Figure 7.

4D printed scales with ‘weave’ bilayer architecture and oriented 10° symmetrically mirrored WPC raster pattern. Using the same 3D printed raster pattern for both sets of samples (a), 4D scales show different shape deformations when fully wet (c) in response to changes to the bilayer constraints in both the longitudinal and lateral axis as well as the boundary edge of the scale (b). Having the WPC and the constraints oriented almost parallel to the longitudinal axis limits the bending deformation as the primary bending axis occurs over a shorter lateral direction. However, the change in angle from 0° to 10° combined with the mirrored symmetry of the raster pattern provides two longer and differentiated bending axis near the apical region. Samples with longitudinal or lateral constrains showed doubly curved shape deformation with a very small amount of two-stage actuation while sample ‘A’ with bidirectional constraints (same specimen for both sets) presented the desired two-stage actuation observed in the pine scale. Subsequent tests indicated that since the longitudinal constraints and the boundary had identical orientation there was not observable difference in the shape-changing behaviour between a continuous and a discontinuous boundary constraint in this case. (Online version in colour.)