Plastics are the king of industrial materials. So successful and wide-ranging are they that even the biobased sector has been devoted to developing plant-based replicas of them for almost imaginable application.
Yet plastics are not the only industry all-rounders that biobased producers should set their sights on. Protein fibres almost rival it for application range and even outperform it in certain niches, balancing strength with flexibility and offering potentially lower environmental impacts.
Common examples of protein fibre are wool, fur, silk, keratin, collagen, and elastin, many of which have been used in the past, as currency, hunting bow strings, paper, textiles, and wound dressings.
Today, protein fibres are most in use for apparel and cosmetics but gene editing techniques are opening wider applications.
What is protein fibre?
Like plastics, proteins are a kind of polymer called polyamide. All proteins consist of repeating amino-acid units, different arrangements of which result in quite different properties.
Some protein can be stiff and brittle but with some processing, can achieve flexibility and strength. This rare combination is useful in applications where materials must withstand high impact stress and heavy loads while also being yielding and soft.
Natural protein needs processing before it is suitable for particular uses. The newest methods of enhanced protein fibre production lie at the intersection of gene editing and fermentation manufacturing.
Do protein fibres have to come from an animal?
Most of the everyday protein fibres we encounter are taken from farmed animals, like wool from lambs or silk from cocoons.
But plants can also be a source of protein fibres. ABrand Technology Company has been making botanic protein fibre from proteins. CoatsKnit Eco S has created a smooth, drapeable apparel textile from a protein fibre made using soybean production byproducts.
What are the sustainability advantages?
The relative sustainability of different materials is highly contextual but there is one area where protein fibres tend to have the edge over bioplastics: biodegradability. Protein fibre textiles are biodegradable, fully recyclable, and do not break down into microplastics.
This marks a departure from bioplastics which are often indistinguishable from oil plastics at a molecular level. This means they are usually incapable of breaking down safety in the natural environment – a problem given the huge gaps in global recycling infrastructure.
There are also land-use related savings. Newer, lab-produced protein fibres involve living creatures but much smaller and less resource-intensive ones than sheep microorganisms.
Japanese textile materials company Spiber, founded in 2007, deploys tailored microbes to produce Brewed Protein, a lab-produced protein fibre that lies somewhere between a natural and a man-made substance.
Such gene-edited protein fibre materials hold sustainability advantages over both traditional protein fibres like wool as they get rid of the need for animal sources, save for an initial tissue sample. This eliminates the need for carbon and land-intensive livestock herds and can mean lab-produced protein fibre achieves a generally lighter ecological footprint.
Another benefit is that the potential applications of protein fibres are constantly expanding thanks to gene editing, allowing them to take on new applications that unmodified proteins could not. This means they could potentially displace the use of biobased and oil-based plastics in a growing number of fields.
Spiber’s fermented spider silk
The protein fibre getting all the attention in the startup scene today is spider silk and its lab-based variants.
Spider silk has been singled out for its industry potential as one of the sturdiest materials on a weight basis. It is also flexible, offering applications in functional clothing such as bullet-proof protective gear and outdoor apparel, where petrochemical-based fibres are dominant today.
Yet the material is difficult to simply harvest from natural sources. Unlike silkworms, spiders are too aggressive to keep in groups and cultivate. Japanese startup Spiber has stepped in to solve the problem of spider silk sourcing with its gene-edited bacterial production line.
But Spiber goes a step further than simply replicating the naturally occurring material. Using gene editing, they improve the functionality of spider silk, resulting in a protein fibre that is never found in nature. The material markets under the brand name Brewed Protein.
Spiber alters the genes responsible for spider silk production so that they code for a slightly optimised silk more useful for human purposes – in their case, apparel.
This altered protein-coding DNA is then inserted into Spiber’s manufacturing bacteria, which replicates the material at scale in their bodies, ready for extraction and then processing.
It also claims its genetically modified spider silk is better even than silkworm silk for its ecological footprint, as it avoids alkalis and other chemicals used in processing.
Fermentation is generally a more ecologically benign way of producing biobased materials than taking it from farmed mammals, which need food, water, and land.
Spiber managed to get $68 million in funding in April 2024, reflecting a huge vote of confidence from the textiles industry, defying a general downturn in venture capital funding for the startup. This reflects huge demand from parts of the apparel industry for materials that tick multiple criteria that the conscious consumer is insistent on: sustainability, animal ethics, and functionality.
Proteins made to order
Spiber is getting the most attention as a synthetic protein fibre company but two other big players are German biotech companies Brain Biotech and AMSilk.
These German silk startups started a collaboration in 2023 to develop new functional materials using computer-aided design and laboratory trials. One year on, the venture has applied for its first patent application registration.
Like Spiber, the partnership also targets apparel. However, its focus ranges wider, on making protein fibre materials for other high-spec ‘performance’ applications such as medical and automotive upholstery.
Brain’s role in the partnership is centred around their synbio software platform which enables researchers to design and develop new protein variants more systematically. Brain uses AI predictions and computer modelling to learn which gene modifications could produce particular results that make for an industrially functional biomaterial.
Using these tools, the company systematically tweaked the amino acid building blocks of silk proteins in their library. After testing these modified proteins in the lab, they hand over the best performing to AMSilk to use them in prototype textiles.
While Brain designs the raw materials, the client-facing Munich-based AMSilk makes and markets usable textiles. Similar to Spiber, AMSilk’s manufacturing method for its proteins is precision fermentation: the company gets bacteria to ‘copy’ the proteins developed by Brain and replicate them at volume.
AMSilk is embarking on scaling its production lines and making them more efficient. Its goal is raising its precision fermentation output from ‘kilos to tonnes’, something it hopes to support through its partnership earlier this year with Danish company 21st.Bio.
Beyond clothing
Protein innovations have so far been targeted at the apparel market. The feed-through between novel protein fibre startups and the apparel industry is unsurprising: fashion multinationals have the wealth to back emerging biomaterials that are still expensive to make at scale.
Yet protein fibres have wider end uses. Among them are elastin and resilin, which are commonly found in mammal and insect bodies and are at least five times stretchier than a rubber hand.
Startup Smart Resilin uses genetic engineering to produce an elastin additive powder for ‘dropping in’ to the manufacturing process for goods that need both durability and a bit of give: sport shoe soles, for example.
Keratin, another type of protein, is usually associated with the cosmetic sector as a conditioner for damaged hair, skin, and nails. However, the European startup Kerline is bringing the chemical into the hard-to-decarbonise area of industrial flame retardants.
Kerline has produced FullKer, a protein-based flame retardant that could replace the use of conventional Antimony TriOxide, a highly toxic material. Kerlin makes its additive using keratin extracted from animal proteins recovered from agri-food and textile industry waste, making it a circular technology as well.
Scientists are also looking at how protein fibres could replace fossil polymers as a material for separation membranes. They have also been proposed as a polymer replacement in ropes, nets, seatbelts, and more.
It’s possible there will be technological spillovers between protein startups targeted at apparel and those aiming to build materials for industrial uses. The refinement of protein genetic editing techniques in startups like Spiber means more powerful tools for the future discovery of novel protein arrangements.
