Microarchitected Stretching-Dominated Mechanical Metamaterials with Minimal Surface Topologies

Historically, the creation of lightweight, yet mechanically robust, materials have been the most sought-after engineering pursuit. For that purpose, research efforts are dedicated to finding pathways to emulate and mimic the resilience offered by natural biological systems (i.e., bone and wood). These natural systems evolved over time to provide the most attainable structural efficiency through their architectural characteristics that can span over multiple length scales. Nature-inspired man-made cellular metamaterials have effective properties that depend largely on their topology rather than composition and are hence remarkable candidates for a wide range of application. Despite their geometrical complexity, the fabrication of such metamaterials is made possible by the emergence of advanced fabrication techniques that permit the fabrication of complex architectures down to the nanometer scale. In this work, we report the fabrication and mechanical testing of nature-inspired, mathematically created, micro-architected, cellular metamaterials with topologies based on triply periodic minimal surfaces (TPMS) with cubic symmetries fabricated through direct laser writing two-photon lithography. These TPMS-based microlattices are sheet/shell- and strut-based metamaterials with high geometrical complexity. Interestingly, results show that TPMS sheet-based microlattices follow a stretching-dominated mode of deformation, and further illustrate their mechanical superiority over the traditional and well-known strut-based microlattices and microlattice composites. The TPMS sheet-based polymeric microlattices exhibited mechanical properties superior to other micrloattices comprising metal- and ceramic-coated polymeric substrates and, interestingly, are less affected by the change in density, which opens the door for fabricating ultralightweight materials without much sacrificing mechanical properties.