A mechanical perspective on the hymenium of the fungal species Fomes fomentarius: Surprising anisotropic elastic properties across multiple scales

Characterising the porous structure and mechanical properties of fungal fruiting bodies remains challenging. Here, we report our findings on the elastic properties of the lightweight hymenium of Fomes fomentarius across multiple length scales. Combining macroscopic tensile tests with digital image correlation yielded macroscale Young’s modulus and Poisson’s ratio values spanning 729–741 MPa and 0.52–0.59, respectively. Based on this and detailed meso- and microstructural data, we performed multiscale simulations to estimate the elastic properties of individual hyphae. We obtained a value of 5.7 GPa, comparable to wood fibers and spider silk. Nanoindentation measurements support this result, with values differing by less than 10 % from the simulation. Importantly, our multiscale analysis revealed fully anisotropic elastic behavior, in contrast to the structural transverse isotropy previously assumed based on microscopic and tomographic visualisation results. Both the meso- and macroscale stiffness matrices reflect the mechanical anisotropy, indicating a significant role for hyphal structure, connectivity, and orientation in the elastic behavior. Our findings provide quantitative estimates of the Young’s moduli across scales and underline the potential of the hymenium of Fomes fomentarius for bioinspired and sustainable material design, such as effective arrangement of tiny fibers in highly porous, light, and yet stiff enough structures.