The stiffness-to-weight ratio is an important figure of merit for structural engineers. But in the ultralight regime—at densities of 10 mg/cm3 or less—few material options exist; one must turn to aerogels or foams. Architecture also matters: Both kinds of material form as a disordered network of cells whose random distribution renders the gel or solid far less stiff than one might predict based on its parent constituents—silica, carbon, polymer, or metal—in bulk form.
Fortunately, engineers have long known how to design structures whose order and symmetry enhance their mechanical properties. The Eiffel Tower, for instance, has a relative density—its mass per unit volume divided by the density of the iron in it—similar to that of aerogels, though the tower is clearly more structurally robust.1 Extending such trusses and frames to the microscopic scale and yet processing them on the macroscopic scale is the vision behind a new method...
