Liquid Metal-Polymer Microlattice Metamaterials with High Fracture Toughness and Damage Recoverability.

Biological materials exhibit excellent fracture toughness due to their ability to dissipate energy during crack propagating through the combination of various constituents with different stiffnesses. Replicating this mechanism in engineering materials is important in mechanical systems and emerging applications such as flexible electronics and soft robotics. Here a novel liquid metal (LM)-filled polymer microlattice metamaterial, fabricated by projection micro-stereolithography (PμSL) 3D printing and vacuum filling of gallium (Ga), exhibiting high fracture toughness of 0.8 MJ m-3 , is reported. Moreover, the LM metamaterials demonstrate shape memory effect and even essentially recover its original shape upon severe fractures. These unique features arise from the tunable properties of gallium at a relatively low temperature range. The result offers new insights into design and manufacturing mechanical metamaterials with tunable properties and high recoverability for soft robots, flexible electronics, and biomedical applications.