Programmable Anisotropy From Inflation Patterns in Pressurized Cellular Solids

Plants are able to move rapidly (Venus flytrap, Mimosa Pudica). Instead of muscles, they use an organ composed of thousands of cells, called the pulvinus. These cells can absorb or release water to dilate or shrink, also affecting the stiffness of the tissue. We draw inspiration from this biological design, which achieves resilience through redundancy, by manufacturing and characterizing a pressurized cellular solid made of silicon with cubic cavities. Nonlinear finite element simulations show that, as the empty cells get pressurized, the mechanical behavior evolves from orthotropic to other programmable anisotropic stiffnesses and Poisson’s ratios. The homogenized mechanical properties that result from the same device with different pressure patterns are studied exhaustively for patterns of size 2x2, 3x3 and 4x4 cells to extrapolate design rules. With the help of miniaturization techniques, this prototype of programmable pneumatic actuator will find applications in soft robotics.