Robotic skins inspired by auxetic metamaterials for programmable bending of soft actuators

This paper presents a class of robotic skins inspired by auxetic metamaterials, which enable programmable bending in soft pneumatic actuators. The efficiency of these robotic skins in controlling bending curvature and hoop expansion of the soft actuators is demonstrated through a combination of experiments and numerical simulations. Parametric studies are then performed to explore how variations in the geometric parameters of the metamaterial skin affect the performance of the bending actuators. Specifically, our study demonstrates that a range of bending curvatures (0.0077 mm⁻¹ to 0.0097 mm⁻¹) and cross-section diameters (38.4 mm to 44.0 mm) can be achieved by adjusting the unit cell numbers of metamaterial skin in the vertical and hoop directions for bending a 2 mm-thickness-walled inflatable cylindrical tube, which is characterized by an initial length of 104.3 mm, an initial cross-section diameter of 29.0 mm, and at an inflation volume of 75 mL. Moreover, a variety of bio-inspired soft actuators exhibiting complex bending behaviors are presented. The work demonstrates the effectiveness of the proposed strategy for achieving customized curved bending and shape-morphing by adjusting the geometric parameters and arrangement of the unit cells in the metamaterial skins.