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Fungal Biology and Biotechnology 8, Article number: 20 (2021) Cite this article

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Abstract

In the context of the ongoing transition from a linear to a circular economy, ecologically friendly renewable solutions are put in place. Filamentous fungi can be grown on various organic feedstocks and functionalized into a range of diverse material types which are biobased and thus more sustainable in terms of their production, use and recycling. Pure mycelium materials, consisting only of mycelial biomass, can adopt versatile properties and appear promising as a substitute for current petrochemically produced polymeric materials or, in the case of myco-leather, as a substitute for animal-based leather. In recent years, a handful of private companies have been innovating to bring products based on pure mycelium materials to the market while scientific interest in these promising biomaterials is now starting to gain momentum. In this primer, we introduce pure mycelium materials, frame different production methods, review existing and potential future applications, thereby offering a vision on future advances for this emerging fungi-based technology.

What are (pure) mycelium materials?

Filamentous fungi display an intrinsic growth pattern that generates a near endless amount of microscopically interconnected tubular cells eventually yielding a vast macroscopic network of biomass, also known as mycelium. In nature, these heterotrophic organisms fulfil key ecological roles by breaking down and recycling diverse sources of biomass, in terrestrial and marine habitats, thanks to their powerful secretion abilities exploited in many biotechnological applications [ 1]. In the last decades, this bioconversion process has been introduced into an anthropogenic context, resulting in a biobased production process of new types of natural materials with highly tuneable properties [ 2, 3, 4, 5]. Clear signs of innovations and a rising trend in patent applications indicate that the use of fungal mycelium as a raw resource will help in providing a scalable solution for sustainable material alternatives [ 6]. Initially, focus was mainly placed on the development of composite mycelium materials (CMM). By inoculating lignocellulosic waste streams from agricultural or forestry origin ( e.g. corn husks or sawdust) with a fungal saprotrophic species, typically belonging to white-rot genera ( e.g. Ganoderma or Pleurotus), inside a mould, colonization of the organic feedstock occurs [ 7]. The expanding fungal filaments bind substrate particles together while filling in void spaces and ultimately a composite material shaped by the mould is formed, which is subsequently processed by drying thereby ending the growth process by dehydrating the organism [ 7, 8]. In essence, the feeding fungus acts as a biological glue for the material by colonizing and binding the loose substrate particles. The resulting lightweight CMM have foam-like material characteristics ( e.g. polystyrene), thereby being suited for applications such as packaging, insulation and lightweight furniture applications (Fig. 1) [ 9, 10, 11, 12, 13].

Composite mycelium material used as packaging alternative to expanded polystyrene ©Ecovative

In contrast to CMM, in which the lignocellulosic substrate is intrinsic to the composition and characteristics of the material, the authors define pure mycelium materials (PMM) as to not contain left-over feedstock particles, so the basic properties of PMM are fully determined by the biological characteristics of the organism and growth conditions. Pure mycelium biomass can be generated by growing the organism in separation of its substrate to yield sustainable materials with tuneable properties ranging from foam-, paper-, leather- to polymer-like characteristics. Additionally, newly developed fermentation processes for PMM further increases possibilities to functionalize this unique material, when combined with the appropriate post-growth processing treatment of the mycelium [ 14, 15, 16, 17]. As the range of properties for PMM expands, a growing number of consumer products from companies ensue ranging from high-performance foams used in apparel or skincare products (Mycoflex™) [ 18] to leather like fabrics (Mylo™, Reishi™, Mylea™, Forager™) to meat alternative products (Atlast™) (Fig. 2) (Additional file 1: Table S1).

Pure mycelium products: A. Mycoflex™ is a foam like material with resilient properties, B. Atlast™ is a mushroom based meat alternative, C. Reishi™ is a mycelium-based leather alternative to animal skins and plastic leathers

Mycelium products have a major advantage with respect to their synthetic counterparts in single use applications in terms of carbon footprint and sustainability. When mycelium materials, encompassing both CMM and PMM, are not treated for long term preservation or not combined with non-biodegradable elements, they are a great solution for short carbon turnover and recyclability [ 19]. Additionally, mycelium materials were shown to have flame-retardant properties and are less likely to combust as compared to petrochemical-derived plastics [ 19, 20, 21]. Finally, the growth phase of mycelium materials is a relatively fast process that can be achieved in 5 to 14 days when using an efficient fermentation setup, depending on fungal species and fermentation conditions [ 14, 22, 23].

