Researchers Develop Enzyme to Efficiently Break Down Polyurethane

A team of researchers has successfully developed a new enzyme capable of breaking down polyurethane, a commonly used plastic, into its basic building blocks. This advancement addresses a significant issue in plastic pollution, as polyurethane represents a substantial portion of the 22 million metric tons produced globally in 2024. The new enzyme integrates seamlessly into existing recycling processes, offering a promising solution to the challenges posed by plastic waste.

Polyurethane, often utilized in products like foam cushioning, is challenging to recycle due to its complex chemical structure. The polymer is held together by urethane bonds, which involve a nitrogen atom bonded to carbon and oxygen atoms. This intricate configuration makes it difficult for enzymes to access and digest the material. Traditional methods, such as using diethylene glycol at high temperatures, can break down the polymer but often result in a hazardous chemical mixture unsuitable for further use.

In their quest for a more effective solution, the research team initially evaluated 15 known enzymes for their ability to degrade polyurethane. Only three exhibited satisfactory activity, with none breaking the polymer down to its fundamental components. This led the researchers to focus on the enzyme displaying the highest activity and to explore related proteins through public databases and the AlphaFold database, which predicts protein structures.

The team utilized an innovative approach with a neural network tool called Pythia-Pocket. This advanced software predicts whether specific amino acids in proteins can bind to certain chemicals, along with assessing other functional characteristics. By integrating another neural network, Pythia, which evaluates protein stability, the researchers aimed to identify an enzyme with the ideal structural features for breaking down polyurethane.

Their newly developed software, named GRASE (Graph Neural Network-based Recommendation of Active and Stable Enzymes), led to remarkable results. Of the 24 proteins evaluated, 21 demonstrated catalytic activity, and eight outperformed the previously known best enzyme. One of the designs showed **30 times** the activity of its predecessor, showcasing the potential of this approach.

When combined with diethylene glycol and heated to **50°C**, the newly engineered enzyme exhibited an astonishing **450 times** the activity of the best-performing natural enzyme. Over the course of **12 hours**, it successfully broke down **98 percent** of the polyurethane in the reaction mixture. Additionally, the enzyme’s stability allowed it to process new mixtures of polyurethane two more times before its effectiveness began to diminish.

The transition from laboratory testing to kilogram-scale digestion confirmed these results, with **95 percent** or more of the material being broken down into its original components. The researchers emphasize that their approach extends beyond structural analysis, incorporating functional aspects such as stability and amino acid interactions, potentially paving the way for the development of other functional proteins.

The findings of this study, published in the journal Science, illustrate a significant step forward in tackling plastic waste. As researchers continue to refine their methods, this enzyme could play a crucial role in enhancing recycling efficiency and reducing environmental impact.