3d Printed Auxetic Metamaterials with Tunable Mechanical Properties and Morphological Fitting Abilities

Abstract

The researches on creating special structures with negative Poisson’s ratio, also called auxetic metamaterials, are widely conducted for the potential use in flexible electronics, aerospace, biomedicine, and other fields. Auxiticity is the phenomenon of transverse expansion that occurs when stretched longitudinally. However, conventional auxetic metamaterials lack tunable properties, expressed as 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 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 SNR, and breathability when collect EMG signals.

Keywords: Auxetic metamaterial, 3D printing, Shape memory polymers, Shape-fitting, EMG signals