Mechanical, physical and thermal properties of composite materials produced with the basidiomycete Fomes fomentarius

BACKGROUND

To achieve climate neutrality, fundamentally new concepts of circularity need to be implemented by the building sector as it contributes to 40% of anthropogenic CO2 emission. Fungal biotechnology can make a significant contribution here and help eliminate fossil dependency for building material production. Recently, we have shown that the medicinal polypore Fomes fomentarius feeds well on renewable lignocellulosic biomass and produces composite materials that could potentially replace fossil fuel-based expanded polystyrene as insulation material.

RESULTS

In this study, we explored the mechanical, physical, and thermal properties of F. fomentarius-based composite materials in more detail and determined key performance parameters that are important to evaluate the usability of F. fomentarius-based composite materials in the construction sector. These parameters were determined according to European standards and included compressive strength, modulus of elasticity, thermal conductivity, water vapour permeability, and flammability of uncompressed composites as well as flexural strength, transverse tensile strength, and water absorption capacity of heat-pressed composites, among others. We could show that uncompressed composites obtained from F. fomentarius and hemp shives display a thermal conductivity of 0.044 W (m K)-1 which is in the range of natural organic fibres. A water vapour permeability of 1.72 and classification into flammability class B1 clearly surpasses fossil-based insulation materials including expanded polystyrene and polyurethane. We could furthermore show that heat-pressing can be used to reliably generate stiff and firm particleboards that have the potential to replace current wood-based particleboards that contain synthetic additives. X-ray microcomputed tomography finally visualized for the first time the growth of hyphae of F. fomentarius on and into the hemp shive substrates and generated high-resolution images of the microstructure of F. fomentarius-based composites.

CONCLUSION

This study demonstrates that fungal-based composites produced with F. fomentarius partially meet or even exceed key performance parameters of currently used fossil fuel-based insulation materials and can also be used to replace particleboards.

Establishment of the basidiomycete Fomes fomentarius for the production of composite materials

Background

Filamentous fungi of the phylum Basidiomycota are considered as an attractive source for the biotechnological production of composite materials. The ability of many basidiomycetes to accept residual lignocellulosic plant biomass from agriculture and forestry such as straw, shives and sawdust as substrates and to bind and glue together these otherwise loose but reinforcing substrate particles into their mycelial network, makes them ideal candidates to produce biological composites to replace petroleum-based synthetic plastics and foams in the near future.

Results

Here, we describe for the first time the application potential of the tinder fungus Fomes fomentarius for lab-scale production of mycelium composites. We used fine, medium and coarse particle fractions of hemp shives and rapeseed straw to produce a set of diverse composite materials and show that the mechanical materials properties are dependent on the nature and particle size of the substrates. Compression tests and scanning electron microscopy were used to characterize composite material properties and to model their compression behaviour by numerical simulations. Their properties were compared amongst each other and with the benchmark expanded polystyrene (EPS), a petroleum-based foam used for thermal isolation in the construction industry. Our analyses uncovered that EPS shows an elastic modulus of 2.37 ± 0.17 MPa which is 4-times higher compared to the F. fomentarius composite materials whereas the compressive strength of 0.09 ± 0.003 MPa is in the range of the fungal composite material. However, when comparing the ability to take up compressive forces at higher strain values, the fungal composites performed better than EPS. Hemp-shive based composites were able to resist a compressive force of 0.2 MPa at 50% compression, rapeseed composites 0.3 MPa but EPS only 0.15 MPa.

Conclusion

The data obtained in this study suggest that F. fomentarius constitutes a promising cell factory for the future production of fungal composite materials with similar mechanical behaviour as synthetic foams such as EPS. Future work will focus on designing materials characteristics through optimizing substrate properties, cultivation conditions and by modulating growth and cell wall composition of F. fomentarius, i.e. factors that contribute on the meso- and microscale level to the composite behaviour.

Supplementary Information

The online version contains supplementary material available at 10.1186/s40694-022-00133-y.

An approach to change the basic polymer composition of the milled Fomes fomentarius fruiting bodies

Background

Chitin and its derivative chitosan are readily exploited, especially in food, cosmetic, pharmaceutical, biomedical, chemical, and textile industries. The biopolymers are currently recovered from the crustacean shells after purification from the large amount of proteins and minerals. The key problems are centered around a lot of chemical waste and allergenic potential of the heat-stable remaining proteins. Fungi can be considered as an alternative eco-friendlier source of the chitin and chitosan due to the lower level of inorganic materials and absence of the allergenic proteins.

