World-first 4D printing method turns sulfur waste into soft robots

A Korean research team has pioneered the first 4D printing technology that transforms industrial sulfur waste—a byproduct of petroleum refining—into recyclable soft robots capable of autonomous movement in response to heat, light, and magnetic fields. Led by Dr. Dong-Gyun Kim (KRICT), Professor Jeong Jae Wie (Hanyang University), and Professor Yong Seok Kim (Sejong University), the team developed a new sulfur-rich polymer called poly(phenylene polysulfide) networks (PSNs) with shape-memory properties. These printed structures can change shape without motors or mechanical parts, and by incorporating magnetic particles, the researchers created small composite robots that move by following external magnetic fields. A key innovation is the assembly process, where near-infrared laser exposure triggers a chemical welding reaction that fuses printed parts without adhesives, allowing modular structures to be built with precision and dynamic capabilities. The researchers demonstrated this by creating complex architectural models, such as a miniature Sagrada Família and a retractable-roof