Researchers use ultrasound to control orientation of small particles

https://phys.org/news/2023-06-ultrasound-small-particles.html

"nanorods half platinum and half gold placed in microchannel nozzle, added hydrogen peroxide burned on platinum half forcing them to swim imitating bacteria, applied ultrasound producing acoustics that separate nanorod extrude from nozzle, control and eject particles based on shape, frequency... nanorods and spherical particles have different responses acoustic radiation and generated fluid flow... bioprinting, 3D printing and drug delivery."