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Living things degrade, die, and decompose. Even when we turn plant and animal material into furniture or clothes, the process is inevitable. Plastics, however, are practically indestructible, taking as long as 1,000 years to decompose. Now, a team of scientists from the Chinese University of Hong Kong are rethinking this characteristic with the question: What if plastics were alive?
“The realization that traditional plastics persist for centuries, while many applications, like packaging, are short-lived, led us to ask: Could we build degradation directly into the material’s life cycle?” said Zhuojun Dai, a corresponding author of the study published in Applied Polymer Materials Journal.
The research team has succeeded in creating a living plastic that can self-destruct on command, achieved by embedding plastic-eating microbes directly into the plastic material. The microbes remain dormant until they are activated by a hot “nutrient broth,” after which they consume the plastic within days, leaving no microplastics behind.
Certain microbes are capable of breaking down long polymer chains, of which plastics are made, using enzymes they produce. The scientists took advantage of this ability by engineering Bacillus subtilis spores to produce plastic-degrading enzymes, before embedding the dormant microbes directly into a plastic matrix. When activated by heat, the spores awaken and begin secreting enzymes that chemically break down the material from within.
This is not the first time scientists have used microbes to break down plastic. In fact, the material the research team used, polycaprolactone (PCL), is itself a biodegradable plastic that has previously been degraded using microbe-produced enzymes. However, the team’s innovation is two-fold. First, most previous attempts to degrade PCL relied on a single enzyme system. In contrast, the researchers engineered separate strains of Bacillus subtilis to produce two cooperative polymer-degrading enzymes that work in tandem.
One of the enzymes cuts the long polymer chains at multiple points, rapidly weakening the plastic structure. The second enzyme progressively breaks the fragmented chains down into much smaller molecules for further microbial processing. Together, the two-enzyme system proved significantly more effective than single-enzyme approaches, enabling near-complete degradation of the PCL matrix within six days.
The second innovation lies in embedding the engineered microbial spores directly into the plastic matrix itself. Doing this makes the plastic “alive” and endows it with a self-destructive characteristic, as the microbes and plastic are now a single material. The resulting material has mechanical properties similar to those of plain PCL films.
The catalyst is a nutrient broth at 122 °F (50 °C). Once the broth comes into contact with the material, it activates the spores, initiating degradation. To test their technology, the researchers created a wearable electrode from the material and added the catalyst. The material completely broke down in two weeks, leaving no microplastics behind.
There are more challenges to overcome, but the researchers believe the potential for the research is significant. The scientists aim to develop a water-based trigger, as most plastic pollution ends up in water bodies. They are also looking to apply the work beyond PCL to other plastic types, especially those commonly used in single-use plastics.
Source: American Chemical Society