Bubble-induced acoustic micromixing

Abstract

A mixing technique based on the principle of bubble-induced acoustic microstreaming was developed. The mixer consists of a piezoelectric disk that is attached to a reaction chamber, which is designed in such a way that a set of air bubbles with desirable size is trapped in the solution. Fluidic experiments showed that air bubbles resting on a solid surface and set into vibration by the sound field generated steady circulatory flows, resulting in global convection flows and thus rapid mixing. The time to fully mix a 22 microL chamber is significantly reduced from hours (for a pure diffusion-based mixing) to tens of seconds. Numerical simulations showed that the induced flowfield and thus degree of mixing strongly depend on bubble positions. Optimal simulated mixing results were obtained for staggered bubble distribution that minimizes the number of internal flow stagnation regions. Immunomagnetic cell capture experiments showed that acoustic microstreaming provided efficient mixing of bacterial cell (Esherichia coli K12) matrix suspended in blood with magnetic capture beads, resulting in highly effective immunomagnetic cell capture. Bacterial viability assay experiments showed that acoustic microstreaming has a relatively low shear strain field since the blood cells and bacteria remained intact after mixing. Acoustic microstreaming has many advantages over most existing chamber micromixing techniques, including simple apparatus, ease of implementation, low power consumption (2 mW), and low cost.

Hydrodynamic mechanisms of cell and particle trapping in microfluidics

“…They are greatly beneficial in a number of proposed applications in chemical, biological, and physical processes such as mixing, [149][150][151] pumping, 152,153 characterizing enzymatic reactions, 154 cell lysis, 155 and sorting and enrichment. 156,157 A thorough review article on applications of oscillating microbubbles in microfluidics is recently written by Hashmi et al 158 Although, there are a number of techniques to generate bubbles in microfluidic channels, 159,160 using a cavity is found to be the simplest.…”

Efficient manipulation of microparticles in bubble streaming flows

“…Such steady streaming flows are useful in deforming and lysing vesicles, 31 directional transport of liquid, 32 and enhancing mixing in microfluidics. 33,34 The latter type of bubble streaming takes a unique position in that the bubble interface is doubtless an active element, but its amplitude is usually very small compared with the flow dimensions, so that for the purposes of flow description it is merely a passive boundary, albeit one that adds an important a) Electronic mail: cwang55@illinois.edu.…”

“…[24][25][26][27][28] Microbubbles, with a size of tens to hundred microns, have been used as powerful actuating elements for microfluidic applications in various contexts. [29][30][31][32][33][34] Cyclic generation, growth and collapse of vapor bubbles from thermal heating can pump liquid. 29 Bubbles from chemical electrolysis are used as active valves.…”

Lateral air cavities for microfluidic pumping with the use of acoustic energy

“…However, recently there has been a growing trend in harnessing this byproduct for a variety of novel applications (Rife et al 2000;Tsai and Lin 2002;Hilgenfeldt 2003, 2004;Dijkink et al 2006;Marmottant et al 2006;Hettiarachchi et al 2007; Kao et al 2007; Tho et al 2007;Xu and Attinger 2007;Chung and Cho 2008;Ahmed et al 2009a, b;Chung and Cho 2009;Tovar and Lee 2009). The first practical use of trapped air bubbles in a microfluidic device utilized acoustic energy to rapidly mix two fluids within a chamber (Liu et al 2002) for the increase of DNA hybridization (Liu et al 2003a, b). The combination of acoustic energy and trapped air bubbles within these microsystems allowed for the generation of localized microstreaming which produced rapid mixing characteristics within a platform that is predominately laminar.…”