Parametric Design and Mechanical Characterization of 3D-Printed PLA Composite Biomimetic Voronoi Lattices Inspired by the Stereom of Sea Urchins

The present work is focused on the analysis of the microstructure of the exoskeleton of the sea urchin Paracentrotus lividus and the extraction of design concepts by implementing geometrically described 3D Voronoi diagrams. Scanning electron microscopy (SEM) analysis of dried sea urchin shells revealed a foam-like microstructure, also known as the stereom. Subsequently, parametric, digital models were created with the aid of the computer-aided design (CAD) software Rhinoceros 3D (v. Rhino 7, 7.1.20343.09491) combined with the visual programming environment Grasshopper. Variables such as node count, rod thickness and mesh smoothness of the biologically-inspired Voronoi lattice were adapted for 3D printing cubic specimens using the fused filament fabrication (FFF) method. The filaments used in the process were a commercial polylactic acid (PLA), a compound of polylactic acid/polyhydroxyalkanoate (PLA/PHA) and a wood fiber polylactic acid/polyhydroxyalkanoate (PLA/PHA) composite. Nanoindentation tests coupled with finite element analysis (FEA) produced the stress-strain response of the materials under study and were used to simulate the Voronoi geometries under a compression loading regime in order to study their deformation and stress distribution in relation to experimental compression testing. The PLA blend with polyhydroxyalkanoate seems to have a minor effect on the mechanical behavior of such structures, whereas when wood fibers are added to the compound, a major decrease in strength occurs. The computational model results significantly coincide with the experimental results.