Auxetic Two-Dimensional Nanostructures from DNA*.

Architectured materials exhibit negative Poisson's ratios and enhanced mechanical properties compared with regular materials. Their auxetic behaviors emerge from periodic cellular structures regardless of the materials used. The majority of such metamaterials are constructed by top-down approaches and macroscopic with unit cells of microns or larger. There are also molecular auxetics including natural crystals which are not designable. There is a gap from few nanometers to microns, which may be filled by biomolecular self-assembly. Herein, we demonstrate two-dimensional auxetic nanostructures using DNA origami. Structural reconfigurations are performed by two-step DNA reactions and complemented by mechanical deformation studies using molecular dynamics simulations. We find that the auxetic behaviors are mostly defined by geometrical designs, yet the properties of the materials also play an important role. From elasticity theory, we introduce design principles for auxetic DNA metamaterials.