Results

The work presents a new chemical assay to change the composition of the milled Fomes fomentarius fruiting bodies. A gradual 13-fold increase of the chitin amount accompanied by 14-fold decrease of the glucan content was obtained after repetitive alkali-acidic treatment. Raw material contained mainly chitin with 30% degree of deacetylation. After the first and second alkali treatment, the polymer was defined as chitosan with comparable amounts of N-acetyl-d-glucosamine and d-glucosamine units. The last treated samples showed an increase of the chitin amount to 80%, along with typical for the natural tinder fibers degree of deacetylation and three-dimensional fibrous hollow structure.

Conclusions

A new approach allowed a gradual enrichment of the pulverized Fomes fomentarius fruiting bodies with chitin or chitosan, depending on the extraction conditions. High stability and fibrous structure of the fungal cell walls with a drastically increased chitin ratio let us suggest a possibility of the targeted production of the chitin-enriched fungal material biotechnologically under eco-friendly conditions.

Unleashing the Biological Potential of Fomes fomentarius via Dry and Wet Milling

Fomes fomentarius, usually referred to as tinder conk, is a common wood-based fungus rich in many interesting phytochemicals and with an unique porous structure. Dry or wet ball milling of this sponge on a planetary mill results in small particles with sizes in the range of 10 µm or below. Suspended in water and without preservatives or other stabilizers, the resulting micro-suspensions are sterile for around six days, probably due to the increased temperatures of around 80 °C especially during the wet milling process. The suspensions also exhibit excellent antioxidant activities as determined in the DPPH, ferric reducing antioxidant potential (FRAP) and 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid (ABTS) assays. In the DPPH assay, IC₅₀ values of 0.02–0.04% w/v and 0.04% w/v were observed for dry and wet milled samples, respectively. In the FRAP assay, IC₅₀ values of <0.02% w/v and 0.04% w/v were observed for dry and wet milled samples, respectively. In contrast, the ABTS assay provided IC₅₀ values of 0.04% w/v and 0.005% w/v, respectively. Notably, this activity is mostly—albeit not exclusively—associated with the highly porous particles and their large surfaces, although some active ingredients also diffuse into the surrounding aqueous medium. Such suspensions of natural particles carrying otherwise insoluble antioxidants on their surfaces provide an interesting avenue to unleash the antioxidant potential of materials such as sponges and barks. As dry milling also enables longer storage and transport, applications in the fields of medicine, nutrition, agriculture, materials and cosmetics are feasible.

Optimization of fermentation of Fomes fomentarius extracellular polysaccharide and antioxidation of derivatized polysaccharides

Fermentation is a metabolic process that converts sugars into acids, gases, or alcohol. This process occurs in yeasts and bacteria, as well as in muscle cells when faced with a lack of oxygen. In this paper, isolation, culture, purification and extracellular polysaccharides of strain Fomes fomentarius were studied. Extraction of polysaccharides from a culture based on F. fomentarius extracellular polysaccharides, extracellular polysaccharides fermentation experiments was optimized and compared, the optimal fermentation method was obtained; extracellular polysaccharides were sulfated, phosphorylated experiments, selenium acidified, discussed the preparation of derivative polysaccharides and microscopic detection, and finally studied extracellular polysaccharides on DPPH, The scavenging ability, superoxide anion radical and hydroxyl radical scavenging ability of the derived polysaccharides were compared. The results showed that the extracellular polysaccharide and derivatized polysaccharide of F. fomentarius had certain antioxidant activity.

