Scientists in Japan have developed a recyclable resin for high-precision 3D printing that can be melted down and reused multiple times without major performance loss.

The team at YOKOHAMA National University said the material could help address one of the biggest problems in stereolithography, a form of 3D printing that uses ultraviolet light to harden liquid resin into detailed structures.

Most photocurable resins used in stereolithography become permanently hardened after printing, making them difficult or impossible to recycle. The researchers said their new resin can return to its original liquid-like state when heated, allowing it to be reused for future prints.

The group tested the material in both single-photon microstereolithography and two-photon lithography systems, techniques used to manufacture highly detailed microscopic structures.

Reprint, reuse, repeat

“Photocured 3D models cannot be recycled, so there are concerns about the negative environmental impact of discarding 3D-printed resin parts,” said Shoji Maruo, professor at YOKOHAMA National University.

According to the researchers, previously proposed recyclable resins often required chemical additives or lost performance after only a few recycling cycles.

To solve that problem, the team turned to anthracene, a chemical compound known for its reversible light-driven reactions. When exposed to light, anthracene forms cross-linked structures through a process called photodimerization. Heating can reverse the reaction, breaking the material back down into its original form.

The researchers used an anthracene-containing compound to build a resin that cures without photoinitiators, chemicals typically required to trigger hardening in UV-based 3D printing systems.

“Previously reported recyclable resins depended on photoinitiators, but the resin in this study cures via stepwise polymerization without the need for initiators,” Maruo said.

The team said removing initiators simplified the resin composition and reduced contamination from additives during recycling.

Precision printing survives

To test the resin, the researchers printed microscopic structures using laser scanning systems. In one demonstration, they created a butterfly-shaped model using two-photon lithography and found the print quality remained comparable to conventional materials.

“These results demonstrate that the recyclable resin can be precisely patterned in arbitrary shapes using laser scanning, confirming its suitability for two-photon lithography,” said Masaru Mukai, specially appointed assistant professor at YOKOHAMA National University.

The researchers also repeatedly printed the letters “YNU” by heating and reusing the same material through 10 print cycles. In another test, they transformed a printed cube into a disc-shaped object by heating the original structure to 150 degrees Celsius for 15 minutes.

The team reported relatively small material degradation during repeated reuse compared to earlier recyclable stereolithography materials.

“Reversible photodimerization of anthracene provides a practical route toward recyclable materials for light-based 3D printing,” Mukai said.

The researchers said the next step is adapting the resin for larger-scale 3D-printing systems while improving long-term material stability.

The study was published in ACS Omega.