PMM represent a promising novel technology, not only because of the versatility of novel material applications but also because of a possible feedstock diversification. Indeed, they can be produced through fermentation processes in which low value agricultural by-products can be upcycled as a nutritive vehicle to promote growth of fungal biomass with the possibility of integrating one or more additional specie(s) in a co-cultivation setup [ 24]. In this primer, we will discuss the most prominent advances in research and development of PMM and highlight future opportunities.

Three advances of research in the last decade

Fermentation strategies to produce pure mycelium materials

In contrast to CMM, for which a customized but relatively uniform production process has been established, PMM can be produced using diverse fermentation technologies. In general, fungi require direct contact with their nutrient source hence, this is why they grow intimately bound to their feedstock. Therefore, liquid fermentation has for a long time been the technique of choice when needing to recover metabolites, enzymes or mycelial biomass. Consequently, bioreactor fermentation is a mature and established technology that has been scaled to large industrial volumes [ 25]. Besides, this way of cultivating fungal mycelium is well-studied and enables to control every process parameter. For this reason, bioreactor fermentation set-up appears very attractive to produce PMM. Recently, scientists at VTT Technical Research Centre of Finland demonstrated continuous mycelium leather production using mycelium from submerged bioreactor fermentation (Fig. 3A) [ 22].

A. Pilot scale of continuous mycelium leather production at VTT bioreactor fermentation [ 86]., B. Outward growth of aerial hyphae in solid state fermentation setup ©Ecovative, C. Virtual animation of the microscopic arrangement of hyphae into an interlocking cellular structure named Fine Mycelium™ [ 87]

Growth of pure mycelial biomass can also be achieved on solid feedstocks. Recent innovations in solid state fermentation (SSF) have determined specific growth conditions that stimulate abundant growth of aerial hyphae as shown for Ganoderma sp. (Fig. 3B) [ 14, 26, 27, 28, 31]. This type of hyphae is characterised by an outwards growth, away from the substrate, into the air [ 29]. To induce this growth behaviour, temperature (± 30 °C), gaseous CO ₂ (50-70 k ppm) and relative humidity (40-99%) are tightly controlled inside incubation chambers [ 14, 26, 27, 28]. These conditions are optimal to prevent any differentiation of the mycelium into fruiting bodies since mushroom growers use lower temperature and CO ₂ concentrations for optimal fruiting yields [ 30]. To our knowledge, there are no detailed reports available on the detailed growth modelling for this new fermentation strategy with respect to fermentation parameters or to specific species or genera used. From the limited available literature, members of the Polyporales such as Ganoderma sp. appear suited to grow mycelium foams [ 31]. According to Greetham et al. [ 14] the main driving force stimulating the outwards growth of the mycelium, in the above-mentioned conditions, is generated by the carbon dioxide gradient induced through cellular respiration. The build-up of CO ₂ inside the substrate vehicle naturally creates a gradient alongside which the mycelium will grow outwards to reach a more hospitable environment [ 14, 26]. A second driving force stimulating vertical expansion results from generating an osmotic potential at the apex. Through the deposition of solute-containing microdroplets (solute being a mineral, protein or carbohydrate), hyphal extension, which is driven by turgor pressure, can be steered and stimulated [ 26, 32]. Furthermore, applying a constant flow of air above the growing mycelium, modulates the outwards growth and shape of the biopolymer [ 26]. As reported by Kaplan-Bie et al. [ 26], the rate at which air is displaced above the substrate boxes combined with relative humidity levels directly impacts the density of the aerial mycelium and modulates the degree of homogeneity from the resulting mycelium foams (Table 1).

Table 1 Influence of varying airflow rates and relative humidities on the dry density and tensile strength of mycological biopolymers from Ganoderma sp. at 5% CO₂ and ± 30 °C in a customized incubator [26, 31]

Processing and functionalization of mycelium

When considering the further processing of PMM, previously established post-growth processing steps of CMM can be inspirational. Lignocellulosic CMM are appealing for applications for which a rigid material is desired (hard packaging, insulation, furniture). In this instance, physical treatments through heat and/or compression are suited to dehydrate the mycelium resulting in an increased rigidity while preventing further growth. Heat pressing the material provides an increased density while promoting heat-induced crosslinking of molecular bonds [ 7, 8].

