Researchers use 4D Printing to turn Sulfur into self moving soft robots

A joint research team has developed the first 4D printing technology built from industrial sulphur waste, producing recyclable soft robots that move autonomously in response to heat, light, and magnetic fields.

Every year, petroleum refining produces millions of tons of elemental sulphur as a byproduct, much of which is stored or thrown away. A Korean research team has found a way to transform this industrial waste into the building blocks for self-moving, fully recyclable soft robots using a 4D printing method shown for the first time.

The team was led by Dr. Dong-Gyun Kim of the Korea Research Institute of Chemical Technology (KRICT), Professor Jeong Jae Wie of Hanyang University, and Professor Yong Seok Kim of Sejong University.

Standard 3D printing produces static objects. 4D printing on the other hand adds the element of time, producing structures that change shape or behaviour after printing when exposed to external triggers.

The KRICT team made this possible by creating a new class of sulphur-rich polymer called poly (phenylene polysulfide) networks, or PSNs, which have shape-memory properties governed by their glass transition temperature.

Once printed, these structures can change shape when exposed to heat or light. They do not need motors or mechanical parts. By adding 20 percent magnetic particles, the team created composite robots smaller than half an inch. These robots can move freely by following external magnetic fields.

One striking feature of this technology is how components are joined. Shining a near-infrared laser for just eight seconds triggers a chemical welding reaction. Internal sulphur bonds temporarily break and reconnect at the joint. This fuses the printed parts without any adhesive.

The researchers showcased the potential of their technology by assembling a variety of modular structures designed to resemble complex architectural forms. Among these, they created a miniature version of the iconic Sagrada Família and a detailed model of a retractable-roof stadium.

Each of these structures was constructed from individually printed blocks, all of which are capable of changing shape on command, demonstrating the precision, versatility, and dynamic capabilities of the 4D printing method.

When a printed structure reaches the end of its use, it can be melted down and repurposed as new printing material without any loss of quality or volume. This process allows the material to be continuously reused, forming what the researchers describe as a closed-loop, fully recyclable manufacturing system that could significantly reduce waste in advanced manufacturing.

Dr. Kim described the significance plainly.

“This study represents the first example of upcycling industrial sulphur waste into advanced robotic materials,” he . “Smart materials that can move autonomously and be recycled are expected to become key drivers of future soft robotics and automation technologies.”

Soft robotics — machines built from flexible, pliable materials rather than rigid metal — are increasingly attractive for applications in medicine, drug delivery, and precision manufacturing. Their biggest limitation has been the materials themselves, which often lack the combination of strength, responsiveness, and sustainability needed for real-world deployment.

The KRICT method solves all three challenges. It uses inexpensive waste material, creates robots that react to several stimuli without external power, and fully closes the loop on manufacturing waste.

This research was supported by the National Research Foundation of Korea and the U.S. Army Research Laboratory.

The findings were in the journal Advanced Materials.

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