Transforming Industrial Waste into Autonomous Soft Robots: A Breakthrough in 4D Printing

A collaborative research team from the Korea Research Institute of Chemical Technology (KRICT), Hanyang University, and Sejong University has pioneered a groundbreaking 4D printing technology that utilizes industrial sulfur waste to create fully recyclable soft robots. This innovative approach addresses the significant issue of sulfur waste generated during petroleum refining, which amounts to millions of tons annually. The team, led by Dr. Dong-Gyun Kim, Professor Jeong Jae Wie, and Professor Yong Seok Kim, has successfully transformed this byproduct into the building blocks for autonomous robots that respond to heat, light, and magnetic fields.

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Unlike traditional 3D printing, which produces static objects, 4D printing incorporates the dimension of time, allowing structures to change shape or behavior post-printing. The KRICT team developed a new class of sulfur-rich polymer known as poly (phenylene polysulfide) networks (PSNs), which exhibit shape-memory properties influenced by their glass transition temperature. These robots, measuring less than half an inch, can move autonomously by following external magnetic fields, thanks to the addition of 20 percent magnetic particles.

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The assembly of these robots is particularly noteworthy; a near-infrared laser activates a chemical welding reaction that fuses printed components without adhesives. This method allows for the creation of complex modular structures, including a miniature version of the Sagrada Família and a retractable-roof stadium, showcasing the versatility and dynamic capabilities of this 4D printing technology.

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The KRICT team's approach not only innovates in robotics but also promotes sustainability through a closed-loop manufacturing system. Once a printed structure reaches the end of its life cycle, it can be melted down and repurposed into new printing material without any degradation in quality or volume. This recycling process significantly reduces waste in advanced manufacturing, aligning with global sustainability goals.

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Dr. Kim emphasized the importance of this research, stating, “This study represents the first example of upcycling industrial sulfur waste into advanced robotic materials.” The development of smart materials capable of autonomous movement and recycling is expected to play a crucial role in the advancement of soft robotics and automation technologies. Soft robotics, characterized by flexible materials, are increasingly sought after for applications in medicine, drug delivery, and precision manufacturing, overcoming previous limitations related to material strength, responsiveness, and sustainability.

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The research received support from the National Research Foundation of Korea and the U.S. Army Research Laboratory, highlighting its significance in both academic and practical applications. The findings were published in the journal *Advanced Materials*, marking a notable contribution to the field of robotics and materials science.

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• “This study represents the first example of upcycling industrial sulfur waste into advanced robotic materials,” — Dr. Dong-Gyun Kim, KRICT

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This innovative research not only addresses environmental concerns but also sets the stage for the future of soft robotics, emphasizing the potential of utilizing waste materials in advanced technologies.

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