In contrast, for PMM, flexibility is preferred over rigidity for applications such as fabrics and flexible foams [ 33]. For this, different chemical treatments can be applied to the fungal tissue (Fig. 4) and also provide pliable or absorbent properties, durability and a protective coating [ 16, 17, 22, 34, 35, 36]. So far it is unclear which exact formulation of post-growth processing elements and steps yield the best results as the combinations are numerous and this research field is ongoing, but we tried to regroup the most relevant steps and elements in Fig. 4 to provide a simplified general overview.

Compounds used in the treatment of mycological tissue for material applications [ 16, 17, 22, 35, 36, 41, 46, 88]

The fungal cell wall contains the prevailing building blocks that physically characterize products made from pure mycelium. These building blocks are glucans, chitin/chitosan and glycoproteins, which can vary in their compositional ratio depending on the species, environmental conditions and developmental stage [ 37, 38, 39]. As such, it provides an attractive platform for the introduction of chemical modifications thereby enabling new properties. Chitin, which is the second most abundant polysaccharide on earth, refers to a N-acetyl-d-glucosamine polymer with an acetylation level > 50% while chitosan terms acetylation levels lower than 50% [ 40]. Deacetylation of this biopolymer liberates amino (NH ₂) groups that can afterwards be used as additional crosslinking sites on the chitosan backbone structure in a similar manner as the already available hydroxyl (OH) group (Fig. 5). Additionally, CaCl ₂ combined with chitosan has been showed to confer antimicrobial properties and is used in food preservation applications [ 41]. These antimicrobial properties could find interesting applications in packaging/wrapping applications for products prone to microbial contamination.

Deacetylation of chitin (N-acetyl-D-glucosamine) to chitosan (D-glucosamine)

PMM are typically coated with the aim to increase longevity and to protect against abrasion. For example, polylactic acid (PLA) offers an effective coating material that can be easily applied when dissolved in water. It is then absorbed by the mycelium and the water evaporates afterwards [ 35]. Although PLA is considered to be a sustainable bioplastic because it is biosynthesized and can be quickly degraded, the latter is only possible under industrial composting conditions with elevated temperatures (> 60 °C) due to the main depolymerization mechanism being abiotic hydrolysis and not enzymatic degradation [ 42]. This means that if PLA ends up in the ocean or another natural ecosystem, it most likely won't have a degradation advantage over other types of plastics [ 43]. Similarly, cellulose biofilms grown from bacteria ( e.g. Acetobacter xylinus) are seemingly envisaged as coating material to be applied as a separate coating or in cocultivation with the mycelium [ 24]. Finally, many other types of coating finishes can be used such as coconut oil, carnauba wax or beeswax [ 28].

Myco-leather as a proof-of-concept application

The use of fungi as a resource for textile and fabrics is an ancient practice as evidenced by the centuries-old use of traditional German felt (Amadou) and by the identification of mycelium mats in pouches crafted by indigenous North-American people [ 44, 45]. Moving fast forward into the early development of modern-day PMM, the main targeted application is its use as a leather substitute using species such as Ganoderma spp., Trametes versicolor, Fomes spp., Pycnoporus spp. and Perenniporia spp. [ 28, 46, 47]. Traditional leather production is tightly bound to the animal farming industry, which is unequivocally responsible for a significant share of the global greenhouse gas emissions and ever-increasing deforestation [ 48, 49, 50]. While the most common alternatives are synthetic leathers originated from the petrochemical industry, they carry the same environmental burden as non-biodegradable plastics [ 51, 52]. Myco-leather offers a cleaner alternative and promotes higher sustainability in a sector for dire need of greener improvements [ 33, 53]. These arguments combined with an annual global market value estimated around USD 394 billion for leather goods in 2020 [ 54], provide a bright future for commercial success of myco-leather. It is therefore no surprise that companies developing mycelium materials are currently focussing on bringing myco-leather products on the market (Fig. 6).

