Programmable self-folding of trilayer and bilayer-hinge structures by time-dependent swelling of tough hydrogels

Abstract

Inspired by nature, active materials are used to developed complex 3D configurations considering their specific characteristics. One of the shape-shifting methods in smart structures is utilizing programmable materials in self-folding structures. Hydrogels due to their biocompatibility, controllable functionalities, large reversible deformations, and their sensitivity to environmental stimuli are vital candidates to be used in self-folding structures. To avoid the mechanical weakness of conventional hydrogels, in this paper polyampholyte tough hydrogel is inspected considering a transient electro-chemo-mechanical constitutive model combining a visco-hyperelastic model with Nernst-Planck and Poisson’s equations. After calibrating the material parameters and verifying the accuracy of the model and its implementation, we present two approaches in order to generate self-folding hydrogel-based structures: polymer structure with bilayer hinges and trilayer structure composed of a hydrogel film sandwiched between two elastomer layers. Next, diverse factors are examined in the self-folding of smart structures which conforms with experimental test data, including hydrogel swelling, structure thickness and stiffness, bilayer configuration and composition, the width of the bilayer as well as opening width in trilayer and layers thickness. Finally, several transient self-folding of 2D flat patterns which turn into 3D complex configurations are scrutinized such as the closure of box, pyramids, and flower-shaper gripper.

Liquid Metal Microdroplet‐Initiated Ultra‐Fast Polymerization of a Stimuli‐Responsive Hydrogel Composite

“…For instance, as demonstrated in Figure 4E, hinges made with the same LM ratio are expected to fold at nearly the same speed and result in a nearly symmetric shape upon deployment. By varying LM ratios in the hinges, the structure can be, in theory, programmed to fold into a variety of 3D geometries [77,80] with their desired curves and surfaces encoded into the LM ratios in the hydrogels. In addition to conventional single-stage folding, the LM-varying method in this work can also potentially apply to sequential folding [81] where the structure goes through multiple folding stages according to the LM ratios.…”

Mechano‐Activated Shape Morphing of Aluminum–Plastic Laminate Composites

“…This approach of creating hinges by creating defects in symmetric trilayers is well-established in the literature on self-folding origami. [22,[32][33][34][35][36][37] When such samples are stretched and released, these asymmetric regions bend. By changing which polymer face is removed at different locations, we can now realize bidirectionally programmable bending either by loading along one direction (Figure 7f,g) or by loading sequentially along two directions, Figure 7h.…”

Kirigami inspired shape programmable and reconfigurable multifunctional nanocomposites for 3D structures

“…Promising 3D shape programming of polymer materials has been achieved through several approaches, such as shape memory polymers (SMP) [5,6], swelling hydrogels [7,8], or liquid crystalline elastomers (LCE) [9,10]. Different bending strategies have been used, including multilayers [11], material gradients [12] and localized activation [13].…”