Mechanically Guided Assembly of Monolithic Three-Dimensional Structures from Elastomer Composites

Mechanically guided assembly is considered a facile and scalable methodology for fabrication of three-dimensional (3D) structures. However, most of the previous methods require multistep processes for bonding bi- or multilayers and only result in non-freestanding 3D structures because of usage of a supporting elastomer substrate. Herein, we report a functional elastomer composite that can be transformed to a freestanding and monolithic 3D structure driven by the mechanically guided assembly. Photolithography can be used to selectively tune the mechanical properties of UV-exposed regions which exhibit enhanced ductility compared with the nonexposed regions. Thus, a gradient of the residual strain in the thickness direction makes the films assemble into 3D structures. These 3D structures are also predicted by our computational models using finite element simulations, which yields a reasonable agreement with the experiments. The systematically designed 2D structures with varied patterns can be transformed to various 3D structures with the control of the residual strain gradient, via key processing parameters including pre-strain, film thickness, and UV exposure time. By integrating different active electronic components on the fabricated 3D structures, potential applications of this 3D platform in electronics were demonstrated. This study offers a unique capability in constructing monolithic and freestanding 3D assembly, paving new routes to many applications such as wearable electronics, smart textiles, soft robotics, and structural health monitoring.