Self-healing soft robots 3D printed with waste sulfur: South Korean research
A South Korean research team has developed a method to convert industrial waste sulfur into a 3D-printable polymer, used to create soft robots capable of moving, grasping objects, and self-repairing. The solution addresses a growing environmental problem: every year the oil industry generates 85 million metric tons of excess sulfur.
The material, called PSN (poly(phenylene polysulfide) network), represents a concrete application of 4D printing applied to the recycling of industrial materials that are otherwise difficult to dispose of.
The problem of industrial sulfur
The oil industry must remove sulfur from crude oil to comply with environmental regulations, but existing industrial applications cannot absorb the entire production.
The removal of sulfur from crude oil is mandatory by law. Its main industrial use, the production of sulfuric acid, has already reached maximum capacity. In 2024, global production reached 85 million metric tons according to the U.S. Geological Survey.
This surplus represents a logistical and environmental problem. The team composed of researchers from KRICT, Hanyang University, and Sejong University has identified a solution: transforming sulfur into a polymer for 4D printing.
- 85 million tons of sulfur produced in 2024 without defined use
- New 3D-printable PSN polymer derived from industrial sulfur
- Soft robots smaller than 1 cm capable of autonomous movement and self-repair
- Closed-loop system with complete material recycling
The technical challenge overcome
The PSN had a molecular structure too rigid to be extruded. The researchers modified the polymer network while keeping the functional properties intact.
Until today, the poly(phenylene polysulfide) network could not be 3D printed. Its overly intertwined internal structure prevented flow through the extruder. The South Korean team stretched the polymer network just enough to print complex geometries without compromising the material's properties.
The result is a structure with shape memory that reacts to heat or light. No motors, cables, or external power are needed.
Miniaturized magnetic robots
By incorporating 20% iron powder, the researchers created a magnetic version of the PSN that responds to external magnetic fields.
The magnetic version of the material, called MPSN, allowed the construction of robots smaller than one centimeter. These devices overcome obstacles, release loads at specific points, or release catalysts to trigger chemical reactions on demand.
I robot si muovono in risposta a calore, luce o campi magnetici. La loro dimensione ridotta e l’assenza di componenti elettronici li rende adatti ad applicazioni in ambienti difficili.
Adhesive-free assembly system
A near-infrared laser allows two printed parts to be fused in eight seconds, creating permanent joints without adhesives.
The assembly system developed by the team eliminates the need for adhesives. By applying a near-infrared laser for eight seconds, it is possible to fuse two printed components. The heat breaks and reconnects the internal bonds of the polymer, joining the parts in a manner similar to LEGO bricks.
This technique simplifies the production of complex structures. The joints are strong and retain the shape-memory properties of the material.
4D printing produces objects that change shape over time in response to external stimuli such as temperature, light, or magnetic fields. The fourth element is time, which transforms static structures into dynamic systems.
Closed-loop recycling
Once its function is exhausted, each component can be melted and reprinted without generating waste. The researchers define the process as a closed-loop system.
After use, the components can be melted and reprinted from scratch. The researchers describe the process as a closed loop in which the material is continuously recycled without producing additional waste.
Dong-Gyun Kim, one of the project leaders, emphasized that this represents the first documented case of complete recycling for this type of polymer. The ability to reuse the material indefinitely reduces environmental impact and production costs.
Application prospects
Technology opens up scenarios for miniaturized medical devices, environmental sensors, and controlled release systems for chemical substances.
Potential applications range from medicine to the chemical industry. Soft robots of millimeter size could operate inside the human body for minimally invasive procedures. In the industrial field, they could act as intelligent sensors or as carriers for catalysts in complex chemical reactions.
The self-repair capability extends the useful life of devices. The combination of recyclable material, small size, and autonomous functionality represents a significant step toward sustainable robotic systems.
article written with the help of artificial intelligence systems
Q&A
What is the raw material used to create the new soft robots?
The robots are made from a polymer called PSN, obtained by converting waste industrial sulfur, of which the oil industry produces 85 million metric tons in excess each year.
How do these robots move without motors or batteries?
The PSN polymer has shape memory and reacts to heat, light, or magnetic fields; the magnetic version MPSN, containing 20% iron powder, responds to external magnetic fields.
How are the components assembled without the use of adhesives?
A near-infrared laser melts two printed parts in eight seconds, breaking and reconnecting the polymer's internal bonds to create permanent joints.
What does it mean that the process is closed-loop?
The components can be melted and reprinted without generating waste, representing the first documented case of complete recycling for this type of polymer.
What are the potential applications of these robots?
Applications include miniaturized medical devices for minimally invasive procedures, environmental sensors, and controlled release systems for chemicals in industrial settings.
