Source: Xampla/University of Cambridge

‘Vegan spider silk’ – a sustainable alternative to single-use fossil fuel based plastics

Researchers at the University of Cambridge have created a plant-based, sustainable, scalable material that could replace single-use plastics in many consumer products.

NATURAL ALTERNATIVES TO SINGLE-USE PLASTIC

New research published this week in Nature Communications could signal the end of fossil fuel single-use plastics as the science behind a new plant protein substitute is made public. Researchers at the University of Cambridge Knowles Lab describe how they can create a polymer film from plant protein that is sustainable, scalable and 100% natural.

Made entirely from plant protein which can be sourced as a by-product of the agriculture industry, the resulting material can be consumed in nature after use like any natural waste, leaving no pollutants behind. The material’s functionality is consistent with conventional plastic, but it requires no chemical cross-linking used in bio-polymers to give them the strength and flexibility of plastic. — Xampla

Xampla, the Cambridge University spin-out commercialising the technology, is developing its applications to replace single-use plastics including flexible packaging films, sachets, microcapsules found in home and personal care products, and carrier bags.
Scientists were inspired by spiders’ silk which is weight-for-weight stronger than steel but has weak molecular bonds, meaning it can break down easily. Xampla, the Cambridge University spin-out commercialising the technology, is developing its applications to replace single-use plastics including flexible packaging films, sachets, microcapsules found in home and personal care products, and carrier bags. Source: Xampla/University of Cambridge

The new material is as strong as many common plastics yet home compostable

Researchers at the University of Cambridge have created a polymer film by mimicking the properties of spider silk, one of the strongest materials in nature. The new material is as strong as many common plastics in use today and could replace plastic in many common household products.

The material was created using a new approach for assembling plant proteins into materials that mimic silk on a molecular level. The energy-efficient method, which uses sustainable ingredients, results in a plastic-like free-standing film, which can be made at industrial scale. Non-fading ‘structural’ colour can be added to the polymer, and it can also be used to make water-resistant coatings.

The material is home compostable, whereas other types of bioplastics require industrial composting facilities to degrade. In addition, the Cambridge-developed material requires no chemical modifications to its natural building blocks, so that it can safely degrade in most natural environments.

The new product will be commercialised by Xampla, a University of Cambridge spin-out company developing replacements for single-use plastic and microplastics. The company will introduce a range of single-use sachets and capsules later this year, which can replace the plastic used in everyday products like dishwasher tablets and laundry detergent capsules. The results are reported in the journal Nature Communications.

Source: cam.ac.uk

a A translucent aqueous soyprotein isolate (SPI) solution (10 w/v% SPI, 30 v/v% acetic acid) was obtained via ultrasonication treatment at elevated temperature (90 °C) for 30 min. The resultant SPI solution was cast on a pre-heated glass Petri dish. Upon cooling, a translucent hydrogel was formed. Following evaporation of the solvent, a free-standing film was obtained (scale bar 1 cm). b–d AFM images (b, c), and TEM image (d) of SPI fibrillar aggregates formed through the self-assembly process. Scale bars are 500 nm for b and d, and 100 nm for c. e SEM image of SPI hydrogel prepared through supercritical CO2 drying. Scale bar is 500 nm. f cryo-SEM image of SPI hydrogel. Scale bar is 500 nm. g TEM image of β-sheet nanocrystals in dried SPI film. Scale bars are 5 nm for the main image and 2 nm for the inset.
Fig. 1: Solvation of plant proteins and generation of films through molecular self-assembly. a A translucent aqueous soyprotein isolate (SPI) solution (10 w/v% SPI, 30 v/v% acetic acid) was obtained via ultrasonication treatment at elevated temperature (90 °C) for 30 min. The resultant SPI solution was cast on a pre-heated glass Petri dish. Upon cooling, a translucent hydrogel was formed. Following evaporation of the solvent, a free-standing film was obtained (scale bar 1 cm). b–d AFM images (b, c), and TEM image (d) of SPI fibrillar aggregates formed through the self-assembly process. Scale bars are 500 nm for b and d, and 100 nm for c. e SEM image of SPI hydrogel prepared through supercritical CO2 drying. Scale bar is 500 nm. f cryo-SEM image of SPI hydrogel. Scale bar is 500 nm. g TEM image of β-sheet nanocrystals in dried SPI film. Scale bars are 5 nm for the main image and 2 nm for the inset. Source: University of Cambridge
a, b ATR-FTIR spectra of SPI solution during cooling down from 90 to 20 °C (a) and their second derivatives (b). c Relative change in the secondary structure during cooling down from 90 to 20 °C. d, e ATR-FTIR spectra of original SPI powder and the dried self-assembled film (d) and their second derivatives (e). f Quantification of secondary structure content calculated from Amide I band of IR spectra for original SPI powder and the dried self-assembled film. The indicated error bars are the s.d. of the average of three different spectra, each one is co-average of 256 scans.
Fig. 2: Secondary structure analysis of SPI self-assembly. a, b ATR-FTIR spectra of SPI solution during cooling down from 90 to 20 °C (a) and their second derivatives (b). c Relative change in the secondary structure during cooling down from 90 to 20 °C. d, e ATR-FTIR spectra of original SPI powder and the dried self-assembled film (d) and their second derivatives (e). f Quantification of secondary structure content calculated from Amide I band of IR spectra for original SPI powder and the dried self-assembled film. The indicated error bars are the s.d. of the average of three different spectra, each one is co-average of 256 scans. Source: University of Cambridge

