A new type of plastic embedded with microbes has emerged to help reduce the environmental footprint of the plastic industry. Researchers at the University of California, San Diego have developed a biodegradable thermoplastic polyurethane (TPU) filled with bacterial spores. When exposed to nutrients in compost, it gradually germinates and decomposes on its own after its lifecycle ends. This research achievement was detailed in a paper published on the 30th in Nature Communications.
Synthesis of biodegradable "living plastic" using thermoplastic polyurethane particles (left) and Bacillus subtilis spores (right).
Different stages of decomposition in compost after 5 months with regular TPU (top) and "live" TPU (bottom) samples. Image source: Jacobs School of Engineering, University of California, San Diego
Biodegradable TPU is enhanced with spores of Bacillus subtilis, a bacterium known for its ability to break down plastic polymer materials. Bacterial spores are a dormant form of bacteria that can withstand harsh environmental conditions. Unlike reproductive fungal spores, bacterial spores have protective protein barriers that allow the bacteria to survive in nutrient-deprived environments.
The bacterial spores used in the study have been genetically engineered to survive at the high temperatures required for TPU production. Researchers employed a technique called adaptive laboratory evolution, involving the cultivation of spores, subjecting them to extreme temperatures for adaptation, inducing natural mutations, isolating surviving strains, and repeating the cycle.
To manufacture biodegradable plastic, researchers combined Bacillus subtilis spores with TPU pellets in a plastic extruder, mixing and melting the components at 135°C before extruding thin plastic strips.
The researchers assessed the material's biodegradability by placing samples in both microbial active and sterile compost environments, maintaining a temperature of 37°C and relative humidity between 44% and 55%. Water and other nutrients in the compost triggered spore germination within the samples, leading to a 90% degradation within 5 months.
Spores can also serve as reinforcing fillers, akin to steel bars in reinforced concrete. TPU produced with added bacterial spores exhibits enhanced mechanical properties, increased fracture resistance, and better tensile strength.
The researchers aim to scale up production to kilograms and are currently focused on small-scale laboratory production for feasibility validation. Future efforts will involve optimizing processes for industrial-scale production, evolving bacteria for faster plastic degradation, and exploring other types of plastics beyond TPU.