A Wild Fomes fomentarius for Biomediation of One Pot Synthesis of Titanium Oxide and Silver Nanoparticles for Antibacterial and Anticancer Application

The present study offers an alternative method for green synthesis of the formation of two types of nanoparticles (NPs). These NPs, titanium oxide and silver NPs (TiO₂ and Ag NPs, respectively), were obtained from the amalgamation of intracellular extract of a wild mushroom, Fomes fomentarius, with aqueous solutions of titanium isopropoxide and silver nitrate, respectively. F. fomentarius was identified phenotypically and by 18S ribosomal RNA gene sequencing (Gene accession no: MK635351). The biosynthesis of TiO₂ and Ag NPs was studied and characterized by X-ray diffraction (XRD), diffuse reflectance UV-Visible spectroscopy (DR-UV), fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM) and transmission electron microscope (TEM). Success was achieved in obtaining NPs of differing sizes and shapes. The antibacterial and anticancer activity of the NPs was significant with morphological damage being caused by both, although Ag NPs (10–20 nm) were found to have profound effects on bacterial and cancer cells in comparison to TiO₂ NPs (100–120 nm). These metal NPs, synthesized using wild mushrooms, hold a great potential in biomedicinedue to an effective enzyme combination, which permits them to modify different chemical compounds to less toxic forms, which is required for ecofriendly and safe biomaterials.

The microbiome profiling of fungivorous black tinder fungus beetle Bolitophagus reticulatus reveals the insight into bacterial communities associated with larvae and adults

Saproxylic beetles play a crucial role in key processes occurring in forest ecosystems, and together with fungi contribute to the decomposition and mineralization of wood. Among this group are mycetophilic beetles which associate with wood-decaying fungi and use the fruiting body for nourishment and development. Therefore, their feeding strategy (especially in the case of fungivorous species) requires special digestive capabilities to take advantage of the nutritional value of fungal tissue. Although polypore-beetle associations have been investigated in numerous studies, detailed studies focusing on the microbiome associated with species feeding on fruiting bodies of polypores remain limited. Here we investigated the bacterial communities associated with larvae and adults of Bolitophagus reticulatus collected from Fomes fomentarius growing on two different host tree: beech (Fagus sp.) and birch (Betula sp.), respectively. Among 24 identified bacterial phyla, three were the most relatively abundant (Proteobacteria, Actinobacteria and Bacteroidetes). Moreover, we tried to find unique patterns of bacteria abundances which could be correlated with the long-term field observation showing that the fruiting bodies of F. fomentarius, growing on birch are more inhabited by beetles than fruiting bodies of the same fungus species growing on beech. Biochemical analyses showed that the level of protease inhibitors and secondary metabolites in F. fomentarius is higher in healthy fruiting bodies than in the inhabited ones. However, tested microbiome samples primarily clustered by developmental stage of B. reticulatus and host tree did not appear to impact the taxonomic distribution of the communities. This observation was supported by statistical analyses.

Fomes fomentarius Ethanol Extract Exerts Inhibition of Cell Growth and Motility Induction of Apoptosis via Targeting AKT in Human Breast Cancer MDA-MB-231 Cells

Fomes fomentarius, an edible mushroom, is known to have anti-cancer, anti-inflammatory, and anti-diabetes effects. However, the underlying anti-cancer mechanism of F. fomentarius is unknown. To determine the molecular mechanism of the anti-cancer effects of F. fomentarius, various methods were used including fluorescence-activated cell sorting, Western blotting, migration, and crystal violet assays. F. fomentarius ethanol extract (FFE) decreased cell viability in six cancer cell lines (MDA-MB-231, MCF-7, A549, H460, DU145, and PC-3). FFE decreased the migration of MDA-MB-231 cells without causing cell toxicity. Furthermore, FFE attenuated the expression of matrix metalloproteinase-9 and phosphorylation of Akt as well as increased E-cadherin in MDA-MB-231 cells. FFE arrested the S and G2/M populations by inhibiting the expression of cell cycle regulatory proteins such as cyclin-dependent kinase 2, cyclin A/E, and S-phase kinase-associated protein 2. FFE increased the sub-G1 population and expression of cleaved caspase-9, -3, and cleaved poly adenosine diphosphate (ADP-ribose) polymerase at 72 h and suppressed B-cell lymphoma 2. Interestingly, FFE and AKT inhibitors showed similar effects in MDA-MB-231 cells. Additionally, FFE contained betulin which inhibited p-AKT in MDA-MB-231 cells. Our findings demonstrate that FFE inhibits cell motility and growth and induces apoptosis by inhibiting the phsphoinositide 3- kinase /AKT pathway and caspase activation.