Surprisingly the discovery came out of research into Alzheimer’s disease

For many years, Professor Tuomas Knowles in Cambridge’s Yusuf Hamied Department of Chemistry has been researching the behaviour of proteins. Much of his research has been focused on what happens when proteins misfold or ‘misbehave’, and how this relates to health and human disease, primarily Alzheimer’s disease.

“We normally investigate how functional protein interactions allow us to stay healthy and how irregular interactions are implicated in Alzheimer’s disease,” said Knowles, who led the current research. “It was a surprise to find our research could also address a big problem in sustainability: that of plastic pollution.”

As part of their protein research, Knowles and his group became interested in why materials like spider silk are so strong when they have such weak molecular bonds. “We found that one of the key features that gives spider silk its strength is the hydrogen bonds are arranged regularly in space and at a very high density,” said Knowles.

Source: cam.ac.uk

Through the ultrasonication treatment in acetic acid solution, the initially insoluble aggregates are solubilised and unfolded, making them avaialble to form new intermolecular interactions. Upon cooling down, the new intermolecular β-sheets structures are formed. The removal of solvent results in the formation of β-sheet nanocrystals within the film.
Fig. 3: Schematic representation of a proposed mechanism for the self-assembly of SPI. Through the ultrasonication treatment in acetic acid solution, the initially insoluble aggregates are solubilised and unfolded, making them avaialble to form new intermolecular interactions. Upon cooling down, the new intermolecular β-sheets structures are formed. The removal of solvent results in the formation of β-sheet nanocrystals within the film. Source: University of Cambridge
a Representative stress–strain curves for the dried nonstructured and the dried self-assembled films. b Mechanical properties of self-assembled SPI film in comparison to previously reported biomaterials, engineered materials6,71,72, and plant-based materials (see Supplementary Table 2 for references). c Zoomed-in graph for self-assembled (orange), nonstructured (blue), and previously reported SPI films (green).
Fig. 4: Mechanical properties of the self-assembled SPI film. a Representative stress–strain curves for the dried nonstructured and the dried self-assembled films. b Mechanical properties of self-assembled SPI film in comparison to previously reported biomaterials, engineered materials6,71,72, and plant-based materials (see Supplementary Table 2 for references). c Zoomed-in graph for self-assembled (orange), nonstructured (blue), and previously reported SPI films (green). Source: University of Cambridge

Researchers successfully replicated the structures found on spider silk by using soy protein isolate

Co-author Dr Marc Rodriguez Garcia, a postdoctoral researcher in Knowles’ group who is now Head of R&D at Xampla, began looking at how to replicate this regular self-assembly in other proteins. Proteins have a propensity for molecular self-organisation and self-assembly, and plant proteins, in particular, are abundant and can be sourced sustainably as by-products of the food industry.

“Very little is known about the self-assembly of plant proteins, and it’s exciting to know that by filling this knowledge gap we can find alternatives to single-use plastics,” said PhD candidate Ayaka Kamada, the paper’s first author.

The researchers successfully replicated the structures found on spider silk by using soy protein isolate, a protein with a completely different composition. “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, who is also a Fellow of St John’s College. “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.”

“Other researchers have been working directly with silk materials as a plastic replacement, but they’re still an animal product,” said Rodriguez Garcia. “In a way, we’ve come up with ‘vegan spider silk’ – we’ve created the same material without the spider.”

Source: cam.ac.uk

a UV–vis spectra of nonstructured (blue) and self-assembled films (orange). b Optical image of nonstructured (right) and self-assembled (left) SPI films. c Photograph of a 30 × 40 cm film fabricated through large-scale processing. d Carrying bag generated by thermal welding.
Fig. 5: Optical appearance of self-assembled films. a UV–vis spectra of nonstructured (blue) and self-assembled films (orange). b Optical image of nonstructured (right) and self-assembled (left) SPI films. c Photograph of a 30 × 40 cm film fabricated through large-scale processing. d Carrying bag generated by thermal welding. Source: University of Cambridge/Xampla
a Schematic illustration of the coating process. A piece of paperboard was dipped in the SPI solution and pulled out slowly, leading to the formation of a gel coating its surface. The paperboard was allowed to dry at room temperature to achieve an anhydrous thin layer of coating. b Optical images of paperboards before and after SPI coating. c, d SEM images of paperboard without (c) and with (d) SPI coating. Scale bars represent 500 μm. e Water uptake of the treated and untreated paperboards measured over 30 min studied through gravimetry. The indicated error bars represent the s.d. of the average of three independent measurements. f, g Colour changes of CoCl2-stained paperboards before and after immersing in water for 5 s. The paperboard was prepared without (f) and with (g) SPI coating, respectively.
Fig. 6: Plant protein film for coating with barrier function. a Schematic illustration of the coating process. A piece of paperboard was dipped in the SPI solution and pulled out slowly, leading to the formation of a gel coating its surface. The paperboard was allowed to dry at room temperature to achieve an anhydrous thin layer of coating. b Optical images of paperboards before and after SPI coating. c, d SEM images of paperboard without (c) and with (d) SPI coating. Scale bars represent 500 μm. e Water uptake of the treated and untreated paperboards measured over 30 min studied through gravimetry. The indicated error bars represent the s.d. of the average of three independent measurements. f, g Colour changes of CoCl2-stained paperboards before and after immersing in water for 5 s. The paperboard was prepared without (f) and with (g) SPI coating, respectively. Source: University of Cambridge

