University of Cambridge researchers have turned to nature to create a sustainable, plant-based, toxic-free, scalable polymer film that could replace single-use plastics in many consumer products. The new plastic alternative mimics the properties of spider silk, one of nature’s most robust materials, resulting in a stronger material than common plastics used today.
The Cambridge team developed the innovative material using a new energy-efficient technique that assembles plant proteins into materials that imitate silk on a molecular level. The process uses sustainable ingredients, resulting in a plastic-like free-standing polymer film, which can be manufactured at a large scale. The polymer can be integrated with a non-fading ‘structural’ color and could be used to make water-resistant coatings.
Unlike other bioplastics that require industrial composting facilities to degrade, the Cambridge-developed material is home compostable. In addition, the material doesn’t require chemical modifications to its natural building blocks, ensuring that it can safely degrade in natural environments.
Xampla, a University of Cambridge spin-out company that specializes in developing replacements for single-use plastic and microplastics, will be commercializing the new product. The company plans to unveil a range of single-use capsules and sachets later this year, which can replace the plastic used in everyday household products like laundry detergent capsules and dishwasher tablets.
Professor Tuomas Knowles, who led the research published in Nature Communications, studied proteins’ behavior for many years. Most of his research has focused on what occurs when proteins misbehave or misfold and how it’s associated with health and human disease, particularly Alzheimer’s disease.
Prof. Knowles explained:
We normally investigate how functional protein interactions allow us to stay healthy and how irregular interactions are implicated in Alzheimer’s disease. It was a surprise to find our research could also address a big problem in sustainability: that of plastic pollution.
While Knowles and his colleagues investigated proteins, they became interested in how organic materials like spider silk are so strong despite their weak 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,” added Knowles.
Postdoctoral researcher Dr. Marc Rodriguez Garcia, the study’s co-author and Head of R&D at Xampla, began exploring how to replicate this regular self-assembly in other proteins. Proteins have a proneness for molecular self-assembly and self-organization, and plant proteins, mainly, are plentiful and can be sourced as by-products of the food industry.
With this in mind, the team used soy protein isolate (SPI) – a protein with an entirely different composition – to replicate the structures found on spider silk successfully. “Because all proteins are made of polypeptide chains, under the right conditions, we can cause plant proteins to self-assemble just like spider silk. In a spider, the silk protein is dissolved in an aqueous solution, which then assembles into an immensely strong fiber through a spinning process which requires very little energy,” explained Knowles.
Dr. Rodriguez Garcia said:
Other researchers have been working directly with silk materials as a plastic replacement, but they’re still an animal product. In a way, we’ve come up with ‘vegan spider silk’—we’ve created the same material without the spider.
Any plastic alternative requires another polymer. Polysaccharides and polypeptides are polymers that exist in abundance in nature. Nanocellulose and cellulose are polysaccharides and are used for various applications but commonly require cross-linking to form strong materials. On the other hand, proteins self-assemble and can create strong materials like silk without requiring any chemical modifications, but they are more challenging to work with.
The Cambridge researchers used SPI as their test plant protein due to its availability as a by-product of soybean oil production. Plant proteins (like SPI) are poorly soluble in water, making it difficult to control their self-assembly into well-ordered structures. The new method uses an eco-friendly mixture of acetic acid and water, combined with high temperatures and ultrasonication, to enhance the solubility of the SPI. This technique creates protein structures with more significant inter-molecular interactions led by hydrogen bond formation. Finally, the solvent is removed, resulting in a water-insoluble film.
Knowles said:
This is the culmination of something we’ve been working on for over ten years, which is understanding how nature generates materials from proteins. 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.
The resulting material’s performance is comparable to high-performance engineering plastics like low-density polyethylene. Its strength is provided by the regular arrangement of the polypeptide chains, meaning chemical cross-linking isn’t required, which is often used to improve biopolymer films’ performance and resistance. However, the most commonly used cross-linking agents are non-sustainable and can be toxic. The Cambridge-developed technique, on the other hand, requires no toxic elements.