Differential Modulation of Lipopolysaccharide-Induced Inflammatory Cytokine Production by and Antioxidant Activity of Fomentariol in RAW264.7 Cells

Medicinal mushrooms have been used worldwide to treat cancer and modulate the immune system. Over the last several years, there has been increasing interest in isolating bioactive compounds from medicinal mushrooms and evaluating their health beneficial effects. Fomes fomentarius is used in traditional oriental medicine and is known to possess antioxidant, anti-inflammatory, antidiabetic, and antitumor effects. In the present study, we isolated fomentariol from Fomes fomentarius and investigated its anti-inflammatory effect in murine macrophages (RAW264.7 cells) stimulated with lipopolysaccharides. Fomentariol inhibited the production of nitric oxide and intracellular reactive oxygen species triggered by lipopolysaccharides. Interestingly, fomentariol differentially regulated cytokine production triggered by lipopolysaccharides. Fomentariol effectively suppressed the production of interleukin-1β and interleukin-6 but not tumor necrosis factor-α. The inhibitory effect of fomentariol against nitric oxide, interleukin-1β, and interleukin-6 production was possibly mediated by downregulation of the extracellular signal-regulated kinase signaling pathway. Taken together, our results suggest that fomentariol differentially modulated inflammatory responses triggered by lipopolysaccharides in macrophages and is one of the bioactive compounds that mediate the physiological effects of Fomes fomentarius.

Methyl 9-Oxo-(10E,12E)-octadecadienoate Isolated from Fomes fomentarius Attenuates Lipopolysaccharide-Induced Inflammatory Response by Blocking Phosphorylation of STAT3 in Murine Macrophages

Fomes fomentarius is a fungus of the Polyporaceae family and is used in traditional oriental therapies. Although the anti-inflammatory activities of this species have been previously reported, the identity of the bioactive compounds responsible for this activity remains unknown. Here, we investigated whether methyl 9-oxo-(10E,12E)-octadecadienoate (FF-8) purified from F. fomentarius exerts anti-inflammatory activity in murine macrophages stimulated with lipopolysaccharide (LPS). FF-8 suppressed secretion of nitric oxide (NO) and prostaglandin E2 through downregulation of inducible NO synthase and cyclooxygenase-2 expression induced by LPS. In addition, pretreatment of cells with FF-8 led to a reduction in levels of secreted inflammatory cytokines such as tumor necrosis factor-α and interleukin-6 in macrophages stimulated with LPS. Conversely, FF-8 did not affect nuclear factor κB, p38, c-Jun NH2-terminal kinase, and extracellular signal-regulated kinase pathways. Instead, FF-8 specifically interfered with signal transducer and activator of transcription 3 (STAT3) phosphorylation induced by LPS. Collectively, this study demonstrated that FF-8 purified from F. fomentarius suppresses inflammatory responses in macrophages stimulated with LPS by inhibiting STAT3 activation. Further studies will be required to elucidate the anti-inflammatory effect of FF-8 in vivo.

European medicinal polypores--a modern view on traditional uses

ETHNOPHARMACOLOGICAL RELEVANCE

In particular five polypore species, i.e. Laetiporus sulphureus, Fomes fomentarius, Fomitopsis pinicola, Piptoporus betulinus, and Laricifomes officinalis, have been widely used in central European folk medicines for the treatment of various diseases, e.g. dysmenorrhoea, haemorrhoids, bladder disorders, pyretic diseases, treatment of coughs, cancer, and rheumatism. Prehistoric artefacts going back to over 5000 years underline the long tradition of using polypores for various applications ranging from food or tinder material to medicinal-spiritual uses as witnessed by two polypore species found among items of Ötzi, the Iceman. The present paper reviews the traditional uses, phytochemistry, and biological activity of the five mentioned polypores.

MATERIALS AND METHODS

All available information on the selected polypore taxa used in traditional folk medicine was collected through evaluation of literature in libraries and searches in online databases using SciFinder and Web of Knowledge.

RESULTS

Mycochemical studies report the presence of many primary (e.g. polysaccharides) and secondary metabolites (e.g. triterpenes). Crude extracts and isolated compounds show a wide spectrum of biological properties, such as anti-inflammatory, cytotoxic, and antimicrobial activities.

CONCLUSIONS

The investigated polypores possess a longstanding ethnomycological tradition in Europe. Here, we compile biological results which highlight their therapeutic value. Moreover, this work provides a solid base for further investigations on a molecular level, both compound- and target-wise.