A programmable multi-stable tensegrity metamaterial with enhanced energy absorption for fall-injury mitigation.

The calls for applying mechanical metamaterials for fall-injury mitigation are growing, yet conventional energy absorption mechanical metamaterials are not well-suited for gravitational, low-velocity, human-scale fall protection. To address these gaps, we propose a programmable centimeter-scale multi-stable tensegrity metamaterial that removes complex prestressing and enhances energy absorption. In our architecture, arrays of bistable units are stacked to form multi-stable "cables" that replace the tensile members in a classic tensegrity structure, simultaneously self-prestressing the structure and dissipating energy through controlled state transitions. Programmability is achieved through a hierarchical design - from the bistable unit to the multi-stable cable and to the full tensegrity structure - guided by a pseudo-rigid-body model (PRBM) that predicts the mechanical responses. The multi-stable tensegrity metamaterials are prototyped using 3D printing techniques, and experiments show a 3.1× increase in energy absorption compared to a non-tensegrity counterpart, allowing fragile eggs to survive drops from 120 cm, comparable to the center-of-mass height of an adult during a typical fall. In summary, this study establishes a pathway for the design, modelling, and fabrication of programmable multi-stable tensegrity metamaterials tailored to low-velocity, human-scale impact protection, with direct relevance to fall injury.