Surface acoustic waves for on-demand production of picoliter droplets and particle encapsulation

Abstract

Microscopic water-in-oil droplets are a versatile chemical and biological platform whose dimensions result in short reaction times and require minuscule amounts of reagent. Methods exist for the production of droplets, though the vast majority are only able to do so in continuous flows, restricting the ability to independently control reactions of individual droplets, a prerequisite for programmable digital microfluidics. Here we present a novel method to produce individual picoliter-scale droplets on-demand using surface acoustic waves (SAW). Acoustic forces arising from SAW act on the oil-water interface, creating a droplet whose volume is defined by the applied power, duration of the force and system geometry. Additionally, this method is able to pre-concentrate particles simultaneously with droplet production, meaning that particles and cells, even if in a dilute mixture, can be easily encapsulated. Our method is expected to be applicable to high-throughput screening, bioreactor creation and other microfluidic processes.

Vertical Hydrodynamic Focusing and Continuous Acoustofluidic Separation of Particles via Upward Migration

“…Acoustophoresis‐based microfluidic separation techniques are preferred due to the contactless handling of the biological samples, low power requirement, and biocompatible nature of the acoustic waves, all of which permit incorporation of acoustophoresis techniques into microscale total analysis systems. Surface acoustic wave (SAW)‐based particle separation devices mostly feature a single‐layered polydimethylsiloxane (PDMS) microfluidic channel and a pair of interdigitated electrodes patterned onto a piezoelectric substrate that produces acoustic waves along the surface of the substrate to manipulate the suspended micro‐objects 17, 18, 19, 20…”

Droplet Manipulations in Two Phase Flow Microfluidics

“…By applying a short pressure pulse a droplet can be generated on demand. Other active methods for on demand drop generation include electrowetting [13,93,94], SAWs [95], pneumatic valves [41,96,97] and laser-induced cavitation [82]. A nice feature of the pneumatic valves is that consecutive pneumatically controlled droplet generators can directly combine different solutions into one droplet at controllable ratios [42].…”

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

“…[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. [19][20][21] Forces and flows induced in a fluid by SAWs separate cells, [22][23][24] align nanowires, and deagglomerate nanotubes.…”