EUROPEAN CONGRESS AND EXHIBITION ON ADVANCED MATERIALS AND PROCESSES - EUROMAT 2021

The green European mistletoe (Viscum album subsp. album) can even be seen with bare eyes on tree branches. It is the most prominent representative of (hemi-)parasitic plants in Central Europe and deprives its host of water. Both the mistletoe and the host can be regarded as composite materials. The scientific question is: "How can two fiber-reinforced composites connect structurally and functionally?”. The results of the morphological-anatomical and biomechanical investigations lead to a deeper understanding of the mistletoe-host tree connection and have the potential for a transfer of the underlying functional principles to technical materials systems. Micro–computed tomography scans and morphometric measurements provided high-resolution insights into the location and distribution of mistletoe tissue in the host and cell orientation at the attachment site. Microscopic analyses displayed (sub-)cellular structures of the junction between mistletoe and host and allowed a visualization of the cell lignification. In biomechanical tests, intact mistletoe-host samples and cut slices from the interaction region were characterized under tensile load until failure. For the latter additional information on local deformation patterns was obtained using digital image correlation. Digital microscopy was used to quantify the roughness of the fracture surface and to provide more precise calculations of various mechanical properties. The results show a distinct cellular boundary line at the mistletoe-host interface. Geometrical arrangements of the tissues and their gradual lignification, however, do not only maximize the mistletoe’s capacity for water uptake from the host but make the connection also very resistant to failure. Multiple pre-failure events occurred in the mechanical tests, suggesting that lateral sinkers fail first, before the disintegration of the main haustorium occurs. These hierarchically structured, graduated and multifunctional materials systems could serve as a model for the technical implementation for secured connections of fiber-reinforced composites.