Healable, memorizable, and transformable lattice structures made of stiff polymers

Emerging transformable lattice structures provide promising paradigms to reversibly switch lattice configurations, thereby enabling their properties to be tuned on demand. The existing transformation mechanisms are limited to nonfracture deformation, such as origami, instability, shape memory, and liquid crystallinity. In this study, we present a class of transformable lattice structures enabled by fracture and shape-memory-assisted healing. The lattice structures are additively manufactured with a molecularly designed photopolymer capable of both fracture healing and shape memory. We show that 3D-architected lattice structures with various volume fractions can heal fractures and fully restore stiffness and strength over two to ten healing cycles. In addition, coupled with the shape-memory effect, the lattice structures can recover fracture-associated distortion and then heal fracture interfaces, thereby enabling healing of lattice wing damages, mode-I fractures, dent-induced crashes, and foreign-object impacts. Moreover, by harnessing the coupling of fracture and shape-memory-assisted healing, we demonstrate reversible configuration transformations of lattice structures to enable switching among property states of different stiffnesses, vibration transmittances, and acoustic absorptions. These healable, memorizable, and transformable lattice structures may find broad applications in next-generation aircraft panels, automobile frames, body armor, impact mitigators, vibration dampers, and acoustic modulators. A lattice structure that switches between different arrangements when fractured and healed has been developed by scientists in the United States. A lattice structure, like a network of struts, can improve a material’s strength without significantly increasing its weight. This approach is seen in the design of bridges, but lattice-based structures are also used on smaller scales, for example, in battery electrodes or biomedical scaffolds. Qiming Wang from the University of Southern California, Los Angeles, and co-workers created a material in which the lattice can be modified dynamically for specific applications through an autonomous healing process. They 3D printed a transformable lattice structure made from a polymer. By heating the structure, they could change it from a so-called kagome lattice to a triangular lattice, thereby altering physical properties such as vibration transmission and stiffness. This transformation was entirely reversible. Existing healing experiments on self-healing bulk materials typically rely on manual contact of fracture interfaces. Development of 3D-architected lattice structures that can autonomously heal fractures or damages is still an outstanding engineering challenge. This paper presents a class of additively manufactured lattice structures that can autonomously heal fractures by first aligning fracture interfaces through a shape-memory process and then repairing fracture interfaces through a fracture-healing process. Through harnessing the coupling of shape-memory and self-healing, this paper also demonstrates reversible configuration transformations of lattice structures among states of different stiffnesses, vibration transmittances, and acoustic absorptions.