Knots are Not for Naught—Design, Properties and Topology of Hierarchical Intertwined Micro-Architected Materials

Lightweight and tough engineered materials are often designed with three-dimensional (3D) hierarchy and interconnected structural members whose junctions are detrimental to their performance because they serve as stress concentrations for damage accumulation and lower mechanical resilience. We introduce a new class of architected materials, whose components are interwoven and contain no junctions, and incorporate micro-knots as building blocks within these hierarchical networks. Tensile experiments, which agree with an analytical model for overhand knots, reveal that knot topology allows a new regime of deformation capable of shape-retention, leading to ~92% increase in absorbed energy and up to ~107% increase in failure strain compared to woven structures. Our exploration unlocks knotting and frictional contact to create highly extensible low-density materials with tunable shape reconfiguration and energy absorption capabilities.