Odd mechanical metamaterials with simultaneously expanding or contracting under both compression and tension

Mechanical metamaterials with negative Poisson's ratio have attracted widespread attention in recent decades due to their unique mechanical properties. This metamaterial often exhibits the characteristic of expansion under tension and contraction under compression, which is different from traditional materials. Currently, almost all related research is focused on the design and further application of such metamaterials. This paper proposes a class of odd mechanical metamaterials, which can exhibit characteristics of expanding (or contracting) under both compression and tension, with the Poisson's ratio showing strong directional dependence. Experimental and simulation methods were employed to verify the conceptual ideas presented in this study, and corresponding three-dimensional and cylindrical shell structures were proposed. The mechanical metamaterials that expand under both compression and tension are ideal scaffolds for human esophagus/vessels, which can ensure the smooth flow of blood and nutrients. And the metamaterials that contract under both compression and tension were prefect choice in bone/gristle repair field, which doesn't compress surrounding tissues and nerves during loading. This study further enriches the understanding of the mechanical metamaterials with negative Poisson's ratio and provides more possibilities for the design of such metamaterials.