Scientists have potentially revolutionized plastic production by developing a method to create more durable and biodegradable plastics using bacterial spores subjected to evolutionary processes.
This innovative “living plastic” can decompose in approximately five months without the need for additional microbes, presenting a significant advancement in addressing plastic waste.
Researchers at the University of California San Diego (UCSD) spearheaded this breakthrough, creating the biodegradable plastic in the form of thermoplastic polyurethane (TPU). TPU is a versatile commercial plastic widely used in products such as footwear, floor mats, cushions, and memory foam due to its soft yet durable properties.
The team incorporated bacterial spores into the TPU to facilitate its breakdown at the end of its lifecycle. These spores, derived from a strain of Bacillus subtilis, possess the capability to decompose plastic polymer materials.
Study co-senior author Professor Jon Pokorski, of UC San Diego Jacobs School of Engineering. “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.”
Bacillus subtilis spores are particularly suited for this purpose due to their resilience against harsh environmental conditions.
Prof. Pokorski explained that unlike fungal spores, which are reproductive, bacterial spores have a protective “protein shield” that enables them to survive in a dormant, vegetative state.
The team incorporated bacterial spores into the TPU to facilitate its breakdown at the end of its lifecycle. These spores, derived from a strain of Bacillus subtilis, possess the capability to decompose plastic polymer materials.
Bacillus subtilis spores are particularly suited from this purpose due to their resilience against harsh environmental conditions. Unlike fungal spores, which are reproductive, bacterial spores have “protective shield” that enables them to survive in a dormant, vegetative state.
To create the biodegradable TPU, researchers mixed Bacillus subtilis spores with TPU pellets and fed the mixture into a plastic extruder. The materials were heated to over 200°F, then extruded into thin plastic strips.
The biodegradability of these strips was tested by placing them in both microbially active and sterile compost environments. The compost setups were maintained at around 100°F with relative humidity levels between 44 and 55%.
The presence of water and nutrients in the compost triggered the germination of the bacterial spores within the plastic strips, leading to 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,” said Professor Pokorski.
“So this ability to self-degrade in a microbe-free environment makes our technology more versatile,” he added.
This significant rate of breakdown demonstrates the potential of this living plastic to reduce long-term plastic waste in the environment.
Although further research is needed to determine the residual materials left after degradation, initial findings suggest that any remaining bacterial spores are likely harmless.
Prof. Pokorski also explained that Bacillus subtilis is commonly used in probiotics and is generally considered safe for humans and animals. It also benefits plant health, making it an environmentally friendly option for biodegradable plastic production.
The study, published in the journal Nature Communications, details how the bacterial spores were evolutionarily adapted to withstand the high temperatures required for TPU manufacturing. Surviving strains were isolated and subjected to the process repeatedly, ensuring the spores’ robustness.
Study co-senior author Dr. Adam Feist, a bioengineering research scientist at UCSD, said, “We continually evolved the cells over and over again until we arrived at a strain that is optimized to tolerate the heat.”
He also shared, “It’s amazing how well this process of bacterial evolution and selection worked for this purpose.”
Additionally, he also said that the spores act as a reinforcing filler, similar to rebar in concrete, enhancing the mechanical properties of the TPU. This variant of TPU exhibits increased strength and stretchability, requiring more force to break.
“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,” said Prof. Pokorski.
The research team is now focused on optimizing this approach for industrial-scale production.
“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,” said Dr. Feist.
As the demand for biodegradable plastics grows, the key challenge will be to ensure the cost-effectiveness of these materials. Mass production of plastics necessitates economical solutions, and for biodegradable options like this to gain widespread adoption, they must be competitively priced and producible in bulk.
The potential for widespread application of this technology is immense. By creating durable and biodegradable plastics that can decompose efficiently, scientists are paving the way for a more sustainable future.
Future research and development could lead to new materials that not only reduce plastic waste but also contribute positively to environmental health.
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