Biological materials are often more difficult to test than artificially produced materials. The biological material’s size and shape often limit the production of samples. In addition, the hierarchical design or certain structuring pushes conventional test setups to their limits. In the case of the fungus Fomes fomentarius, the honeycomb structure in the mm range leads to difficulties when clamping the sample. Additionally, the experimental measurement of single fibers, in the case of the fungus hyphae, shows similar problems of slippage. With our tensile test setup, we tested the macroscopic properties of the hymenium of F. fomentarius. We simulated the single fiber properties by using µCT scans on different length scales in a multi-scale approach.

In the macroscopic scale, the hymenium of the F. fomentarius shows a honeycomb structure. Tensile tests on this structure reveal a Young’s modulus of 477.5 MPa and an ultimate tensile strength of 8.5 MPa. With our approach, we prevent the samples from slipping, which we track with Digital Image Correlation (DIC). With volume scans of the microstructure via phase-contrast enhanced computed microtomography and volume scans of the mesostructure by laboratory computed microtomography the material properties were homogenized in a two-step approach, using the macroscopic properties measured by tensile testing. This approach leads to an assumed Young’s modulus of 5 GPa for a single hyphae. Which is in the range of some wood species fibres and spider silks. Laboratory µCT samples scanned before and after the tensile test helped to understand the fracture process, showing that irregularities in the sample enhance fracture formation.

As fungi are an emerging group of studied materials, naturally grown or lab grown, we hope that this approach helps to improve and standardize testing methods for this kind of material and similar biological materials from the very beginning.