3D printed auxetic metamaterials with tunable mechanical properties and morphological fitting abilities

Research on creating special structures with a negative Poisson's ratio, known as auxetic metamaterials, is widely conducted for potential applications in flexible electronics, aerospace, biomedicine, and other fields. Auxiticity is the phenomenon of transverse expansion that occurs when stretched longitudinally. However, conventional metamaterial tunable properties have certain limitations, mainly in the form of limited Poisson's ratio tuning range and transverse deformation. In this work, a series of symmetric antichiral auxetic structures with significant auxetic effect and low Poisson's ratio of −5 are designed and fabricated by 3D printing. Based on the manipulating of unit parameters and the use of shape memory polymers, the auxetic metamaterials exhibit tunable mechanical properties and programmable shape memory behaviors. Owing to these features, the auxetic metamaterials are demonstrated to achieve excellent shape-fitting and size-fitting capabilities, which are followed by expanding in a full range to contact any objects (due to auxiticity) and then contract to conform their shapes (due to shape memory). By integrating flexible electromyography(EMG) electrodes, the shape memory auxetic metamaterials can be used as self-adaptive wearable devices to fit with human limbs, which can ensure the good attachment, high signal to Noise Ratio (SNR), and breathability when collect EMG signals.