Fungi are almost everywhere - in the air you breathe, the soil you walk on, we eat them and yes, they do also live inside of us.
For industrial biotechnology, fungi like yeast are commonly used catalysts for bioprocesses such as beer brewing or bakery. Yet, there is more that fungi are capable of. In nature, the fungal kingdom represents the most abundant group of organisms bearing various important roles such as degrading dead organic matter, delivering nutrients to plants, detoxifying soil and purifying water from heavy metals. Some fungal species have been used for drug development (antibiotics), composite scaffolds made of fungi are applied in biomedicine[1]. In Chinese medicine, shiitake, reishi and other mushrooms have been long used for both medicinal or nutritional purposes.
Today, the fungal biotechnology industry is experiencing a renaissance and is helping to create a circular economy by transitioning from an oil-based, to one based on bio-resources. Recent factory-scale, cost-competitiveness and environmentally friendly production of mycelium-grown materials for construction, furniture, transportation and packaging industries has the potential to significantly contribute to the United Nations' Sustainable Development Goals[2]. The valorisation of lignocellulosic wastes high in lignin and cellulose seems especially promising for the development of composite materials (Ecovative Design, Mushroom Packaging), fibers (MycoWorks), membranes, or even leather (Mylo, Bolt Threads). Hence, the exploration of fungal species and the development of technologies to produce mycelium-based materials continue to rise.
What is Mycelium Material?
The cultivation of fungi is a biotechnological process. Mycelium-based materials are fabricated by selecting the desired components (species, substrates) and following a specific synthesis process. White rot fungi such as Ganoderma lucidum and Pleurotus ostreatus can break down the same natural polymers in order to uptake them and grow. These fungal species can grow on various substrates - agricultural raw materials like straw, grains, coffee granules, or sawdust. They also require sufficient water. The growth of the fungal network is started via inoculation (Figure 1) using a mushroom spawn. Through the development of hyphae, the fungus creates a network of interconnected mycelium that surrounds and connects the discrete material to form a self-supporting composite. Aseptic techniques as well as monitoring of thermodynamic conditions (temperature, humidity, access to oxygen and light) are intrinsic to process design and will shape the formation and properties of the biomaterial.
Mycelium filaments are called hyphae, which consist of elongated cells. The mycelium cell wall is made up of chitin, glucans, proteins, and lipids, the concentration of which depends upon the feeding substrate that ultimately defines the properties of the synthesized materials[3]. Lignocellulosic feedstocks compose of approximately 60-70% fermentable sugars and 20-30% aromatic compounds that filamentous fungi like Pichia spp or Fusarium spp are natural experts at processing[4]. By secreting specific enzymes, fungi can access the nutrients (carbon, nitrogen etc) and will ultimately break down the polysaccharide networks that serve as structural sheets that surround the hyphae[5]. So, mycelium is a tenacious blend of chitin-glucan matrices and filamentous intracellular crosslinking. After full colonization, fruit-bodies characteristic to Basidiomycota species will emerge on top of the mycelial structure. The growing procedure can be discontinued at required time by thermal treatment or drying. In comparison to other advanced materials (conductive or electronic, inorganic composites, polymers), fungal biocomposites require a significantly simplified manufacturing process whilst offering unprecedented design freedom and functionality.
How to Create Mycelium Material with Different Properties?
Firstly, the functional properties of the mycelium material can be tweaked according to its need and use of it. Pure mycelium materials display different structural properties depending on the fungal strain, substrate, growth conditions, and processing after synthesis. The mechanical properties are generally defined by species (morphology) - elongated fibrous mycelium has more elasticity and thus can be used for myco-leather, in contrast with tougher mycelium, building materials stronger than concrete can be obtained.
Secondly, in combination with controlled processing techniques, a variety of substrates and additives can be utilized to bind discrete lignocellulosic particles into mycelium composites with defined geometry (Figure 2). All raw-materials and additives which are of organic origin contribute to biodegradability at the product’s end-of-life stage[6]. Interestingly, some groups of fungi produce non-toxic materials by degrading the toxic compounds, like terpenes, in the feeding substrate[7]. These attributes help to introduce new ways to create eco-friendly materials, as well as reduce the need for hard chemicals, coloring agents and thereby bring down production costs.
Next, we look at the process parameters and post-treatment. The interaction between white rot fungi and their feedstock as well as the process variables during manufacturing (protocol, sterilization, inoculation, packing, incubation, growing period and drying method) are critical to design and product development[8]. The right level of temperature, humidity, light (or the absence of it) all contribute to the formation and functionality of the end-product. For instance, the development of a more dense mycelial web can make the material more durable, the addition of dextrose can make the material more elastic, and special minerals can reduce the appetite for rodents and insects. Important to notice, fungal mycelium is water repellent. The weight increase by humidity absorption occurs mainly in the residual feedstocks[9].
