Fig. 5. Two-dimensional dynamic rolling manipulation.

a In situ rotation of microchains at two-dimensional acoustic pressure nodal points. b Rolling of microchains along a predesigned square path. The last subfigure is a superimposed time-lapse image showing the full path. The green curved arrow, yellow arrow, and white arrow respectively denote the rotational direction, rolling direction, and historical path. c Using reconfigurable acoustic virtual walls to write the word “ETH” with rolling microchains. The acoustic excitation frequency was 1.55 MHz and the magnetic intensity was 21 mT. Inset figures show the rolling direction. Scale bar, 100 μm.