Biomimetic 3D printed lightweight constructions: a comparison of profiles with various geometries for efficient material usage inspired by square-shaped plant stems

Abstract

Within a bottom-up approach in biomimetics, this study was inspired by the plant motherwort (Leonurus cardiaca), which has stems divided longitudinally into hollow internodes and solid nodes, a lightweight concept well-known in biology. The square cross-sections show a specific geometric arrangement of various tissues, each with different mechanical properties. We have used CAD software and selective laser sintering technology to produce (1) extruded hollow profiles with various cross-sections analogous to internodes, and (2) integrated additional elements mimicking nodes. The design of the individual profiles with their different geometries is based on an increasing degree of abstraction, starting with profile A, which comes closest to the plant model, through profile B in the form of a greatly simplified material distribution, to profile C with the simplest geometry of a square hollow profile. In the context of resource-saving constructions, we have determined the flexural and torsional stiffness, the twist to bend ratio, and the lightweight efficiency of each individual profile. In general, profiles A, B, and C and all profiles from the A- and C-family show higher torsional stiffness than flexural stiffness. However, the profiles of the B-family exhibit no such uniform mechanical behavior. Interestingly, profile A has a higher lightweight efficiency than profile B but a lower efficiency than the most abstracted profile C. This indicates that a simple blueprint of nature is not useful, because, in plants, the geometric designs of various tissues and of globally and locally adaptable material properties are coupled to optimize performance based on multifunctionality. In contrast, 3D laser sintered profiles consist of a single isotropic and homogeneous material with defined material properties and therefore show different flexural and torsional efficiency because of their diverse geometries alone. These results reveal the influences of the geometric arrangement on the bending and torsional stiffness of the plant without interference from variations in material properties (reverse biomimetics).