Architectured materials exhibit negative Poissons ratios and enhanced mechanical properties compared with regular materials.T heir auxetic behaviors emerge from periodic cellular structures regardless of the materials used. The majority of such metamaterials are constructed by topdown approaches and macroscopic with unit cells of microns or larger.T here are also molecular auxetics including natural crystals whicha re not designable.T here is ag ap from few nanometers to microns,w hichm ay be filled by biomolecular self-assembly.H erein, we demonstrate two-dimensional auxetic nanostructures using DNAo rigami. Structural reconfigurations are performed by two-step DNAr eactions and complemented by mechanical deformation studies using molecular dynamics simulations.W ef ind that the auxetic behaviors are mostly defined by geometrical designs,y et the properties of the materials also playa ni mportant role.F rom elasticity theory,w ei ntroduce design principles for auxetic DNAmetamaterials.

Deployable geometries are 2D or 3D finite structures that preserve their global shapes during expansion and contraction. [1] The structural transformation shows auxetic behaviors, which may be characterized by a negative Poisson's ratio (ν). Such topological behaviors emerge from their unique, intricate geometrical designs. In a Jitterbug transformer, for example, eight rigid equilateral triangles are linked at vertices, and the triangles can rotate around the linkages. [2] This allows deployable reconfigurations between octahedron (one of five Platonic solids) and cuboctahedron (one of thirteen Archimedean solids). By varying the shape and length of elements (regular polygons) in the transformer, multiple variants such as other deployable Platonic and Archimedean solids have been studied mathematically. [3] Another example is the Hoberman sphere, a commercially available, popular toy for kids and a possible choice for sculptures. The Hoberman sphere is also formed by rigid edges with flexible linkages, [4] and can shrink and expand by scissor-like actions at the joints while maintaining the overall spherical shape. In theory, it can be constructed regardless of materials and lengthscale. There is a 6-m-diameter Hoberman sphere from aluminum in the AHHAA Science Center in Tartu, Estonia, while the commercial toys made of plastics are typically ≈10 cm in length. [5] In nature, the shell of cowpea Deployable geometries are finite auxetic structures that preserve their overall shapes during expansion and contraction. The topological behaviors emerge from intricately arranged elements and their connections. Despite the considerable utility of such configurations in nature and in engineering, deployable nanostructures have never been demonstrated. Here a deployable flight ring, a simplified planar structure of Hoberman sphere is shown, using DNA origami. The DNA flight ring consists of topologically assembled six triangles in two layers that can slide against each other, thereby switching between two distinct (open and closed) states. The origami topology is a trefoil knot, and its auxetic reconfiguration results in negative Poisson's ratios. This work shows the feasibility of deployable nanostructures, providing a versatile platform for topological studies and opening new opportunities for bioengineering.

DNA origami has emerged as a versatile method to synthesize nanostructures with high precision. This bottom-up self-assembly approach can produce not only complex static architectures, but also dynamic reconfigurable structures with tunable properties. While DNA origami has been explored increasingly for diverse applications, such as biomedical and biophysical tools, related mechanics are also under active investigation. Here we studied the structural properties of DNA origami and investigated the energy needed to deform the DNA structures. We used a single-layer rectangular DNA origami tile as a model system and studied its cyclization process. This origami tile was designed with an inherent twist by placing crossovers every 16 base-pairs (bp), corresponding to a helical pitch of 10.67 bp/turn, which is slightly different from that of native B-form DNA (~10.5 bp/turn). We used molecular dynamics (MD) simulations based on a coarse-grained model on an open-source computational platform, oxDNA. We calculated the energies needed to overcome the initial curvature and induce mechanical deformation by applying linear spring forces. We found that the initial curvature may be overcome gradually during cyclization and a total of ~33.1 kcal/mol is required to complete the deformation. These results provide insights into the DNA origami mechanics and should be useful for diverse applications such as adaptive reconfiguration and energy absorption.

DNA origami has garnered great attention due to its excellent programmability and precision. It offers a powerful means to create complex nanostructures which may not be possible by other methods. The macromolecular structures may be used as static templates for arranging proteins and other molecules. They are also capable of undergoing structural transformation in response to external signals, which may be exploited for sensing and actuation at the nanoscale. Such on-demand reconfigurations are executed mostly by DNA oligomers through base-pairing and/or strand displacement, demonstrating drastic shape changes between two different states, for example, open and close. Recent studies have developed new mechanisms to modulate the origami conformation in a controllable, progressive manner. Here we present several methods for conformational control of DNA origami nanostructures including chemical adducts and UV light as well as widely applied DNA oligomers. The detailed methods should be useful for beginners in the field of DNA nanotechnology.

Architectured materials exhibit negative Poisson’s ratios and possess enhanced mechanical properties compared with regular materials. Their auxetic behaviors emerge from periodic cellular structures rather than chemistry. The majority of such metamaterials are constructed by top-down approaches and macroscopic with unit cells of microns or larger. On the other extreme, there are molecular-scale auxetics including naturally-occurring crystals which are not designable. There is a gap from few nanometers to microns, which may be filled by bottom-up biomolecular self-assembly. Here we demonstrate two-dimensional (2D) auxetic nanostructures using DNA origami. Structural deformation experiments are performed by strand displacement and complemented by mechanical deformation studies using coarse-grained molecular dynamics (MD) simulations. We find that the auxetic properties of DNA nanostructures are mostly defined by geometrical designs, yet materials’ chemistry also plays a role. From elasticity theory, we introduce a set of design principles for auxetic DNA materials which should be useful for diverse applications.