Fungal composites are attracting growing interest in the development of sustainable, degradable structures, but little is known about the structure-property relationship of their natural counterparts. The fruiting bodies of Fomes fomentarius are surprisingly resilient and lightweight materials. We investigate the interplay between hierarchical structure and mechanical resistance in different segments (crust, trama, hymenium and mycelium core) of the fruiting body.

Our analysis encompasses the structural, chemical, and mechanical characterization of the fungal structure, with a specific focus on the composition of the cell wall, including chitin and glucan content, degree of deacetylation, and trace element distribution. Notably, the hymenium exhibited superior mechanical properties alongside the lowest porosity. Our findings suggest that this exceptional strength can be attributed to the abundance of skeletal hyphae, the highest chitin content in the cell wall, and the honeycomb structure. Additionally, an elevated calcium content was observed in the hymenium and crust, with SEM-EDX confirming the presence of calcium oxalate crystals.

Interestingly, the crust displayed layers with varying densities and different calcium and potassium content, along with the presence of α-glucan, while β-glucan was identified in the other segments. These results underscore the significance of considering the diverse structural and compositional characteristics of different segments when designing materials and products inspired by fungi. Moreover, the porous yet sturdy structure of the hymenium holds promise as a blueprint for the development of modern smart materials.