Your next trendy handbag could be made from ‘leather’ made from a fungus. Today, researchers will describe how they harnessed this organism to convert food waste into durable faux leather, as well as paper products and cotton substitutes, with properties comparable to traditional materials. They explain that this fungal leather takes less time to produce than existing substitutes already on the market, and, unlike some, is 100% bio-based.
The researchers will present their findings today at the American Chemical Society (ACS) Spring Meeting. ACS Spring 2022 is a hybrid meeting that will be held virtually and in person March 20-24, with on-demand access available March 21-April 8. The meeting features more than 12,000 presentations on a wide range of scientific topics.
Cotton is scarce and, like petroleum-based textiles and leather, its production is associated with environmental concerns. During this time, a lot of food is wasted. Akram Zamani, Ph.D., set out to solve these seemingly unrelated problems with new biobased and sustainable materials derived from fungi. “We hope they can replace cotton or synthetic fibers and animal leather, which can have negative environmental and ethical aspects,” says Zamani, the project’s lead researcher. “During the development of our process, we were careful not to use toxic chemicals or anything that could harm the environment.”
Just like humans, mushrooms need to eat. To feed the organisms, the team collected unsold supermarket bread, which they dried and ground into breadcrumbs. The researchers mixed the breadcrumbs with water in a pilot-scale reactor and added spores of Rhizopus delemar, which is usually found on rotting food. When this fungus fed on bread, it produced microscopic natural fibers composed of chitin and chitosan that accumulated in its cell walls. After two days, the scientists collected the cells and removed the lipids, proteins and other by-products that could be used in human or animal food. The remaining gelatinous residue made up of the fibrous cell walls was then spun into thread, which could be used in sutures or healing textiles and perhaps in clothing.
Alternatively, the fungal cell suspension was laid out flat and dried to make materials resembling paper or leather. The first prototypes of fungal leather produced by the team were thin and not flexible enough, says Zamani, who is at the University of Borås in Sweden. Now the group is working on thicker versions made up of multiple layers to more closely mimic real animal leather. These composites include layers treated with tree-derived tannins – which give the structure softness – combined with layers treated with alkalis which give it strength. Flexibility, strength and gloss have also been improved by treatment with glycerol and a bio-based binder. “Our recent tests show that fungal leather has quite comparable mechanical properties to genuine leather,” says Zamani. For example, the relationship between density and Young’s modulus, which measures stiffness, is similar for both materials.
While other fungal leathers have already hit the market, little information about their production has been released and their properties do not yet match real leather, according to Zamani. From what she can verify, commercial products are made from harvested mushrooms or mushrooms grown thinly on food scraps or sawdust using solid-state fermentation. Such methods take several days or weeks to produce enough fungal material, she notes, whereas her fungus is submerged in water and only takes a few days to produce the same amount of material. A few other researchers are also experimenting with submerged culture, but on a much smaller scale than his group’s efforts.
Additionally, some of the fungal leathers on the market contain environmentally harmful coatings or backing layers of petroleum-derived synthetic polymers, such as polyester. This contrasts with the University of Borås team’s products, which consist only of natural materials and will therefore be biodegradable, Zamani expects.
His team is working to further refine their fungal products. They also recently started testing other types of food waste, including fruits and vegetables. An example is the mass left after squeezing juice from fruits. “Instead of being thrown away, it could be used to grow mushrooms,” says Zamani. “So we don’t limit ourselves to bread, because I hope there will be a day when there is no more wasted bread.”
The researchers acknowledge Vinnova’s support and funding. A video of Zamani’s research is available from Borås University here.