Examples of leather-like mycelium fabrics A. Reishi™ from Mycoworks, B. Mylea™ from Mycotech Lab, C. Mylo™ from Bolt threads, D. VTT mycelium leather

Variations in mechanical and physical properties between myco-leather brands are noticeable in the reported testing results from the companies (Additional file 1: Figures S1 and S2). To offer a competitive alternative, different strategies can be implemented to enhance the mechanical strength of the material so that it matches that of classical leather. For example, Mylea™ (Fig. 6B) includes a structural fabric-like material that is colonized by the mycelium for improved tear strength properties of the myco-leather product [ 55]. This fabric can be either natural or synthetic ( e.g. plant skin, cotton, gauze, grass fibres or artificial polymer fibres) [ 56]. Such a hybrid material, in which a biobased material is combined with artificial polymers begs questions on the sustainability and biodegradability of the material. As a natural solution, nanocellulose fibrils [ 57, 58] appear to be a promising biopolymer additive for mycelium leather as they were previously shown to increase tensile strength properties by 271% with a 15% cellulose content and up to 626% for higher cellulose contents in submerged bioreactor fermentation [ 22].

Bolt Threads' production process of mycelium leather, based on Ecovative's fermentation technology, involves compressing a thick mycelium foam (Fig. 3B) into a thin compact tissue [ 59]. Further downstream treatment of the mycelium, involving bonding agents, ensures sufficient strength to the material in order to fulfil the role of a leather substitute. Interestingly, while Bolt Threads' Mylo™ product is not plastic free but petroleum free, Ecovative's Forager™ hides are labelled as 100% plastic free.

Lastly, MycoWorks' strategy involves arranging the orientation of aerial hyphae to create weaved patterns, similar to regular fabrics, in their Reishi™ product [ 27, 28]. A recently developed alternative method named Fine Mycelium™ technology, allows them to direct hyphae into a bundled spiral arrangement resulting in highly organized structures similar to rope twisting (Fig. 3C). The company claims that this procedure results in superior mechanical properties with respect to existing mycelium leathers, synthetic leathers and animal leather (Additional file 1: Figure S1). Like traditional textile weaving and lattices, directing changes in fibre orientation creates an overall stronger material composition [ 60].

Three areas ripe for development

Improving production strains

Different fungal species have been successfully demonstrated for their use to grow mycelium in bulk for mycelium material applications. They typically belong to either Basidio- or Ascomycetes although according to the fermentation process and desired application, one might be more suitable than the other. White rot Basidiomycetes belonging to the Agaricales or Polyporales have been reported as suitable candidates to efficiently grow mycelium materials on lignocellulosic substrates ( e.g. the genera Ganoderma, Trametes, Pleurotus, Fomes and Schizophyllum) [ 7]. In contrast, when cultivated in bioreactor setups, Ascomycetes ( e.g. Penicillium, Aspergillus and Trichoderma) are widely used for biotechnological applications [ 61]. Besides differences in growth behaviour in different fermentation setups, other valuable traits can provide some significant advantages, such as for example the capability of producing chlamydospores during vegetative mycelium growth. This perennate survival structure enables asexual spore formation, independently from fruiting bodies, which avoids reshuffling of the genetic legacy and is therefore ideal as inoculum source to conserve strain-specific features [ 62]. An additional aspect to keep in mind when selecting a strain, is the specific cell wall composition. For example, species can vary in the compositional ratio of the chitin/protein content of their cell wall [ 39], which in turn affects post-processing efficiency ( e.g. amount of available chemical crosslinking sites) and thus material properties. Taken together, it is important to select the most suited species according to the substrate, fermentation setup and desired material application by screening the existing fungal biodiversity before considering further strain improvements.

In a second instance, strain improvements can be achieved through genetic modifications, which has already been applied for many biotechnological applications [ 63, 64]. A recent leap forward in targeted genetic modification was made possible with the development of CRISPR/Cas9 as a versatile genetic engineering tool [ 65, 66]. CRISPR/Cas9-based systems have been established for a range of filamentous fungi but with some remaining challenges [ 67]. An interesting solution allowing to bypass host-specific transcription systems for non-model organisms is the use of in vitro assembled Cas9 ribonucleoprotein (RNP) complexes [ 68]. These RNPs can be used across diverse species through polyethylene glycol (PEG) -mediated protoplast transformation without the need for species-specific adaptations as is the case with in vivo expression systems requiring validation of promotors, genetic elements and plasmids. However, it should be noted that protoplastation is not straightforward for many species of filamentous fungi and that other transformation methods might have to be considered [ 67, 68].

