Sustainably produced, biodegradable materials are becoming a focal point in modern materials science. Researchers face a significant challenge when working with natural substances such as cellulose, lignin, or chitin. While these materials are inherently biodegradable, they often lack the performance characteristics needed for practical applications. Although chemical processing can enhance their strength and flexibility, it usually compromises their sustainability. However, researchers at Empa’s Cellulose and Wood Materials laboratory have developed a revolutionary bio-based material that effectively sidesteps this compromise. Not only is this new material completely biodegradable, but it is also tear-resistant and boasts a range of functional properties—all achieved with minimal processing steps and no chemicals. Remarkably, this innovative material is even safe to eat.
The foundation of this advanced material is the mycelium of the split-gill mushroom, a common edible fungus that thrives on decaying wood. Mycelium consists of root-like structures called hyphae, which researchers are increasingly studying as promising sources of sustainable materials. Traditionally, mycelial fibers undergo cleaning and chemical processing, which leads to the aforementioned trade-off between sustainability and performance. In contrast, the Empa team took a novel approach by utilizing the mycelium in its entirety. As the fungus grows, it forms hyphae and an extracellular matrix—a network of fiber-like macromolecules, proteins, and other biological substances secreted by living cells. This matrix provides structural integrity and functional properties to the fungus. Empa researcher Ashutosh Sinha questions, "Why shouldn't we do the same?" He believes that nature has already optimized this system, a sentiment echoed by Gustav Nyström, head of the Cellulose and Wood Materials lab.
To enhance the material's properties, the researchers selected a specific strain of the split-gill mushroom known for producing high levels of two unique macromolecules: the long-chain polysaccharide schizophyllan and the soap-like protein hydrophobin. These biomolecules contribute significantly to the living mycelium’s versatility. Hydrophobins, due to their structural properties, effectively stabilize interfaces between polar and non-polar liquids, while schizophyllan acts as a nanofiber—extremely thin yet incredibly long. Together, these components enable the mycelium to develop a versatile range of applications.
The researchers conducted laboratory experiments to showcase the potential of this living material, demonstrating its ability to form a plastic-like film and an emulsion. Emulsions are mixtures of two or more liquids that typically do not mix, such as milk, salad dressing, and mayonnaise. One significant challenge in creating emulsions is maintaining stability over time. The living mycelium proves advantageous here, as both schizophyllan fibers and hydrophobins function as emulsifiers, continuously releasing more stabilizing molecules. Sinha remarks, "This is probably the only type of emulsion that becomes more stable over time." Importantly, both the mycelial filaments and their extracellular components are completely non-toxic, biologically compatible, and edible, making this material particularly appealing for applications in the food and cosmetics industries.
The living fungal network is also applicable in traditional material contexts. In another experiment, the researchers created thin films from mycelium. The extracellular matrix, enriched with long schizophyllan fibers, provides exceptional tensile strength, which can be further improved by aligning the fibers strategically. Nyström explains, "We combine the proven methods for processing fiber-based materials with the emerging field of living materials." The properties of this living fiber composite can be manipulated by altering the growth conditions of the fungus, and the potential exists to explore other fungal strains that produce different functional macromolecules.
While working with living materials presents unique challenges, the biodegradability of mycelium is just one aspect of its utility. The split-gill mushroom can actively decompose wood and other plant materials. Sinha proposes a revolutionary idea: instead of conventional compostable plastic bags, why not create bags that compost organic waste themselves? Furthermore, the potential applications of mycelium extend into sustainable electronics. The fungal material's reversible reaction to moisture could lead to the development of biodegradable moisture sensors. Nyström and his team are also exploring innovative applications that involve combining this living material with other projects, such as the fungal biobattery and paper-based batteries. "We want to produce a compact, biodegradable battery whose electrodes consist of a living 'fungal paper'," Sinha concludes.
