Bio-inspired gradient metamaterials with exceptional mechanical performance

Gradient design is an effective way to enhance the mechanical performance of metamaterials, while current gradient designs generally offer only uni-gradient enhancement performance. To fully leverage the advantages of gradient design, we report a bio-inspired gradient design strategy derived from gradient microstructures of sunflower stems, creating multi-gradient metamaterials. Through a combination of theoretical analyses, experimental tests, and numerical simulations, we demonstrate that bio-inspired tri-gradient designs achieve exceptional enhancements of mechanical performance. This unique phenomenon breaks the upper limitations of performance of conventional uni-gradient metamaterials. The optimum bio-inspired structure exhibits 199.6% and 558.8% enhancements in energy absorption and stiffness performance compared to existing uni-gradient metamaterials. Furthermore, the generalizability of this bio-inspired gradient design strategy is validated, indicating that the exceptional performance brought by this design concept can be extended to other metamaterials with different topological structures. This discovery provides insights for the structural design of multifunctional metamaterials with exceptional mechanical performance.