The promise of using genetic engineering to tune mycelium materials has been successfully demonstrated for Schizophyllum commune [ 69]. A S. commune mutant strain Δsc3, which is unable to express hydrophobin sc3, was shown to result in mycelium materials with increased density and mechanical strength, thereby shifting their classification from the category of natural materials to thermoplastic-like materials. As another example, the introduction of a S. cerevisiae CDA1 chitin deacetylase-encoding gene under control of glyceraldehyde-3-phosphate dehydrogenase (GPD) promoter in a mycelium material production strain has given rise to materials with significantly higher compressive modulus ( i.e. a material's stress-to-strain ratio) [ 70]. Similarly, engineered expression of β-1,3-glucan synthases (BGS1 and BGS2) under control of constitutive promoter of GPD yielded transformants with 135-165% higher β-glucan content in Ganoderma sp. [ 70]. Besides fungi, engineering bacterial strains used during co-cultivation can also be greatly beneficial to improve material properties and avoid contaminants. For example, co-cultivation with engineered Bacillus strains secreting polygama-glutamic acid as a biofilm resulted in twofold increased elastic modulus or engineering of melanin production conferred higher protection to UV in mycelium materials [ 70, 71]. Finally, co-cultivation with an engineered Streptomyces natalensis strain producing natamycin (an Ascomycete-specific antibiotic) enabled to supress recurring contaminants like Trichoderma sp. [ 70].

Upscaling towards industrial production

It is now clear that improvements in fermentation and post-growth processing of mycelium materials that were realized during the past decade have been instrumental in showing their potential as a new class of a sustainable material [ 26, 31, 33, 72, 73]. As for every prototype design, as challenging as it might be, cost-efficient upscaling for large-scale manufacturing of a new technology will come with new challenges and added complexity. Fortunately, industrial-scale fermentation of filamentous fungi is already established in the food and industrial biotechnological industry. According to the fermentation setup, whether this is a submerged bioreactor or solid-state fermentation strategy, one might need more adaptation to the industrial process than the other. Either way, both strategies come with their own characteristics and result in common and unique material application outcomes.

Some companies have invested in the development of a large-scale infrastructure for solid-state fermentations. Ecovative showcased their large climate-controlled incubation chamber (Fig. 7A) used to grow substantial quantities of pure mycelium foams at once (Fig. 7B) [ 26]. Opposed to this, Mycoworks describes their fermentation setup for growing aerial hyphae as consisting of individual boxes, which would be advantageous to minimize the impact of contamination events [ 27].

A. Incubation chamber for large scale production ©Ecovative, B. vertical farming of aerial mycelium foam ©Bolt Threads

Another important factor to keep in mind for industrial-scale production of mycelium materials is the growth substrate. The larger the production plant, the higher the need for substrate will be and if this substrate is not locally sourced, the carbon footprint to produce mycelium materials will increase. Therefore, it is important to identify local sources for mycelium growth substrate and to design the production capacity in function of substrate availability.

Future applications and transitioning towards a sustainable and circular production model.

So far, Ecovative has demonstrated that lignocellulosic CMM can be a viable alternative to replace expanded polystyrene packaging [ 74]. Mycelium was also shown to be an interesting support material for electronic circuit boards instead of commonly used acrylic plastics or as e-textiles and reactive fungal wearables [ 75, 76, 77]. Mycelium material properties that are appreciated features for electronic support applications are their heat and thermal resistance, light weight, modulable shape and hydrophobic nature [ 75].

Recently, attention is shifting towards consumer product applications for PMM. Renowned players in the fashion industry such as Hermès, Stella McCartney, Lululemon or even Adidas have partnered with mycelium leather companies to design prototype consumer products from mycelium leather (Fig. 8). These examples will facilitate the introduction of mycelium materials to a wider range of consumers. In the future, mycelium materials might become more versatile and omnipresent with few noticeable changes. This will not only be stimulated by the expected increase in research and development efforts for this new class of materials, but also because transitioning away from petrol-derived synthetic polymers and animal hides will become an increasing environmental necessity.

Examples of mycelium-based consumer products by established designer brands: A Sylvania by Hermès, B. Stan Smith by Adidas, C. Yoga mat by Lululemon, D. Mylo garment by Stella McCartney.

Another big impact application is the use of fungi to manufacture meat alternative products. This is not new since Quorn® was the first protein rich meat alternative made from Fusarium venenatum going back to 1985 [ 78], but as reported by the latest Good Food Institute report, many new companies are betting on fermentation technologies and more specifically mycoproteins to further innovate in this space ( e.g. Nature's Fynd™, 3F Bio, Atlast Food Co., Chunk, Fybrawork Foods, Kinoko-Tech, Meati, Mycovation, Prime Roots) [ 79].

