Controlling the force and the position of acoustic traps with a tunable acoustofluidic chip: Application to spheroid...

A multi-node acoustofluidic chip working on a broadband spectrum and beyond the resonance is designed for cell manipulations. A simple one-dimensional (1D) multi-layer model is used to describe the stationary standing waves generated inside a cavity. The transmissions and reflections of the acoustic wave through the different layers and interfaces lead to the creation of pressure nodes away from the resonance condition. A transparent cavity and a broadband ultrasonic transducer allow the measurement of the acoustic energy over a wide frequency range using particle image velocimetry measurements and the relation between acoustic energy and the particles velocity. The automation of the setup allows the acquisition over a large spectrum with a high frequency definition. The results show a wide continuous operating range for the acoustofluidic chip, which compares well with the 1D model. The variation of the acoustic radiation force when varying the frequency can be compensated to ensure a constant amplitude for the ARF. This approach is finally applied to mesenchymal stem cell (MCS) spheroids cultured in acoustic levitation. The MSC spheroids can be moved and merged just by varying the acoustic frequency. This approach opens the path to various acoustic manipulations and to complex 3D tissue engineering in acoustic levitation.