Journal Article metamaterials Research Support, Non-U.S. Gov't mechanical metamaterials phonons Polymers active metamaterials auxetic auxetics back-folded modes band gaps buckling cable networks crosslinking dispersion engineering dispersion relations elastic waves hierarchical metamaterials instabilities laser lithography microlattices microscale mode hybridization monomode elastic metamaterials multi-photon absorption nonlocal interactions polarizations polymer chemistry radical polymerization roton-like bands