By Stephen Beech via SWNS
A revolutionary new “living plastic” could slash damage to the environment, claims a new study.
The biodegradable material houses bacterial spores that help it break down, say American scientists.
Researchers led by scientists at the University of California San Diego have developed a form of thermoplastic polyurethane (TPU), a soft but durable commercial plastic used in footwear, floor mats, cushions and memory foam.
They explained that the material is filled with bacterial spores that, when exposed to nutrients present in compost, germinate and break it down at the end of its life cycle.
The biodegradable TPU was made with bacterial spores from a strain of Bacillus subtilis that has the ability to break down plastic polymer materials.
Study co-senior author Professor Jon Pokorski, of UC San Diego Jacobs School of Engineering, said: “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.”
The research team used bacterial spores, a dormant form of bacteria, due to their resistance to harsh environmental conditions.
Prof Pokorski explained that unlike fungal spores, which serve a reproductive role, bacterial spores have a protective “protein shield” that enables bacteria to survive while in a vegetative state.
To make the biodegradable plastic, the researchers fed Bacillus subtilis spores and TPU pellets into a plastic extruder.
The ingredients were mixed and melted at 135 degrees Celsius, then extruded as thin strips of plastic.
To assess the material’s biodegradability, the strips were placed in both microbially active and sterile compost environments.
Prof Pokorski said the compost setups were maintained at 37C with a relative humidity ranging from 44 to 55 percent.
Water and other nutrients in the compost triggered germination of the spores within the plastic strips, which reached 90 percent degradation within five months.
Prof Pokorski said: “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.”
Although the researchers still need to study what gets left behind after the material degrades, they believe that any lingering bacterial spores are likely harmless.
Prof Pokorski explained that Bacillus subtilis is a strain used in probiotics and is generally regarded as safe to humans and animals – it can even be beneficial to plant health.
For the study, published in the journal Nature Communications, the bacterial spores were evolutionary engineered to survive the high temperatures necessary for TPU production.
The research team used a technique called adaptive laboratory evolution to create a strain that is resilient to extrusion temperatures.
Prof Pokorski says the process involves growing the spores, subjecting them to extreme temperatures for escalating periods of time, then allowing them to naturally mutate.
The strains that survive this process are then isolated and put through the cycle again.
Study co-senior author Dr Adam Feist, a bioengineering research scientist at the UC San Diego Jacobs School of Engineering, said: “We continually evolved the cells over and over again until we arrived at a strain that is optimized to tolerate the heat.
“It’s amazing how well this process of bacterial evolution and selection worked for this purpose.”
He said the spores also serve as a strengthening filler, similar to how rebar reinforces concrete, resulting in a TPU variant with enhanced mechanical properties – requiring more force to break and showing greater stretchability.
Dr. Pokorski said: “Both of these properties are greatly improved just by adding the spores.
“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.”
While the current study focused on producing smaller lab-scale quantities to understand feasibility, the research team are now working on optimizing the approach for use on an industrial scale.
Dr. Feist added: “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.”
