Modular reprogrammable 3D mechanical metamaterials with unusual hygroscopic deformation modes.

The majority of polymer-based materials demonstrate expansion upon absorbing water from the air. Mechanical metamaterials provide an interesting way to achieve unusual hygroscopic deformation. However, previous studies have only accommodated the limited tunability of negative hygroscopic expansion by theoretical analysis but have never involved other deformation modes.

Moisture-sensitive mechanical metamaterials with unusual and re-programmable hygroscopic deformation modes.

Mechanical metamaterials are of great interest due to their counterintuitive deformation under various physical fields. However, the research on metamaterials responding to moisture is still rare and controllable hygroscopic deformation is vital for sensoring, actuating, and stress elimination in a moisture environment. Inspired by the hygroscopic deformation of pinecones, this work studies 2D moisture-sensitive mechanical metamaterials exploiting bi-material curved strips as building blocks by simulations and experiments, which especially demonstrates repeatable programming ability to realize customized unusual hygroscopic deformations.

Programmable Mechanical Metamaterials with Tailorable Negative Poisson's Ratio and Arbitrary Thermal Expansion in Multiple Thermal Deformation Modes.

Mechanical metamaterials pave a way for designing and optimizing microstructure topology to achieve counterintuitive deformation including negative Poisson's ratio (NPR) and negative thermal expansion (NTE). Previous studies were always limited to single anomalous mechanical or thermal deformation, but current applications for high-precision mechanical or optical equipment always require their combination and customized and anisotropic deformation parameters. This work develops programmable two-dimensional (2D) mechanical metamaterials based on chiral and antichiral structures constructed with curved bimaterial strips to produce tailorable NPR and arbitrary thermal deformation.