Proteins self-assemble and can form strong materials like silk without chemicals

Any replacement for plastic requires another polymer – the two in nature that exist in abundance are polysaccharides and polypeptides. Cellulose and nanocellulose are polysaccharides and have been used for a range of applications, but often require some form of cross-linking to form strong materials. Proteins self-assemble and can form strong materials like silk without any chemical modifications, but they are much harder to work with.

The researchers used soy protein isolate (SPI) as their test plant protein, since it is readily available as a by-product of soybean oil production. Plant proteins such as SPI are poorly soluble in water, making it hard to control their self-assembly into ordered structures.

The new technique uses an environmentally friendly mixture of acetic acid and water, combined with ultrasonication and high temperatures, to improve the solubility of the SPI. This method produces protein structures with enhanced inter-molecular interactions guided by the hydrogen bond formation. In a second step, the solvent is removed, which results in a water-insoluble film.

Source: cam.ac.uk

a Schematic illustration of the soft lithography process to pattern SPI film. b Optical image of the micro-patterned film. Scale bar represents 5 mm. c SEM image of the side view (top) and top view (bottom) of patterned micropillars. Scale bars represent 25 μm (top) and 100 μm (bottom). d Optical images of a water droplet on the film without (top) and with (bottom) micropillars. Scale bars represent 1 mm. e Water contact angles of the films, showing an increase of hydrophobicity in the patterned film. The indicated error bars are the s.d. of the average of three independent measurements. f, g Optical image of non-patterned (f) and nano-patterned photonic film (g). h, i SEM image of the nano-patterned film. Scale bars represent 20 μm (h) and 2 μm (i).
Fig. 7: Micro- and nanopatterning of plant protein film. a Schematic illustration of the soft lithography process to pattern SPI film. b Optical image of the micro-patterned film. Scale bar represents 5 mm. c SEM image of the side view (top) and top view (bottom) of patterned micropillars. Scale bars represent 25 μm (top) and 100 μm (bottom). d Optical images of a water droplet on the film without (top) and with (bottom) micropillars. Scale bars represent 1 mm. e Water contact angles of the films, showing an increase of hydrophobicity in the patterned film. The indicated error bars are the s.d. of the average of three independent measurements. f, g Optical image of non-patterned (f) and nano-patterned photonic film (g). h, i SEM image of the nano-patterned film. Scale bars represent 20 μm (h) and 2 μm (i). Source: University of Cambridge

This is the culmination of over ten years work into how nature generates materials from proteins

The material has a performance equivalent to high-performance engineering plastics such as low-density polyethylene. Its strength lies in the regular arrangement of the polypeptide chains, meaning there is no need for chemical cross-linking, which is frequently used to improve the performance and resistance of biopolymer films. The most commonly used cross-linking agents are non-sustainable and can even be toxic, whereas no toxic elements are required for the Cambridge-developed technique.

“This is the culmination of something we’ve been working on for over ten years, which is understanding how nature generates materials from proteins,” said 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.”

“The key breakthrough here is being able to control self-assembly, so we can now create high-performance materials,” said Rodriguez Garcia. “It’s exciting to be part of this journey. There is a huge, huge issue of plastic pollution in the world, and we are in the fortunate position to be able to do something about it.”

Xampla’s technology has been patented by Cambridge Enterprise, the University’s commercialisation arm. Cambridge Enterprise and Amadeus Capital Partners co-led a £2 million seed funding round for Xampla, joined by Sky Ocean Ventures and the University of Cambridge Enterprise Fund VI, which is managed by Parkwalk.

Reference:

A. Kamada et al. ‘Self-assembly of plant proteins into high-performance multifunctional nanostructured films.’ Nature Communications (2021). DOI: 10.1038/s41467-021-23813-6

Xampla – introduction to the science behind their products by Professor Tuomas Knowles The abundance of plant-derived proteins, as well as their biodegradability and low environmental impact make them attractive polymeric feedstocks for next-generation functional materials to replace current petroleum-based systems. Source: Vimeo

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