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

Abstract

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.

Acoustic levitation as a tool for cell‐driven self‐organization of human cell spheroids during long‐term 3D culture

“…During the first minutes of cell culture in acoustic levitation, self‐assembly is mainly driven by the ARF (externally‐driven assembly), leading to the initial cell sheet layer formation. Generator‐controlled variations in voltage can increase or decrease the speed of cell sheet formation (modification of the acoustic energy), whereas modulations in frequency affect the axial position of spheroids (Jeger‐Madiot et al, 2022). It creates cell–cell interactions very quickly, which is one of the major interests of cell culture in acoustic levitation.…”

“…Therefore, the smallest amplitude ($$3.5\,{V}_{pp}$$) was used for most cultures, to be as gentle as possible with the cells, according to the As Low As Reasonably Achievable principle (ALARA). The frequency used was $${F}_{ac}=2.2$$ MHz, a value contained in the levitation range from 1.5 to 2.5 MHz, as shown by Dron and Aider (2013) and Jeger‐Madiot et al (2022) and maximizing the acoustic energy (matching of the resonance condition). After emission by the transducer, the acoustic wave travels through a thin oil layer, used as an acoustic matching layer, and a PDMS membrane, before reaching the bulk of the cavity filled with cell medium.…”

Microgravity stimulates network activity of 3D neuronal spheroids in an acoustic trap

“…It has already been used to form and culture cell spheroids of MSCs (Mesenchymatous Stromal Cells) or hepatocytes for several days (14, 15). Once acoustically levitated, objects (cell sheets, spheroids) can be further manipulated by variations in the magnitude of the force or by changing the distance between the acoustic pressure nodes (16, 17, 32, 33).…”

Engineered Human Organoids for Biomedical Applications

“…Of particular, the angle of individual organoids can be finely adjusted by these forces, and thereby heterogeneous assembloids can be constructed. [112,117] In sum, the assembloid cultures do have some limitations. For instance, they often lack vascular networks and do not contain all cell types as observed in human body.…”

“…Generally, assembloid derivation protocols mainly rely on the manual patterning and fusion of different organoids, and thereby are often involved with tedious operations. To solve this problem, many techniques can be incorporated to automate the manual process for assembloid generation, such as acoustic wave, [ 112 ] magnetic force, [ 113 ] electrostatic force, [ 114 ] microgravity, [ 115 ] and microfluidics. [ 116 ] These techniques contribute to selecting, moving and steering of cell spheroids in a non‐invasive, non‐contacting and non‐labeling manner.…”