A bubble-driven microfluidic transport element for bioengineering

Abstract

Microfluidics typically uses channels to transport small objects by actuation forces such as an applied pressure difference or thermocapillarity. We propose that acoustic streaming is an alternative means of directional transport at small scales. Microbubbles on a substrate establish well controlled fluid motion on very small scales; combinations (''doublets'') of bubbles and microparticles break the symmetry of the motion and constitute flow transport elements. We demonstrate the principle of doublet streaming and describe the ensuing transport. Devices based on doublet flow elements work without microchannels and are thus potentially cheap and highly parallelizable.

Efficient manipulation of microparticles in bubble streaming flows

“…2(a), similar to the flows generated from hemispherical bubbles. 31,32 The streaming flow velocity reaches its maximum u s near the bubble surface and increases quadratically with the increasing oscillation amplitude (i.e., driving voltage), as shown in Fig. 2(c).…”

“…4. A further distinction between particles of different sizes is the induction of secondary streaming around a particle exposed to an oscillatory flow field, 32 which can contribute to the crossing of trajectories. 45 Ideally, particles of the same size have a unique characteristic trajectory in bubble streaming flows.…”

“…30 Ultrasound driven microbubbles rectify rapid oscillatory motion of the air/liquid interface into steady streaming flow in the bulk liquid around the bubbles. 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.…”

A Microfluidic Approach for Screening Submicroliter Volumes against Multiple Reagents by Using Preformed Arrays of Nanoliter Plugs in a Three‐Phase Liquid/Liquid/Gas Flow

“…Formation of air bubbles in microfluidic devices has been previously described, [16] and gas bubbles have been used to separate liquid slugs of reagents in a liquid/gas two-phase flow, with applications for the synthesis of nanoparticles in microfluidic devices, [17,18] and have been used for actuation of steady microfluidic flow. [19] In addition, air bubbles have been widely used in biochemical analyzers. [20] Herein, we use a liquid/liquid/gas three-phase flow system, in which the aqueous phase remains surrounded by the fluorocarbon, because the surface tension of the water-air interface (≈70 mNm −1 ) is significantly higher than both the surface tension of the water-fluorocarbon interface (≈15 mNm −1 with fluorosurfactants) [11] and the surface tension of the airfluorocarbon interface.…”