Design and 3D Printing of Four Multimaterial Mechanical Metamaterial Using PolyJet Technology and Digital Materials for Impact Injury Prevention.

Impact injuries are very common daily problems in sports. Over the last years there has been advances in the prevention of impact injuries with the creation of new energy-absorbing materials, but the field is still novel. Mechanical metamaterials are three-dimensional materials whose mechanical properties are strongly related to its structure and not only to the material of which they are made. The materials showed in this work are composed of various unit cells with a specific geometry. Because of the unit cells' complex architecture, 3D printers are more convenient to manufacture them. Thus, PolyJet is a perfect technology for metamaterials because it allows printing complex structures with high resolution and mixing the raw materials in order to obtain different properties such as flexibility and shock absorption.In this work, we aim to analyze the printing parameters of the Octet-Truss Lattice, Kelvin Foam, Convex-Concave Foam and Truss-Lattice auxetic unit cells (UC). In addition, the structures are composites of VeroPlus and Agilus. Finally, we 3D-printed all the metamaterials designed using the PolyJet printer Objet 500 Connex 3 to analyze the feasibility of manufacturing with suitable parameters. The results showed that the support material in the printing of the UC made of Truss-Lattice and Kelvin Foam could be removed more easily than in the Octet-Truss Lattice and Convex-Concave Foam. This happened because of the free space between the beams in the UC.