RIT researchers develop self-healing polymers for more durable 3D-printed components

A research team at the Rochester Institute of Technology (RIT) is working on materials capable of repairing themselves to extend the lifespan of 3D-printed parts. Led by Christopher Lewis, the team has developed a light-sensitive polymer solution that can autonomously repair mechanical damage after printing. These so-called stimuli-responsive photopolymers are cured layer by layer during the additive manufacturing process and combine both thermoplastic and thermoset properties.

The central problem of many 3D printing materials lies in their brittleness. Cracks caused by mechanical stress often lead to structural failure. The RIT team discovered that adding a thermoplastic healing agent to a UV-curable resin matrix not only increases fracture toughness but also enables the autonomous closure of microscopic damage.

“When you break a bone, or cut yourself, we take it for granted that there is a self-repairing mechanism that allows for bones or skin to rejuvenate themselves, at least to some extent,” said Lewis. “We also learn that it is not true for synthetic materials or man-made objects. And our work in self-healing materials is a futuristics look at how we can develop systems that mimic those natural material properties.”

“It makes the material much stronger than it used to be. One of the problems with these soft, elastomeric materials is that they are traditionally weak.  And it also engenders another type of property—shape memory behavior, and we are just starting to focus our efforts on better understanding this behavior,” said Lewis.

The mechanism is based on a process called “Polymerization Induced Phase Separation” (PIPS), in which thermoplastic and thermoset phases separate during curing. This creates microscopic structures that, under UV light, shift shape much like a lava lamp, activating a kind of “healing process.” This property could be particularly relevant in fields such as soft robotics, printed electronics, or additive manufacturing of medical prosthetics.

“The approach we have taken is one where we have a mixture of two different things. We have our photoreactive, thermosetting polymer that once cured becomes a soft rubber. To this, we also add a thermoplastic healing agent. We were able to get light to pass through the system, and we achieved that by utilizing polymerization induced phase separation (PIPS). It is a process where the thermoset and thermoplastic materials separate during curing,” he said. “That is key to this whole thing.”

“Earlier work on thermoplastic polymer blends that are able to be processed using conventional techniques like injection molding or extrusion suggested that it was that phase separation that seemed to be driving the self-healing behavior of those systems. That understanding led us down this path of experimentation with this same healing agent and photo reactive polymer system, and then, a little bit of luck,” said Lewis.

The research is funded in part by the U.S. Department of Defense and conducted at RIT’s AMPrint Center. The goal is to develop materials that can respond to damage similarly to biological systems. In the long term, this technology could reduce maintenance costs for high-precision components and open up new possibilities for long-lasting 3D-printed applications.