Figure 1. The Schematic graphs of the design concept of the two-way reversible actuator.

(a) The reversible actuation component by 3D printing where the hydrogel is confined by the SMP and the elastomer layers. (b) The key dimensions in the design. (c) Schematic plots for a typical two way actuation: In S1, the sample is immersed in water at low temperature; in S2, it is brought to a high temperature environment and bends; in S3, it is cooled down to a low temperature; in S4, it is allowed to dry for an elongated time period; in S5, it is heated to recover the original printed shape. This finishes one actuation cycle, which can be repeated many times.