Four-dimensional printed hierarchical mechanical metamaterials with piezoelectric sensing function integration

This work presents a hierarchical 4D-printed mechanical metamaterial with reconfigurable, nonlinear mechanical behavior. An analytical framework is developed to predict its effective mechanical properties, demonstrating good agreement with finite-element simulations and experimental measurements. The metamaterial exhibits biomimetic, J-shaped stress-strain curves, indicating enhanced flexibility and compliance desirable for deployable structures. Moreover, the auxetic metamaterials achieve negative Poisson’s ratios with high stretchability, thereby expanding the operational domain of metamaterials. Furthermore, these metamaterials are integrated with flexible piezoelectric electrodes to enable a self-sensing function. Experiments demonstrate that the proposed self-sensing metamaterials are capable of accurately sensing pressure signals while maintaining high flexibility and conformal contact. Owing to the thermally activated shape-memory effects of the metamaterial skeleton, the device allows reversible reconfiguration of mechanical and sensing responses under external stimuli. These results highlight the potential of self-sensing metamaterials for deployable space structures, morphing aircraft, and wearable electronics.