Three-dimensional poroelastic metamaterials with extremely negative or positive effective static volume compressibility

Recently, three-dimensional poroelastic metamaterials have been introduced that show an unusual isotropic increase of their effective volume when increasing the hydrostatic pressure of the surrounding air. This behavior corresponds to a negative effective static volume compressibility. Here, we present significantly simplified metamaterial architectures, which are composed of just one rather than eight hollow sealed functional elements within each cubic unit cell. On cubic symmetry microstructured polymer samples made by 3D laser printing, we measure a negative effective compressibility of about κeff=−4.7%∕bar under pressure control. This value is six times larger than previous values. Furthermore, we present related modified architectures with an extremely large positive effective compressibility of about κeff=5.0%∕bar. Finally, we show that, in principle, the positive effective metamaterial compressibility can exceed the isothermal compressibility of the surrounding air of κ=101%∕bar under ambient conditions.