Influence of gravity variations on the activity of neuronal spheroids in an acoustic trap.

Among biological models, cell culture constitutes an important paradigm that allows rapid examination of cell phenotype and behavior. While cell cultures are classically grown on a 2D substrate, the recent development of organoid technologies represents a paradigmatic shift in biological experimentation as they pave the way for reconstructing of minimalist organs in 3D. Manipulating these 3D cell assemblies presents a considerable challenge. While there is growing interest in studying the behavior of cells and organs in the space environment, manipulating 3D cultures in microgravity remains a challenge. But with cellular research underway aboard the International Space Station (ISS), optimizing techniques for handling 3D cellular assemblies is essential. Here, in order to cultivate 3D models of spheroids in microgravity, we developed and used an acoustic bioreactor to trap levitating cellular organoids in a liquid cell culture medium. Indeed, in a Bulk Acoustic Wave (BAW) resonator, spherical objects, such as cells, can be maintained in an equilibrium position, inside a resonant cavity, away from the walls. In the acoustic trapping plane, gravity is counterbalanced by the acoustic radiation force (ARF) making it possible to maintain an object even in weightlessness. A dedicated setup was designed and built to perform live calcium imaging during parabolic flights. During a parabolic flight campaign, we were able to monitor the calcium activity of 3D neural networks trapped in an acoustic field during changes in gravity during different parabolas. Our results clearly demonstrate that variations in gravitational force correlate with changes in calcium activity.