Improvements in aerial hyphae fermentation unlocks new structures components that enables to mimic meat texture in a closer way [ 80]. Additionally, the matrix structure of mycelium materials can be used as wound care material [ 81, 82] or as a biomedical scaffold to grow biopsies [ 83]. This self-growing scaffold could serve as a tool to produce lab-grown meat products by culturing myocytes and thereby growing hybrid animal-fungi food products.

Finally, fungal melanin introduces new properties to next-generation engineered melanin-producing mycelium materials as they confer some degree of radioprotection, antioxidant activity to heavy metal chelation and organic compound absorption [ 84]. It is even considered as a promising option to provide a self-growing radiation shield for humans during future deep-space explorations [ 85].

Conclusions

The increasing number of functional applications for mycelium materials qualifies it as a next generation biomaterial even though much of this technology is still in its infancy. So far, major advances in fermentation techniques have resulted in opening new doors for functional applications but many improvements are still required to make it an all-purpose type of material such as plastics. Due to the growth of the organism being highly modulable at the microscopic and macroscopic level, in combination with numerous polymeric or fibre additives and chemical alteration possibilities of cell wall components, mycelium can be referred to as a future platform material with a wide range of tuneable properties. In addition, we strongly believe that the biodegradable characteristics of mycelium materials and circular nature of the production process are the major properties that will further stimulate their breakthrough into consumer markets as a nature friendly product.

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Acknowledgements

The authors thank Geza Szilvay and Manuel Arias Barrantes for their valuable input as well as all companies mentioned in this manuscript for providing illustrative material.

Funding

This work was supported by the Vrije Universiteit Brussel and funding by Research Foundation Flanders (FWO-Vlaanderen) [FWO-SB PhD fellowships to EE (Grant Number 1S36417N), SV (Grant Number 1SC9220N) and AVW (Grant Number 1SA9721N)].

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1. Research Group of Microbiology, Department of Bioengineering Sciences, Vrije Universiteit Brussel, Pleinlaan 2, B-1050, Brussels, Belgium

Simon Vandelook, Elise Elsacker, Aurélie Van Wylick & Eveline Peeters

2. Research Group of Architectural Engineering, Department of Architectural Engineering, Vrije Universiteit Brussel, Pleinlaan 2, B-1050, Brussels, Belgium

Elise Elsacker, Aurélie Van Wylick & Lars De Laet

3. Hub for Biotechnology in the Built Environment, Devonshire Building, Newcastle University, Newcastle upon Tyne, NE1 7RU, UK

Elise Elsacker

Contributions

SV performed: Investigation, analysis, writing of original draft. EE, AVW and LDL performed reviewing, EP performed supervision, editing and reviewing. All authors read and approved the manuscript.

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Correspondence to Eveline Peeters.

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Vandelook, S., Elsacker, E., Van Wylick, A. et al. Current state and future prospects of pure mycelium materials. Fungal Biol Biotechnol 8, 20 (2021). https://doi.org/10.1186/s40694-021-00128-1
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DOI: https://doi.org/10.1186/s40694-021-00128-1

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Current state and future prospects of pure mycelium materials - Fungal Biology and Biotechnology

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In the context of the ongoing transition from a linear to a circular economy, ecologically friendly renewable solutions are put in place. Filamentous fungi can be grown on various organic feedstocks and functionalized into a range of diverse material types which are biobased and thus more sustainable in terms of their production, use and recycling.

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Mycelium Materials: The Future of Growing our Homes

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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.
What is Mycelium Material? How to Create Mycelium Material with Different Properties?
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.

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.
What are the Applications of Fungal Materials?
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.
What is the Environmental Footprint of the Mycelium Material?
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.

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.

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 CO ₂ equivalents which means that we can quantify the whole life cycle CO ₂ output, as well as understand which steps need improvements to bring down the product's environmental footprint.
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, .
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 CO ₂ 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 CO 2 per 1 kg of mushroom material. Since the mycelium actually binds carbon, each kilogram holds ca 1 kg of CO ₂. 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.

