On-chip droplet production regimes using surface acoustic waves

Abstract

Aqueous droplets suspended in an immiscible carrier fluid are a key tool in microfluidic chemical analysis platforms. The approaches for producing droplets in microfluidic devices can be divided into three general categories: batch emulsification, continuous production and tailored on-demand production. The major distinctions between each category are the rate of production and the degree of control over the droplet formation process in terms of the size and quantity. On-demand methods are highly desirable when, for example, small numbers or even single droplets of one sample type are required at a time. Here, we present a method for the on-demand production of femtolitre droplets, utilising a pressure source generated by high frequency surface acoustic waves (SAW). An increase in the continuous phase flow rate is enabled by a quasi-3D feature at the droplet production nozzle. A wide range of accessible flow rates permits the identification of different physical regimes in which droplets of different dimensions are produced. In the system investigated droplets measuring as little as 200 fl have been produced, ∼1/60th of the minimum volume previously reported. The experimental findings are supported by a numerical model which demonstrates the link between the number of droplets formed and the pulse length used.

Advances in Micromanipulation Actuated by Vibration-Induced Acoustic Waves and Streaming Flow

“…Fakhfouri et al [10] showed that the acoustic streaming produced by TSAW can make particles swirl and thus form patterns. Brenker et al [23] and Sesen et al [24] proposed droplet generation and droplet fusion methods, respectively, based on TSAW with similar equipment, verifying the effectiveness of TSAW in droplet operations.…”

“…Similar to magnetic and dielectrophoretic manipulation, VAW uses vibration to excite a wide range of acoustic fields in the medium, where gradient forces are used to manipulate the particles or cells. Acoustic radiation manipulation devices can be used for transport [13][14][15], sorting and filtering [16,17], trapping [18,19], patterning of particles or cells [20][21][22], droplet generation [23], and fusion [24]. Acoustic radiation force can be generated using many methods such as surface acoustic waves (SAWs) and bulk acoustic waves (BAWs).…”

Separation efficiency maximization in acoustofluidic systems: study of the sample launch-position

“…Acoustouidics has been successfully applied to many different research studies, ranging from micro-droplet production and manipulation to micro-particle (or cell) sorting, focusing, separation, mixing and arraying. [16][17][18][19][20][21][22][23][24][25][26][27] Among these possible applications, cell separation has attracted a lot of attention including substantial effort devoted towards enabling the isolation of circulating tumor cells from human blood samples. [28][29][30][31][32][33][34][35][36] Several groups have demonstrated the possibility of isolating target cells from a given sample containing a mix of cells with different characteristics using acoustouidics.…”

Vacuum‐driven fluid manipulation by a piezoelectric diaphragm micropump for microfluidic droplet generation with a rapid system response time

“…Some research groups have developed compact, low‐cost, and simple fluid pumping systems for microfluidic droplet generation and there have been a few implementations of such devices. These include piezoelectric (PZT) actuator‐based pumps , responsive hydrogel‐based pumps , degassed poly(dimethylsiloxane) (PDMS)‐powered pumps , and finger squeeze‐driven pumps .…”