Thread-pulling-induced assembly strategy for complex 3D structures

• A simple low-cost fabrication method relying on the 2D-to-3D geometric transformation • A point-to-point spatial loading path is established during assembly. • Thread-pulling-induced strategy for 3D assembly • Assembly of closed, multi-layered, and rotational-symmetric architectures Three-dimensional (3D) architectures in complexly shaped thin-film configurations have arisen increasing attention in flexible electronics, biomedical devices, microrobots and other fields. However, a simple low-cost fabrication method relying on the 2D-to-3D geometric transformation of a patterned thin film remains underexplored. Herein, a thread-pulling-induced assembly strategy is proposed to allow formation of diverse freestanding mesoscale 3D structures, such as closed, multi-layered, and rotational-symmetric architectures. A point-to-point spatial loading path is established, taking advantage of controlled perforation in planar fabrication technology. In this assembly strategy, the final 3D configuration is determined mainly by the structural design of 2D precursors and the thread-pulling-induced loading condition. In particular, two primary deformation modes induced by the thread pulling, including the bending-dominated mode and bending-twisting coupled mode, are exploited to extend the range of accessible 3D configurations. FEA predictions and optical images of various assembled 3D structures illustrate the effectiveness of the strategy. This work could offer new insights into the mechanism of geometric transformation for the construction of complex 3D thin-film structures and devices.