Composite Material Researchers Develop Living Composite Material

Empa researchers have developed a new material based on a fungal mycelium and its extracellular matrix. It is not only fully biodegradable but also tear-resistant and possesses versatile functional properties. All this with minimal processing steps and completely without chemicals—you can even eat it. Its secret: It is alive.

Sustainably produced, biodegradable materials are an important focus of modern materials research. However, processing natural materials such as cellulose, lignin, or chitin presents researchers with a trade-off. In their pure form, natural materials are biodegradable but often not efficient enough. Through chemical processing steps, they can be made stronger, more resistant, or more flexible—but in doing so, they lose some of their sustainability.

Empa researchers from the "Cellulose and Wood Materials" lab have now developed a bio-based material that cleverly bypasses this compromise. It is not only fully biodegradable but also tear-resistant and possesses versatile functional properties. All this with minimal processing steps and completely without chemicals—you can even eat it. Its secret: It is alive.

The fungus uses this extracellular matrix to impart structure and other functional properties. Why shouldn't we do the same?

Ashutosh Sinha

As the basis for their material, the researchers used the mycelium of the common split-gill mushroom, a widely distributed edible fungus that grows on dead wood. Mycelia are root-like thread-like fungal structures that are already being actively explored as potential material sources. Typically, the mycelial fibers—known as hyphae—are cleaned and possibly chemically processed, which involves the known trade-off between performance and sustainability.

The Empa researchers chose a different approach. Instead of extensively processing the mycelium, they use it as a whole. During growth, the fungus not only forms the hyphae but also an extracellular matrix: a network of different fiber-like macromolecules, proteins, and other biological substances secreted by the living cells. "The fungus uses this extracellular matrix to provide itself with structure and other functional properties. Why shouldn't we do the same?" explains Empa researcher Ashutosh Sinha. "Nature has already developed an optimized system," adds Gustav Nyström, head of the "Cellulose and Wood Materials" lab.

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With a bit of targeted optimization, the researchers helped nature along. From the vast genetic diversity of the common split-gill mushroom, they selected a strain that produces a particularly large amount of two specific macromolecules: the long-chain polysaccharide schizophyllan and the soap-like protein hydrophobin. Due to their structure, hydrophobins gather at interfaces between polar and non-polar liquids, such as water and oil. Schizophyllan is a nanofiber: less than a nanometer thick but more than a thousand times as long. Together, these two biomolecules give the living mycelium material properties that make it suitable for a variety of applications.

A Living Emulsifier

The researchers demonstrated the versatility of their material directly in the lab. In their study published in the journal "Advanced Materials," they presented two application possibilities for the living material: a plastic-like film and an emulsion. Emulsions are mixtures of two or more liquids that typically do not blend. If you want to see an example, just open the refrigerator: milk, salad dressing, or mayonnaise are examples. But various cosmetics, paints, and varnishes are also emulsions.

The use as an emulsifier in the cosmetics and food industries is therefore particularly interesting.

Gustav Nyström

One challenge is stabilizing such mixtures so they do not "demix" back into the individual liquids over time. Here, the living mycelium shows its best side: both the schizophyllan fibers and the hydrophobins act as emulsifiers. And the living fungus constantly releases more of these molecules. "This is probably the only kind of emulsion that becomes more stable over time," says Sinha. Both the fungal threads themselves and their helper molecules are completely non-toxic, biologically compatible, and even edible—the common split-gill mushroom is considered an edible mushroom in many parts of the world. "The application as an emulsifier in the cosmetics and food industry is therefore particularly interesting," notes Nyström.

From Compost Bags to Batteries

But the living fungal network is also suitable for classic material applications. In a second experiment, the researchers produced thin films from their mycelium. The extracellular matrix with the long schizophyllan fibers gives the material very good tear resistance, which can be further enhanced by the targeted alignment of the fungal and polysaccharide fibers.

"We are combining established methods for processing fiber-based materials with the emerging field of living materials," explains Nyström. Sinha adds, "Our mycelium is, so to speak, a living fiber composite material." The researchers can control the properties of this material by altering the conditions under which the fungus grows. The use of other fungal strains or species that produce different functional macromolecules is also conceivable.

Instead of compostable plastic bags for kitchen waste, one could make bags from them that compost the organic waste themselves.

Ashutosh Sinha

Working with the living material also brings certain challenges. "Biodegradable materials always react to their environment," Nyström notes. "We want to find application possibilities where this interaction is not a hindrance—or even an advantage." However, biodegradability is only one part of the story for the mycelium. It is also biologically degrading: the common split-gill mushroom can actively decompose wood and plant materials. Here, Sinha sees another application possibility: "Instead of compostable plastic bags for kitchen waste, one could make bags that compost the organic waste themselves," says the researcher.

Next Goal: Biodegradable Battery

There are also promising applications for mycelium in the field of sustainable electronics. For example, the fungal material responds reversibly to moisture and could be used to manufacture biodegradable moisture sensors. Another application that Nyström's team is currently working on combines the living material with two other research projects from the "Cellulose and Wood Materials" lab: the fungal battery and the paper battery. "We want to create a compact, biodegradable battery whose electrodes consist of a living 'fungal paper'," says Sinha.

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