Fig. 4. Multiple locomotion strategies of interlocked micromachines.

a A cage-bar-ring structure connected to five helical legs can either rotate in-plane, which would not result in any net locomotion, or tumble out-of-plane. b A longer aspect ratio structure with multiple magnetic elements can either move forward, roll along its short axis, or change its direction by switching the direction of the external magnetic field, illustrating that multiple locomotion mechanisms can be exploited, despite the soft magnetic behavior of the metals used in this work. When compared to other rolling microrobots³⁶, the method presented in this chapter introduces new possibilities and a considerably easier fabrication method. c–d Demonstration of an out-of-plane tumbling and rolling motion in silicone oil and DI water. The magnetic cage is free to rotate around the polymeric bar. If they intercept in-plane, the structure is allowed to rotate. If they intercept through the out-of-plane direction, the structure is forced to tumble, resulting in net locomotion (c). As schematized in (b), a rolling robot is capable of quickly changing its direction and avoiding obstacles using different locomotion modes (d). The scale bars are 150 μm.