A team of university and industry researchers has been awarded funding from the US National Science Foundation (NSF) to develop mechanisms to produce sturdy and reusable bioplastics.
Plastic production is a nearly US$1trillion industry with more than 400 million tonnes produced in 2022. However, only about ten per cent of plastics are recycled. Karthik Sankaranarayanan (pictured above), assistant professor of agricultural and biological engineering at Purdue University, and his collaborators jointly received a US$7million grant from NSF to design novel enzymes that convert various biomaterials into biodegradable plastics.
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The bioplastics (polyhydroxyalkanoates (PHAs)) developed by this research programme will have similar levels of toughness and malleability to the types of plastics that currently dominate the market. However, rather than relying on petroleum-based chemicals, they would be generated using domestically produced feedstocks such as corn, sugar or agricultural waste.
‘Nearly 99 per cent of the plastics produced today are made from petrochemicals derived from oil or gas, which often must be imported from outside the USA,’ Sankaranarayanan said. ‘We want to take advantage of locally available materials, such as those commonly used throughout the state of Indiana.’
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Additionally, while retaining their mechanical strength, they would be infinitely recyclable, according to Sankaranarayanan. ‘You can take these polymers and break them down into their individual units and reuse them again and again,’ he said. ‘PHAs were discovered nearly a century ago, but they can be fragile and unstable at high temperatures, hindering their widespread use in consumer goods or medical devices. Our platform will enable the tuning of the chemical structure of the final polymer to have the proper level of mechanical strength and thermal stability. This will open the door for applications that range from packaging to biomedical devices.’
The primary focus of the three-year project is on biocatalysis – using enzymes to speed up highly specific reactions that produce desired products without harsh chemicals or extreme conditions. Biocatalysis makes biomanufacturing a more sustainable and efficient alternative to traditional chemical manufacturing. Creating the computational tool to identify opportunities for biocatalysis is the key to unlocking its potential.
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Purdue researchers are developing algorithms to select the enzymes and the reactions required for creating the desired bioplastics. Then, researchers at the University of California, San Francisco (UCSF) will engineer these enzymes using advanced protein computational design methods that harness deep learning, a machine learning technique that mimics how the brain recognises patterns.
Once the enzymes are engineered, they will be sent to researchers at Stanford University to test their functionality and then to Purdue, where researchers will analyse the speed of their reactions as well as their ability to tune the chemical structure of the polymer. Finally, researchers at the University of California, Berkeley will determine their properties and commercialisation potential, as well as how microorganisms can be engineered to scale up for biomanufacturing.
Sankaranarayanan cites finding adaptable enzymes as one of the major challenges associated with this project. ‘The enzymes that we’re working with – polyketide synthases (PKSs) – are sophisticated enzymes capable of catalysing sequential chemical reactions in an assembly-line fashion to produce complex antibiotics,’ Sankaranarayanan said. ‘However, they aren’t designed to work in the types of industrial processes that create bioplastics. So we’re trying to figure out how we can both alter their natural chemical reaction to produce desired bioplastics and simultaneously improve the stability of the engineered enzymes so that they’re amenable to biomanufacturing at scale.’
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Another challenge to using these enzymes in a manufacturing setting is the makeup of their DNA. PKSs have a high content of guanine and cytosine – two of the four bases that carry genetic information in DNA – which poses significant challenges for synthetic manufacturing of the DNA for subsequent enzyme production. Twist Bioscience, an additional partner on the project, has developed the technology that will enable researchers to engineer the necessary enzymes.
In addition to the team’s contributions to biomanufacturing, they will provide research opportunities for students as well as resources for the broader scientific community. Three graduate students have already been hired to work on the project, and the researchers will be recruiting undergraduate students in agricultural and biological engineering, computer science, chemistry and chemical engineering.
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Sankaranarayanan said they will also provide open-source access to all their tools and workflows since, with some minor tweaks, they can be applied to pharmaceuticals, agrochemicals, pesticides or herbicides, and even other types of biomaterials, such as rubber. They will also develop a workshop on protein design led by UCSF, with Purdue contributing modules on designing step-by-step enzyme processes.
‘One thing I really enjoy about this grant is we have investigators, postdocs and graduate students from all these different universities, each of whom bring a unique set of strengths,’ Sankaranarayanan said. ‘So, this opportunity for students here at Purdue to interact with some of these other faculty members and their lab members is quite exciting.’