4D-printing of light-driven soft actuator with programmed printing density.

There is a growing interest in concept of 4D-printing that combines 3D-manifacturing process with dynamic modulation for bioinspired soft materials exhibiting more complex functionality. However, conventional approaches have drawbacks in low resolution, control of internal micro/nanostructure, and creation of fast, complex actuation due to lack of high-resolution fabrication technology and suitable photoresist for soft materials. Here we report an approach of 4D-printing that develops a bioinspired soft actuator with defined 3D-geometry and programmed printing density. Multiphoton lithography (MPL) allows for controlling printing density in gels at pixel-by-pixel with a resolution of a few hundreds of nanometers, which tune swelling behaviors of gels in response to external stimuli. We printed 3D-soft actuator composed of thermoresponsive, poly(N-isopropylacrylamide) (PNIPAm) and gold nanorods (AuNRs). To improve the resolution of printing, we synthesized functional, thermoresponsive macrocrosslinker. Through plasmonic heating by AuNRs, nanocomposite-based soft actuators undergo nonequilibrium, programmed, and fast actuation. Light-mediated manufacture and manipulation (MPL and photothermal effect) offer the feasibility of 4D-printing toward adaptive bioinspired soft materials.