Engineers at Nanyang Technological University, Singapore have created a new class of light-activated molecules, called aryl diazirine photoinitiators, designed to harden liquid resins into solid plastic without relying on compounds now being restricted for reproductive toxicity. Early lab testing shows the new chemistry is not toxic to human cells, reduces shrinkage during curing, and works in water-based formulations.
Why current photoinitiators are disappearing
Photoinitiators are the chemical trigger inside UV resins used for 3D printing, dental materials, coatings and gel nail polish. Exposure to light causes them to kick-start a reaction that turns liquid resin solid within seconds. Two of the most widely used examples, TPO and BAPO, have been identified as reproductive toxins and are being phased out in regions including the European Union. That regulatory shift has already created supply problems for gel nail polish manufacturers, who depended on TPO for fast, dependable curing, and it threatens similar disruption across other resin-based industries.
"The industry is facing a major challenge as the most effective and widely used photoinitiators are being regulated out of existence due to toxicity," said Professor Terry W. J. Steele of NTU's School of Materials Science and Engineering, who led the research team. The group aimed to design a replacement that is both biocompatible and at least as effective as the chemicals it would replace.
How the new compounds address shrinkage
Beyond toxicity, resin shrinkage is a persistent technical problem: most photopolymer resins contract as they cure, which can throw off precision in 3D-printed parts and dental applications. The aryl diazirine compounds release nitrogen gas during curing, and researchers say that gas release can be tuned to counteract the contraction, producing more dimensionally stable finished parts.
Several of the compounds are liquid at room temperature and dissolve directly in water, allowing them to be incorporated into water-based resins that avoid organic solvents. That property is particularly useful for biomedical applications where solvent exposure must be minimized.
Early demonstrations and remaining limits
The researchers tested the chemistry in several prototype applications: watertight gaskets formed and cured in place with a handheld UV light, and 3D-printed microfluidic channels made from a soybean-oil-based resin. In a medical demonstration, the team produced a stretchy skin bioadhesive capable of extending more than three and a half times its original length without harming the underlying skin, and noted the same material could serve as a protective barrier around long-term medical catheters. The researchers also point to possible future uses in live-cell encapsulation, food packaging and wearable electronics.
The work remains at laboratory scale, and the team is explicit about what comes next. "Our next step is to bridge the gap between our laboratory findings and industrial-scale manufacturing, ensuring these safe activators can be easily adopted by global partners," said lead author Naziruddin Ali. Scaling lab chemistry to commercial manufacturing, validating long-term safety data, and matching the cost and performance of established photoinitiators remain open questions before the compounds could reach consumer or industrial products.