Mould at home is not a pleasant thought. But there are researchers who want to make it happen, and they are researching ways to build houses and furniture from fungi. These researchers are talking specifically about mycelium, the network of filaments that fungi produce as they grow, which can be dried into a lightweight, durable and easy-to-use product. And the possibilities with it seem almost endless. 

To make mycelium materials, you mix fungi with a substrate that acts as a food source, then place it in a warm and humid room to grow. When you have enough material, you bake it to kill the fungi and you are left with a fairly porous looking but strong material. ‘The fungi grow through the waste stream and bind the particles together with their filaments’, says Han Wösten, professor of microbiology at Utrecht University. ‘It’s a fairly simple process that’s very sustainable, because fungi love waste products like sawdust. They can extract nutrients from almost anything.’ 

Combination 

The biggest challenge, therefore, does not lie in the source of the nutrients, but in finding the right combination of fungi and substrates. ‘There are a number of commonly used fungal species’, says Karin Scholtmeijer, a researcher at Wageningen University & Research. ‘These are well-known species such as oyster mushrooms and champignons, but also edible mushroom species that are not grown commercially. And where one species grows best on straw, others are better suited to potato peels.’ 

’Fungi can extract nutrients from almost anything’

Han Wösten

Finding the best combinations first requires answers to some fundamental questions. ‘We still know very little about the exact composition of the mycelium’, says Wösten. ‘Researchers often grind up the whole mycelium before analysing it, which only gives an average. So we fused fluorescent molecules to proteins to see how these proteins are distributed in the filaments of the mycelium, and used fluorescent sugar analogues to see which filaments take up food.’ 

Using this approach, Wösten and his colleagues discovered that different mycelial threads have different functions and compositions. One thread appears to secrete enzymes that break down substrate and release nutrients, while another does not secrete enzymes but is resistant to stresses such as antibiotics. Wösten: ‘When the fungus encounters a bacterium, some of the filaments are resistant and can continue to grow. So there is a huge division of labour that we still know very little about.’ 

The composition of individual cells also turns out to be different than previously thought. ‘We used solid-state NMR to look at the cell walls of fungal filaments and found all kinds of new structures.’ The variation is almost reminiscent of the differences between human cells. ‘Fungi are actually quite complex, they are more like animals than plants. But we have only just begun to realise this, so there is still a lot to discover.’ 

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Bandwagon 

There is still a lot to learn about mycelium. But many companies have already jumped on the bandwagon. Soundproof panels, bags, packaging and even coffins made from mycelium are already on the market. ‘The field has really exploded in the last twenty years and we see a lot of start-ups and big companies wanting to do something with mycelium’, says Scholtmeijer. ‘These companies want to get to market quickly, while we are just starting to figure out all the details of the material, which is sometimes a tricky balance.’ 

’Fungi-based materials have really exploded over the last twenty years’

Karin Scholtmeijer

Apart from food, the most researched application for mycelium is in building materials. This is partly due to its flexibility, says Wösten. ‘Depending on the substrate and processing, mycelium can be as strong as wood or as flexible as leather or plastic. Straw, for example, gives a more airy network than sawdust. So you can play with the composition.’ 

Wood and metal

The researchers have already succeeded in producing materials similar to wood, paper, leather, plastic and rubber. Wösten’s group is even trying to make a material that resembles metal. ‘You can compress mycelium very well, which gives you a kind of chipboard. I think it should be possible to press several of these layers together even harder, and then you get metal-like strength.’ 

When it comes to fungi, Scholtmeijer agrees that no application seems too far-fetched. ‘It’s a super dynamic field that is developing very quickly. And when we really understand fungi in a few years’ time, I think things will really take off.’ Perhaps the threads will even go beyond our own planet, says Wösten. ‘Last month, I helped NASA think about fungi as a building material on the Moon or Mars. I dream of a construction market full of fungal materials, but maybe we will go far beyond that. We’ll find out!’