Figure 5.

4D printed scales with ‘weave’ bilayer architecture and oriented 80° 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). The high aspect ratio of the pine scale also has an impact on the amount of displacement that can be observed between different regions of the scale. When the primary axis of deformation is perpendicular to the longitudinal axis (longer axis) a higher level of displacement can be seen between the basal and the apical region. Therefore, having the WPC and the constraints oriented almost perpendicular to the longitudinal axis allowed for the bending deformation to occur over the longest length of the scale, resulting in a larger deformation with smaller curvature radius (sets 5 and 6, samples A and B) (c). The additional lateral or boundary constraints in the A samples do not appear to have any significant impact in the shape deformation (c) while a significant longitudinal bending change can be observed between the C samples of both sets 3 and 4 as a result of the boundary constraint. Both C samples have lateral constraints that are parallel to the raster pattern and direction of expansion, which results in limited bending, so the addition of the longitudinal boundary constraint results in a noticeable change in bending radius between set 5 and 4. Since the objective is to achieve the pine scale's bi-axial two-stage motion, as per $1.2 (cf. figure 1m), the consistent single-axis curvature change across the entire scale, achieved by samples A and B (for both sets), is not suitable for the required performance goals. (Online version in colour.)