Fig. 4.

Reverse navigation. (A) Schematic of a robot with two muscles and a single bistable element. The first muscle, $M_1$, is fabricated with a material that activates at $T_{\mathrm{L}}$. The second muscle, $M_2$, activates at $T_{\mathrm{H}}$, which is higher than $T_{\mathrm{L}}$. (B) Sequence of activation. (I) At room temperature, $T_{\mathrm{R}.\mathrm{T}.}$, both muscles are programed. (II) As water temperature increases to $T_{\mathrm{L}}$, the first muscle triggers the bistable element and propels the swimmer forward. (III) As water heats to $T_{\mathrm{H}}$, the grippers relax and release the cargo. (IV) When the water temperature reaches $T_{\mathrm{H}}$, the second muscle reverses both the bistable element and reprograms the first muscle. (C) Snapshots from the deployment of the robot showing the four different phases.