Reversible Self-Assembly of 3D Architectures Actuated by Responsive Polymers.

An assembly of three-dimensional (3D) architectures with defined configurations has important applications in broad areas. Among various approaches of constructing 3D structures, a stress-driven assembly provides the capabilities of creating 3D architectures in a broad range of functional materials with unique merits. However, 3D architectures built via previous methods are simple, irreversible, or not free-standing. Furthermore, the substrates employed for the assembly remain flat, thus not involved as parts of the final 3D architectures. Herein, we report a reversible self-assembly of various free-standing 3D architectures actuated by the self-folding of smart polymer substrates with programmed geometries. The strategically designed polymer substrates can respond to external stimuli, such as organic solvents, to initiate the 3D assembly process and subsequently become the parts of the final 3D architectures. The self-assembly process is highly controllable via origami and kirigami designs patterned by direct laser writing. Self-assembled geometries include 3D architectures such as "flower", "rainbow", "sunglasses", "box", "pyramid", "grating", and "armchair". The reported self-assembly also shows wide applicability to various materials including epoxy, polyimide, laser-induced graphene, and metal films. The device examples include 3D architectures integrated with a micro light-emitting diode and a flex sensor, indicting the potential applications in soft robotics, bioelectronics, microelectromechanical systems, and others.