Many plastic items are used only once, yet remain in the environment for years. Researchers have developed a new method where plastic can degrade on command. The new method incorporates newly activatable microbes to break down the polymer. Previous attempts focused on a single enzyme. However, Zhuojun Dai, Jin Geng, Dianpeng Qi, and colleagues improved the breakdown process with more efficiency. In a study published in ACS Applied Polymer Materials, a team utilized two cooperating bacterial strains that decomposed the polymer without producing microplastics.
Microorganisms can break down long polymeric chains into smaller fragments. Plastics are considered polymers, and enzymes, or microbes that produce them, can be integrated into plastic. Zhuojun Dai, a corresponding author on the paper, describes “the realization that traditional plastics persist for centuries, while many applications, like packaging, are short-lived, led us [them] to ask: Could we build degradation directly into the material’s life?” The team engineered Bacillus subtilis to produce two polymer-degrading enzymes that work as a sequence. The first enzyme cuts long polymer chains into shorter sections at random points, while the second enzyme further degrades the sections into their individual monomer building blocks. Dai explains how “by embedding these microbes, plastics could effectively ‘come alive’ and self-destruct on command, turning durability from a problem into a programmable feature.”
The team combined dormant spore form of B. subtilis with polycaprolactone (a polymer common in 3D printing and some surgical sutures). The combination allowed the microbes to be protected until the team was ready to conduct the degradation process. The resulting living plastic had mechanical properties similar to those of ordinary polycaprolactone films. Under normal conditions, the plastic was strong and functional, concluding that the additional spores had not significantly weakened the product. The bacteria was activated by the addition of a nutrient broth heated to 122 degrees Fahrenheit (50 degrees Celsius). The spores became active and degraded the plastic into its basic building blocks within six days so efficiently without producing microplastics during decomposition.
To demonstrate a preliminary presentation of a real-world use, the team of researchers created a wearable plastic electrode from the living material. The instrument performed as intended and degraded completely in two weeks. The final result advocates that living plastics can be implemented towards products that need to remain durable for a short period of time, while not persisting after use. In future research, the team hopes to develop a method to activate spores in water, where the largest accumulation of plastic pollution resides. Despite the fact that the experiments focused on one polymer, the researchers speculate similar strategies can be applied to other materials, including single-use plastics.
