Robin Seidel, Tom Masselter, Olga Speck, Thomas Speck
Plant Biomechanics Group Freiburg, Botanic Garden, Faculty of Biology, University of Freiburg
Title: Innovative biomimetic materials inspired by plants
Bio-inspired materials are becoming of major interest in light-weight constructions, enhanced materials (e.g. self-x-materials), functionalized surfaces and interfaces as well as in architecture. The main difference of natural materials compared to classic technical materials is their limited number of basic components which are then hierarchically structured to allow them to fulfill a vast number of functions e.g. self-healing, mechanical stability, high toughness and stiffness. The creative process of transferring the inspirations from biology into technical applications typically includes several levels of abstraction and modification. An example of this process is the Flectofin®, which is a new façade-shading system based on the opening mechanism of the perch in the flower of the Bird-of-Paradise Strelitzia reginae. Birds landing on the perch to feed on nectar induce two lamina flaps to bend sideways, which exposes the pollen on the stamina. The pollen is then transferred by the bird to the next flower. The bending of the structure is fully reversible and can be repeated over a thousand times without almost any signs of wear. The deformation of the perch has been abstracted and converted into glass fiber reinforced façade shading systems which undergo a major shape change by only a minute deformation of their backbone. Also regarding self-repairing materials plants provide excellent role models.Internal growth stresses in Aristolochia macrophylla cause its sclerenchymatous outer ring to be continuously fissured. A natural self-sealing process is mediated by turgescent parenchymatous cortex cells. These cells are pressurized and thereby expand into the fissures and restore the integrity of the cortex. This functional principle has been successfully transferred into a PU-foam coating for membranes used for self-repairing pneumatic structures. Delosperma cooperi provides a promising role model for rapid self-sealing materials. It grows in arid habitats and thereby has a major selective advantage by being able to reduce dehydration due to external damage. To reduce external damage caused by impact is a major challenge for light weight materials which are used for protection, packaging or padding.
The pomello, Citrus maxima has evolved its fruit wall to provide an excellent damping system. Under natural conditions the fruits drop from heights of up to 15m. More than 90% of the initial potential energy is dissipated during impact with negligible damage of the pulp. The structural analysis of the fruit wall shows a complex hierarchically structured system of sandwich layers – open pored and closed pored – combined with branched fiber networks. The layers are connected by a gradual mixture of the adjacent tissues which reduces the risk of disintegration of the structure. These features have now been transferred in a first approach to a technical system using metal foams to provide enhanced crash absorbers for automotives and polymers to provide enhanced body protection. All these examples show how inspiring a more thorough look into the plant world can be and what results can be achieved by a technical transfer.
Contribution to the Workshop “Smart Solution from the Plant Kingdom”