After the product has fully ingrown into the mould, it is either dried completely to stop further growth, or partially dried so that it may rehydrate and grow into adjacent parts, thereby forming a single, fabricated section. By applying cold or heat pressing, the structural properties of mycelium-based composites can be improved. Pressing increases material density and reduces porosity. It also helps reorient fibers horizontally in a plane and reduces their thickness, thereby increasing contact between overlapping fibers[10]. The material can be further treated with natural oils to make it more durable.
What are the Applications of Fungal Materials?
Coming from the aforementioned, the bio-inspired design and engineering of materials presents a ripe area of research given the complex materials that biology is capable of producing. In addition to being cost-effective, biodegradable, and less dense and impactful on the environment, fungal materials have many other benefits over traditional materials. Due to their high acoustic absorption, low thermal conductivity, and fire resistance nature, mycelium-based materials have been compared with expanded polystyrene (EPS), a petroleum-based foam used for thermal insulation in the construction industry[11,12]. Furthermore, the porous structure of mycelium is beneficial to thermal insulation performance. A number of patents exist on fabricated composite materials made from mycelium in the automotive and packaging segment[13]. In addition to their various functional attributes for uses in textile, packaging, isolation, or automotive industries, mycelium-based interior decor elements have exceptionally quirky designs (Figure 3).
Our studies and tests so far show that the mycelium material has great strength (stronger than EPS), at the same time as great insulation properties as fiberglass or sheep’s wool (thermal conductivity, λ = 0.04 W/mk), tunable acoustic properties, as well as high fire resistance compared to other organic materials. Obtaining similar or better features than composite and plastic alternatives is critical for mass adoption. Coming from our experience, there needs to be a lot of educational work done on the market as traditional industries are usually slow to adopt these novel solutions. Mycelium materials’ functional attributes can be explained in the context of their application. Hence, specific comparative tests that were mentioned before are critical for financial viability and knowledge transfer. Proof-of-concept studies with universities (Figure 4) along with pilot customers help to boost collaborations at a broader range.
What is the Environmental Footprint of the Mycelium Material?
A new class of biomaterials produced by fungal biotechnology could soon replace plastics, foams, textiles and other materials derived from petroleum-based resources[14]. In terms of carbon footprint and sustainability, mycelium products have an advantage over synthetic counterparts in single use applications especially. Environmental footprint is the core thesis of mycelium material because one can actually say that growing mycelium is carbon negative! To reach this conclusion, we use a methodology called Life Cycle Analysis (LCA) that looks at the whole product life cycle from cradle to grave. In particular, this analysis takes into account all the materials used in the production, logistics, energy, transportation, packaging, and the end life of the products. Each of these steps and inputs are given CO2 equivalents which means that we can quantify the whole life cycle CO2 output, as well as understand which steps need improvements to bring down the product’s environmental footprint.
But how can we justify that it’s carbon negative? Let’s take our most popular raw material sawdust. Every kilogram of wood contains 1.5 kg of CO2 when it is released, and usually, it’s used for energy by simply burning it. Our production as a whole emits less than 0.5 kg of CO2 per 1 kg of mushroom material. Since the mycelium actually binds carbon, each kilogram holds ca 1 kg of CO2. To be fair, at the end of the product life cycle, the carbon is released again into the environment. However, as it is of natural origin and compostable, it’s food for soil (compared to most of our troublesome materials). The main environmental aspects of mycelium materials:
- Perfect afterlife: 100% natural and compostable after use (if you don’t treat it with chemicals);
- Low energy production: mycelium material grows itself at 25 degrees;
- Circular Economy: we are using other industries’ organic leftovers, such as sawdust, hay, hemp shives, beer bagasse, coffee waste, etc;
- Safe and natural living environment, mycelium materials don’t cause allergies or emit toxins, the material is inert when provided relatively dry and stable conditions.
To conclude, mycelium materials introduce a great solution for short carbon turnover and recyclability. The need for sustainable materials grows with the realization of the crisis we are in, whether environmental, economic, or geopolitical. As changes are painful it is necessary to show successful examples to speed up the adoption period. The technology is here but will there be enough willpower to get to a point where instead of building our homes we grow them.
Myceen is a sustainable research and design entity focusing on the development of mushroom mycelium-based materials. These carbon-negative and compostable materials are grown by combining mycelium and organic by-products. Myco-materials can potentially replace plastics and problematic composites while valorizing other industries’ leftovers. Currently focusing on furniture and interior products but also researching the material’s potential application in the building sector.
This article is part of the ArchDaily Topics: The Future of Construction Materials. Every month we explore a topic in-depth through articles, interviews, news, and projects. Learn more about our ArchDaily topics. As always, at ArchDaily we welcome the contributions of our readers; if you want to submit an article or project, contact us.
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