Natural systems underwent an extremely long evolutionary optimization process when compared with anthropogenic inventions. Many human-made processes and materials are therefore inspired by these systems. Fungal mycelium is the biggest networker in nature: while mycorrhizal fungi connect plants in the forest, wood-decaying fungi use their hyphal nets to degrade dead trees and plant matter, building up fertile top soil. Combining the ideas of connection and the ability of utilizing biomass for growth, led to the concept of using mycelium as a binder for disperse organic particles or fibers. Fungal hyphae grow into the substrates, reaching every nook and cranny of it to access the nutrients. Terminating this growth process after complete interconnection can lead to a composite material with promising properties. While the main focus was on forestry and agricultural by-products as substrates so far, we investigated several different lignocellulosic waste streams that have not yet been described as substrates for mycelium composites. Apple pomace, sugar beet pulp, spent brewer’s grains, cotton fibers, digested biogas substrate, green waste, paper sludge, and beech sawdust were inoculated with Ganoderma sessile and some of them also with Pleurotus pulmonarius and Trametes versicolor. For the quantification of fungal growth, a new method was established. The fungal DNA was quantified in a certain amount of composite and then converted into mycelial biomass based on DNA quantification in pure mycelium. The result gives an insight into how well the mycelium grows on different substrates and allows to compare between fungal species. In future studies, the influence of fungal colonization rate on different material properties can be investigated.
With the established method, clear differences between the fungal species and the colonization rates were observed. Some of the substrates resulted in very poor growth for all fungi during the 21 days of incubation. In general, the mycelium content together with the density of the substrate corresponds well to the handling stability of the materials. However, a higher amount of mycelium is not necessarily indicating good stability because Ganoderma sessile shows stronger surface growth than the other two candidates which has only little contribution to particle binding. Ganoderma sessile performed best in terms of fungal biomass production for all substrates with the exception of sugar beet pulp, where Trametes versicolor grew better. This indicates that not only the fungal species and the chosen substrate are relevant for successful composite fabrication, but also their combination.