When air is pumped back in, the ridges disappear as the surface returns to flat. When all the air is evacuated from the material, the ligaments separating the pores buckle outward, causing ridges to appear on the surface of the material. After cutting the material at a 45-degree angle, the team covered both sides of the material with a thin elastic film and attached an air pump. Those transformations have historically been studied in-plane, meaning the surface of the material remained flat during the entire actuation process.īut by simply cutting this periodic geometry at an angle, the Harvard researchers figured out how to enable out-of-plane, or three-dimensional transformations, in the material.
This reversible morphological change has been harnessed to build structures with unusual mechanical properties that can be used as photonic and phononic switches, color displays, and soft robots capable of grasping and walking. Previous studies, including those performed in the Bertoldi Lab, demonstrated that when porous metamaterials with a square array of holes or channels are compressed, the beam-like ligaments separating the pores buckle and lead to a sudden transformation of the circular holes into ellipses.
This structure is made by slicing a block (shown in gray), containing a square array of cylindrical holes, at an angle.
