Mechanical metamaterials are classified as artificially designed structures and exhibit intriguing and sometimes counterintuitive properties that cannot be achieved in natural materials. Generally, the unit cells in the metamaterial tessellation are of one type with identical deformation properties, which leads to that the resultant metamaterials’ characteristics are limited to a small range during the flexible deformation. The shape-reconfigurable system through structural deformation has been identified as an effective method to realize programmability and tunability. Of particular interest here are mechanism-based metamaterials with inherently reliable deformation path and which is essential for programmable and tunable properties. However, the current works focus on programmable metamaterials that reconfigure along a single deformation path. Efforts also have been made to investigate enhanced reconfigurable ones with multiple motion paths for programmable metamaterials, yet it turns out to be typically multiple degree-of-freedoms, resulting in a challenging controllable deformation process.
        Therefore, Professor Yan Chen and her research team from Tianjin University as well as Professor Hanqing Jiang from Westlake University collaborated to develop a one-degree-of-freedom reconfigurable module with multiple predefined and reliable deformation paths. This construction module of the metamaterials can continuously bifurcate between expandable cube path, elongated prism path, and locked twist path through inherent kinematic bifurcation, accompanied by negative Poisson's ratio, positive Poisson's ratio, and zero Poisson's ratio behaviors as well as local and global chirality and tunable stiffness. Further, configurations of the module in expandable cube path and elongated prism path are used to construct 3D metamaterials yet without the frustration that impedes functionality due to compatible topological features. By regulating the proportion of modules in PPR or NPR states through reconfiguration, Poisson’s ratios of metamaterials can be programmed independently in orthogonal planes within a wide range of negative Poisson's ratio, positive Poisson's ratio, and even zero Poisson's ratio for the first time.
        This work has been published in Advanced Functional Materials, which opens up avenues for the design of programmable metamaterials based on the perspective of kinematic bifurcation generating from single DOF systems, and could readily be applied in shape-morphing systems in various fields, such as flexible metamaterials, morphing architectures and robotics. (More detailed introduction is shown in Video 1)

Video 1

Figure 1. The mechanism basis of the module.

Figure 2. Mechanical properties of a single module.

Figure 3. The series assembly with (mz+nz) modules, of which mz modules in PPR state and nz modules in NPR state.

Figure 4. Metamaterials with the 3D tessellation of mechanism modules.

Liu W, Jiang H, Chen Y, 3D Programmable Metamaterials Based on Reconfigurable Mechanism Modules, Advanced Functional Materials, 2021, 2109865.
(https://doi.org/10.1002/adfm.202109865 )