Sophie Klemm

Fungal mycelium‐based materials are highly valued for their versatility and for harnessing renewable plant biomass through sustainable biotechnological production. Heat pressing is often used to produce fungal particle boards and leather substitutes. In this study, the impact of heat pressing on fungal mycelium from the basidiomycete Fomes fomentarius under lignocellulose‐based solid‐state and glucose‐based liquid cultivation conditions is investigated, focusing on the changes in cell wall gene expression, morphology, chemical composition, hydrophobicity, and mechanical characteristics. With varying effects between two cultivations, heat pressing at 100 MPa changes hydrophobicity, increases tensile strength and stiffness, in line with hyphal compaction and bonding. Compared to mycelium grown on glucose‐based medium, lignocellulosic substrate leads to mycelium with higher β ‐glucan content, less densely packed mycelium structure and thus lower mechanical strength, probably due to the different expression of genes involved in glucan and chitin biosynthesis. This study highlights the impact of heat pressing on fungal mycelium obtained from different cultivation conditions, offering insights to tailor their performance.

Efficient design strategies found in nature have led to innovative materials and technologies. One promising blueprint for lightweight applications is the hymenium of Fomes fomentarius, a cellular, hierarchically structured, light, strong, and failure‐resistant biological tissue. Phase‐contrast enhanced micro‐computed tomography is used to investigate deformation and failure during in situ compression testing of the tubular honeycomb structure. Specimens are loaded parallel or transverse to the long axis of the tubes , in wet or dry condition. Displacements are evaluated between defined loading steps with three‐dimensional optical flow and morphological image analysis is used to correlate the micro‐ and mesostructure with local strains and structural damage. Key findings include that displacements are about five times larger in transverse than parallel loading, with greater displacements in regions of lower density. Higher hyphae density is found in struts compared to vertices, which leads to uniform displacements without significant local strain concentration. While cracks are observed in both struts and vertices, surprisingly, fracture is more catastrophic in the struts. Parallel loading results in plastic buckling and delamination in dry samples, while their wet counterparts show telescopic shortening from the first loading step and fewer fatal cracks, probably due to greater hyphae elasticity.

To advance the concept of a circular economy, fungal mycelium-based materials are drawing increased attention as substitutes for nonsustainable materials, such as petroleum-based and animal-derived products, due to their biodegradability, low carbon footprint, and cruelty-free nature. Addressing the challenge of mechanical properties in fungal mycelium products, this study presents a straightforward approach for reinforcing fungal mycelium mats. This is achieved by using two bio-based and biodegradable polymers, poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBH) and polylactic acid (PLA), via material extrusion additive manufacturing (MEX AM), commonly known as 3D printing, to produce fungal mycelium-biopolymer composites. By analyzing the mechanical properties, roughness, and morphology, this study demonstrates significant improvements in ultimate tensile strength with the application of PHBH and even more with PLA, while elasticity is reduced. The study also discusses potential improvements to enhance the quality of the fungal mycelium-biopolymer composites without trading off bio-based and biodegradable features, offering a promising pathway for the development of more durable and sustainable fungal mycelium products.

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.

The attachment of bacteria and other microbes to natural and artificial surfaces leads to the development of biofilms, which can further cause nosocomial infections. Thus, an important field of research is the development of new materials capable of preventing the initial adhesion of pathogenic microorganisms. In this work, novel polymer/particle composite materials, based on a polythiourethane (PTU) matrix and either spherical (s-ZnO) or tetrapodal (t-ZnO) shaped ZnO fillers, were developed and characterized with respect to their mechanical, chemical and surface properties. To then evaluate their potential as anti-fouling surfaces, the adhesion of two different pathogenic microorganism species, Staphylococcus aureus and Candida glabrata, was studied using atomic force microscopy (AFM). Our results show that the adhesion of both S. aureus and C. glabrata to PTU and PTU/ZnO is decreased compared to a model surface polydimethylsiloxane (PDMS). It was furthermore found that the amount of both s-ZnO and t-ZnO filler had a direct influence on the adhesion of S. aureus, as increasing amounts of ZnO particles resulted in reduced adhesion of the cells. For both microorganisms, material composites with 5 wt.% of t-ZnO particles showed the greatest potential for anti-fouling with significantly decreased adhesion of cells. Altogether, both pathogens exhibit a reduced capacity to adhere to the newly developed nanomaterials used in this study, thus showing their potential for bio-medical applications.