A plant-based material may be the solution to replace single-use plastics, according to a team from the University of Cambridge, UK (1). The team has developed a new sustainable and scalable material, which is as strong as standard plastic.
This material was created using a method for combining plant proteins into a structure that resembles spider silk, one of the most robust materials in nature. It’s produced with sustainable ingredients and can be made in large quantities on an industrial scale. What’s more, users can simply compost it at home after use, in contrast to others types of bioplastics which need special facilities to degrade.
To commercialise this product, a team from the University of Cambridge created a spin-out company called Xampla, specifically to develop replacements for single-use plastic and microplastics. Xampla’ s first product will be single-use capsules and sachets to replace plastic used in products like laundry detergent capsules and dishwasher tablets.
Curiously, this was not the team’s primary focus of research. “We normally investigate how functional protein interactions allow us to stay healthy and how irregular interactions are implicated in Alzheimer’s disease,” said Professor Tuomas Knowles, who led this study. “It was a surprise to find our research could also address a big problem in sustainability: that of plastic pollution.”
During their research, Knowles and his team were curious to find out how materials like spider silk are so strong, even though they don’t have strong molecular bonds. “We found that one of the key features that give spider silk its strength is the hydrogen bonds are arranged regularly in space and at a very high density,” said the researcher.
Inspired by this design, the team replicated the structure but using a protein found in soy. “Because all proteins are made of polypeptide chains, under the right conditions, we can cause plant proteins to self-assemble just like spider silk,” said Knowles. “In a spider, the silk protein is dissolved in an aqueous solution, which then assembles into an immensely strong fibre through a spinning process which requires very little energy.”
The team quickly realised that, although soy proteins can self-assemble and form a strong material like silk, they are more challenging to work with. The primary issue is that these plant proteins are not soluble in water, making it harder to control their self-assembly into the desired structure.
The team overcome this issue with a mixture of acetic acid and water, followed by ultrasonication at high temperatures to improve the solubility of soy proteins. After this initial step, as the solvent is removed, the soy proteins arrange themselves in a water-insoluble film. The resultant product can be compared to high-performance engineering plastics like low-density polyethylene.
Its strength lies in the regular arrangement of the polypeptide chains, without the need for extra chemical cross-linking, which is often used to increase resistance in other products. Most of the chemicals used are non-sustainable, and some are even toxic, but all this is avoided in the new product developed by the Cambridge team.
“This is the culmination of something we’ve been working on for over ten years, which is understanding how nature generates materials from proteins,” concluded Knowles. “We didn’t set out to solve a sustainability challenge — we were motivated by curiosity as to how to create strong materials from weak interactions.”
(1) Kamada, A., Rodriguez-Garcia, M., Ruggeri, F.S. et al. Controlled self-assembly of plant proteins into high-performance multifunctional nanostructured films. Nat Commun 12, 3529 (2021). https://doi.org/10.1038/s41467-021-23813-6