A novel approach to making leather

If you love leather boots, handbags and wallets but feel iffy about their animal or synthetic sources, fungi may be the answer.

They offer an alternative that is sustainable, ethical and environmentally friendly, according to a paper published in the journal Nature Sustainability.

“Fungi are the ideal natural biorefinery breaking down biomass, which can be from wood residues or food waste, to produce a range of other structural biopolymers, dyes and proteins,” says senior author Alexander Bismarck, from Vienna University, Austria.

In recent years, researchers have discovered that fungi polymers can be used to make sustainable substitutes for plastic, rubber, wood and leather, and they have even been used to make vases, chairs and lampshades. But leather research has gone somewhat under the radar.

“Fungi-derived leather-like materials have more or less been independently developed by industry with little to no involvement from the academic sector,” says first author Mitchell Jones, and much of the information about them is hidden by intellectual property.

Bismarck and Jones have done their own fungal research using species such as the white button mushroom (Agaricus bisporus) and bracket fungus (Daedaleopsis confragosa) to produce paper and foam-like construction materials such as insulation.

To bring leather into the limelight, they saw the need for an independent scientific review, including an appraisal of fungal benefits as a viable alternative to existing options.

Traditionally, leather has been derived from animal hides, a co-product of the livestock industry, but social and environmental concerns about animal slaughter, methane emissions and deforestation have been mounting.

Added to that, the tanning processes uses toxic chemicals such as chromium salts and generates huge amounts of waste.

To offset these concerns, synthetic leather materials have been produced from plastics such as polyvinyl chloride (PVC) or polyurethane (PU). But they depend on chemicals from fossil fuels and take as long as their plastic derivatives to break down.

“This is where leather-like materials from fungi come into play,” says Bismarck, “which, in general, are CO2 neutral as well as biodegradable at the end of their life span.”

The key is mycelium, a mass of elongated tubular root-like structures that are the vegetative part of fungus and contain chitin, which is much like the cellulose that gives plants their structure.

To make the leather, mycelium is grown in a couple of weeks using very little energy from low-cost agricultural and forestry by-products such as sawdust that would otherwise go to waste.

These are inoculated in a shallow tray, explains Jones, then allowed to grow in a carbon dioxide-rich environment. This stops fruiting body and spore formation, forcing the mycelium filaments to grow outwards in search of oxygen.

“In doing so, they form a thick mat. Mild acids, alcohols and dyes can then be used to modify the material properties of the mat, which is then compressed, dried and embossed,” he says. “The end result resembles leather in mechanical and tactile properties.”

Biotech companies have already developed and sold fungi leather prototypes in the US, Asia and Europe, and say it will be competitive in cost with traditional leather, which Jones thinks is a reasonable claim. The main challenge, the authors say, is achieving homogeneity, “exhibiting uniform growth and consistent thickness, colour and mechanical properties”.

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