Bacteria-seeded plastic is tough and degradable

Unassuming little bacteria can make plastic stronger while in use but then help break it down at the end of life (Nat. Commun. 2024, DOI: 10.1038/s41467-024-47132-8). Engineers embedded spores of a polymer-munching bacteria into thermoplastic polyurethane (TPU), a rubbery plastic used to make shoe insoles, cushions, and phone cases. When the material is thrown into compost, the bacteria germinate and disintegrate the plastic.

Most TPU plastics used today end up in landfills. Some researchers are starting with biobased materials to make degradable or recyclable TPUs, but the materials’ mechanical properties are inferior to those of conventional TPU.

Nanoengineer Jonathan K. Pokorski and bioengineer Adam M. Feist of the University of California San Diego and their colleagues harnessed bacteria because some strains have been found to employ polyurethanes and polyesters as a carbon source. After evaluating several strains, the researchers chose Bacillus subtilis, which is a component in probiotics. They used lab-based evolution and selection to create microbes that tolerate high heat. They then mixed dormant spores of these microbes into melted TPU and made strips of the composite plastic.

Just as carbon nanofiber reinforces composites, so the spores increased the toughness of the TPU by up to 37%. Placed in sterile compost, the strips degraded by more than 90% in 5 months. As long as enough moisture and nutrients are around, the bacteria should wake up and degrade the polymer, Pokorski says.

Katrina Knauer, a polymer scientist at the National Renewable Energy Laboratory, calls the work “pioneering and truly exciting.” This study offers a scalable method for fabricating advanced biocomposites, “pushing the boundaries of material science and bridging the gap with biochemistry,” she says.

Next, Feist says, “we plan to figure out the exact enzymes and pathways involved, the end products, and the range of different polymers we can apply this towards.” Bacteria-embedded plastic might be a stretch for food packaging, Pokorski adds, “but a little bit of spores in your shoe insoles? I mean your feet are already pretty dirty.”