Bibliography

[1] Vandelook, S., Elsacker, E., Van Wylick, A. et al. Current state and future prospects of pure mycelium materials. Fungal Biol Biotechnol 8, 20 (2021). https://doi.org/10.1186/s40694-021-00128-1

[2] BioMed Central Ltd. Connecting material science and fungal biology. Springer Nature, 2022. https://www.biomedcentral.com/collections/cmsfb

[3] Ruiz-Herrera, J., & Ortiz-Castellanos, L. (2019). Cell wall glucans of fungi. a review. The Cell Surface 5, 100022. https://doi.org/10.1016/j.tcsw.2019.100022

[4] Hyde, K. D., Xu, J., Rapior, S., Jeewon, R., Lumyong, S., Niego, A. G. T., ... Brooks, S. (2019). The amazing potential of fungi: 50 ways we can exploit fungi industrially. Fungal Diversity. https://doi.org/10.1007/s13225-019-00430-9

[5] Haneef, M., Ceseracciu, L., Canale, C., Bayer, I. S., Heredia-Guerrero, J. A., & Athanassiou, A. (2017). Advanced Materials From Fungal Mycelium: Fabrication and Tuning of Physical Properties. Scientific Reports, 7(1). https://doi.org/10.1038/srep41292

[6] Manan, S., Ullah, M. W., Ul-Islam, M., Atta, O. M., & Yang, G. (2021). Synthesis and applications of fungal mycelium-based advanced functional materials. Journal of Bioresources and Bioproducts, 6(1), pp. 1-10. https://doi.org/10.1016/j.jobab.2021.01.001

[7] Chambergo, F. S., & Valencia, E. Y. (2016). Fungal biodiversity to biotechnology. Applied Microbiology and Biotechnology, 100(6), pp. 2567-2577. https://doi.org/10.1007/s00253-016-7305-2

[8] Vanden Elsacker, E., De Laet, L., & Peeters, E. (2019). Mycelium-based materials at the dawn of the Anthropocene. In Structures and Architecture - Bridging the Gap and Crossing Borders: Proceedings of the Fourth International Conference on Structures and Architecture (ICSA 2019), pp. 1083-1090. CRC Press, Taylor & Francis, Boca Raton. https://doi.org/10.1201/9781315229126-129

[9] Zhang, X., Hu, J., Fan, X., Yu, X. (2022). Naturally grown mycelium-composite as sustainable building insulation materials. Journal of Cleaner Production, 342, 130784. https://doi.org/10.1016/j.jclepro.2022.130784

[10] Thoemen, H., & Humphrey, P. E. (2005). Modeling the physical processes relevant during hot pressing of wood-based composites. Part I. Heat and mass transfer. Holz Als Roh- Und Werkstoff, 64(1), pp. 1-10. https://doi.org/10.1007/s00107-005-0027-2

[11] Pohl, C., Schmidt, B., Nunez Guitar, T. et al. (2022). Establishment of the basidiomycete Fomes fomentarius for the production of composite materials. Fungal Biol Biotechnol 9, (4). https://doi.org/10.1186/s40694-022-00133-y

[12] Kuznetsova, I.; Zaitsev, B.; Krasnopolskaya, L.; Teplykh, A.; Semyonov, A.; Avtonomova, A.; Ziangirova, M.; Smirnov, A.; Kolesov, V. (2020). Influence of Humidity on the Acoustic Properties of Mushroom Mycelium Films Used as Sensitive Layers for Acoustic Humidity Sensors. Sensors 2020, 20, 2711. http://dx.doi.org/10.3390/s20092711

[13] Cerimi, K., Akkaya, K. C., Pohl, C., Schmidt, B., & Neubauer, P. (2019). Fungi as source for new bio-based materials: a patent review. Fungal Biology and Biotechnology, 6 (1). https://doi.org/10.1186/s40694-019-0080-y

[14] Meyer, V., Basenko, E. Y., Benz, J. P., Braus, G. H., Caddick, M. X., Csukai, M., Wösten, H. A. B. (2020). Growing a circular economy with fungal biotechnology: a white paper. Fungal Biology and Biotechnology, 7(1). https://doi.org/10.1186/s40694-020-00095-z

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archdaily topic 2022 the future of construction materials

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Mycelium Materials: The Future of Growing our Homes

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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.

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Symbiocene Living: Exploring the Potential of Mycelium Blocks for Sustainable Architecture

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Discover the potential of mycelium bio-composites in architecture. Explore sustainable materials and a symbiotic relationship with nature.