined positions without any prior sample dilution. Conversely, in the regime dominated by acoustic streaming (h ≫ λf), the microbeads follow vortical streamlines in a pattern characterized by three different phases during microchannel filling. This makes it possible to generate a cell-concentration gradient within whole-blood samples, a behavior not previously reported in any acoustic-streaming device. By careful device design, a new class of SAW pumping devices is presented that allows the manipulation and pretreatment of whole-blood samples for portable and integrable biological chips and is compatible with hand-held battery-operated devices.

Radiation dominated acoustophoresis driven by surface acoustic waves

“…In our SAW-based microfluidic device, the channel height is much smaller than the SAW wavelength, resulting in very limited acoustic attenuation along the fluid, and acoustic streaming is thus negligible in this study. This acoustic radiation dominated region has also been observed in other experimental studies [44,45]. The developed numerical model is able to simulate the piezoelectric effect in the solid substrate and the SSAW field in the fluid.…”

A Review of Design Considerations for Hemocompatibility within Microfluidic Systems

“…Many of these methods are summarized in ►Fig. 3(C), and include capillary forces, 171 vacuum driven flow, 146 gravity driven flow, 199 mechanical peristaltic pumps, 200 centrifugation, 201 surface acoustic wave actuation, 202 manual finger-press actuation, 203 and pneumatic peristaltic pumps. 204,205 While numerous on-chip blood actuation methods are outlined in the literature, generally very little consideration is given to material hemocompatibility, or functional effects of the manipulation mechanisms regarding operational hemocompatibility, factors that may severely hamper application of on-chip blood handling systems.…”

Surface acoustic wave electric field effect on acoustic streaming: Numerical analysis

“…A SAW is able to drive the mixing of components in a small volume of fluids [4][5][6][7] and to pump fluids in microchannels. [8][9][10][11] With the aid of SAWs, it is possible to produce droplets, move them along specified directions, and create conditions stimulating either droplet coalescence or droplet breakup. [12][13][14][15][16][17][18] If the SAW amplitude is high enough, then fluid atomization, i.e., aerosol generation, occurs.…”