Abstract
Manipulation of cells, droplets, and particles via ultrasound within microfluidic chips is a rapidly growing field, with applications in cell and particle sorting, blood fractionation, droplet transport, and enrichment of rare or cancerous cells, among others. However, current methods with a single ultrasonic transducer offer limited control of the position of single particles. In this paper, we demonstrate closed-loop two-dimensional manipulation of particles inside closed-channel microfluidic chips, by controlling the frequency of a single ultrasound transducer, based on machine-vision-measured positions of the particles. For the control task, we propose using algorithms derived from the family of multi-armed bandit algorithms. We show that these algorithms can achieve controlled manipulation with no prior information on the acoustic field shapes. The method learns as it goes: there is no need to restart the experiment at any point. Starting with no knowledge of the field shapes, the algorithms can (eventually) move a particle from one position inside the chamber to another. This makes the method very robust to changes in chip and particle properties. We demonstrate that the method can be used to manipulate a single particle, three particles simultaneously, and also a single particle in the presence of a bubble in the chip. Finally, we demonstrate the practical applications of this method in active sorting of particles, by guiding each particle to exit the chip through one of three different outlets at will. Because the method requires no model or calibration, the work paves the way toward the acoustic manipulation of microparticles inside unstructured environments.
Highlights
Manipulation of cells, droplets, and particles via ultrasound within microfluidic chips, acoustofluidics, is a rapidly growing field, with applications in cell and particle sorting,[1] cell patterning,[2] blood fractionation,[3,4] droplet transport,[5] and enrichment of rare or cancerous cells.[6,7] The nature of this manipulation is contactless, which is why it is suitable for so many biological applications.[8]
The devices can be actuated via vibrations through the bulk or by exciting surface acoustic waves along the surface of a piezoelectric substrate.[9]
We showed that particles can be controllably manipulated and sorted within closed microfluidic chambers using bulk acoustic waves
Summary
Manipulation of cells, droplets, and particles via ultrasound within microfluidic chips, acoustofluidics, is a rapidly growing field, with applications in cell and particle sorting,[1] cell patterning,[2] blood fractionation,[3,4] droplet transport,[5] and enrichment of rare or cancerous cells.[6,7] The nature of this manipulation is contactless, which is why it is suitable for so many biological applications.[8]. Integrating acoustic functionalities into microfluidic chips is a promising approach toward the realization of entire laboratories on chips. Such chips consist of structured chambers, ports, and closed channels, with dimensions ranging from a few micrometers to a few millimeters. The devices can be actuated via vibrations through the bulk (the whole chip or the chamber vibrated by a piezoelectric transducer) or by exciting surface acoustic waves along the surface of a piezoelectric substrate.[9]
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