Researchers at Yokohama National University in Japan have developed a photocurable resin for stereolithography that can be melted down and reprinted more than ten times, and with minimal material degradation. The development represents a marked improvement on the one to three cycles that are typically achieved by comparable recyclable resins.

The study, published in ACS Omega, set out to tackle a significant limitation of stereolithography: once cured by ultraviolet light, conventional resins form highly cross-linked polymer networks that resist heat and solvents. This makes end-of-life recycling difficult and, as a result, uncommon.

How the resin works

The team built the material around anthracene, a compound whose molecular bonds form and break in response to light and heat. Ultraviolet exposure triggers photodimerization, cross-linking the resin into a solid, and the application of heat reverses the reaction, to return it to a printable liquid.

Because the resin cures through stepwise polymerization, it requires none of the additives typically needed to trigger hardening in UV-based systems (photoinitiators). The reduction in compositional complexity and elimination of contamination sources during recycling opens up the opportunity for reuse.

Ten-cycle validation

Testing covered both single-photon microstereolithography and two-photon lithography, the latter of which is capable of sub-micrometer resolution. In repeated trials, the researchers printed, erased by heating, and reprinted the letters “YNU” across more than ten cycles.

In a separate test, a printed cube was heated to 150°C for 15 minutes and reprinted as a disc.

Mechanical testing showed the elastic modulus rose by approximately 9% between the first and second cycles, a change that was attributed to cumulative thermal effects rather than photochemical breakdown. 

Minimum curing line width reached 0.61 micrometers, at least an order of magnitude finer than comparable recyclable resins reported in prior literature, according to the study.

The paper indicated that the research team’s next step is to adapt the material for larger-scale printing platforms, while improving long-term stability.