Sustainable photopolymer resins New recyclable resin could enable sustainable 3D printing

Photopolymer resins enable highly precise 3D printing, but their cured structures are usually difficult to recycle. Researchers at Yokohama National University have now developed an initiator-free anthracene-based resin that can be reshaped and reused multiple times while remaining compatible with high-resolution stereolithography.

Once only achievable in the far-fetched imaginations of science fiction writers, 3D printing has gone mainstream. Relatively inexpensive machines allow individuals to design and print everything from board games and desk accessories to replacement parts for household appliances and more. One of the biggest selling points is the ability to recycle a printed piece into something new, offering a potential pathway to more sustainable living. However, the highest quality 3D printing used to create extremely precise structures at the atomic scale — a method called stereolithography — uses process that involves photocuring resin by exposing the material to ultraviolet (UV) light. This irreversibly chemically changes the resin, making it impossible to recycle.

Until now, that is. A team led by researchers based at YOKOHAMA National University developed a new recyclable resin that could enable high-resolution and sustainable 3D printing. They published their approach in ACS Omega. on February 21, 2026.

“Photocured 3D models cannot be recycled, so there are concerns about the negative environmental impact of discarding 3D-printed resin parts,” said co-corresponding author Shoji Maruo, professor on the Faculty of Engineering at YOKOHAMA National University. “Research into reusable photocurable resins is progressing, but conventional resins form irreversible cross-linked networks. As a result, previously proposed ‘recyclable’ resins either require the addition of chemical additives for reuse or rapidly degrade after one or a few reuse cycles.”

The researchers set out to investigate whether a unique property of anthracene and its derivatives, a material used to produce dyes and plastics and to preserve woods, could offer a solution. When exposed to light, anthracene undergoes a process called photodimerization. This process forms the chemical bonds into cross-linked 3D structures that, when heated, can revert to their original 2D format.

“We found that the reversible photodimerization reaction of anthracene could be a practical method for developing a truly reusable resin free from initiators, or chemicals used to induce a reaction, that can maintain performance through multiple recycling cycles while supporting high-precision stereolithography,” Maruo said.

The team used a chemical compound previously developed as a reversible adhesive to produce the resin that then contains the anthracene chemical group. They then custom built two systems to cure the new resin: single-photon microstereolithography that employs one photon of light to precisely cure of the resin layer-by-layer; and two-photon lithography that induces simultaneous absorption of two photons by the resin. To test the two-photo lithography system, they 3D printed a butterfly-shaped model and assessed the printing accuracy at different speeds, finding that their resin behaved similarly to other resins.

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“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 co-corresponding and co-first author Masaru Mukai, specially appointed assistant professor on the Faculty of Engineering at YOKOHAMA National University who is currently at the Tokyo University of Science.

Their resin undergoes step-growth polymerization, meaning the resin is cured without an additive agent such as an initiator, instead of chain-growth reactions, where the light exposure initiation reaction that initiates another and so on.

“Previously reported recyclable resins depended on photoinitiators, but the resin in this study cures via stepwise polymerization without the need for initiators,” Maruo said. “This unique feature simplifies resin formulation, eliminates contamination from additives and enables near-complete recyclability. We demonstrated that the resin could be recycled at least 10 times using two-photon lithography.”

They 3D printed one of three letters of “YNU,” the acronym for YOKOHAMA National University, and then “erased it” by heating and printing the next of letter 10 times. The team also printed a cube shape, heated it to 150 degrees for 15 minutes and then printed a disc shape from the melted cube. They compared material degradation during reprocessing and found that the degradation was relatively minor even when compared to previous studies on reusable stereolithography resins.

“Reversible photodimerization of anthracene provides a practical route toward recyclable materials for light‑based 3D printing,” Mukai said. “By using an initiator‑free, step‑growth mechanism, we show that a photocurable resin can be recycled multiple times with comparatively small changes in material performance, while remaining compatible with both two‑photon and single‑photon stereolithography. Our results indicate that reusability and high‑precision fabrication can be combined more effectively than in previously reported recyclable resins.”

Next, the researchers said they plan to adapt the resin to a larger scale 3D-printing system and to improve the thermal response and long-term stability of the material.

Original Publication: Initiator-Free Recyclable Anthracene-Based Photocurable Resin Enabling Sustainable 3D Printing via Single- and Two-Photon Stereolithography; ACS Omega; DOI:10.1021/acsomega.5c09643

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