DNA-silica nanolattices as mechanical metamaterials

Mechanical metamaterials consist of intricate periodic structures made
using additive manufacturing techniques. Yet, nanoscale (<10 nm)
features cannot be directly printed using these fabrication techniques,
although this is the size regime in which enhanced material properties
appear. In addition, current additive manufacturing techniques cannot
easily combine disparate materials (e.g., soft, biological polymers with
hard ceramics) into structural motifs. Here, we show that DNA origami can
be used to construct octahedral-based isotropic and anisotropic
nanolattices. When coated with a thin silica layer, these nanolattices
obtain strength and energy absorption competitive with the best additively
manufactured nanolattices. The DNA nanolattices have strut 6 nm diameters
and  ~50 nm unit cells, which are two orders of magnitude smaller
than lithography-based lattices. The silica coating is as thin as ~1.65
nm, which results in enhanced strength. Atom probe tomography confirms the
nanoscale distribution of DNA and silica in the octahedral lattice
geometry. Finite element modeling (FEM) reveals two dominant failure
modes: buckling at lower coating thicknesses and tensile fracture at
higher thicknesses. Molecular dynamics (MD) simulations reveal that the
DNA delays failure by suppressing buckling within the lattice struts,
while the nanoscale silica undergoes a surface buckling mode which
contributes to increased strength at large strains.