Design and analysis of 2D/3D negative hydration expansion Metamaterial driven by hydrogel

In this paper, we developed a new design and preparation method of 2D and 3D composite metamaterial with adjustable isotropic negative hydration expansion (NHE) function based on re-entrant auxetic honeycomb. The metamaterial is composed of composite lattice microstructure with hydrogel driving layer and re-entrant framework and prepared by multi-material 3D printer. Experimental, simulation and theoretical investigation were carried out to demonstrate the design method and NHE deformation effects of the metamaterial. It was shown that the effective NHE coefficient depends on the length of the driving layer and the straight bar connecting the lattice microstructures. In addition, a non-monotonic relationship was found between the bandings angle theta 2 and the length ratio (s/a) due to the constraint effect on both ends of the composite beam. Through the parameter design of the lattice microstructure, the NHE coefficient of can be adjusted within the range of 0-22.4%. For the 3D sample, the value of the NHE coefficient is among the largest achieved in experiments to date. This work provides a practical method for obtaining 2D and 3D metamaterial with adjustable NHE and can be applied to the design of macro-, microand nano-metamaterial. (c) 2020 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http:// creativecommons.org/licenses/by-nc-nd/4.0/).