Fig. 8: Flow-assisted object rotation and orientation control.

a Micro-disk collectives within ring-shaped objects of different sizes; the object rotates in the same direction as the collective. b Collectives encapsulate and rotate ring-shaped objects; the object rotates in the opposite direction as the collective. Red line in (a, b) shows the rotational trajectory of the rings. The same rings are used for (a), (b). c Angular velocity of a ring-like object (ID 3.4 mm and OD 6.5 mm) when there are 60 micro-disks inside or outside the structure. Error bars represent standard deviations over 10 s. d Collective rotates a rod-shaped object and e a star-shaped object. f Two collectives within adjacent objects enable coupled object rotation. g A collective within one of two adjacent ring-like objects rotates the structure it is in and exerts a torque on the neighboring object to enable gear-like motion. h A collective enters a C-shaped object, rotates it, and exits the structure. A red circle is added to highlight the orientation of the rings (a, b) and (g, f). The red dashed arrows in (d–g) show the direction of rotation of the individual objects (thin arrows) and their center of mass (thick arrows). The brightness of the images in (a, b) and (d–h) is enhanced using photoshop for better visualization. The symbols on top of the sub-images in (a, b) and (h) represent the mode that the collective exhibits. These symbols correspond to those shown in Fig. 1a. The sub-images in (h) are labeled at the bottom with the function that the collective performs.