Biodegradable ‘living plastic’ contains bacterial spores that break it down

Researchers at the University of California San Diego have developed an innovative biodegradable thermoplastic polyurethane (TPU), commonly used in products like footwear and memory foam. 

This new bioplastic, which incorporates bacterial spores capable of decomposing the material at the end of its life cycle, represents a significant advancement in efforts to reduce the environmental footprint of the plastic industry. According to the experts, this development could transform the way commercial plastics are viewed in terms of environmental sustainability.

Biodegradable living plastic

Thermoplastic polyurethane is valued for its soft yet durable properties, but its resistance to natural decomposition poses environmental challenges. The scientists aimed to address this issue by embedding spores from the bacterium Bacillus subtilis into the plastic. These spores can break down polymer materials, a feature that the team capitalized on. 

“It’s an inherent property of these bacteria. We took a few strains and evaluated their ability to use TPUs as a sole carbon source, then picked the one that grew the best,” said Jon Pokorski, a nanoengineering professor at the UC San Diego.

Remarkably biodegradable plastic 

The process involved feeding Bacillus subtilis spores and TPU pellets into a plastic extruder, where they were mixed and melted at 135 degrees Celsius and then extruded as thin strips. 

To test the material’s biodegradability, these strips were placed in both microbially active and sterile compost environments maintained at 37 degrees Celsius. The water and nutrients in the compost activated the spores, which facilitated the plastic’s degradation. Remarkably, the strips achieved 90% degradation within five months. 

“What’s remarkable is that our material breaks down even without the presence of additional microbes. Chances are, most of these plastics will likely not end up in microbially rich composting facilities. So this ability to self-degrade in a microbe-free environment makes our technology more versatile,” Pokorski said.

The safety of the degradation process is supported by the benign nature of Bacillus subtilis, which is not only used in probiotics but is also generally regarded as safe for humans and animals and beneficial to plant health. 

Adapting the bacterial spores 

Addressing the durability and safety of the process, the researchers adapted the bacterial spores to withstand the high temperatures necessary for plastic production using adaptive laboratory evolution. 

“We continually evolved the cells over and over again until we arrived at a strain that is optimized to tolerate the heat,” explained co-senior author Adam Feist, a bioengineering research scientist at UC San Diego.

Moreover, the spores serve a dual function by also acting as a strengthening filler within the plastic, which is comparable to how rebar reinforces concrete. 

“Both of these properties are greatly improved just by adding the spores,” Pokorski said. “This is great because the addition of spores pushes the mechanical properties beyond known limitations where there was previously a trade off between tensile strength and stretchability.”

Scaling up the technology

While the research currently focuses on laboratory-scale production, the team is actively working to scale up the technology for industrial application and extend it to other types of plastics. 

“There are many different kinds of commercial plastics that end up in the environment – TPU is just one of them. One of our next steps is to broaden the scope of biodegradable materials we can make with this technology,” concluded Feist. 

More about biodegradable plastic

Biodegradable plastic is a type of plastic designed to decompose naturally in the environment under the action of living organisms, primarily bacteria. 

Unlike traditional plastics, which can take hundreds of years to break down and can leave harmful residues, biodegradable plastics are made from natural materials such as corn starch, sugarcane, or other plant-based substances. These materials enable the plastic to break down more quickly and safely when exposed to natural elements like heat, moisture, and microorganisms.

The production and use of biodegradable plastics are seen as environmentally friendly alternatives to conventional plastics because they are derived from renewable resources and are intended to reduce the accumulation of waste in landfills and oceans. 

However, the effectiveness of biodegradation depends on specific conditions such as temperature and the presence of microbes, which can vary widely in different environments. 

This means that while these plastics are designed to degrade in industrial composting facilities, they may not break down as efficiently in cooler, less active composting settings or in natural environments, leading to potential misunderstandings about their environmental benefits.

The study is published in the journal Nature Communications.

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